Tribological characteristics of ceramic conversion treated NiTi shape memory alloy

International Nuclear Information System (INIS)

Ju, X; Dong, H

2007-01-01

NiTi shape memory alloys are very attractive for medical implants and devices (such as orthopaedic and orthodontic implants) and various actuators. However, wear is a major concern for such applications and a novel surface engineering process, ceramic conversion treatment, has recently been developed to address this problem. In this study, the tribological characteristics of ceramic conversion treated NiTi alloy have been systematically investigated under dry unidirectional wear, reciprocating-corrosion wear and fretting-corrosion wear condition. Based on the experimental results, the wear behaviour under different conditions is compared and wear mechanisms involved are discussed

Tribological characteristics of ceramic conversion treated NiTi shape memory alloy

Energy Technology Data Exchange (ETDEWEB)

Ju, X; Dong, H [Department of Metallurgy and Materials, School of Engineering, University of Birmingham, Edgbaston, Birmingham B15 2TT (United Kingdom)

2007-09-21

NiTi shape memory alloys are very attractive for medical implants and devices (such as orthopaedic and orthodontic implants) and various actuators. However, wear is a major concern for such applications and a novel surface engineering process, ceramic conversion treatment, has recently been developed to address this problem. In this study, the tribological characteristics of ceramic conversion treated NiTi alloy have been systematically investigated under dry unidirectional wear, reciprocating-corrosion wear and fretting-corrosion wear condition. Based on the experimental results, the wear behaviour under different conditions is compared and wear mechanisms involved are discussed.

X-ray diffraction studies of NiTi shape memory alloys

OpenAIRE

E. Łągiewka; Z. Lekston

2007-01-01

Purpose: The purpose of this paper is to present the results of the investigations of phase transitions of TiNiCo and Ni-rich NiTi shape memory alloys designed for medical applications.Design/methodology/approach: Temperature X-ray diffraction (TXRD), differential scanning calorimetry (DSC), electrical resistivity (ER) and the temperature shape recovery measurements in three-point bending ASTM 2082-01 tests were used.Findings: It has been found in this work that ageing after solution treatme...

Thermomechanical model for NiTi shape memory wires

International Nuclear Information System (INIS)

Frost, M; Sedlák, P; Sippola, M; Šittner, P

2010-01-01

A simple one-dimensional rate-independent model is proposed. It is able to capture responses of a NiTi shape memory alloy wire element to mechanical and thermal loadings. Since the model takes into account martensitic phase transformation as well as deformation processes in the martensite, both shape memory effects and pseudoelasticity can be simulated. The model introduces non-hysteretic transformation strain. Particular attention was paid to description of partial loading cycles. By changing the input parameters the model can be adapted to various types of NiTi-based materials. The model was implemented in the finite element code Abaqus as a User routine and several simulations were performed to validate the implementation

Void formation in NiTi shape memory alloys by medium-voltage electron irradiation

International Nuclear Information System (INIS)

Schlossmacher, P.; Stober, T.

1995-01-01

In-situ electron irradiation experiments of NiTi shape memory alloys, using high-voltage transmission electron microscopes, result in amorphization of the intermetallic compound. In all of these experiments high-voltages more than 1.0 MeV had to be applied in order to induce the crystalline-to-amorphous transformation. To their knowledge no irradiation effects of medium-voltage electrons of e.g. 0.5 MeV have been reported in the literature. In this contribution, the authors describe void formation in two different NiTi shape memory alloys, resulting from in-situ electron irradiation, using a 300 kV electron beam in a transmission electron microscope. First evidence is presented that void formation is correlated with the total oxygen content of the alloys

Surface treatment of NiTi shape memory alloy by modified advanced oxidation process

Institute of Scientific and Technical Information of China (English)

CHU Cheng-lin; WANG Ru-meng; YIN Li-hong; PU Yue-pu; DONG Yin-sheng; GUO Chao; SHENG Xiao-bo; LIN Ping-hua; CHU Paul-K

2009-01-01

A modified advanced oxidation process(AOP) utilizing a UV/electrochemically-generated peroxide system was used to fabricate titania films on chemically polished NiTi shape memory alloy(SMA). The microstructure and biomedical properties of the film were characterized by scanning electron microscopy(SEM), X-ray photoelectron spectroscopy(XPS), inductively-coupled plasma mass spectrometry(ICPMS), hemolysis analysis, and blood platelet adhesion test. It is found that the modified AOP has a high processing effectiveness and can result in the formation of a dense titania film with a Ni-free zone near its top surface. In comparison, Ni can still be detected on the outer NiTi surface by the conventional AOP using the UV/H2O2 system. The depth profiles of O, Ni, Ti show that the film possesses a smooth graded interface structure next to the NiTi substrate and this structure enhances the mechanical stability of titania film. The titania film can dramatically reduce toxic Ni ion release and also improve the hemolysis resistance and thromboresistance of biomedical NiTi SMA.

Thermomechanical behavior of Ti-rich NiTi shape memory alloys

International Nuclear Information System (INIS)

Paula, A.S.; Mahesh, K.K.; Santos, C.M.L. dos; Braz Fernandes, F.M.; Costa Viana, C.S. da

2008-01-01

Phase transformations associated with shape memory effect in nickel-titanium (NiTi) alloys can be one-stage, B19' (martensite) ↔ B2 (austenite), two-stage including an intermediate R-phase stage, or multiple-stage depending on the thermal and/or mechanical history of the alloy. In the present paper, we highlight the effect of (i) deformation by cold-rolling (from 10% to 40% thickness reduction) and (ii) final annealing on the transformation characteristics of a Ti-rich NiTi shape memory alloy. For this purpose, one set of samples initially heat treated at 773 K followed by cold-rolling (10-40% thickness reduction), has been further heat treated at various temperatures between 673 and 1073 K. Another sample was subjected to heat treatment at 1040 K for 300 s followed by hot rolling (50%) after cooling in air to 773 K and water quenching to room temperature (T room ). Phase transformations were studied using differential scanning calorimetry, electrical resistivity measurements and in situ X-ray diffraction. A specific pattern of transformation sequences is found as a result of combination of the competing effects due to mechanical-working and annealing

Thermal processing of polycrystalline NiTi shape memory alloys

International Nuclear Information System (INIS)

Frick, Carl P.; Ortega, Alicia M.; Tyber, Jeffrey; Maksound, A.El.M.; Maier, Hans J.; Liu Yinong; Gall, Ken

2005-01-01

The objective of this study is to examine the effect of heat treatment on polycrystalline Ti-50.9 at.% Ni in hot-rolled and cold-drawn states. In particular, we examine microstructure, transformation temperatures as well as mechanical behavior in terms of both uniaxial monotonic testing and instrumented Vickers micro-indentation. The results constitute a fundamental understanding of the effect of heat treatment on thermal/stress-induced martensite and resistance to plastic flow in NiTi, all of which are critical for optimizing the mechanical properties. The high temperature of the hot-rolling process caused recrystallization, recovery, and hindered precipitate formation, essentially solutionizing the NiTi. The subsequent cold-drawing-induced a high density of dislocations and martensite. Heat treatments were carried out on hot-rolled, as well as, hot-rolled then cold-drawn materials at various temperatures for 1.5 h. Transmission Electron Microscopy observations revealed that Ti 3 Ni 4 precipitates progressively increased in size and changed their interface with the matrix from being coherent to incoherent with increasing heat treatment temperature. Accompanying the changes in precipitate size and interface coherency, transformation temperatures were observed to systematically shift, leading to the occurrence of the R-phase and multiple-stage transformations. Room temperature stress-strain tests illustrated a variety of mechanical responses for the various heat treatments, from pseudoelasticity to shape memory. The changes in stress-strain behavior are interpreted in terms of shifts in the primary martensite transformation temperatures, rather then the occurrence of the R-phase transformation. The results confirm that Ti 3 Ni 4 precipitates can be used to elicit a desired isothermal stress-strain behavior in polycrystalline NiTi. Instrumented micro-indention tests revealed that Martens (Universal) Hardness values are more dependent on the resistance to dislocation

Experimental investigation on local mechanical response of superelastic NiTi shape memory alloy

International Nuclear Information System (INIS)

Xiao, Yao; Zeng, Pan; Lei, Liping

2016-01-01

In this paper, primary attention is paid to the local mechanical response of NiTi shape memory alloy (SMA) under uniaxial tension. With the help of in situ digital image correlation, sets of experiments are conducted to measure the local strain field at various thermomechanical conditions. Two types of mechanical responses of NiTi SMA are identified. The residual strain localization phenomena are observed, which can be attributed to the localized phase transformation (PT) and we affirm that most of the irreversibility is accumulated simultaneously during PT. It is found that temperature and PT play important roles in inducing delocalization of the reverse transformation. We conclude that forward transformation has more influence on the transition of mechanical response in NiTi SMA than reverse transformation in terms of the critical transition temperature for inducing delocalized reverse transformation. (technical note)

Review on structural fatigue of NiTi shape memory alloys: Pure mechanical and thermo-mechanical ones

Directory of Open Access Journals (Sweden)

Guozheng Kang

2015-11-01

Full Text Available Structural fatigue of NiTi shape memory alloys is a key issue that should be solved in order to promote their engineering applications and utilize their unique shape memory effect and super-elasticity more sufficiently. In this paper, the latest progresses made in experimental and theoretical analyses for the structural fatigue features of NiTi shape memory alloys are reviewed. First, macroscopic experimental observations to the pure mechanical and thermo-mechanical fatigue features of the alloys are summarized; then the state-of-arts in the mechanism analysis of fatigue rupture are addressed; further, advances in the construction of fatigue failure models are provided; finally, summary and future topics are outlined.

Scale up of NiTi shape memory alloy production by EBM

Science.gov (United States)

Otubo, J.; Rigo, O. D.; Moura Neto, C.; Kaufman, M. J.; Mei, P. R.

2003-10-01

The usual process to produce NiTi shape memory alloy is by vacuum induction melting (VIM) using a graphite crucible, which causes contamination of the melt with carbon. Contamination with oxygen originates from the residual oxygen inside the melting chamber. An alternative process to produce NiTi alloys is by electron beam melting (EBM) using a water-cooled copper crucible that eliminates carbon contamination, and the oxygen contamination would be minimal due to operation in a vacuum of better than 10^{-2} Pa. In a previous work, it was demonstrated that the technique is feasible for button shaped samples weighing around 30g. The present work presents the results on the scale up program that enables the production of larger samples/ingots. The results are very promising in terms of chemical composition homogeneity as well as in terms of carbon contamination, the latter being four to ten times lower than the commercially-produced VIM products, and in terms of final oxygen content which is shown to depend primarily on the starting raw materials.

Characterization of NiTi Shape Memory Damping Elements designed for Automotive Safety Systems

Science.gov (United States)

Strittmatter, Joachim; Clipa, Victor; Gheorghita, Viorel; Gümpel, Paul

2014-07-01

Actuator elements made of NiTi shape memory material are more and more known in industry because of their unique properties. Due to the martensitic phase change, they can revert to their original shape by heating when subjected to an appropriate treatment. This thermal shape memory effect (SME) can show a significant shape change combined with a considerable force. Therefore such elements can be used to solve many technical tasks in the field of actuating elements and mechatronics and will play an increasing role in the next years, especially within the automotive technology, energy management, power, and mechanical engineering as well as medical technology. Beside this thermal SME, these materials also show a mechanical SME, characterized by a superelastic plateau with reversible elongations in the range of 8%. This behavior is based on the building of stress-induced martensite of loaded austenite material at constant temperature and facilitates a lot of applications especially in the medical field. Both SMEs are attended by energy dissipation during the martensitic phase change. This paper describes the first results obtained on different actuator and superelastic NiTi wires concerning their use as damping elements in automotive safety systems. In a first step, the damping behavior of small NiTi wires up to 0.5 mm diameter was examined at testing speeds varying between 0.1 and 50 mm/s upon an adapted tensile testing machine. In order to realize higher testing speeds, a drop impact testing machine was designed, which allows testing speeds up to 4000 mm/s. After introducing this new type of testing machine, the first results of vertical-shock tests of superelastic and electrically activated actuator wires are presented. The characterization of these high dynamic phase change parameters represents the basis for new applications for shape memory damping elements, especially in automotive safety systems.

Processing and Characterization of NiTi Shape Memory Alloy Particle Reinforced Sn-In Solders

National Research Council Canada - National Science Library

Chung, Kohn C

2006-01-01

.... In previous work, it was proposed that reinforcement of solder by NiTi shape memory alloy particles to form smart composite solder reduces the inelastic strain of the solder and hence, may enhance...

French experience with electropolishing

International Nuclear Information System (INIS)

Saurin, P.; Weber, C.; Brissaud, A.; Gouillardou, G.

1989-01-01

Among the various techniques to minimize corrosion products deposition on out of core areas, surface polishing has been researched. The attention of French partners was drawn to this technique and a test was conducted at Chinon B1 NPP in 1984 using six manway covers with various surface finishing (mechanical polishing, electropolishing, mechanical plus electropolishing/on reference). On the basis of the good results obtained and with beneficial cost considerations the electropolishing of SGCH has been decided for new EDF reactors. Once the decision was made feasibility and qualifications programs were developed. Taking into account the promising results obtained, EDF asked FRAMATOME to perform the first electropolishing operation on one steam generator channel head at Nogent 1 in 1987. Since 1988 the French experience consists of the electropolishing of 4SG at Nogent 2, 4SG at Cattenom 3, 4SG at Penly 1 and 4SG at Golfech 1 (NPP), and is perfectly satisfactory. The industrial operation provides excellent polishing and does not create undesired effects. The French partners are now thinking of a new device which could be realised at FRAMATOME especially for steam generator replacement. (author)

Characterisation of melt spun Ni-Ti shape memory Ribbons' microstructure

Science.gov (United States)

Mehrabi, Kambiz; Brunčko, Mihael; Kneissl, Albert C.; Čolič, Miodrag; Stamenković, Dragoslav; Ferčec, Janko; Anžel, Ivan; Rudolf, Rebeka

2012-06-01

NiTi alloys are the most technologically important medical Shape Memory Alloys in a wide range of applications used in Orthopaedics, Neurology, Cardiology and interventional Radiology as guide-wires, self-expandable stents, stent grafts, inferior vena cava filters and clinical instruments. This paper discusses the use of rapid solidification by the melt spinning method for the preparation of thin NiTi ribbons for medical uses. Generally, the application of rapid solidification via melt-spinning can change the microstructure drastically, which improves ductility and shape memory characteristics and leads to samples with small dimensions. As the increase in the wheel speed led to a reduced ribbon thickness, the cooling rate increased and, therefore, the martensitic substructure became finer. Furthermore, no transition from the crystalline phase to the amorphous phase was obtained by increasing the cooling rate, even at a wheel speed of 30 m/s. Specimens for our metallographic investigation were cut from the longitudinal cross sections of melt-spun ribbons. Conventional TEM studies were carried out with an acceleration voltage of 120 kV. Additionally, the chemical composition of the samples was examined with a TEM equipped with an EDX analyser. The crystallographic structure was determined using Bragg-Brentano x-ray diffraction with Cu-Kα radiation at room temperature.

Sn buffered by shape memory effect of NiTi alloys as high-performance anodes for lithium ion batteries

International Nuclear Information System (INIS)

Hu Renzong; Zhu Min; Wang Hui; Liu Jiangwen; Liuzhang Ouyang; Zou Jin

2012-01-01

By applying the shape memory effect of the NiTi alloys to buffer the Sn anodes, we demonstrate a simple approach to overcome a long-standing challenge of Sn anode in the applications of Li-ion batteries – the capacity decay. By supporting the Sn anodes with NiTi shape memory alloys, the large volume change of Sn anodes due to lithiation and delithiation can be effectively accommodated, based on the stress-induced martensitic transformation and superelastic recovery of the NiTi matrix respectively, which leads to a decrease in the internal stress and closing of cracks in Sn anodes. Accordingly, stable cycleability (630 mA h g −1 after 100 cycles at 0.7C) and excellent high-rate capabilities (478 mA h g −1 at 6.7C) were attained with the NiTi/Sn/NiTi film electrode. These shape memory alloys can also combine with other high-capacity metallic anodes, such as Si, Sb, Al, and improve their cycle performance.

NiTi shape memory via solid-state nudge-elastic band

Science.gov (United States)

Zarkevich, Nikolai A.; Johnson, Duane D.

2014-03-01

We determine atomic mechanisms of the shape memory effect in NiTi from a generalized solid-state nudge elastic band (SSNEB) method. We consider transformation between the austenite B2 and the ground-state base-centered orthorhombic (BCO) structures. In these pathways we obtain the R-phase and discuss its structure. We confirm that BCO is the ground state, and determine the pathways to BCO martensite, which dictate transition barriers. While ideal B2 is unstable, we find a B2-like NiTi high-temperature solid phase with significant local displacement disorder, which is B2 on average. This B2-like phase appears to be entropically stabilized. This work is supported by the U.S. Department of Energy, Office of Basic Energy Science, Division of Materials Science and Engineering. Ames Laboratory is operated for the U.S. DOE by Iowa State University under contract DE-AC02-07CH11358.

Mechanical response of nitrogen ion implanted NiTi shape memory alloy

International Nuclear Information System (INIS)

Kucharski, S.; Levintant-Zayonts, N.; Luckner, J.

2014-01-01

Highlights: • The effect of ion implantation process on shape memory alloy was investigated. • In the implantation process both surface layer and bulk material are modified. • The microstructure is modified and superelastic effect is destroyed in surface layer. • The parameters of superelastic phenomena are changed in bulk material. - Abstract: In the paper a change of material (mechanical) parameters of NiTi shape memory alloy subjected to ion implantation treatment is investigated. The spherical indentation tests in micro- and nano-scale and tension test have been performed to study an evolution of local superelastic effect in different volumes of nonimplanted and nitrogen ion implanted NiTi alloy. The differential scanning calorimetry has been applied to measure the change of characteristic temperatures due to ion implantation treatment. The structure of implanted material has been investigated using electron microscopy technique. It has been found that the ion implantation process changes the properties not only in a thin surface layer but also in bulk material. In the layer the pseudoelastic effect is destroyed, and in the substrate is preserved, however its parameters are changed. The characteristic phase transformation temperatures in substrate are also modified

Tensile and superelastic fatigue characterization of NiTi shape memory cables

Science.gov (United States)

Sherif, Muhammad M.; Ozbulut, Osman E.

2018-01-01

This paper discusses the tensile response and functional fatigue characteristics of a NiTi shape memory alloy (SMA) cable with an outer diameter of 5.5 mm. The cable composed of multiple strands arranged as one inner core and two outer layers. The results of the tensile tests revealed that the SMA cable exhibits good superelastic behavior up to 10% strain. Fatigue characteristics were investigated under strain amplitudes ranging from 3% to 7% and a minimum of 2500 loading cycles. The evolutions of maximum tensile stress, residual strains, energy dissipation, and equivalent viscous damping under a number of loading cycles were analyzed. The fracture surface of a specimen subjected to 5000 loading cycles and 7% strain was discussed. Functional fatigue test results indicated a very high superelastic fatigue life cycle for the tested NiTi SMA cable.

Influence of Structure and Microstructure on Deformation Localization and Crack Growth in NiTi Shape Memory Alloys

Science.gov (United States)

Paul, Partha P.; Fortman, Margaret; Paranjape, Harshad M.; Anderson, Peter M.; Stebner, Aaron P.; Brinson, L. Catherine

2018-04-01

Porous NiTi shape memory alloys have applications in the biomedical and aerospace fields. Recent developments in metal additive manufacturing have made fabrication of near-net-shape porous products with complicated geometries feasible. There have also been developments in tailoring site-specific microstructures in metals using additive manufacturing. Inspired by these developments, we explore two related mechanistic phenomena in a simplified representation of porous shape memory alloys. First, we computationally elucidate the connection between pore geometry, stress concentration around pores, grain orientation, and strain-band formation during tensile loading of NiTi. Using this, we present a method to engineer local crystal orientations to mitigate the stress concentrations around the pores. Second, we experimentally document the growth of cracks around pores in a cyclically loaded superelastic NiTi specimen. In the areas of stress concentration around holes, cracks are seen to grow in large grains with [1 1 0] oriented along the tensile axis. This combined work shows the potential of local microstructural engineering in reducing stress concentration and increasing resistance to propagation of cracks in porous SMAs, potentially increasing the fatigue life of porous SMA components.

Atomistic to Continuum Multiscale and Multiphysics Simulation of NiTi Shape Memory Alloy

Science.gov (United States)

Gur, Sourav

Shape memory alloys (SMAs) are materials that show reversible, thermo-elastic, diffusionless, displacive (solid to solid) phase transformation, due to the application of temperature and/ or stress (/strain). Among different SMAs, NiTi is a popular one. NiTi shows reversible phase transformation, the shape memory effect (SME), where irreversible deformations are recovered upon heating, and superelasticity (SE), where large strains imposed at high enough temperatures are fully recovered. Phase transformation process in NiTi SMA is a very complex process that involves the competition between developed internal strain and phonon dispersion instability. In NiTi SMA, phase transformation occurs over a wide range of temperature and/ or stress (strain) which involves, evolution of different crystalline phases (cubic austenite i.e. B2, different monoclinic variant of martensite i.e. B19', and orthorhombic B19 or BCO structures). Further, it is observed from experimental and computational studies that the evolution kinetics and growth rate of different phases in NiTi SMA vary significantly over a wide spectrum of spatio-temporal scales, especially with length scales. At nano-meter length scale, phase transformation temperatures, critical transformation stress (or strain) and phase fraction evolution change significantly with sample or simulation cell size and grain size. Even, below a critical length scale, the phase transformation process stops. All these aspects make NiTi SMA very interesting to the science and engineering research community and in this context, the present focuses on the following aspects. At first this study address the stability, evolution and growth kinetics of different phases (B2 and variants of B19'), at different length scales, starting from the atomic level and ending at the continuum macroscopic level. The effects of simulation cell size, grain size, and presence of free surface and grain boundary on the phase transformation process

Impurity levels and fatigue lives of pseudoelastic NiTi shape memory alloys

International Nuclear Information System (INIS)

Rahim, M.; Frenzel, J.; Frotscher, M.; Pfetzing-Micklich, J.; Steegmüller, R.; Wohlschlögel, M.; Mughrabi, H.; Eggeler, G.

2013-01-01

In the present work we show how different oxygen (O) and carbon (C) levels affect fatigue lives of pseudoelastic NiTi shape memory alloys. We compare three alloys, one with an ultrahigh purity and two which contain the maximum accepted levels of C and O. We use bending rotation fatigue (up to cycle numbers >10 8 ) and scanning electron microscopy (for investigating microstructural details of crack initiation and growth) to study fatigue behavior. High cycle fatigue (HCF) life is governed by the number of cycles required for crack initiation. In the low cycle fatigue (LCF) regime, the high-purity alloy outperforms the materials with higher number densities of carbides and oxides. In the HCF regime, on the other hand, the high-purity and C-containing alloys show higher fatigue lives than the alloy with oxide particles. There is high experimental scatter in the HCF regime where fatigue cracks preferentially nucleate at particle/void assemblies (PVAs) which form during processing. Cyclic crack growth follows the Paris law and does not depend on impurity levels. The results presented in the present work contribute to a better understanding of structural fatigue of pseudoelastic NiTi shape memory alloys

Influence of compressive load conditions and thickness on the two-way shape memory behavior in tube-shaped NiTi alloy

International Nuclear Information System (INIS)

Yoo, Young Ik; Shin, Dong Kil; Lee, Jung Ju; Lee, Chang Ho

2012-01-01

The two-way shape memory behavior of Ni 55 Ti 45 was investigated to develop a tube-shaped NiTi actuator which could generate a large amount of force. The two-way shape memory effect (TWSME) was induced by thermal cycling under various amounts of constant compressive stress. Six specimens with the same outer diameter and different thickness were used to apply the TWSME to an actuator. A fast saturation tendency of the recovery strain was shown through training at each level of constant stress, after which the two-way shape memory strain was quantitatively measured during thermal cycling for each level of applied stress. From the results, the maximum two-way strain value was obtained after training at a constant level of stress and then decreased thereafter. In addition, the two-way strain was found to depend on the thickness of the tube-shaped specimen. All specimens could be divided into two groups depending on the rate of increase in the two-way strain. After two-way strain was obtained, the two-way recovery stress was measured to verify the performance of the sample as an actuator. The results showed that the two-way recovery stress behavior was similar to the two-way strain; if the optimal thickness of the specimen and the stress applied for training are used for the development of the TWSME, tube-shaped NiTi using the TWSME can replace one-way shape memory alloys. (paper)

Electron energy-loss spectroscopy study of NiTi shape memory alloys

International Nuclear Information System (INIS)

Yang, Z.Q.; Schryvers, D.

2008-01-01

Electron energy loss spectroscopy (EELS) investigations were carried out on NiTi shape memory alloys. The composition of lens-shaped precipitates is determined to be Ni 4 Ti 3 by model-based EELS quantification, and the Ni-depleted zone in the B2 matrix surrounding the Ni 4 Ti 3 precipitates was quantified. The Young's modulus Y m of the B2 matrix with 51 at.% Ni and the Ni 4 Ti 3 precipitates was evaluated to be about 124 and 175 GPa, respectively. The intensity of the Ni L 3 edge for the precipitate is slightly higher than that for the B2 phase

Laser welding of NiTi shape memory alloy: Comparison of the similar and dissimilar joints to AISI 304 stainless steel

Science.gov (United States)

Mirshekari, G. R.; Saatchi, A.; Kermanpur, A.; Sadrnezhaad, S. K.

2013-12-01

The unique properties of NiTi alloy, such as its shape memory effect, super-elasticity and biocompatibility, make it ideal material for various applications such as aerospace, micro-electronics and medical device. In order to meet the requirement of increasing applications, great attention has been given to joining of this material to itself and to other materials during past few years. Laser welding has been known as a suitable joining technique for NiTi shape memory alloy. Hence, in this work, a comparative study on laser welding of NiTi wire to itself and to AISI 304 austenitic stainless steel wire has been made. Microstructures, mechanical properties and fracture morphologies of the laser joints were investigated using optical microscopy, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction analysis (XRD), Vickers microhardness (HV0.2) and tensile testing techniques. The results showed that the NiTi-NiTi laser joint reached about 63% of the ultimate tensile strength of the as-received NiTi wire (i.e. 835 MPa) with rupture strain of about 16%. This joint also enabled the possibility to benefit from the pseudo-elastic properties of the NiTi component. However, tensile strength and ductility decreased significantly after dissimilar laser welding of NiTi to stainless steel due to the formation of brittle intermetallic compounds in the weld zone during laser welding. Therefore, a suitable modification process is required for improvement of the joint properties of the dissimilar welded wires.

Biocompatibility and corrosion behavior of the shape memory NiTi alloy in the physiological environments simulated with body fluids for medical applications

International Nuclear Information System (INIS)

Khalil-Allafi, Jafar; Amin-Ahmadi, Behnam; Zare, Mehrnoush

2010-01-01

Due to unique properties of NiTi shape memory alloys such as high corrosion resistance, biocompatibility, super elasticity and shape memory behavior, NiTi shape memory alloys are suitable materials for medical applications. Although TiO 2 passive layer in these alloys can prevent releasing of nickel to the environment, high nickel content and stability of passive layer in these alloys are very debatable subjects. In this study a NiTi shape memory alloy with nominal composition of 50.7 atom% Ni was investigated by corrosion tests. Electrochemical tests were performed in two physiological environments of Ringer solution and NaCl 0.9% solution. Results indicate that the breakdown potential of the NiTi alloy in NaCl 0.9% solution is higher than that in Ringer solution. The results of Scanning Electron Microscope (SEM) reveal that low pitting corrosion occurred in Ringer solution compared with NaCl solution at potentiostatic tests. The pH value of the solutions increases after the electrochemical tests. The existence of hydride products in the X-ray diffraction analysis confirms the decrease of the concentration of hydrogen ion in solutions. Topographical evaluations show that corrosion products are nearly same in all samples. The biocompatibility tests were performed by reaction of mouse fibroblast cells (L929). The growth and development of cells for different times were measured by numbering the cells or statistics investigations. The figures of cells for different times showed natural growth of cells. The different of the cell numbers between the test specimen and control specimen was negligible; therefore it may be concluded that the NiTi shape memory alloy is not toxic in the physiological environments simulated with body fluids.

Characterization of Sputtered Nickel-Titanium (NiTi) Stress and Thermally Actuated Cantilever Bimorphs Based on NiTi Shape Memory Alloy (SMA)

Science.gov (United States)

2015-11-01

necessary anneal . Following this, a thin film of NiTi was blanket sputtered at 600 °C. This NiTi blanket layer was then wet -etch patterned using a...varying the sputter parameters during NiTi deposition, such as thickness, substrate temperature during deposition and anneal , and argon pressure during...6 Fig. 4 Surface texture comparison between NiTi sputtered at RT, then annealed at 600 °C, and NiTi

Surface mechanical attrition treatment induced phase transformation behavior in NiTi shape memory alloy

International Nuclear Information System (INIS)

Hu, T.; Wen, C.S.; Lu, J.; Wu, S.L.; Xin, Y.C.; Zhang, W.J.; Chu, C.L.; Chung, J.C.Y.; Yeung, K.W.K.; Kwok, D.T.K.; Chu, Paul K.

2009-01-01

The phase constituents and transformation behavior of the martensite B19' NiTi shape memory alloy after undergoing surface mechanical attrition treatment (SMAT) are investigated. SMAT is found to induce the formation of a parent B2 phase from the martensite B19' in the top surface layer. By removing the surface layer-by-layer, X-ray diffraction reveals that the amount of the B2 phase decreases with depth. Differential scanning calorimetry (DSC) further indicates that the deformed martensite in the sub-surface layer up to 300 μm deep exhibits the martensite stabilization effect. The graded phase structure and transformation behavior in the SMATed NiTi specimen can be attributed to the gradient change in strain with depth.

Evaluation of the interfacial shear strength between pseudoplastic NiTi shape memory alloy wires and epoxy by the pull-out method

International Nuclear Information System (INIS)

Spārniņš, E; Michaud, V; Leterrier, Y; Andersons, J

2015-01-01

The interfacial shear strength (IFSS) between nickel–titanium (NiTi) shape memory alloy wires, characterized by a nonlinear stress–strain behavior, and epoxy matrix was determined by pull-out tests. Tests were carried out at several temperatures and levels of pre-strain in the wires, to evaluate the effects of embedded wire length and of crystalline state of the alloy. The IFSS between the twinned NiTi and epoxy was estimated at 24 MPa, and found to increase to 47 MPa for completely detwinned and preloaded martensitic NiTi. This increase in IFSS values was attributed to microcracking of the superficial TiO 2 layer and the resulting roughening of the NiTi wire surface. (paper)

Comparative study of root-canal shaping with stainless steel and rotary NiTi files performed by preclinical dental students.

Science.gov (United States)

Alrahabi, Mothanna

2015-01-01

We evaluated the use of NiTi rotary and stainless steel endodontic instruments for canal shaping by undergraduate students. We also assessed the quality of root canal preparation as well as the occurrence of iatrogenic events during instrumentation. In total, 30 third-year dental students attending Taibah University Dental College prepared 180 simulated canals in resin blocks with NiTi rotary instruments and stainless steel hand files. Superimposed images were prepared to measure the removal of material at different levels from apical termination using the GSA image analysis software. Preparation time, procedural accidents, and canal shape after preparation were analyzed using χ 2 and t-tests. The statistical significance level was set at P instruments and stainless steel files; the former was associated with shorter preparation time, less ledge formation (1.1% vs. 14.4%), and greater instrument fracture (5.56% vs. 1.1%). These results indicate that NiTi rotary instruments result in better canal geometry and cause less canal transportation. Manual instrumentation using stainless steel files is safer than rotary instrumentation for inexperienced students. Intensive preclinical training is a prerequisite for using NiTi rotary instruments. These results prompted us to reconsider theoretical and practical coursework when teaching endodontics.

Atomistic characterization of pseudoelasticity and shape memory in NiTi nanopillars

International Nuclear Information System (INIS)

Zhong Yuan; Gall, Ken; Zhu Ting

2012-01-01

Molecular dynamics simulations are performed to study the atomistic mechanisms governing the pseudoelasticity and shape memory in nickel–titanium (NiTi) nanostructures. For a 〈1 1 0〉 – oriented nanopillar subjected to compressive loading–unloading, we observe either a pseudoelastic or shape memory response, depending on the applied strain and temperature that control the reversibility of phase transformation and deformation twinning. We show that irreversible twinning arises owing to the dislocation pinning of twin boundaries, while hierarchically twinned microstructures facilitate the reversible twinning. The nanoscale size effects are manifested as the load serration, stress plateau and large hysteresis loop in stress–strain curves that result from the high stresses required to drive the nucleation-controlled phase transformation and deformation twinning in nanosized volumes. Our results underscore the importance of atomistically resolved modeling for understanding the phase and deformation reversibilities that dictate the pseudoelasticity and shape memory behavior in nanostructured shape memory alloys.

Rapid Obtaining of Nano-Hydroxyapatite Bioactive Films on NiTi Shape Memory Alloy by Electrodeposition Process

Science.gov (United States)

Lobo, A. O.; Otubo, J.; Matsushima, J. T.; Corat, E. J.

2011-07-01

Nano-hydroxyapatite (n-HA) crystalline films have been developed in this study by electrodeposition method on NiTi shape memory alloy (SMA). The electrodeposition of the n-HA films was carried out using 0.042 mol/L Ca(NO3)2 · 4H2O + 0.025 mol/L (NH4) · 2HPO4 electrolytes by applying a constant potential of -2.0 V for 120 min and keeping the solution temperature at 70 °C. The characterization of n-HA films is of special importance since bioactive properties related to n-HA have been directly identified with its specific composition and crystalline structure. AFM, XRD, EDX, FEG-SEM and Raman spectroscopy shows a homogeneous film, with high crystallinity, special composition, and bioactivity properties (Ca/P = 1.93) of n-HA on NiTi SMA surfaces. The n-HA coating with special structure would benefit the use of NiTi alloy in orthopedic applications.

Nanoscale compositional analysis of NiTi shape memory alloy films deposited by DC magnetron sputtering

Energy Technology Data Exchange (ETDEWEB)

Sharma, S. K.; Mohan, S. [Centre for Nano Science and Engineering, Indian Institute of Science, Bangalore-560012 (India); Bysakh, S. [Central Glass and Ceramics Research Institute, Kolkata-700032 (India); Kumar, A.; Kamat, S. V. [Defence Metallurgical Research Laboratory, Hyderabad-500058 (India)

2013-11-15

The formation of surface oxide layer as well as compositional changes along the thickness for NiTi shape memory alloy thin films deposited by direct current magnetron sputtering at substrate temperature of 300 °C in the as-deposited condition as well as in the postannealed (at 600 °C) condition have been thoroughly studied by using secondary ion mass spectroscopy, x-ray photoelectron spectroscopy, and scanning transmission electron microscopy-energy dispersive x-ray spectroscopy techniques. Formation of titanium oxide (predominantly titanium dioxide) layer was observed in both as-deposited and postannealed NiTi films, although the oxide layer was much thinner (8 nm) in as-deposited condition. The depletion of Ti and enrichment of Ni below the oxide layer in postannealed films also resulted in the formation of a graded microstructure consisting of titanium oxide, Ni{sub 3}Ti, and B2 NiTi. A uniform composition of B2 NiTi was obtained in the postannealed film only below a depth of 200–250 nm from the surface. Postannealed film also exhibited formation of a ternary silicide (Ni{sub x}Ti{sub y}Si) at the film–substrate interface, whereas no silicide was seen in the as-deposited film. The formation of silicide also caused a depletion of Ni in the film in a region ∼250–300 nm just above the film substrate interface.

Forming and control of pores by capsule-free hot isostatic pressing in NiTi shape memory alloys

International Nuclear Information System (INIS)

Yuan, B; Zhu, M; Gao, Y; Li, X; Chung, C Y

2008-01-01

In this study, the pore evolution process of porous NiTi shape memory alloys (SMAs) fabricated by capsule-free hot isostatic pressing (CF-HIP) was investigated by adopting different fabricating parameters. It is shown that porous NiTi SMAs with homogeneous pore distribution and nearly spherical pore shape can be prepared by CF-HIP under suitable conditions. In addition, two novel pore structures were produced, one with a sandwich-like structure, and another with controlled gradient of porosity along the radial direction, with pore size increasing from the outside towards the center of the specimen. The former was obtained by balancing the pressure in the HIP chamber and the gas pressure resulting from the gas expansion in the green sample. The latter resulted from the formation of air bubbles in the liquid phase during the sintering

Cyclic deformation of NiTi shape memory alloys

International Nuclear Information System (INIS)

Liu Yong; Van Humbeeck, J.; Xie Zeliang

1999-01-01

Recently, there is an increasing interest in applying the high damping capacity of shape memory alloys (SMAs). The purpose is to explore the feasibility of those materials for the protection of buildings and other civil constructions as a result of earthquake damages. So far, few experimental results have been reported concerning the mechanical cyclic behaviour of SMAs in their martensitic state (ferroelastic). In the present work, the experimental results on the mechanical behaviour of martensitic NiTi SMAs under tension-compression cyclic deformation up to strains of ±4% are summarized with major attention to the damping capacity, characteristic stresses and strains as a function of deformation cycles. Effect of strain rate, strain amplitude and annealing condition on the martensite damping is summarized. Explanation of the cyclic hardening and cyclic softening phenomenon is proposed based on TEM observations. (orig.)

A micromechanical constitutive model for anisotropic cyclic deformation of super-elastic NiTi shape memory alloy single crystals

Science.gov (United States)

Yu, Chao; Kang, Guozheng; Kan, Qianhua

2015-09-01

Based on the experimental observations on the anisotropic cyclic deformation of super-elastic NiTi shape memory alloy single crystals done by Gall and Maier (2002), a crystal plasticity based micromechanical constitutive model is constructed to describe such anisotropic cyclic deformation. To model the internal stress caused by the unmatched inelastic deformation between the austenite and martensite phases on the plastic deformation of austenite phase, 24 induced martensite variants are assumed to be ellipsoidal inclusions with anisotropic elasticity and embedded in the austenite matrix. The homogeneous stress fields in the austenite matrix and each induced martensite variant are obtained by using the Mori-Tanaka homogenization method. Two different inelastic mechanisms, i.e., martensite transformation and transformation-induced plasticity, and their interactions are considered in the proposed model. Following the assumption of instantaneous domain growth (Cherkaoui et al., 1998), the Helmholtz free energy of a representative volume element of a NiTi shape memory single crystal is established and the thermodynamic driving forces of the internal variables are obtained from the dissipative inequalities. The capability of the proposed model to describe the anisotropic cyclic deformation of super-elastic NiTi single crystals is first verified by comparing the predicted results with the experimental ones. It is concluded that the proposed model can capture the main quantitative features observed in the experiments. And then, the proposed model is further used to predict the uniaxial and multiaxial transformation ratchetting of a NiTi single crystal.

High quality vacuum induction melting of small quantities of NiTi shape memory alloys in graphite crucibles

International Nuclear Information System (INIS)

Frenzel, J.; Zhang, Z.; Neuking, K.; Eggeler, G.

2004-01-01

Binary NiTi based shape memory alloys can be produced starting from the pure elements (Ni-pellets, Ti-rods) by using vacuum induction melting (VIM). VIM ingot metallurgy is known to produce materials with a good chemical homogeneity; it, moreover, is cheaper than vacuum arc melting (VAM) when small quantities of laboratory materials are needed. In a VIM procedure, graphite crucibles are attractive because they have appropriate electrical properties. For NiTi melting, graphite crucibles are interesting because they are reasonably priced and they show a good resistance against thermal cracking. On the other hand, it is well known that melting of Ti alloys in graphite crucibles is associated with a vigorous interface reaction. And the carbon concentration of NiTi alloys needs to be kept below a certain minimum in order to assure that the functional properties of the alloys meet the required targets. Therefore, it is important to minimize the carbon pick up of the melt. The present work presents experimental results and discusses thermodynamic and kinetic aspects of the reaction of NiTi melts with graphite crucibles; a method is suggested to keep the carbon dissolution into the melt at a minimum

Improvement of Ti-plasma coating on Ni-Ti shape memory alloy applying to implant materials and its evaluation

International Nuclear Information System (INIS)

Okuyama, Masaru; Endo, Jun; Take, Seisho; Itoi, Yasuhiko; Kambe, Satoshi

2002-01-01

Utilizing of Ni-Ti shape memory alloy for implant materials has been world-widely studied. it is, however, known that Ni-Ti alloy is easily attacked by chloride ion contained in body liquid. To prevent Ni dissolution, the authors tried to coat the alloy surface with titanium metal by means of plasma-spray coating method. The plasma coating films resulted in rather accelerating pitting corrosion because of their high porosity. Therefore, sealing of the porous films was required. In order to solve this problem and satisfy prolonged lifetime in the body, the authors tried to use the vacuum evaporation technique of titanium metal. Two types of Ti vacuum evaporation procedures were employed. The one was to cover a thin film on Ni-Ti alloy surface prior to massive Ti plasma spray coating. The other was to first coat plasma spray films on Ni-Ti alloy and then to cover them with vacuum evaporation films of Ti. Protective ability against pitting corrosion was examined by electrochemical polarization measurement in physiological solution and the coating films were characterized by microscopic and SEM observation and EPMA analysis. Vacuum evaporation thin films could not protect Ni-Ti alloy from pitting corrosion. In the case of plasma spray coating over the Ti vacuum evaporation thin film, the substrate Ni-Ti alloy could not be better protected. On the contrary, vacuum evaporation of Ti over the porous plasma spray coating layer remarkably improved corrosion protective performance

Laser shock wave assisted patterning on NiTi shape memory alloy surfaces

Science.gov (United States)

Seyitliyev, Dovletgeldi; Li, Peizhen; Kholikov, Khomidkhodza; Grant, Byron; Karaca, Haluk E.; Er, Ali O.

2017-02-01

An advanced direct imprinting method with low cost, quick, and less environmental impact to create thermally controllable surface pattern using the laser pulses is reported. Patterned micro indents were generated on Ni50Ti50 shape memory alloys (SMA) using an Nd:YAG laser operating at 1064 nm combined with suitable transparent overlay, a sacrificial layer of graphite, and copper grid. Laser pulses at different energy densities which generates pressure pulses up to 10 GPa on the surface was focused through the confinement medium, ablating the copper grid to create plasma and transferring the grid pattern onto the NiTi surface. Scanning electron microscope (SEM) and optical microscope images of square pattern with different sizes were studied. One dimensional profile analysis shows that the depth of the patterned sample initially increase linearly with the laser energy until 125 mJ/pulse where the plasma further absorbs and reflects the laser beam. In addition, light the microscope image show that the surface of NiTi alloy was damaged due to the high power laser energy which removes the graphite layer.

Damage-based life prediction model for uniaxial low-cycle stress fatigue of super-elastic NiTi shape memory alloy microtubes

Science.gov (United States)

Song, Di; Kang, Guozheng; Kan, Qianhua; Yu, Chao; Zhang, Chuanzeng

2015-08-01

Based on the experimental observations for the uniaxial low-cycle stress fatigue failure of super-elastic NiTi shape memory alloy microtubes (Song et al 2015 Smart Mater. Struct. 24 075004) and a new definition of damage variable corresponding to the variation of accumulated dissipation energy, a phenomenological damage model is proposed to describe the damage evolution of the NiTi microtubes during cyclic loading. Then, with a failure criterion of Dc = 1, the fatigue lives of the NiTi microtubes are predicted by the damage-based model, the predicted lives are in good agreement with the experimental ones, and all of the points are located within an error band of 1.5 times.

Damage-based life prediction model for uniaxial low-cycle stress fatigue of super-elastic NiTi shape memory alloy microtubes

International Nuclear Information System (INIS)

Song, Di; Kang, Guozheng; Kan, Qianhua; Yu, Chao; Zhang, Chuanzeng

2015-01-01

Based on the experimental observations for the uniaxial low-cycle stress fatigue failure of super-elastic NiTi shape memory alloy microtubes (Song et al 2015 Smart Mater. Struct. 24 075004) and a new definition of damage variable corresponding to the variation of accumulated dissipation energy, a phenomenological damage model is proposed to describe the damage evolution of the NiTi microtubes during cyclic loading. Then, with a failure criterion of D c = 1, the fatigue lives of the NiTi microtubes are predicted by the damage-based model, the predicted lives are in good agreement with the experimental ones, and all of the points are located within an error band of 1.5 times. (paper)

Effects of water plasma immersion ion implantation on surface electrochemical behavior of NiTi shape memory alloys in simulated body fluids

International Nuclear Information System (INIS)

Liu, X.M.; Wu, S.L.; Chu, Paul K.; Chung, C.Y.; Chu, C.L.; Yeung, K.W.K.; Lu, W.W.; Cheung, K.M.C.; Luk, K.D.K.

2007-01-01

Water plasma immersion ion implantation (PIII) was conducted on orthopedic NiTi shape memory alloy to enhance the surface electrochemical characteristics. The surface composition of the NiTi alloy before and after H 2 O-PIII was determined by X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) was utilized to determine the roughness and morphology of the NiTi samples. Potentiodynamic polarization tests and electrochemical impedance spectroscopy (EIS) were carried out to investigate the surface electrochemical behavior of the control and H 2 O-PIII NiTi samples in simulated body fluids (SBF) at 37 deg. C as well as the mechanism. The H 2 O-PIII NiTi sample showed a higher breakdown potential (E b ) than the control sample. Based on the AFM results, two different physical models with related equivalent electrical circuits were obtained to fit the EIS data and explain the surface electrochemical behavior of NiTi in SBF. The simulation results demonstrate that the higher resistance of the oxide layer produced by H 2 O-PIII is primarily responsible for the improvement in the surface corrosion resistance

Electropolished Titanium Implants with a Mirror-Like Surface Support Osseointegration and Bone Remodelling

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Cecilia Larsson Wexell

2016-01-01

Full Text Available This work characterises the ultrastructural composition of the interfacial tissue adjacent to electropolished, commercially pure titanium implants with and without subsequent anodisation, and it investigates whether a smooth electropolished surface can support bone formation in a manner similar to surfaces with a considerably thicker surface oxide layer. Screw-shaped implants were electropolished to remove all topographical remnants of the machining process, resulting in a thin spontaneously formed surface oxide layer and a smooth surface. Half of the implants were subsequently anodically oxidised to develop a thickened surface oxide layer and increased surface roughness. Despite substantial differences in the surface physicochemical properties, the microarchitecture and the composition of the newly formed bone were similar for both implant surfaces after 12 weeks of healing in rabbit tibia. A close spatial relationship was observed between osteocyte canaliculi and both implant surfaces. On the ultrastructural level, the merely electropolished surface showed the various stages of bone formation, for example, matrix deposition and mineralisation, entrapment of osteoblasts within the mineralised matrix, and their morphological transformation into osteocytes. The results demonstrate that titanium implants with a mirror-like surface and a thin, spontaneously formed oxide layer are able to support bone formation and remodelling.

Electropolishing-Orthodontic Office: A Simplified Approach

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Sudhir Munjal

2014-01-01

Full Text Available Electropolishing plays an important role in dentistry by providing enhanced mechanical properties, better corrosion protection, physical appearance and ease of cleaning various metallic attachments. To achieve all these objectives, we present here a simple and economical way to fabricate a electropolisher which has wide applications in orthodontic office (recycle brackets, anneal retention wires, etc..

Exploiting NiTi shape memory alloy films in design of tunable high frequency microcantilever resonators

Science.gov (United States)

Stachiv, I.; Sittner, P.; Olejnicek, J.; Landa, M.; Heller, L.

2017-11-01

Shape memory alloy (SMA) films are very attractive materials for microactuators because of their high energy density. However, all currently developed SMA actuators utilize martensitic transformation activated by periodically generated heating and cooling; therefore, they have a slow actuation speed, just a few Hz, which restricts their use in most of the nanotechnology applications such as high frequency microcantilever based physical and chemical sensors, atomic force microscopes, or RF filters. Here, we design tunable high frequency SMA microcantilevers for nanotechnology applications. They consist of a phase transforming NiTi SMA film sputtered on the common elastic substrate material; in our case, it is a single-crystal silicon. The reversible tuning of microcantilever resonant frequencies is then realized by intentionally changing the Young's modulus and the interlayer stress of the NiTi film by temperature, while the elastic substrate guarantees the high frequency actuation (up to hundreds of kHz) of the microcantilever. The experimental results qualitatively agree with predictions obtained from the dedicated model based on the continuum mechanics theory and a phase characteristic of NiTi. The present design of SMA microcantilevers expands the capability of current micro-/nanomechanical resonators by enabling tunability of several consecutive resonant frequencies.

Finding the energy source for self-propagating high-temperature synthesis production of NiTi shape memory alloy

Czech Academy of Sciences Publication Activity Database

Novák, P.; Školáková, A.; Pignol, D.; Průša, F.; Salvetr, P.; Kubatík, Tomáš František; Perriere, L.; Karlík, M.

2016-01-01

Roč. 181, September (2016), s. 295-300 ISSN 0254-0584 Institutional support: RVO:61389021 Keywords : NiTi * Shape memory alloys * Powder metallurgy * Microstructure Subject RIV: JG - Metallurgy Impact factor: 2.084, year: 2016 http://www.sciencedirect.com/science/article/pii/S025405841630476X

Martensitic transformation and shape memory effect in NiTi alloy covered by chitosan/silver layer

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Goryczka Tomasz

2015-01-01

Full Text Available The NiTi shape memory alloy was covered with chitosan/silver layer. Coatings were deposited at room temperature using combination of processing parameters such as deposition voltage and amount of silver in colloidal suspension. Structure of layers was studied by means of X-ray diffraction. Quality of the coatings was evaluated basing on observations done in scanning electron microscopy. Transformation behaviour of coated samples was studied with use of differential scanning calorimeter. The covered sample revealed presence of the reversible martensitic transformation and ability to deformation (in bending mode up to 8%. Forward martensitic transformation, in as-received NiTi alloy and in alloy after layer deposition occurred in two steps B2-R-B19’. After deformation quality of the chitosan/silver layer remained unchanged.

Application of Taguchi method to optimization of surface roughness during precise turning of NiTi shape memory alloy

Science.gov (United States)

Kowalczyk, M.

2017-08-01

This paper describes the research results of surface quality research after the NiTi shape memory alloy (Nitinol) precise turning by the tools with edges made of polycrystalline diamonds (PCD). Nitinol, a nearly equiatomic nickel-titanium shape memory alloy, has wide applications in the arms industry, military, medicine and aerospace industry, and industrial robots. Due to their specific properties NiTi alloys are known to be difficult-to-machine materials particularly by using conventional techniques. The research trials were conducted for three independent parameters (vc, f, ap) affecting the surface roughness were analyzed. The choice of parameter configurations were performed by factorial design methods using orthogonal plan type L9, with three control factors, changing on three levels, developed by G. Taguchi. S/N ratio and ANOVA analyses were performed to identify the best of cutting parameters influencing surface roughness.

Characteristics and in vitro biological assessment of (Ti, O, N)/Ti composite coating formed on NiTi shape memory alloy

International Nuclear Information System (INIS)

Sun Tao; Wang Langping; Wang Min; Tong, Ho-Wang; Lu, William W.

2011-01-01

In this investigation, plasma immersion ion implantation and deposition (PIIID) was used to fabricate a (Ti, O, N)/Ti coating on NiTi shape memory alloy (SMA) to improve its long-term biocompatibility and wear resistance. The surface morphology, composition and roughness of uncoated and coated NiTi SMA samples were examined. Energy dispersive X-ray elemental mapping of cross-sections of (Ti, O, N)/Ti coated NiTi SMA revealed that Ni was depleted from the surface of coated samples. No Ni was detected by X-ray photoelectron spectroscopy on the surface of coated samples. Furthermore, three-point bending tests showed that the composite coating could undergo large deformation without cracking or delamination. After 1 day cell culture, SaOS-2 cells on coated samples spread better than those on uncoated NiTi SMA samples. The proliferation of SaOS-2 cells on coated samples was significantly higher at day 3 and day 7 of cell culture.

Ni4Ti3 precipitate structures in Ni-rich NiTi shape memory alloys

Czech Academy of Sciences Publication Activity Database

Holec, David; Bojda, Ondřej; Dlouhý, Antonín

2008-01-01

Roč. 481, Sp. Iss. (2008), s. 462-465 ISSN 0921-5093. [ESOMAT 2006. Bochum, 10.09.2006-15.09.2006] R&D Projects: GA ČR(CZ) GA106/05/0918 Institutional research plan: CEZ:AV0Z20410507 Keywords : NiTi shape memory alloys * Ni4Ti3 precipitates * Multi-step martensitic transformations Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.806, year: 2008

Vehicle for surface decontamination by electropolishing

International Nuclear Information System (INIS)

Maury, A.

1984-01-01

The invention concerns a remote controlled, electric powered vehicle for continuous decontamination of several supports forming an angle for instance the bottom and the walls of nuclear swimming pools. The vehicle is provided with all the means required for electropolishing (electrolyte, pumps, effluent recovery etc...) and two electropolishing units, one under the vehicle for horizontal surface treatment the other adjustable in height on a bracket for vertical surface treatment [fr

Powder-metallurgy preparation of NiTi shape-memory alloy using mechanical alloying and spark-plasma sintering.

Czech Academy of Sciences Publication Activity Database

Novák, P.; Moravec, H.; Vojtěch, V.; Knaislová, A.; Školáková, A.; Kubatík, Tomáš František; Kopeček, Jaromír

2017-01-01

Roč. 51, č. 1 (2017), s. 141-144 ISSN 1580-2949 R&D Projects: GA ČR(CZ) GA14-03044S Institutional support: RVO:61389021 ; RVO:68378271 Keywords : mechanical alloying * spark plasma sintering * NiTi * shape memory alloy Subject RIV: JG - Metallurgy; JG - Metallurgy (FZU-D) OBOR OECD: Materials engineering ; Materials engineering (FZU-D) Impact factor: 0.436, year: 2016 https://www.researchgate.net/publication/313900224_Powder-metallurgy_preparation_of_NiTi_shape-memory_alloy_using_mechanical_alloying_and_spark-plasma_sintering

Energy landscape for martensitic phase transformation in shape memory NiTi

International Nuclear Information System (INIS)

Kibey, S.; Sehitoglu, H.; Johnson, D.D.

2009-01-01

First-principles calculations are presented for parent B2 phase and martensitic B19 and B19' phases in NiTi. The results indicate that both B19 and B19' are energetically more stable than the parent B2 phase. By means of ab initio density functional theory, the complete distortion-shuffle energy landscape associated with B2 → B19 transformation in NiTi is then determined. In addition to accounting for the Bain-type deformation through the Cauchy-Born rule, the study explicitly accounts for the shuffle displacements experienced by the internal ions in NiTi. The energy landscape allows the energy barrier associated with the B2 → B19 transformation pathway to be identified. The results indicate that a barrier of 0.48 mRyd atom -1 (relative to the B2 phase) must be overcome to transform the parent B2 NiTi to orthorhombic B19 martensite

NiTi shape-memory alloy oxidized in low-temperature plasma with carbon coating: Characteristic and a potential for cardiovascular applications

Science.gov (United States)

Witkowska, Justyna; Sowińska, Agnieszka; Czarnowska, Elżbieta; Płociński, Tomasz; Borowski, Tomasz; Wierzchoń, Tadeusz

2017-11-01

Surface layers currently produced on NiTi alloys do not meet all the requirements for materials intended for use in cardiology. Plasma surface treatments of titanium and its alloys under glow discharge conditions make it possible to produce surface layers, such as TiN or TiO2, which increases corrosion resistance and biocompatibility. The production of layers on NiTi alloys with the same properties, and maintaining their shape memory and superelasticity features, requires the use of low-temperature processes. At the same time, since it is known that the carbon-based layers could prevent excessive adhesion and aggregation of platelets, we examined the composite a-CNH + TiO2 type surface layer produced by means of a hybrid method combining oxidation in low-temperature plasma and Radio Frequency Chemical Vapor Deposition (RFCVD) processes. Investigations have shown that this composite layer increases the corrosion resistance of the material, and both the low degree of roughness and the chemical composition of the surface produced lead to decreased platelet adhesion and aggregation and proper endothelialization, which could extend the range of applications of NiTi shape memory alloys.

Tribological performance of near equiatomic and Ti-rich NiTi shape memory alloy thin films

International Nuclear Information System (INIS)

Tillmann, Wolfgang; Momeni, Soroush

2015-01-01

Near equiatomic and Ti-rich NiTi shape memory alloy thin films were magnetron sputtered with the same processing parameters and thickness of 3 μm. The microstructure, composition, shape memory behavior, mechanical and tribological properties of the deposited thin films were analyzed by using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), differential scanning calorimetry (DSC), nanoindentation, ball-on-disc, scratch test, and three dimensional (3D) optical microscopy. The obtained results clearly show how the crystallization evolution and precipitation formation of these two sets of thin films can drastically influence their mechanical and tribological performances

Influence of NiTi alloy on the root canal shaping capabilities of the ProTaper Universal and ProTaper Gold rotary instrument systems

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Jussaro Alves DUQUE

Full Text Available Abstract Objective This study aimed to evaluate the influence of the NiTi wire in Conventional NiTi (ProTaper Universal PTU and Controlled Memory NiTi (ProTaper Gold PTG instrument systems on the quality of root canal preparation. Material and Methods Twelve mandibular molars with separate mesial canals were scanned using a high-definition microcomputed tomography system. The PTU and PTG instruments were used to shape twelve mesial canals each. The canals were scanned after preparation with F2 and F3 instruments of the PTU and PTG systems. The analyzed parameters included the remaining dentin thickness at the apical and cervical levels, root canal volume and untouched canal walls. Data was analyzed for statistical significance by the Friedman and Dunn’s tests. For the comparison of data between groups, the Mann-Whitney test was used. Results In the pre-operative analysis, there were no statistically significant differences between the groups in terms of the area and volume of root canals (P>.05. There was also no statistically significant difference between the systems with respect to root canal volume after use of the F2 and F3 instruments. There was no statistical difference in the dentin thickness at the first apical level between, before and after instrumentation for both systems. At the 3 cervical levels, the PTG maintained centralization of the preparation on the transition between the F2 and F3 instruments, which did not occur with the PTU. Conclusion The Conventional NiTi (PTU and Controlled Memory NiTi (PTG instruments displayed comparable capabilities for shaping the straight mesial root canals of mandibular molars, although the PTG was better than the PTU at maintaining the centralization of the shape in the cervical portion.

Influence of NiTi alloy on the root canal shaping capabilities of the ProTaper Universal and ProTaper Gold rotary instrument systems

Science.gov (United States)

DUQUE, Jussaro Alves; VIVAN, Rodrigo Ricci; CAVENAGO, Bruno Cavalini; AMOROSO-SILVA, Pablo Andrés; BERNARDES, Ricardo Affonso; de VASCONCELOS, Bruno Carvalho; DUARTE, Marco Antonio Hungaro

2017-01-01

Abstract Objective This study aimed to evaluate the influence of the NiTi wire in Conventional NiTi (ProTaper Universal PTU) and Controlled Memory NiTi (ProTaper Gold PTG) instrument systems on the quality of root canal preparation. Material and Methods Twelve mandibular molars with separate mesial canals were scanned using a high-definition microcomputed tomography system. The PTU and PTG instruments were used to shape twelve mesial canals each. The canals were scanned after preparation with F2 and F3 instruments of the PTU and PTG systems. The analyzed parameters included the remaining dentin thickness at the apical and cervical levels, root canal volume and untouched canal walls. Data was analyzed for statistical significance by the Friedman and Dunn’s tests. For the comparison of data between groups, the Mann-Whitney test was used. Results In the pre-operative analysis, there were no statistically significant differences between the groups in terms of the area and volume of root canals (P>.05). There was also no statistically significant difference between the systems with respect to root canal volume after use of the F2 and F3 instruments. There was no statistical difference in the dentin thickness at the first apical level between, before and after instrumentation for both systems. At the 3 cervical levels, the PTG maintained centralization of the preparation on the transition between the F2 and F3 instruments, which did not occur with the PTU. Conclusion The Conventional NiTi (PTU) and Controlled Memory NiTi (PTG) instruments displayed comparable capabilities for shaping the straight mesial root canals of mandibular molars, although the PTG was better than the PTU at maintaining the centralization of the shape in the cervical portion. PMID:28198973

Precipitation of Ni4Ti3-variants in a polycrystalline Ni-rich NiTi shape memory alloy

Czech Academy of Sciences Publication Activity Database

Bojda, Ondřej; Eggeler, G.; Dlouhý, Antonín

2005-01-01

Roč. 53, č. 1 (2005), s. 99-104 ISSN 1359-6462 R&D Projects: GA ČR(CZ) GA106/05/0918 Institutional research plan: CEZ:AV0Z20410507 Keywords : NiTi shape memory alloys * Ni4Ti3 precipitation * Transmission electron microscopy Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 2.228, year: 2005

The effect of annealing on the mechanical properties and microstructural evolution of Ti-rich NiTi shape memory alloy

Energy Technology Data Exchange (ETDEWEB)

Tadayyon, Ghazal [Department of Metallurgical and Materials Engineering Faculty of Engineering, Ferdowsi University of Mashhad (Iran, Islamic Republic of); Centre for Research in Medical Devices (CURAM), National University of Ireland, Galway (Ireland); Mazinani, Mohammad, E-mail: mazinani@um.ac.ir [Department of Metallurgical and Materials Engineering Faculty of Engineering, Ferdowsi University of Mashhad (Iran, Islamic Republic of); Guo, Yina [Materials and Surface Science Institute, University of Limerick, Limerick (Ireland); Zebarjad, Seyed Mojtaba [Department of Materials Science and Engineering, School of Engineering, Shiraz University, Shiraz (Iran, Islamic Republic of); Tofail, Syed A.M. [Materials and Surface Science Institute, University of Limerick, Limerick (Ireland); Biggs, Manus J. [Centre for Research in Medical Devices (CURAM), National University of Ireland, Galway (Ireland)

2016-04-26

An investigation was carried out into the influence of the annealing temperatures on the thermo-mechanical behavior of Ti-rich NiTi alloy with regard to transformation temperatures, mechanical properties at room temperature and microstructure evolution under deformation. It was found that annealing above the recrystallization temperature (600 °C) modulated the mechanical behavior of the alloy significantly. Based on tensile and DSC analysis, it was observed that by increasing the annealing temperature, the shape memory behavior of the alloys improved. Scanning and transmission electron microscopy were used to investigate the fracture surfaces and microstructural evolution of the NiTi samples after failure. Fractography revealed the brittle fracture area produced through the propagation of cleavage cracks; however, ductile fracture via nucleation growth and coalescence of micro-dimples in the martensitic phase at room temperature were also observed. During plastic deformation, the NiTi alloy was also observed to undergo a detwinning process, dislocation slip and the formation of submicrocrystalline grains, nanocrystallization and amorphous bands.

The Effect of Particles Shape and Size on Feedstock Flowibility and Chemical content of As-sintered NiTi Alloys

Science.gov (United States)

Kadir, R. A. Abdul; Razali, R.; Mohamad Nor, N. H.; Subuki, I.; Ismail, M. H.

2018-05-01

This paper presents a comparative study of two different titanium powders in fabrication of NiTi alloys by metal injection moulding (MIM) route. Two batches of powder mixture consisted of Ni-Ti and Ni-TiH2 with atomic ratio (at%) of 50-50 were prepared. TiH2 powder was used as a substitution for pure Ti powder owing to its relatively cheaper cost and has been claimed favourable in producing less impurity uptake in sintering process. The binder system used for both mixtures comprised of composite binder of palm stearin (PS) and polyethylene (PE) at weigth ratio (wt%) of 60-40. The flow behaviour of the mixtures was analysed using a capillary rheometer at different shear rates and temperatures. The results showed that owing to irregular shape of TiH2 compared to Ti powder, the viscosity of the feedstock was significantly higher, thus required greater temperature in order to improve the mouldability of the feedstock. Nevertheless, both feedstocks exhibited pseudoplastic, a shear thinning behavior with shear rate and temperature, desirable properties for injection moulding process. Samples prepared with Ni-Ti feedstock were sintered in a high vacuum furnace, while Ni-TiH2 feedstock was sintered in a tube furnace under a flowing of Argon gas. The results showed that the impurity contents (Carbon and Oxygen) for both feedstocks were almost comparable, suggesting NiTi alloy samples prepared with TiH2 powder is an attractive route for manufacturing of NiTi alloys.

Characteristics of the stress-induced formation of R-phase in ultrafine-grained NiTi shape memory wire

International Nuclear Information System (INIS)

Olbricht, J.; Yawny, A.; Pelegrina, J.L.; Eggeler, G.; Yardley, V.A.

2013-01-01

Highlights: •We investigated the stress-induced formation of R-phase in NiTi shape memory wires. •The R-phase related strains were isolated from the overall stress-strain-behavior. •The stress–strain characteristics of R-phase suggest a homogeneous transformation. •Thermography confirms the homogeneous R-phase formation in ultrafine-grained NiTi. -- Abstract: The transformation between the cubic B2 and monoclinic B19′ phases in ultrafine-grained pseudoelastic NiTi can occur as a two-step process involving the intermediate rhombohedral R-phase. Experimental work using differential scanning calorimetry, electrical resistance measurements and transmission electron microscopy has demonstrated the formation of this intermediate phase during thermal cycling and during mechanical loading. In the present paper, complementary mechanical and thermographic results are presented which allow to further assess the character of the stress-induced R-phase formation. The transformation from B2 to R-phase is demonstrated to occur homogeneously within the gauge length rather than via advancing Lüders-type transition regions as it is the case in the localized transformation from B2 or R-phase to B19′

Confining jackets for concrete cylinders using NiTiNb and NiTi shape memory alloy wires

Energy Technology Data Exchange (ETDEWEB)

Choi, Eunsoo; Yoon, Soon-Jong [Department of Civil Engineering, Hongik University, Seoul 121-791 (Korea, Republic of); Nam, Tae-Hyun [School of Materials Science and Engineering and ERI, Gyeongsang National University, Jinju, Gyeongnam 600-701 (Korea, Republic of); Cho, Sun-Kyu [School of Civil Engineering, Seoul National University of Technology, Seoul 139-743 (Korea, Republic of); Park, Joonam, E-mail: eunsoochoi@hongik.ac.k [Department of Railroad Structure Research, Korea Railroad Research Institute, Uiwang 437-050, Korea (Korea, Republic of)

2010-05-01

This study used prestrained NiTiNb and NiTi shape memory alloy (SMA) wires to confine concrete cylinders. The recovery stress of the wires was measured with respect to the maximal prestrain of the wires. SMA wires were preelongated during the manufacturing process and then wrapped around concrete cylinders of 150 mmx300 mm ({phi}xL). Unconfined concrete cylinders were tested for compressive strength and the results were compared to those of cylinders confined by SMA wires. NiTiNb SMA wires increased the compressive strength and ductility of the cylinders due to the confining effect. NiTiNb wires were found to be more effective in increasing the peak strength of the cylinders and dissipating energy than NiTi wires. This study showed the potential of the proposed method to retrofit reinforced concrete columns using SMA wires to protect them from earthquakes.

Precipitation-induced of partial annealing of Ni-rich NiTi shape memory alloy

Science.gov (United States)

Nashrudin, Muhammad Naqib; Mahmud, Abdus Samad; Mohamad, Hishamiakim

2018-05-01

NiTi shape memory alloy behavior is very sensitive to alloy composition and heat treatment processes. Thermomechanical behavior of near-equiatomic alloy is normally enhanced by partial anneal of a cold-worked specimen. The shape memory behavior of Ni-rich alloy can be enhanced by ageing precipitation. This work studied the effect of simultaneous partial annealing and ageing precipitation of a Ni-rich cold drawn Ti-50.9at%Ni wire towards martensite phase transformation behavior. Ageing treatment of a non-cold worked specimen was also done for comparison. It was found that the increase of heat treatment temperature caused the forward transformation stress to decrease for the cold worked and non-cold worked specimens. Strain recovery on the reverse transformation of the cold worked wire improved compared to the non-cold worked wire as the temperature increased.

Narrow thermal hysteresis of NiTi shape memory alloy thin films with submicrometer thickness

Energy Technology Data Exchange (ETDEWEB)

Hou, Huilong; Hamilton, Reginald F., E-mail: rfhamilton@psu.edu; Horn, Mark W. [Department of Engineering Science and Mechanics, The Pennsylvania State University, University Park, Pennsylvania 16802 (United States)

2016-09-15

NiTi shape memory alloy (SMA) thin films were fabricated using biased target ion beam deposition (BTIBD), which is a new technique for fabricating submicrometer-thick SMA thin films, and the capacity to exhibit shape memory behavior was investigated. The thermally induced shape memory effect (SME) was studied using the wafer curvature method to report the stress-temperature response. The films exhibited the SME in a temperature range above room temperature and a narrow thermal hysteresis with respect to previous reports. To confirm the underlying phase transformation, in situ x-ray diffraction was carried out in the corresponding phase transformation temperature range. The B2 to R-phase martensitic transformation occurs, and the R-phase transformation is stable with respect to the expected conversion to the B19′ martensite phase. The narrow hysteresis and stable R-phase are rationalized in terms of the unique properties of the BTIBD technique.

Electropolishing as a decontamination process: progress and applications

International Nuclear Information System (INIS)

Allen, R.P.; Arrowsmith, H.W.; Charlot, L.A.; Hooper, J.L.

1978-04-01

Research studies demonstrated the ability of electropolishing to reduce the radiation levels of steel tools and stainless steel vacuum system components, which were heavily contaminated with plutonium oxide, from 1 million dis/min x 100 cm 2 to background in less than 10 min. Other examples of objects that have been decontaminated within minutes using electropolishing include hot cell manipulator assemblies, analytical instrument components, laboratory transfer containers, offsite shipping containers, fission product storage capsules, laboratory animal cages, and nuclear reactor process tube components. One of the major activities of this research has been the establishment and intensive operation of a 400-gal immersion electropolishing system. Progress has also been made in developing in situ electropolishing techniques that can be used to decontaminate metallic surfaces that cannot readily be transported to or immersed in a conventional electropolishing tank. Sectioning/pretreatment studies are under way to develop and demonstrate optimum disassembly, sectioning, surface preparation, and gross contamination removal procedures. Arc saw, plasma arc torch, and explosive cutting techniques are being evaluated in terms of the thickness and characteristics of the disturbed metal layer. Some of the pretreatment methods under consideration for removal of paint, grease, corrosion layers, and gross contamination include vibratory finishing, ultrasonics, dry and liquid abrasive blasting, and high-pressure spray systems. Other supporting studies are also in progress to provide a sound technical basis for scale-up and widespread application of this new decontamination process. 44 figures

Cleaning of dismantled metals by electropolishing

International Nuclear Information System (INIS)

Wei, T.Y.; Chung, Z.J.; Lu, D.L.; Hsieh, J.C.

1995-01-01

A project of cleaning dismantled metals is going on at INER. The test work has been performed. Results showed that the activity decreased from 45 microSv/h to background level after 20 minutes electrolytic polishing. These cleaned metals could be reused through melting and fabricating. These metals could also be classified as BRC waste to facilitate the waste management if they can pass the identification and be admitted by the government authority. In order to achieve the planned target, some electro-decontamination facilities have been established. An automatic electropolishing facility with six cells was designed to clean the contaminated metals in plate type with dimensions less than 50 cm x 50 cm. Another automatic electropolishing facility was specially designed for treating the contaminated pipes. In addition, mobile electropolishing facilities were also established for large pieces of metal and some fixed equipment. In this cleaning project, a practical recycling and treatment method for electrolyte has been developed in order to comply with the requirement of secondary waste minimization

PIIID-formed (Ti, O)/Ti, (Ti, N)/Ti and (Ti, O, N)/Ti coatings on NiTi shape memory alloy for medical applications

Energy Technology Data Exchange (ETDEWEB)

Sun Tao, E-mail: taosun@hotmail.com.hk [Department of Mechanical Engineering, University of Hong Kong, Pokfulam Road (Hong Kong); Institute of Microelectronics, Agency for Science, Technology and Research (A-STAR) (Singapore); Wang Langping, E-mail: aplpwang@hit.edu.cn [State Key Lab of Advanced Welding and Joining, Harbin Institute of Technology (China); Wang Min; Tong Howang [Department of Mechanical Engineering, University of Hong Kong, Pokfulam Road (Hong Kong); Lu, William W. [Department of Orthopedics and Traumatology, University of Hong Kong, Sassoon Road (Hong Kong)

2012-08-01

(Ti, O)/Ti, (Ti, N)/Ti and (Ti, O, N)/Ti composite coatings were fabricated on NiTi shape memory alloy via plasma immersion ion implantation and deposition (PIIID). Surface morphology of samples was investigated using atomic force microscopy (AFM) and scanning electron microscopy (SEM). Cross-sectional morphology indicated that the PIIID-formed coatings were dense and uniform. X-ray diffraction (XRD) was used to characterize the phase composition of samples. X-ray photoelectron spectroscopy (XPS) results showed that the surface of coated NiTi SMA samples was Ni-free. Nanoindentation measurements and pin-on-disc tests were carried out to evaluate mechanical properties and wear resistance of coated NiTi SMA, respectively. For the in vitro biological assessment of the composite coatings in terms of cell morphology and cell viability, osteoblast-like SaOS-2 cells and breast cancer MCF-7 cells were cultured on NiTi SMA samples, respectively. SaOS-2 cells attached and spread better on coated NiTi SMA. Viability of MCF-7 cells showed that the PIIID-formed composite coatings were noncytotoxic and coated samples were more biocompatible than uncoated samples. - Highlights: Black-Right-Pointing-Pointer PIIID-formed coatings were fabricated on NiTi SMA to improve its biocompatibility. Black-Right-Pointing-Pointer Microstructure, mechanical properties and biocompatibility of coatings were investigated. Black-Right-Pointing-Pointer All PIIID-formed composite coatings were noncytotoxic and cytocompatible.

Effects of Hydrogen Charging on the Phase Transformation of Martensitic NiTi Shape Memory Alloy Wires

Science.gov (United States)

Snir, Yoav; Carl, Matthew; Ley, Nathan A.; Young, Marcus L.

2017-12-01

Ti-rich martensitic NiTi shape memory alloy (SMA) wires of 0.5 mm diameter were tested under hydrogen-charging conditions to reveal the effects on phase transformation. Hydrogen charging was performed by immersion testing for several durations. The SMA wires were characterized by differential scanning calorimetry (DSC), scanning electron microscopy with energy dispersive spectroscopy, and synchrotron radiation X-ray diffraction (SR-XRD) for the the as-received, polished, and hydrogen-charged conditions. The DSC revealed the phase-transformation behavior of the NiTi SMA wires. Single and triple heating/cooling cycles in the DSC show the relationship between hydrogen and temperature on the material. Five distinct peaks (peaks I-V) are observed during heating/cooling in the DSC. Peak I corresponds to the martensite-to-austenite (M → A) transformation. Peaks II, III, and IV are related to hydrogen charging. Peak II appears at about 210-230 °C, while peaks III and IV appear at about 350 and 440 °C, respectively. These higher temperature peaks, peaks II-IV, were observed for the first time for a martensitic NiTi SMA due to the large temperature range covered using the DSC. Only one peak (peak V) appears during cooling and corresponds to the austenite-to-martensite transformation peak. Ex situ and in situ SR-XRD revealed the phases and the crystallographic relationship to peaks I-V in the DSC.

Effect of different stages of deformation on the microstructure evolution of Ti-rich NiTi shape memory alloy

Energy Technology Data Exchange (ETDEWEB)

Tadayyon, Ghazal, E-mail: Ghazal.tadayyon@gmail.com [Department of Metallurgical and Materials Engineering, Faculty of Engineering, Ferdowsi University of Mashhad (Iran, Islamic Republic of); Centre for Research in Medical Devices (CURAM), National University of Ireland, Galway (Ireland); Guo, Yina, E-mail: Yina.Guo@ul.ie [Materials and Surface Science Institute, University of Limerick, Limerick (Ireland); Mazinani, Mohammad, E-mail: mazinani@um.ac.ir [Department of Metallurgical and Materials Engineering, Faculty of Engineering, Ferdowsi University of Mashhad (Iran, Islamic Republic of); Zebarjad, Seyed Mojtaba, E-mail: mojtabazebarjad@shirazu.ac.ir [Department of Materials Science and Engineering, School of Engineering, Shiraz University, Shiraz (Iran, Islamic Republic of); Tiernan, Peter, E-mail: Peter.Tiernan@ul.ie [Materials and Surface Science Institute, University of Limerick, Limerick (Ireland); Tofail, Syed A.M., E-mail: Tofail.Syed@ul.ie [Materials and Surface Science Institute, University of Limerick, Limerick (Ireland); Biggs, Manus J.P., E-mail: manus.biggs@nuigalway.ie [Centre for Research in Medical Devices (CURAM), National University of Ireland, Galway (Ireland)

2017-03-15

The main objective of this work was to investigate the thermomechanical behavior and microstructural changes of a Ti-rich NiTi shape memory alloy (SMA). The microstructural and texture evolution of aged NiTi alloy at different degrees of deformation were elicited by transmission electron microscopy (TEM). An effort was made to correlate results obtained from the tensile test with results from microstructure studies. The undeformed sample reveals a self-accommodated morphology with straight and well defined twin boundaries. At different stages of deformation, diverse mechanisms were involved. These mechanisms include marstraining, detwinning accompanied by dislocation movement, and finally, severe plastic deformation, subdivision and amorphization of the matrix. Under increasing strains, high density lattice defects were generated and the morphology of B19’ became disordered. - Graphical abstract: The summary of microstructure changes of the martensite twins during tensile deformation in polycrystalline NiTi SMAs. - Highlights: • Initial elastic response, dislocation avalanche and deformation bands were studied. • < 011 > Type II twin accompanied by detwinned area after 2% cold work was observed. • Visible parallel fine stacking faults showed plastic flow of the material. • At higher strains, subgrains changed to recrystallized, finely amorphous structure.

Wafer-level integration of NiTi shape memory alloy on silicon using Au–Si eutectic bonding

International Nuclear Information System (INIS)

Gradin, Henrik; Bushra, Sobia; Braun, Stefan; Stemme, Göran; Van der Wijngaart, Wouter

2013-01-01

This paper reports on the wafer level integration of NiTi shape memory alloy (SMA) sheets with silicon substrates through Au–Si eutectic bonding. Different bond parameters, such as Au layer thicknesses and substrate surface treatments were evaluated. The amount of gold in the bond interface is the most important parameter to achieve a high bond yield; the amount can be determined by the barrier layers between the Au and Si or by the amount of Au deposition. Deposition of a gold layer of more than 1 μm thickness before bonding gives the most promising results. Through patterning of the SMA sheet and by limiting bonding to small areas, stresses created by the thermal mismatch between Si and NiTi are reduced. With a gold layer of 1 μm thickness and bond areas between 200 × 200 and 800 × 800 μm 2 a high bond strength and a yield above 90% is demonstrated. (paper)

Electropolishing decontamination system for high-level waste canisters

International Nuclear Information System (INIS)

Larson, D.E.; Berger, D.N.; Allen, R.P.; Bryan, G.H.; Place, B.G.

1988-10-01

As part of a US Department of Energy (DOE) project agreement with the Federal Ministry for Research and Technology (BMFT) in the Federal Republic of Germany (FRG). The Nuclear Waste Treatment Program at the Pacific Northwest Laboratory (PNL) is preparing 30 radioactive canisters containing borosilicate glass for use in high-level waste repository related tests at the Asse Salt Mine. After filling, the canisters will be welded closed and decontaminated in preparation for shipping to the FRG. Electropolishing was selected as the primary decontamination approach, and an electropolishing system with associated canister inspection equipment has been designed and fabricated for installation in a large hot cell. This remote electropolishing system, which is currently undergoing preliminary testing, is described in this report. 3 refs., 3 figs., 1 tab

Development of an advanced electropolishing setup for multicell high gradient niobium cavities

Directory of Open Access Journals (Sweden)

F. Éozénou

2012-08-01

Full Text Available Reproducible operation at high performances of superconducting cavities is required for linear accelerators. High beta elliptical cavities are thus of concern and, to achieve required performances for such resonators, surface preparation including electropolishing is recommended. We have designed and operate a setup for electropolishing in the vertical position of multicell cavities in order to: (i obtain high yield with large elliptical cavities for Superconducting Linac (SPL or European Spallation Source projects; (ii develop a reference installation demonstrating that this process is appropriate for the large scale treatment of cavities in industry. The setup described here is the first one able to electropolish vertically multicell cavities with circulating acid and high safety standards. This equipment makes it possible to use a wide range of parameters such as voltage, acid flow rate, temperature, and nitrogen injection with an R&D purpose in mind. Optimization is studied using modeling with COMSOL software for different cavities. As examples, we present some results for the 704 MHz high-beta SPL cavity and the 1300 MHz International Linear Collider cavity and show the influence of cathode shape on both acid flow and electric field distribution during the process. Importance of the size of the cavity and first results achieved on single-cell and nine-cell cavities will be discussed.

Texture memory and strain-texture mapping in a NiTi shape memory alloy

International Nuclear Information System (INIS)

Ye, B.; Majumdar, B. S.; Dutta, I.

2007-01-01

The authors report on the near-reversible strain hysteresis during thermal cycling of a polycrystalline NiTi shape memory alloy at a constant stress that is below the yield strength of the martensite. In situ neutron diffraction experiments are used to demonstrate that the strain hysteresis occurs due to a texture memory effect, where the martensite develops a texture when it is cooled under load from the austenite phase and is thereafter ''remembered.'' Further, the authors quantitatively relate the texture to the strain by developing a calculated strain-texture map or pole figure for the martensite phase, and indicate its applicability in other martensitic transformations

Formation of titanium oxide coatings on NiTi shape memory alloys by selective oxidation

International Nuclear Information System (INIS)

Pohl, M.; Glogowski, T.; Kuehn, S.; Hessing, C.; Unterumsberger, F.

2008-01-01

Materials used for medical devices that are in contact with human tissue must have good corrosion resistance and biocompatibility. NiTi shape memory alloys (SMAs) are often used in medical applications due to their special functional and mechanical properties (shape memory effect, pseudo elasticity). Because of the high Ni content in nearly stoichiometric NiTi SMAs, the possibility of Ni being released needs to be considered as Ni may cause problems in the human body. SMAs exhibit a high intrinsic corrosion resistance because of the thermodynamic stability of Ni (thermodynamic reason) and the low degree of disorder in a thin protective TiO 2 -layer (kinetic reason). While therefore there is no need to be concerned too much about a normal corrosive attack in the human body, it has to be kept in mind that in medical applications, these materials represent one part of a tribological system where wear processes need to be considered. The formation of a uniform TiO 2 -layer can be beneficial in this respect. The selective oxidation of Ti to TiO 2 on the surface is a promising method to decrease the Ni release significantly. This can be achieved by controlling the partial pressure of oxygen during a controlled oxidation process. The atmosphere must be adjusted so that TiO 2 is stable while NiO cannot yet form. The result of a selective oxidation is a TiO 2 -layer that has an excellent degree of purity and represents a safe barrier against Ni emission

An overview of NiTi shape memory alloy: Corrosion resistance and antibacterial inhibition for dental application

Energy Technology Data Exchange (ETDEWEB)

Fadlallah, Sahar A., E-mail: sahar.fadlallah@yahoo.com [Materials and Corrosion Lab. (MCL), Faculty of Science, Taif University, Taif (Saudi Arabia); Chemistry Department, Faculty of Science, Cairo University, Cairo (Egypt); El-Bagoury, Nader [Materials and Corrosion Lab. (MCL), Faculty of Science, Taif University, Taif (Saudi Arabia); Casting Technology Lab., Manufacturing Technology Dept., CMRDI, P.O. Box 87, Helwan, Cairo (Egypt); Gad El-Rab, Sanaa M.F. [Biotechnology Department, Faculty of Science, Taif University, Taif (Saudi Arabia); Botany Department, Faculty of Science, Asuit University, Asuit (Egypt); Ahmed, Rasha A. [Materials and Corrosion Lab. (MCL), Faculty of Science, Taif University, Taif (Saudi Arabia); Forensic Chemistry Laboratories, Medico Legal Department, Ministry of Justice, Cairo (Egypt); El-Ousamii, Ghaida [Materials and Corrosion Lab. (MCL), Faculty of Science, Taif University, Taif (Saudi Arabia)

2014-01-15

Highlights: • Evaluate the corrosion resistance of NiTi alloy by using electrochemical techniques. • Estimate the Antibacterial inhibition rate of NiTi alloy. • Assessment the mechanical properties of NiTi from the hardness measurements. • Comparsion the microstructures of cast NiTi with Ti, this indicate the role of Ni to change the behavior of alloy in oral environment. • Advise drinking green tea in small quantities in small quantities in the event of present NiTi alloy in the oral cavity. • Recommendation to use NiTi for dental application. -- Abstract: Nowadays, Nickel–titanium nearly equiatomic is considered as one of the best biomaterials. The aim of the present work deals with the evolution of the electrochemical behavior of NiTi in simulated oral environment. The hardness, microstructures corrosion resistance and antibacterial performance of NiTi alloy were compared with pure titanium. The hardness of NiTi is twice the hardness of pure titanium. Electrochemical techniques were used to detect the corrosion resistance of both biomaterials in Hank’s solution containing (−)-epigallocatechin gallate (EGCG) which used to simulate the oral environment. In the physiological solution selected for the present study, the impedance spectroscopy (EIS) results showed that EGCG sharply increase the corrosion resistance of NiTi from 129 kΩ cm{sup 2} to 1.10 T Ω cm{sup 2} while slowly increase the corrosion resistance of pure titanium from 9.4 kΩ cm{sup 2} to 11.3 kΩ cm{sup 2} during the duration time of immersion at 37 °C. The plate-counting method was used to evaluate the antibacterial performance against Staphylococcus aureus (ATCC 6538). Among the two specimens of biomaterials studied, the antibacterial performance results revealed that the NiTi alloy is better than the pure titanium. The morphology and chemical structure of NiTi and Ti samples were systematically investigated by scanning electron microscope (SEM) and energy dispersive X

An overview of NiTi shape memory alloy: Corrosion resistance and antibacterial inhibition for dental application

International Nuclear Information System (INIS)

Fadlallah, Sahar A.; El-Bagoury, Nader; Gad El-Rab, Sanaa M.F.; Ahmed, Rasha A.; El-Ousamii, Ghaida

2014-01-01

Highlights: • Evaluate the corrosion resistance of NiTi alloy by using electrochemical techniques. • Estimate the Antibacterial inhibition rate of NiTi alloy. • Assessment the mechanical properties of NiTi from the hardness measurements. • Comparsion the microstructures of cast NiTi with Ti, this indicate the role of Ni to change the behavior of alloy in oral environment. • Advise drinking green tea in small quantities in small quantities in the event of present NiTi alloy in the oral cavity. • Recommendation to use NiTi for dental application. -- Abstract: Nowadays, Nickel–titanium nearly equiatomic is considered as one of the best biomaterials. The aim of the present work deals with the evolution of the electrochemical behavior of NiTi in simulated oral environment. The hardness, microstructures corrosion resistance and antibacterial performance of NiTi alloy were compared with pure titanium. The hardness of NiTi is twice the hardness of pure titanium. Electrochemical techniques were used to detect the corrosion resistance of both biomaterials in Hank’s solution containing (−)-epigallocatechin gallate (EGCG) which used to simulate the oral environment. In the physiological solution selected for the present study, the impedance spectroscopy (EIS) results showed that EGCG sharply increase the corrosion resistance of NiTi from 129 kΩ cm 2 to 1.10 T Ω cm 2 while slowly increase the corrosion resistance of pure titanium from 9.4 kΩ cm 2 to 11.3 kΩ cm 2 during the duration time of immersion at 37 °C. The plate-counting method was used to evaluate the antibacterial performance against Staphylococcus aureus (ATCC 6538). Among the two specimens of biomaterials studied, the antibacterial performance results revealed that the NiTi alloy is better than the pure titanium. The morphology and chemical structure of NiTi and Ti samples were systematically investigated by scanning electron microscope (SEM) and energy dispersive X-ray analysis (EDX). The

Processing and Characterization of Liquid-Phase Sintered NiTi Woven Structures

Science.gov (United States)

Erdeniz, Dinc; Weidinger, Ryan P.; Sharp, Keith W.; Dunand, David C.

2018-03-01

Porous NiTi is of interest for bone implants because of its unique combination of biocompatibility (encouraging osseointegration), high strength (to prevent fracture), low stiffness (to reduce stress shielding), and shape memory or superelasticity (to deploy an implant). A promising method for creating NiTi structures with regular open channels is via 3D weaving of NiTi wires. This paper presents a processing method to bond woven NiTi wire structures at contact points between wires to achieve structural integrity: (i) a slurry consisting of a blend of NiTi and Nb powders is deposited on the surface of the NiTi wires after the weaving operation; (ii) the powders are melted to create a eutectic liquid phase which collects at contact points; and (iii) the liquid is solidified and binds the NiTi woven structures. The bonded NiTi wire structures exhibited lower transformation temperatures compared to the as-woven NiTi wires because of Nb diffusion into the NiTi wires. A bonded woven sample was deformed in bending and showed near-complete recovery up to 6% strain and recovered nearly half of the deformation up to 19% strain.

Improvement of Electropolishing of 1100 Al Alloy for Solar Thermal Applications

Science.gov (United States)

Aguilar-Sierra, Sara María; Echeverría E, Félix

2018-03-01

Aluminum sheets-based mirrors are finding applicability in high-temperature solar concentrating technologies because they are cost-effective, lightweight and have high mechanical properties. Nonetheless, the reflectance percentages obtained by electropolishing are not close to the reflectance values of the currently used evaporated films. Therefore, controlling key factors affecting electropolishing processes became essential in order to achieve highly reflective aluminum surfaces. This study investigated the effect of both the electropolishing process and previous heat treatment on the total reflectance of the AA 1100 aluminum alloy. An acid electrolyte and a modified Brytal process were evaluated. Total reflectance was measured by means of UV-Vis spectrophotometry. Reflectance values higher than 80% at 600 nm were achieved for both electrolytes. Optical microscopy and scanning electron microscopy images showed uneven dissolution for the acid electropolished samples causing a reflectance drop in the 200-450 nm region. The influence of heat treatment, previously to electropolishing, was tested at two different temperatures and various holding times. It was found that reflectance increases around 15% for the heat-treated and electropolished samples versus the non-heat-treated ones. A heat treatment at low temperature combined with a short holding time was enough to improve the sample total reflectance.

The effect of martensite plasticity on the cyclic deformation of super-elastic NiTi shape memory alloy

International Nuclear Information System (INIS)

Song, Di; Kang, Guozheng; Kan, Qianhua; Yu, Chao; Zhang, Chuanzeng

2014-01-01

Based on stress-controlled cyclic tension–unloading experiments with different peak stresses, the effect of martensite plasticity on the cyclic deformation of super-elastic NiTi shape memory alloy micro-tubes is investigated and discussed. The experimental results show that the reverse transformation from the induced martensite phase to the austenite phase is gradually restricted by the plastic deformation of the induced martensite phase caused by an applied peak stress that is sufficiently high (higher than 900 MPa), and the extent of such restriction increases with further increasing the peak stress. The residual and peak strains of super-elastic NiTi shape memory alloy accumulate progressively, i.e., transformation ratchetting occurs during the cyclic tension–unloading with peak stresses from 600 to 900 MPa, and the transformation ratchetting strain increases with the increase of the peak stress. When the peak stress is higher than 900 MPa, the peak strain becomes almost unchanged, but the residual strain accumulates and the dissipation energy per cycle decreases very quickly with the increasing number of cycles due to the restricted reverse transformation by the martensite plasticity. Furthermore, a quantitative relationship between the applied stress and the stabilized residual strain is obtained to reasonably predict the evolution of the peak strain and the residual strain. (paper)

Multiscale Modeling of Polycrystalline NiTi Shape Memory Alloy under Various Plastic Deformation Conditions by Coupling Microstructure Evolution and Macroscopic Mechanical Response.

Science.gov (United States)

Hu, Li; Jiang, Shuyong; Zhou, Tao; Tu, Jian; Shi, Laixin; Chen, Qiang; Yang, Mingbo

2017-10-13

Numerical modeling of microstructure evolution in various regions during uniaxial compression and canning compression of NiTi shape memory alloy (SMA) are studied through combined macroscopic and microscopic finite element simulation in order to investigate plastic deformation of NiTi SMA at 400 °C. In this approach, the macroscale material behavior is modeled with a relatively coarse finite element mesh, and then the corresponding deformation history in some selected regions in this mesh is extracted by the sub-model technique of finite element code ABAQUS and subsequently used as boundary conditions for the microscale simulation by means of crystal plasticity finite element method (CPFEM). Simulation results show that NiTi SMA exhibits an inhomogeneous plastic deformation at the microscale. Moreover, regions that suffered canning compression sustain more homogeneous plastic deformation by comparison with the corresponding regions subjected to uniaxial compression. The mitigation of inhomogeneous plastic deformation contributes to reducing the statistically stored dislocation (SSD) density in polycrystalline aggregation and also to reducing the difference of stress level in various regions of deformed NiTi SMA sample, and therefore sustaining large plastic deformation in the canning compression process.

Multiscale Modeling of Polycrystalline NiTi Shape Memory Alloy under Various Plastic Deformation Conditions by Coupling Microstructure Evolution and Macroscopic Mechanical Response

Directory of Open Access Journals (Sweden)

Li Hu

2017-10-01

Full Text Available Numerical modeling of microstructure evolution in various regions during uniaxial compression and canning compression of NiTi shape memory alloy (SMA are studied through combined macroscopic and microscopic finite element simulation in order to investigate plastic deformation of NiTi SMA at 400 °C. In this approach, the macroscale material behavior is modeled with a relatively coarse finite element mesh, and then the corresponding deformation history in some selected regions in this mesh is extracted by the sub-model technique of finite element code ABAQUS and subsequently used as boundary conditions for the microscale simulation by means of crystal plasticity finite element method (CPFEM. Simulation results show that NiTi SMA exhibits an inhomogeneous plastic deformation at the microscale. Moreover, regions that suffered canning compression sustain more homogeneous plastic deformation by comparison with the corresponding regions subjected to uniaxial compression. The mitigation of inhomogeneous plastic deformation contributes to reducing the statistically stored dislocation (SSD density in polycrystalline aggregation and also to reducing the difference of stress level in various regions of deformed NiTi SMA sample, and therefore sustaining large plastic deformation in the canning compression process.

Effect of surface modification by nitrogen ion implantation on the electrochemical and cellular behaviors of super-elastic NiTi shape memory alloy.

Science.gov (United States)

Maleki-Ghaleh, H; Khalil-Allafi, J; Sadeghpour-Motlagh, M; Shakeri, M S; Masoudfar, S; Farrokhi, A; Beygi Khosrowshahi, Y; Nadernezhad, A; Siadati, M H; Javidi, M; Shakiba, M; Aghaie, E

2014-12-01

The aim of this investigation was to enhance the biological behavior of NiTi shape memory alloy while preserving its super-elastic behavior in order to facilitate its compatibility for application in human body. The surfaces of NiTi samples were bombarded by three different nitrogen doses. Small-angle X-ray diffraction was employed for evaluating the generated phases on the bombarded surfaces. The electrochemical behaviors of the bare and surface-modified NiTi samples were studied in simulated body fluid (SBF) using electrochemical impedance and potentio-dynamic polarization tests. Ni ion release during a 2-month period of service in the SBF environment was evaluated using atomic absorption spectrometry. The cellular behavior of nitrogen-modified samples was studied using fibroblast cells. Furthermore, the effect of surface modification on super-elasticity was investigated by tensile test. The results showed the improvement of both corrosion and biological behaviors of the modified NiTi samples. However, no significant change in the super-elasticity was observed. Samples modified at 1.4E18 ion cm(-2) showed the highest corrosion resistance and the lowest Ni ion release.

Development of vertical electropolishing process applied on 1300 and 704 MHz superconducting niobium resonators

Directory of Open Access Journals (Sweden)

F. Eozénou

2014-08-01

Full Text Available An advanced setup for vertical electropolishing of superconducting radio-frequency niobium elliptical cavities has been installed at CEA Saclay. Cavities are vertically electropolished with circulating standard HF-HF-H_{2}SO_{4} electrolytes. Parameters such as voltage, cathode shape, acid flow, and temperature have been investigated. A low voltage (between 6 and 10 V depending on the cavity geometry, a high acid flow (25  L/min, and a low acid temperature (20° C are considered as promising parameters. Such a recipe has been tested on single-cell and nine-cell International Linear Collider (ILC as well as 704 MHz five-cell Super Proton Linac (SPL cavities. Single-cell cavities showed similar performances at 1.6 K being either vertically or horizontally electropolished. The applied baking process provides similar benefit. An asymmetric removal is observed with faster removal in the upper half-cells. Multicell cavities (nine-cell ILC and five-cell SPL cavities exhibit a standard Q_{0} value at low and medium accelerating fields though limited by power losses due to field emitted electrons.

Tungsten inert gas (TIG) welding of Ni-rich NiTi plates: functional behavior

Science.gov (United States)

Oliveira, J. P.; Barbosa, D.; Braz Fernandes, F. M.; Miranda, R. M.

2016-03-01

It is often reported that, to successfully join NiTi shape memory alloys, fusion-based processes with reduced thermal affected regions (as in laser welding) are required. This paper describes an experimental study performed on the tungsten inert gas (TIG) welding of 1.5 mm thick plates of Ni-rich NiTi. The functional behavior of the joints was assessed. The superelasticity was analyzed by cycling tests at maximum imposed strains of 4, 8 and 12% and for a total of 600 cycles, without rupture. The superelastic plateau was observed, in the stress-strain curves, 30 MPa below that of the base material. Shape-memory effect was evidenced by bending tests with full recovery of the initial shape of the welded joints. In parallel, uniaxial tensile tests of the joints showed a tensile strength of 700 MPa and an elongation to rupture of 20%. The elongation is the highest reported for fusion-welding of NiTi, including laser welding. These results can be of great interest for the wide-spread inclusion of NiTi in complex shaped components requiring welding, since TIG is not an expensive process and is simple to operate and implement in industrial environments.

Electropolishing effect on roughness metrics of ground stainless steel: a length scale study

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Nakar, Doron; Harel, David; Hirsch, Baruch

2018-03-01

Electropolishing is a widely-used electrochemical surface finishing process for metals. The electropolishing of stainless steel has vast commercial application, such as improving corrosion resistance, improving cleanness, and brightening. The surface topography characterization is performed using several techniques with different lateral resolutions and length scales, from atomic force microscopy in the nano-scale (filter are adopted. While the commonly used roughness amplitude parameters (Ra, Rq and Rz) fail to characterize electropolished textures, the root mean square slope (RΔq) is found to better describe the electropolished surfaces and to be insensitive to scale.

Grain size effects on stability of nonlinear vibration with nanocrystalline NiTi shape memory alloy

Science.gov (United States)

Xia, Minglu; Sun, Qingping

2017-10-01

Grain size effects on stability of thermomechanical responses for a nonlinear torsional vibration system with nanocrystalline superelastic NiTi bar are investigated in the frequency and amplitude domains. NiTi bars with average grain size from 10 nm to 100 nm are fabricated through cold-rolling and subsequent annealing. Thermomechanical responses of the NiTi bar as a softening nonlinear damping spring in the torsional vibration system are obtained by synchronised acquisition of rotational angle and temperature under external sinusoidal excitation. It is shown that nonlinearity and damping capacity of the NiTi bar decrease as average grain size of the material is reduced below 100 nm. Therefore jump phenomena of thermomechanical responses become less significant or even vanish and the vibration system becomes more stable. The work in this paper provides a solid experimental base for manipulating the undesired jump phenomena of thermomechanical responses and stabilising the mechanical vibration system through grain refinement of NiTi SMA.

Biocorrosion investigation of two shape memory nickel based alloys: Ni-Mn-Ga and thin film NiTi.

Science.gov (United States)

Stepan, L L; Levi, D S; Gans, E; Mohanchandra, K P; Ujihara, M; Carman, G P

2007-09-01

Thin film nitinol and single crystal Ni-Mn-Ga represent two new shape memory materials with potential to be used as percutaneously placed implant devices. However, the biocompatibility of these materials has not been adequately assessed. Immersion tests were conducted on both thin film nitinol and single crystal Ni-Mn-Ga in Hank's balanced salt solution at 37 degrees C and pH 7.4. After 12 h, large pits were found on the Ni-Mn-Ga samples while thin film nitinol displayed no signs of corrosion. Further electrochemical tests on thin film nitinol samples revealed breakdown potentials superior to a mechanically polished nitinol disc. These results suggest that passivation or electropolishing of thin film nitinol maybe unnecessary to promote corrosion resistance.

Tailoring Selective Laser Melting Process Parameters for NiTi Implants

Science.gov (United States)

Bormann, Therese; Schumacher, Ralf; Müller, Bert; Mertmann, Matthias; de Wild, Michael

2012-12-01

Complex-shaped NiTi constructions become more and more essential for biomedical applications especially for dental or cranio-maxillofacial implants. The additive manufacturing method of selective laser melting allows realizing complex-shaped elements with predefined porosity and three-dimensional micro-architecture directly out of the design data. We demonstrate that the intentional modification of the applied energy during the SLM-process allows tailoring the transformation temperatures of NiTi entities within the entire construction. Differential scanning calorimetry, x-ray diffraction, and metallographic analysis were employed for the thermal and structural characterizations. In particular, the phase transformation temperatures, the related crystallographic phases, and the formed microstructures of SLM constructions were determined for a series of SLM-processing parameters. The SLM-NiTi exhibits pseudoelastic behavior. In this manner, the properties of NiTi implants can be tailored to build smart implants with pre-defined micro-architecture and advanced performance.

Experimental observations on uniaxial whole-life transformation ratchetting and low-cycle stress fatigue of super-elastic NiTi shape memory alloy micro-tubes

Science.gov (United States)

Song, Di; Kang, Guozheng; Kan, Qianhua; Yu, Chao; Zhang, Chuanzeng

2015-07-01

In this work, the low-cycle fatigue failure of super-elastic NiTi shape memory alloy micro-tubes with a wall thickness of 150 μm is investigated by uniaxial stress-controlled cyclic tests at human body temperature 310 K. The effects of mean stress, peak stress, and stress amplitude on the uniaxial whole-life transformation ratchetting and fatigue failure of the NiTi alloy are observed. It is concluded that the fatigue life depends significantly on the stress levels, and the extent of martensite transformation and its reverse play an important role in determining the fatigue life. High peak stress or complete martensite transformation shortens the fatigue life.

Experimental observations on uniaxial whole-life transformation ratchetting and low-cycle stress fatigue of super-elastic NiTi shape memory alloy micro-tubes

International Nuclear Information System (INIS)

Song, Di; Kang, Guozheng; Kan, Qianhua; Yu, Chao; Zhang, Chuanzeng

2015-01-01

In this work, the low-cycle fatigue failure of super-elastic NiTi shape memory alloy micro-tubes with a wall thickness of 150 μm is investigated by uniaxial stress-controlled cyclic tests at human body temperature 310 K. The effects of mean stress, peak stress, and stress amplitude on the uniaxial whole-life transformation ratchetting and fatigue failure of the NiTi alloy are observed. It is concluded that the fatigue life depends significantly on the stress levels, and the extent of martensite transformation and its reverse play an important role in determining the fatigue life. High peak stress or complete martensite transformation shortens the fatigue life. (paper)

Atomistic study on shock behaviour of NiTi shape memory alloy

Science.gov (United States)

Yin, Qiuyun; Wu, Xianqian; Huang, Chenguang

2017-06-01

The shock behaviour of NiTi shape memory alloy is investigated by using molecular dynamics simulation. The nano-pillar samples of the alloy are subjected to the impact of a piston with a velocity of 350 m/s at initial environment temperatures of 325 and 500 K. At 325 K, we observe two different pathways of the formation of BCO phase, the gradient twins, and the detwinning phenomena, strongly depending on the local stress and the deformation state. As the initial temperature increases to 500 K, the plasticity is dominated by the dislocation movements rather than the twinning at 325 K. The phase transformation and plasticity result in stress attenuation when the stress wave propagates through the nano-pillar. Furthermore, it is interesting to note that multiple stress peaks occur due to the formation of local complex atomic structures with various wave speeds, leading to the catch up and overlap of the stress waves.

On the Ni-Ion release rate from surfaces of binary NiTi shape memory alloys

Science.gov (United States)

Ševčíková, Jana; Bártková, Denisa; Goldbergová, Monika; Kuběnová, Monika; Čermák, Jiří; Frenzel, Jan; Weiser, Adam; Dlouhý, Antonín

2018-01-01

The study is focused on Ni-ion release rates from NiTi surfaces exposed in the cell culture media and human vascular endothelial cell (HUVEC) culture environments. The NiTi surface layers situated in the depth of 70 μm below a NiTi oxide scale are affected by interactions between the NiTi alloys and the bio-environments. The finding was proved with use of inductively coupled plasma mass spectrometry and electron microscopy experiments. As the exclusive factor controlling the Ni-ion release rates was not only thicknesses of the oxide scale, but also the passivation depth, which was two-fold larger. Our experimental data strongly suggested that some other factors, in addition to the Ni concentration in the oxide scale, admittedly hydrogen soaking deep below the oxide scale, must be taken into account in order to rationalize the concentrations of Ni-ions released into the bio-environments. The suggested role of hydrogen as the surface passivation agent is also in line with the fact that the Ni-ion release rates considerably decrease in NiTi samples that were annealed in controlled hydrogen atmospheres prior to bio-environmental exposures.

Cyclic fatigue resistances of Hyflex EDM, WaveOne gold, Reciproc blue and 2shape NiTi rotary files in different artificial canals.

Science.gov (United States)

Özyürek, Taha; Gündoğar, Mustafa; Uslu, Gülşah; Yılmaz, Koray; Staffoli, Simone; Nm, Grande; Plotino, Gianluca; Polimeni, Antonella

2018-01-30

The aim of the present study was to compare the cyclic fatigue resistances of HyFlex EDM (HEDM), WaveOne Gold (WOG), Reciproc Blue (RB), and 2Shape (TS) NiTi systems having different metallurgic properties. HEDM, WOG, RB, and TS instruments were rotated in artificial canals which were made of stainless steel with an inner diameter of 1.5 mm, 45°, and 90° angles of curvatures and a radius of curvature of 5 mm until fracture occurred, and the time to fracture (TTF) was recorded in seconds. Also, number of cycles to fracture was calculated (NCF). Data were statistically analyzed using Kruskal-Wallis and t test. The statistical significance level was set at P  0.05). When the NCF values were taken into consideration, HEDM reported a significantly higher cyclic fatigue resistance than TS in both canal curvatures analyzed (P < 0.05). Within the limitations of the present study, RB NiTi files showed statistically higher cyclic fatigue resistance in artificial canals with 45° and 90° than the other NiTi files tested.

Loading Path and Control Mode Effects During Thermomechanical Cycling of Polycrystalline Shape Memory NiTi

Science.gov (United States)

Nicholson, D. E.; Benafan, O.; Padula, S. A.; Clausen, B.; Vaidyanathan, R.

2018-01-01

Loading path dependencies and control mode effects in polycrystalline shape memory NiTi were investigated using in situ neutron and synchrotron X-ray diffraction performed during mechanical cycling and thermal cycling at constant strain. Strain-controlled, isothermal, reverse loading (to ± 4%) and stress-controlled, isothermal, cyclic loading (to ± 400 MPa for up to ten cycles) at room temperature demonstrated that the preferred martensite variants selected correlated directly with the macroscopic uniaxial strain and did not correlate with the compressive or tensile state of stress. During cyclic loading (up to ten cycles), no significant cycle-to-cycle evolution of the variant microstructure corresponding to a given strain was observed, despite changes in the slope of the stress-strain response with each cycle. Additionally, thermal cycling (to above and below the phase transformation) under constant strain (up to 2% tensile strain) showed that the martensite variant microstructure correlated directly with strain and did not evolve following thermal cycling, despite relaxation of stress in both martensite and austenite phases. Results are presented in the context of variant reorientation and detwinning processes in martensitic NiTi, the fundamental thermoelastic nature of such processes and the ability of the variant microstructure to accommodate irreversible deformation processes.

Laser Annealing on the Surface Treatment of Thin Super Elastic NiTi Wire

Science.gov (United States)

Samal, S.; Heller, L.; Brajer, J.; Tyc, O.; Kadrevek, L.; Sittner, P.

2018-05-01

Here the aim of this research is annealing the surface of NiTi wire for shape memory alloy, super-elastic wire by solid state laser beam. The laser surface treatment was carried out on the NiTi wire locally with fast, selective, surface heat treatment that enables precisely tune the localized material properties without any precipitation. Both as drawn (hard) and straight annealing NiTi wire were considered for laser annealing with input power 3 W, with precisely focusing the laser beam height 14.3 % of the Z-axis with a spot size of 1 mm. However, straight annealing wire is more interest due to its low temperature shape setting behavior and used by companies for stent materials. The variable parameter such as speed of the laser scanning and tensile stress on the NiTi wire were optimized to observe the effect of laser response on the sample. Superelastic, straight annealed NiTi wires (d: 0.10 mm) were held prestrained at the end of the superelastic plateau (ε: 5 ∼6.5 %) above the superelastic region by a tensile machine ( Mitter: miniature testing rig) at room temperature (RT). Simultaneously, the hardness of the wires along the cross-section was performed by nano-indentation (NI) method. The hardness of the NiTi wire corresponds to phase changes were correlated with NI test. The laser induced NiTi wire shows better fatigue performance with improved 6500 cycles.

Annealing behavior and shape memory effect in NiTi alloy processed by equal-channel angular pressing at room temperature

International Nuclear Information System (INIS)

Shahmir, Hamed; Nili-Ahmadabadi, Mahmoud; Wang, Chuan Ting; Jung, Jai Myun; Kim, Hyoung Seop; Langdon, Terence G.

2015-01-01

A martensitic NiTi shape memory alloy was processed successfully by equal-channel angular pressing (ECAP) for one pass at room temperature using a core–sheath billet design. The annealing behavior and shape memory effect of the ECAP specimens were studied followed by post-deformation annealing (PDA) at 673 K for various times. The recrystallization and structural evolution during annealing were investigated by differential scanning calorimetry, dilatometry, X-ray diffraction, transmission electron microscopy and microhardness measurements. The results indicate that the shape memory effect improves by PDA after ECAP processing. Annealing for 10 min gives a good shape memory effect which leads to a maximum in recoverable strain of 6.9 pct upon heating where this is more than a 25 pct improvement compared with the initial state

PEEK (polyether-ether-ketone)-coated nitinol wire: Film stability for biocompatibility applications

Science.gov (United States)

Sheiko, Nataliia; Kékicheff, Patrick; Marie, Pascal; Schmutz, Marc; Jacomine, Leandro; Perrin-Schmitt, Fabienne

2016-12-01

High quality biocompatible poly-ether-ether-ketone (PEEK) coatings were produced on NiTi shape memory alloy wires using dipping deposition from colloidal aqueous PEEK dispersions after substrate surface treatment. The surface morphology and microstructure were investigated by Scanning Electron Microscopy at every step of the process from the as-received Nitinol substrate to the ultimate PEEK-coated NiTi wire. Nanoscratch tests were carried out to access the adhesive behavior of the polymer coated film to the NiTi. The results indicate that the optimum process conditions in cleaning, chemical etching, and electropolishing the NiTi, were the most important and determining parameters to be achieved. Thus, high quality PEEK coatings were obtained on NiTi wires, straight or curved (even with a U-shape) with a homogeneous microstructure along the wire length and a uniform thickness of 12 μm without any development of cracks or the presence of large voids. The biocompatibility of the PEEK coating film was checked in fibrobast cultured cells. The coating remains stable in biological environment with negligible Ni ion release, no cytotoxicity, and no delamination observed with time.

Electropolishing of replacement steam generator channel heads at Millstone-2 PWR

International Nuclear Information System (INIS)

Hudson, M.J.B.; Raney, H.; Raney, D.; Spalaris, C.N.

1992-07-01

A field application of EPRI-developed steam generator electropolishing technique was performed at Millstone-2 PWR. The process was qualified under previous programs on a laboratory scale, but it was thought appropriate to scale up application to full size components. Replacement of steam generators at Millstone-2 provided a unique opportunity to demonstrate that electropolishing can be applied safely and at a cost which was judged to be recoverable after a small number of fuel cycles. The project, preparation, electropolishing and cleanup, was completed at the reactor site in 25 working days. An alternate, less costly electrolyte solution was qualified for use in future applications

Phase volume fractions and strain measurements in an ultrafine-grained NiTi shape-memory alloy during tensile loading

International Nuclear Information System (INIS)

Young, M.L.; Wagner, M.F.-X.; Frenzel, J.; Schmahl, W.W.; Eggeler, G.

2010-01-01

An ultrafine-grained pseudoelastic NiTi shape-memory alloy wire with 50.9 at.% Ni was examined using synchrotron X-ray diffraction during in situ uniaxial tensile loading (up to 1 GPa) and unloading. Both macroscopic stress-strain measurements and volume-averaged lattice strains are reported and discussed. The loading behavior is described in terms of elasto-plastic deformation of austenite, emergence of R phase, stress-induced martensitic transformation, and elasto-plastic deformation, grain reorientation and detwinning of martensite. The unloading behavior is described in terms of stress relaxation and reverse plasticity of martensite, reverse transformation of martensite to austenite due to stress relaxation, and stress relaxation of austenite. Microscopically, lattice strains in various crystallographic directions in the austenitic B2, martensitic R, and martensitic B19' phases are examined during loading and unloading. It is shown that the phase transformation occurs in a localized manner along the gage length at the plateau stress. Phase volume fractions and lattice strains in various crystallographic reflections in the austenite and martensite phases are examined over two transition regions between austenite and martensite, which have a width on the order of the wire diameter. Anisotropic effects observed in various crystallographic reflections of the austenitic phase are also discussed. The results contribute to a better understanding of the tensile loading behavior, both macroscopically and microscopically, of NiTi shape-memory alloys.

Parameters Selection for Electropolishing Process of Products Made of Copper and Its Alloys

Directory of Open Access Journals (Sweden)

Maciąg T.

2017-09-01

Full Text Available Electropolishing is electrochemical method used in metal working that has a vital role in production of medical apparatus, in food or electric industry. The purpose of this paper is to determine optimal current parameters and time required for conducting electropolishing process from the perspective of changes of surface microgeometry. Furthermore, effect of different types of mechanical working used before electropolishing on final surface state was evaluated by observation in changes of topography. Research was conducted on electrolytic copper and brass. Analysis of surface geometry and its parameters (Ra, Sa was used as criterion describing efficiency of chemical electropolishing. Results of the experiment allow for current parameter optimization of electrochemical polishing process for selected non-ferrous alloys with preliminary mechanical preparation of the surface.

NiTi bonded space regainer/maintainer

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Negi K

2010-06-01

Full Text Available Early orthodontic interventions are often initiated in the developing dentition to promote favorable developmental changes. Interceptive orthodontic can eliminate or reduce the severity of a developing malocclusion, the complexity of orthodontic treatment, overall treatment time and cost. Premature loss of deciduous tooth or teeth can often destroy the integrity of normal occlusion. There are many space regaining and maintaining devices mentioned in literature. In this article, I present a simple space regaining method by a piece of nickel titanium (NiTi wire bonded between the teeth in active loop form, and the unique shape memory property of NiTi wire will upright or move the teeth and the lost space can be regained easily.

Observation on the transformation domains of super-elastic NiTi shape memory alloy and their evolutions during cyclic loading

International Nuclear Information System (INIS)

Xie, Xi; Kan, Qianhua; Kang, Guozheng; Li, Jian; Qiu, Bo; Yu, Chao

2016-01-01

The strain field of a super-elastic NiTi shape memory alloy (SMA) and its variation during uniaxial cyclic tension-unloading were observed by a non-contact digital image correlation method, and then the transformation domains and their evolutions were indirectly investigated and discussed. It is seen that the super-elastic NiTi (SMA) exhibits a remarkable localized deformation and the transformation domains evolve periodically with the repeated cyclic tension-unloading within the first several cycles. However, the evolutions of transformation domains at the stage of stable cyclic transformation depend on applied peak stress: when the peak stress is low, no obvious transformation band is observed and the strain field is nearly uniform; when the peak stress is large enough, obvious transformation bands occur due to the residual martensite caused by the prevention of enriched dislocations to the reverse transformation from induced martensite to austenite. Temperature variations measured by an infrared thermal imaging method further verifies the formation and evolution of transformation domains. (paper)

Observation on the transformation domains of super-elastic NiTi shape memory alloy and their evolutions during cyclic loading

Science.gov (United States)

Xie, Xi; Kan, Qianhua; Kang, Guozheng; Li, Jian; Qiu, Bo; Yu, Chao

2016-04-01

The strain field of a super-elastic NiTi shape memory alloy (SMA) and its variation during uniaxial cyclic tension-unloading were observed by a non-contact digital image correlation method, and then the transformation domains and their evolutions were indirectly investigated and discussed. It is seen that the super-elastic NiTi (SMA) exhibits a remarkable localized deformation and the transformation domains evolve periodically with the repeated cyclic tension-unloading within the first several cycles. However, the evolutions of transformation domains at the stage of stable cyclic transformation depend on applied peak stress: when the peak stress is low, no obvious transformation band is observed and the strain field is nearly uniform; when the peak stress is large enough, obvious transformation bands occur due to the residual martensite caused by the prevention of enriched dislocations to the reverse transformation from induced martensite to austenite. Temperature variations measured by an infrared thermal imaging method further verifies the formation and evolution of transformation domains.

Ni4Ti3 precipitate structures in Ni-rich NiTi shape memory alloys

International Nuclear Information System (INIS)

Holec, D.; Bojda, O.; Dlouhy, A.

2008-01-01

Non-uniform distributions of Ni 4 Ti 3 precipitate crystallographic variants are investigated in a Ni-rich NiTi shape memory alloy after aging, assisted by external stress. A finite-element method model is presented that considers the elastic anisotropy of the B2 parent phase and also mutual misorientations of grains in a polycrystalline sample. On loading by the external stress, the stress is redistributed in the microstructure and the precipitation of some Ni 4 Ti 3 crystallographic variants becomes distinctly favorable in grain boundary regions since these variant configurations minimize the elastic interaction energy. The volume fraction of the affected grain boundary regions is calculated and the numerical results are compared with the data obtained by differential scanning calorimetry and transmission electron microscopy

The effects of vacuum induction melting and electron beam melting techniques on the purity of NiTi shape memory alloys

Energy Technology Data Exchange (ETDEWEB)

Otubo, J. [Instituto Tecnologico de Aeronautica (ITA), 12228-900 S.J. Campos, SP (Brazil) and DEMA-FEM-UNICAMP, 13083-000 Campinas, SP (Brazil)]. E-mail: jotubo@ita.br; Rigo, O.D. [DEMA-FEM-UNICAMP, 13083-000 Campinas, SP (Brazil); Neto, C. Moura [Instituto Tecnologico de Aeronautica (ITA), 12228-900 S.J. Campos, SP (Brazil); Mei, P.R. [DEMA-FEM-UNICAMP, 13083-000 Campinas, SP (Brazil)

2006-11-25

The usual process to produce NiTi shape memory alloys is by vacuum induction melting (VIM) using graphite crucible that contaminates the bath with carbon. The contamination by oxygen comes from residual oxygen inside the melting chamber. A new alternative process to produce NiTi alloys is by electron beam melting (EBM) using water-cooled copper crucible that eliminates the carbon contamination and the oxygen contamination would be minimized due to operation in high vacuum. This work compares the two processes and shows that the carbon contamination is four to ten times lower for EBM compared to VIM products and that the final oxygen content is much more dependent on the starting raw materials. The purity of the final product should be very important mainly in terms of biomedical applications and the contaminations by carbon and oxygen affect the direct and reverse martensitic transformation temperatures.

Machining NiTi micro-parts by micro-milling

International Nuclear Information System (INIS)

Weinert, K.; Petzoldt, V.

2008-01-01

The machinability of NiTi by milling has been examined using solid carbide end milling cutters. First results were obtained from machining simple slots applying TiAlN-coated tools with a diameter of 0.4 mm. The machining process was evaluated in terms of tool wear, cutting forces and machining quality. The tool wear and work piece quality was analysed with a scanning electron microscope and a white-light confocal microscope. Despite the poor machinability of NiTi good results concerning tool wear and shape accuracy of the milled slots were achieved. Essential for a good machining result is the application of minimum quantity lubrication. This clearly reduces NiTi adherences compared to dry machining. Work piece quality is improved and tool life is extended. Based on these results different structures could be produced by micro-milling

Laser Shock Wave-Assisted Patterning on NiTi Shape Memory Alloy Surfaces

Science.gov (United States)

Ilhom, Saidjafarzoda; Seyitliyev, Dovletgeldi; Kholikov, Khomidkohodza; Thomas, Zachary; Er, Ali O.; Li, Peizhen; Karaca, Haluk E.; San, Omer

2018-01-01

Shape memory alloys (SMAs) are a unique class of smart materials and they were employed in various applications in engineering, biomedical, and aerospace technologies. Here, we report an advanced, efficient, and low-cost direct imprinting method with low environmental impact to create thermally controllable surface patterns. Patterned microindents were generated on Ni50Ti50 (at. %) SMAs using an Nd:YAG laser with 1064 nm wavelength at 10 Hz. Laser pulses at selected fluences were focused on the NiTi surface and generated pressure pulses of up to a few GPa. Optical microscope images showed that surface patterns with tailorable sizes can be obtained. The depth of the patterns increases with laser power and irradiation time. Upon heating, the depth profile of SMA surfaces changed where the maximum depth recovery ratio of 30% was observed. Recovery ratio decreased and stabilized when the number of pulses and thus the well depth were further increased. A numerical simulation of pressure evolution in shape memory alloys showed a good agreement with the experimental results. The stress wave closely followed the rise time of the laser pulse to its peak value and initial decay. Rapid attenuation and dispersion of the stress wave were found in our simulation.

Laser Shock Wave-Assisted Patterning on NiTi Shape Memory Alloy Surfaces

Science.gov (United States)

Ilhom, Saidjafarzoda; Seyitliyev, Dovletgeldi; Kholikov, Khomidkohodza; Thomas, Zachary; Er, Ali O.; Li, Peizhen; Karaca, Haluk E.; San, Omer

2018-03-01

Shape memory alloys (SMAs) are a unique class of smart materials and they were employed in various applications in engineering, biomedical, and aerospace technologies. Here, we report an advanced, efficient, and low-cost direct imprinting method with low environmental impact to create thermally controllable surface patterns. Patterned microindents were generated on Ni50Ti50 (at. %) SMAs using an Nd:YAG laser with 1064 nm wavelength at 10 Hz. Laser pulses at selected fluences were focused on the NiTi surface and generated pressure pulses of up to a few GPa. Optical microscope images showed that surface patterns with tailorable sizes can be obtained. The depth of the patterns increases with laser power and irradiation time. Upon heating, the depth profile of SMA surfaces changed where the maximum depth recovery ratio of 30% was observed. Recovery ratio decreased and stabilized when the number of pulses and thus the well depth were further increased. A numerical simulation of pressure evolution in shape memory alloys showed a good agreement with the experimental results. The stress wave closely followed the rise time of the laser pulse to its peak value and initial decay. Rapid attenuation and dispersion of the stress wave were found in our simulation.

Reactive Ni/Ti nanolaminates

International Nuclear Information System (INIS)

Adams, D. P.; Bai, M. M.; Rodriguez, M. A.; McDonald, J. P.; Jones, E. Jr.; Brewer, L.; Moore, J. J.

2009-01-01

Nickel/titanium nanolaminates fabricated by sputter deposition exhibited rapid, high-temperature synthesis. When heated locally, self-sustained reactions were produced in freestanding Ni/Ti multilayer foils characterized by average propagation speeds between ∼0.1 and 1.4 m/s. The speed of a propagating reaction front was affected by total foil thickness and bilayer thickness (layer periodicity). In contrast to previous work with compacted Ni-Ti powders, no preheating of Ni/Ti foils was required to maintain self-propagating reactions. High-temperature synthesis was also stimulated by rapid global heating demonstrating low ignition temperatures (T ig )∼300-400 deg. C for nanolaminates. Ignition temperature was influenced by bilayer thickness with more coarse laminate designs exhibiting increased T ig . Foils reacted in a vacuum apparatus developed either as single-phase B2 cubic NiTi (austenite) or as a mixed-phase structure that was composed of monoclinic B19 ' NiTi (martensite), hexagonal NiTi 2 , and B2 NiTi. Single-phase, cubic B2 NiTi generally formed when the initial bilayer thickness was made small.

Research and development for electropolishing of Nb for ILC accelerator cavities

International Nuclear Information System (INIS)

Kelley, Michael J.

2009-01-01

The objectives of this project are to 1, Expand the scientific and technological understanding of the effect of post-treatment (electropolish, buffered chemical polish, low-temperature baking) on the surface of niobium; 2, Relate the knowledge to the performance of niobium superconducting radiofrequency accelerator cavities; and, 3, Thereby design and demonstrate an electropolish process that can be applied to complete cavities

Influence of Test Procedures on the Thermomechanical Properties of a 55NiTi Shape Memory Alloy

Science.gov (United States)

Padula, Santo A., II; Gaydosh, Darrell J.; Noebe, Ronald D.; Bigelow, Glen S.; Garg, Anita; Lagoudas, Dimitris; Karaman, Ibrahim; Atli, Kadri C.

2008-01-01

Over the past few decades, binary NiTi shape memory alloys have received attention due to their unique mechanical characteristics, leading to their potential use in low-temperature, solid-state actuator applications. However, prior to using these materials for such applications, the physical response of these systems to mechanical and thermal stimuli must be thoroughly understood and modeled to aid designers in developing SMA-enabled systems. Even though shape memory alloys have been around for almost five decades, very little effort has been made to standardize testing procedures. Although some standards for measuring the transformation temperatures of SMA s are available, no real standards exist for determining the various mechanical and thermomechanical properties that govern the usefulness of these unique materials. Consequently, this study involved testing a 55NiTi alloy using a variety of different test methodologies. All samples tested were taken from the same heat and batch to remove the influence of sample pedigree on the observed results. When the material was tested under constant-stress, thermal-cycle conditions, variations in the characteristic material responses were observed, depending on test methodology. The transformation strain and irreversible strain were impacted more than the transformation temperatures, which only showed an affect with regard to applied external stress. In some cases, test methodology altered the transformation strain by 0.005-0.01mm/mm, which translates into a difference in work output capability of approximately 2 J/cu cm (290 in!lbf/cu in). These results indicate the need for the development of testing standards so that meaningful data can be generated and successfully incorporated into viable models and hardware. The use of consistent testing procedures is also important when comparing results from one research organization to another. To this end, differences in the observed responses will be presented, contrasted and

Effect of thermal cycling on the transformation temperature ranges of a Ni-Ti shape memory alloy

International Nuclear Information System (INIS)

Paula, A.S.; Canejo, J.P.H.G.; Martins, R.M.S.; Braz Fernandes, F.M.

2003-01-01

Shape memory alloys (SMA) represents a class of metallic materials that has the capability of recovering a previously defined initial shape when subject to an adequate thermomechanical treatment. The present work aims to study the influence of thermal cycles on the transition temperatures of a Ni-Ti alloy. In this system, small variations around the equiatomic composition give rise to significant transformation temperature variations ranging from 173 to 373 K. SMA usually presents the shape memory effect after an annealing treatment at ca. 973 K. The optimisation of the thermomechanical treatment will allow to 'tune' the material to different transformation temperature ranges from the same starting material, just by changing the processing conditions. Differential scanning calorimeter (DSC) and in situ high-temperature X-ray diffraction (XRD) have been used to identify the transformation temperatures and the phases that are present after different thermal cycles. The results concerning a series of thermal cycles with different heating and cooling rates (from 1.67x10 -2 to 1.25x10 -1 K/s) and different holding temperatures (from 473 to 1033 K) are presented

Feasibility of Shape-Memory Ni/Ti Alloy Wire Containing Tube Elevators for Transcrestal Detaching Maxillary Sinus Mucosa: Ex Vivo Study

Directory of Open Access Journals (Sweden)

Yanfeng Li

2016-12-01

Full Text Available Background: Osteotome sinus floor elevation is a less invasive approach to augment an insufficient alveolar bone at the posterior maxilla for dental implantation. However, this approach has some limitations due to the lack of sinus lift tools available for clinical use and the small transcrestal access to the maxillary sinus floor. We recently invented shape-memory Ni/Ti alloy wire containing tube elevators for transcrestal detaching maxillary sinus mucosa, and developed goat ex vivo models for direct visualizing the effectiveness of detaching sinus mucosa in real time during transcrestal maxillary sinus floor elevation. Methods: We evaluated our invented elevators, namely elevator 012 and elevator 014, for their effectiveness for transcrestal detaching maxillary sinus mucosa using the goat ex vivo models. We measured the length of sinus mucosa detached in mesial and distal directions or buccal and palatal directions, and the space volume created by detaching maxillary sinus mucosa in mesial, distal, buccal and palatal directions using the invented elevators. Results: Elevator 012 had a shape-memory Ni/Ti alloy wire with a diameter of 0.012 inch, while elevator 014 had its shape-memory Ni/Ti alloy wire with a diameter of 0.014 inch. Elevator 012 could detach the goat maxillary sinus mucosa in the mesial or distal direction for 12.1±4.3 mm, while in the buccal or palatal direction for 12.5±6.7 mm. The elevator 014 could detach the goat maxillary sinus mucosa for 23.0±4.9 mm in the mesial or distal direction, and for 19.0±8.1 mm in the buccal or palatal direction. An average space volume of 1.7936±0.2079 ml was created after detaching the goat maxillay sinus mucosa in both mesial/distal direction and buccal/palatal direction using elevator 012; while the average space volume created using elevator 014 was 1.8764±0.2366 ml. Conclusion: Both two newly invented tube elevators could effectively detach the maxillary sinus mucosa on the goat ex

Feasibility of Shape-Memory Ni/Ti Alloy Wire Containing Tube Elevators for Transcrestal Detaching Maxillary Sinus Mucosa: Ex Vivo Study.

Science.gov (United States)

Li, Yanfeng; Wang, Fuli; Hu, Pin; Fan, Jiadong; Han, Yishi; Liu, Bin; Liu, Tao; Yang, Chunhao; Gu, Xiangmin

2016-01-01

Osteotome sinus floor elevation is a less invasive approach to augment an insufficient alveolar bone at the posterior maxilla for dental implantation. However, this approach has some limitations due to the lack of sinus lift tools available for clinical use and the small transcrestal access to the maxillary sinus floor. We recently invented shape-memory Ni/Ti alloy wire containing tube elevators for transcrestal detaching maxillary sinus mucosa, and developed goat ex vivo models for direct visualizing the effectiveness of detaching sinus mucosa in real time during transcrestal maxillary sinus floor elevation. We evaluated our invented elevators, namely elevator 012 and elevator 014, for their effectiveness for transcrestal detaching maxillary sinus mucosa using the goat ex vivo models. We measured the length of sinus mucosa detached in mesial and distal directions or buccal and palatal directions, and the space volume created by detaching maxillary sinus mucosa in mesial, distal, buccal and palatal directions using the invented elevators. Elevator 012 had a shape-memory Ni/Ti alloy wire with a diameter of 0.012 inch, while elevator 014 had its shape-memory Ni/Ti alloy wire with a diameter of 0.014 inch. Elevator 012 could detach the goat maxillary sinus mucosa in the mesial or distal direction for 12.1±4.3 mm, while in the buccal or palatal direction for 12.5±6.7 mm. The elevator 014 could detach the goat maxillary sinus mucosa for 23.0±4.9 mm in the mesial or distal direction, and for 19.0±8.1 mm in the buccal or palatal direction. An average space volume of 1.7936±0.2079 ml was created after detaching the goat maxillay sinus mucosa in both mesial/distal direction and buccal/palatal direction using elevator 012; while the average space volume created using elevator 014 was 1.8764±0.2366 ml. Both two newly invented tube elevators could effectively detach the maxillary sinus mucosa on the goat ex vivo sinus models. Moreover, elevator 014 has advantages over

Behavior and effect of Ti2Ni phase during processing of NiTi shape memory alloy wire from cast ingot

International Nuclear Information System (INIS)

Bhagyaraj, J.; Ramaiah, K.V.; Saikrishna, C.N.; Bhaumik, S.K.; Gouthama

2013-01-01

Highlights: •Ti 2 Ni second phase particles forms in different sizes and shapes in cast ingot. •TEM evidences showed shearing/fragmentation of Ti 2 Ni during processing. •Matrix close to Ti 2 Ni experienced severe plastic deformation lead to amorphisation. •Ti 2 Ni interfaces were mostly faceted and assist in nucleation of martensite. •Heterogeneity of microstructure observed near to and away from Ti 2 Ni. -- Abstract: Binary NiTi alloy is one of the commercially successful shape memory alloys (SMAs). Generally, the NiTi alloy composition used for thermal actuator application is slightly Ti-rich. In the present study, vacuum arc melted alloy of 50.2Ti–Ni (at.%) composition was prepared and characterized using optical, scanning and transmission electron microcopy. Formation of second phase particles (SPPs) in the cast alloy and their influence on development of microstructure during processing of the alloy into wire form has been investigated. Results showed that the present alloy contained Ti 2 Ni type SPPs in the matrix. In the cast alloy, the Ti 2 Ni particles form in varying sizes (1–10 μm) and shapes. During subsequent thermo-mechanical processing, these SPPs get sheared/fragmented into smaller particles with low aspect ratio. The presence of SPPs plays a significant role in refinement of the microstructure during processing of the alloy. During deformation of the alloy, the matrix phase around the SPPs experiences conditions similar to that observed in severe plastic deformation of metallic materials, leading to localized amorphisation of the matrix phase

Effect of chemical treatment on surface characteristics of sputter deposited Ti-rich NiTi shape memory alloy thin-films

International Nuclear Information System (INIS)

Sharma, S.K.; Mohan, S.

2014-01-01

Graphical abstract: FTIR spectra recorded for sputter deposited (a) untreated and (b) chemically treated NiTi SMA thin-films. - Highlights: • The effect of chemical treatment on surface properties of NiTi films demonstrated. • Chemically treated films offer strong ability to form protective TiO 2 layer. • TiO 2 layer formation offer great application prospects in biomedical fields. - Abstract: NiTi thin-films were deposited by DC magnetron sputtering from single alloy target (Ni/Ti:45/55 at.%). The rate of deposition and thickness of sputter deposited films were maintained to ∼35 nm min −1 and 4 μm respectively. A set of sputter deposited NiTi films were selected for specific chemical treatment with the solution comprising of de-ionized water, HF and HNO 3 respectively. The influence of chemical treatment on surface characteristics of NiTi films before and after chemical treatment was investigated for their structure, micro-structure and composition using different analytical techniques. Prior to chemical treatment, the composition of NiTi films using energy dispersive X-ray dispersive spectroscopy (EDS), were found to be 51.8 atomic percent of Ti and 48.2 atomic percent of Ni. The structure and morphology of these films were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). XRD investigations, demonstrated the presence of dominant Austenite (1 1 0) phase along with Martensite phase, for untreated NiTi films whereas some additional diffraction peaks viz. (1 0 0), (1 0 1), and (2 0 0) corresponding to Rutile and Anatase phase of Titanium dioxide (TiO 2 ) along with parent Austenite (1 1 0) phase were observed for chemically treated NiTi films. FTIR studies, it can be concluded that chemically treated films have higher tendency to form metal oxide/hydroxide than the untreated NiTi films. XPS investigations, demonstrated the presence of Ni-free surface and formation of a protective metal oxide (TiO 2 ) layer on the surface of

[TRU waste storage, technical data and calculations electropolishing, October 21, 1977--April 1978

Energy Technology Data Exchange (ETDEWEB)

Allen, R. P.

1977-12-31

This document contains copies of three reports on electropolishing. Electropolishing is a key step in the processing of solid wastes. It is the design basis for decontaminating alpha, as well as beta-gamma, waste metals in spite of incomplete data on the process and associated equipment.

Electropolishing of AISI-304 stainless steel using an oxidizing solution originally used for electrochemical coloration

International Nuclear Information System (INIS)

Andrade, Leonardo S.; Xavier, Sandro C.; Rocha-Filho, Romeu C.; Bocchi, Nerilso; Biaggio, Sonia R.

2005-01-01

Chemical polishing or electropolishing, instead of mechanical polishing, are recommended for the attainment of metallic surface polishes without the introduction of contaminants or tensions in the surface layers of the metal. The fundamental difference between the chemical and electrochemical polishing processes is that in the latter anodic currents/potentials are used to help in the dissolution and passivation of the metal. In this paper, the use of an oxidizing electrolytic solution (2.5 mol L -1 CrO 3 + 5.0 mol L -1 H 2 SO 4 ) originally employed in electrochemical coloration processes is reported for the electropolishing of AISI-314 stainless steel. Parameters involved in this electropolishing process, such as temperature, current density and time, were optimized so as to attain the best possible results evaluated by the obtained surface brightness measured by reflectance spectra. Surface analyses by scanning electron microscopy allowed a clear correlation between obtained brightness and surface smoothing. The best conditions obtained for the electropolishing process are: temperature of 45 deg. C, electrolysis time of 10 min and current density of around 25 A dm -2 . It should be pointed out that an electropolishing process signature (periodic oscillations of the cell potential) was established; this may be an important tool for optimizing and monitoring electropolishing processes

Electropolishing and in-situ baking of 1.3 GHz niobium cavities

Energy Technology Data Exchange (ETDEWEB)

Lilje, L.; Reschke, D. [DESY, Notkestrasse, Hamburg (Germany); Schmueser, P. [Hamburg Univ. (Germany)] [and others

2000-02-01

Three electropolished one-cell cavities were measured before and after in-situ bakeout under ultra-high vacuum conditions. Before bakeout the cavities showed a strong reduction in quality factor at fields above 25 MV/m. After the bakeout the Q drop was no longer present and gradients of up to 39 MV/m were achieved. This indicates that electropolishing yields highest accelerating gradients in niobium cavities only in combination with in-situ bakeout. (author)

Geometric analysis of root canals prepared by four rotary NiTi shaping systems.

Science.gov (United States)

Hashem, Ahmed Abdel Rahman; Ghoneim, Angie Galal; Lutfy, Reem Ahmed; Foda, Manar Yehia; Omar, Gihan Abdel Fatah

2012-07-01

A great number of nickel-titanium (NiTi) rotary systems with noncutting tips, different cross-sections, superior resistance to torsional fracture, varying tapers, and manufacturing method have been introduced to the market. The purpose of this study was to evaluate and compare the effect of 4 rotary NiTi preparation systems, Revo-S (RS; Micro-Mega, Besancon Cedex, France), Twisted file (TF; SybronEndo, Amersfoort, The Netherlands), ProFile GT Series X (GTX; Dentsply, Tulsa Dental Specialties, Tulsa, OK), and ProTaper (PT; Dentsply Maillefer, Ballaigues, Switzerland), on volumetric changes and transportation of curved root canals. Forty mesiobuccal canals of mandibular molars with an angle of curvature ranging from 25° to 40° were divided according to the instrument used in canal preparation into 4 groups of 10 samples each: group RS, group TF, group GTX, and group PT. Canals were scanned using an i-CAT CBCT scanner (Imaging Science International, Hatfield, PA) before and after preparation to evaluate the volumetric changes. Root canal transportation and centering ratio were evaluated at 1.3, 2.6, 5.2, and 7.8 mm from the apex. The significance level was set at P ≤ .05. The PT system removed a significantly higher amount of dentin than the other systems (P = .025). At the 1.3-mm level, there was no significant difference in canal transportation and centering ratio among the groups. However, at the other levels, TF maintained the original canal curvature recording significantly the least degree of canal transportation as well as the highest mean centering ratio. The TF system showed superior shaping ability in curved canals. Revo-S and GTX were better than ProTaper regarding both canal transportation and centering ability. Copyright © 2012 American Association of Endodontists. Published by Elsevier Inc. All rights reserved.

Training and two-way shape memory in NiTi alloys: influence on thermal parameters

International Nuclear Information System (INIS)

Lahoz, R.; Puertolas, J.A.

2004-01-01

The two-way shape memory effect (TWSME) was studied in a near equiatomic commercial alloy. A training procedure based on a constant load applied in the temperature range of the parent → martensite transformation was carried out on NiTi wires. The efficiency of the method was determined from deformation-temperature measurements by MTA at different training stress and number of cycles. A maximum of two shape memory strain was obtained for a stress training of 115 MPa, independently of number of training cycles. A correlation was established between the TWSME arisen and the permanent strain generated during the training. The A s and A f transitions present a positive shift and the M s and M f a negative one with increasing training stress. All the transitions temperatures decrease with the training cycling. In the trained material, the P→M and M→P temperatures and the latent heat of these conversions undergoes a strong decrease with increasing training stress, with a strong asymmetry between the forward and the reversed transitions. The changes of these thermal parameters as a function of the training parameters were studied on a thermodynamic frame

Preparation of Ni-Ti shape memory alloy by spark plasma sintering method

Czech Academy of Sciences Publication Activity Database

Salvetr, P.; Kubatík, Tomáš František; Novák, P.

2016-01-01

Roč. 16, č. 4 (2016), s. 804-808 ISSN 1213-2489 Institutional support: RVO:61389021 Keywords : Ni-Ti alloy * Powder metallurgy * Reactive sintering * Spark plasma sintering Subject RIV: JK - Corrosion ; Surface Treatment of Materials

Development of Vertical Buffered Electropolishing for Its Post-Treatment Technology on 1.5 GHz Niobium SRF Cavities

International Nuclear Information System (INIS)

Jin Song; Lu Xiang-Yang; Lin Lin; Zhao Kui; Wu, A. T.; Rimmer, R. A.

2011-01-01

We report the latest research development of vertical buffered electropolishing on its post-treatment procedure as well as the effects of several major post-treatment techniques for buffered electropolishing (BEP) processed 1.5 GHz niobium (Nb) superconducting radio frequency (SRF) cavities. With the established post-treatment procedure, an accelerating gradient of 28.4 MV/m is obtained on a single cell cavity of the cebaf shape. This is the best result in the history of BEP development. The cavity is limited by quench with a high quality factor over 1.2 × 10 10 at the quench point. Analyses from optical inspection and temperature-mapping show that the quench should be originated from the pits that were already present on the cavity before this BEP treatment. All of these factors indicate that this procedure will have a great potential to produce better results if cavities without intrinsic performance limiting imperfections are used. (nuclear physics)

Three-dimensional modeling for deformation of austenitic NiTi shape memory alloys under high strain rate

Science.gov (United States)

Yu, Hao; Young, Marcus L.

2018-01-01

A three-dimensional model for phase transformation of shape memory alloys (SMAs) during high strain rate deformation is developed and is then calibrated based on experimental results from an austenitic NiTi SMA. Stress, strain, and martensitic volume fraction distribution during high strain rate deformation are simulated using finite element analysis software ABAQUS/standard. For the first time, this paper presents a theoretical study of the microscopic band structure during high strain rate compressive deformation. The microscopic transformation band is generated by the phase front and leads to minor fluctuations in sample deformation. The strain rate effect on phase transformation is studied using the model. Both the starting stress for transformation and the slope of the stress-strain curve during phase transformation increase with increasing strain rate.

On the effect of TiC particles on the tensile properties and on the intrinsic two way effect of NiTi shape memory alloys produced by powder metallurgy

International Nuclear Information System (INIS)

Johansen, K.; Voggenreiter, H.; Eggeler, G.

1999-01-01

The present study investigates the tensile properties of a nickel titanium (NiTi) shape memory alloy (SMA) produced by powder metallurgy (PM) with and without TiC-particles. It discusses the effect of the addition of particles on the mechanical behavior in tension and studies the intrinsic two way effect (ε 2W ) after thermomechanical training. Special emphasis is placed on the stability of ε 2W after subsequent thermal cycling. The results are discussed on the basis of an analysis of the thermomechanical data and microstructural results. The present study shows that the PM route can produce NiTi SMAs with tensile properties which match those of materials produced by classical ingot metallurgy. Adding TiC particles to NiTi SMAs alters the phase transition temperatures (PTTs) and affects the SMA performance. Adding more than ten volume percent TiC particles results in early and brittle rupture during tensile loading. (orig.)

Modeling, Simulation, Additive Manufacturing, and Experimental Evaluation of Solid and Porous NiTi

Science.gov (United States)

Taheri Andani, Mohsen

In recent years, shape memory alloys (SMAs) have entered a wide range of engineering applications in fields such as aerospace and medical applications. Nickel-titanium (NiTi) is the most commonly used SMAs due to its excellent functional characteristics (shape memory effect and superelasticity behavior). These properties are based on a solid-solid phase transformation between martensite and austenite. Beside these two characteristics, low stiffness, biocompatibility and corrosion properties of NiTi make it an attractive candidate for biomedical applications (e.g., bone plates, bone screws, and vascular stents). It is well know that manufacturing and processing of NiTi is very challenging. The functional properties of NiTi are significantly affected by the impurity level and due to the high titanium content, NiTi are highly reactive. Therefore, high temperature processed parts through methods such as melting and casting which result in increased impurity levels have inadequate structural and functional properties. Furthermore, high ductility and elasticity of NiTi, adhesion, work hardening and spring back effects make machining quite challenging. These unfavorable effects for machining cause significant tool wear along with decreasing the quality of work piece. Recently, additive manufacturing (AM) has gained significant attention for manufacturing NiTi. Since AM can create a part directly from CAD data, it is predicted that AM can overcome most of the manufacturing difficulties. This technique provides the possibility of fabricating highly complex parts, which cannot be processed by any other methods. Curved holes, designed porosity, and lattice like structures are some examples of mentioned complex parts. This work investigates manufacturing superelastic NiTi by selective laser melting (SLM) technique (using PXM by Phenix/3D Systems). An extended experimental study is conducted on the effect of subsequent heat treatments with different aging conditions on phase

In Vitro Corrosion Assessment of Additively Manufactured Porous NiTi Structures for Bone Fixation Applications

Directory of Open Access Journals (Sweden)

Hamdy Ibrahim

2018-03-01

Full Text Available NiTi alloys possess distinct functional properties (i.e., shape memory effect and superelasticity and biocompatibility, making them appealing for bone fixation applications. Additive manufacturing offers an alternative method for fabricating NiTi parts, which are known to be very difficult to machine using conventional manufacturing methods. However, poor surface quality, and the presence of impurities and defects, are some of the major concerns associated with NiTi structures manufactured using additive manufacturing. The aim of this study is to assess the in vitro corrosion properties of additively manufactured NiTi structures. NiTi samples (bulk and porous were produced using selective laser melting (SLM, and their electrochemical corrosion characteristics and Ni ion release levels were measured and compared with conventionally fabricated NiTi parts. The additively manufactured NiTi structures were found to have electrochemical corrosion characteristics similar to those found for the conventionally fabricated NiTi alloy samples. The highest Ni ion release level was found in the case of 50% porous structures, which can be attributed to their significantly higher exposed surface area. However, the Ni ion release levels reported in this work for all the fabricated structures remain within the range of most of values for conventionally fabricated NiTi alloys reported in the literature. The results of this study suggest that the proposed SLM fabrication process does not result in a significant deterioration in the corrosion resistance of NiTi parts, making them suitable for bone fixation applications.

Understanding the shape-memory alloys used in orthodontics.

Science.gov (United States)

Fernandes, Daniel J; Peres, Rafael V; Mendes, Alvaro M; Elias, Carlos N

2011-01-01

Nickel-titanium (NiTi) shape-memory alloys (SMAs) have been used in the manufacture of orthodontic wires due to their shape memory properties, super-elasticity, high ductility, and resistance to corrosion. SMAs have greater strength and lower modulus of elasticity when compared with stainless steel alloys. The pseudoelastic behavior of NiTi wires means that on unloading they return to their original shape by delivering light continuous forces over a wider range of deformation which is claimed to allow dental displacements. The aim of this paper is to discuss the physical, metallurgical, and mechanical properties of NiTi used in Orthodontics in order to analyze the shape memory properties, super-elasticity, and thermomechanical characteristics of SMA.

Experimental study on Response Parameters of Ni-rich NiTi Shape Memory Alloy during Wire Electric Discharge Machining

Science.gov (United States)

Bisaria, Himanshu; Shandilya, Pragya

2018-03-01

Nowadays NiTi SMAs are gaining more prominence due to their unique properties such as superelasticity, shape memory effect, high fatigue strength and many other enriched physical and mechanical properties. The current studies explore the effect of machining parameters namely, peak current (Ip), pulse off time (TOFF), and pulse on time (TON) on wire wear ratio (WWR), and dimensional deviation (DD) in WEDM. It was found that high discharge energy was mainly ascribed to high WWR and DD. The WWR and DD increased with the increase in pulse on time and peak current whereas high pulse off time was favourable for low WWR and DD.

Novel micro-patterning processes for thin film NiTi vascular devices

International Nuclear Information System (INIS)

Chun, Y J; Mohanchandra, K P; Carman, G P; Levi, D S; Fishbein, M C

2010-01-01

In order to create microscale features in thin film NiTi for use in vascular endografts, a novel 'lift-off process' was developed for use with deep reactive ion etching. A wet etching approach is compared to two variations of this new 'lift-off' process. The first lift-off process (lift-off I) used Si posts to define the features of NiTi film deposited on the Si substrate. This method produced fractures in the NiTi when the film was released. The lift-off II process used Si islands as substrate for the film while the Si wafer defined the specific geometric features. Lift-off II process allowed for the creation of various shape patterns (i.e., ellipse, diamond, circle, square, etc) in the range of 5–180 µm. The lift-off II process produced smooth and well aligned micro-patterns in thin film NiTi without the undercutting found in wet etching techniques. The micro-patterned thin film NiTi formed from the lift-off II process was used to cover a stent. In vivo tests were performed to evaluate the endothelialization though patterned thin films. Angiography, histopathology and SEM showed patency of the artery and uniformly promoted endothelial layer covering without thrombosis in both a medium and small artery

Atomic Layer-Deposited TiO2 Coatings on NiTi Surface

Science.gov (United States)

Vokoun, D.; Racek, J.; Kadeřávek, L.; Kei, C. C.; Yu, Y. S.; Klimša, L.; Šittner, P.

2018-02-01

NiTi shape-memory alloys may release poisonous Ni ions at the alloys' surface. In an attempt to prepare a well-performing surface layer on an NiTi sample, the thermally grown TiO2 layer, which formed during the heat treatment of NiTi, was removed and replaced with a new TiO2 layer prepared using the atomic layer deposition (ALD) method. Using x-ray photoelectron spectroscopy, it was found that the ALD layer prepared at as low a temperature as 100 °C contained Ti in oxidation states + 4 and + 3. As for static corrosion properties of the ALD-coated NiTi samples, they further improved compared to those covered by thermally grown oxide. The corrosion rate of samples with thermally grown oxide was 1.05 × 10-5 mm/year, whereas the corrosion rate of the ALD-coated samples turned out to be about five times lower. However, cracking of the ALD coating occurred at about 1.5% strain during the superelastic mechanical loading in tension taking place via the propagation of a localized martensite band.

Microstructure and corrosion behavior of laser processed NiTi alloy.

Science.gov (United States)

Marattukalam, Jithin J; Singh, Amit Kumar; Datta, Susmit; Das, Mitun; Balla, Vamsi Krishna; Bontha, Srikanth; Kalpathy, Sreeram K

2015-12-01

Laser Engineered Net Shaping (LENS™), a commercially available additive manufacturing technology, has been used to fabricate dense equiatomic NiTi alloy components. The primary aim of this work is to study the effect of laser power and scan speed on microstructure, phase constituents, hardness and corrosion behavior of laser processed NiTi alloy. The results showed retention of large amount of high-temperature austenite phase at room temperature due to high cooling rates associated with laser processing. The high amount of austenite in these samples increased the hardness. The grain size and corrosion resistance were found to increase with laser power. The surface energy of NiTi alloy, calculated using contact angles, decreased from 61 mN/m to 56 mN/m with increase in laser energy density from 20 J/mm(2) to 80 J/mm(2). The decrease in surface energy shifted the corrosion potentials to nobler direction and decreased the corrosion current. Under present experimental conditions the laser power found to have strong influence on microstructure, phase constituents and corrosion resistance of NiTi alloy. Copyright © 2015 Elsevier B.V. All rights reserved.

Negative and Zero Thermal Expansion NiTi Superelastic Shape Memory Alloy by Microstructure Engineering

Science.gov (United States)

Sun, Qingping; Yu, Chao; Kang, Guozheng

2018-03-01

We report recent progress in tailoring the thermal expansion (TE) of nanocrystalline (NC) NiTi by microstructure hierarchical design and control without composition change. Fabrication and characterization methods are outlined and preliminary results of both experiment and mechanism-based modeling are presented to understand and get insight into the unusual TE phenomena. The important roles of the intrinsic thermal expansion anisotropy of B19' lattice and the suppression of phase transition by the extrinsic fabricated microstructure (cold rolling and annealing, grain size, defects, textures and volume fractions of nanoscaled B2 and B19' lattices) in the overall macroscopic TE behaviors of the superelastic NC NiTi polycrystal SMAs are emphasized.

Negative and Zero Thermal Expansion NiTi Superelastic Shape Memory Alloy by Microstructure Engineering

Science.gov (United States)

Sun, Qingping; Yu, Chao; Kang, Guozheng

2018-02-01

We report recent progress in tailoring the thermal expansion (TE) of nanocrystalline (NC) NiTi by microstructure hierarchical design and control without composition change. Fabrication and characterization methods are outlined and preliminary results of both experiment and mechanism-based modeling are presented to understand and get insight into the unusual TE phenomena. The important roles of the intrinsic thermal expansion anisotropy of B19' lattice and the suppression of phase transition by the extrinsic fabricated microstructure (cold rolling and annealing, grain size, defects, textures and volume fractions of nanoscaled B2 and B19' lattices) in the overall macroscopic TE behaviors of the superelastic NC NiTi polycrystal SMAs are emphasized.

In Situ Synchrotron Radiation X-ray Diffraction Study on Phase and Oxide Growth during a High Temperature Cycle of a NiTi-20 at.% Zr High Temperature Shape Memory Alloy

Science.gov (United States)

Carl, Matthew; Van Doren, Brian; Young, Marcus L.

2018-02-01

Ternary additions to binary NiTi shape memory alloys are known to significantly affect the characteristic martensite-to-austenite phase transformation, i.e., decrease or increase transformation temperatures. High temperature shape memory alloys can be created by adding Au, Pt, Pd, Hf, or Zr to binary NiTi in appropriate amounts; however, the majority of these ternary additions are exceedingly expensive, unfortunately making them impractical for most commercial applications. Zr is the exception of the group, but it is often disregarded because of its poor workability and thermal stability. In an effort to find a temperature range that allows for the potential workability of NiTiZr alloys in normal atmosphere environments and to gain understanding as to the cause of failure during processing, a NiTi-20 at.% Zr was subjected to a thermal cycle ranging from RT to 1000 °C with short 15 min holds at select temperatures during both heating and cooling while simultaneously collecting high-energy synchrotron radiation X-ray diffraction measurements. This study provides valuable insight into the kinetics of precipitation and oxide formation and its relationship to processing. In addition, scanning electron microscopy was performed on five samples, each isothermally held to examine precipitation and oxide structure and growth.

METHOD OF ELECTROPOLISHING URANIUM

Science.gov (United States)

Walker, D.E.; Noland, R.A.

1959-07-14

A method of electropolishing the surface of uranium articles is presented. The process of this invention is carried out by immersing the uranium anticle into an electrolyte which contains from 35 to 65% by volume sulfuric acid, 1 to 20% by volume glycerine and 25 to 50% by volume of water. The article is made the anode in the cell and polished by electrolyzing at a voltage of from 10 to 15 volts. Discontinuing the electrolysis by intermittently withdrawing the anode from the electrolyte and removing any polarized film formed therein results in an especially bright surface.

Effect of ageing temperatures on pseudoelasticity of Ni-rich NiTi shape memory alloy

Science.gov (United States)

Mohamad, Hishamiakim; Mahmud, Abdus Samad; Nashrudin, Muhammad Naqib; Razali, Muhammad Fauzinizam

2018-05-01

The shape memory behavior of NiTi alloy is very sensitive to alloy composition and heat treatments, particularly annealing and ageing. This paper analysed the effect of ageing towards the thermomechanical behaviour of Ti-51at%Ni wire. The analysis focused on the effect of ageing at the different temperature on thermal transformation sequence and tensile deformation behaviour with respect to the recoverability of the alloy. It was found that B2-R transformation peak appeared in the differential scanning calorimetry (DSC) measurement when the alloys were aged at the temperature between 400°C to 475°C for 30 minutes. Further ageing at 500°C to 550°C yielded two stage transformation, B2-R-B19' in cooling. All aged wires exhibited good pseudoelastic behaviour when deformed at room temperature and yielded below 1% residual strain upon unloading. Ageing at 450°C resulted the smallest unrecovered strain of about 0.4%.

Microstructure, mechanical properties and superelasticity of biomedical porous NiTi alloy prepared by microwave sintering.

Science.gov (United States)

Xu, J L; Bao, L Z; Liu, A H; Jin, X J; Tong, Y X; Luo, J M; Zhong, Z C; Zheng, Y F

2015-01-01

Porous NiTi alloys were prepared by microwave sintering using ammonium hydrogen carbonate (NH4HCO3) as the space holder agent to adjust the porosity in the range of 22-62%. The effects of porosities on the microstructure, hardness, compressive strength, bending strength, elastic modulus, phase transformation temperature and superelasticity of the porous NiTi alloys were investigated. The results showed that the porosities and average pore sizes of the porous NiTi alloys increased with increasing the contents of NH4HCO3. The porous NiTi alloys consisted of nearly single NiTi phase, with a very small amount of two secondary phases (Ni3Ti, NiTi2) when the porosities are lower than 50%. The amount of Ni3Ti and NiTi2 phases increased with further increasing of the porosity proportion. The porosities had few effects on the phase transformation temperatures of the porous NiTi alloys. By increasing the porosities, all of the hardness, compressive strength, elastic modulus, bending strength and superelasticity of the porous NiTi alloys decreased. However, the compressive strength and bending strength were higher or close to those of natural bone and the elastic modulus was close to the natural bone. The superelastic recovery strain of the trained porous NiTi alloys could reach between 3.1 and 4.7% at the pre-strain of 5%, even if the porosity was up to 62%. Moreover, partial shape memory effect was observed for all porosity levels under the experiment conditions. Therefore, the microwave sintered porous NiTi alloys could be a promising candidate for bone implant. Copyright © 2014 Elsevier B.V. All rights reserved.

Influence of electropolishing and anodic oxidation on morphology, chemical composition and corrosion resistance of niobium

Energy Technology Data Exchange (ETDEWEB)

Sowa, Maciej; Greń, Katarzyna [Faculty of Chemistry, Silesian University of Technology, B. Krzywoustego Street 6, 44-100 Gliwice (Poland); Kukharenko, Andrey I. [Institute of Metal Physics, Russian Academy of Sciences-Ural Division, S. Kovalevskoi Street 18, 620990 Yekaterinburg (Russian Federation); Ural Federal University, Mira Street 19, 620002 Yekaterinburg, Mira str. 19 (Russian Federation); Korotin, Danila M. [Institute of Metal Physics, Russian Academy of Sciences-Ural Division, S. Kovalevskoi Street 18, 620990 Yekaterinburg (Russian Federation); Michalska, Joanna [Faculty of Materials Engineering and Metallurgy, Silesian University of Technology, Krasińskiego Street 8, 40-019 Katowice (Poland); Szyk-Warszyńska, Lilianna; Mosiałek, Michał [Jerzy Haber Institute of Catalysis and Surface Chemistry PAS, Niezapominajek Street 8, 30-239 Kraków (Poland); Żak, Jerzy [Faculty of Chemistry, Silesian University of Technology, B. Krzywoustego Street 6, 44-100 Gliwice (Poland); Pamuła, Elżbieta [AGH University of Science and Technology, Faculty of Materials Science and Ceramics, Mickiewicza Avenue 30, 30-059 Kraków (Poland); Kurmaev, Ernst Z. [Institute of Metal Physics, Russian Academy of Sciences-Ural Division, S. Kovalevskoi Street 18, 620990 Yekaterinburg (Russian Federation); Cholakh, Seif O. [Ural Federal University, Mira Street 19, 620002 Yekaterinburg, Mira str. 19 (Russian Federation); Simka, Wojciech, E-mail: wojciech.simka@polsl.pl [Faculty of Chemistry, Silesian University of Technology, B. Krzywoustego Street 6, 44-100 Gliwice (Poland)

2014-09-01

The work presents results of the studies performed on electropolishing of pure niobium in a bath that contained: sulphuric acid, hydrofluoric acid, ethylene glycol and acetanilide. After the electropolishing, the specimens were subjected to anodic passivation in a 1 mol dm{sup −3} phosphoric acid solution at various voltages. The surface morphology, thickness, roughness and chemical composition of the resulting oxide layers were analysed. Thusly prepared niobium samples were additionally investigated in terms of their corrosion resistance in Ringer's solution. The electropolished niobium surface was determined to be smooth and lustrous. The anodisation led to the growth of barrier-like oxide layers, which were enriched in phosphorus species. - Highlights: • Pure niobium was electropolished and subsequently anodised in a H{sub 3}PO{sub 4} solution. • Phosphorus was successfully introduced into the oxide layers after the treatment. • Corrosion resistance of niobium in Ringer's solution was improved after anodising.

NiTi Alloys for Tribological Applications: The Role of In-Situ Nanotechnology

Science.gov (United States)

Dellacorte, Christopher

2016-01-01

Beginning in 2004, NASA initiated the investigation and development of, Nitinol 60, a nickel-rich and dimensionally stable version of shape memory alloy Nitinol 55, as an alternative to bearing steel. Early investigations showed it to be hard and impervious to aqueous corrosion but the fundamental reasons for these properties were unknown. Shape memory alloys made from equiatomic Ni-Ti are widely known for their unique dimensional instability behavior that can be triggered by thermal and mechanical stress. The nickel-rich alloys exhibit no such dimension change property and have high hardness but have largely been overlooked by industry and the engineering community. Though steel is the dominant material of choice for mechanical components (bearings and gears) it has intrinsic limitations related to corrosion and plastic deformation. In contrast, Ni-Ti alloys are intrinsically rustproof and can withstand high contact loads without damage (denting). Over the last decade, focused RD to exploit these alloys for new applications has revealed that in-situ nano-scale phases that form during processing are largely responsible for NiTis remarkable properties. In this presentation, the state-of-art of nickel-rich NiTi alloys will be introduced and the nanotechnology behind their intriguing behavior will be addressed. The presentation will include discussion of how NASA is adopting this new technology inside the space station water recycling system as a pathfinder for more down-to-earth tribological challenges.

The effect of surfactants on the electropolishing behavior of copper in orthophosphoric acid

Energy Technology Data Exchange (ETDEWEB)

Taha, A.A., E-mail: asia_taha@yahoo.com; Ahmed, A.M.; Rahman, H.H. Abdel; Abouzeid, F.M.

2013-07-15

The electropolishing behavior of copper was studied in orthophosphoric acid with Triton X-100, sodium dodecyl sulphate and cetyl pyridinium chloride as additives for improving the finish obtained on copper surface. This was investigated by measuring and comparing anode potential-limiting current relationships in solutions of gradually increasing concentration of surfactants. The addition of surfactants to the electropolishing solution results in a lower limiting current. This confirms the mass transport of dissolved species from the anode surface to the bulk of solution as the rate-determining step in the presence of three surfactants in all concentrations investigated. Scanning electron microscope (SEM), atomic force microscope (AFM) and measured brightness values were used to investigate the copper surface after electropolishing and the results were compared to polishing done in absence of surfactants. According to SEM images and brightness values, addition of Triton X-100 was effective to enhance levelling and brightening more than sodium dodecyl sulphate and cetyl pyridinium chloride. AFM analysis showed that the roughness values (R{sub a}) for an electropolished copper surface, in presence of surfactants, is significantly lower than in absence of surfactants. Different reaction conditions and the physical properties of solutions are studied to obtain dimensionless correlation among all these parameters.

Shaping ability of two M-wire and two traditional nickel-titanium instrumentation systems in S-shaped resin canals.

Science.gov (United States)

Ceyhanli, K T; Kamaci, A; Taner, M; Erdilek, N; Celik, D

2015-01-01

The aim of this study was to evaluate the shaping effects of two M-wire and two traditional nickel-titanium (NiTi) rotary systems in simulated S-shaped resin canals. Forty simulated S-shaped canals in resin blocks were instrumented with two traditional (ProTaper, Sendoline S5) and two M-wire (WaveOne, GT series X) NiTi systems according to the manufacturers' instructions. Ten resin blocks were used for each system. Pre- and post-instrumentation images were captured using a stereomicroscope and superimposed with an image program. Canal transportation, material removal, and aberrations were evaluated and recorded as numeric parameters. Data were analyzed using one-way ANOVA and post-hoc Tukey tests with a 95% confidence interval. There were significant differences between systems in terms of transportation and material removal (Pwire or traditional NiTi) and kinematics (rotary or reciprocating motion) did not affect the shaping abilities of the systems. The extended file designs of highly tapered NiTi systems (ProTaper, WaveOne) resulted in greater deviations from the original root canal trace and more material removal when compared to less tapered systems (Sendoline S5, GT series X).

Influence of compaction pressure on the morphology and phase evolution of porous NiTi alloy prepared by SHS technique

Directory of Open Access Journals (Sweden)

Sirikul Wisutmethangoon

2008-08-01

Full Text Available The influence of compaction pressure on the pore morphology of porous NiTi shape memory alloys (SMAs fabricated by self-propagating high-temperature synthesis (SHS was investigated. The compaction pressure has a significant effect on the combustion temperature and pore morphology. The porous NiTi (SMAs thus obtained have the porosity of product in the range of 37.4-57.9 vol.%. The open porosity ratios were observed to be greater than 88%, which indicatesthat porous NiTi (SMAs are suitable for biomedical applications. In addition, the predominant phases in the porous product are B2(NiTi and B19’(NiTi with small amounts of secondary phases, NiTi2 and Ni4Ti3.

Mechanical characterisation of orthodontic superelastic Ni-Ti wires

Energy Technology Data Exchange (ETDEWEB)

Arrigoni, M.; Pietrabissa, R. [Politecnico di Milano, Milano (Italy). Lab. of Biological Structure Mechanics; Auricchio, F.; Petrini, L. [Politecnico di Milano, Milano (Italy). Lab. of Biological Structure Mechanics; Pavia Univ. (Italy). Dept. of Structural Mechanics; Cacciafesta, V. [Politecnico di Milano, Milano (Italy). Lab. of Biological Structure Mechanics; Pavia Univ. (Italy). Dept. of Orthodontia

2001-11-01

Nowadays, the orthodontic treatment is improving thanks to the introduction of Ni-Ti super-elastic alloy wires in the ordinary therapy. Indeed, laboratory tests performed in the last decade have shown that Ni-Ti superelastic wires are able to satisfy the ideal requirements for fixed arch-wire appliance: high flexibility, minimal distortion or plastic deformation, light constant force production over a wide range of displacements. On the other hand, many orthodontic companies produce Ni-Ti arch-wires, without giving detailed specifications on their superelastic characteristics. To improve the knowledge on real properties for these products, an experimental campaign on different commercial arch-wires has been started at the Laboratory of Biological Structure Mechanics (LABS) at the Politecnico di Milano (Italy). This work presents the first step of the research, concerning the comparison between the behaviour of four types of wires (two produced by ORMCO and two produced by 3M/Unitek) under monotonic and cyclic isothermal tensile tests. The results show significant differences between the products in terms of elastic modulus, stress values of the loading-unloading plateau, hysteresis amplitude, spring-back capacity, shape recovery capability, strain rate effect and fatigue behaviour. (orig.)

Device for surface decontamination by electropolishing

International Nuclear Information System (INIS)

Maury, A.

1984-01-01

The movable cleaning unit for continuous operation comprises an electropolishing apparatus on a support that can be moved in translation on a bracket which can take all orientations. The apparatus is provided with an electrode feeded in electrolyte, scraping means, hot air drying and a tank connected to vacuum for recovery of effluents that are send, with a pump, to a regeneration unit. Application is made for cleaning the walls of nuclear swimming pools [fr

Comparative evaluation of apically extruded debris during root canal instrumentation using two Ni-Ti single file rotary systems: An in vitro study.

Science.gov (United States)

Singbal, Kiran; Jain, Disha; Raja, Kranthi; Hoe, Tan Ming

2017-01-01

Apical extrusion of debris during instrumentation is detrimental to the patient. The aim of this study was to evaluate the apical extrusion of debris during root canal instrumentation using two single file rotary Ni-Ti systems. Thirty freshly extracted mandibular premolars with straight roots were sterilized and divided into two groups instrumented using: One Shape rotary Ni-Ti system with Endoflare orifice shaper (Group 1) and Neo-Niti rotary Ni-Ti system with C1 orifice shaper (Group 2). Preweighed Eppendorf tubes fitted for each tooth before instrumentation. During instrumentation, 1 mL of distilled water with a 30-gauge needle was used to irrigate after every instrument. Tips of the tooth were irrigated with 2 ml distilled water after removal from Eppendorf tubes. The total volume of irrigant in each group was the same 8 ml. All tubes were incubated at 68°C for 15 days and subsequently weighed. The difference between pre- and post-debris weights was calculated, and statistical analysis was performed using independent t -test and level of significance was set at 0.05. The difference between pre- and post-weights was significantly greater for the One Shape system. The Neolix Niti single file was associated with less extrusion compared to One Shape single file system.

A Two-Way Shape Memory Study on Ni-Rich NiTi Shape Memory Alloy by Combination of the All-Round Treatment and the R-Phase Transformation

Science.gov (United States)

Wu, Z. H.; Vokoun, D.; Leu, C. C.; Hu, C. T.

2017-12-01

Ni4Ti3 precipitates are formed in Ni-rich NiTi shape memory alloys (SMAs) after a certain heat treatment. Such a treatment then results in the changed phase transformation behavior of the alloy switching from the one-step reversible phase change B2 ↔ B19' to the two-step, B2 ↔ R ↔ B19', phase change. The present study reports a two-way shape memory (TWSM) due to an all-round treatment followed by an R-phase constraint aging at room temperature. The enhanced TWSM behavior was observed upon temperature cycling between 273 K (R-phase) and 77 K (B19' phase). The effect of various constraint strains in R-phase aging by employing different diameters of the constraint ring was studied. However, the TWSM effect due to constraining the R-phase will be eliminated after a temperature rise of specimen to the fully parent phase (373 K).

Fundamental Study of Micro-Defects in Electropolished EB-Welded and Hydroformed SRF Accelerating Structures

Energy Technology Data Exchange (ETDEWEB)

Sumption, Mike

2014-08-29

In the area of niobium elecropolishing fundamentals, we focused on understanding the influence of the surface topology, and geometry (with effects from gravity included. The formation of a viscous film is essential for the electropolishing process to take place. The exact nature and composition of the film formed on niobium is still unknown because of its solubility in the electrolyte. Extensive pitting may take place at surface where a stable film cannot form. This has to be taken into consideration while determining the speed with which the SRF cavities are rotated while EP. Hydrodynamic aspects must be taken into consideration while optimizing the polishing parameters. There is improvement in surface finish with polishing time. There is a huge change in surface quality when the EP time is increased from 2 hours to 4 hours but not much change takes place when the time is further increased to 6 hours. So keeping the economic points in view, about 100 um defect layer removal may be sufficient to get the desired performance. In the area of Electropolishing of untreated and treated niobium with Weld Joints we studied untreated and treated Nb, especially for the heat affected areas next to welded bumps, electropolished for different durations. The electropolishing of the untreated Nb caused the formation of pits on the surface at about 15 min but they disappeared when the electropolishing duration was more than 15 min. Electropolishing for 120 min smoothened the surface of untreated Nb by levelling the surface, but the severe formation of pits on the whole surface was found after 240 min. The treatment of Nb significantly changed the Nb surface morphology which was covered by grains of different size that looked light or dark in the optical microscope. The treated Nb was susceptible to pitting during the entire electropolishing starting from 15 min and the dark grains had more susceptibility to pitting than the light grains. In addition, electropolishing for 240 min

Dynamic actuation of a novel laser-processed NiTi linear actuator

International Nuclear Information System (INIS)

Pequegnat, A; Daly, M; Wang, J; Zhou, Y; Khan, M I

2012-01-01

A novel laser processing technique, capable of locally modifying the shape memory effect, was applied to enhance the functionality of a NiTi linear actuator. By altering local transformation temperatures, an additional memory was imparted into a monolithic NiTi wire to enable dynamic actuation via controlled resistive heating. Characterizations of the actuator load, displacement and cyclic properties were conducted using a custom-built spring-biased test set-up. Monotonic tensile testing was also implemented to characterize the deformation behaviour of the martensite phase. Observed differences in the deformation behaviour of laser-processed material were found to affect the magnitude of the active strain. Furthermore, residual strain during cyclic actuation testing was found to stabilize after 150 cycles while the recoverable strain remained constant. This laser-processed actuator will allow for the realization of new applications and improved control methods for shape memory alloys. (paper)

Texture development and strain hysteresis in a NiTi shape-memory alloy during thermal cycling under load

International Nuclear Information System (INIS)

Ye, B.; Majumdar, B.S.; Dutta, I.

2009-01-01

Thermal cycling experiments were conducted on a NiTi shape-memory alloy at different constant applied stresses below the yield strength of the martensite. The mechanical strain response manifested as strain hysteresis loops, whose range was proportional to the applied stress. In situ neutron diffraction experiments show that the strain hysteresis occurs as a result of the establishment of a stress-dependent crystallographic texture of the martensite during the first cool-down from austenite, and thereafter repeated during thermal cycling under the same load. This texture is found to depend on the stress during the thermal cycling experiments. A strain-pole map is derived and shown to explain the observed texture during thermal cycling. The strain-pole methodology is shown to work with similar martensitic transformations in other material systems.

Orientation dependence of stress-induced martensite formation during nanoindentation in NiTi shape memory alloys

International Nuclear Information System (INIS)

Laplanche, G.; Pfetzing-Micklich, J.; Eggeler, G.

2014-01-01

In the present work we used nanoindentation with a spherical indenter tip to study the formation of stress-induced martensite in NiTi shape memory alloys. Prior to nanoindentation, orientation imaging was performed to select austenite grains with specific crystallographic orientations, including the principal crystallographic directions [0 0 1], [1 0 1] and [1 1 1]. We studied a material where stress-induced martensite is stable at room temperature and found surface patterns with four-, two- and threefold symmetries for the [0 0 1], [1 0 1] and [1 1 1] crystallographic indentation directions, respectively. Atomic force microscopy investigations of the topography showed that the surface patterns were associated with sink-ins. The crystallographic sink-in patterns disappeared during heating, which proved their martensitic origin. Our results provide clear experimental evidence which shows that the crystallographic anisotropy of nanoindentation is governed by the crystallographic anisotropy of the stress-induced formation of martensite

Effect of pre-strain on microstructure of Ni-Ti orthodontic archwires

Energy Technology Data Exchange (ETDEWEB)

Jafari, J. [Department of Materials Science and Engineering, Engineering Faculty, Ferdowsi University of Mashhad, Azadi Square, P.O. Box 91775-1111, Mashhad (Iran, Islamic Republic of); Zebarjad, S.M. [Department of Materials Science and Engineering, Engineering Faculty, Ferdowsi University of Mashhad, Azadi Square, P.O. Box 91775-1111, Mashhad (Iran, Islamic Republic of)], E-mail: Zebarjad@um.ac.ir; Sajjadi, S.A. [Department of Materials Science and Engineering, Engineering Faculty, Ferdowsi University of Mashhad, Azadi Square, P.O. Box 91775-1111, Mashhad (Iran, Islamic Republic of)

2008-01-25

One of the most important applications of shape memory alloy is in medicine, especially orthodontic archwires. In this category Ni-Ti orthodontic archwires is one of the oldest used materials. Biocompatibility, corrosion resistance, super elasticity, etc. are its outstanding properties. In spite of the importance of dependency of pre-strain on microstructure of Ni-Ti there are limited sources concentrated on the subject. For this reason the main purpose of the current study is determination of the effect of pre-strain on microstructure of Ni-Ti orthodontic archwires. In this regard, three-point bending was performed on the orthodontic archwire specimens to apply different amount of strain. The microstructures were compared with the un-strained wire using optical and scanning electron microscopes. The results showed that the stable phase depends strongly on the value of pre-strain. Increasing pre-strain causes to decrease martensite laths and leads the microstructure toward austenite phase.

Effect of pre-strain on microstructure of Ni-Ti orthodontic archwires

International Nuclear Information System (INIS)

Jafari, J.; Zebarjad, S.M.; Sajjadi, S.A.

2008-01-01

One of the most important applications of shape memory alloy is in medicine, especially orthodontic archwires. In this category Ni-Ti orthodontic archwires is one of the oldest used materials. Biocompatibility, corrosion resistance, super elasticity, etc. are its outstanding properties. In spite of the importance of dependency of pre-strain on microstructure of Ni-Ti there are limited sources concentrated on the subject. For this reason the main purpose of the current study is determination of the effect of pre-strain on microstructure of Ni-Ti orthodontic archwires. In this regard, three-point bending was performed on the orthodontic archwire specimens to apply different amount of strain. The microstructures were compared with the un-strained wire using optical and scanning electron microscopes. The results showed that the stable phase depends strongly on the value of pre-strain. Increasing pre-strain causes to decrease martensite laths and leads the microstructure toward austenite phase

Mechanical and shape memory properties of porous Ni50.1Ti49.9 alloys manufactured by selective laser melting.

Science.gov (United States)

Taheri Andani, Mohsen; Saedi, Soheil; Turabi, Ali Sadi; Karamooz, M R; Haberland, Christoph; Karaca, Haluk Ersin; Elahinia, Mohammad

2017-04-01

Near equiatomic NiTi shape memory alloys were fabricated in dense and designed porous forms by Selective Laser Melting (SLM) and their mechanical and shape memory properties were systematically characterized. Particularly, the effects of pore morphology on their mechanical responses were investigated. Dense and porous NiTi alloys exhibited good shape memory effect with a recoverable strain of about 5% and functional stability after eight cycles of compression. The stiffness and residual plastic strain of porous NiTi were found to depend highly on the pore shape and the level of porosity. Since porous NiTi structures have lower elastic modulus and density than dense NiTi with still good shape memory properties, they are promising materials for lightweight structures, energy absorbers, and biomedical implants. Copyright © 2017 Elsevier Ltd. All rights reserved.

PEEK (polyether-ether-ketone)-coated nitinol wire: Film stability for biocompatibility applications

Energy Technology Data Exchange (ETDEWEB)

Sheiko, Nataliia [Institut Charles Sadron, C.N.R.S. UPR 22, Université de Strasbourg, 23 rue du Loess, BP 84047, 67034 Strasbourg Cedex 2 (France); Kékicheff, Patrick, E-mail: patrick.kekicheff@ics-cnrs.unistra.fr [Institut Charles Sadron, C.N.R.S. UPR 22, Université de Strasbourg, 23 rue du Loess, BP 84047, 67034 Strasbourg Cedex 2 (France); Marie, Pascal; Schmutz, Marc; Jacomine, Leandro [Institut Charles Sadron, C.N.R.S. UPR 22, Université de Strasbourg, 23 rue du Loess, BP 84047, 67034 Strasbourg Cedex 2 (France); Perrin-Schmitt, Fabienne [Faculté de Médecine, INSERM, UMR-S 1121, “Biomaterials and Bioengineering”, Université de Strasbourg, 11 rue Humann, 67085 Strasbourg Cedex (France)

2016-12-15

Highlights: • A thin (12 μm) homogeneous PEEK film without any defects or voids is deposited on NiTi wires. • The coating remains stable in biological environment with negligible Ni ion release and no cytotoxicity. • Large pressure (>2 GPa) can only disrupt the coating film as shown by nanoscratch tests. • Coated spring wires sustain mechanical stress in continuous cycles of axial compression/stretching for >7 million cycles. - Abstract: High quality biocompatible poly-ether-ether-ketone (PEEK) coatings were produced on NiTi shape memory alloy wires using dipping deposition from colloidal aqueous PEEK dispersions after substrate surface treatment. The surface morphology and microstructure were investigated by Scanning Electron Microscopy at every step of the process from the as-received Nitinol substrate to the ultimate PEEK-coated NiTi wire. Nanoscratch tests were carried out to access the adhesive behavior of the polymer coated film to the NiTi. The results indicate that the optimum process conditions in cleaning, chemical etching, and electropolishing the NiTi, were the most important and determining parameters to be achieved. Thus, high quality PEEK coatings were obtained on NiTi wires, straight or curved (even with a U-shape) with a homogeneous microstructure along the wire length and a uniform thickness of 12 μm without any development of cracks or the presence of large voids. The biocompatibility of the PEEK coating film was checked in fibrobast cultured cells. The coating remains stable in biological environment with negligible Ni ion release, no cytotoxicity, and no delamination observed with time.

PEEK (polyether-ether-ketone)-coated nitinol wire: Film stability for biocompatibility applications

International Nuclear Information System (INIS)

Sheiko, Nataliia; Kékicheff, Patrick; Marie, Pascal; Schmutz, Marc; Jacomine, Leandro; Perrin-Schmitt, Fabienne

2016-01-01

Highlights: • A thin (12 μm) homogeneous PEEK film without any defects or voids is deposited on NiTi wires. • The coating remains stable in biological environment with negligible Ni ion release and no cytotoxicity. • Large pressure (>2 GPa) can only disrupt the coating film as shown by nanoscratch tests. • Coated spring wires sustain mechanical stress in continuous cycles of axial compression/stretching for >7 million cycles. - Abstract: High quality biocompatible poly-ether-ether-ketone (PEEK) coatings were produced on NiTi shape memory alloy wires using dipping deposition from colloidal aqueous PEEK dispersions after substrate surface treatment. The surface morphology and microstructure were investigated by Scanning Electron Microscopy at every step of the process from the as-received Nitinol substrate to the ultimate PEEK-coated NiTi wire. Nanoscratch tests were carried out to access the adhesive behavior of the polymer coated film to the NiTi. The results indicate that the optimum process conditions in cleaning, chemical etching, and electropolishing the NiTi, were the most important and determining parameters to be achieved. Thus, high quality PEEK coatings were obtained on NiTi wires, straight or curved (even with a U-shape) with a homogeneous microstructure along the wire length and a uniform thickness of 12 μm without any development of cracks or the presence of large voids. The biocompatibility of the PEEK coating film was checked in fibrobast cultured cells. The coating remains stable in biological environment with negligible Ni ion release, no cytotoxicity, and no delamination observed with time.

Electropolishing or chemical milling of beryllium to remove machining defects

International Nuclear Information System (INIS)

Helms, J.R.

1975-12-01

The techniques of electropolishing and chemical milling to remove machine damage from beryllium are compared. Both techniques are found to be effective; chemical milling is recommended because it is easier to use and control

Finite element simulations of internal stresses generated during the ferroelastic deformation of NiTi bodies

International Nuclear Information System (INIS)

Manach, P.Y.; Favier, D.; Rio, G.

1996-01-01

The aim of this paper is to analyse the generation of internal stresses during the predeformation of NiTi shape memory alloys in the martensitic state. This allows to determine the initial stress state in which the material will transform during the shape memory effect due to heating consecutively to this prestrain. In that way a three-dimensional finite element model of the deformation of shape memory alloys has been developed, the constitutive law being defined using an elastohysteresis tensor model. The influence of behavioural and geometrical factors are illustrated considering the numerical simulation of different cases of practical importance for industrial applications : the study of the bending behaviour of a NiTi cantilever beam as well as the study of the swelling of a pipe connection under both uniform and non uniform internal displacement fields. (orig.)

Surface Characteristics of Machined NiTi Shape Memory Alloy: The Effects of Cryogenic Cooling and Preheating Conditions

Science.gov (United States)

Kaynak, Y.; Huang, B.; Karaca, H. E.; Jawahir, I. S.

2017-07-01

This experimental study focuses on the phase state and phase transformation response of the surface and subsurface of machined NiTi alloys. X-ray diffraction (XRD) analysis and differential scanning calorimeter techniques were utilized to measure the phase state and the transformation response of machined specimens, respectively. Specimens were machined under dry machining at ambient temperature, preheated conditions, and cryogenic cooling conditions at various cutting speeds. The findings from this research demonstrate that cryogenic machining substantially alters austenite finish temperature of martensitic NiTi alloy. Austenite finish ( A f) temperature shows more than 25 percent increase resulting from cryogenic machining compared with austenite finish temperature of as-received NiTi. Dry and preheated conditions do not substantially alter austenite finish temperature. XRD analysis shows that distinctive transformation from martensite to austenite occurs during machining process in all three conditions. Complete transformation from martensite to austenite is observed in dry cutting at all selected cutting speeds.

Shaping Ability of Reciproc, WaveOne GOLD, and HyFlex EDM Single-file Systems in Simulated S-shaped Canals.

Science.gov (United States)

Özyürek, Taha; Yılmaz, Koray; Uslu, Gülşah

2017-05-01

The aim of the present study was to compare the shaping ability of Reciproc (RPC; VDW, Munich, Germany), HyFlex EDM (HEDM; Coltene/Whaledent AG, Altstätten, Switzerland), and WaveOne GOLD (WOG; Dentsply Maillefer, Ballaigues, Switzerland) nickel-titanium (NiTi) files made of different NiTi alloys in S-shaped simulated canals. Sixty S-shaped canals in resin blocks were prepared to an apical size of 0.25 mm using RPC R25, WOG Primary, and HEDM OneFile (n = 20 canal/per group) systems. Composite images were made from the superimposition of pre- and postinstrumentation images. The amount of resin removed by each system was measured using a digital template and image analysis software in 22 different points. Canal aberrations were also recorded. Data were statistically analyzed using the Kruskal-Wallis and post hoc Dunn tests at the 5% level. NiTi file fracture was not observed during shaping of the simulated canals although a danger zone formation in 1 sample and a ledge in 1 sample were observed in the RPC group. There was no statistically significant difference between the WOG and HEDM groups' apical, medial, and coronal regions (P > .05). However, it was determined that the RPC group removed a statistically significantly higher amount of resin from all the canal regions when compared with the WOG and HEDM groups (P < .05). Within the limitation of the present study, it was determined that all of the tested NiTi files caused various levels of resin removal. However, WOG and HEDM NiTi files were found to cause a lower level of resin removal than RPC NiTi files. Copyright © 2017 American Association of Endodontists. All rights reserved.

Microstructure and mechanical behavior of a shape memory Ni-Ti bi-layer thin film

Energy Technology Data Exchange (ETDEWEB)

Mohri, Maryam [School of Metallurgy and Materials Engineering, College of Engineering, University of Tehran, Tehran (Iran, Islamic Republic of); Karlsruhe Institute of Technology, Institute of Nanotechnology, 76021 Karlsruhe (Germany); Nili-Ahmadabadi, Mahmoud, E-mail: nili@ut.ac.ir [School of Metallurgy and Materials Engineering, College of Engineering, University of Tehran, Tehran (Iran, Islamic Republic of); Center of Excellence for High Performance Materials, University of Tehran, Tehran (Iran, Islamic Republic of); Ivanisenko, Julia [Karlsruhe Institute of Technology, Institute of Nanotechnology, 76021 Karlsruhe (Germany); Schwaiger, Ruth [Karlsruhe Institute of Technology, Institute for Applied Materials, 76021 Karlsruhe (Germany); Hahn, Horst; Chakravadhanula, Venkata Sai Kiran [Karlsruhe Institute of Technology, Institute of Nanotechnology, 76021 Karlsruhe (Germany)

2015-05-29

Two different single-layers and a bi-layer Ni-Ti thin films with chemical compositions of Ni{sub 45}Ti{sub 50}Cu{sub 5}, Ni{sub 50.8}Ti{sub 49.2} and Ni{sub 50.8}Ti{sub 49.2}/Ni{sub 45}Ti{sub 50}Cu{sub 5} (numbers indicate at.%) determined by energy dispersive X-ray spectroscopy were deposited on Si (111) substrates using DC magnetron sputtering. The structures, surface morphology and transformation temperatures of annealed thin films at 500 °C for 15 min and 1 h were studied using grazing incidence X-ray diffraction, transmission electron microscopy (TEM), atomic force microscopy and differential scanning calorimetry (DSC), respectively. Nanoindentation was used to characterize the mechanical properties. The DSC and X-ray diffraction results indicated the austenitic structure of the Ni{sub 50.8}Ti{sub 49.2} and martensitic structure of the Ni{sub 45}Ti{sub 50}Cu{sub 5} thin films while the bi-layer was composed of austenitic and martensitic thin films. TEM study revealed that copper encourages crystallization in the bi-layer such that crystal structure containing nano-precipitates in the Ni{sub 45}Ti{sub 50}Cu{sub 5} layer was detected after 15 min annealing while the Ni{sub 50.8}Ti{sub 49.2} layer crystallized after 60 min at 500 °C. Furthermore, after annealing at 500 °C for 15 min, a precipitate free zone and thin layer amorphous were observed closely to the interface in the top layer. The bi-layer was completely crystallized at 500 °C for 1 h and the orientation of the Ni-rich precipitates indicated a stress gradient in the bi-layer. The bi-layer thin film showed different transformation temperatures and mechanical behavior from the single-layers. The developed bi-layer has different phase transformation temperatures, the higher temperatures of shape memory effect and lower temperature of pseudo-elastic behavior compared to the single-layers. Also, the bi-layer thin film exhibited a combined pseudo-elastic behavior and shape memory effect with a reduced

A study on poly (N-vinyl-2-pyrrolidone covalently bonded NiTi surface for inhibiting protein adsorption

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Hongyan Yu

2016-12-01

Full Text Available Near equiatomic NiTi alloys have been extensively applied as biomaterials owing to its unique shape memory effect, superelasticity and biocompatibility. It has been demonstrated that surfaces capable of preventing plasma protein adsorption could reduce the reactivity of biomaterials with human blood. This motivated a lot of researches on the surface modification of NiTi alloy. In the present work, following heat and alkaline treatment and silanization by trichlorovinylsilane (TCVS, coating of poly (N-vinyl-2-pyrrolidone (PVP was produced on the NiTi alloy by gamma ray induced chemical bonding. The structures and properties of modified NiTi were characterized and in vitro biocompatibility of plasma protein adsorption was investigated. The results indicated that heat treatment at 823 K for 1 h could result in the formation of a protective TiO2 layer with “Ni-free” zone on NiTi surface. It was found that PVP was covalently bonded on NiTi surface to create a hydrophilic layer for inhibiting protein adsorption on the surface. The present work offers a green approach to introduce a bioorganic surface on metal and other polymeric or inorganic substrates by gamma irradiation.

Corrosion of NiTi wires with cracked oxide layer

Czech Academy of Sciences Publication Activity Database

Racek, Jan; Šittner, Petr; Heller, Luděk; Pilch, Jan; Petrenec, M.; Sedlák, Petr

2014-01-01

Roč. 23, č. 7 (2014), s. 2659-2668 ISSN 1059-9495. [International Conference on Shape Memory and Superelastic Technologies (SMST 2013). Praha, 21.05.2013-24.05.2013] R&D Projects: GA ČR GPP108/12/P111; GA ČR GAP107/12/0800; GA MŠk(CZ) 7E11058 EU Projects: European Commission(XE) 262806 - SmartNets Institutional support: RVO:68378271 ; RVO:61388998 Keywords : bending * electrochemical corrosion tests * martensitic transformation * shape memory alloy * superelastic NiTi wires Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 0.998, year: 2014

A comparison of the shaping ability of reciprocating NiTi instruments in simulated curved canals

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Young-Sil Yoo

2011-11-01

Full Text Available Objectives The study was to compare the shaping ability of Reciproc (VDW and WaveOne (Dentsply Maillefer instruments compared with ProTaper, Profile and hand instrument during the preparation of simulated root canals. Materials and Methods Five groups (n = 5 were established. Reciproc, WaveOne, ProTaper, Profile and K file (K-flexo file were used to prepare the resin simulated canals. A series of preoperative and postoperative images were taken by a microscope and superimposed in 2 different layers. The amount of resin removed from both the inner and the outer sides of the canal was measured to the level of 10 mm from the apical tip, with a 1 mm increment. Results The mean of resin removal from the inner canal wall was not different from the outer canal wall for Reciproc and WaveOne groups at apical third (1 - 3 mm level. There was no difference in the change of working length and maintenance of canal curvature. NiTi instruments are superior to stainless-steel K file in their shaping ability. Conclusions Within the limitation of this present study, Reciproc and WaveOne instruments maintained the original canal curvature in curved canals better than ProTaper and Profile, which tend to transport towards the outer canal wall of the curve in the apical part of the canal.

Comportamento termomecânico de compósitos ativos preparados com nanocompósitos epóxi/argila organofílica e fios de liga Ni-Ti com memória de forma Thermomechanical behavior of active composites prepared with epoxy/organoclay nanocomposites and Ni-Ti shape memory alloy wires

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Artur S. C. Leal

2012-01-01

Full Text Available Neste trabalho, nanocompósitos epóxi/argila organofílica foram selecionados como matriz por apresentarem valores de temperatura de transição vítrea (Tg e estabilidade térmica suficientemente alta para que fios de uma liga com memória de forma (LMF possam ser incorporados. Para tanto, quatro frações volumétricas de fios LMF de Ni-Ti (1,55, 2,56, 3,57 e 4,54% foram embebidas na matriz epoxídica diglicidil éter do bisfenol-A (DGEBA, reticulada com a amina aromática 4,4’-diamino difenil sulfona (DDS contendo 1 pcr da argila bentonita purificada organofiliada (APOC. A formação do nanocompósito foi confirmada por análise de difração de raio X, enquanto a transformação de fase dos fios de Ni-Ti foi determinada por análise dinâmico-mecânica (DMA. As amostras dos compósitos ativos preparados a partir da matriz de nanocompósito e fios de Ni-Ti foram caracterizadas principalmente por DMA. De acordo com os resultados obtidos foi constatada uma recuperação do módulo de armazenamento do compósito ativo durante o aquecimento na faixa de transformação de fase dos fios de Ni-Ti quando a fração volumétrica foi mantida em torno de 3,5%.In this work, epoxy/organoclay nanocomposites were selected as matrix for presenting high enough glass transition temperature (Tg and thermal stability values in order to be incorporated in shape memory alloys (SMA. Four volume fractions of SMA wires containing Ni-Ti (1.55, 2.56, 3.57 and 4.54% were embedded in diglycidyl ether of bisphenol A (DGEBA, cured with the aromatic amine 4,4’-diamino diphenyl sulfone (DDS and containing 1 phr of purified organobentonite (APOC. The formation of nanocomposite was confirmed by X ray diffraction analysis, while the phase transformation of Ni-Ti wires was determined by dynamic mechanical analysis (DMA. Samples of the active composites prepared from nanocomposite matrix and Ni-Ti wires were mainly characterized by DMA. A recovery of the storage modulus of

Grain Nucleation and Growth in Deformed NiTi Shape Memory Alloys: An In Situ TEM Study

Science.gov (United States)

Burow, J.; Frenzel, J.; Somsen, C.; Prokofiev, E.; Valiev, R.; Eggeler, G.

2017-12-01

The present study investigates the evolution of nanocrystalline (NC) and ultrafine-grained (UFG) microstructures in plastically deformed NiTi. Two deformed NiTi alloys were subjected to in situ annealing in a transmission electron microscope (TEM) at 400 and 550 °C: an amorphous material state produced by high-pressure torsion (HPT) and a mostly martensitic partly amorphous alloy produced by wire drawing. In situ annealing experiments were performed to characterize the microstructural evolution from the initial nonequilibrium states toward energetically more favorable microstructures. In general, the formation and evolution of nanocrystalline microstructures are governed by the nucleation of new grains and their subsequent growth. Austenite nuclei which form in HPT and wire-drawn microstructures have sizes close to 10 nm. Grain coarsening occurs in a sporadic, nonuniform manner and depends on the physical and chemical features of the local environment. The mobility of grain boundaries in NiTi is governed by the local interaction of each grain with its microstructural environment. Nanograin growth in thin TEM foils seems to follow similar kinetic laws to those in bulk microstructures. The present study demonstrates the strength of in situ TEM analysis and also highlights aspects which need to be considered when interpreting the results.

Corrosion behaviour of electropolished AISI 316L austenitic biomaterial in physiological solution

Science.gov (United States)

Zatkalíková, V.; Markovičová, L.; Škorvanová, M.

2017-11-01

Due to suitable mechanical properties, satisfactory corrosion resistance and relatively low cost, austenitic stainless steels are important biomaterials for manufacture of implants and various medical instruments and devices. Their corrosion properties and biocompatibility are significantly affected by protective passive surface film quality, which depends on used mechanical and chemical surface treatment. This article deals with corrosion resistance of AISI 316L stainless steel, which is the most widely used Cr-Ni-Mo austenitic biomaterial. Corrosion behaviour of five various surfaces (original, electropolished, three surfaces with combined treatment finished by electropolishing) is evaluated on the bases of cyclic potentiodynamic polarization tests performed in physiological solution at the temperature of 37± 0.5 °C.

Investigation of the Self-Healing Behavior of Sn-Bi Metal Matrix Composite Reinforced with NiTi Shape Memory Alloy Strips Under Flexural Loading

Science.gov (United States)

Poormir, Mohammad Amin; Khalili, Seyed Mohammad Reza; Eslami-Farsani, Reza

2018-06-01

Utilizing intelligent materials such as shape memory alloys as reinforcement in metal matrix composites is a novel method to mimic self-healing behavior. In this study, the bending behavior of a self-healing metal matrix composite made from Sn-13 wt.% Bi alloy as matrix and NiTi shape memory alloy (SMA) strips as reinforcement is investigated. Specimens were fabricated in different reinforcement vol.% (0.78, 1.55, 2.33) and in various pre-strains (0, 2, 6%) and were healed at three healing temperatures (170°C, 180°C, 190°C). Results showed that shape recovery was accomplished in all the specimens, but not all of them were able to withstand second loading after healing. Only specimens with 2.33 vol.% of SMA strips, 1.55 vol.% of SMA, and 6% pre-strain could endure bending force after healing, and they gained 35.31-51.83% of bending force self-healing efficiency.

Smooth Nb surfaces fabricated by buffered electropolishing

International Nuclear Information System (INIS)

Wu, Andy T.; Mammosser, John; Phillips, Larry; Delayen, Jean; Reece, Charles; Wilkerson, Amy; Smith, David; Ike, Robert

2007-01-01

It was demonstrated that smooth Nb surfaces could be obtained through buffered electropolishing (BEP) employing an electrolyte consisting of lactic, sulfuric, and hydrofluoric acids. Parameters that control the polishing process were optimized to achieve a smooth surface finish. The polishing rate of BEP was determined to be 0.646 μm/min which was much higher than 0.381 μm/min achieved by the conventional electropolishing (EP) process widely used in the superconducting radio frequency (SRF) community. Root mean square measurements using a 3D profilometer revealed that Nb surfaces treated by BEP were an order of magnitude smoother than those treated by the optimized EP process. The chemical composition of the Nb surfaces after BEP was analyzed by static and dynamic secondary ion mass spectrometry (SIMS) systems. SIMS results implied that the surface oxide structure of Nb might be more complicated than what usually believed and could be inhomogeneous. Preliminary results of BEP on Nb SRF single cell cavities and half-cells were reported. It was shown that smooth and bright surfaces could be obtained in 1800 s when the electric field inside a SRF cavity was uniform during a BEP process. This study showed that BEP is a promising technique for surface treatment on Nb SRF cavities to be used in particle accelerators

Work production using the two-way shape memory effect in NiTi and a Ni-rich NiTiHf high-temperature shape memory alloy

International Nuclear Information System (INIS)

Atli, K C; Karaman, I; Noebe, R D; Bigelow, G; Gaydosh, D

2015-01-01

The work output capacity of the two-way shape memory effect (TWSME) in a Ni 50.3 Ti 29.7 Hf 20 (at%) high-temperature shape memory alloy (HTSMA) was investigated and compared to that of binary Ni 49.9 Ti 50.1 (at%). TWSME was induced through a training procedure of 100 thermomechanical cycles under different tensile stresses. It was observed that TWSME in as-extruded and trained Ni 50.3 Ti 29.7 Hf 20 could produce 0.7% strain against a compressive stress of 100 MPa, corresponding to a maximum work output of 0.08 J g −1 , compared to a maximum value of 0.06 J g −1 for binary NiTi. A peak aging heat treatment of 3 h at 550 °C, which previously has been shown to result in near-perfect functional stability in Ni 50.3 Ti 29.7 Hf 20 during isobaric thermal cycling, did not improve the TWSME and actually resulted in a decrease in the magnitude and stability of the TWSME and its work output capacity. Nevertheless, the magnitude of TWSM behavior of Ni 50.3 Ti 29.7 Hf 20 , in the absence of an aging heat treatment, renders it an attractive candidate for high-temperature TWSM actuation. (paper)

Effect of cooling rate on the phase transformation behavior and mechanical properties of Ni-rich NiTi shape memory alloy

Energy Technology Data Exchange (ETDEWEB)

Motemani, Y. [School of Mechanical and Aerospace Engineering, Nanyang Technological University, Singapore 639798 (Singapore); Nili-Ahmadabadi, M. [School of Metallurgy and Materials Engineering, Faculty of Engineering, University of Tehran, 14395-731 Tehran (Iran, Islamic Republic of); Tan, M.J. [School of Mechanical and Aerospace Engineering, Nanyang Technological University, Singapore 639798 (Singapore)], E-mail: mmjtan@ntu.edu.sg; Bornapour, M.; Rayagan, Sh. [School of Metallurgy and Materials Engineering, Faculty of Engineering, University of Tehran, 14395-731 Tehran (Iran, Islamic Republic of)

2009-02-05

TiNi alloy is a well-known shape memory alloy and has been widely used for bio-medical, mechanical and electrical applications. In this study, a Ni-rich NiTi alloy was prepared by vacuum arc melting in a water-cooled copper crucible. Three samples of this alloy were heated to 1000 deg. C and cooled in three media: furnace, water, and dry-ice bath. Differential scanning calorimetry (DSC), X-ray diffraction (XRD), hardness measurement and tensile test were carried out to investigate the effect of cooling rate on transformation temperature and mechanical properties. The results show that Ni{sub 3}Ti intermetallic compounds have a great influence on martensitic phase transformation temperature. These tests clearly showed the correlation between cooling rate and properties of the alloy.

Influence of SLM on compressive response of NiTi scaffolds

Science.gov (United States)

Shayesteh Moghaddam, Narges; Saedi, Soheil; Amerinatanzi, Amirhesam; Jahadakbar, Ahmadreza; Saghaian, Ehsan; Karaca, Haluk; Elahinia, Mohammad

2018-03-01

Porous Nickel-Titanium shape memory alloys (NiTi-SMAs) have attracted much attention in biomedical applications due to their high range of pure elastic deformability (i.e., superelasticity) as well as their bone-level modulus of elasticity (E≈12-20 GPa). In recent years, Selective Laser Melting (SLM) has been used to produce complex NiTi components. The focus of this study is to investigate the superelasticity and compressive properties of SLM NiTi-SMAs. To this aim, several NiTi components with different level of porosities (32- 58%) were fabricated from Ni50.8Ti (at. %) powder via SLM PXM by Phenix/3D Systems, using optimum processing parameter (Laser power-P=250 W, scanning speed-v=1250mm/s, hatch spacing-h=120μm, layer thickness-t=30μm). To tailor the superelasticity behavior at body temperature, the samples were solution annealed and aged for 15 min at 350°C. Then, transformation temperatures (TTs), superelastic response, and cyclic behavior of NiTi samples were studied. As the porosity was increased, the irrecoverable strain was observed to be higher in the samples. At the first superelastic cycle, 3.5%, 3.5%, and 2.7% strain recovery were observed for the porosity levels of 32%, 45%, and 58%, respectively. However, after 10 cycles, the superelastic response of the samples was stabilized and full strain recovery was observed. Finally, the modulus of elasticity of dense SLM NiTi was decreased from 47 GPa to 9 GPa in the first cycle by adding 58% porosity.

Powder metallurgy of NiTi-alloys with defined shape memory properties

International Nuclear Information System (INIS)

Bram, M.; Ahmad-Khanlou, A.; Buchkremer, H.P.; Stoever, D.

2001-01-01

The aim of the present work is the development of fabrication processes for NiTi shape memory alloys by powder metallurgical means. The starting materials used were prealloyed powders as well as elemental powder mixtures. Three techniques seem to be very promising for shaping of NiTi compacts. Hot Isostatic Pressing (HIP) has been examined for the production of dense semi-finished components. A promising technique for the production of dense and porous coatings with an increased wear resistance is Vacuum Plasma Spraying (VPS). Metal Injection Moulding (MIM) is especially suitable for near-net shape fabrication of small components with a complex geometry considering that large numbers of units have to be produced for compensating high tool and process costs. Subsequently, thermal treatments are required to establish defined shape memory properties. The reproducibility and stability of the shape memory effect are main aspects thinking about a production of NiTi components in an industrial scale. (author)

On the multiplication of dislocations during martensitic transformations in NiTi shape memory alloys

Czech Academy of Sciences Publication Activity Database

Simon, T.; Kröger, A.; Somsen, Ch.; Dlouhý, Antonín; Eggeler, G.

2010-01-01

Roč. 58, č. 5 (2010), s. 1850-1860 ISSN 1359-6454 R&D Projects: GA ČR GA106/09/1913 Institutional research plan: CEZ:AV0Z20410507 Keywords : NiTi * Martensitic transformations * Dislocation multiplication mechanism * Martensite variants * Dislocations Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 3.781, year: 2010

Behaviour of human endothelial cells on surface modified NiTi alloy.

Science.gov (United States)

Plant, Stuart D; Grant, David M; Leach, Lopa

2005-09-01

Intravascular stents are being designed which utilise the shape memory properties of NiTi alloy. Despite the clinical advantages afforded by these stents their application has been limited by concerns about the large nickel ion content of the alloy. In this study, the surface chemistry of NiTi alloy was modified by mechanical polishing and oxidising heat treatments and subsequently characterised using X-ray photon spectroscopy (XPS). The effect of these surfaces on monolayer formation and barrier integrity of human umbilical vein endothelial cells (HUVEC) was then assessed by confocal imaging of the adherens junctional molecule VE-cadherin, perijunctional actin and permeability to 42kDa dextrans. Dichlorofluoroscein assays were used to measure oxidative stress in the cells. XPS analysis of NiTi revealed its surface to be dominated by TiO(2). However, where oxidation had occurred after mechanical polishing or post polishing heat treatments at 300 and 400 degrees C in air, a significant amount of metallic nickel or nickel oxide species (10.5 and 18.5 at%) remained on the surface. Exposure of HUVECs to these surfaces resulted in increased oxidative stress within the cells, loss of VE-cadherin and F-actin and significantly increased paracellular permeability. These pathological phenomena were not found in cells grown on NiTi which had undergone heat treatment at 600 degrees C. At this temperature thickening of the TiO(2) layer had occurred due to diffusion of titanium ions from the bulk of the alloy, displacing nickel ions to sub-surface areas. This resulted in a significant reduction in nickel ions detectable on the sample surface (4.8 at%). This study proposes that the integrity of human endothelial monolayers on NiTi is dependent upon the surface chemistry of the alloy and that this can be manipulated, using simple oxidising heat treatments.

Mechanical Degradation of Porous NiTi Alloys Under Static and Cyclic Loading

Science.gov (United States)

Hosseini, Seyyed Alireza

2017-12-01

Pore characteristics and morphology have significant effect on mechanical behavior of porous NiTi specimens. In this research, porous NiTi with different pore sizes, shapes and morphology were produced by powder metallurgy methods using space-holder materials. The effect of the pore characteristics on the mechanical properties was investigated by static and cyclic compression tests at body temperature. The results show that specimens with low porosity and isolated pores exhibit more mechanical strength and recoverable strain. The specimen with 36% porosity produced without space holder could preserve its properties up to 10% strain and its strain recovery was complete after cyclic compression tests. On the other hand, the specimens produced by a urea space holder with more than 60% interconnected porosity show rapid degradation of their scaffolds. The highly porous specimens degraded even below 5% strain due to crack formation and propagation in the thin pore walls. For highly porous specimens produced by a NaCl space holder, the pores are partially interconnected with a cubic shape; nevertheless, their mechanical behavior is close to low-porosity specimens.

New developments in Ni/Ti multilayers

Energy Technology Data Exchange (ETDEWEB)

Anderson, I; Hoghoj, P [Institut Max von Laue - Paul Langevin (ILL), 38 - Grenoble (France)

1997-04-01

It is now 20 years since super-mirrors were first used as a neutron optical element. Since then the field of multilayer neutron-optics has matured with multilayers finding their way to application in many neutron scattering instruments. However, there is still room for progress in terms of multilayer quality, performance and application. Along with work on multilayers for neutron polarisation Ni/Ti super-mirrors have been optimised. The state-of-the-art Ni/Ti super-mirror performance and the results obtained in two neutron-optics applications of Ni/Ti multilayers are presented. (author).

The Corrosion Resistance of Composite Arch Wire Laser-Welded By NiTi Shape Memory Alloy and Stainless Steel Wires with Cu Interlayer in Artificial Saliva with Protein

Science.gov (United States)

Zhang, Chao; Sun, Xinhua; Hou, Xu; Li, Hongmei; Sun, Daqian

2013-01-01

In this paper, the corrosion resistance of laser-welded composite arch wire (CoAW) with Cu interlayer between NiTi shape memory alloy and stainless steel wire in artificial saliva with different concentrations of protein was studied. It was found that protein addition had a significant influence on the corrosion behavior of CoAW. Low concentration of protein caused the corrosion resistance of CoAW decrease in electrochemical corrosion and immersion corrosion tests. High concentration of protein could reduce this effect. PMID:23801895

Advance in Vertical Buffered Electropolishing on Niobium for Particle Accelerators

International Nuclear Information System (INIS)

Wu, A.T.; Jin, S.; Mammosser, J.D.; Reece, C.E.; Rimmer, R.A.; Lin, L.; Lu, X.Y.; Zhao, K.

2011-01-01

Niobium (Nb) is the most popular material that has been employed for making superconducting radio frequency (SRF) cavities to be used in various particle accelerators over the last couple of decades. One of the most important steps in fabricating Nb SRF cavities is the final chemical removal of 150 μm of Nb from the inner surfaces of the SRF cavities. This is usually done by either buffered chemical polishing (BCP) or electropolishing (EP). Recently a new Nb surface treatment technique called buffered electropolishing (BEP) has been developed at Jefferson Lab. It has been demonstrated that BEP can produce the smoothest surface finish on Nb ever reported in the literature while realizing a Nb removal rate as high as 10 μm/min that is more than 25 and 5 times quicker than those of EP and BCP(112) respectively. In this contribution, recent advance in optimizing and understanding BEP treatment technique is reviewed. Latest results from RF measurements on BEP treated Nb single cell cavities by our unique vertical polishing system will be reported.

Spallation in NiTi under One-Dimensional Shock Loading

International Nuclear Information System (INIS)

Wallwork, A.; Workman, A.; Meziere, Y. J. E.; Millett, J. C. F.; Bourne, N. K.

2006-01-01

The dynamic response of the shape memory alloy NiTi has been of interest to a number of investigators because it displays a shape memory effect. The dynamic tensile (spall) strength of this material is measured under one-dimensional shock loading. The loading stress pulse length and impact stress were varied to a peak stress of 15 GPa. The pull back stress (σpbs) was found to increase with the applied pulse length. This suggests that the dynamic tensile strength is dependent upon the generation of a deformation micro structure that evolves behind the shock front. In contrast, increasing stress levels result in a near-constant pull back stress, although at the lowest applied stress, spallation did not occur

Thin NiTi Films Deposited on Graphene Substrates

Science.gov (United States)

Hahn, S.; Schulze, A.; Böhme, M.; Hahn, T.; Wagner, M. F.-X.

2017-03-01

We present experimental results on the deposition of Nickel Titanium (NiTi) films on graphene substrates using a PVD magnetron sputter process. Characterization of the 2-4 micron thick NiTi films by electron microscopy, electron backscatter diffraction, and transmission electron microscopy shows that grain size and orientation of the thin NiTi films strongly depend on the type of combination of graphene and copper layers below. Our experimental findings are supported by density functional theory calculations: a theoretical estimation of the binding energies of different NiTi-graphene interfaces is in line with the experimentally determined microstructural features of the functional NiTi top layer.

Effects of electropolishing surface treatment on the cyclic fatigue resistance of BioRace nickel-titanium rotary instruments.

Science.gov (United States)

Lopes, Hélio P; Elias, Carlos N; Vieira, Victor T L; Moreira, Edson J L; Marques, Raquel V L; de Oliveira, Julio C Machado; Debelian, Gilberto; Siqueira, José F

2010-10-01

This study evaluated the influence of electropolishing surface treatment on the number of cycles to fracture of BioRace rotary nickel-titanium endodontic instruments. BioRace size BR5C instruments with or without electropolishing surface treatment were used in an artificial curved canal under rotational speed of 300 rpm until fracture. Fractured surfaces and the helical shafts of fractured instruments were analyzed by scanning electron microscopy (SEM). Polished instruments displayed a significantly higher number of cycles to fracture when compared with nonpolished instruments (P ductile morphologic characteristics. Evaluation of the separated fragments after cyclic fatigue testing showed the presence of microcracks near the fracture surface. Polished instruments exhibited fine cracks that assumed an irregular path (zigzag crack pattern), whereas nonpolished instruments showed cracks running along the machining grooves. Electropolishing surface treatment of BioRace endodontic instruments significantly increased the cyclic fatigue resistance. Copyright © 2010 American Association of Endodontists. Published by Elsevier Inc. All rights reserved.

Improvement on corrosion resistance of NiTi orthopedic materials by carbon plasma immersion ion implantation

International Nuclear Information System (INIS)

Poon, Ray W.Y.; Ho, Joan P.Y.; Luk, Camille M.Y.; Liu Xuanyong; Chung, Jonathan C.Y.; Chu, Paul K.; Yeung, Kelvin W.K.; Lu, William W.; Cheung, Kenneth M.C.

2006-01-01

Nickel-titanium shape memory alloys (NiTi) have potential applications as orthopedic implants because of their unique super-elastic properties and shape memory effects. However, the problem of out-diffusion of harmful Ni ions from the alloys during prolonged use inside a human body must be overcome before they can be widely used in orthopedic implants. In this work, we enhance the corrosion resistance of NiTi using carbon plasma immersion ion implantation and deposition (PIII and D). Our corrosion and simulated body fluid tests indicate that either an ion-mixed amorphous carbon coating fabricated by PIII and D or direct carbon PIII can drastically improve the corrosion resistance and block the out-diffusion of Ni from the materials. Results of atomic force microscopy (AFM) indicate that both C 2 H 2 -PIII and D and C 2 H 2 -PIII do not roughen the original flat surface to an extent that can lead to degradation in corrosion resistance

Influence of temperature of the short-period heat treatment on mechanical properties of the NiTi alloy

Directory of Open Access Journals (Sweden)

Jaroslav Čapek

2014-01-01

Full Text Available The equiatomic alloy of nickel and titanium, known as nitinol, possesses unique properties such as superelasticity, pseudoplasticity, shape memory, while maintaining good corrosion resistance and sufficient biocompatibility. Therefore it is used for production of various devices including surgery implants. Heat treatment of nickel-rich NiTi alloys can result in precipitation of nickel-rich phases, which strongly influence tensile and fatigue behaviour of the material.In this work we have studied influence of short-period heat treatment on tensile behaviour and fatigue life of the NiTi (50.9 at. % Ni wire intended for fabrication of surgery stents.

In situ neutron diffraction studies of martensitic transformations in NiTi polycrystals under tension and compression stress

Czech Academy of Sciences Publication Activity Database

Šittner, Petr; Lukáš, Petr; Novák, Václav; Daymond, M. R.; Swallowe, G. M.

2004-01-01

Roč. 378, - (2004), s. 97-104 ISSN 0921-5093 Institutional research plan: CEZ:AV0Z1010914 Keywords : martensitic transformation * shape memory alloy * neutron diffraction * NiTi Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.445, year: 2004

Biased Target Ion Beam Deposition and Nanoskiving for Fabricating NiTi Alloy Nanowires

Science.gov (United States)

Hou, Huilong; Horn, Mark W.; Hamilton, Reginald F.

2016-12-01

Nanoskiving is a novel nanofabrication technique to produce shape memory alloy nanowires. Our previous work was the first to successfully fabricate NiTi alloy nanowires using the top-down approach, which leverages thin film technology and ultramicrotomy for ultra-thin sectioning. For this work, we utilized biased target ion beam deposition technology to fabricate nanoscale (i.e., sub-micrometer) NiTi alloy thin films. In contrast to our previous work, rapid thermal annealing was employed for heat treatment, and the B2 austenite to R-phase martensitic transformation was confirmed using stress-temperature and diffraction measurements. The ultramicrotome was programmable and facilitated sectioning the films to produce nanowires with thickness-to-width ratios ranging from 4:1 to 16:1. Energy dispersive X-ray spectroscopy analysis confirmed the elemental Ni and Ti make-up of the wires. The findings exposed the nanowires exhibited a natural ribbon-like curvature, which depended on the thickness-to-width ratio. The results demonstrate nanoskiving is a potential nanofabrication technique for producing NiTi alloy nanowires that are continuous with an unprecedented length on the order of hundreds of micrometers.

Influence of the thermal treatment on the stability of partially constrained recovery of NiTi actuator wire

International Nuclear Information System (INIS)

Mertmann, M.; Bracke, A.; Hornbogen, E.

1995-01-01

NiTi shape memory wire may be used for actuation purposes in flexible robotic grippers, which have to be able to handle objects of different size, shape or weight. Therefore it is advantageous to develop an electrically driven shape memory actuator, which may perform any combination of shape change and exerted force within the following limiting boundaries: - free recovery: gripping of a very small and lightweight object, - constrained recovery: gripping of an object with maximum size and weight. Several NiTi actuator wires are fabricated and annealed between 400 and 600 C after cold working in the martensitic state. After prestraining each wire is embedded in a silicone matrix material. The polymer works as a bias spring and is able to store elastic deformation energy. This paper investigates the influence of thermal treatment on the stability of the exerted force between the two boundaries of completely free and constrained recovery, the ''partially constrained recovery''. The stability of recovery strain and stress is measured in a test assembly, in which different modes of partially constrained recovery are simulated. The work is supplemented by dilatometric measurements carried out with each actuator wire before and after the test procedure. (orig.)

Surface chemistry and cytotoxicity of reactively sputtered tantalum oxide films on NiTi plates

Energy Technology Data Exchange (ETDEWEB)

McNamara, K. [Materials and Surface Science Institute, University of Limerick, Limerick (Ireland); Department of Physics & Energy, University of Limerick, Limerick (Ireland); Kolaj-Robin, O.; Belochapkine, S.; Laffir, F. [Materials and Surface Science Institute, University of Limerick, Limerick (Ireland); Gandhi, A.A. [Materials and Surface Science Institute, University of Limerick, Limerick (Ireland); Department of Physics & Energy, University of Limerick, Limerick (Ireland); Tofail, S.A.M., E-mail: tofail.syed@ul.ie [Materials and Surface Science Institute, University of Limerick, Limerick (Ireland); Department of Physics & Energy, University of Limerick, Limerick (Ireland)

2015-08-31

NiTi, an equiatomic alloy containing nickel and titanium, exhibits unique properties such as shape memory effect and superelasticity. NiTi also forms a spontaneous protective titanium dioxide (TiO{sub 2}) layer that allows its use in biomedical applications. Despite the widely perceived biocompatibility there remain some concerns about the sustainability of the alloy's biocompatibility due to the defects in the TiO{sub 2} protective layer and the presence of high amount of sub-surface Ni, which can give allergic reactions. Many surface treatments have been investigated to try to improve both the corrosion resistance and biocompatibility of this layer. For such purposes, we have sputter deposited tantalum (Ta) oxide thin films onto the surface of the NiTi alloy. Despite being one of the promising metals for biomedical applications, Ta, and its various oxides and their interactions with cells have received relatively less attention. The oxidation chemistry, crystal structure, morphology and biocompatibility of these films have been investigated. In general, reactive sputtering especially in the presence of a low oxygen mixture yields a thicker film with better control of the film quality. The sputtering power influenced the surface oxidation states of Ta. Both microscopic and quantitative cytotoxicity measurements show that Ta films on NiTi are biocompatible with little to no variation in cytotoxic response when the surface oxidation state of Ta changes. - Highlights: • Reactive sputtering in low oxygen mixture yields thicker better quality films. • Sputtering power influenced surface oxidation states of Ta. • Cytotoxicity measurements show Ta films on NiTi are biocompatible. • Little to no variation in cytotoxic response when oxidation state changes.

The High Performance Shape Memory Effect (HP-SME in Ni Rich NiTi Wires: In Situ X-Ray Diffraction on Thermal Cycling

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Coduri Mauro

2015-01-01

Full Text Available A novel approach for using Shape Memory Alloys (SMA was recently proposed and named highperformance shape memory effect (HP-SME. The HP-SME exploits the thermal cycling of stress-induced martensite for producing extremely high mechanical work with a very stable functional fatigue behaviour in Ni rich NiTi alloy. The latter was found to differ significantly from the functional fatigue behaviour observed for conventional SMA. This study was undertaken in order to elucidate the microstructural modifications at the basis of this particular feature. To this purpose, the functional fatigue was coupled to in situ Synchrotron Radiation X-Ray Diffraction, by recording patterns on wires thermally cycled by Joule effect under a constant applied stress (800 MPa. The accurate analysis the line profile XRD data suggests the accumulation of defects upon functional cycling, while the fibre texture was not observed to change. The functional fatigue exhibits a very similar behaviour as the line broadening of XRD peaks, thus suggesting the accumulation of dislocations as the origin of the mechanism of the permanent deformation.

Evaluation of the diffusion coefficient of fluorine during the electropolishing of niobium

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Hui Tian

2010-08-01

Full Text Available Future accelerators require unprecedented cavity performance, which is strongly influenced by interior surface nanosmoothness. Electropolishing (EP is the technique of choice being developed for high-field superconducting radio frequency (SRF cavities. Previous study has shown that the mechanism of Nb electropolishing proceeds by formation and dissolution of a compact salt film under fluorine diffusion-limited mass transport control. We pursue an improved understanding of the microscopic conditions required for optimum surface finishing. The viscosity of the standard electrolyte has been measured using a commercial viscometer, and the diffusion coefficient of fluorine was derived at a variety of temperatures from 0 to 50°C using a Nb rotating disk electrode. In addition, data indicate that electrode kinetics becomes competitive with the mass transfer current limitation and increases dramatically with temperature. These findings are expected to guide the optimization of EP process parameters for achieving controlled, reproducible, and uniform nanosmooth surface finishing of SRF cavities.

Engineering solutions for the electro-polishing of multi-cell superconducting accelerators structures

International Nuclear Information System (INIS)

Schulz, E.; Bandelmann, R.; Escherich, K.; Keese, D.; Leenen, M.; Lilje, L.; Matheisen, A.; Morales, H.; Schmueser, P.; Seidel, M.; Steinhau-Kuehl, N.; Tiessen, J.

2003-01-01

Due to surface treatment with electro-polishing superconducting niobium resonators can potentially reach accelerating gradients well beyond 35 MV/m at a frequency of 1.3 GHz. The anticipated gradient for the 500GeV version of the TESLA collider is 23.4 MV/m. In view of the extendibility of the collider towards higher energies this technology is therefore of great importance for the TESLA project. In this paper we discuss the engineering aspects of the planned electro-polishing facility at DESY. The facility will allow for the treatment of single cell cavities as well as the standard TESLA 9-cell structure, and also a so called superstructure that consists of 2 x 9 cells. The issues described cover the acid circulation including cooling requirements, the required current densities resulting in the specifications of the electrical circuit, removal of oxyhydrogen gas, rotating feed-through and the overall mechanical layout. Furthermore we report on recent tests of critical components. (author)

Electropolishing of Re-melted SLM Stainless Steel 316L Parts Using Deep Eutectic Solvents: 3 × 3 Full Factorial Design

Science.gov (United States)

Alrbaey, K.; Wimpenny, D. I.; Al-Barzinjy, A. A.; Moroz, A.

2016-07-01

This three-level three-factor full factorial study describes the effects of electropolishing using deep eutectic solvents on the surface roughness of re-melted 316L stainless steel samples produced by the selective laser melting (SLM) powder bed fusion additive manufacturing method. An improvement in the surface finish of re-melted stainless steel 316L parts was achieved by optimizing the processing parameters for a relatively environmentally friendly (`green') electropolishing process using a Choline Chloride ionic electrolyte. The results show that further improvement of the response value-average surface roughness ( Ra) can be obtained by electropolishing after re-melting to yield a 75% improvement compared to the as-built Ra. The best Ra value was less than 0.5 μm, obtained with a potential of 4 V, maintained for 30 min at 40 °C. Electropolishing has been shown to be effective at removing the residual oxide film formed during the re-melting process. The material dissolution during the process is not homogenous and is directed preferentially toward the iron and nickel, leaving the surface rich in chromium with potentially enhanced properties. The re-melted and polished surface of the samples gave an approximately 20% improvement in fatigue life at low stresses (approximately 570 MPa). The results of the study demonstrate that a combination of re-melting and electropolishing provides a flexible method for surface texture improvement which is capable of delivering a significant improvement in surface finish while holding the dimensional accuracy of parts within an acceptable range.

Effect of particle size of titanium and nickel on the synthesis of NiTi by TE-SHS

Czech Academy of Sciences Publication Activity Database

Novák, P.; Veselý, T.; Marek, I.; Dvořák, P.; Vojtěch, V.; Salvetr, P.; Karlík, M.; Haušild, P.; Kopeček, Jaromír

2016-01-01

Roč. 47, č. 2 (2016), s. 932-938 ISSN 1073-5615 R&D Projects: GA ČR(CZ) GA14-03044S Institutional support: RVO:68378271 Keywords : shape memory alloys * behavior * NiTi Subject RIV: JG - Metallurgy Impact factor: 1.642, year: 2016

Electropolishing of Stainless Steel Implants for Stable Functional Osteosynthesis

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Omel’chuk, A.О.

2016-01-01

Full Text Available A new method for the electropolishing stainless steel for stable functional osteosynthesis has been developed. The polishing of implants was carried out in solutions, based on the ternary system H2SO4—H3PO4—H2O with stepwise decreasing the current density and increasing the orthophosphoric acid concentration. The optimal polishing conditions (current density, solution composition, temperature and duration have been determined. The developed method improves the quality and mechanical properties of the surface.

A comparison of EDS microanalysis in FIB-prepared and electropolished TEM thin foils

International Nuclear Information System (INIS)

Hutchinson, C.R.; Hackenberg, R.E.; Shiflet, G.J.

2003-01-01

This paper reports the results of a fine-probe EDS microanalytical study of cellular precipitation in a Cu-Ti binary alloy. Compositional profiles across the solute depleted Cu-rich FCC lamellae and the Cu 4 Ti lamellae within isothermally formed cellular colonies were measured in a FEG-TEM from thin-foil specimens prepared by conventional electropolishing and by a technique using a Ga + focused ion-beam (FIB). The Cliff-Lorimer ratio method, with an absorption correction, was employed to quantify the compositions. Two FIB samples were prepared with different orientations of the lamellae with respect to the ion-milling direction. The compositional profiles across the Cu-rich FCC lamellae and the Cu 4 Ti compound lamellae in both the FIB-prepared samples and the electropolished sample were, within experimental error, numerically equivalent. The composition of the Cu 4 Ti compound phase lamellae was very close to the ideal stoichiometric composition of 20 at% Ti. It is concluded that for this system, and for the specimen preparation procedures used in this study, the Ga + ion-milling process has had no detectable effect on the chemistry changes across the interlamellar interface at the scale studied. These results indicate that the possible sources of chemical artifacts which include redeposition, preferential sputtering and ion-induced atomic migration can be minimized if several precautions are taken during milling in the FIB. Consistent with previous investigators, it was also found that the ion-milling process does introduce significant structural artifacts (e.g., dislocations) into the softer FCC Cu-rich phase compared with a specimen produced by conventional electropolishing

Characterization and tribocorrosion behavior of sputtered NiTi coatings

Energy Technology Data Exchange (ETDEWEB)

Jin, XiaoMin; Gao, Lizhen [Taiyuan University of Technology (China). College of Environmental Science and Engineering; Wang, Hefeng [Taiyuan University of Technology (China). College of Mechanics; Liu, Erqiang [Taiyuan University of Technology (China). Inst. of Applied Mechanics and Biomedical Engineering

2016-02-15

In this study, NiTi coatings were deposited onto AISI 316L stainless steel substrates by closed field unbalanced magnetron sputtering. The microstructure and properties of the coatings were characterized by means of X-ray diffraction, scanning electron microscopy, and nano-indentation. The tribocorrosion resistance and corrosion behavior of the stainless steel substrates and NiTi coatings were investigated in Hanks' solution. The experimental results indicated the NiTi coatings show higher corrosion polarization resistance and a more stable corrosion potential in the Hanks' solution than the uncoated stainless steel substrate. The NiTi coatings also exhibited excellent wear resistance and chemical stability in sliding tests with an Si{sub 3}N{sub 4} ball in the Hanks' solution. The tested samples showed different wear mechanisms in the sliding tests. Compared to the SS substrates, the NiTi coatings were more compatible with the Si{sub 3}N{sub 4} ball.

Self-centering and damping capabilities of a tension-compression device equipped with superelastic NiTi wires

International Nuclear Information System (INIS)

Soul, H; Yawny, A

2015-01-01

The hysteretic damping capacity and high recoverable strains characterizing the superelastic response of shape memory alloys (SMA) make these materials attractive for protection systems of structures subjected to dynamic loads. A successful implementation however is conditioned by functional fatigue exhibited by the SMA when subjected to cyclic loading. The residual deformation upon cycling and the efficiency in material usage are the two most restrictive issues in this sense. In this paper, a device equipped with superelastic NiTi SMA wires and capable of supporting external tension compression loads with optimized properties is presented. It is shown how the introduction of the wires’ pre-straining allows for the absorption of deleterious residual deformation without affecting the self-centering capabilities upon unloading, in contrast with what occurs for pre-strained tendons. These features were experimentally verified in an in-scale prototype composed of two 1.2 mm diameter superelastic NiTi SMA wires. In order to numerically assess the dynamic response of a simple structure subjected to seismic excitations, a multilinear superelasticity model for the NiTi wires was developed. (paper)

The effects of parametric changes in electropolishing process on surface properties of 316L stainless steel

Energy Technology Data Exchange (ETDEWEB)

Rahman, Zia ur [School of Engineering and Technology, Central Michigan University, Mt. Pleasant, MI 48859 (United States); Science of Advanced Materials, Central Michigan University, Mt. Pleasant, MI 48859 (United States); Deen, K.M. [Department of Materials Engineering, University of British Columbia, Vancouver, BC V6T 1Z4 (Canada); Department of Metallurgy and Materials Engineering, CEET, University of the Punjab, Lahore, 54590 (Pakistan); Cano, Lawrence [Department of Mechanical Engineering, The University of Texas Rio Grande Valley, Edinburg, TX 78539 (United States); Haider, Waseem, E-mail: haide1w@cmich.edu [School of Engineering and Technology, Central Michigan University, Mt. Pleasant, MI 48859 (United States); Science of Advanced Materials, Central Michigan University, Mt. Pleasant, MI 48859 (United States)

2017-07-15

Highlights: • 316L stainless steel was electropolished at the oxygen evolution (EPO) and below the oxygen evolution (EPBO) potentials. • EPBO samples displayed low fractional polarity and surface roughness when compared to EPO. • Both electropolished samples (EPO and EPBO) showed higher resistance to corrosion when compared to mechanically polished samples. • EPO and EPBO samples showed enhanced cell proliferation and stellar morphology after 24 h. - Abstract: Corrosion resistance and biocompatibility of 316L stainless steel implants depend on the surface features and the nature of the passive film. The influence of electropolishing on the surface topography, surface free energy and surface chemistry was determined by atomic force microscopy, contact angle meter and X-ray photoelectron spectroscopy, respectively. The electropolishing of 316L stainless steel was conducted at the oxygen evolution potential (EPO) and below the oxygen evolution potential (EPBO). Compared to mechanically polished (MP) and EPO, the EPBO sample depicted lower surface roughness (Ra = 6.07 nm) and smaller surface free energy (44.21 mJ/m{sup 2}). The relatively lower corrosion rate (0.484 mpy) and smaller passive current density (0.619 μA/cm{sup 2}) as determined from cyclic polarization scans was found to be related with the presence of OH, Cr(III), Fe(0), Fe(II) and Fe(III) species at the surface. These species assured the existence of relatively uniform passive oxide film over EPBO surface. Moreover, the relatively large charge transfer (R{sub ct}) and passive film resistance (R{sub f}) registered by EPBO sample from impedance spectroscopy analysis confirmed its better electrochemical performance. The in vitro response of these polished samples toward MC3T3 pre-osteoblast cell proliferation was determined to be directly related with their surface and electrochemical properties.

Development of Biomimetic NiTi Alloy: Influence of Thermo-Chemical Treatment on the Physical, Mechanical and Biological Behavior

Science.gov (United States)

Rupérez, Elisa; Manero, José María; Bravo-González, Luis-Alberto; Espinar, Eduardo; Gil, F.J.

2016-01-01

A bioactive layer, free of nickel, has been performed for its greater acceptability and reliability in clinical applications for NiTi shape memory alloys. In the first step, a safe barrier against Ni release has been produced on the surface by means of a thicker rutile/anastase protective layer free of nickel. In the second step, a sodium alkaline titanate hydrogel, which has the ability to induce apatite formation, has been performed from oxidized surface. An improvement of host tissue–implant integration has been achieved in terms of Ni ions release and the bioactivity of the treated NiTi alloys has been corroborated with both in vitro and in vivo studies. The transformation temperatures (As, Af, Ms, and Mf), as well as the critical stresses (σβ⇔M), have been slightly changed due to this surface modification. Consequently, this fact must be taken into account in order to design new surface modification on NiTi implants. PMID:28773526

Development of Biomimetic NiTi Alloy: Influence of Thermo-Chemical Treatment on the Physical, Mechanical and Biological Behavior

Directory of Open Access Journals (Sweden)

Elisa Rupérez

2016-05-01

Full Text Available A bioactive layer, free of nickel, has been performed for its greater acceptability and reliability in clinical applications for NiTi shape memory alloys. In the first step, a safe barrier against Ni release has been produced on the surface by means of a thicker rutile/anastase protective layer free of nickel. In the second step, a sodium alkaline titanate hydrogel, which has the ability to induce apatite formation, has been performed from oxidized surface. An improvement of host tissue–implant integration has been achieved in terms of Ni ions release and the bioactivity of the treated NiTi alloys has been corroborated with both in vitro and in vivo studies. The transformation temperatures (As, Af, Ms, and Mf, as well as the critical stresses (σβ⇔M, have been slightly changed due to this surface modification. Consequently, this fact must be taken into account in order to design new surface modification on NiTi implants.

Mechanical behaviour of Nd:YAG laser welded superelastic NiTi

International Nuclear Information System (INIS)

Vieira, L. Alberty; Fernandes, F.M. Braz; Miranda, R.M.; Silva, R.J.C.; Quintino, L.; Cuesta, A.; Ocana, J.L.

2011-01-01

Highlights: → The main innovations claimed are: understand rolling direction effect on mechanical cycling of laser welded NiTi. → Functionality confirmed by stabilization of hysteretic response up to 8% strain. → Welds tensile cycled exhibited superior functional mechanical behaviour. → For applied stresses of 50 MPa below UTS the joints showed superelastic behaviour. - Abstract: Joining techniques for shape memory alloys (SMA) has become of great interest, as their functional properties, namely shape memory effect (SME) and superelasticity (SE), present unique solutions for state-of-the-art applications, although limited results concerning mechanical properties are reported. This paper reports experimental work performed with Nd:YAG continuous wave laser welding of superelastic cold-rolled plates of NiTi 1 mm thick. The mechanical behaviour was evaluated by means of tensile tests performed both to failure and to cycling. The superelastic behaviour of the welded joints was observed for applied stresses close to about 50 MPa below the ultimate tensile strength of the welds. The functionality was confirmed by analyzing the stabilization of the mechanical hysteretic response to strain levels up to 8%. For tensile cycling involving strain levels larger than 6%, welded specimens were found to exhibit superior functional mechanical behaviour presenting larger recoverable strain levels. The fracture surfaces were observed by scanning electron microscopy (SEM) and the effect of the rolling direction on mechanical properties was evaluated and discussed, reinforcing the importance of joint design when laser welding these alloys.

Mechanical Properties of TiTaHfNbZr High-Entropy Alloy Coatings Deposited on NiTi Shape Memory Alloy Substrates

Science.gov (United States)

Motallebzadeh, A.; Yagci, M. B.; Bedir, E.; Aksoy, C. B.; Canadinc, D.

2018-04-01

TiTaHfNbZr high-entropy alloy (HEA) thin films with thicknesses of about 750 and 1500 nm were deposited on NiTi substrates by RF magnetron sputtering using TiTaHfNbZr equimolar targets. The thorough experimental analysis on microstructure and mechanical properties of deposited films revealed that the TiTaHfNbZr films exhibited amorphous and cauliflower-like structure, where grain size and surface roughness increased concomitant with film thickness. More importantly, the current findings demonstrate that the TiTaHfNbZr HEA films with mechanical properties of the same order as those of the NiTi substrate constitute promising biomedical coatings effective in preventing Ni release.

Mechanical Properties of TiTaHfNbZr High-Entropy Alloy Coatings Deposited on NiTi Shape Memory Alloy Substrates

Science.gov (United States)

Motallebzadeh, A.; Yagci, M. B.; Bedir, E.; Aksoy, C. B.; Canadinc, D.

2018-06-01

TiTaHfNbZr high-entropy alloy (HEA) thin films with thicknesses of about 750 and 1500 nm were deposited on NiTi substrates by RF magnetron sputtering using TiTaHfNbZr equimolar targets. The thorough experimental analysis on microstructure and mechanical properties of deposited films revealed that the TiTaHfNbZr films exhibited amorphous and cauliflower-like structure, where grain size and surface roughness increased concomitant with film thickness. More importantly, the current findings demonstrate that the TiTaHfNbZr HEA films with mechanical properties of the same order as those of the NiTi substrate constitute promising biomedical coatings effective in preventing Ni release.

Cutting NiTi with Femtosecond Laser

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L. Quintino

2013-01-01

Full Text Available Superelastic shape memory alloys are difficult to machine by thermal processes due to the facility for Ti oxidation and by mechanical processes due to their superelastic behavior. In this study, femtosecond lasers were tested to analyze the potential for machining NiTi since femtosecond lasers allow nonthermal processing of materials by ablation. The effect of processing parameters on machining depth was studied, and material removal rates were computed. Surfaces produced were analyzed under SEM which shows a resolidified thin layer with minimal heat affected zones. However, for high cutting speeds, that is, for short interaction times, this layer was not observed. A depletion of Ni was seen which may be beneficial in biomedical applications since Ni is known to produce human tissue reactions in biophysical environments.

Effect of laser welding parameters on the austenite and martensite phase fractions of NiTi

Energy Technology Data Exchange (ETDEWEB)

Oliveira, J.P., E-mail: jp.oliveira@campus.fct.unl.pt [CENIMAT/i3N, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa (Portugal); Braz Fernandes, F.M. [CENIMAT/i3N, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa (Portugal); Miranda, R.M. [UNIDEMI, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa (Portugal); Schell, N. [Institute of Materials Research, Helmholtz-Zentrum Geesthacht, Max-Planck-Str. 1, D-21502 Geesthacht (Germany); Ocaña, J.L. [Centro Láser UPM, Universidad Politécnica de Madrid, Edificio “La Arboleda”, Ctra. Valencia, km 7,300, Campus Sur UPM, 28031 Madrid (Spain)

2016-09-15

Although laser welding is probably the most used joining technique for NiTi shape memory alloys there is still a lack of understanding about the effects of laser welding parameters on the microstructural induced changes: in both the heat affected and fusion zones martensite may be present, while the base material is fully austenitic. Synchrotron X-ray diffraction was used for fine probing laser welded NiTi joints. Through Rietveld refinement the martensite and austenite phase fractions were determined and it was observed that the martensite content increases towards the weld centreline. This is related to a change of the local transformation temperatures on these regions, which occurs due to compositional variation in those regions. The martensite phase fraction in the thermally affected regions may have significant implications on functional properties on these joints. - Highlights: •Synchrotron X-ray diffraction was used for fine probing of the microstructure in laser welded NiTi joints. •Rietveld refinement allowed to determine the content of martensite along the heat affected and fusion zones. •The martensite content increases from the base material towards the weld centreline.

In situ observation and neutron diffraction of NiTi powder sintering

International Nuclear Information System (INIS)

Chen, Gang; Liss, Klaus-Dieter; Cao, Peng

2014-01-01

This study investigated NiTi powder sintering behaviour from elemental powder mixtures of Ni/Ti and Ni/TiH 2 using in situ neutron diffraction and in situ scanning electron microscopy. The sintered porous alloys have open porosities ranging from 2.7% to 36.0%. In comparison to the Ni/Ti compact, dehydrogenation occurring in the Ni/TiH 2 compact leads to less densification yet higher chemical homogenization only after high-temperature sintering. For the first time, direct evidence of the eutectoid phase transformation of NiTi at 620 °C is reported by in situ neutron diffraction. A comparative study of cyclic stress–strain behaviours of the porous NiTi alloys made from Ni/Ti and Ni/TiH 2 compacts indicate that the samples sintered from the Ni/TiH 2 compact exhibited a much higher porosity, larger pore size, lower fracture strength, lower close-to-overall porosity ratio and lower Young’s modulus. Instead of enhanced densification by the use of TiH 2 as reported in the literature, this study shows an adverse effect of TiH 2 on powder densification in NiTi

An in situ Study of NiTi Powder Sintering Using Neutron Diffraction

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Gang Chen

2015-04-01

Full Text Available This study investigates phase transformation and mechanical properties of porous NiTi alloys using two different powder compacts (i.e., Ni/Ti and Ni/TiH2 by a conventional press-and-sinter means. The compacted powder mixtures were sintered in vacuum at a final temperature of 1373 K. The phase evolution was performed by in situ neutron diffraction upon sintering and cooling. The predominant phase identified in all the produced porous NiTi alloys after being sintered at 1373 K is B2 NiTi phase with the presence of other minor phases. It is found that dehydrogenation of TiH2 significantly affects the sintering behavior and resultant microstructure. In comparison to the Ni/Ti compact, dehydrogenation occurring in the Ni/TiH2 compact leads to less densification, yet higher chemical homogenization, after high temperature sintering but not in the case of low temperature sintering. Moreover, there is a direct evidence of the eutectoid decomposition of NiTi at ca. 847 and 823 K for Ni/Ti and Ni/TiH2, respectively, during furnace cooling. The static and cyclic stress-strain behaviors of the porous NiTi alloys made from the Ni/Ti and Ni/TiH2 compacts were also investigated. As compared with the Ni/Ti sintered samples, the samplessintered from the Ni/TiH2 compact exhibited a much higher porosity, a higher close-to-total porosity, a larger pore size and lower tensile and compressive fracture strength.

Development of a Nano-Satellite Micro-Coupling Mechanism with Characterization of a Shape Memory Alloy Interference Joint

Science.gov (United States)

2010-12-01

for the softer martensitic phase was greater than that of the harder austenite phase [8]. When comparing NiTi to stainless steel 304 for resistance...interference joint, consisting of a detwinned martensitic NiTi SMA ring and stainless steel hub, could obtain sufficient axial coupling strength to...titanium (NiTi), shape memory alloy (SMA) cylindrical ring that is press-fit, in its detwinned martensitic phase, into a steel bushing, creating an

Finite Element Simulation and Additive Manufacturing of Stiffness-Matched NiTi Fixation Hardware for Mandibular Reconstruction Surgery

Directory of Open Access Journals (Sweden)

Ahmadreza Jahadakbar

2016-12-01

Full Text Available Process parameters and post-processing heat treatment techniques have been developed to produce both shape memory and superelastic NiTi using Additive Manufacturing. By introducing engineered porosity, the stiffness of NiTi can be tuned to the level closely matching cortical bone. Using additively manufactured porous superelastic NiTi, we have proposed the use of patient-specific, stiffness-matched fixation hardware, for mandible skeletal reconstructive surgery. Currently, Ti-6Al-4V is the most commonly used material for skeletal fixation devices. Although this material offers more than sufficient strength for immobilization during the bone healing process, the high stiffness of Ti-6Al-4V implants can cause stress shielding. In this paper, we present a study of mandibular reconstruction that uses a dry cadaver mandible to validate our geometric and biomechanical design and fabrication (i.e., 3D printing of NiTi skeletal fixation hardware. Based on the reference-dried mandible, we have developed a Finite Element model to evaluate the performance of the proposed fixation. Our results show a closer-to-normal stress distribution and an enhanced contact pressure at the bone graft interface than would be in the case with Ti-6Al-4V off-the-shelf fixation hardware. The porous fixation plates used in this study were fabricated by selective laser melting.

Two-way shape memory effect induced by repetitive compressive loading cycles

International Nuclear Information System (INIS)

Kim, Hyun-Chul; Yoo, Young-Ik; Lee, Jung-Ju

2009-01-01

The NiTi alloy can be trained by repetitive loading or heating cycles. As a result of the training, a two-way shape memory effect (TWSME) can be induced. Considerable research has been reported regarding the TWSME trained by tensile loading. However, the TWSME trained by compressive loading has not been investigated nearly as much. In this paper, the TWSME is induced by compressive loading cycles and the two-way shape memory strain is evaluated by using two types of specimen: a solid cylinder type and a tube type. The TWSME trained by compressive loading is different from that trained by tensile loading owing to the severe tension/compression asymmetry as described in previous research. After repetitive compressive loading cycles, strain variation upon cooling is observed, and this result proves that the TWSME is induced by compressive loading cycles. By performing compressive loading cycles, plastic deformation in NiTi alloy occurs more than for tensile loading cycles, which brings about the appearance of TWSME. It can be said that the TWSME is induced by compressive loading cycles more easily. The two-way shape memory strain increases linearly as the maximum strain of compressive loading cycles increases, regardless of the shape and the size of the NiTi alloy; this two-way shape memory strain then shows a tendency towards saturation after some repeated cycles

Fatigue behavior of lubricated Ni-Ti endodontic rotary instruments

Directory of Open Access Journals (Sweden)

A. Brotzu

2014-04-01

Full Text Available The use of Ni-Ti alloys in the practice of endodontic comes from their important properties such as shape memory and superelasticity phenomena, good corrosion resistance and high compatibility with biological tissues. In the last twenty years a great variety of nickel-titanium rotary instruments, with various sections and taper, have been developed and marketed. Although they have many advantages and despite their increasing popularity, a major concern with the use of Ni-Ti rotary instruments is the possibility of unexpected failure in use due to several reasons: novice operator handling, presence manufacturing defects, fatigue etc. Recently, the use of an aqueous gel during experimental tests showed a longer duration of the instruments. The aim of the present work is to contribute to the study of the fracture behavior of these endodontic rotary instruments particularly assessing whether the use of the aqueous lubricant gel can extend their operative life stating its reasons. A finite element model (FEM has been developed to support the experimental results. The results were rather contradictory, also because the Perspex (Poly-methyl methacrylate, PMMA cannot simulate completely the dentin mechanical behavior; however the results highlight some interesting points which are discussed in the paper.

Automated detection of a prostate Ni-Ti stent in electronic portal images.

Science.gov (United States)

Carl, Jesper; Nielsen, Henning; Nielsen, Jane; Lund, Bente; Larsen, Erik Hoejkjaer

2006-12-01

Planning target volumes (PTV) in fractionated radiotherapy still have to be outlined with wide margins to the clinical target volume due to uncertainties arising from daily shift of the prostate position. A recently proposed new method of visualization of the prostate is based on insertion of a thermo-expandable Ni-Ti stent. The current study proposes a new detection algorithm for automated detection of the Ni-Ti stent in electronic portal images. The algorithm is based on the Ni-Ti stent having a cylindrical shape with a fixed diameter, which was used as the basis for an automated detection algorithm. The automated method uses enhancement of lines combined with a grayscale morphology operation that looks for enhanced pixels separated with a distance similar to the diameter of the stent. The images in this study are all from prostate cancer patients treated with radiotherapy in a previous study. Images of a stent inserted in a humanoid phantom demonstrated a localization accuracy of 0.4-0.7 mm which equals the pixel size in the image. The automated detection of the stent was compared to manual detection in 71 pairs of orthogonal images taken in nine patients. The algorithm was successful in 67 of 71 pairs of images. The method is fast, has a high success rate, good accuracy, and has a potential for unsupervised localization of the prostate before radiotherapy, which would enable automated repositioning before treatment and allow for the use of very tight PTV margins.

Automated detection of a prostate Ni-Ti stent in electronic portal images

International Nuclear Information System (INIS)

Carl, Jesper; Nielsen, Henning; Nielsen, Jane; Lund, Bente; Larsen, Erik Hoejkjaer

2006-01-01

Planning target volumes (PTV) in fractionated radiotherapy still have to be outlined with wide margins to the clinical target volume due to uncertainties arising from daily shift of the prostate position. A recently proposed new method of visualization of the prostate is based on insertion of a thermo-expandable Ni-Ti stent. The current study proposes a new detection algorithm for automated detection of the Ni-Ti stent in electronic portal images. The algorithm is based on the Ni-Ti stent having a cylindrical shape with a fixed diameter, which was used as the basis for an automated detection algorithm. The automated method uses enhancement of lines combined with a grayscale morphology operation that looks for enhanced pixels separated with a distance similar to the diameter of the stent. The images in this study are all from prostate cancer patients treated with radiotherapy in a previous study. Images of a stent inserted in a humanoid phantom demonstrated a localization accuracy of 0.4-0.7 mm which equals the pixel size in the image. The automated detection of the stent was compared to manual detection in 71 pairs of orthogonal images taken in nine patients. The algorithm was successful in 67 of 71 pairs of images. The method is fast, has a high success rate, good accuracy, and has a potential for unsupervised localization of the prostate before radiotherapy, which would enable automated repositioning before treatment and allow for the use of very tight PTV margins

Instability of cyclic superelastic deformation of NiTi investigated by synchrotron X-ray diffraction

Czech Academy of Sciences Publication Activity Database

Sedmák, P.; Šittner, Petr; Pilch, Jan; Curfs, C.

2015-01-01

Roč. 94, Aug (2015), s. 257-270 ISSN 1359-6454 R&D Projects: GA ČR GB14-36566G; GA ČR GPP108/12/P111; GA ČR GA14-15264S; GA ČR GAP107/12/0800 Institutional support: RVO:68378271 Keywords : shape memory alloy * NiTi * superelasticity * cyclic deformation * in situ X-ray diffraction Subject RIV: JG - Metallurgy Impact factor: 5.058, year: 2015

Comparison of air-driven vs electric torque control motors on canal centering ability by ProTaper NiTi rotary instruments.

Science.gov (United States)

Zarei, Mina; Javidi, Maryam; Erfanian, Mahdi; Lomee, Mahdi; Afkhami, Farzaneh

2013-01-01

Cleaning and shaping is one of the most important phases in root canal therapy. Various rotary NiTi systems minimize accidents and facilitate the shaping process. Todays NiTi files are used with air-driven and electric handpieces. This study compared the canal centering after instrumentation using the ProTaper system using Endo IT, electric torque-control motor, and NSK air-driven handpiece. This ex vivo randomized controlled trial study involved 26 mesial mandibular root canals with 10 to 35° curvature. The roots were randomly divided into 2 groups of 13 canals each. The roots were mounted in an endodontic cube with acrylic resin, sectioned horizontally at 2, 6 and 10 mm from the apex and then reassembled. The canals were instrumented according to the manufacturer's instructions using ProTaper rotary files and electric torque-control motors (group 1) or air-driven handpieces (group 2). Photographs of the cross-sections included shots before and after instrumentation, and image analysis was performed using Photoshop software. The centering ability and canal transportation was also evaluated. Repeated measurement and independent t-test provided statistical analysis of canal transportation. The comparison of the rate of transportation toward internal or external walls between the two groups was not statistically significant (p = 0.62). Comparison of the rate of transportation of sections within one group was not significant (p = 0.28). Use of rotary NiTi file with either electric torquecontrol motor or air-driven handpiece had no effect on canal centering. NiTi rotary instruments can be used with air-driven motors without any considerable changes in root canal anatomy, however it needs the clinician to be expert.

An in situ neutron diffraction study of shape setting shape memory NiTi

International Nuclear Information System (INIS)

Benafan, O.; Padula, S.A.; Noebe, R.D.; Brown, D.W.; Clausen, B.; Vaidyanathan, R.

2013-01-01

A bulk polycrystalline Ni 49.9 Ti 50.1 (at.%) shape memory alloy specimen was shape set while neutron diffraction spectra were simultaneously acquired. The objective was to correlate internal stress, phase volume fraction, and texture measurements (from neutron diffraction spectra) with the macroscopic stress and shape changes (from load cell and extensometry measurements) during the shape setting procedure and subsequent shape recovery. Experimental results showed the evolution of the martensitic transformation (lattice strains, phase fractions and texture) against external constraints during both heating and cooling. Constrained heating resulted in a build-up of stresses during the martensite to austenite transformation, followed by stress relaxation due to thermal expansion, final conversion of retained martensite, and recovery processes. Constrained cooling also resulted in stress build-up arising from thermal contraction and early formation of martensite, followed by relaxation as the austenite fully transformed to martensite. Comparisons were also made between specimens pre-shape set and post-shape set with and without external constraints. The specimens displayed similar shape memory behavior consistent with the microstructure of the shape set sample, which was mostly unchanged by the shape setting process and similar to that of the as-received material

Effect of load deflection on corrosion behavior of NiTi wire.

Science.gov (United States)

Liu, I H; Lee, T M; Chang, C Y; Liu, C K

2007-06-01

For dental orthodontic applications, NiTi wires are used under bending conditions in the oral environment for a long period. The purpose of this study was to investigate the effect of bending stress on the corrosion of NiTi wires using potentiodynamic and potentiostatic tests in artificial saliva. The results indicated that bending stress induces a higher corrosion rate of NiTi wires in passive regions. It is suggested that the passive oxide film of specimens would be damaged under bending conditions. Auger electron spectroscopic analysis showed a lower thickness of passive films on stressed NiTi wires compared with unstressed specimens in the passive region. By scanning electron microscopy, localized corrosion was observed on stressed Sentalloy specimens after a potentiodynamic test at pH 2. In conclusion, this study indicated that bending stress changed the corrosion properties and surface characteristics of NiTi wires in a simulated intra-oral environment.

Comparative studies on ultrasonic, friction, laser and resistance pressure welding of NiTi shape memory alloys with high-alloy steels. Final report; Vergleichende Untersuchungen zum Ultraschall-, Reib-, Laserstrahl- und Widerstandspressschweissen von NiTi-Shape-Memory-Metall mit hochlegierten Staehlen. Abschlussbericht

Energy Technology Data Exchange (ETDEWEB)

Zuckschwerdt, K.

2000-04-01

The suitability of different welding techniques for welding of NiTi shape memory alloys with high-alloy steel (C12CrNi17-7, X5CrNiNb19-9, X20Cr13) was investigated. The quality of the welds was analyzed using mechanical-technological, fractographic, metallographic and electron microscopy analysis. [German] Ziel dieses Forschungsvorhabens ist es, die Eignung der einzelnen Schweissverfahren fuer das Fuegen von NiTi-Formgedaechtnislegierungen mit hochlegiertem Stahl (X12CrNi17-7, X5CrNiNb19-9, X20Cr13) darzustellen und zu beurteilen. Die Qualitaet der Fuegeverbindungen wird mit Hilfe mechanisch-technologischer, fraktographischer, metallographischer und elektronenmikroskopischer Untersuchungen bewertet.

A preliminary study of cladding steel with NiTi by microwave-assisted brazing

International Nuclear Information System (INIS)

Chiu, K.Y.; Cheng, F.T.; Man, H.C.

2005-01-01

Nickel titanium (NiTi) plate of 1.2 mm thickness was successfully clad on AISI 316L stainless steel substrate by a microwave-assisted brazing process. Brazing was conducted in a multimode microwave oven in air using a copper-based brazing material in tape form. The brazing material was melted in a few minutes by microwave-induced plasma initiated by conducting wires surrounding the brazing assembly. Metallographic study by scanning-electron microscopy (SEM) and compositional analysis by energy-dispersive spectroscopy (EDS) of the brazed joint revealed metallurgical bonding formed via inter-diffusion between the brazing filler and the adjacent materials. A shear bonding strength in the range of 100-150 MPa was recorded in shear tests of the brazed joint. SEM and X-ray diffractometry (XRD) analysis for the surface of as-received NiTi plate and NiTi cladding showed similar microstructure and phase composition. Nanoindentation tests also indicated that the superelastic properties of NiTi were essentially retained. The cavitation erosion resistance of the NiTi cladding was essentially the same as that of as-received NiTi plate, and higher than that obtained in laser or TIG (tungsten-inert gas) surfacing. The high resistance could be attributed to avoidance of dilution and defect formation in the NiTi clad since the cladding did not undergo melting and solidification in the brazing process. Electrochemical tests also recorded similar corrosion resistance in both as-received NiTi and NiTi cladding. Thus, the present study indicates that microwave-assisted brazing is a simple, economical, and feasible process for cladding NiTi on 316L stainless steel for enhancing cavitation erosion resistance

Smear layer and debris removal using manual Ni-Ti files compared with rotary Protaper Ni- Ti files - An In-Vitro SEM study.

Science.gov (United States)

Reddy, J M V Raghavendra; Latha, Prasanna; Gowda, Basavana; Manvikar, Varadendra; Vijayalaxmi, D Benal; Ponangi, Kalyana Chakravarthi

2014-02-01

Predictable successful endodontic therapy depends on correct diagnosis, effective cleaning, shaping and disinfection of the root canals and adequate obturation. Irrigation serves as a flush to remove debris, tissue solvent and lubricant from the canal irregularities; however these irregularities can restrict the complete debridement of root canal by mechanical instrumentation.Various types of hand and rotary instruments are used for the preparation of the root canal system to obtain debris free canals. The purpose of this study was to evaluate the amount of smear layer and debris removal on canal walls following the using of manual Nickel-Titanium (NiTi) files compared with rotary ProTaperNiTi files using a Scanning Electron Microscope in two individual groups. A comparative study consisting of 50 subjects randomized into two groups - 25 subjects in Group A (manual) and 25 subjects in Group B (rotary) was undertaken to investigate and compare the effects of smear layer and debris between manual and rotary NiTi instruments. Chi square test was used to find the significance of smear layer and debris removal in the coronal, middle and apical between Group A and Group B. Both systems of Rotary ProTaperNiTi and manual NiTi files used in the present study, did not create completely clean root canals. Manual NiTi files produced significantly less smear layer and debris compared to Rotary ProTaperNiTi instruments. Rotary instruments were less time consuming when compared to manual instruments. Instrument separation was not found to be significant with both the groups. Both systems of Rotary ProTaperNiTi and manual NiTi files used did not produce completely clean root canals. Manual NiTi files produced significantly less smear layer and debris compared to Rotary protaper instruments. How to cite the article: Reddy JM, Latha P, Gowda B, Manvikar V, Vijayalaxmi DB, Ponangi KC. Smear layer and debris removal using manual Ni-Ti files compared with rotary Protaper Ni-Ti files

The Effect of Pre-Stressing on the Static Indentation Load Capacity of the Superelastic 60NiTi

Science.gov (United States)

DellaCorte, Christopher; Moore, Lewis E., III; Clifton, Joshua S.

2013-01-01

Superelastic nickel-titanium alloys, such as 60NiTi (60Ni-40Ti by wt.%), are under development for use in mechanical components like rolling element bearings and gears. Compared to traditional bearing steels, these intermetallic alloys, when properly heat-treated, are hard but exhibit much lower elastic modulus (approx.100 GPa) and a much broader elastic deformation range (approx.3 percent or more). These material characteristics lead to high indentation static load capacity, which is important for certain applications especially space mechanisms. To ensure the maximum degree of elastic behavior, superelastic materials must be pre-stressed, a process referred to as "training" in shape memory effect (SME) terminology, at loads and stresses beyond expected use conditions. In this paper, static indentation load capacity tests are employed to assess the effects of pre-stressing on elastic response behavior of 60NiTi. The static load capacity is measured by pressing 12.7 mm diameter ceramic Si3N4 balls into highly polished, hardened 60NiTi flat plates that have previously been exposed to varying levels of pre-stress (up to 2.7 GPa) to determine the load that results in shallow but measurable (0.6 m, 25 in. deep) permanent dents. Hertz stress calculations are used to estimate contact stress. Without exposure to pre-stress, the 60NiTi surface can withstand an approximately 3400 kN load before significant denting (>0.4 m deep) occurs. When pre-stressed to 2.7 GPa, a static load of 4900 kN is required to achieve a comparable dent, a 30 percent increase. These results suggest that stressing contact surfaces prior to use enhances the static indentation load capacity of the superelastic 60NiTi. This approach may be adaptable to the engineering and manufacture of highly resilient mechanical components such as rolling element bearings.

Microstructure, mechanical and functional properties of NiTi-based shape memory ribbons

International Nuclear Information System (INIS)

Mehrabi, K.; Bruncko, M.; Kneissl, A.C.

2012-01-01

Highlights: ► Melt-spun samples exhibited martensite structure and shape memory effects immediately after processing at room temperature. ► Using a new etchant and interference contrast, it is possible to reveal the fine microstructures and grain boundaries. ► The martensite structure in NiTi is very fine, and nano-sized twin boundaries could be revealed using TEM only. ► Two-way effects have been successfully introduced by different thermomechanical training methods in NiTi, NiTiCu and NiTiW alloys, which can be used for several applications, e.g. microsensors and microactuators. - Abstract: The present work has been aimed to study the microstructures, functional properties and the influence of different thermomechanical training methods on the two-way shape memory effect in NiTi-based melt-spun ribbons. In order to get small-dimensioned shape memory alloys (SMAs) with good functional and mechanical properties, a rapid solidification technique was employed. Their fracture and elasticity characteristics have been determined, as well as shape memory properties by thermomechanical cycling. The ribbons were trained under tensile and bending deformation by thermal cycling through the phase transformation temperature range. The results displayed that all different training methods were effective in developing a two-way shape memory effect (TWSME). The influence of copper (5–25 at.% Cu) and tungsten (2 at.% W) on the microstructure, and the functional and mechanical behavior of NiTi thin ribbons was also investigated. All samples show a shape memory effect immediately after processing without further heat treatment. The melt-spun ribbons were trained under constant strain (bending and tensile deformation) by thermal cycling through the phase transformation temperature range. The addition of copper was effective to narrow the transformation hysteresis. The W addition has improved the TWSME stability of the NiTi alloys and mechanical properties. Results about

Torsion and bending properties of shape memory and superelastic nickel-titanium rotary instruments.

Science.gov (United States)

Ninan, Elizabeth; Berzins, David W

2013-01-01

Recently introduced into the market are shape memory nickel-titanium (NiTi) rotary files. The objective of this study was to investigate the torsion and bending properties of shape memory files (CM Wire, HyFlex CM, and Phoenix Flex) and compare them with conventional (ProFile ISO and K3) and M-Wire (GT Series X and ProFile Vortex) NiTi files. Sizes 20, 30, and 40 (n = 12/size/taper) of 0.02 taper CM Wire, Phoenix Flex, K3, and ProFile ISO and 0.04 taper HyFlex CM, ProFile ISO, GT Series X, and Vortex were tested in torsion and bending per ISO 3630-1 guidelines by using a torsiometer. All data were statistically analyzed by analysis of variance and the Tukey-Kramer test (P = .05) to determine any significant differences between the files. Significant interactions were present among factors of size and file. Variability in maximum torque values was noted among the shape memory files brands, sometimes exhibiting the greatest or least torque depending on brand, size, and taper. In general, the shape memory files showed a high angle of rotation before fracture but were not statistically different from some of the other files. However, the shape memory files were more flexible, as evidenced by significantly lower bending moments (P < .008). Shape memory files show greater flexibility compared with several other NiTi rotary file brands. Copyright © 2013 American Association of Endodontists. Published by Elsevier Inc. All rights reserved.

Glide path preparation in S-shaped canals with rotary pathfinding nickel-titanium instruments.

Science.gov (United States)

Ajuz, Natasha C C; Armada, Luciana; Gonçalves, Lucio S; Debelian, Gilberto; Siqueira, José F

2013-04-01

This study compared the incidence of deviation along S-shaped (double-curved) canals after glide path preparation with 2 nickel-titanium (NiTi) rotary pathfinding instruments and hand K-files. S-shaped canals from 60 training blocks were filled with ink, and preinstrumentation images were obtained by using a stereomicroscope. Glide path preparation was performed by an endodontist who used hand stainless steel K-files (up to size 20), rotary NiTi PathFile instruments (up to size 19), or rotary NiTi Scout RaCe instruments (up to size 20). Postinstrumentation images were taken by using exactly the same conditions as for the preinstrumentation images, and both pictures were superimposed. Differences along the S-shaped canal for the mesial and distal aspects were measured to evaluate the occurrence of deviation. Intragroup analysis showed that all instruments promoted some deviation in virtually all levels. Overall, regardless of the group, deviations were observed in the mesial wall at the canal terminus and at levels 4, 5, 6 and 7 mm and in the distal wall at levels 1, 2, and 3 mm. These levels corresponded to the inner walls of each curvature. Both rotary NiTi instruments performed significantly better than hand K-files at all levels (P instruments showed significantly better results than PathFiles at levels 0, 2, 3, 5, and 6 mm (P rotary NiTi instruments are suitable for adequate glide path preparation because they promoted less deviation from the original canal anatomy when compared with hand-operated instruments. Of the 2 rotary pathfinding instruments, Scout RaCe showed an overall significantly better performance. Copyright © 2013 American Association of Endodontists. Published by Elsevier Inc. All rights reserved.

[Utility of nickel-titanium shape memory alloys of vertebral body reduction fixator with assisted distraction bar].

Science.gov (United States)

Man, Yi; Zheng, Yue-huan; Cao, Peng; Chen, Bo; Zheng, Tao; Sun, Chang-hui; Lu, Jiong

2011-06-07

To test the nickel-titanium (Ni-Ti) shape memory alloys of vertebral body reduction fixator with assisted distraction bar for the treatment of traumatic and osteoporotic vertebral body fracture. A Ni-Ti shape memory alloys of vertebral body reduction fixator with assisted distraction bar was implanted into the compressed fracture specimens through vertebral pedicle with the radiographic monitoring to reduce the collapsed endplate as well as distract the compressed vertebral fracture. Radiographic film and computed tomographic reconstruction technique were employed to evaluate the effects of reduction and distraction. A biomechanic test machine was used to measure the fatigue and the stability of deformation of fixation segments. Relying on the effect of temperature shape memory, such an assembly could basically reduce the collapsed endplate as well as distract the compressed vertebral fracture. And when unsatisfied results of reduction and distraction occurred, its super flexibility could provide additional distraction strength. A Ni-Ti shape memory alloys of vertebral body reduction fixator with assisted distraction bar may provide effective endplate reduction, restore the vertebral height and the immediate biomechanic spinal stability. So the above assembly is indicated for the treatment of traumatic and osteoporotic vertebral body fracture.

Effects of HVEM irradiation on ordered phases in Ni-Ti

International Nuclear Information System (INIS)

Pelton, A.R.

1983-01-01

Various ordered phases in the Ni-Ti system were subjected to electron irradiation in the Berkeley HVEM. Austenitic NiTi (B2 structure) disorders and turns amorphous with room-temperature irradiations at accelerating potentials between 1 and 1.5 MeV. Total doses for the onset of amorphiticity range between 0.7 x 10 22 and 3 x 10 22 e.cm -2 (0.4 to 1.0dpa). At 90K the dose requirement decreases to 4 x 10 20 e.cm -2 (approx. 10 -2 dpa). Martensitic NiTi (distorted monoclinic structure) readily detwins and transforms to austenite when irradiated for short times (approx. 10 seconds). Vapor-deposited amorphous films were crystallized to produce NiTi, Phase X (ordered nickel-rich phase with unknown structure) and Ni 3 Ti (DO 24 structure). Upon electron irradiation, NiTi and Phase X disorder and become amorphous, while Ni 3 Ti disorders but does not turn amorphous with doses up to 4 x 10 22 e.cm -2 at 90K. These results are discussed in terms of the requirement of a critical concentration of defects and their relative mobilities. Brimhall's solubility criteria for amorphization of ordered alloys by ion bombardment is apparantly applicable to electron-induced crystalline to amorphous transitions in this alloy

Evolution of microstructure and property of NiTi alloy induced by cold rolling

International Nuclear Information System (INIS)

Li, Y.; Li, J.Y.; Liu, M.; Ren, Y.Y.; Chen, F.; Yao, G.C.; Mei, Q.S.

2015-01-01

We investigated the combination effect of plastic deformation and phase transformation on the evolution of microstructure and property of NiTi alloy. Samples of Ni 50.9 Ti 49.1 alloy were deformed by cold rolling to different strains/thickness reductions (4%–56%). X-ray diffraction, transmission electronic microscopy (TEM) and microhardness measurements were applied for characterization of the microstructure and property of the cold-rolled samples. Experimental results indicated the non-monotonic variations of microstructure parameters and mechanical property with strain, indicating the different processes in microstructure and property evolution of NiTi subjected to cold rolling. TEM observations further showed the dominating mechanisms of microstructure evolution at different strain levels, leading to the gradual reduction of grain size of NiTi to the nanoscale by cold rolling. The results were discussed and related to deformation of martensite, forward and reverse martensitic transformations and dynamic recrystallization. The present study provided experimental evidences for the enhanced formation of nanograins in NiTi by plastic deformation coupled with phase transformation. - Highlights: • Cold rolling of NiTi to thickness reductions from 4% to 56%. • Fluctuation behaviors in microstructure and property evolutions of NiTi. • Deformation coupled with phase transformation enhanced nanocrystallization of NiTi.

Highly smooth Nb surfaces fabricated by buffered electropolishing

International Nuclear Information System (INIS)

Wu, Andy T; John Mammossor; Phillips, H.; Jean Delayen; Charles Reece; Amy Wilkerson; David Smith; Robert Ike

2005-01-01

It is demonstrated that highly smooth Nb surfaces can be obtained through Buffered ElectroPolishing (BEP) employing an electrolyte consisting of lactic, sulfuric, and hydrofluoric acids. Parameters that control the polishing process are optimized to achieve the smoothest surface finish with the help of surface observations using a scanning electron microscope and a Metallographic Optical Microscope (MOM). The polishing rate of BEP is determined to be 0.646 (micro)m/min that is much higher than 0.381 (micro)m/min achieved by the conventional ElectroPolishing (EP) process widely used in the Superconducting Radio Frequency (SRF) community. A high precision and large scan area 3-D profilometer is used to view morphology of the treated Nb surfaces. Statistical data, such as, rms, total indicator runout, and arithmetic mean deviation of the Nb surfaces are extracted from the profilometer images. It is found that Nb surfaces treated by BEP are an order of magnitude smoother than those treated by the optimized EP process. The chemical composition of the Nb surfaces after BEP is analyzed by static and dynamic Secondary Ion Mass Spectrometer (SIMS) systems. Cracking patterns of the Nb surfaces under different primary ion sources of Ga + , Au + , and Ar + are reported. The depth profile of the surface niobium oxides is studied through continuously monitoring niobium and its relevant oxides' peaks as a function of time. Dynamic SIMS results imply that the surface oxide structure of Nb may be more complicated than what usually believed and can be inhomogeneous. Preliminary results of BEP on Nb SRF single cell cavities and half-cells are reported. It is shown that smooth and bright surfaces can be obtained in 30 minutes when the electric field inside a SRF cavity is uniform during a BEP process. This study reveals that BEP is a highly promising technique for surface treatment on Nb SRF cavities to be used in particle accelerators

Evaluation of deformation and fracture of three single-file NiTi rotary instruments: ProTaper F2, WaveOne Primary and OneShape in simulated curved canals

Directory of Open Access Journals (Sweden)

Mina A. Shenouda

2018-06-01

Full Text Available Purpose. The aim of the current study was to compare the incidence of deformation and fracture in three single-file NiTi instruments: ProTaper F2, WaveOne Primary and OneShape. Methods. Fifteen instruments were equally divided into three groups: ProTaper F2 in reciprocation, WaveOne Primary in reciprocation and OneShape in continuous rotation. Each instrument was used to prepare standardized simulated curved canals in resin blocks until fracture had occurred. Following each canal preparation, the instruments were examined for deformation both by naked eye inspection and stereomicroscopic examination. The average number of canals prepared until the first incidence of cracks and the average lifespan of the instruments were calculated. Data were analysed using one-way ANOVA and two-sample t-test. Results. There was no statistically significant difference between ProTaper and WaveOne instruments in both the incidence of cracks and the average lifespan (P > 0.05. OneShape instruments had a significantly delayed incidence of cracks and a longer lifespan than both ProTaper and WaveOne instruments (P < 0.05; however, OneShape instruments showed a noticeable early plastic deformation. Conclusion: PT F2 instrument was comparable to WO Primary instrument in terms of fracture resistance, while OS instrument had more fracture resistance than both PT F2 and WO Primary instruments.

Laser cladding of austenitic stainless steel using NiTi strips for resisting cavitation erosion

International Nuclear Information System (INIS)

Chiu, K.Y.; Cheng, F.T.; Man, H.C.

2005-01-01

Being part of a larger project on using different forms of nickel titanium (NiTi) in the surface modification of stainless steel for enhancing cavitation erosion resistance, the present study employs NiTi strips as the cladding material. Our previous study shows that laser surfacing using NiTi powder can significantly increase the cavitation erosion resistance of AISI 316 L stainless steel [K.Y. Chiu, F.T. Cheng, H.C. Man, Mater. Sci. Eng. A 392 (2005) 348-358]. However, from an engineering point of view, NiTi strips are more attractive than powder because NiTi powder is very expensive due to high production cost. In the present study, NiTi strips were preplaced on AISI 316 L samples and remelted using a high-power CW Nd:YAG laser to form a clad layer. To lower the dilution due to the substrate material, samples doubly clad with NiTi were prepared. The volume dilution ratio in the singly clad sample was high, being in the range of 13-30% depending on the processing parameters, while that of the doubly clad sample was reduced to below 10%. Analysis by scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS) and X-ray diffractometry (XRD) reveals that the clad layer is composed of a NiTi B2 based matrix together with fine precipitates of a tetragonal structure. Vickers indentation shows a tough cladding/substrate interface. The microhardness of the clad layer is increased from 200 HV of the substrate to about 750 HV due to the dissolution of elements like Fe, Cr and N in the matrix. Nanoindentation tests record a recovery ratio near to that of bulk NiTi, a result attributable to a relatively low dilution. The cavitation erosion resistance of the doubly clad samples is higher than that of 316-NiTi-powder (samples laser-surfaced with NiTi powder) and approaches that of NiTi plate. The high erosion resistance is attributed to a high hardness, high indentation recovery ratio and the absence of cracks or pores

Fluid Flow in a Porous Tree-Shaped Network

OpenAIRE

Miguel, A. F.

2014-01-01

Tree-shaped flow networks connect one point to an infinity of points and are everywhere in Nature. These networks often own minimal flow resistance and vessel sizes obey to scaling power-laws. In this paper presents a model for fluid flow through a tree-shaped network with porous tubes. Hagen–Poiseuille flow is assumed for tubes and Darcy flow for the porous wall.

Shape memory materials

Institute of Scientific and Technical Information of China (English)

无

2001-01-01

Compared with piezoelectric ceramics and magnetostrictive materials, the shape memory materials possess larger recoverable strain and recovery stress but slower response to external field. It is expected that the magneto-shape memory materials may develop considerable strain as well as rapid and precise shape control. Pseudoelasticity and shape memory effect (SME) resulted from martensitic transformation and its reverse transformation in shape memory materials were generally described. The requirements of appearing the shape memory effect in materials and the criteria for thermoelastic martensitic transformation were given. Some aspects concerning characteristics of martensitic transformation, and factors affecting SME in Ni-Ti, Cu-Zn-Al and Fe-Mn-Si based alloys as well as ZrO2 containing ceramics were briefly reviewed. Thermodynamic calculation of Ms temperature as function of grain size and parent ordering in Cu-Zn-Al was presented. The works on prediction of Ms in Fe-Mn-Si based alloys and in ZrO2-CeO2 were mentioned. Magnetic shape memory materials were briefly introduced.

Velcro-like fasteners based on NiTi micro-hook arrays

International Nuclear Information System (INIS)

Vokoun, D; Pilch, J; Majtás, D; Šittner, P; Sedlák, P; Frost, M

2011-01-01

A recently developed Velcro-like fastener utilizes superelastic deformation of two interlocked NiTi hooks when pulled apart. This work focuses on experimental analysis (evaluation of normal detachment force at different temperatures) and modeling (simulation by a finite element implemented SMA model) of the unhooking process. It is claimed that nonlinear superelastic deformation of NiTi leads to unique properties of the NiTi hook fasteners such as high strength (∼15 000 kg m −2 ), a significant increase of strength with increasing temperature, absorption of impact loads, damping of mechanical vibrations, forceless contact or silent release and better functioning in dirty environments compared to conventional Velcro fasteners

Investigation of oxidation resistance of Ni-Ti film used as oxygen diffusion barrier layer

International Nuclear Information System (INIS)

Liu, B.T.; Yan, X.B.; Zhang, X.; Zhou, Y.; Guo, Y.N.; Bian, F.; Zhang, X.Y.

2009-01-01

Ni-Ti films prepared at 10 W and 70 W by rf magnetron sputtering are investigated as the oxygen diffusion barrier layer, it is found that crystallinity of Ni-Ti film does not greatly depend on the deposition power. X-ray photoelectron spectroscopy indicates that Ni is still in the form of metallic state from the binding energies of both Ni 2p 3/2 and Ni 2p 1/2 spectra for the sample with 10 W prepared Ni-Ti, however, Ni is oxidized for 70 W prepared Ni-Ti film. Moreover, the (La 0.5 Sr 0.5 )CoO 3 /Pb(Zr 0.40 Ti 0.60 )O 3 /(La 0.5 Sr 0.5 )CoO 3 capacitor grown on high power prepared Ni-Ti film is leaky, however, the capacitor on low power prepared Ni-Ti film possesses very promising physical properties (i.e. remnant polarization of ∼27 μC/cm 2 at 5 V and maximum dielectric constant of 940). Leakage current density of the capacitor grown on low power prepared Ni-Ti film is further investigated, it meets ohmic behavior ( 1.0 V).

Neutron, x-ray scattering and TEM studies of Ni-Ti multilayers

International Nuclear Information System (INIS)

Keem, J.E.; Wood, J.; Grupido, N.; Hart, K.; Nutt, S.; Reichel, D.G.; Yelon, W.B.

1988-01-01

The authors present an analysis of Ni-Ti multilayer neutron reflectors and supermirrors undertaken to identify the causes of the lower than expected observed scattering power and critical angle enhancement of Ni-Ti supermirrors. Results of these investigations focus attention on cusp formation in the Ni-Ti bilayers as probable cause for the reduced neutron scattering power. Grazing angle x-ray and neutron scattering, wide angle neutron diffraction and analytical cross sectional TEM have been used. The multilayers were produced by magnetron sputtering and ion-beam deposition on float glass substrates and silicon wafers

Ni-Ti Next Generation Bearings for Space Applications

Science.gov (United States)

DellaCorte, Christopher

2018-01-01

NASA applications challenge traditional bearing materials. The rigors of launch often include heavy shock loads and exposure to corrosive environments (e.g., salt spray). Unfortunately, ball and roller bearings made from hardened steels are vulnerable to Brinell denting and rust which can limit performance and life. Ceramic materials can eliminate corrosion concerns but their high stiffness and extreme hardness actually makes denting problems worse. In this presentation, an emerging superelastic alloy, NiTi, is introduced for rolling element bearing applications. Through a decade of RD, NiTi alloy bearings have been put through a comprehensive series of life and performance tests. Hardness, corrosion, strength, stiffness, and rolling contact fatigue tests have been conducted and reported. Ball bearings ranging in size from 12 to 50mm bore have been successfully engineered and operated over a wide range of speeds and test conditions including being submerged in water. The combination of high hardness, moderate elastic modulus, low density, and intrinsic corrosion immunity provide new possibilities for mechanisms that operate under extreme conditions. Recent preliminary tests indicate that bearings can be made from NiTi alloys that are easily lubricated by conventional oils and greases and exhibit acceptable rolling contact fatigue resistance. This presentation introduces the NiTi materials systems and shows how NASA is using it to alleviate several specific problems encountered in advanced space applications.

Fracture analysis of Ag nanobrazing of NiTi to Ti alloy

Directory of Open Access Journals (Sweden)

L. Quintino

2013-09-01

Full Text Available Dissimilar joining of shape memory alloys to Ti alloys has long been attempted by several research groups due to the foreseen potential industrial applications. However, the very dissimilar thermo-physical properties of both materials place several difficulties. Brazing can be a solution since the base materials are subjected to a less sharp thermal cycle. In the present study brazed overlap joints of 1 mm thick plates of equiatomic NiTi and Ti6Al4V were produced using nano silver based filler materials. Surfaces were analyzed to assess the type of fracture and the capability of achieving bonding and involved mechanisms are discussed.

Cell adhesion on NiTi thin film sputter-deposited meshes

Energy Technology Data Exchange (ETDEWEB)

Loger, K. [Inorganic Functional Materials, Institute for Materials Science, Faculty of Engineering, University of Kiel (Germany); Engel, A.; Haupt, J. [Department of Cardiovascular Surgery, University Hospital of Schleswig-Holstein, Kiel (Germany); Li, Q. [Biocompatible Nanomaterials, Institute for Materials Science, Faculty of Engineering, University of Kiel (Germany); Lima de Miranda, R. [Inorganic Functional Materials, Institute for Materials Science, Faculty of Engineering, University of Kiel (Germany); ACQUANDAS GmbH, Kiel (Germany); Quandt, E. [Inorganic Functional Materials, Institute for Materials Science, Faculty of Engineering, University of Kiel (Germany); Lutter, G. [Department of Cardiovascular Surgery, University Hospital of Schleswig-Holstein, Kiel (Germany); Selhuber-Unkel, C. [Biocompatible Nanomaterials, Institute for Materials Science, Faculty of Engineering, University of Kiel (Germany)

2016-02-01

Scaffolds for tissue engineering enable the possibility to fabricate and form biomedical implants in vitro, which fulfill special functionality in vivo. In this study, free-standing Nickel–Titanium (NiTi) thin film meshes were produced by means of magnetron sputter deposition. Meshes contained precisely defined rhombic holes in the size of 440 to 1309 μm{sup 2} and a strut width ranging from 5.3 to 9.2 μm. The effective mechanical properties of the microstructured superelastic NiTi thin film were examined by tensile testing. These results will be adapted for the design of the holes in the film. The influence of hole and strut dimensions on the adhesion of sheep autologous cells (CD133 +) was studied after 24 h and after seven days of incubation. Optical analysis using fluorescence microscopy and scanning electron microscopy showed that cell adhesion depends on the structural parameters of the mesh. After 7 days in cell culture a large part of the mesh was covered with aligned fibrous material. Cell adhesion is particularly facilitated on meshes with small rhombic holes of 440 μm{sup 2} and a strut width of 5.3 μm. Our results demonstrate that free-standing NiTi thin film meshes have a promising potential for applications in cardiovascular tissue engineering, particularly for the fabrication of heart valves. - Highlights: • Freestanding NiTi thin film scaffolds were fabricated with magnetron sputtering process. • Effective mechanical properties of NiTi scaffolds can be adapted by the mesh structure parameters. • Cell adhesion on the NiTi thin film scaffold is controlled by the structure parameters of the mesh. • Cells strongly adhere after seven days and form a confluent layer on the mesh.

Cell adhesion on NiTi thin film sputter-deposited meshes

International Nuclear Information System (INIS)

Loger, K.; Engel, A.; Haupt, J.; Li, Q.; Lima de Miranda, R.; Quandt, E.; Lutter, G.; Selhuber-Unkel, C.

2016-01-01

Scaffolds for tissue engineering enable the possibility to fabricate and form biomedical implants in vitro, which fulfill special functionality in vivo. In this study, free-standing Nickel–Titanium (NiTi) thin film meshes were produced by means of magnetron sputter deposition. Meshes contained precisely defined rhombic holes in the size of 440 to 1309 μm 2 and a strut width ranging from 5.3 to 9.2 μm. The effective mechanical properties of the microstructured superelastic NiTi thin film were examined by tensile testing. These results will be adapted for the design of the holes in the film. The influence of hole and strut dimensions on the adhesion of sheep autologous cells (CD133 +) was studied after 24 h and after seven days of incubation. Optical analysis using fluorescence microscopy and scanning electron microscopy showed that cell adhesion depends on the structural parameters of the mesh. After 7 days in cell culture a large part of the mesh was covered with aligned fibrous material. Cell adhesion is particularly facilitated on meshes with small rhombic holes of 440 μm 2 and a strut width of 5.3 μm. Our results demonstrate that free-standing NiTi thin film meshes have a promising potential for applications in cardiovascular tissue engineering, particularly for the fabrication of heart valves. - Highlights: • Freestanding NiTi thin film scaffolds were fabricated with magnetron sputtering process. • Effective mechanical properties of NiTi scaffolds can be adapted by the mesh structure parameters. • Cell adhesion on the NiTi thin film scaffold is controlled by the structure parameters of the mesh. • Cells strongly adhere after seven days and form a confluent layer on the mesh.

Photostress analysis of stress-induced martensite phase transformation in superelastic NiTi

International Nuclear Information System (INIS)

Katanchi, B.; Choupani, N.; Khalil-Allafi, J.; Baghani, M.

2017-01-01

Phase transformation in shape memory alloys is the most important factor in their unique behavior. In this paper, the formation of stress induced martensite phase transformation in a superelastic NiTi (50.8% Ni) shape memory alloy was investigated by using the photo-stress method. First, the material's fabrication procedure has been described and then the material was studied using the metallurgical tests such as differential scanning calorimetry and X-ray diffraction to characterize the material features and the mechanical tensile test to investigate the superelastic behavior. As a new method in observation of the phase transformation, photo-stress pictures showed the formation of stress induced martensite in a superelastic dog-bone specimen during loading and subsequently it's disappearing during unloading. Finally, finite element analysis was implemented using the constitutive equations derived based on the Boyd-Lagoudas phenomenological model.

Photostress analysis of stress-induced martensite phase transformation in superelastic NiTi

Energy Technology Data Exchange (ETDEWEB)

Katanchi, B. [Mechanical Engineering Faculty, Sahand University of Technology, Tabriz (Iran, Islamic Republic of); Choupani, N., E-mail: choupani@sut.ac.ir [Mechanical Engineering Faculty, Sahand University of Technology, Tabriz (Iran, Islamic Republic of); Khalil-Allafi, J. [Research Center for Advance Materials, Faculty of Materials Engineering, Sahand University of Technology, Tabriz (Iran, Islamic Republic of); Baghani, M. [School of Mechanical Engineering, College of Engineering, University of Tehran (Iran, Islamic Republic of)

2017-03-14

Phase transformation in shape memory alloys is the most important factor in their unique behavior. In this paper, the formation of stress induced martensite phase transformation in a superelastic NiTi (50.8% Ni) shape memory alloy was investigated by using the photo-stress method. First, the material's fabrication procedure has been described and then the material was studied using the metallurgical tests such as differential scanning calorimetry and X-ray diffraction to characterize the material features and the mechanical tensile test to investigate the superelastic behavior. As a new method in observation of the phase transformation, photo-stress pictures showed the formation of stress induced martensite in a superelastic dog-bone specimen during loading and subsequently it's disappearing during unloading. Finally, finite element analysis was implemented using the constitutive equations derived based on the Boyd-Lagoudas phenomenological model.

Capability of Sputtered Micro-patterned NiTi Thick Films

Science.gov (United States)

Bechtold, Christoph; Lima de Miranda, Rodrigo; Quandt, Eckhard

2015-09-01

Today, most NiTi devices are manufactured by a combination of conventional metal fabrication steps, e.g., melting, extrusion, cold working, etc., and are subsequently structured by high accuracy laser cutting. This combination has been proven to be very successful; however, there are several limitations to this fabrication route, e.g., in respect to the fabrication of more complex device designs, device miniaturization or the combination of different materials for the integration of further functionality. These issues have to be addressed in order to develop new devices and applications. The fabrication of micro-patterned films using magnetron sputtering, UV lithography, and wet etching has great potential to overcome limitations of conventional device manufacturing. Due to its fabrication characteristics, this method allows the production of devices with complex designs, high structural accuracy, smooth edge profile, at layer thicknesses up to 75 µm. The aim of this study is to present recent developments in the field of NiTi thin film technology, its advantages and limitations, as well as new possible applications in the medical and in non-medical fields. These developments include among others NiTi scaffold structures covered with NiTi membranes for their potential use as filters, heart valve components or aneurysm treatments, as well as micro-actuators for consumable electronics or automotive applications.

Improvements of anti-corrosion and mechanical properties of NiTi orthopedic materials by acetylene, nitrogen and oxygen plasma immersion ion implantation

International Nuclear Information System (INIS)

Poon, Ray W.Y.; Ho, Joan P.Y.; Liu Xuanyong; Chung, C.Y.; Chu, Paul K.; Yeung, Kelvin W.K.; Lu, William W.; Cheung, Kenneth M.C.

2005-01-01

Nickel-titanium shape memory alloys (NiTi) are useful materials in orthopedics and orthodontics due to their unique super-elasticity and shape memory effects. However, the problem associated with the release of harmful Ni ions to human tissues and fluids has been raising safety concern. Hence, it is necessary to produce a surface barrier to impede the out-diffusion of Ni ions from the materials. We have conducted acetylene, nitrogen and oxygen plasma immersion ion implantation (PIII) into NiTi alloys in an attempt to improve the surface properties. All the implanted and annealed samples surfaces exhibit outstanding corrosion and Ni out-diffusion resistance. Besides, the implanted layers are mechanically stronger than the substrate underneath. XPS analyses disclose that the layer formed by C 2 H 2 PIII is composed of mainly TiC x with increasing Ti to C concentration ratios towards the bulk. The nitrogen PIII layer is observed to be TiN, whereas the oxygen PIII layer is composed of oxides of Ti 4+ , Ti 3+ and Ti 2+

Simultaneous electropolishing and electrodeposition of aluminum in ionic liquid under ambient conditions

Science.gov (United States)

Hou, Yuanyuan; Li, Ruiqian; Liang, Jun

2018-03-01

Electrodeposition and electropolishing of aluminum are achieved simultaneously in the ionic liquid composed of anhydrous aluminum chloride and trimethylamine hydrochloride. With the protection of a hydrocarbon layer, the process can be carried out under ambient atmosphere. As a result, a smooth mirror-like surface with the roughness only several nanometers is obtained on the anode Al and a uniform Al coating with the thickness about 5 μm is covered on the cathode. Importantly, this work presents the recycling of Al resource in a closed system.

Behaviour of smart reinforced concrete beam with super elastic shape memory alloy subjected to monotonic loading

Science.gov (United States)

Hamid, Nubailah Abd; Ibrahim, Azmi; Adnan, Azlan; Ismail, Muhammad Hussain

2018-05-01

This paper discusses the superelastic behavior of shape memory alloy, NiTi when used as reinforcement in concrete beams. The ability of NiTi to recover and reduce permanent deformations of concrete beams was investigated. Small-scale concrete beams, with NiTi reinforcement were experimentally investigated under monotonic loads. The behaviour of simply supported reinforced concrete (RC) beams hybrid with NiTi rebars and the control beam subject to monotonic loads were experimentally investigated. This paper is to highlight the ability of the SMA bars to recover and reduce permanent deformations of concrete flexural members. The size of the control beam is 125 mm × 270 mm × 1000 mm with 3 numbers of 12 mm diameter bars as main reinforcement for compression and 3 numbers of 12 mm bars as tension or hanger bars while 6 mm diameter at 100 mm c/c used as shear reinforcement bars for control beam respectively. While, the minimal provision of 200mm using the 12.7mm of superelastic Shape Memory Alloys were employed to replace the steel rebar at the critical region of the beam. In conclusion, the contribution of the SMA bar in combination with high-strength steel to the conventional reinforcement showed that the SMA beam has exhibited an improve performance in term of better crack recovery and deformation. Therefore the usage of hybrid NiTi with the steel can substantially diminish the risk of the earthquake and also can reduce the associated cost aftermath.

Low Temperature Creep of Hot-Extruded Near-Stoichiometric NiTi Shape Memory Alloy. Part I; Isothermal Creep

Science.gov (United States)

Raj, S. V.; Noebe, R. D.

2013-01-01

This two-part paper is the first published report on the long term, low temperature creep of hot-extruded near-stoichiometric NiTi. Constant load tensile creep tests were conducted on hot-extruded near-stoichiometric NiTi at 300, 373 and 473 K under initial applied stresses varying between 200 and 350 MPa as long as 15 months. These temperatures corresponded to the martensitic, two-phase and austenitic phase regions, respectively. Normal primary creep lasting several months was observed under all conditions indicating dislocation activity. Although steady-state creep was not observed under these conditions, the estimated creep rates varied between 10(exp -10) and 10(exp -9)/s. The creep behavior of the two phases showed significant differences. The martensitic phase exhibited a large strain on loading followed by a primary creep region accumulating a small amount of strain over a period of several months. The loading strain was attributed to the detwinning of the martensitic phase whereas the subsequent strain accumulation was attributed to dislocation glide-controlled creep. An "incubation period" was observed before the occurrence of detwinning. In contrast, the austenitic phase exhibited a relatively smaller loading strain followed by a primary creep region, where the creep strain continued to increase over several months. It is concluded that the creep of the austenitic phase occurs by a dislocation glide-controlled creep mechanism as well as by the nucleation and growth of deformation twins.

Pattern formation during electropolishing

International Nuclear Information System (INIS)

Yuzhakov, V.V.; Chang, H.; Miller, A.E.

1997-01-01

Using atomic force microscopy, we find that the surface morphology of a dissolving aluminum anode in a commercial electropolishing electrolyte can exhibit both highly regular and randomly packed stripe and hexagonal patterns with amplitudes of about 5 nm and wavelengths of 100 nm. The driving instability of this pattern formation phenomenon is proposed to be the preferential adsorption of polar or polarizable organic molecules on surface ridges where the contorted double layer produces a higher electric potential gradient. The enhanced relative coverage shields the anode and induces a smaller dissolution rate at the ridges. The instability is balanced by surface diffusion of the adsorbate to yield a length scale of 4π(D s /k d ) 1/2 , where D s is the surface diffusivity and k d is the desorption coefficient of the adsorbate, which correlates well with the measured wavelength. A long-wavelength expansion of the double-layer field yields an interface evolution equation that reproduces all of the observed patterns. In particular, bifurcation analysis and numerical simulation yield a single voltage-dependent dimensionless parameter ξ that measures a balance between smoothing of adsorbate concentration by electric-field-dependent surface diffusion and fluctuation due to interfacial curvature and stretching. Randomly oriented stripes are favored at large ξ (low voltage), while random hills dominate at small ξ (high voltage) with perfectly periodic stripes and hexagonal hill patterns within a small window near ξ=1. These predictions are in qualitative and quantitative agreement with our measurements. copyright 1997 The American Physical Society

Corrosion Control of Alloy 690 by Shot Peening and Electropolishing under Simulated Primary Water Condition of PWRs

Directory of Open Access Journals (Sweden)

Kyung Mo Kim

2015-01-01

Full Text Available This work clarifies the effect of surface modifications on the corrosion rate of Alloy 690, a nickel-based alloy for steam generator tubes, under the simulated test conditions of the primary water chemistry in nuclear power plants. The surface stress was modified by the shot peening and electropolishing methods. The shot peening treatment was applied using ceramic beads with different intensities by varying the air pressure and projection angle. The corrosion rate was evaluated by gravimetric analysis and the surface was analyzed by scanning electron microscopy (SEM. The corrosion rate of Alloy 690 was evaluated from the influence of the stress state on the metal surface. Based on the observation of the surface after the corrosion test, the oxide composition and its structure were affected by the surface modifications. The corrosion behavior of Alloy 690 was distinguished by the shot peening intensity on the surface, and additional electropolishing was effective at reducing the dissolution of nickel ions from the metal surface.

Effects of surface finish and mechanical training on Ni-Ti sheets for elastocaloric cooling

DEFF Research Database (Denmark)

Engelbrecht, Kurt; Tusek, Jaka; Sanna, Simone

2016-01-01

Elastocaloric cooling has emerged as a promising alternative to vapor compression in recent years. Although the technology has the potential to be more efficient than current technologies, there are many technical challenges that must be overcome to realize devices with high performance...... and acceptable durability. We study the effects of surface finish and training techniques on dog bone shaped polycrystalline samples of NiTi. The fatigue life of several samples with four different surface finishes was measured and it was shown that a smooth surface, especially at the edges, greatly improved...

The microscopic origin of self-organized nanostripe pattern formation on an electropolished aluminium surface

International Nuclear Information System (INIS)

Sarkar, Jaya; Basumallick, A; Khan, Gobinda Gopal

2009-01-01

By correlating the experimental evidence obtained from atomic force microscopy, conventional x-ray diffraction, and a surface sensitive modified x-ray diffraction technique with the results of density functional theory based computations, we demonstrate that self-organized nanostripe patterns formed on the electropolished surface of aluminium originate as a consequence of relaxation and reconstruction of the new surfaces exposed and textural changes at the surface caused by the dissolution during polishing.

Textural Evolution During Micro Direct Metal Deposition of NiTi Alloy

Science.gov (United States)

Khademzadeh, Saeed; Bariani, Paolo F.; Bruschi, Stefania

2018-03-01

In this research, a micro direct metal deposition process, newly developed as a potential method for micro additive manufacturing was used to fabricate NiTi builds. The effect of scanning strategy on grain growth and textural evolution was investigated using scanning electron microscope equipped with electron backscattered diffraction detector. Investigations showed that, the angle between the successive single tracks has an important role in grain size distribution and textural evolution of NiTi phase. Unidirectional laser beam scanning pattern developed a fiber texture; conversely, a backward and forward scanning pattern developed a strong ‖‖ RD texture on the surface of NiTi cubic samples produced by micro direct metal deposition.

Release of metal ions from round and rectangular NiTi wires

Directory of Open Access Journals (Sweden)

Arash Azizi

2016-04-01

Full Text Available Abstract Background The aim of this study was to evaluate the amount of nickel and titanium ions released from two wires with different shapes and a similar surface area. Methods Forty round nickel-titanium (NiTi arch wires with the diameter of 0.020 in. and 40 rectangular NiTi arch wires with the diameter of 0.016 × 0.016 in. were immersed in artificial saliva during a 21-day period. The surface area of both wires was 0.44 in.2. Wires were separately dipped into polypropylene tubes containing 50 ml of buffer solution and were incubated and maintained at 37 °C. Inductively coupled plasma atomic emission spectrometry (ICP-AES was used to measure the amount of ions released after exposure lengths of 1 h, 24 h, 1 week, and 3 weeks. Repeated measures ANOVA and Tukey tests were used to evaluate the data. Results The results indicated that the amount of nickel and titanium concentrations was significantly higher in the rectangular wire group. The most significant release of all metals was measured after the first hour of immersion. In the rectangular wire group, 243 ± 4.2 ng/ml of nickel was released after 1 h, while 221.4 ± 1.7 ng/ml of nickel was released in the round wire group. Similarly, 243.3 ± 2.8 ng/ml of titanium was released in the rectangular wire group and a significantly lower amount of 211.9 ± 2.3 ng/ml of titanium was released in the round wire group. Conclusions Release of metal ions was influenced by the shape of the wire and increase of time.

Electromagnetic heating of a shape memory alloy translator

Science.gov (United States)

Giroux, E.-A.; Maglione, M.; Gueldry, A.; Mantoux, J.-L.

1996-03-01

The active part of a linear translator is a shape memory alloy (SMA) made of nickel and titanium (NiTi) wire which is to be thermally cycled. We have achieved heating using electromagnetic radiation with a magnetic sheath and low-frequency waves at 8 kHz and without magnetic sheath and radio frequency waves at 28 MHz. The heating is equivalent for these two arrangements. In vitro experiments have been confirmed by computer simulations of the radiation distribution within the implant. We thus show that electromagnetic radiation could specifically heat a NiTi wire inside a stainless steel tube without heating the tube. An application could be a femoral prosthesis for the lengthening of the bone.

Macroscopic electrical field distribution and field-induced surface stresses of needle-shaped field emitters

Energy Technology Data Exchange (ETDEWEB)

Moy, Charles K.S., E-mail: charles.moy@sydney.edu.au [Australian Centre for Microscopy and Microanalysis, The University of Sydney, Sydney, NSW 2006 (Australia); ARC Centre of Excellence for Design in Light Metals, The University of Sydney, Sydney, NSW 2006 (Australia); School of Civil Engineering, The University of Sydney, Sydney, NSW 2006 (Australia); Ranzi, Gianluca [ARC Centre of Excellence for Design in Light Metals, The University of Sydney, Sydney, NSW 2006 (Australia); School of Civil Engineering, The University of Sydney, Sydney, NSW 2006 (Australia); Petersen, Timothy C. [Australian Centre for Microscopy and Microanalysis, The University of Sydney, Sydney, NSW 2006 (Australia); Ringer, Simon P. [Australian Centre for Microscopy and Microanalysis, The University of Sydney, Sydney, NSW 2006 (Australia); ARC Centre of Excellence for Design in Light Metals, The University of Sydney, Sydney, NSW 2006 (Australia)

2011-05-15

One major concern since the development of the field ion microscope is the mechanical strength of the specimens. The macroscopic shape of the imaging tip greatly influences field-induced stresses and there is merit in further study of this phenomenon from a classical perspective. Understanding the geometrical, as opposed to localized electronic, factors that affect the stress might improve the quality and success rate of atom probe experiments. This study uses macroscopic electrostatic principles and finite element modelling to investigate field-induced stresses in relation to the shape of the tip. Three two-dimensional idealized models are considered, namely hyperbolic, parabolic and sphere-on-orthogonal-cone; the shapes of which are compared to experimental tips prepared by electro-polishing. Three dimensional morphologies of both a nano-porous and single-crystal aluminium tip are measured using electron tomography to quantitatively test the assumption of cylindrical symmetry for electro-polished tips. The porous tip was prepared and studied to demonstrate a fragile specimen for which such finite element studies could determine potential mechanical failure, prior to any exhaustive atom probe investigation. -- Research highlights: {yields} We use electrostatic principles and finite element to model field-induced stresses. {yields} We study two-dimensional idealized needle-shaped field emitters. {yields} Stress distribution of hyperbolic, parabolic and sphere-on-orthogonal-cone tips mapped. {yields} Electron tomography to obtain the morphology of three-dimensional aluminium tips. {yields} Studies of the morphology of the porous tip demonstrate a fragile specimen.

In Vivo Force Decay of Niti Closed Coil Springs

Science.gov (United States)

Cox, Crystal; Nguyen, Tung; Koroluk, Lorne; Ko, Ching-Chang

2014-01-01

Introduction Nickel-titanium (NiTi) closed coil springs are purported to deliver constant forces over extended ranges of activation and working times. In vivo studies supporting this claim are limited. The objective of this study is to evaluate changes in force decay properties of NiTi closed coil springs after clinical use. Methods Pseudoelastic force-deflection curves for 30 NiTi coil springs (used intra-orally) and 15 matched laboratory control springs (simulated intra-oral conditions - artificial saliva, 37°C) were tested pre- and post-retrieval via Dynamic Mechanical Analysis (DMA) and the Instron machine, respectively, to evaluate amount of force loss and hysteresis change following 4, 8, or 12 weeks of working time (n=10 per group). Effect of the oral environment and clinical use on force properties were evaluated by comparing in vivo and in vitro data. Results The springs studied showed a statistically significant decrease in force (~12%) following 4 weeks of clinical use (pspace closure at an average rate of 0.91mm per month was still observed despite this decrease in force. In vivo and in vitro force loss data were not statistically different. Conclusions NiTi closed coil springs do not deliver constant forces when used intra-orally, but they still allow for space closure rates of ~1mm/month. PMID:24703289

Atomic layer-deposited Al.sub.2./sub.O.sub.3./sub. coatings on NiTi alloy

Czech Academy of Sciences Publication Activity Database

Kei, C.C.; Yu, Y.S.; Racek, Jan; Vokoun, David; Šittner, Petr

2014-01-01

Roč. 23, č. 7 (2014), s. 2641-2649 ISSN 1059-9495. [International Conference on Shape Memory and Superelastic Technologies (SMST 2013). Praha, 21.05.2013-24.05.2013] R&D Projects: GA ČR(CZ) GA101/09/0702; GA MŠk(CZ) 7E11058 EU Projects: European Commission(XE) 262806 - SmartNets Institutional support: RVO:68378271 Keywords : ALD * Al 2 O 3 coating * corrosion * NiTi Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 0.998, year: 2014

Development and assessment of two decontamination processes: closed electropolishing system for decontamination of underwater surfaces -vibratory decontamination with abrasives

International Nuclear Information System (INIS)

Benavides, E.; Fajardo, M.

1992-01-01

Two decontamination processes have been developed to decontaminate the stainless steel components of nuclear power plants. The first process uses an underwater closed electropolishing system for the decontamination of large stainless steel surfaces in flooded systems without loss of electrolyte. Large underwater contaminated areas can be treated with an electropolishing head covering an area of 2 m 2 in one step. The decontamination factors achieved with this technique range between 100 and 1000. The second process consists in the decontamination of nuclear components using vibratory equipment with self-cleaning abrasives generating a minimum quantity of waste. This technique may reach contamination factors similar to those obtained with other abrasive methods (brush abrasion, abrasive blasting, etc...). The obtained decontamination factors range between 5 and 50. Only a small quantity of waste is generated, which is treated and reduced in volume by filtration and evaporation

Pseudo-creep in Shape Memory Alloy Wires and Sheets

Science.gov (United States)

Russalian, V. R.; Bhattacharyya, A.

2017-10-01

Interruption of loading during reorientation and isothermal pseudoelasticity in shape memory alloys with a strain arrest ( i.e., holding strain constant) results in a time-dependent evolution in stress or with a stress arrest ( i.e., holding stress constant) results in a time-dependent evolution in strain. This phenomenon, which we term as pseudo-creep, is similar to what was reported in the literature three decades ago for some traditional metallic materials undergoing plastic deformation. In a previous communication, we reported strain arrest of isothermal pseudoelastic loading, isothermal pseudoelastic unloading, and reorientation in NiTi wires as well as a rate-independent phase diagram. In this paper, we provide experimental results of the pseudo-creep phenomenon during stress arrest of isothermal pseudoelasticity and reorientation in NiTi wires as well as strain arrest of isothermal pseudoelasticity and reorientation in NiTi sheets. Stress arrest in NiTi wires accompanied by strain accumulation or recovery is studied using the technique of multi-video extensometry. The experimental results were used to estimate the amount of mechanical energy needed to evolve the wire from one microstructural state to another during isothermal pseudoelastic deformation and the difference in energies between the initial and the final rest state between which the aforementioned evolution has occurred.

Improved Functional Properties and Efficiencies of Nitinol Wires Under High-Performance Shape Memory Effect (HP-SME)

Science.gov (United States)

Casati, R.; Saghafi, F.; Biffi, C. A.; Vedani, M.; Tuissi, A.

2017-10-01

Martensitic Ti-rich NiTi intermetallics are broadly used in various cyclic applications as actuators, which exploit the shape memory effect (SME). Recently, a new approach for exploiting austenitic Ni-rich NiTi shape memory alloys as actuators was proposed and named high-performance shape memory effect (HP-SME). HP-SME is based on thermal recovery of de-twinned martensite produced by mechanical loading of the parent phase. The aim of the manuscript consists in evaluating and comparing the fatigue and actuation properties of austenitic HP-SME wires and conventional martensitic SME wires. The effect of the thermomechanical cycling on the actuation response and the changes in the electrical resistivity of both shape memory materials were studied by performing the actuation tests at different stages of the fatigue life. Finally, the changes in the transition temperatures before and after cycling were also investigated by differential calorimetric tests.

NiTi Alloys: New Materials that enable Shockproof, Corrosion Immune Bearings

Science.gov (United States)

DellaCorte, Christopher

2017-01-01

Though steel is the dominant material of choice for mechanical components (bearings and gears) it has intrinsic limitations related to corrosion and plastic deformation. In contrast, dimensionally stable nickel-rich Ni-Ti alloys, such as Nitinol 60, are intrinsically rustproof and can withstand high contact loads without damage (denting). Over the last decade, focused RD to exploit these alloys for new applications has revealed the science behind NiTi's remarkable properties. In this presentation, the state-of-the-art of nickel-rich NiTi alloys will be introduced along with a discussion of how NASA is adopting this new technology inside the space station water recycling system as a pathfinder for more down-to-earth tribological challenges.

Selective laser melting of Ni-rich NiTi: selection of process parameters and the superelastic response

Science.gov (United States)

Shayesteh Moghaddam, Narges; Saedi, Soheil; Amerinatanzi, Amirhesam; Saghaian, Ehsan; Jahadakbar, Ahmadreza; Karaca, Haluk; Elahinia, Mohammad

2018-03-01

Material and mechanical properties of NiTi shape memory alloys strongly depend on the fabrication process parameters and the resulting microstructure. In selective laser melting, the combination of parameters such as laser power, scanning speed, and hatch spacing determine the microstructural defects, grain size and texture. Therefore, processing parameters can be adjusted to tailor the microstructure and mechanical response of the alloy. In this work, NiTi samples were fabricated using Ni50.8Ti (at.%) powder via SLM PXM by Phenix/3D Systems and the effects of processing parameters were systematically studied. The relationship between the processing parameters and superelastic properties were investigated thoroughly. It will be shown that energy density is not the only parameter that governs the material response. It will be shown that hatch spacing is the dominant factor to tailor the superelastic response. It will be revealed that with the selection of right process parameters, perfect superelasticity with recoverable strains of up to 5.6% can be observed in the as-fabricated condition.

New decontamination techniques: chemical gels, electropolishing and abrasives

International Nuclear Information System (INIS)

Brunel, G.; Gauchon, J.P.; Kervegant, Y.; Josso, F.

1991-01-01

The decommissioning of nuclear installations requires decontamination techniques that are efficient, simple to apply and producing a small amount of wastes, which are easy to process. With a view to this, three decontamination methods, which appear to be particularly suited to decommissioning, have been studied. These three methods are: - spraying of gels carrying chemical decontaminating agents, - electropolishing with a swab device, - abrasives blasting. After parametric tests on non-radioactive and active samples, the industrial application of these methods in the dismantling of installations was studied. These industrial applications concern: - decontamination of pieces coming from the German BWR ISAR by immersion and gel spraying, - decontamination, mainly by gel spraying, and dismantling of the BRENNILIS bituminisation plant, - decontamination of part of the cooling circuit of the graphite gas reactor G2 by gel spraying, - decontamination of a component of the FBR SuperPhenix, using dry abrasives blasting. During the first three applications, generated secondary wastes volume and form were determined. 33 tabs., 16 figs., 12 refs

Effects of Fluoride on NiTi Orthodontic Archwires: An X-ray Diffraction Study

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Sumit Kumar Yadav

2013-01-01

Results: Unloading force values of NiTi orthodontic wires were significantly decreased after exposure to both fluoride solutions (p < 0.001. Corrosive changes in surface topography were observed for both fluoride solutions. Wires exposed to acidic fluoride appeared as more severely affected. X-ray diffraction analysis showed no change in crystal lattice of NiTi wires in both solutions. Conclusion: The results suggest that using topical fluoride agents with NiTi wire could decrease the functional unloading mechanical properties of the wire and contribute to prolonged orthodontic treatment.

Shape memory behavior of single and polycrystalline nickel rich nickel titanium alloys

Science.gov (United States)

Kaya, Irfan

NiTi is the most commonly used shape memory alloy (SMA) and has been widely used for bio-medical, electrical and mechanical applications. Nickel rich NiTi shape memory alloys are coming into prominence due to their distinct superelasticity and shape memory properties as compared to near equi-atomic NiTi shape memory alloys. Besides, their lower density and higher work output than steels makes these alloys an excellent candidate for aerospace and automotive industry. Shape memory properties and phase transformation behavior of high Ni-rich Ni54Ti46 (at.%) polycrystals and Ni-rich Ni 51Ti49 (at.%) single-crystals are determined. Their properties are sensitive to heat treatments that affect the phase transformation behavior of these alloys. Phase transformation properties and microstructure were investigated in aged Ni54Ti46 alloys with differential scanning calorimetry (DSC) and transmission electron microscopy (TEM) to reveal the precipitation characteristics and R-phase formation. It was found that Ni54Ti46 has the ability to exhibit perfect superelasticity under high stress levels (~2 GPa) with 4% total strain after 550°C-3h aging. Stress independent R-phase transformation was found to be responsible for the change in shape memory behavior with stress. The shape memory responses of [001], [011] and [111] oriented Ni 51Ti49 single-crystals alloy were reported under compression to reveal the orientation dependence of their shape memory behavior. It has been found that transformation strain, temperatures and hysteresis, Classius-Clapeyron slopes, critical stress for plastic deformation are highly orientation dependent. The effects of precipitation formation and compressive loading at selected temperatures on the two-way shape memory effect (TWSME) properties of a [111]- oriented Ni51Ti49 shape memory alloy were revealed. Additionally, aligned Ni4Ti3 precipitates were formed in a single crystal of Ni51Ti49 alloy by aging under applied compression stress along the

Anti-corrosion performance of oxidized and oxygen plasma-implanted NiTi alloys

International Nuclear Information System (INIS)

Poon, Ray W.Y.; Ho, Joan P.Y.; Liu, Xuanyong; Chung, C.Y.; Chu, Paul K.; Yeung, Kelvin W.K.; Lu, William W.; Cheung, Kenneth M.C.

2005-01-01

Nickel-titanium shape memory alloys are useful orthopedic biomaterials on account of its super-elastic and shape memory properties. However, the problem associated with out-diffusion of harmful nickel ions in prolonged use inside the human body raises a critical safety concern. Titanium oxide films are deemed to be chemically inert and biocompatible and hence suitable to be the barrier layers to impede the leaching of Ni from the NiTi substrate to biological tissues and fluids. In the work reported in this paper, we compare the anti-corrosion efficacy of oxide films produced by atmospheric-pressure oxidation and oxygen plasma ion implantation. Our results show that the oxidized samples do not possess improved corrosion resistance and may even fare worse than the untreated samples. On the other hand, the plasma-implanted surfaces exhibit much improved corrosion resistance. Our work also shows that post-implantation annealing can further promote the anti-corrosion capability of the samples

The effect of heating rate on the surface chemistry of NiTi.

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Undisz, Andreas; Hanke, Robert; Freiberg, Katharina E; Hoffmann, Volker; Rettenmayr, Markus

2014-11-01

The impact of the heating rate on the Ni content at the surface of the oxide layer of biomedical NiTi is explored. Heat treatment emulating common shape-setting procedures was performed by means of conventional and inductive heating for similar annealing time and temperature, applying various heating rates from ~0.25 K s(-1) to 250 K s(-1). A glow discharge optical emission spectroscopy method was established and employed to evaluate concentration profiles of Ni, Ti and O in the near-surface region at high resolution. The Ni content at the surface of the differently treated samples varies significantly, with maximum surface Ni concentrations of ~20 at.% at the lowest and ~1.5 at.% at the highest heating rate, i.e. the total amount of Ni contained in the surface region of the oxide layer decreases by >15 times. Consequently, the heating rate is a determinant for the biomedical characteristics of NiTi, especially since Ni available at the surface of the oxide layer may affect the hemocompatibility and be released promptly after surgical application of a respective implant. Furthermore, apparently contradictory results presented in the literature reporting surface Ni concentrations of ~3 at.% to >20 at.% after heat treatment are consistently explained considering the ascertained effect of the heating rate. Copyright © 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

The effect of TiO2 coating on biological NiTi alloys after micro-arc oxidation treatment for corrosion resistance.

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Sukuroglu, Ebru Emine; Sukuroglu, Suleyman; Akar, Kubra; Totik, Yasar; Efeoglu, Ihsan; Arslan, Ersin

2017-08-01

NiTi alloys exhibit good properties, such as shape memory behavior, high corrosion resistant, having the closest elasticity modulus of a human bone and superior biocompatibility properties. However, the surface problems that arise during the use of this alloy limit the usage in the industry and health sector. In recent years, micro-arc oxidation method is used to improve the surface properties and increase the usage of these alloys. In this study, the TiO 2 coatings were deposited on the NiTi substrates. The surface topography, morphology, crystallographic structure, and thickness of the coatings were determined using scanning electron microscopy and X-ray diffraction. The corrosion properties were investigated using potentiostat test unit in two different media such as NaCl solution and simulated body fluid. The results show that the coated samples have higher corrosion resistance than uncoated samples in the two different media.

Safety and efficacy of the NiTi Shape Memory Compression Anastomosis Ring (CAR/ColonRing) for end-to-end compression anastomosis in anterior resection or low anterior resection.

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Kang, Jeonghyun; Park, Min Geun; Hur, Hyuk; Min, Byung Soh; Lee, Kang Young; Kim, Nam Kyu

2013-04-01

Compression anastomoses may represent an improvement over traditional hand-sewn or stapled techniques. This prospective exploratory study aimed to assess the efficacy and complication rates in patients undergoing anterior resection (AR) or low anterior resection (LAR) anastomosed with a novel end-to-end compression anastomosis ring, the ColonRing. In all, 20 patients (13 male) undergoing AR or LAR were enrolled to be anastomosed using the NiTi Shape Memory End-to-End Compression Anastomosis Ring (NiTi Medical Technologies Ltd, Netanya, Israel). Demographic, intraoperative, and postoperative data were collected. Patients underwent AR (11/20) or LAR using laparoscopy (75%), robotic (10%) surgery, or an open laparotomy (15%) approach, with a median anastomotic level of 14.5 cm (range, 4-25 cm). Defunctioning loop ileostomies were formed in 6 patients for low anastomoses. Surgeons rated the ColonRing device as either easy or very easy to use. One patient developed an anastomotic leakage in the early postoperative period; there were no late postoperative complications. Mean time to passage of first flatus and commencement of oral fluids was 2.5 days and 3.2 days, respectively. Average hospital stay was 12.6 days (range, 8-23 days). Finally, the device was expelled on average 15.3 days postoperatively without difficulty. This is the first study reporting results in a significant number of LAR patients and the first reported experience from South Korea; it shows that the compression technique is surgically feasible, easy to use, and without significant complication rates. A large randomized controlled trial is warranted to investigate the benefits of the ColonRing over traditional stapling techniques.

Superelastic NiTi memory alloy micro-tube under tension - nucleation and propagation of martensite band

International Nuclear Information System (INIS)

Li, Z.Q.; Sun, Q.P.

2000-01-01

The superelastic behavior of polycrystalline NiTi shape memory alloy micro-tube under tension is studied experimentally. The nominal stress-strain curve of the micro-tube is recorded. By using a special surface coating it is found that the deformation of the tube is via the nucleation and propagation of stress-induced martensite band. The experiments show that the martensite nucleates in the form of a spiral lens-shaped narrow band that is inclined at 61 to the axis of loading when the stress reaches the peak of stress-strain curve. The width and the length of the band grew gradually with increase of loading and finally joined and merged into a single band. The subsequent deformation of the tube is realized by the propagation of this cylindrical martensite band. (orig.)

Low-Pressure and Low-Temperature Hydriding-Pulverization-Dehydriding Method for Producing Shape Memory Alloy Powders

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Murguia, Silvia Briseño; Clauser, Arielle; Dunn, Heather; Fisher, Wendy; Snir, Yoav; Brennan, Raymond E.; Young, Marcus L.

2018-04-01

Shape memory alloys (SMAs) are of high interest as active, adaptive "smart" materials for applications such as sensors and actuators due to their unique properties, including the shape memory effect and pseudoelasticity. Binary NiTi SMAs have shown the most desirable properties, and consequently have generated the most commercial success. A major challenge for SMAs, in particular, is their well-known compositional sensitivity. Therefore, it is critical to control the powder composition and morphology. In this study, a low-pressure, low-temperature hydriding-pulverization-dehydriding method for preparing well-controlled compositions, size, and size distributions of SMA powders from wires is presented. Starting with three different diameters of as-drawn martensitic NiTi SMA wires, pre-alloyed NiTi powders of various well-controlled sizes are produced by hydrogen charging the wires in a heated H3PO4 solution. After hydrogen charging for different charging times, the wires are pulverized and subsequently dehydrided. The wires and the resulting powders are characterized using scanning electron microscopy, differential scanning calorimetry, and X-ray diffraction. The relationship between the wire diameter and powder size is investigated as a function of hydrogen charging time. The rate of diameter reduction after hydrogen charging of wire is also examined. Finally, the recovery behavior due to the shape memory effect is investigated after dehydriding.

Evaluation of the lower incisor inclination during alignment and leveling using superelastic NiTi archwires: a laboratory study

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Carolina Baratieri

2012-06-01

Full Text Available OBJECTIVE: The aim of this laboratory study is to evaluate the influence of the shape and the length limitation of superelastic nickel-titanium (NiTi archwires on lower incisors inclination during alignment and leveling. METHODS: Metal teeth mounted on a typodont articulator device were used to simulate a malocclusion of the mandibular arch (-3.5 mm model discrepancy. Three different shapes (Standard, Accuform and Ideal of superelastic NiTi archwires (Sentalloy, GAC, USA were tested. Specimens were divided in two groups: Group I, with no limitation of the archwire length; and Group II, with distal limitation. Each group had thirty specimens divided into three subgroups differentiated by the archwire shape. All groups used round wires with diameters of 0.014-in, 0.016-in, 0.018-in and 0.020-in. The recording of all intervals was accomplished using standardized digital photographs with orthogonal norm in relation to median sagittal plane. The buccolingual inclination of the incisor was registered using photographs and software CorelDraw. RESULTS: The results were obtained using ANOVA and Tukey's test at a significant level of 5%. The inclination of the lower incisor increased in both groups and subgroups. The shape of the archwire had statistically significant influence only in Group I - Standard (11.76º, Ideal (5.88º and Accuform (1.93º. Analyzing the influence of the length limitation, despite the mean incisor tipping in Group II (3.91º had been smaller than Group I (6.52º, no statistically significant difference was found, except for Standard, 3.89º with limitation and 11.76º without limitation. The greatest incisor tipping occurred with the 0.014-in archwires.

Effect of nano-hydroxyapatite reinforcement in mechanically alloyed NiTi composites for biomedical implant

International Nuclear Information System (INIS)

Akmal, Muhammad; Raza, Ahmad; Khan, Muhammad Mudasser; Khan, M. Imran; Hussain, Muhammad Asif

2016-01-01

Equi-atomic NiTi alloy composites reinforced with 0, 2, 4 and 6 vol.% nano-hydroxyapatite (HA) were successfully synthesized using pressureless sintering. Pure Ni and Ti elements were ball milled for 10 h in order to produce a mechanically alloyed equi-atomic NiTi alloy (MA-NiTi). Mechanically alloyed NiTi and HA powders were blended, compacted and then sintered for 3 h at 1325 K. The sintered density varied inversely with volume percent of HA reinforcement. The X-Ray diffraction spectra and SEM images showed the formation of multiple phases like NiTi, NiTi 2 , Ni 3 Ti, and Ni 4 Ti 3 . The back scattered-SEM image analysis confirmed the presence of Ni-rich and Ti-rich phases with increasing HA content. The 6 vol.% HA reinforced composite showed Ni 3 Ti as the major phase having the highest hardness value which can be attributed to the presence of relatively harder phases along with higher HA content as a reinforcement. The composite of MA-NiTi with 2 vol.% HA manifested the most desirable results in the form of better sintering density mainly due to the minute decomposition of NiTi into other phases. Therefore, the 2 vol.% reinforced MA-NiTi composite can be exploited as a novel material for manufacturing biomedical implants. - Highlights: • NiTi-HA composites were synthesized using powder metallurgy route. • New phases such as NiTi 2 , Ni 3 Ti and Ni 4 Ti 3 were observed for sintered composites. • Mechanical properties enhanced with the increasing content of HA and new phases. • No martensitic transformation was observed for all composites by DSC analysis. • 2 vol.% HA composite is a novel candidate for biomedical implants.

Polymer Hydrogel/Polybutadiene/Iron Oxide Nanoparticle Hybrid Actuators for the Characterization of NiTi Implants

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Aleksandra Jeličić

2009-03-01

Full Text Available One of the main issues with the use of nickel titanium alloy (NiTi implants in cardiovascular implants (stents is that these devices must be of very high quality in order to avoid subsequent operations due to failing stents. For small stents with diameters below ca. 2 mm, however, stent characterization is not straightforward. One of the main problems is that there are virtually no methods to characterize the interior of the NiTi tubes used for fabrication of these tiny stents. The current paper reports on a robust hybrid actuator for the characterization of NiTi tubes prior to stent fabrication. The method is based on a polymer/hydrogel/magnetic nanoparticle hybrid material and allows for the determination of the inner diameter at virtually all places in the raw NiTi tubes. Knowledge of the inner structure of the raw NiTi tubes is crucial to avoid regions that are not hollow or regions that are likely to fail due to defects inside the raw tube. The actuator enables close contact of a magnetic polymer film with the inner NiTi tube surface. The magnetic signal can be detected from outside and be used for a direct mapping of the tube interior. As a result, it is possible to detect critical regions prior to expensive and slow stent fabrication processes.

A comparison of nickel-titanium rotary instruments manufactured using different methods and cross-sectional areas: ability to resist cyclic fatigue.

Science.gov (United States)

Oh, So-Ram; Chang, Seok-Woo; Lee, Yoon; Gu, Yu; Son, Won-Jun; Lee, Woocheol; Baek, Seung-Ho; Bae, Kwang-Shik; Choi, Gi-Woon; Lim, Sang-Min; Kum, Kee-Yeon

2010-04-01

This study examined the effect of the manufacturing methods (ground, electropolished, and twisted) and the cross-sectional area (CSA) of nickel-titanium (NiTi) rotary instruments on their cyclic fatigue resistance. A total of 80 NiTi rotary instruments (ISO 25/.06 taper) from 4 brands (K3, ProFile, RaCe, and TF) were rotated in a simulated root canal with pecking motion until fracture. The number of cycles to failure (NCF) was calculated. The CSA at 3 mm from the tip of new instruments of each brand was calculated. The correlation between the CSA and NCF was evaluated. All fractured surfaces were analyzed using a scanning electron microscope to determine the fracture mode. The TF instruments were the most resistant to fatigue failure. The resistance to cyclic failure increased with decreasing CSA. All fractured surfaces showed the coexistence of ductile and brittle properties. The CSA had a significant effect on the fatigue resistance of NiTi rotary instruments. Copyright 2010 Mosby, Inc. All rights reserved.

The Characterization of Thin Film Nickel Titanium Shape Memory Alloys

Science.gov (United States)

Harris Odum, Nicole Latrice

Shape memory alloys (SMA) are able to recover their original shape through the appropriate heat or stress exposure after enduring mechanical deformation at a low temperature. Numerous alloy systems have been discovered which produce this unique feature like TiNb, AgCd, NiAl, NiTi, and CuZnAl. Since their discovery, bulk scale SMAs have undergone extensive material property investigations and are employed in real world applications. However, its thin film counterparts have been modestly investigated and applied. Researchers have introduced numerous theoretical microelectromechanical system (MEMS) devices; yet, the research community's overall unfamiliarity with the thin film properties has delayed growth in this area. In addition, it has been difficult to outline efficient thin film processing techniques. In this dissertation, NiTi thin film processing and characterization techniques will be outlined and discussed. NiTi thin films---1 mum thick---were produced using sputter deposition techniques. Substrate bound thin films were deposited to analysis the surface using Scanning Electron Microscopy; the film composition was obtained using Energy Dispersive Spectroscopy; the phases were identified using X-ray diffraction; and the transformation temperatures acquired using resistivity testing. Microfabrication processing and sputter deposition were employed to develop tensile membranes for membrane deflection experimentation to gain insight on the mechanical properties of the thin films. The incorporation of these findings will aid in the movement of SMA microactuation devices from theory to fruition and greatly benefit industries such as medicinal and aeronautical.

A comparative study of the cytotoxicity and corrosion resistance of nickel-titanium and titanium-niobium shape memory alloys.

Science.gov (United States)

McMahon, Rebecca E; Ma, Ji; Verkhoturov, Stanislav V; Munoz-Pinto, Dany; Karaman, Ibrahim; Rubitschek, Felix; Maier, Hans J; Hahn, Mariah S

2012-07-01

Nickel-titanium (NiTi) shape memory alloys (SMAs) are commonly used in a range of biomedical applications. However, concerns exist regarding their use in certain biomedical scenarios due to the known toxicity of Ni and conflicting reports of NiTi corrosion resistance, particularly under dynamic loading. Titanium-niobium (TiNb) SMAs have recently been proposed as an alternative to NiTi SMAs due to the biocompatibility of both constituents, the ability of both Ti and Nb to form protective surface oxides, and their superior workability. However, several properties critical to the use of TiNb SMAs in biomedical applications have not been systematically explored in comparison with NiTi SMAs. These properties include cytocompatibility, corrosion resistance, and alterations in alloy surface composition in response to prolonged exposure to physiological solutions. Therefore, the goal of the present work was to comparatively investigate these aspects of NiTi (49.2 at.% Ti) and TiNb (26 at.% Nb) SMAs. The results from the current studies indicate that TiNb SMAs are less cytotoxic than NiTi SMAs, at least under static culture conditions. This increased TiNb cytocompatibility was correlated with reduced ion release as well as with increased corrosion resistance according to potentio-dynamic tests. Measurements of the surface composition of samples exposed to cell culture medium further supported the reduced ion release observed from TiNb relative to NiTi SMAs. Alloy composition depth profiles also suggested the formation of calcium phosphate deposits within the surface oxide layers of medium-exposed NiTi but not of TiNb. Collectively, the present results indicate that TiNb SMAs may be promising alternatives to NiTi for certain biomedical applications. Copyright © 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Surface Modification of NiTi Alloy via Cathodic Plasma Electrolytic Deposition and its Effect on Ni Ion Release and Osteoblast Behaviors

International Nuclear Information System (INIS)

Yan Ying; Cai Kaiyong; Yang Weihu; Liu Peng

2013-01-01

To reduce Ni ion release and improve biocompatibility of NiTi alloy, the cathodic plasma electrolytic deposition (CPED) technique was used to fabricate ceramic coating onto a NiTi alloy surface. The formation of a coating with a rough and micro-textured surface was confirmed by X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy, respectively. An inductively coupled plasma mass spectrometry test showed that the formed coating significantly reduced the release of Ni ions from the NiTi alloy in simulated body fluid. The influence of CPED treated NiTi substrates on the biological behaviors of osteoblasts, including cell adhesion, cell viability, and osteogenic differentiation function (alkaline phosphatase), was investigated in vitro. Immunofluorescence staining of nuclei revealed that the CPED treated NiTi alloy was favorable for cell growth. Osteoblasts on CPED modified NiTi alloy showed greater cell viability than those for the native NiTi substrate after 4 and 7 days cultures. More importantly, osteoblasts cultured onto a modified NiTi sample displayed significantly higher differentiation levels of alkaline phosphatase. The results suggested that surface functionalization of NiTi alloy with ceramic coating via the CPED technique was beneficial for cell proliferation and differentiation. The approach presented here is useful for NiTi implants to enhance bone osteointegration and reduce Ni ion release in vitro

Surface Modification of NiTi Alloy via Cathodic Plasma Electrolytic Deposition and its Effect on Ni Ion Release and Osteoblast Behaviors

Science.gov (United States)

Yan, Ying; Cai, Kaiyong; Yang, Weihu; Liu, Peng

2013-07-01

To reduce Ni ion release and improve biocompatibility of NiTi alloy, the cathodic plasma electrolytic deposition (CPED) technique was used to fabricate ceramic coating onto a NiTi alloy surface. The formation of a coating with a rough and micro-textured surface was confirmed by X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy, respectively. An inductively coupled plasma mass spectrometry test showed that the formed coating significantly reduced the release of Ni ions from the NiTi alloy in simulated body fluid. The influence of CPED treated NiTi substrates on the biological behaviors of osteoblasts, including cell adhesion, cell viability, and osteogenic differentiation function (alkaline phosphatase), was investigated in vitro. Immunofluorescence staining of nuclei revealed that the CPED treated NiTi alloy was favorable for cell growth. Osteoblasts on CPED modified NiTi alloy showed greater cell viability than those for the native NiTi substrate after 4 and 7 days cultures. More importantly, osteoblasts cultured onto a modified NiTi sample displayed significantly higher differentiation levels of alkaline phosphatase. The results suggested that surface functionalization of NiTi alloy with ceramic coating via the CPED technique was beneficial for cell proliferation and differentiation. The approach presented here is useful for NiTi implants to enhance bone osseointegration and reduce Ni ion release in vitro.

Estudio de polvos y recubrimientos metaestables de NiTi obtenidos por proyección térmica de plasma

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Cano, I. G.

2008-06-01

Full Text Available NiTi intermetallic is widely known for its shape memory effect and pseudoelasticity. Due to its high corrosion resístanse (biocompatibility, most of the studies carried out deal with its use for medical applications. With regard to surface technologies, many reported investigations focus on Vacuum Thermal Spray to provide NiTi coatings with minimal oxide content.The Thermal Spray Center has attempted to obtain metastable NiTi powders and coatings by means of Atmospheric Plasma Spraying with a liquid nitrogen cooling system. Starting from two different Ni-45wt%Ti feedstock powders. One powder is a blend of Ti and Ni particles, whereas the other has been alloyed by gas atomization. Both powders were sprayed obtaining better results starting from the gas atomized powder resulting in a final deposit where NiTi was the main phase with minimal oxidation. Different spraying parameters were tested and microstructural characterization was performed by SEM-EDS. XRD patterns showed some peak broadening; that seems to be produced by structural metastability of the coatings.

El compuesto intermetálico de NiTi es conocido por su capacidad de memoria de forma así como por su pseudoelasticidad. Debido, además, a su alta resistencia a corrosión (biocompatiblidad, la gran mayoría de estudios se centran en su uso para aplicaciones médicas. Dentro del conjunto de las tecnologías de superficie, las investigaciones actuales utilizan la técnica de Proyección Térmica de Plasma al Vacío para producir recubrimientos de NiTi con contenidos mínimos de porosidad y de óxidos.El Centro de Proyección Térmica se planteó como objetivo la obtención de polvos y recubrimientos metaestables de NiTi a través de la técnica de Proyección de Plasma acoplado a un sistema de refrigeración con nitrógeno líquido. Se estudiaron dos polvos con diferentes características, pero de la misma composición nominal (Ni-45 % peso Ti. Uno de ellos, es el resultado de

Effect of temperature on the orthodontic clinical applications of niti closed-coil springs

Science.gov (United States)

Espinar-Escalona, Eduardo; Llamas-Carreras, José M.; Barrera-Mora, José M.; Abalos-Lasbrucci, Camilo

2013-01-01

NiTi spring coils were used to obtain large deformation under a constant force. The device consists on a NiTi coil spring, superelastic at body temperature, in order to have a stress plateau during the austenitic retransformation during the unloading. The temperature variations induced changes in the spring force. Objectives: The aim of this study is to investigate the effect of the temperature variations in the spring forces and corrosion behaviour simulating the ingestion hot/cold drinks and food. Study Design: The springs were subjected to a tensile force using universal testing machine MTS-Adamel (100 N load cell). All tests were performed in artificial saliva maintained at different temperatures. The corrosion tests were performed according to the ISO-standard 10993-15:2000. Results: The increase in temperature of 18oC induced an increase in the spring force of 30%. However, when the temperature returns to 37oC the distraction force recovers near the initial level. After cooling down the spring to 15oC, the force decreased by 46%. This investigation show as the temperature increase, the corrosion potential shifts towards negative values and the corrosion density is rising. Conclusions: The changes of the temperatures do not modify the superelastic behaviour of the NiTi closed-coil springs. The corrosion potential of NiTi in artificial saliva is decreasing by the rise of the temperatures. Key words:Superelasticity, NiTi, springs, orthodontic, coils, recovery, temperature. PMID:23722142

Effect of electropolishing on vacuum furnace design

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Sutanwi Lahiri

2015-03-01

Full Text Available The use of thermal shields of materials having low emissivity in vacuum furnaces is well-known. However, the surface condition of the heat shields is one of the most important factors governing their efficiency as radiation resistances. The emissivity of the thermal shields dictates the power rating of the heaters in furnace design. The unpolished materials used in the heater tests showed poor performance leading to loss of a signi­ficant percentage of the input power. The present work deals with the refur­bishment of the radiation heat shields used in a furnace for heating graphite structure. The effect of refurbishment of the heat shields by the buffing and subsequently electro­polishing was found to improve the performance of the shields as heat reflectors. The com­position of the electrolyte was chosen in such a way that the large shields of Mo, Inconel and SS can be polished using the same reagents in different ratios. The present work deals with the development of a standard electropolishing procedure for large metallic sheets and subsequently qualifying them by roughness and emissivity measure­ments. The improvement noted in the shielding efficiency of the furnace in the subsequent runs is also discussed here.

A Constitutive Model for Superelastic Shape Memory Alloys Considering the Influence of Strain Rate

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Hui Qian

2013-01-01

Full Text Available Shape memory alloys (SMAs are a relatively new class of functional materials, exhibiting special thermomechanical behaviors, such as shape memory effect and superelasticity, which enable their applications in seismic engineering as energy dissipation devices. This paper investigates the properties of superelastic NiTi shape memory alloys, emphasizing the influence of strain rate on superelastic behavior under various strain amplitudes by cyclic tensile tests. A novel constitutive equation based on Graesser and Cozzarelli’s model is proposed to describe the strain-rate-dependent hysteretic behavior of superelastic SMAs at different strain levels. A stress variable including the influence of strain rate is introduced into Graesser and Cozzarelli’s model. To verify the effectiveness of the proposed constitutive equation, experiments on superelastic NiTi wires with different strain rates and strain levels are conducted. Numerical simulation results based on the proposed constitutive equation and experimental results are in good agreement. The findings in this paper will assist the future design of superelastic SMA-based energy dissipation devices for seismic protection of structures.

Orthodontic buccal tooth movement by nickel-free titanium-based shape memory and superelastic alloy wire.

Science.gov (United States)

Suzuki, Akihiro; Kanetaka, Hiroyasu; Shimizu, Yoshinaka; Tomizuka, Ryo; Hosoda, Hideki; Miyazaki, Shuichi; Okuno, Osamu; Igarashi, Kaoru; Mitani, Hideo

2006-11-01

To examine the mechanical properties and the usefulness of titanium-niobium-aluminum (Ti-Nb-Al) wire in orthodontic tooth movement as compared with nickel-titanium (Ni-Ti) wire. The load deflection of expansion springs was gauged with an original jig. The gradient of the superelastic region was measured during the unloading process. Expansion springs comprising the two types of alloy wires were applied to upper first molars of rats. The distance between the first molars was measured with micrometer calipers. The force magnitude of the Ti-Nb-Al expansion spring was lower than that of the Ni-Ti expansion spring over the entire deflection range. The initial force magnitude and the gradient in the superelastic region of the Ti-Nb-Al expansion springs were half those of the Ni-Ti expansion springs. Thus, Ti-Nb-Al expansion springs generated lighter and more continuous force. Tooth movement in the Ni-Ti group proceeded in a stepwise fashion. On the other hand, tooth movement in the Ti-Nb-Al group showed relatively smooth and continuous progression. At 17 days after insertion of expansion springs, there were no significant differences between the Ti-Nb-Al and Ni-Ti groups in the amount of tooth movement. These results indicate that Ti-Nb-Al wire has excellent mechanical properties for smooth, continuous tooth movement and suggest that Ti-Nb-Al wire may be used as a practical nickel-free shape memory and superelastic alloy wire for orthodontic treatment as a substitute for Ni-Ti wire.

A micro-computed tomographic evaluation of dentinal microcrack alterations during root canal preparation using single-file Ni-Ti systems.

Science.gov (United States)

Li, Mei-Lin; Liao, Wei-Li; Cai, Hua-Xiong

2018-01-01

The aim of the present study was to evaluate the length of dentinal microcracks observed prior to and following root canal preparation with different single-file nickel-titanium (Ni-Ti) systems using micro-computed tomography (micro-CT) analysis. A total of 80 mesial roots of mandibular first molars presenting with type II Vertucci canal configurations were scanned at an isotropic resolution of 7.4 µm. The samples were randomly assigned into four groups (n=20 per group) according to the system used for root canal preparation, including the WaveOne (WO), OneShape (OS), Reciproc (RE) and control groups. A second micro-CT scan was conducted after the root canals were prepared with size 25 instruments. Pre- and postoperative cross-section images of the roots (n=237,760) were then screened to identify the lengths of the microcracks. The results indicated that the microcrack lengths were notably increased following root canal preparation (Pfiles. Among the single-file Ni-Ti systems, WO and RE were not observed to cause notable microcracks, while the OS system resulted in evident microcracks.

Anisotropic microstructure and superelasticity of additive manufactured NiTi alloy bulk builds using laser directed energy deposition

Energy Technology Data Exchange (ETDEWEB)

Bimber, Beth A. [Department of Engineering Science and Mechanics, The Pennsylvania State University, 212 Earth-Engineering Sciences Building, University Park, PA 16802 (United States); Hamilton, Reginald F., E-mail: rfh13@psu.edu [Department of Engineering Science and Mechanics, The Pennsylvania State University, 212 Earth-Engineering Sciences Building, University Park, PA 16802 (United States); Keist, Jayme; Palmer, Todd A. [Applied Research Laboratory, The Pennsylvania State University, State College, PA 16804 (United States)

2016-09-30

The microstructure and superelasticity in additive manufactured NiTi shape memory alloys (SMAs) were investigated. Using elementally blended Ni and Ti powder feedstock, Ni-rich build coupons were fabricated via the laser-based directed energy deposition (LDED) technique. The build volumes were large enough to extract tensile and compressive test specimens from selected locations for spatially resolving microconstituents and the underlying stress-induced martensitic phase transformation (SIMT) morphology. In the as-deposited condition, X-ray diffraction identified the B2 atomic crystal structure of the austenitic parent phase in NiTi SMAs, and Ni{sub 4}Ti{sub 3} precipitates were the predominant microconstituent identified through scanning electron microscopy. The microstructure exhibited anisotropy, which was characterized by the Ni{sub 4}Ti{sub 3} precipitate morphology being coarsest nearest the substrate, while a finer morphology was observed farthest from the substrate. In-situ full-field deformation measurements calculated using digital image correlation confirmed that the SIMT predominately occurred in the finer precipitate morphology. Heat treatment reduced the degree of anisotropy, and DIC analysis revealed localized SIMT strains increased compared to the as-deposited condition.

Impaired bacterial attachment to light activated Ni-Ti alloy

International Nuclear Information System (INIS)

Chrzanowski, Wojciech; Valappil, Sabeel P.; Dunnill, Charles W.; Abou Neel, Ensanya A.; Lee, Kevin; Parkin, Ivan P.; Wilson, Michael; Armitage, David A.; Knowles, Jonathan C.

2010-01-01

Ni-Ti alloy due to its unique mechanical properties, is used for many types of implants. Failure of these implants can be attributed to many different factors; however infections are a common problem. In this paper, the attachment of the bacteria, Staphylococcus aureus, to the Ni-Ti surface modified by a range of processes with and without of light activation (used to elicit antimicrobial properties of materials) was assessed and related to different surface characteristics. Before the light activation the number of bacterial colony forming units was the greatest for the samples thermally oxidised at 600 deg. C. This sample and the spark oxidised samples showed the highest photocatalytic activity but only the thermally oxidised samples at 600 deg. C showed a significant drop of S. aureus attachment. The findings in this study indicate that light activation and treating samples at 600 deg. C is a promising method for Ni-Ti implant applications with inherent antimicrobial properties. Light activation was shown to be an effective way to trigger photocatalytic reactions on samples covered with relatively thick titanium dioxide via accumulation of photons in the surface and a possible increase in defects which may result in free oxygen. Moreover, light activation caused an increase in the total surface energy.

Experimental characterization of shape memory alloy actuator cables

Science.gov (United States)

Biggs, Daniel B.; Shaw, John A.

2016-04-01

Wire rope (or cables) are a fundamental structural element in many engineering applications. Recently, there has been growing interest in stranding NiTi wires into cables to scale up the adaptive properties of NiTi tension elements and to make use of the desirable properties of wire rope. Exploratory experiments were performed to study the actuation behavior of two NiTi shape memory alloy cables and straight monofilament wire of the same material. The specimens were held under various dead loads ranging from 50 MPa to 400 MPa and thermally cycled 25 times from 140°C to 5°C at a rate of 12°C/min. Performance metrics of actuation stroke, residual strain, and work output were measured and compared between specimen types. The 7x7 cable exhibited similar actuation to the single straight wire, but with slightly longer stroke and marginally more shakedown, while maintaining equivalent specific work output. This leads to the conclusion that the 7x7 cable effectively scaled up the adaptive properties the straight wire. Under loads below 150 MPa, the 1x27 cable had up to double the actuation stroke and work output, but exhibited larger shakedown and poorer performance when loaded higher.

Shape memory effect and superelasticity of titanium nickelide alloys implanted with high ion doses

International Nuclear Information System (INIS)

Pogrebnjak, A D; Bratushka, S N; Beresnev, V M; Levintant-Zayonts, N

2013-01-01

The state of the art in ion implantation of superelastic NiTi shape memory alloys is analyzed. Various technological applications of the shape memory effect are outlined. The principles and techiques of ion implantation are described. Specific features of its application for modification of surface layers in surface engineering are considered. Key properties of shape memory alloys and problems in utilization of ion implantation to improve the surface properties of shape memory alloys, such as corrosion resistance, friction coefficient, wear resistance, etc. are discussed. The bibliography includes 162 references

Do Mechanical and Physicochemical Properties of Orthodontic NiTi Wires Remain Stable In Vivo?

Directory of Open Access Journals (Sweden)

Michał Sarul

2016-01-01

Full Text Available Introduction and Aim. Exceptional properties of the NiTi archwires may be jeopardized by the oral cavity; thus its long-term effect on the mechanical and physiochemical properties of NiTi archwires was the aim of work. Material and Methods. Study group comprised sixty 0.016 × 0.022 NiTi archwires from the same manufacturer evaluated (group A after the first 12 weeks of orthodontic treatment. 30 mm long pieces cut off from each wire prior to insertion formed the control group B. Obeying the strict rules of randomization, all samples were subjected to microscopic evaluation and nanoindentation test. Results. Both groups displayed substantial presence of nonmetallic inclusions. Heterogeneity of the structure and its alteration after usage were found in groups B and A, respectively. Conclusions. Long-term, reliable prediction of biomechanics of NiTi wires in vivo is impossible, especially new archwires from the same vendor display different physiochemical properties. Moreover, manufacturers have to decrease contamination in the production process in order to minimize risk of mutual negative influence of nickel-titanium archwires and oral environment.

Endodontic Shaping Performance Using Nickel–Titanium Hand and Motor ProTaper Systems by Novice Dental Students

OpenAIRE

Tu, Ming-Gene; Chen, San-Yue; Huang, Heng-Li; Tsai, Chi-Cheng

2008-01-01

Preparing a continuous tapering conical shape and maintaining the original shape of a canal are obligatory in root canal preparation. The purpose of this study was to compare the shaping performance in simulated curved canal resin blocks of the same novice dental students using hand-prepared and engine-driven nickel–titanium (NiTi) rotary ProTaper instruments in an endodontic laboratory class. Methods: Twenty-three fourth-year dental students attending China Medical University Dental Schoo...

Shape memory alloys

International Nuclear Information System (INIS)

Kaszuwara, W.

2004-01-01

Shape memory alloys (SMA), when deformed, have the ability of returning, in certain circumstances, to their initial shape. Deformations related to this phenomenon are for polycrystals 1-8% and up to 15% for monocrystals. The deformation energy is in the range of 10 6 - 10 7 J/m 3 . The deformation is caused by martensitic transformation in the material. Shape memory alloys exhibit one directional or two directional shape memory effect as well as pseudoelastic effect. Shape change is activated by temperature change, which limits working frequency of SMA to 10 2 Hz. Other group of alloys exhibit magnetic shape memory effect. In these alloys martensitic transformation is triggered by magnetic field, thus their working frequency can be higher. Composites containing shape memory alloys can also be used as shape memory materials (applied in vibration damping devices). Another group of composite materials is called heterostructures, in which SMA alloys are incorporated in a form of thin layers The heterostructures can be used as microactuators in microelectromechanical systems (MEMS). Basic SMA comprise: Ni-Ti, Cu (Cu-Zn,Cu-Al, Cu-Sn) and Fe (Fe-Mn, Fe-Cr-Ni) alloys. Shape memory alloys find applications in such areas: automatics, safety and medical devices and many domestic appliances. Currently the most important appears to be research on magnetic shape memory materials and high temperature SMA. Vital from application point of view are composite materials especially those containing several intelligent materials. (author)

Surface characterization of Nb samples electropolished with real superconducting rf accelerator cavities

Directory of Open Access Journals (Sweden)

Xin Zhao

2010-12-01

Full Text Available We report the results of surface characterizations of niobium (Nb samples electropolished together with a single cell superconducting radio-frequency accelerator cavity. These witness samples were located in three regions of the cavity, namely at the equator, the iris, and the beam pipe. Auger electron spectroscopy was utilized to probe the chemical composition of the topmost four atomic layers. Scanning electron microscopy with energy dispersive x ray for elemental analysis was used to observe the surface topography and chemical composition at the micrometer scale. A few atomic layers of sulfur (S were found covering the samples nonuniformly. Niobium oxide granules with a sharp geometry were observed on every sample. Some Nb-O granules appeared to also contain sulfur.

Civil Engineering Applications: Specific Properties of NiTi Thick Wires and Their Damping Capabilities, A Review

Science.gov (United States)

Torra, Vicenç; Martorell, Ferran; Lovey, Francisco C.; Sade, Marcos Leonel

2017-12-01

This study describes two investigations: first, the applicability of NiTi wires in the damping of oscillations induced by wind, rain, or traffic in cable-stayed bridges; and second, the characteristic properties of NiTi, i.e., the effects of wire diameter and particularly the effects of summer and winter temperatures and strain-aging actions on the hysteretic behavior. NiTi wires are mainly of interest because of their high number of available working cycles, reliable results, long service lifetime, and ease in obtaining sets of similar wires from the manufacturer.

Stress Relaxation Of Superelastic Shape Memory Alloy Under Bending And Torsional Load

Directory of Open Access Journals (Sweden)

Sakib Tanvir

2017-04-01

Full Text Available Stress Relaxation of Superelastic Shape memory NiTi Alloy under bending and torsion is uncommon in literature. Therefore experimental set up has been devised and test results are obtained for superelastic SMA.Unlike the other common engineering materials superelastic SMA it gives dramatic reduction in stress. In this paper therefore results of stress relaxation of superelastic shape memory alloy under bending and torsion are presented graphically and interpreted in terms of stress induced martensitic transformation.

60NiTi Intermetallic Material Evaluation for Lightweight and Corrosion Resistant Spherical Sliding Bearings for Aerospace Applications

Science.gov (United States)

DellaCorte, Christopher; Jefferson, Michael

2015-01-01

NASA Glenn Research Center and the Kamatics subsidiary of the Kaman Corporation conducted the experimental evaluation of spherical sliding bearings made with 60NiTi inner races. The goal of the project was to assess the feasibility of manufacturing lightweight, corrosion resistant bearings utilizing 60NiTi for aerospace and industrial applications. NASA produced the bearings in collaboration with Abbott Ball Corporation and Kamatics fabricated bearing assemblies utilizing their standard reinforced polymer liner material. The assembled bearings were tested in oscillatory motion at a load of 4.54kN (10,000 lb), according to the requirements of the plain bearing specification SAE AS81820. Several test bearings were exposed to hydraulic fluid or aircraft deicing fluid prior to and during testing. The results show that the 60NiTi bearings exhibit tribological performance comparable to conventional stainless steel (440C) bearings. Further, exposure of 60NiTi bearings to the contaminant fluids had no apparent performance effect. It is concluded that 60NiTi is a feasible bearing material for aerospace and industrial spherical bearing applications.

Automated detection of a prostate Ni-Ti stent in electronic portal images

OpenAIRE

Carl, Jesper; Nielsen, Henning; Nielsen, Jane; Lund, Bente; Larsen, Erik Hoejkjaer

2006-01-01

  Udgivelsesdato: DEC  Planning target volumes (PTV) in fractionated radiotherapy still have to be outlined with wide margins to the clinical target volume due to uncertainties arising from daily shift of the prostate position. A recently proposed new method of visualization of the prostate is based on insertion of a thermo-expandable Ni-Ti stent. The current study proposes a new detection algorithm for automated detection of the Ni-Ti stent in electronic portal images. The algorithm is ba...

[Properties of NiTi wires with direct electric resistance heat treatment method in three-point bending tests].

Science.gov (United States)

Wang, Hong-mei; Wang, Bang-kang; Ren, Chao-chao; Bai, Yu-xing

2011-03-01

To investigate the mechanical properties of Ni-Ti wires with direct electric resistance heat treatment (DERHT) method in three-point bending tests. Two superelastic Ni-Ti wires (wire A: Smart SE, wire B: SENTALLOY SE, 0.406 mm × 0.559 mm) and 2 heat-actived Ni-Ti wires (wire C: Smart SM, wire D: L&H TITAN, 0.406 mm × 0.559 mm) were selected. They were heat-treated using the DERHT method by a controlled electric current (6.36 A) applied for different period of time [0 (control), 1.0, 1.5, 2.0, 2.5 seconds). Then, a three-point bending test was performed under controlled temperature (37°C) to examine the relationships between the deflection and the load in the bending of wires. After DERHT treatment, the plateau in the force-deflection curve of superelastic Ni-Ti wires and heat-activated Ni-Ti wires were increased. When the wires were heated for 2.0 seconds and deflected to 1.5 mm, the loading force of A, B, C and D Ni-Ti wires increased from (3.85 ± 0.11), (3.62 ± 0.07), (3.28 ± 0.09), (2.91 ± 0.23) N to (4.33 ± 0.07), (4.07 ± 0.05), (4.52 ± 0.08), (3.27 ± 0.15) N respectively. DERHT method is very convenient for clinical use. It is possible to change the arch form and superelastic force of NiTi wires. The longer the heating time is, the more the superelastic characteristics of the wires are altered.

Electrodeposition of milligram amounts of uranium on electropolished stainless steel disks

International Nuclear Information System (INIS)

Aggarwal, S.K.; Shah, P.M.; Duggal, R.K.; Jain, H.C.

1991-01-01

Investigations have been carried out for the electrodeposition of milligram amounts of uranium on electropolished stainless steel disks with an objective of preparing good quality sources for α-spectrometric studies on uranium. The parameters studied include the vatiation of electrodeposition yield as a function of voltage, time, distance between the cathode and anode, and the volume of 0.2M ammonium oxalate solution. The conditions selected for preparing good quality sources with nearly 100% yield were: electrodeposition voltage 25 V, time of deposition 15 min, volume of 0.2M ammonium oxalate solution in the cell 4 ml and a distance of 2 cm between the cathode and anode. The sources prepared using this method have been used successfully for the α-spectrometric determination of 234 U/ 238 U ratios in uranium samples. (author) 6 refs.; 4 figs

Annealing to Mitigate Pitting in Electropolished Niobium Coupons and SRF Cavities

Energy Technology Data Exchange (ETDEWEB)

Cooley, L.D.; Hahn, E.; Hicks, D.; Romanenko, A.; Schuessler, R.; Thompson, C.; /Fermilab

2011-06-08

Ongoing studies at Fermilab investigate whether dislocations and other factors instigate pitting during cavity electropolishing (EP), despite careful processing controls and the inherent leveling mechanism of EP itself. Here, cold-worked niobium coupons, which exhibited increased tendencies for pitting in our past study, were annealed in a high vacuum furnace and subsequently processed by EP. Laser confocal scanning microscopy and special defect counting algorithms were used to assess the population of pits formed. Hardness measurements indicated that annealing for 2 hours at 800 C produced recovery, whereas annealing for 12 hours at 600 C did not, as is consistent with known changes for cavities annealed in a similar way. The 800 C anneal was effective in some cases but not others, and we discuss reasons why tendencies for pitting remain. We discuss implications for cavities and continued work to understand pitting.

Characterization of NiTi shape memory alloys using dual kriging interpolation

International Nuclear Information System (INIS)

Trochu, F.; Sacepe, N.; Volkov, O.; Turenne, S.

1999-01-01

A large number of industrial applications could benefit from the remarkable properties of shape memory alloys (SMA). The development of a general material law is the first important step before reliable design calculations of shape memory devices can be carried out. This paper presents a new phenomenological constitutive law based on dual kriging, which is a powerful mathematical tool used here as interpolation method to simulate the macroscopic mechanical behavior of shape memory alloys. From a set of experimental strain-temperature curves at constant loads, two deformation surfaces are constructed in the stress, strain and temperature space which describe the cooling and heating behaviors of the material for any stress. The response of a specimen subjected to complex thermomechanical loading can be calculated by dual kriging form a general 3-dimensional parametric solid constructed inside the hysteretic domain delimited by the main cooling and heating deformation surfaces. This approach presents the advantage of yielding immediately the explicit equation of any partial cycle inside the main hysteretic domain, thus yielding a general material law for shape memory alloys. Preliminary validation for a set of simple examples demonstrates the potential of this new model that includes in a single formulation superelasticity, rubber-like behavior and shape memory effect. (orig.)

Physical characterisation of endodontic instruments in NiTi alloy

International Nuclear Information System (INIS)

Torrisi, L.

2000-01-01

NiTi based endodontic instruments are investigated in functionality and wear. The instrument surfaces have been studied applying Auger electron spectroscopy, mechanical analysis, differential-scanning calorimetry, wear tests, and scanning electron microscopy. (orig.)

Thermo-Mechanical Behavior and Shakedown of Shape Memory Alloy Cable Structures

Science.gov (United States)

Biggs, Daniel B.

Shape memory alloys (SMAs) are a versatile class of smart materials that exhibit adaptive properties which have been applied to solve engineering problems in wide-ranging fields from aerospace to biomedical engineering. Yet there is a lack of understanding of the fundamental nature of SMAs in order to effectively apply them to challenging problems within these engineering fields. Stranding fine NiTi wires into a cable form satisfies the demands of many aerospace and civil engineering applications which require actuators to withstand large tensile loads. The impact of increased bending and twisting in stranded NiTi wire structures, as well as introducing contact mechanics to the unstable phase transformation is not well understood, and this work aims to fill that void. To study the scalability of NiTi cables, thermo-mechanical characterization tests are conducted on cables much larger than those previously tested. These cables are found to have good superelastic properties and repeatable cyclic behavior with minimal induced plasticity. The behavior of additional cables, which have higher transition temperatures that can be used in a shape memory mode as thermo-responsive, high force actuator elements, are explored. These cables are found to scale up the performance of straight wire by maintaining an equivalent work output. Moreover, this work investigates the degradation of the thermal actuation of SMA wires through novel stress-temperature paths, discovering several path dependent behaviors of transformation-induced plasticity. The local mechanics of NiTi cable structures are explored through experiments utilizing digital image correlation, revealing new periodic transformation instabilities. Finite element simulations are presented, which indicate that the instabilities are caused by friction and relative sliding between wires in a cable. Finally, a study of the convective heat transfer of helical wire involving a suite of wind tunnel experiments, numerical

Internal stresses in steel plate generated by shape memory alloy inserts

International Nuclear Information System (INIS)

Malard, B.; Pilch, J.; Sittner, P.; Davydov, V.; Sedlák, P.; Konstantinidis, K.; Hughes, D.J.

2012-01-01

Graphical abstract: Display Omitted Highlights: ► Thermoresponsive internal stresses introduced into steel by embedding SMA inclusions. ► Neutron strain scanning on steel plate coupons with NiTi inserts at 21 °C and 130 °C. ► Internal stress field in steel evaluated directly from strains and by FE simulation. ► Internal stress generation by SMA insert resistant to thermal and mechanical fatigue. - Abstract: Neutron strain scanning was employed to investigate the internal stress fields in steel plate coupons with embedded prestrained superelastic NiTi shape memory alloy inserts. Strain fields in steel were evaluated at T = 21 °C and 130 °C on virgin coupons as well as on mechanically and thermally fatigued coupons. Internal stress fields were evaluated by direct calculation of principal stress components from the experimentally measured lattice strains as well as by employing an inverse finite element modeling approach. It is shown that if the NiTi inserts are embedded into the elastic steel matrix following a carefully designed technological procedure, the internal stress fields vary with temperature in a reproducible and predictable way. It is estimated that this mechanism of internal stress generation can be safely applied in the temperature range from −20 °C to 150 °C and is relatively resistant to thermal and mechanical fatigue. The predictability and fatigue endurance of the mechanism are of essential importance for the development of future smart metal matrix composites or smart structures with embedded shape memory alloy components.

Rheological study of feed stock for NiTi alloy molded parts

International Nuclear Information System (INIS)

Subuki, I; Abdullah, Z; Razali, R; Ismail, M H

2015-01-01

A rheological behaviour of the powder-binder mixture is one of essential analysis upon to success of Metal Injection Moulding (MIM) process. The purpose of this experimental work is to investigate the rheological behavior of feedstock containing mixtures of elemental Ni and Ti powders mixed with composite binder of palm stearin (PS) and polyethylene (PE) binder system. An equiatomic Ni-Ti (50-50) ratio was used in the present work for all formulations owing to excellent shape memory behaviour. The experimental rheological result indicated that all the feedstocks exhibited pseudo plastic flow behaviour; viscosity decreasing with temperature and shear rate. Increasing the powder loading resulted in higher viscosity, particularly at the low-range of shear rate. Owing to pseudo-plastic flow, it was found that the feedstock prepared exhibit promising rheological properties, thus resulting successfully injection moulding at an optimum temperature of 130°C. (paper)

The amorphous phase transition in irradiated NiTi alloy

International Nuclear Information System (INIS)

Brimhall, J.L.; Kissinger, H.E.; Pelton, A.R.

1985-01-01

Observed supralinear dose dependence for the amorphous transformation during irradiation of NiTi is compatible with a cascade overlap model for heavy ion (2.5 MeV Ni + , 6 MeV Ta +++ ) irradiations. A model based on total defect build-up, however, is necessary to explain the amorphous transition induced by electron irradiation and can also be applied to heavy ion irradiation. The cascade effects in this latter model are manifested by non-uniform defect distribution in the lattice. The defect build-up model requires a high activation energy for interstitial migration which is not incompatible with recent findings. The form of the temperature dependence can also be rationalized using a defect build-up model (amorphous phase transition, heavy-ion irradiation, electron irradiation, NiTi, defect build-up, cascade overlap). (author)

Surface microstructures and corrosion resistance of Ni-Ti-Nb shape memory thin films

Science.gov (United States)

Li, Kun; Li, Yan; Huang, Xu; Gibson, Des; Zheng, Yang; Liu, Jiao; Sun, Lu; Fu, Yong Qing

2017-08-01

Ni-Ti-Nb and Ni-Ti shape memory thin films were sputter-deposited onto silicon substrates and annealed at 600 °C for crystallization. X-ray diffraction (XRD) measurements indicated that all of the annealed Ni-Ti-Nb films were composed of crystalline Ni-Ti (Nb) and Nb-rich grains. X-ray photoelectron spectroscopy (XPS) tests showed that the surfaces of Ni-Ti-Nb films were covered with Ti oxides, NiO and Nb2O5. The corrosion resistance of the Ni-Ti-Nb films in 3.5 wt.% NaCl solution was investigated using electrochemical tests such as open-circuit potential (OCP) and potentio-dynamic polarization tests. Ni-Ti-Nb films showed higher OCPs, higher corrosion potentials (Ecorr) and lower corrosion current densities (icorr) than the binary Ni-Ti film, which indicated a better corrosion resistance. The reason may be that Nb additions modified the passive layer on the film surface. The OCPs of Ni-Ti-Nb films increased with further Nb additions, whereas no apparent difference of Ecorr and icorr was found among the Ni-Ti-Nb films.

Cyclic degradation of antagonistic shape memory actuated structures

International Nuclear Information System (INIS)

Sofla, A Y N; Elzey, D M; Wadley, H N G

2008-01-01

Antagonistic shape memory actuated structures exploit opposing pairs of one-way shape memory alloy (SMA) linear actuators to create devices capable of a fully reversible response. Unlike many conventional reversible SMA devices they do not require bias force components (springs) to return them to their pre-actuated configuration. However, the repeated use of SMA antagonistic devices results in the accumulation of plastic strain in the actuators which can diminish their actuation stroke. We have investigated this phenomenon and the effect of shape memory alloy pre-strain upon it for near equi-atomic NiTi actuators. We find that the degradation eventually stabilizes during cycling. A thermomechanical treatment has been found to significantly reduce degradation in cyclic response of the actuators

Surface microstructures and corrosion resistance of Ni-Ti-Nb shape memory thin films

Energy Technology Data Exchange (ETDEWEB)

Li, Kun [School of Materials Science and Engineering, Beihang University, Beijing 100191 (China); Beijing Key Laboratory for Advanced Functional Materials and Thin Film Technology, Beihang University, Beijing 100191 (China); Faculty of Engineering and Environment, Northumbria University, Newcastle Upon Tyne NE1 8ST (United Kingdom); Li, Yan, E-mail: liyan@buaa.edu.cn [School of Materials Science and Engineering, Beihang University, Beijing 100191 (China); Beijing Key Laboratory for Advanced Functional Materials and Thin Film Technology, Beihang University, Beijing 100191 (China); Huang, Xu [Memry Corporation, Bethel, CT 06801 (United States); Gibson, Des [Institute of Thin Films, Sensors & Imaging, Scottish Universities Physics Alliance, University of the West of Scotland, Paisley PA1 2BE (United Kingdom); Zheng, Yang; Liu, Jiao; Sun, Lu [School of Materials Science and Engineering, Beihang University, Beijing 100191 (China); Beijing Key Laboratory for Advanced Functional Materials and Thin Film Technology, Beihang University, Beijing 100191 (China); Fu, Yong Qing, E-mail: richard.fu@northumbria.ac.uk [Faculty of Engineering and Environment, Northumbria University, Newcastle Upon Tyne NE1 8ST (United Kingdom)

2017-08-31

Highlights: • The corrosion resistance of Ni-Ti-Nb shape memory thin films is investigated. • Modified surface oxide layers improve the corrosion resistance of Ni-Ti-Nb films. • Further Nb additions reduce the potential corrosion tendency of the films. - Abstract: Ni-Ti-Nb and Ni-Ti shape memory thin films were sputter-deposited onto silicon substrates and annealed at 600 °C for crystallization. X-ray diffraction (XRD) measurements indicated that all of the annealed Ni-Ti-Nb films were composed of crystalline Ni-Ti (Nb) and Nb-rich grains. X-ray photoelectron spectroscopy (XPS) tests showed that the surfaces of Ni-Ti-Nb films were covered with Ti oxides, NiO and Nb{sub 2}O{sub 5}. The corrosion resistance of the Ni-Ti-Nb films in 3.5 wt.% NaCl solution was investigated using electrochemical tests such as open-circuit potential (OCP) and potentio-dynamic polarization tests. Ni-Ti-Nb films showed higher OCPs, higher corrosion potentials (E{sub corr}) and lower corrosion current densities (i{sub corr}) than the binary Ni-Ti film, which indicated a better corrosion resistance. The reason may be that Nb additions modified the passive layer on the film surface. The OCPs of Ni-Ti-Nb films increased with further Nb additions, whereas no apparent difference of E{sub corr} and i{sub corr} was found among the Ni-Ti-Nb films.

Cellular Shape Memory Alloy Structures: Experiments & Modeling (Part 1)

Science.gov (United States)

2012-08-01

High -­‐ temperature  SMAs 24 Braze  Joint  between  two  wrought  pieces  of  a  Ni24.5Pd25Ti50.5  HTSMA   (HTSMA  from...process  can  be  used   to  join  other  metal  alloys  and   high -­‐ temperature   SMAs 25 Cellular  Shape  Memory...20 30 40 50 60 910 3 4 8 5 2 T (°C) Shape memory & superelasticity 1 0 e (%) (GPa) 6 7 A NiTi wire

On the widths of the hysteresis of mechanically and thermally induced martensitic transformations in Ni-Ti-based shape memory alloys

Energy Technology Data Exchange (ETDEWEB)

Jaeger, Stefanie; Maass, Burkhard; Frenzel, Jan; Schmidt, Marvin; Ullrich, Johannes; Seelecke, Stefan; Schuetze, Andreas; Kastner, Oliver; Eggeler, Gunther [Bochum Univ. (Germany). Inst. fuer Werkstoffe

2015-10-15

It is well known that a good crystallographic compatibility between austenite and martensite in Ni-Ti-based shape memory alloys results in narrow thermal hystereses (e.g. Ball and James, Arch. Ration. Mech. Anal., 1987). The present work suggests that a good crystallographic fit is moreover associated with a small mechanical hysteresis width, observed during a forward and reverse stress-induced transformation. Furthermore, shape memory alloys with a good crystallographic fit show smaller transformation strains. The results obtained in the present study suggest that these correlations are generic and apply to binary Ni-Ti (with varying Ni contents) and quaternary Ni-Ti-Cu-X (X = Cr, Fe, V) alloys. For binary Ni-Ti, it was observed that Ni-rich compositions (good lattice fit) show a lower accumulation of irreversible strains during pseudoelastic cycling.

Effect of the Addition of 3% Co in NiTi Alloy on Loading/Unloading Force

Science.gov (United States)

Phukaoluan, A.; Dechkunakorn, S.; Anuwongnukroh, N.; Khantachawana, A.; Kaewtathip, P.; Kajornchaiyakul, J.; Wichai, W.

2017-11-01

The study evaluated the loading-unloading force in the load-deflection curve of the fabricated NiTiCo and NiTi wires. Wire alloys with Nickel, Titanium, and Cobalt (purity-99.95%) with atomic weight ratio 47Ni:50Ti:3Co and 50.6Ni:49.4Ti were prepared, sliced, and cold-rolled at 30% reduction, followed by heat treatment in a furnace at 400oC for 1 hour. The specimens of wire size of 0.016 x 0.022 inch2 were cut and subjected to three-point bending test to investigate the load-deflection curve at deflection point 0.25, 0.5, 0.75, 1.0, 1.25, and 1.5 mm. Descriptive statistic was used to evaluate each variables and independent t-test was used to compare between the groups. The results presented a load-deflection curve that resembled a typical superelastic wire. However, significant differences were seen in the loading-unloading forces between the two with an average loading force of 412.53g and 304.98g and unloading force of 292.40g and 208.08g for NiTiCo and NiTi wire, respectively. The force at each deflection point of NiTiCo in loading-unloading force was higher than NiTi wire. This study concluded that the addition of 3%Co in NiTi alloy can increase the loading-unloading force of NiTi wire but were within the range for orthodontic tooth movement.

Outcome of self-expandable metallic stent deployment in patients with malignant gastroduodenal outlet obstruction and Niti-S and WallFlex comparison: a multicenter retrospective clinical study.

Science.gov (United States)

Kato, Hironari; Kawamoto, Hirofumi; Matsumoto, Kazuya; Moriyama, Ichiro; Kamada, Hideki; Tsutsumi, Koichiro; Goto, Daisuke; Fukuba, Nobuhiko; Kato, Kiyohito; Sonoyama, Hiroki; Isomoto, Hajime; Okada, Hiroyuki

2016-08-01

Several studies report on the outcomes of self-expandable metallic stents (SEMSs) deployment for malignant gastric outlet obstruction (GOO). However, data was mostly based on the analysis of single-center studies including only a small number of patients. This study aimed to evaluate clinical outcomes after the deployment of SEMS in patients with malignant GOO and to compare the clinical outcomes of two metallic stents with different designs. Altogether 125 consecutive patients from five institutions were included. Clinical outcomes were evaluated according to technical success, clinical success, stent patency period, survival period and complications. A comparison of clinical outcomes between Niti-S pyloric/duodenal and WallFlex duodenal stents was also undertaken. Rates for clinical and technical success were 100% and 92.0%, respectively. The median stent patency and survival periods were 72.0 days (range 3-775 days) and 75.0 days (range 3-775 days), respectively. The rate of overall adverse events was 28.8%. The rate of stent dysfunction was 16.8%, and that of adverse events, except stent dysfunction was 12.0%. Massive bleeding occurred in two patients as a late complication. The clinical success rate for Niti-S stent was significantly higher than that for WallFlex stent (96.2% vs 84.8%, P = 0.023). We successfully deployed a SEMS in malignant GOO. The selection of a SEMS with a lower axial force may be important for patients to resume the oral food intake. Additionally, consideration must be given to the appropriate management of fatal bleeding as a late complication. © 2016 Chinese Medical Association Shanghai Branch, Chinese Society of Gastroenterology, Renji Hospital Affiliated to Shanghai Jiaotong University School of Medicine and John Wiley & Sons Australia, Ltd.

Surface modification of AISI H13 tool steel by laser cladding with NiTi powder

Science.gov (United States)

Norhafzan, B.; Aqida, S. N.; Chikarakara, E.; Brabazon, D.

2016-04-01

This paper presents laser cladding of NiTi powder on AISI H13 tool steel surface for surface properties enhancement. The cladding process was conducted using Rofin DC-015 diffusion-cooled CO2 laser system with wavelength of 10.6 µm. NiTi powder was pre-placed on H13 tool steel surface. The laser beam was focused with a spot size of 90 µm on the sample surface. Laser parameters were set to 1515 and 1138 W peak power, 18 and 24 % duty cycle and 2300-3500 Hz laser pulse repetition frequency. Hardness properties of the modified layer were characterized by Wilson Hardness tester. Metallographic study and chemical composition were conducted using field emission scanning electron microscope and energy-dispersive X-ray spectrometer (EDXS) analysis. Results showed that hardness of NiTi clad layer increased three times that of the substrate material. The EDXS analysis detected NiTi phase presence in the modified layer up to 9.8 wt%. The metallographic study shows high metallurgical bonding between substrate and modified layer. These findings are significant to both increased hardness and erosion resistance of high-wear-resistant components and elongating their lifetime.

Fatigue of orthodontic nickel-titanium (NiTi) wires in different fluids under constant mechanical stress

International Nuclear Information System (INIS)

Prymak, O.; Klocke, A.; Kahl-Nieke, B.; Epple, M.

2003-01-01

The aim of this study was to analyze in vitro the fatigue resistance of nickel-titanium (NiTi) and CuNiTi orthodontic wires when subjected to forces and fluids which are present intraorally. The wires were subjected to dynamic mechanical analysis (DMA) while they were immersed into different fluids with mechanical loading parameters similar to those that are subjected in the mouth. The characteristic temperatures of transitions and a rough surface structure on the perimeter of the wires were determined by differential scanning calorimetry (DSC) and scanning electron microscopy (SEM), respectively, before and after the DMA experiments. Stainless steel wires were used for comparison. In general, NiTi wires fractured earlier than the stainless steel specimens. Survival times were lower for the NiTi wires when immersed in fluids (water, citric acid, NaCl solution, artificial saliva, and fluoridated artificial saliva) than in air. SEM surface analysis showed that the NiTi and CuNiTi wires had a rougher surface than steel wires. The fracture occurred within a short number of loading cycles. Until fracture occurred, the mechanical properties remained mostly constant

Fatigue of orthodontic nickel-titanium (NiTi) wires in different fluids under constant mechanical stress

Energy Technology Data Exchange (ETDEWEB)

Prymak, O.; Klocke, A.; Kahl-Nieke, B.; Epple, M

2003-07-25

The aim of this study was to analyze in vitro the fatigue resistance of nickel-titanium (NiTi) and CuNiTi orthodontic wires when subjected to forces and fluids which are present intraorally. The wires were subjected to dynamic mechanical analysis (DMA) while they were immersed into different fluids with mechanical loading parameters similar to those that are subjected in the mouth. The characteristic temperatures of transitions and a rough surface structure on the perimeter of the wires were determined by differential scanning calorimetry (DSC) and scanning electron microscopy (SEM), respectively, before and after the DMA experiments. Stainless steel wires were used for comparison. In general, NiTi wires fractured earlier than the stainless steel specimens. Survival times were lower for the NiTi wires when immersed in fluids (water, citric acid, NaCl solution, artificial saliva, and fluoridated artificial saliva) than in air. SEM surface analysis showed that the NiTi and CuNiTi wires had a rougher surface than steel wires. The fracture occurred within a short number of loading cycles. Until fracture occurred, the mechanical properties remained mostly constant.

Enhanced corrosion resistance and hemocompatibility of biomedical NiTi alloy by atmospheric-pressure plasma polymerized fluorine-rich coating

Energy Technology Data Exchange (ETDEWEB)

Li, Penghui; Li, Limin [Department of Physics and Materials Science, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong (China); Wang, Wenhao [Department of Physics and Materials Science, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong (China); Division of Spine Surgery, Department of Orthopaedics and Traumatology, Pokfulam, Hong Kong (China); Jin, Weihong [Department of Physics and Materials Science, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong (China); Liu, Xiangmei [Department of Physics and Materials Science, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong (China); Ministry of Education Key Laboratory for the Green Preparation and Application of Functional Materials, Hubei University, Wuhan, Hubei 430062 (China); Yeung, Kelvin W.K. [Division of Spine Surgery, Department of Orthopaedics and Traumatology, Pokfulam, Hong Kong (China); Chu, Paul K., E-mail: paul.chu@cityu.edu.hk [Department of Physics and Materials Science, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong (China)

2014-04-01

Highlights: • Fluoropolymer is deposited on NiTi alloy via atmospheric-pressure plasma polymerization. • The corrosion resistance of NiTi alloy in SBF and DMEM is evidently improved. • The adsorption ratio of albumin to fibrinogen is increased on the coated surface. • The reduced platelet adhesion number indicates better in vitro hemocompatibility. - Abstract: To improve the corrosion resistance and hemocompatibility of biomedical NiTi alloy, hydrophobic polymer coatings are deposited by plasma polymerization in the presence of a fluorine-containing precursor using an atmospheric-pressure plasma jet. This process takes place at a low temperature in air and can be used to deposit fluoropolymer films using organic compounds that cannot be achieved by conventional polymerization techniques. The composition and chemical states of the polymer coatings are characterized by fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). The corrosion behavior of the coated and bare NiTi samples is assessed and compared by polarization tests and electrochemical impedance spectroscopy (EIS) in physiological solutions including simulated body fluids (SBF) and Dulbecco's Modified Eagle's medium (DMEM). The corrosion resistance of the coated NiTi alloy is evidently improved. Protein adsorption and platelet adhesion tests reveal that the adsorption ratio of albumin to fibrinogen is increased and the number of adherent platelets on the coating is greatly reduced. The plasma polymerized coating renders NiTi better in vitro hemocompatibility and is promising as a protective and hemocompatible coating on cardiovascular implants.

Mechanical behavior of M-Wire and conventional NiTi wire used to manufacture rotary endodontic instruments.

Science.gov (United States)

Pereira, Erika S J; Gomes, Renata O; Leroy, Agnès M F; Singh, Rupinderpal; Peters, Ove A; Bahia, Maria G A; Buono, Vicente T L

2013-12-01

Comparison of physical and mechanical properties of one conventional and a new NiTi wire, which had received an additional thermomechanical treatment. Specimens of both conventional (NiTi) and the new type of wire, called M-Wire (MW), were subjected to tensile and three-point bending tests, Vickers microhardness measurements, and to rotating-bending fatigue tests at a strain-controlled level of 6%. Fracture surfaces were observed by scanning electron microscopy and the non-deformed microstructures by transmission electron microscopy. The thermomechanical treatment applied to produce the M-Wire apparently increased the tensile strength and Vickers microhardness of the material, but its apparent Young modulus was smaller than that of conventionally treated NiTi. The three-point bending tests showed a higher flexibility for MW which also exhibited a significantly higher number of cycles to failure. M-Wire presented mechanical properties that can render endodontic instruments more flexible and fatigue resistant than those made with conventionally processed NiTi wires. Copyright © 2013 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

Thermomechanical model for NiTi shape memory wires

Czech Academy of Sciences Publication Activity Database

Frost, Miroslav; Sedlák, Petr; Sippola, M.; Šittner, Petr

2010-01-01

Roč. 19, č. 9 (2010), s. 1-10 ISSN 0964-1726 R&D Projects: GA MŠk(CZ) 1M06031; GA ČR(CZ) GA106/09/1573; GA ČR(CZ) GP106/09/P302; GA ČR GAP108/10/1296 Institutional research plan: CEZ:AV0Z20760514; CEZ:AV0Z10100520 Keywords : shape memory alloys * modeling * proportional loading Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 2.094, year: 2010 http://apps.isiknowledge.com/full_record.do?product=WOS&search_mode=GeneralSearch&qid=3&SID=U2fe5mHN9p3gHClCdF1&page=1&doc=1

A preliminary study of laser cladding of AISI 316 stainless steel using preplaced NiTi wire

International Nuclear Information System (INIS)

Cheng, F.T.; Lo, K.H.; Man, H.C.

2004-01-01

NiTi wire of diameter 1 mm was preplaced on AISI 316 stainless steel samples by using a binder. Melting of the NiTi wire to form a clad track on the steel substrate was achieved by means of a high-power CW Nd:YAG laser using different processing parameters. The geometry and microstructure of the clad deposit were studied by optical microscopy and scanning electron microscopy (SEM), respectively. The hardness and compositional profiles along the depth of the deposit were acquired by microhardness testing and energy-dispersive spectroscopy (EDS), respectively. The elastic behavior of the deposit was analyzed using nanoindentation, and compared with that of the NiTi wire. The dilution of the NiTi clad by the substrate material beneath was substantial in single clad tracks, but could be successively reduced in multiple clad layers. A strong fusion bonding with tough interface could be obtained as evidenced by the integrity of Vickers indentations in the interfacial region. In comparison with the NiTi cladding on AISI 316 using the tungsten inert gas (TIG) process, the laser process was capable of producing a much less defective cladding with a more homogeneous microstructure, which is an essential cladding quality with respect to cavitation erosion and corrosion resistance. Thus, the present preliminary study shows that laser cladding using preplaced wire is a feasible method to obtain a thick and homogeneous NiTi-based alloy layer on AISI 316 stainless steel substrate

Effect of nano-hydroxyapatite reinforcement in mechanically alloyed NiTi composites for biomedical implant

Energy Technology Data Exchange (ETDEWEB)

Akmal, Muhammad, E-mail: muhammad.akmal@giki.edu.pk [Faculty of Materials and Chemical Engineering, GIK Institute of Engineering Sciences and Technology, Topi 23640 (Pakistan); Raza, Ahmad, E-mail: ahmadrazac@yahoo.com [Faculty of Materials and Chemical Engineering, GIK Institute of Engineering Sciences and Technology, Topi 23640 (Pakistan); Khan, Muhammad Mudasser; Khan, M. Imran [Faculty of Materials and Chemical Engineering, GIK Institute of Engineering Sciences and Technology, Topi 23640 (Pakistan); Hussain, Muhammad Asif [Department of Chemical Engineering, Kangwon National University, Samcheok, 25913 (Korea, Republic of)

2016-11-01

Equi-atomic NiTi alloy composites reinforced with 0, 2, 4 and 6 vol.% nano-hydroxyapatite (HA) were successfully synthesized using pressureless sintering. Pure Ni and Ti elements were ball milled for 10 h in order to produce a mechanically alloyed equi-atomic NiTi alloy (MA-NiTi). Mechanically alloyed NiTi and HA powders were blended, compacted and then sintered for 3 h at 1325 K. The sintered density varied inversely with volume percent of HA reinforcement. The X-Ray diffraction spectra and SEM images showed the formation of multiple phases like NiTi, NiTi{sub 2}, Ni{sub 3}Ti, and Ni{sub 4}Ti{sub 3}. The back scattered-SEM image analysis confirmed the presence of Ni-rich and Ti-rich phases with increasing HA content. The 6 vol.% HA reinforced composite showed Ni{sub 3}Ti as the major phase having the highest hardness value which can be attributed to the presence of relatively harder phases along with higher HA content as a reinforcement. The composite of MA-NiTi with 2 vol.% HA manifested the most desirable results in the form of better sintering density mainly due to the minute decomposition of NiTi into other phases. Therefore, the 2 vol.% reinforced MA-NiTi composite can be exploited as a novel material for manufacturing biomedical implants. - Highlights: • NiTi-HA composites were synthesized using powder metallurgy route. • New phases such as NiTi{sub 2}, Ni{sub 3}Ti and Ni{sub 4}Ti{sub 3} were observed for sintered composites. • Mechanical properties enhanced with the increasing content of HA and new phases. • No martensitic transformation was observed for all composites by DSC analysis. • 2 vol.% HA composite is a novel candidate for biomedical implants.

Powder Metallurgy Fabrication of Porous 51(at.%)Ni-Ti Shape Memory Alloys for Biomedical Applications

Science.gov (United States)

Ibrahim, Mustafa K.; Hamzah, E.; Saud, Safaa N.; Nazim, E. M.

2018-05-01

The effect of time and temperature on the microwave sintering of 51(at.%)Ni-Ti shape memory alloys (SMAs) was investigated in the current research. Furthermore, the microstructure, mechanical properties, and bio-corrosion properties were analyzed based on the sintering conditions. The results revealed that the sintering condition of 700 °C for 15 min produced a part with coherent surface survey that does not exhibit gross defects. Increasing the sintering time and temperature created defects on the outer surface, while reducing the temperature to 550 °C severely affected the mechanical properties. The microstructure of these samples showed two regions of Ni-rich region and Ti-rich region between them Ti2Ni, NiTi, and Ni3Ti phases. The differential scanning calorimeter (DSC) curves of Ni-Ti samples exhibited a multi-step phase transformation B19'-R-B2 during heating and cooling. An increase in the sintering temperature from 550 to 700 °C was found to increase the fracture strength significantly and decreased the fracture strain slightly. Reducing the sintering temperature from 700 to 550 °C severely affected the corrosion behaviors of 51%Ni-Ti SMAs. This research aims to select the optimum parameters to produce Ni-Ti alloys with desired microstructure, mechanical properties, and corrosion behaviors for biomedical applications.

Influence of sliding friction on leveling force of superelastic NiTi arch wire: A computational analysis

Science.gov (United States)

Razali, M. F.; Mahmud, A. S.; Mokhtar, N.; Abdullah, J.

2017-10-01

This study investigated the influence of sliding friction toward the effective force of superelastic NiTi arch wire applied in orthodontic bracing for tooth leveling. A three-dimensional finite-element model integrated with superelastic subroutine and contact interaction was used to predict the contribution of friction on force-deflection curve of NiTi wire in three brackets bending configuration. It was found that the friction between the wire and the bracket increased proportionally as a function of wire deflection, thus transforming the constant force characteristic of NiTi material into a slope. The highest magnitude of sliding friction was measured to be 3.1 N and 2.2 N with respect to the activation and deactivation of the arch wire.

Cavitation erosion resistance of AISI 316L stainless steel laser surface-modified with NiTi

International Nuclear Information System (INIS)

Chiu, K.Y.; Cheng, F.T.; Man, H.C.

2005-01-01

The present study is part of a project on the surface modification of AISI 316 stainless steel using various forms of NiTi for enhancing cavitation erosion resistance. In this study, NiTi powder was preplaced on the AISI 316L substrate and melted with a high-power CW Nd:YAG laser. With appropriate laser processing parameters, an alloyed layer of a few hundred micrometers thick was formed and fusion bonded to the substrate without the formation of a brittle interface. EDS analysis showed that the layer contained Fe as the major constituent element while the XRD patterns of the surface showed an austenitic structure, similar to that of 316 stainless steel. The cavitation erosion resistance of the modified layer (316-NiTi-Laser) could reach about 29 times that of AISI 316L stainless steel. The improvement could be attributed to a much higher surface hardness and elasticity as revealed by instrumented nanoindentation tests. Among various types of samples, the cavitation erosion resistance was ranked in descending order as: NiTi plate > 316-NiTi-Laser > 316-NiTi-TIG > AISI 316L, where 316-NiTi-TIG stands for samples surfaced with the tungsten inert gas (TIG) process using NiTi wire. Though the laser-surfaced samples and the TIG-surfaced samples had similar indentation properties, the former exhibited a higher erosion resistance mainly because of a more homogeneous alloyed layer with much less defects. In both the laser-surfaced and TIG-surfaced samples, the superelastic behavior typical of austenitic NiTi was only partially retained and the superior cavitation erosion resistance was thus still not fully attained

Electron-phonon interactions and the phonon anomaly in β-phase NiTi

International Nuclear Information System (INIS)

Zhao, G.L.; Harmon, B.N.

1993-01-01

The electronic structure of β-phase NiTi has been calculated using a first-principles linear-combination-of-atomic-orbitals method. The resulting band structure was fitted with a nonorthogonal tight-binding Hamiltonian from which electron-phonon matrix elements were evaluated. The soft phonon near Q 0 =(2/3, 2) / (3 ,0)π/a, which is responsible for the premartensitic phase transition in β-phase NiTi, is found to arise from the strong electron-phonon coupling of nested electronic states on the Fermi surface. Thermal vibrations and changes in electronic occupation cause a smearing of the nested features, which in turn cause a hardening of the phonon anomaly

Fast Torsional Artificial Muscles from NiTi Twisted Yarns.

Science.gov (United States)

Mirvakili, Seyed M; Hunter, Ian W

2017-05-17

Torsional artificial muscles made of multiwalled carbon nanotube/niobium nanowire yarns have shown remarkable torsional speed and gravimetric torque. The muscle structure consists of a twisted yarn with half of its length infiltrated with a stimuli-responsive guest material such as paraffin wax. The volumetric expansion of the guest material creates the torsional actuation in the yarn. In the present work, we show that this type of actuation is not unique to wax-infiltrated carbon multiwalled nanotube (MWCNT) or niobium nanowire yarns and that twisted yarn of NiTi alloy fibers also produces fast torsional actuation. By gold-plating half the length of a NiTi twisted yarn and Joule heating it, we achieved a fully reversible torsional actuation of up to 16°/mm with peak torsional speed of 10 500 rpm and gravimetric torque of 8 N·m/kg. These results favorably compare to those of MWCNTs and niobium nanowire yarns.

Low Temperature Creep of Hot-Extruded Near-Stoichiometric NiTi Shape Memory Alloy. Part 2; Effect of Thermal Cycling

Science.gov (United States)

Raj, S. V.; Noebe, R. D.

2013-01-01

This paper is the first report on the effect prior low temperature creep on the thermal cycling behavior of NiTi. The isothermal low temperature creep behavior of near-stoichiometric NiTi between 300 and 473 K was discussed in Part I. The effect of temperature cycling on its creep behavior is reported in the present paper (Part II). Temperature cycling tests were conducted between either 300 or 373 K and 473 K under a constant applied stress of either 250 or 350 MPa with hold times lasting at each temperature varying between 300 and 700 h. Each specimen was pre-crept either at 300 or at 473 K for several months under an identical applied stress as that used in the subsequent thermal cycling tests. Irrespective of the initial pre-crept microstructures, the specimens exhibited a considerable increase in strain with each thermal cycle so that the total strain continued to build-up to 15 to 20 percent after only 5 cycles. Creep strains were immeasurably small during the hold periods. It is demonstrated that the strains in the austenite and martensite are linearly correlated. Interestingly, the differential irrecoverable strain, in the material measured in either phase decreases with increasing number of cycles, similar to the well-known Manson-Coffin relation in low cycle fatigue. Both phases are shown to undergo strain hardening due to the development of residual stresses. Plots of true creep rate against absolute temperature showed distinct peaks and valleys during the cool-down and heat-up portions of the thermal cycles, respectively. Transformation temperatures determined from the creep data revealed that the austenitic start and finish temperatures were more sensitive to the pre-crept martensitic phase than to the pre-crept austenitic phase. The results are discussed in terms of a phenomenological model, where it is suggested that thermal cycling between the austenitic and martensitic phase temperatures or vice versa results in the deformation of the austenite and

Synthesis and characterization of hybrid micro/nano-structured NiTi surfaces by a combination of etching and anodizing

Science.gov (United States)

Huan, Z.; Fratila-Apachitei, L. E.; Apachitei, I.; Duszczyk, J.

2014-02-01

The purpose of this study was to generate hybrid micro/nano-structures on biomedical nickel-titanium alloy (NiTi). To achieve this, NiTi surfaces were firstly electrochemically etched and then anodized in fluoride-containing electrolyte. With the etching process, the NiTi surface was micro-roughened through the formation of micropits uniformly distributed over the entire surface. Following the subsequent anodizing process, self-organized nanotube structures enriched in TiO2 could be superimposed on the etched surface under specific conditions. Furthermore, the anodizing treatment significantly reduced water contact angles and increased the surface free energy compared to the surfaces prior to anodizing. The results of this study show for the first time that it is possible to create hybrid micro/nano-structures on biomedical NiTi alloys by combining electrochemical etching and anodizing under controlled conditions. These novel structures are expected to significantly enhance the surface biofunctionality of the material when compared to conventional implant devices with either micro- or nano-structured surfaces.

Synthesis and characterization of hybrid micro/nano-structured NiTi surfaces by a combination of etching and anodizing

International Nuclear Information System (INIS)

Huan, Z; Fratila-Apachitei, L E; Apachitei, I; Duszczyk, J

2014-01-01

The purpose of this study was to generate hybrid micro/nano-structures on biomedical nickel–titanium alloy (NiTi). To achieve this, NiTi surfaces were firstly electrochemically etched and then anodized in fluoride-containing electrolyte. With the etching process, the NiTi surface was micro-roughened through the formation of micropits uniformly distributed over the entire surface. Following the subsequent anodizing process, self-organized nanotube structures enriched in TiO 2 could be superimposed on the etched surface under specific conditions. Furthermore, the anodizing treatment significantly reduced water contact angles and increased the surface free energy compared to the surfaces prior to anodizing. The results of this study show for the first time that it is possible to create hybrid micro/nano-structures on biomedical NiTi alloys by combining electrochemical etching and anodizing under controlled conditions. These novel structures are expected to significantly enhance the surface biofunctionality of the material when compared to conventional implant devices with either micro- or nano-structured surfaces. (paper)

Synthesis and characterization of hybrid micro/nano-structured NiTi surfaces by a combination of etching and anodizing.

Science.gov (United States)

Huan, Z; Fratila-Apachitei, L E; Apachitei, I; Duszczyk, J

2014-02-07

The purpose of this study was to generate hybrid micro/nano-structures on biomedical nickel-titanium alloy (NiTi). To achieve this, NiTi surfaces were firstly electrochemically etched and then anodized in fluoride-containing electrolyte. With the etching process, the NiTi surface was micro-roughened through the formation of micropits uniformly distributed over the entire surface. Following the subsequent anodizing process, self-organized nanotube structures enriched in TiO2 could be superimposed on the etched surface under specific conditions. Furthermore, the anodizing treatment significantly reduced water contact angles and increased the surface free energy compared to the surfaces prior to anodizing. The results of this study show for the first time that it is possible to create hybrid micro/nano-structures on biomedical NiTi alloys by combining electrochemical etching and anodizing under controlled conditions. These novel structures are expected to significantly enhance the surface biofunctionality of the material when compared to conventional implant devices with either micro- or nano-structured surfaces.

Recent activities of association of shape memory alloys (ASMA) in Japan

International Nuclear Information System (INIS)

Kobayashi, J.; Yamauchi, K.; Miyashita, T.; Ohkata, I.; Narumi, S.; Suzuki, Y.

1995-01-01

The Association of Shape Memory Alloys(ASMA) was established in 1983 and systematic surveys on the Ni-Ti and Cu based SMAs were carried out until 1986. The ASMA is now reorganized as a private association. In this paper, we briefly introduce several SMA products of the member companies and present a couple of products, a static rock breaking system and a thermostatic mixing valve in detail. (orig.)

Recent activities of association of shape memory alloys (ASMA) in Japan

Energy Technology Data Exchange (ETDEWEB)

Kobayashi, J [ASMA, Yokohama (Japan); Yamauchi, K [TOKIN Corp., Sendai (Japan); Miyashita, T [Nishimatsu Construction Co., Ltd., Yamato (Japan); Ohkata, I [Kato Hatsujo Kaisha, Ltd., Yokohama (Japan); Narumi, S [Sogo Hatsujo Co., Ltd. (Japan); Suzuki, Y [Furukawa Electric Co. Ltd., Tokyo (Japan)

1995-12-01

The Association of Shape Memory Alloys(ASMA) was established in 1983 and systematic surveys on the Ni-Ti and Cu based SMAs were carried out until 1986. The ASMA is now reorganized as a private association. In this paper, we briefly introduce several SMA products of the member companies and present a couple of products, a static rock breaking system and a thermostatic mixing valve in detail. (orig.).

Microstructural and Material Quality Effects on Rolling Contact Fatigue of Highly Elastic Intermetallic NiTi Ball Bearings

Science.gov (United States)

Dellacorte, Christopher; Howard, S. Adam; Thomas, Fransua; Stanford, Malcolm K.

2017-01-01

Rolling element bearings made from highly-elastic intermetallic materials (HIM)s, such as 60NiTi, are under development for applications that require superior corrosion and shock resistance. Compared to steel, intermetallics have been shown to have much lower rolling contact fatigue (RCF) stress capability in simplified 3-ball on rod (ASTM STP 771) fatigue tests. In the 3-ball tests, poor material quality and microstructural flaws negatively affect fatigue life but such relationships have not been established for full-scale 60NiTi bearings. In this paper, 3-ball-on-rod fatigue behavior of two quality grades of 60NiTi are compared to the fatigue life of full-scale 50mm bore ball bearings made from the same materials. 60NiTi RCF rods with material or microstructural flaws suffered from infant mortality failures at all tested stress levels while high quality 60NiTi rods exhibited no failures at lower stress levels. Similarly, tests of full-scale bearings made from flawed materials exhibited early surface fatigue and through crack type failures while bearings made from high quality material did not fail even in long-term tests. Though the full-scale bearing test data is yet preliminary, the results suggest that the simplified RCF test is a good qualitative predictor of bearing performance. These results provide guidance for materials development and to establish minimum quality levels required for successful bearing operation and life.

Surface modification of NiTi by plasma based ion implantation for application in harsh environments

Energy Technology Data Exchange (ETDEWEB)

Oliveira, R.M., E-mail: rogerio@plasma.inpe.br [Instituto Nacional de Pesquisas Espaciais (INPE), S. J. Campos, SP (Brazil); Fernandes, B.B.; Carreri, F.C.; Goncalves, J.A.N.; Ueda, M.; Silva, M.M.N.F. [Instituto Nacional de Pesquisas Espaciais (INPE), S. J. Campos, SP (Brazil); Silva, M.M. [Instituto Tecnologico de Aeronautica (ITA), S. J. Campos, SP (Brazil); Pichon, L. [Laboratoire de Metallurgie Physique, University of Poitiers, Poitiers (France); Camargo, E.N.; Otubo, J. [Instituto Tecnologico de Aeronautica (ITA), S. J. Campos, SP (Brazil)

2012-12-15

Highlights: Black-Right-Pointing-Pointer New nitrogen PBII set up was used to treat samples of NiTi in moderate temperature of 450 Degree-Sign C. Black-Right-Pointing-Pointer A very rich nitrogen atomic concentration was achieved on the top surface. Black-Right-Pointing-Pointer Nitrogen diffused at least for 11 {mu}m depth. Black-Right-Pointing-Pointer Improved tribological and corrosion properties were achieved. Black-Right-Pointing-Pointer A concentration dependent diffusion coefficient was calculated. - Abstract: The substitution of conventional components for NiTi in distinct devices such as actuators, valves, connectors, stents, orthodontic arc-wires, e.g., usually demands some kind of treatment to be performed on the surface of the alloy. A typical case is of biomaterials made of NiTi, in which the main drawback is the Ni out-diffusion, an issue that has been satisfactorily addressed by plasma based ion implantation (PBII). Even though PBII can tailor selective surface properties of diverse materials, usually, only thin modified layers are attained. When NiTi alloys are to be used in the harsh space environment, as is the case of devices designed to remotely release the solar panels and antenna arrays of satellites, e.g., superior mechanical and tribological properties are demanded. For this case the thickness of the modified layer must be larger than the one commonly achieved by conventional PBII. In this paper, new nitrogen PBII set up was used to treat samples of NiTi in moderate temperature of 450 Degree-Sign C, with negative voltage pulses of 7 kV/250 Hz/20 {mu}s, in a process lasting 1 h. A rich nitrogen atomic concentration of 85 at.% was achieved on the near surface and nitrogen diffused at least for 11 {mu}m depth. Tribological properties as well as corrosion resistance were evaluated.

Efficacy and safety of a NiTi CAR 27 compression ring for end-to-end anastomosis compared with conventional staplers: A real-world analysis in Chinese colorectal cancer patients

Science.gov (United States)

Lu, Zhenhai; Peng, Jianhong; Li, Cong; Wang, Fulong; Jiang, Wu; Fan, Wenhua; Lin, Junzhong; Wu, Xiaojun; Wan, Desen; Pan, Zhizhong

2016-01-01

OBJECTIVES: This study aimed to evaluate the safety and efficacy of a new nickel-titanium shape memory alloy compression anastomosis ring, NiTi CAR 27, in constructing an anastomosis for colorectal cancer resection compared with conventional staples. METHODS: In total, 234 consecutive patients diagnosed with colorectal cancer receiving sigmoidectomy and anterior resection for end-to-end anastomosis from May 2010 to June 2012 were retrospectively analyzed. The postoperative clinical parameters, postoperative complications and 3-year overall survival in 77 patients using a NiTi CAR 27 compression ring (CAR group) and 157 patients with conventional circular staplers (STA group) were compared. RESULTS: There were no statistically significant differences between the patients in the two groups in terms of general demographics and tumor features. A clinically apparent anastomotic leak occurred in 2 patients (2.6%) in the CAR group and in 5 patients (3.2%) in the STA group (p=0.804). These eight patients received a temporary diverting ileostomy. One patient (1.3%) in the CAR group was diagnosed with anastomotic stricture through an electronic colonoscopy after 3 months postoperatively. The incidence of postoperative intestinal obstruction was comparable between the two groups (p=0.192). With a median follow-up duration of 39.6 months, the 3-year overall survival rate was 83.1% in the CAR group and 89.0% in the STA group (p=0.152). CONCLUSIONS: NiTi CAR 27 is safe and effective for colorectal end-to-end anastomosis. Its use is equivalent to that of the conventional circular staplers. This study suggests that NiTi CAR 27 may be a beneficial alternative in colorectal anastomosis in Chinese colorectal cancer patients. PMID:27276395

The effect of mucin, fibrinogen and IgG on the corrosion behaviour of Ni-Ti alloy and stainless steel.

Science.gov (United States)

Chao, Zhang; Yaomu, Xiao; Chufeng, Liu; Conghua, Liu

2017-06-01

In this study, Ni-Ti alloy and stainless steal were exposed to artificial saliva containing fibrinogen, IgG or mucin, and the resultant corrosion behavior was studied. The purpose was to determine the mechanisms by which different types of protein contribute to corrosion. The effect of different proteins on the electrochemical resistance of Ni-Ti and SS was tested by potentiodynamic polarization, and the repair capacity of passivation film was tested by cyclic polarization measurements. The dissolved corrosion products were determined by ICP-OES, and the surface was analyzed by SEM and AFM. The results showed fibrinogen, IgG or mucin could have different influences on the susceptibility to corrosion of the same alloy. Adding protein lead to the decrease of corrosion resistance of SS, whereas protein could slow down the corrosion process of Ni-Ti. For Ni-Ti, adding mucin could enhance the corrosion stability and repair capacity of passivation film. The susceptibility to pitting corrosion of Ni-Ti and stainless steal in fibrinogen AS is not as high as mucin and IgG AS. There are different patterns of deposition formation on the metal surface by different types of protein, which is associated with their effects on the corrosion process of the alloys.

Additive Manufacturing of Shape Memory Alloys

Science.gov (United States)

Van Humbeeck, Jan

2018-04-01

Selective Laser Melting (SLM) is an additive manufacturing production process, also called 3D printing, in which functional, complex parts are produced by selectively melting patterns in consecutive layers of powder with a laser beam. The pattern the laser beam is following is controlled by software that calculates the pattern by slicing a 3D CAD model of the part to be constructed. Apart from SLM, also other additive manufacturing techniques such as EBM (Electron Beam Melting), FDM (Fused Deposition Modelling), WAAM (Wire Arc Additive Manufacturing), LENS (Laser Engineered Net Shaping such as Laser Cladding) and binder jetting allow to construct complete parts layer upon layer. But since more experience of AM of shape memory alloys is collected by SLM, this paper will overview the potentials, limits and problems of producing NiTi parts by SLM.

Influence of Thin-Film Adhesives in Pullout Tests Between Nickel-Titanium Shape Memory Alloy and Carbon Fiber-Reinforced Polymer Matrix Composites

Science.gov (United States)

Quade, Derek J.; Jana, Sadhan; McCorkle, Linda S.

2018-01-01

Strips of nickel-titanium (NiTi) shape memory alloy (SMA) and carbon fiber-reinforced polymer matrix composite (PMC) were bonded together using multiple thin film adhesives and their mechanical strengths were evaluated under pullout test configuration. Tensile and lap shear tests were conducted to confirm the deformation of SMAs at room temperature and to evaluate the adhesive strength between the NiTi strips and the PMC. Optical and scanning electron microscopy techniques were used to examine the interfacial bonding after failure. Simple equations on composite tensile elongation were used to fit the experimental data on tensile properties. ABAQUS models were generated to show the effects of enhanced bond strength and the distribution of stress in SMA and PMC. The results revealed that the addition of thin film adhesives increased the average adhesive strength between SMA and PMC while halting the room temperature shape memory effect within the pullout specimen.

CT evaluation of canal preparation using rotary and hand NI-TI instruments: An in vitro study.

Science.gov (United States)

Nagaraja, Shruthi; Sreenivasa Murthy, B V

2010-01-01

Controlled, uniformly tapered radicular preparation is a great challenge in endodontics. Improper preparation can lead to procedural errors like transportation of foramen, uneven dentine thickness, stripping of root canal, formation of ledge, zip, and elbow in curved canals. These procedural errors and their sequel can adversely affect the prognosis of treatment. The present in vitro study aims to evaluate canal preparation based on the following factors: canal transportation, remaining dentine thickness and comparing centering ability between hand Ni-Ti K files and ProTaper rotary Ni-Ti instruments using computed tomography (CT). For evaluation, 30 mesiobuccal roots of maxillary molars were selected. Of these, 15 roots were distributed into two groups where Group 1 included hand instrumentation with Ni-Ti K-files; and Group 2 comprised ProTaper NiTi rotary system. Pre instrumentation and post instrumentation three-dimensional CT images were obtained from root cross-sections that were 1 mm thick from apex to the canal orifice; scanned images were then superimposed and compared. It was observed that the manual technique using hand Ni-Ti K-file produced lesser canal transportation and maintained greater dentine thickness than the rotary ProTaper technique at middle and coronal third and this difference was statistically significant. No significant difference was seen with regard to canal transportation and remaining root dentine at apical levels. With regard to centering ratio, no significant difference was seen between both the groups at all levels. ProTaper should be used judiciously, especially in curved canals, as it causes higher canal transportation and thinning of root dentine at middle and coronal levels. None of the groups showed optimal centering ability.

Effect of Cooling Rates on the Transformation Behavior and Mechanical Properties of a Ni-Rich NiTi Alloy

Science.gov (United States)

Coan, Stephen; Shamimi, Ali; Duerig, T. W.

2017-12-01

Slightly nickel-rich Ni-Ti alloys (typically 50.5-51% atomic percent nickel) are commonly used to produce devices that are superelastic at body temperature. This excess nickel can be tolerated in the NiTi matrix when its temperature is above the solvus of about 600 °C, but will precipitate out during lower temperatures. Recent work has been done on exploring the effect lower temperatures have on the material properties of NiTi. Findings showed that properties begin to change at temperatures as low as 100 °C. It is because of these results that it was deemed important to better understand what may be happening during the quenching process itself. Through running a combination of DSC and tensile tests on samples cooled at varying rates, it was found that the cooling rate has an effect on properties when heat treated above a specific temperature. Understanding how quickly the alloy must be cooled to fully retain the supersaturated NiTi matrix is important to optimizing processes and anticipating material properties after a heat treatment.

Mechanical response of nickel-titanium instruments with different cross-sectional designs during shaping of simulated curved canals.

Science.gov (United States)

Kim, H C; Kim, H J; Lee, C J; Kim, B M; Park, J K; Versluis, A

2009-07-01

To evaluate how different cross-sectional designs affect stress distribution in nickel-titanium (NiTi) instruments during bending, torsion and simulated shaping of a curved canal. Four NiTi rotary instruments with different cross-sectional geometries were selected: ProFile and HeroShaper systems with a common triangle-based cross section, Mtwo with an S-shaped rectangle-based design and NRT with a modified rectangle-based design. The geometries of the selected files were scanned in a micro-CT and three-dimensional finite-element models were created for each system. Stiffness characteristics for each file system were determined in a series of bending and torsional conditions. Canal shaping was simulated by inserting models of the rotating file into a 45 degrees curved canal model. Stress distribution in the instruments was recorded during simulated shaping. After the instruments were retracted from the canal, residual stresses and permanent bending of their tips due to plastic deformation were determined. The greatest bending and torsional stiffness occurred in the NRT file. During simulated shaping, the instruments with triangle-based cross-sectional geometry had more even stress distributions along their length and had lower stress concentrations than the instruments with rectangle-based cross sections. Higher residual stresses and plastic deformations were found in the Mtwo and NRT with rectangle-based cross-sectional geometries. Nickel-titanium instruments with rectangle-based cross-sectional designs created higher stress differentials during simulated canal shaping and may encounter higher residual stress and plastic deformation than instruments with triangle-based cross sections.

Surface Characterization of Nb Samples Electro-polished Together With Real Superconducting Radio-frequency Accelerator Cavities

International Nuclear Information System (INIS)

Zhao, Xin; Geng, Rong-Li; Tyagi, P.V.; Hayano, Hitoshi; Kato, Shigeki; Nishiwaki, Michiru; Saeki, Takayuki; Sawabe, Motoaki

2010-01-01

We report the results of surface characterizations of niobium (Nb) samples electropolished together with a single cell superconducting radio-frequency accelerator cavity. These witness samples were located in three regions of the cavity, namely at the equator, the iris and the beam-pipe. Auger electron spectroscopy (AES) was utilized to probe the chemical composition of the topmost four atomic layers. Scanning electron microscopy with energy dispersive X-ray for elemental analysis (SEM/EDX) was used to observe the surface topography and chemical composition at the micrometer scale. A few atomic layers of sulfur (S) were found covering the samples non-uniformly. Niobium oxide granules with a sharp geometry were observed on every sample. Some Nb-O granules appeared to also contain sulfur.

The influence of interstitial impurities on temperature ranges of deuterium retention in austenitic stainless steel 18Cr10NiTi

International Nuclear Information System (INIS)

Neklyudov, I.M.; Morozov, O.M.; Kulish, V.G.; Zhurba, V.I.; Galytsky, A.G.; Piatenko, E.V.

2009-01-01

The influence of nitrogen, oxygen and helium on the temperature range of deuterium retention in 18Cr10NiTi stainless steel (of AISI304L type) has been investigated. It is demonstrated that the introduction of oxygen, nitrogen or helium into 18Cr10NiTi steel extends the upper limit in the high-temperature range of deuterium retention. It has been found that for 18Cr10NiTi stainless steel, pre-irradiated with helium ions, the increase in the temperature range of deuterium retention occurs in steps: on attainment of helium concentration of ∼0.5 at.% He the temperature range increases by ∼100 K, and on attainment of helium concentration of ∼2.5 at.% He the temperature range increases by ∼350 K. The introduction of oxygen into 18Cr10NiTi stainless steel results in the increase of the temperature range of deuterium retention in the direction of rise in temperature. In the deuterium thermodesorption spectrum, this manifests itself by the occurrence of an additional low-amplitude peak with the maximum temperature T m ∼ 560 K. The introduction of nitric impurity into 18Cr10NiTi stainless steel results in the extension of the temperature range of deuterium retention towards higher temperatures.

Elastocaloric effect of a Ni-Ti plate to be applied in a regenerator-based cooling device

DEFF Research Database (Denmark)

Tusek, Jaka; Engelbrecht, Kurt; Pryds, Nini

2016-01-01

The aim of this article is to analyze the elastocaloric effect of a commercial Ni-Ti plate for its application in a cooling device. In the first part, the article shows numerical results of the cooling characteristics of a regenerator-based elastocaloric cooling device with different thickness...... of the Ni-Ti plates based on a previously developed numerical model. It is shown that such a device (with a plate thickness of 0.1 mm) can produce a specific cooling power up to 7 kW/kg and coefficient of performance values up to 5 at the 30 K of the temperature span. In the second part of the article...... and the temperature irreversibilities during unloading are presented and discussed. It can be concluded that thin Ni-Ti plates with suitable austenitic finish temperature are good candidates to be applied in a proof-of-concept regenerator-based cooling device....

CT evaluation of canal preparation using rotary and hand NI-TI instruments: An in vitro study

Science.gov (United States)

Nagaraja, Shruthi; Sreenivasa Murthy, B V

2010-01-01

Background: Controlled, uniformly tapered radicular preparation is a great challenge in endodontics. Improper preparation can lead to procedural errors like transportation of foramen, uneven dentine thickness, stripping of root canal, formation of ledge, zip, and elbow in curved canals. These procedural errors and their sequel can adversely affect the prognosis of treatment. Aim/Objectives: The present in vitro study aims to evaluate canal preparation based on the following factors: canal transportation, remaining dentine thickness and comparing centering ability between hand Ni-Ti K files and ProTaper rotary Ni-Ti instruments using computed tomography (CT). Materials and Methods: For evaluation, 30 mesiobuccal roots of maxillary molars were selected. Of these, 15 roots were distributed into two groups where Group 1 included hand instrumentation with Ni-Ti K-files; and Group 2 comprised ProTaper NiTi rotary system. Pre instrumentation and post instrumentation three-dimensional CT images were obtained from root cross-sections that were 1 mm thick from apex to the canal orifice; scanned images were then superimposed and compared. Result: It was observed that the manual technique using hand Ni-Ti K-file produced lesser canal transportation and maintained greater dentine thickness than the rotary ProTaper technique at middle and coronal third and this difference was statistically significant. No significant difference was seen with regard to canal transportation and remaining root dentine at apical levels. With regard to centering ratio, no significant difference was seen between both the groups at all levels. Conclusion: ProTaper should be used judiciously, especially in curved canals, as it causes higher canal transportation and thinning of root dentine at middle and coronal levels. None of the groups showed optimal centering ability. PMID:20582214

Design and Characterization of a Small-Scale Solar Sail Prototype by Integrating NiTi SMA and Carbon Fibre Composite

Directory of Open Access Journals (Sweden)

Girolamo Costanza

2017-01-01

Full Text Available Solar sails are propellantless systems where the propulsive force is given by the momentum exchange of reflecting photons. In this study, a self-deploying system based on NiTi shape memory wires and sheets has been designed and manufactured. A small-scale prototype of solar sail with carbon fibre loom has been developed. Different configurations have been tested to optimize material and structure design of the small-scale solar sail. In particular the attention has been focused on the surface/weight ratio and the deployment of the solar sail. By reducing weight and enlarging the surface, it is possible to obtain high values of characteristic acceleration that is one of the main parameters for a successful use of the solar sail as propulsion system. Thanks to the use of shape memory alloys for self-actuation of the system, complexity of the structure itself decreases. Moreover, sail deployment is simpler.

Internal stresses in steel plate generated by shape memory alloy inserts

Czech Academy of Sciences Publication Activity Database

Malard, B.; Pilch, Jan; Šittner, Petr; Davydov, V.; Sedlák, Petr; Konstantinidis, K.; Hughes, D. J.

2012-01-01

Roč. 60, č. 3 (2012), s. 1378-1394 ISSN 1359-6454 R&D Projects: GA ČR GAP108/10/1296 Grant - others:SMARTNETS(XE) FP7-NMP2-2011-262806 Institutional research plan: CEZ:AV0Z10100520; CEZ:AV0Z20760514 Keywords : shape memory alloy * NiTi * residual stress * neutron diffraction * strain scanning Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 3.941, year: 2012 http://www.sciencedirect.com/science/article/pii/S1359645411007294

NiTi intermetallic surface coatings by laser metal deposition for improving wear properties of Ti-6Al-4V substrates

CSIR Research Space (South Africa)

Mokgalaka, MN

2014-03-01

Full Text Available The NiTi intermetallic possesses a number of good properties, such as high wear, oxidation, and corrosion resistance. This paper focuses on the deposition of NiTi intermetallic coatings on Ti6Al4V substrate by laser melting of Ti and Ni elemental...

Combining thermodynamic principles with Preisach models for superelastic shape memory alloy wires

International Nuclear Information System (INIS)

Doraiswamy, S; Rao, A; Srinivasa, A R

2011-01-01

We present a simple model for simulating the response of a superelastic shape memory alloy wire based on the thermodynamics of irreversible processes, which can simulate the full thermomechanical response including internal hysteresis loops, at different temperatures, with minimal data input. The key idea is to separate the dissipative response and the elastic response of shape memory alloys using a Gibbs potential based formulation, and then use a Preisach model for the dissipative part of the response. This enables better handling of the features observed in the superelastic response such as those due to changes in temperature and internal hysteresis loops. We compare the predicted response with experiments performed on 0.75 mm NiTi shape memory alloy wires at three different temperatures

Shape Memory Alloys (Part II: Classification, Production and Application

Directory of Open Access Journals (Sweden)

I. Ivanic

2014-09-01

Full Text Available Shape memory alloys (SMAs have been extensively investigated because of their unique shape memory behaviour, i.e. their ability to recover their original shape they had before deformation. Shape memory effect is related to the thermoelastic martensitic transformation. Austenite to martensite phase transformation can be obtained by mechanical (loading and thermal methods (heating and cooling. Depending on thermomechanical conditions, SMAs demonstrate several thermomechanical phenomena, such as pseudoelasticity, superelasticity, shape memory effect (one-way and two-way and rubber-like behaviour. Numerous alloys show shape memory effect (NiTi-based alloys, Cu-based alloys, Fe-based alloys etc.. Nitinol (NiTi is the most popular and the most commonly used SMA due to its superior thermomechanical and thermoelectrical properties. NiTi alloys have greater shape memory strain and excellent corrosion resistance compared to Cu – based alloys. However, they are very costly. On the other hand, copper-based alloys (CuZn and CuAl based alloys are much less expensive, easier to manufacture and have a wider range of potential transformation temperatures. The characteristic transformation temperatures of martensitic transformation of CuAlNi alloys can lie between −200 and 200 °C, and these temperatures depend on Al and Ni content. Among the Cu – based SMAs, the most frequently applied are CuZnAl and CuAlNi alloys. Although CuZnAl alloys with better mechanical properties are the most popular among the Cu-based SMAs, they lack sufficient thermal stability, while CuAlNi shape memory alloys, in spite of their better thermal stability, have found only limited applications due to insufficient formability owing to the brittle γ2 precipitates. The most important disadvantage of polycrystalline CuAlNi alloys is a small reversible deformation (one-way shape memory effect: up to 4 %; two-way shape memory effect: only approximately 1.5 % due to intergranular

Failure Analysis and Recovery of a 50-mm Highly Elastic Intermetallic NiTi Ball Bearing for an ISS Application

Science.gov (United States)

DellaCorte, Christopher; Howard, S. Adam; Moore, Lewis

2016-01-01

Ball bearings used inside the ISS Distillation Assembly centrifuge require superior corrosion and shock resistance to withstand acidic wastewater exposure and heavy spacecraft launch related loads. These requirements challenge conventional steel bearings and provide an ideal pathfinder application for 50-mm bore, deep-groove ball bearings made from the corrosion immune and highly elastic intermetallic material 60NiTi. During early ground testing in 2014 one 60NiTi bearing unexpectedly and catastrophically failed after operating for only 200 hr. A second bearing running on the same shaft was completely unaffected. An investigation into the root cause of the failure determined that an excessively tight press fit of the bearing outer race coupled with NiTi's relatively low elastic modulus were key contributing factors. The proposed failure mode was successfully replicated by experiment. To further corroborate the root cause theory, a successful bearing life test using improved installation practices (selective fitting) was conducted. The results show that NiTi bearings are suitable for space applications provided that care is taken to accommodate their unique material characteristics.

Canal shaping with WaveOne Primary reciprocating files and ProTaper system: a comparative study.

Science.gov (United States)

Berutti, Elio; Chiandussi, Giorgio; Paolino, Davide Salvatore; Scotti, Nicola; Cantatore, Giuseppe; Castellucci, Arnaldo; Pasqualini, Damiano

2012-04-01

This study compared the canal curvature and axis modification after instrumentation with WaveOne Primary reciprocating files (Dentsply Maillefer, Ballaigues, Switzerland) and nickel-titanium (NiTi) rotary ProTaper (Dentsply Maillefer). Thirty ISO 15, 0.02 taper, Endo Training Blocks (Dentsply Maillefer) were used. In all specimens, the glide path was achieved with PathFile 1, 2, and 3 (Dentsply Maillefer) at the working length (WL). Specimens were then assigned to 1 of 2 groups for shaping: specimens in group 1 were shaped with ProTaper S1-S2-F1-F2 at the WL and specimens in group 2 were shaped with WaveOne Primary reciprocating files at the WL. Pre- and postinstrumentation digital images were superimposed and processed with Matlab r2010b (The MathWorks Inc, Natick, MA) software to analyze the curvature-radius ratio (CRr) and the relative axis error (rAe), representing canal curvature modification. Data were analyzed with one-way balanced analyses of variance at 2 levels (P < .05). The instrument factor was extremely significant for both the CRr parameter (F(1) = 9.59, P = .004) and the rAe parameter (F(1) = 13.55, P = .001). Canal modifications are reduced when the new WaveOne NiTi single-file system is used. Copyright © 2012 American Association of Endodontists. Published by Elsevier Inc. All rights reserved.

Observations of pretransformation lattice instability in near-equiatomic NiTi alloy

International Nuclear Information System (INIS)

Aboelfotoh, M.O.; Aboelfotoh, H.A.; Washburn, J.

1978-01-01

Observations were made on the pretransformation effects in near-equiatomic NiTi alloy using the technique of transmission electron microscopy and diffraction. The pretransformation effects are discussed in terms of lattice displacement waves arising from the instability of the B2 lattice

Mechanical behavior of NiTi arc wires under pseudoelastic cycling and cathodically hydrogen charging

Science.gov (United States)

Sarraj, R.; Hassine, T.; Gamaoun, F.

2018-01-01

NiTi wires are mainly used to design orthodontic devices. However, they may be susceptible to a delayed fracture while they are submitted to cyclic loading with the presence of hydrogen in the oral cavity. Hydrogen may cause the embrittlement of the structure, leading to lower ductility and to a change in transformation behavior. The aim of the present study is to predict the NiTi behavior under cyclic loading with hydrogen charging. One the one hand, samples are submitted to superelastic cyclic loading, which results in investigating their performance degradations. On the other hand, after hydrogen charging, cyclic tensile aging tests are carried out on NiTi orthodontic wires at room temperature in the air. During cyclic loading, we notice that the critical stress for the martensite transformation evolves, the residual strain is accumulated in the structure and the hysteresis loop changes. Thus, via this work, we can assume that the embrittlement is due to the diffusion of hydrogen and the generation of dislocations after aging. The evolution of mechanical properties of specimens becomes more significant with hydrogen charging rather than without it.

Fatigue behaviour of NiTi shape memory alloy scaffolds produced by SLM, a unit cell design comparison.

Science.gov (United States)

Speirs, M; Van Hooreweder, B; Van Humbeeck, J; Kruth, J-P

2017-06-01

Selective laser melting (SLM) is an additive manufacturing technique able to produce complex functional parts via successively melting layers of metal powder. This process grants the freedom to design highly complex scaffold components to allow bone ingrowth and aid mechanical anchorage. This paper investigates the compression fatigue behaviour of three different unit cells (octahedron, cellular gyroid and sheet gyroid) of SLM nitinol scaffolds. It was found that triply periodic minimal surfaces display superior static mechanical properties in comparison to conventional octahedron beam lattice structures at identical volume fractions. Fatigue resistance was also found to be highly geometry dependent due to the effects of AM processing techniques on the surface topography and notch sensitivity. Geometries minimising nodal points and the staircase effect displayed the greatest fatigue resistance when normalized to yield strength. Furthermore oxygen analysis showed a large oxygen uptake during SLM processing which must be altered to meet ASTM medical grade standards and may significantly reduce fatigue life. These achieved fatigue properties indicate that NiTi scaffolds produced via SLM can provide sufficient mechanical support over an implants lifetime within stress range values experienced in real life. Copyright © 2017 Elsevier Ltd. All rights reserved.

Density functional theory simulation of titanium migration and reaction with oxygen in the early stages of oxidation of equiatomic NiTi alloy.

Science.gov (United States)

Nolan, Michael; Tofail, Syed A M

2010-05-01

The biocompatibility of NiTi shape memory alloys (SMA) has made possible applications in self-expandable cardio-vascular stents, stone extraction baskets, catheter guide wires and other invasive and minimally invasive biomedical devices. The NiTi intermetallic alloy spontaneously forms a thin passive layer of TiO(2), which provides its biocompatibility. The oxide layer is thought to form as the Ti in the alloy surface reacts with oxygen, resulting in a depletion of Ti in the subsurface region - experimental evidence indicates formation of a Ni-rich layer below the oxide film. In this paper, we study the initial stages of oxide growth on the (110) surface of the NiTi alloy to understand the formation of alloy/oxide interface. We initially adsorb atomic and molecular oxygen on the (110) surface and then successively add O(2) molecules, up to 2 monolayer of O(2). Oxygen adsorption always results in a large energy gain. With atomic oxygen, Ti is pulled out of the surface layer leaving behind a Ni-rich subsurface region. Molecular O(2), on the other hand adsorbs dissociatively and pulls a Ti atom farther out of the surface layer. The addition of further O(2) up to 1 monolayer is also dissociative and results in complete removal of Ti from the initial surface layer. When further O(2) is added up to 2 monolayer, Ti is pulled even further out of the surface and a single thin layer of composition O-Ti-O is formed. The electronic structure shows that the metallic character of the alloy is unaffected by interaction with oxygen and formation of the oxide layer, consistent with the oxide layer being a passivant. Copyright 2010 Elsevier Ltd. All rights reserved.

Numerical simulation of the force generated by a superelastic NiTi orthodontic archwire during tooth alignment phase: comparison between different constitutive models

Science.gov (United States)

Gannoun, M.; Laroussi Hellara, M.; Bouby, C.; Ben Zineb, T.; Bouraoui, T.

2018-04-01

Nickel Titanium (NiTi) Superelastic (SE) Shape Memory Alloys (SMAs) are widely considered for applications that need high reversible strain or high recovery forces. In particular, the SE SMAs present a high interest for biomedical applications such as endodontic and orthodontic apparatus. They are available in a large variety of archwires exerting continuum forces to ensure the dental displacement. The purpose of this study is to report the clinical implications of NiTi SE wires for dental treatment in a given configuration. Three main constitutive models of the literature (Lagoudas and Boyd 1996 Int. J. Plast. 12 805–842, Auricchio and Petrini 2004 Int. J. Numer. Meth. Engng. 61 807–836 and Chemisky et al 2011 Mech. Mater. 68 361–376) are considered for the finite element (FE) numerical simulations of the SMA archwires response. Tensile tests had been carried out in order to identify the material parameters of these constitutive models. The FE numerical study allowed to predict the dental displacement and its corresponding orthodontic force level exerted by the wire in similar conditions to those in the oral environment. This work allows to predict the orthodontic generated load by a NiTi SE archwire with a 0.64 × 0.46 mm2 rectangular cross section under prescribed thermomechanical conditions. The effect of the temperature and the alveolar bone stiffness on the orthodontic load level and the tooth displacement degree has been investigated. The performed numerical simulations demonstrate that the orthodontic load is sensitive to the displacement magnitude, to the tooth stiffness and to the temperature variations. The obtained forces applied continuously and at a constant level are within the acceptable orthodontic force level range. Some directives are therefore provided to help orthodontists to select the optimal archwire.

Electrodeposition of polypyrrole onto NiTi and the corrosion behaviour of the coated alloy

International Nuclear Information System (INIS)

Flamini, D.O.; Saidman, S.B.

2010-01-01

Polypyrrole (PPy) films were electrodeposited onto nickel--titanium alloy (NiTi) employing sodium bis(2-ethylhexyl) sulfosuccinate (Aerosol OT or AOT) solutions. Polarizing anodically NiTi samples recovered by PPy in a monomer-free solution increases adhesion of the coating. Electrochemical techniques, scanning electron microscopy (SEM) and element analysis were used in determining the corrosion performance of the coated samples in chloride solution. The polymer improves the corrosion performance at the open circuit potential and at potentials where the bare substrate suffers pitting attack. The improvement in both, adhesion and corrosion performance, is discussed considering substrate/polymer interaction, overoxidation of PPy and the role played by AOT.

An adjustment in NiTi closed coil spring for an extended range of activation.

Science.gov (United States)

Ravipati, Raghu Ram; Sivakumar, Arunachalam; Sudhakar, P; Padmapriya, C V; Bhaskar, Mummudi; Azharuddin, Mohammad

2014-01-01

The Nickel Titanium (NiTi) closed coil springs serve as an efficient force delivery system in orthodontic space closure mechanics. The closed coil springs with the eyelets come in various lengths to broaden its force characteristics for an expedient space closure. However, at a certain point of time of progressive space closure, the coil spring can be expanded no further for an adequate force delivery. In such situations, the clinician prefers to replace the existing spring with another short length spring. The present article describes a simple conservative technique for progressively re-activating the same NiTi closed coil spring for complete space closure.

The use of shape memory compression anastomosis clips in cholecystojejunostomy in pigs – a preliminary study

Directory of Open Access Journals (Sweden)

Piotr Holak

2015-01-01

Full Text Available This paper reports on the use of compression anastomosis clips (CAC in cholecystoenterostomy in an animal model. Cholecystojejunostomy was performed in 6 pigs using implants made of nickel-titanium alloy in the form of elliptical springs with two-way shape memory. The applied procedure led to the achievement of tight anastomosis with a minimal number of complications and positive results of histopathological evaluations of the anastomotic site. The results of the study indicate that shape memory NiTi clips are a promising surgical tool for cholecystoenterostomy in cats and dogs.

Need for baby friendly commu- nity initiative to improve the low ...

African Journals Online (AJOL)

Ekanem EE. Fajola AO. Need for baby friendly commu- nity initiative to improve the low exclusive breastfeeding rates in. Nigeria. Accepted: 26th April 2016. Ekanem EE. Department of Paediatrics,. University of Calabar, Calabar, Nigeria. Email:emmanuelekanem@unical.edu.ng. Fajola AO. Regional Community Health,.

The effect of addition of various elements on properties of NiTi-based shape memory alloys for biomedical application

Science.gov (United States)

Kök, Mediha; Ateş, Gonca

2017-04-01

In biomedical applications, NiTi and NiTi-based alloys that show their shape memory effects at body temperature are preferred. In this study, the purpose is to produce NiTi and NiTi-based alloys with various chemical rates and electron concentrations and to examine their various physical properties. N45Ti55, Ni45Ti50Cr2.5Cu2.5, Ni48Ti51X (X=Mn, Sn, Co) alloys were produced in an arc melter furnace in this study. After the homogenization of these alloys, the martensitic phase transformation temperatures were determined with differential-scanner calorimeter. The transformation temperature was found to be below the 37 ° C (body temperature) in Ni45Ti50Cr2.5Cu2.5, Ni48Ti51X (X=Mn, Co) alloys; and the transformation temperature of the N45Ti55, Ni48Ti51Sn alloys was found to be over 37 ° C . Then, the micro and crystal structure analyses of the alloys were made, and it was determined that Ni45Ti50Cr2.5Cu2.5, Ni48Ti51X (X=Mn, Co) alloys, which were in austenite phase at room temperature, included B2 (NiTi) phase and Ti2Ni precipitation phase, and the alloys that were in the martensite phase at room temperature included B19ı (NiTi) phase and Ti2Ni phase. The common phase in both alloy groups is the Ti2Ni phase, and this type of phase is generally seen in NiTi alloys that are rich in titanium (Ti-rich).

Deformation of shape memory alloys associated with twinned domain re-configurations

International Nuclear Information System (INIS)

Liu Yong; Van Humbeeck, J.; Xie Zeliang; Delaey, L.

1999-01-01

Most of the applications of shape memory alloys (SMAs) imply deformation of martensite; it is therefore one of the fundamental research topics on the shape memory effect. So far, several classifications of the deformation mechanisms have been made as a function of deformation amplitude. However, the deformation details of martensitic SMAs are still not yet satisfactorily understood and these classifications need to be refined, because several incoherencies have been found lately by mechanical testing and transmission electron microscopy (TEM) observations. The present work summarizes some new results on the deformation mechanisms of martensitic NiTi SMAs under tension. As a result, the deformation process of martensite twins as a function of the deformation strain amplitude is refined. (orig.)

Effects of surface finish and mechanical training on Ni-Ti sheets for elastocaloric cooling

Directory of Open Access Journals (Sweden)

Kurt Engelbrecht

2016-06-01

Full Text Available Elastocaloric cooling has emerged as a promising alternative to vapor compression in recent years. Although the technology has the potential to be more efficient than current technologies, there are many technical challenges that must be overcome to realize devices with high performance and acceptable durability. We study the effects of surface finish and training techniques on dog bone shaped polycrystalline samples of NiTi. The fatigue life of several samples with four different surface finishes was measured and it was shown that a smooth surface, especially at the edges, greatly improved fatigue life. The effects of training both on the structure of the materials and the thermal response to an applied strain was studied. The load profile for the first few cycles was shown to change the thermal response to strain, the structure of the material at failure while the final structure of the material was weakly influenced by the surface finish.

Microfabricated Cantilevers Based on Sputtered Thin-Film Ni50Ti50 Shape Memory Alloy (SMA)

Science.gov (United States)

2015-08-01

surface coating developed during the NiTi deposition or anneal that is relatively resistant to the wet etch. Fig. 2 SEMs after the NiTi wet -etch...SEMs of NiTi devices after the 600 °C anneal , wet -etch patterning of the NiTi. A 120-nm Au capping layer was also sputtered. Figure 3a shows a 200-nm...Ni50Ti50 Cantilever 2 3. Results and Discussion 3 3.1 Wet -Etch Patterning NiTi 3 3.2 Dry-Etch Release of NiTi Devices 5 3.3 Thermal Actuation of

Microstructure of NiTi orthodontic wires observations using transmission electron microscopy

Directory of Open Access Journals (Sweden)

J. Ferčec

2014-10-01

Full Text Available This work presents the results of the microstructure observation of six different types of NiTi orthodontic wires by using Transmission Electron Microscopy (TEM. Within these analyses the chemical compositions of each wire were observed in different places by applying the EDS detector. Namely, the chemical composition in the orthodontic wires is very important because it shows the dependence between the phase temperatures and mechanical properties. Microstructure observations showed that orthodontic wires consist of nano-sized grains containing precipitates of Ti2Ni and/or TiC. The first precipitated Ti2Ni are rich in Ti, while the precipitated TiC is rich in C. Further investigation showed that there was a difference in average grain size in the NiTi matrix. The sizes of grains in orthodontic wires are in the range from approximately 50 to 160 nm and the sizes of precipitate are in the range from 0,3 μm to 5 μm.

Do NiTi instruments show defects before separation? Defects caused by torsional fatigue in hand and rotary nickel-titanium (NiTi) instruments which lead to failure during clinical use.

Science.gov (United States)

Chakka, N V Murali Krishna; Ratnakar, P; Das, Sanjib; Bagchi, Anandamy; Sudhir, Sudhir; Anumula, Lavanya

2012-11-01

Visual and microscopic evaluation of defects caused by torsional fatigue in hand and rotary nickel titanium (NiTi) instruments. Ninety-six NiTi greater taper instruments which were routinely used for root canal treatment only in anterior teeth were selected for the study. The files taken include ProTaper for hand use, ProTaper Rotary files and Endowave rotary files. After every use, the files were observed visually and microscopically (Stereomicroscope at 10×) to evaluate the defects caused by torsional fatigue. Scoring was given according to a new classification formulated which gives an indication of the severity of the defect or damage. Data was statistically analyzed using KruskallWallis and Mann-Whitney U test. Number of files showing defects were more under stereomicroscope than visual examination. But, the difference in the evaluation methods was not statistically significant. The different types of defects observed were bent instrument, straightening/stretching of twist contour and partial reverse twisting. Endowave files showed maximum number of defects followed by ProTaper for hand use and least in ProTaper Rotary. Visible defects due to torsional fatigue do occur in NiTi instruments after clinical use. Both visual and microscopic examinations were efficient in detecting defects caused due to torsional fatigue. This study emphasizes that all files should be observed for any visible defects before and after every instrumentation cycle to minimize the risk of instrument separation and failure of endodontic therapy.

Diffusion of titanium and nickel in B2 NiTi

Czech Academy of Sciences Publication Activity Database

Divinski, S.V.; Stloukal, Ivo; Král, Lubomír; Herzig, Ch.

289-292, - (2009), s. 377-382 ISSN 1012-0386. [DIMAT 2008, International Conference on Diffusion in Materials /7./. Lanzarote, Canary Islands , 28.10.2008-31.10.2008] Institutional research plan: CEZ:AV0Z20410507 Keywords : intermetallic compound NiTi * nickel nad titanium diffusion * diffusion mechanism Subject RIV: BJ - Thermodynamics http://www.scientific.net/DDF.289-292.377/

Three-Dimensional Cellular Structures Enhanced By Shape Memory Alloys

Science.gov (United States)

Nathal, Michael V.; Krause, David L.; Wilmoth, Nathan G.; Bednarcyk, Brett A.; Baker, Eric H.

2014-01-01

This research effort explored lightweight structural concepts married with advanced smart materials to achieve a wide variety of benefits in airframe and engine components. Lattice block structures were cast from an aerospace structural titanium alloy Ti-6Al-4V and a NiTi shape memory alloy (SMA), and preliminary properties have been measured. A finite element-based modeling approach that can rapidly and accurately capture the deformation response of lattice architectures was developed. The Ti-6-4 and SMA material behavior was calibrated via experimental tests of ligaments machined from the lattice. Benchmark testing of complete lattice structures verified the main aspects of the model as well as demonstrated the advantages of the lattice structure. Shape memory behavior of a sample machined from a lattice block was also demonstrated.

Stress induced martensite at the crack tip in NiTi alloys during fatigue loading

Directory of Open Access Journals (Sweden)

E. Sgambitterra

2014-10-01

Full Text Available Crack tip stress-induced phase transformation mechanisms in nickel-titanium alloys (NiTi were analyzed by Digital Image Correlation (DIC, under fatigue loads. In particular, Single Edge Crack (SEC specimens, obtained from a commercial pseudoelastic NiTi sheet, and an ad-hoc experimental setup were used, for direct measurements of the near crack tip displacement field by the DIC technique. Furthermore, a fitting procedure was developed to calculate the mode I Stress Intensity Factor (SIF, starting from the measured displacement field. Finally, cyclic tensile tests were performed at different operating temperature, in the range 298-338 K, and the evolution of the SIF was studied, which revealed a marked temperature dependence.

Performance of Small Bore 60NiTi Hybrid Ball Bearings: Preliminary Life Test Results

Science.gov (United States)

Dellacorte, Christopher; Howard, S. Adam

2016-01-01

Small bore (R8 size) hybrid ball bearings made with 60NiTi races and silicon nitride balls are under development for highly corrosive aerospace applications that are also exposed to heavy static (shock) loads. The target application is the vacuum pump used inside the wastewater recycling system on the International Space Station. To verify bearing longevity, life tests are run at 2000rpm for time periods up to 5000 hours. Accelerometers with data tracking are used to monitor operation and the bearings are disassembled and inspected at intervals to assess wear. Preliminary tests show that bearings made from 60NiTi are feasible for this aerospace and potentially other industrial applications that must endure similar operating environments.

An analytical mechanical model to describe the response of NiTi rotary endodontic files in a curved root canal

Energy Technology Data Exchange (ETDEWEB)

Leroy, Agnes Marie Francoise [Department of Metallurgical and Materials Engineering, School of Engineering, Universidade Federal de Minas Gerais (UFMG), Belo Horizonte, MG (Brazil); Department of Mechanical and Materials Engineering, Ecole des Ponts Paristech (ENPC), Champs-sur-Marne (France); Bahia, Maria Guiomar de Azevedo [Department of Restorative Dentistry, Faculty of Dentistry, Universidade Federal de Minas Gerais (UFMG), Belo Horizonte, MG (Brazil); Ehrlacher, Alain [Department of Mechanical and Materials Engineering, Ecole des Ponts Paristech (ENPC), Champs-sur-Marne (France); Buono, Vicente Tadeu Lopes, E-mail: vbuono@demet.ufmg.br [Department of Metallurgical and Materials Engineering, School of Engineering, Universidade Federal de Minas Gerais (UFMG), Belo Horizonte, MG (Brazil)

2012-08-01

Aim: To build a mathematical model describing the mechanical behavior of NiTi rotary files while they are rotating in a root canal. Methodology: The file was seen as a beam undergoing large transformations. The instrument was assumed to be rotating steadily in the root canal, and the geometry of the canal was considered as a known parameter of the problem. The formulae of large transformations mechanics then allowed the calculation of the Green-Lagrange strain field in the file. The non-linear mechanical behavior of NiTi was modeled as a continuous piecewise linear function, assuming that the material did not reach plastic deformation. Criteria locating the changes of behavior of NiTi were established and the tension field in the file, and the external efforts applied on it were calculated. The unknown variable of torsion was deduced from the equilibrium equation system using a Coulomb contact law which solved the problem on a cycle of rotation. Results: In order to verify that the model described well reality, three-point bending experiments were managed on superelastic NiTi wires, whose results were compared to the theoretical ones. It appeared that the model gave a good mentoring of the empirical results in the range of bending angles that interested us. Conclusions: Knowing the geometry of the root canal, one is now able to write the equations of the strain and stress fields in the endodontic instrument, and to quantify the impact of each macroscopic parameter of the problem on its response. This should be useful to predict failure of the files under rotating bending fatigue, and to optimize the geometry of the files. - Highlights: Black-Right-Pointing-Pointer A mechanical model of the behavior of a NiTi endodontic instrument was developed. Black-Right-Pointing-Pointer The model was validated with results of three-point bending tests on NiTi wires. Black-Right-Pointing-Pointer The model is appropriate for the optimization of instruments' geometry.

An analytical mechanical model to describe the response of NiTi rotary endodontic files in a curved root canal

International Nuclear Information System (INIS)

Leroy, Agnès Marie Françoise; Bahia, Maria Guiomar de Azevedo; Ehrlacher, Alain; Buono, Vicente Tadeu Lopes

2012-01-01

Aim: To build a mathematical model describing the mechanical behavior of NiTi rotary files while they are rotating in a root canal. Methodology: The file was seen as a beam undergoing large transformations. The instrument was assumed to be rotating steadily in the root canal, and the geometry of the canal was considered as a known parameter of the problem. The formulae of large transformations mechanics then allowed the calculation of the Green–Lagrange strain field in the file. The non-linear mechanical behavior of NiTi was modeled as a continuous piecewise linear function, assuming that the material did not reach plastic deformation. Criteria locating the changes of behavior of NiTi were established and the tension field in the file, and the external efforts applied on it were calculated. The unknown variable of torsion was deduced from the equilibrium equation system using a Coulomb contact law which solved the problem on a cycle of rotation. Results: In order to verify that the model described well reality, three-point bending experiments were managed on superelastic NiTi wires, whose results were compared to the theoretical ones. It appeared that the model gave a good mentoring of the empirical results in the range of bending angles that interested us. Conclusions: Knowing the geometry of the root canal, one is now able to write the equations of the strain and stress fields in the endodontic instrument, and to quantify the impact of each macroscopic parameter of the problem on its response. This should be useful to predict failure of the files under rotating bending fatigue, and to optimize the geometry of the files. - Highlights: ► A mechanical model of the behavior of a NiTi endodontic instrument was developed. ► The model was validated with results of three-point bending tests on NiTi wires. ► The model is appropriate for the optimization of instruments' geometry.

Ni-Ti Alloys for Tribological Applications: The Effects of Serendipity on Research and Development

Science.gov (United States)

DellaCorte, Christopher

2016-01-01

Novel superelastic materials based upon Nickel-Titanium (NiTi) alloys are an emerging technology that almost escaped recognition. Though steel is the dominant material of choice for mechanical components (bearings and gears) it has intrinsic limitations related to corrosion and plastic deformation. In 2004, at the request of a small manufacturing firm, Nitinol 60 was assessed as an alternative to bearing steel. Early investigations showed it to be hard and impervious to aqueous corrosion but its tribological properties were not fully explored. Conventional wisdom in the field of tribology suggests that alloys rich in titanium are poor candidate bearing materials but NiTi, an intermetallic, demonstrates that such thinking can be and often is, wrong. Though early stage tests reveal acceptable friction and wear behavior, extensive materials engineering and processing development was essential in producing the precision microstructures needed for long-life bearings and gears. In the course of exploring this new material system other game-changing and unexpected properties, such as superelastic resilience, were observed. Today, the aerospace community is exploiting the unique characteristics of the NiTi alloy materials to solve problems on earth, underwater and in space. A fortunate decision to acknowledge a single industrial request turned out to be the key to an entirely new technology.

The effect of surface treatment and clinical use on friction in NiTi orthodontic wires.

Science.gov (United States)

Wichelhaus, Andrea; Geserick, Marc; Hibst, Raimund; Sander, Franz G

2005-10-01

Since the low friction of NiTi wires allows a rapid and efficient orthodontic tooth movement, the aim of this research was to investigate the friction and surface roughness of different commercially available superelastic NiTi wires before and after clinical use. The surface of all of the wires had been pre-treated by the manufacturer. Forty superelastic wires (Titanol Low Force, Titanol Low Force River Finish Gold, Neo Sentalloy, Neo Sentalloy Ionguard) of diameter 0.016 x 0.022 in. were tested. The friction for each type of NiTi archwire ligated into a commercial stainless steel bracket was determined with a universal testing machine. Having ligated the wire into the bracket, it could then be moved forward and backwards along a fixed archwire whilst a torquing moment was applied. The surface roughness was investigated using a profilometric measuring device on defined areas of the wire. Statistical data analysis was conducted by means of the Wilcoxon test. The results showed that initially, the surface treated wires demonstrated significantly (p < 0.01) less friction than the non-treated wires. The surface roughness showed no significant difference between the treated and the non-treated surfaces of the wires. All 40 wires however showed a significant increase in friction and surface roughness during clinical use. Whilst the Titanol Low Force River Finish Gold (Forestadent, Pforzheim, Germany) wires showed the least friction of all the samples and consequently should be more conservative on anchorage, the increase in friction of all the surface treated wires during orthodontic treatment almost cancels out this initial effect on friction. It is therefore recommended that surface treated NiTi orthodontic archwires should only be used once.

Performance characteristics of shape memory alloy and its applications for fusion technology

International Nuclear Information System (INIS)

Nishikawa, Masahiro; Watanabe, Kenji

1987-01-01

As a shape memory alloy, Au-Cd alloy was found in 1951. Thereafter, also in In-Tl alloy, shape memory effect was found. The U.S. Naval Ordinance Laboratory developed Ni-Ti alloy, and published in 1965 as NITINOL. As Cu group shape memory alloys, there are Cu-Zn-Al alloy, Cu-Al-Be alloy and Cu-Al-Ni alloy. Recently, iron group shape memory alloy was published. In 1975, 'Shape memory effect and its application' symposium, in 1978, 'NITINOL heat engine international conference', and in 1982 and 1986, 'Martensite transformation international conference' were held, and the method of the proper use of shape memory alloys and the problems of the alloys themselves such as fatigue have been gradually clarified. In this report, the fundamental action characteristics of shape memory alloys are discribed from the viewpoint of the application, and the possibility of applying these characteristics to nuclear fusion devices and the advantage obtained as the result are explained. Shape memory effect and pseudo-elasticity, reversible shape memory effect, the thermodynamic behavior of shape memory alloys, transformation temperature range and using temperature range and so on are described. (Kako, I.)

Method for decontaminating radiation metal waste

International Nuclear Information System (INIS)

Onuma, Tsutomu; Tanaka, Akio; Akimoto, Hidetoshi

1991-01-01

This report describes a method for decontaminating radiation metal waste characterized by the following properties: in order to decontaminate radiation metal waste of various shapes produced by facilities involved with radioactive substances, non-complex shapes are decontaminated by electropolishing the materials in a neutral saline solution. Complex shapes are chemically decontaminated by means of an acid solution containing permanganic acid or an alkaline solution and a mineral acid solution. After neutralizing the solutions used for chemical decontamination, the radioactive material is separated and removed. Further, in the decontamination method for radioactive metal waste, a supernatant liquid is reused as the electrolyte in electropolishing decontamination. Permanganic ions (MnO 4 - ) are reduced to manganese dioxide (MnO 2 ) and deposited prior to neutralizing the solution used for chemical decontamination. Once manganese dioxide (MnO 2 ) has been separated and removed, it is re-used as the electrolyte in electropolishing decontamination by means of a process identical to the separation process for radioactive substances. 3 figs

Effect of Annealing on Strain-Temperature Response under Constant Tensile Stress in Cold-Worked NiTi Thin Wire

OpenAIRE

Yan, Xiaojun; Van Humbeeck, Jan

2011-01-01

The present paper aims to understand the influence of annealing on the strain-temperature response of a cold-worked NiTi wire under constant tensile stress. It was found that transformation behavior, stress-strain relationship, and strain-temperature response of the cold-worked NiTi wire are strongly affected by the annealing temperature. Large martensitic strains can be reached even though the applied stress is below the plateau stress of the martensite phase. At all stress levels transforma...

An original architectured NiTi silicone rubber structure for biomedical applications

Czech Academy of Sciences Publication Activity Database

Rey, T.; Le Cam, J.B.; Chagnon, G.; Favier, D.; Rebouah, M.; Razan, F.; Robin, E.; Didier, P.; Heller, Luděk; Faure, S.; Janouchová, Kateřina

2014-01-01

Roč. 45, Dec (2014), s. 184-190 ISSN 0928-4931 Institutional support: RVO:68378271 Keywords : adhesion * interface * NiTi * filled silicone rubber * biomedical applications * architectured composite Subject RIV: BM - Solid Matter Physics ; Magnetism OBOR OECD: Condensed matter physics (including formerly solid state physics, supercond.) Impact factor: 3.088, year: 2014

Validated finite element analyses of WaveOne Endodontic Instruments: a comparison between M-Wire and NiTi alloys.

Science.gov (United States)

Bonessio, N; Pereira, E S J; Lomiento, G; Arias, A; Bahia, M G A; Buono, V T L; Peters, O A

2015-05-01

To validate torsional analysis, based on finite elements, of WaveOne instruments against in vitro tests and to model the effects of different nickel-titanium (NiTi) materials. WaveOne reciprocating instruments (Small, Primary and Large, n = 8 each, M-Wire) were tested under torsion according to standard ISO 3630-1. Torsional profiles including torque and angle at fracture were determined. Test conditions were reproduced through Finite Element Analysis (FEA) simulations based on micro-CT scans at 10-μm resolution; results were compared to experimental data using analysis of variance and two-sided one sample t-tests. The same simulation was performed on virtual instruments with identical geometry and load condition, based on M-Wire or conventional NiTi alloy. Torsional profiles from FEA simulations were in significant agreement with the in vitro results. Therefore, the models developed in this study were accurate and able to provide reliable simulation of the torsional performance. Stock NiTi files under torsional tests had up to 44.9%, 44.9% and 44.1% less flexibility than virtual M-Wire files at small deflections for Small, Primary and Large instruments, respectively. As deflection levels increased, the differences in flexibility between the two sets of simulated instruments decreased until fracture. Stock NiTi instruments had a torsional fracture resistance up to 10.3%, 8.0% and 7.4% lower than the M-Wire instruments, for the Small, Primary and Large file, respectively. M-Wire instruments benefitted primarily through higher material flexibility while still at low deflection levels, compared with conventional NiTi alloy. At fracture, the instruments did not take complete advantage of the enhanced fractural resistance of the M-Wire material, which determines only limited improvements of the torsional performance. © 2014 International Endodontic Journal. Published by John Wiley & Sons Ltd.

Application of the Superelastic NiTi Spring in Ankle Foot Orthosis (AFO to Create Normal Ankle Joint Behavior

Directory of Open Access Journals (Sweden)

Amirhesam Amerinatanzi

2017-12-01

Full Text Available Hinge-based Ankle Foot Orthosis (HAFO is one of the most common non-surgical solutions for the foot drop. In conventional HAFOs, the ankle joint is almost locked, and plantar flexion is restricted due to the high stiffness of the hinge mechanism. This often leads to a rigid walking gate cycle, poor muscle activity, and muscle atrophy. Since the ankle torque-angle loop has a non-linear profile, the use of a superelastic NiTi spring within the hinge, due to its nonlinear behavior, could recreate a close-to-normal stiffness of the normal ankle joint, which, in turn, could create a more natural walk. The focus of this study is to evaluate the performance of a superelastic NiTi spring versus a conventional Stainless Steel spring in a hinge mechanism of a custom-fit HAFO. To this aim, a custom-fit HAFO was fabricated via the fast casting technique. Then, motion analysis was performed for two healthy subjects (Case I and Case II: (i subjects with bare foot; (ii subjects wearing a conventional HAFO with no spring; (iii subjects wearing a conventional Stainless Steel-based HAFO; and (iv subjects wearing a NiTi spring-based HAFO. The data related to the ankle angle and the amount of moment applied to the ankle during walking were recorded using Cortex software and used for the evaluations. Finally, Finite Element Analysis (FEA was performed to evaluate the safety of the designed HAFO. The NiTi spring offers a higher range of motion (7.9 versus 4.14 degree and an increased level of moment (0.55 versus 0.36 N·m/kg. Furthermore, a NiTi spring offers an ankle torque-angle loop closer to that of the healthy subjects.

Application of the Superelastic NiTi Spring in Ankle Foot Orthosis (AFO) to Create Normal Ankle Joint Behavior.

Science.gov (United States)

Amerinatanzi, Amirhesam; Zamanian, Hashem; Shayesteh Moghaddam, Narges; Jahadakbar, Ahmadreza; Elahinia, Mohammad

2017-12-07

Hinge-based Ankle Foot Orthosis (HAFO) is one of the most common non-surgical solutions for the foot drop. In conventional HAFOs, the ankle joint is almost locked, and plantar flexion is restricted due to the high stiffness of the hinge mechanism. This often leads to a rigid walking gate cycle, poor muscle activity, and muscle atrophy. Since the ankle torque-angle loop has a non-linear profile, the use of a superelastic NiTi spring within the hinge, due to its nonlinear behavior, could recreate a close-to-normal stiffness of the normal ankle joint, which, in turn, could create a more natural walk. The focus of this study is to evaluate the performance of a superelastic NiTi spring versus a conventional Stainless Steel spring in a hinge mechanism of a custom-fit HAFO. To this aim, a custom-fit HAFO was fabricated via the fast casting technique. Then, motion analysis was performed for two healthy subjects (Case I and Case II): (i) subjects with bare foot; (ii) subjects wearing a conventional HAFO with no spring; (iii) subjects wearing a conventional Stainless Steel-based HAFO; and (iv) subjects wearing a NiTi spring-based HAFO. The data related to the ankle angle and the amount of moment applied to the ankle during walking were recorded using Cortex software and used for the evaluations. Finally, Finite Element Analysis (FEA) was performed to evaluate the safety of the designed HAFO. The NiTi spring offers a higher range of motion (7.9 versus 4.14 degree) and an increased level of moment (0.55 versus 0.36 N·m/kg). Furthermore, a NiTi spring offers an ankle torque-angle loop closer to that of the healthy subjects.

Parametric investigations on the influence of nano-second Nd{sup 3+}:YAG laser wavelength and fluence in synthesizing NiTi nano-particles using liquid assisted laser ablation technique

Energy Technology Data Exchange (ETDEWEB)

Patra, Nandini, E-mail: nandinipatra2007@gmail.com [Centre for Material Science and Engineering, Indian Institute of Technology, Indore, Madhya Pradesh, Pin-453441 (India); Akash, K.; Shiva, S.; Gagrani, Rohit; Rao, H. Sai Pranesh; Anirudh, V.R. [Mechatronics and Instrumentation lab, Discipline of Mechanical Engineering, Indian Institute of Technology, Indore, Madhya Pradesh, Pin-453441 (India); Palani, I.A., E-mail: palaniia@iiti.ac.in [Centre for Material Science and Engineering, Indian Institute of Technology, Indore, Madhya Pradesh, Pin-453441 (India); Mechatronics and Instrumentation lab, Discipline of Mechanical Engineering, Indian Institute of Technology, Indore, Madhya Pradesh, Pin-453441 (India); Singh, Vipul [Centre for Material Science and Engineering, Indian Institute of Technology, Indore, Madhya Pradesh, Pin-453441 (India)

2016-03-15

Graphical abstract: - Highlights: • Influence of laser wavelengths (1064 nm, 532 nm and 355 nm) and fluences (40 J/cm{sup 2}, 30 J/cm{sup 2} and 20 J/cm{sup 2}) on generation of underwater laser ablated NiTi nanoparticles. • Particle size range of 140–10 nm was generated at varying laser wavelengths. • The alloy formation of NiTi nanoparticles was confirmed from XRD and TEM analysis where the crystalline peaks of NiTi, Ni{sub 4}Ti{sub 3} and Ni{sub 3}Ti were observed from XRD. • Formation efficiency of NiTi nanoparticles was maximum at 1064 nm wavelength and 40 J/cm{sup 2} fluence. - Abstract: This paper investigates the influence of laser wavelengths and laser fluences on the size and quality of the NiTi nanoparticles, generated through underwater solid state Nd:YAG laser ablation technique. The experiments were performed on Ni55%–Ti45% sheet to synthesize NiTi nano-particles at three different wavelengths (1064 nm, 532 nm and 355 nm) with varying laser fluences ranging from 20 to 40 J/cm{sup 2}. Synthesized NiTi nano-particles were characterized through SEM, DLS, XRD, FT-IR, TEM and UV–vis spectrum. It was observed that, maximum particle size of 140 nm and minimum particle size of 10 nm were generated at varying laser wavelengths. The crystallinity and lattice spacing of NiTi alloy nanoparticles were confirmed from the XRD analysis and TEM images, respectively.

Effect of aging treatment on the in vitro nickel release from porous oxide layers on NiTi

Energy Technology Data Exchange (ETDEWEB)

Huan, Z.; Fratila-Apachitei, L.E., E-mail: e.l.fratila-apachitei@tudelft.nl; Apachitei, I.; Duszczyk, J.

2013-06-01

Despite the ability of creating porous oxide layers on nickel–titanium alloy (NiTi) surface for biofunctionalization, the use of plasma electrolytic oxidation (PEO) has raised concerns over the possible increased levels of Ni release. Therefore, the primary aim of this study was to investigate the effect of aging in boiling water on Ni release from porous NiTi surfaces that have been formed by the PEO process. Based on different oxidation conditions, e.g. electrolyte composition and electrical parameters, three kinds of oxide layers with various characteristics were prepared on NiTi substrate. The process was followed by aging in boiling water for different durations. The Ni release was assessed by immersion tests in phosphate buffer saline and the Ni concentration was measured using the flame atomic absorption spectrometry. The results showed that aging in boiling water can significantly reduce the Ni release from oxidized porous samples, given that the duration of the treatment is finely adjusted according to the parameters of the as-formed oxide layer. Surface examination of the samples before and after aging in boiling water suggested that such a treatment is non-destructive while improving the corrosion resistance of oxidized samples, as evidenced by potentiodynamic polarization tests. The results of this study indicate that water boiling may be a suitable post-treatment required to minimize Ni release from porous oxides produced on NiTi by PEO for biomedical applications.

Heat treatment of thin NiTi filaments by electric current

Czech Academy of Sciences Publication Activity Database

Pilch, Jan; Heller, Luděk; Šittner, Petr

2010-01-01

Roč. 2, č. 1 (2010), 1-4 ISSN N R&D Projects: GA ČR GAP108/10/1296; GA AV ČR(CZ) IAA200100627 Grant - others:EC "UPWIND" -Integrated Wind Turbine Design(XE) 019945 (SES6) Institutional research plan: CEZ:AV0Z10100520 Keywords : NiTi * SMA * heat treatment * martensitic transformation Subject RIV: BM - Solid Matter Physics ; Magnetism

Additive Manufacturing of NiTiHf High Temperature Shape Memory Alloy

Science.gov (United States)

Benafan, Othmane; Bigelow, Glen S.; Elahinia, Mohammad; Moghaddam, Narges Shayesteh; Amerinatanzi, Amirhesam; Saedi, Soheil; Toker, Guher Pelin; Karaca, Haluk

2017-01-01

Additive manufacturing of a NiTi-20Hf high temperature shape memory alloy (HTSMA) was investigated. A selective laser melting (SLM) process by Phenix3D Systems was used to develop components from NiTiHf powder (of approximately 25-75 m particle fractions), and the thermomechanical response was compared to the conventionally vacuum induction skull melted counterpart. Transformation temperatures of the SLM material were found to be slightly lower due to the additional oxygen pick up from the gas atomization and melting process. The shape memory response in compression was measured for stresses up to 500 MPa, and transformation strains were found to be very comparable (Up to 1.26 for the as-extruded; up to 1.52 for SLM).

60NiTi Intermetallic Material Evaluation for Lightweight and Corrosion Resistant Spherical Sliding Bearings for Aerospace Applications, Report on NASA-Kamatics SAA3-1288

Science.gov (United States)

Dellacorte, Christopher; Jefferson, Michael

2015-01-01

Under NASA Space Act Agreement (SAA3-1288), NASA Glenn Research Center and the Kamatics subsidiary of the Kaman Corporation conducted the experimental evaluation of spherical sliding bearings made with 60NiTi inner races. The goal of the project was to assess the feasibility of manufacturing lightweight, corrosion resistant bearings utilizing 60NiTi for aerospace and industrial applications. NASA produced the bearings in collaboration with Abbott Ball Corporation and Kamatics fabricated bearing assemblies utilizing their standard reinforced polymer liner material. The assembled bearings were tested in oscillatory motion at a load of 4.54 kN (10,000 lb), according to the requirements of the plain bearing specification SAE AS81820. Several test bearings were exposed to hydraulic fluid or aircraft deicing fluid prior to and during testing. The results show that the 60NiTi bearings exhibit tribological performance comparable to conventional stainless steel (440C) bearings. Further, exposure of 60NiTi bearings to the contaminant fluids had no apparent performance effect. It is concluded that 60NiTi is a feasible bearing material for aerospace and industrial spherical bearing applications.

Shape rheocasting of high purity aluminium

CSIR Research Space (South Africa)

Curle, UA

2011-03-01

Full Text Available silica. The electro-polishing step with 5ml perchloric acid in 95 ml acetic acid at 30 V DC potential and room temperature [13] already revealed the microstructure. A Leica DMI5000 M optical microscope equipped with a Leica DFC480 camera and Image...

Combinatorial experiment in Ni-Ti thin films by laser interference structuring

International Nuclear Information System (INIS)

Liu, K.W.; Gachot, C.; Leibenguth, P.; Muecklich, F.

2005-01-01

Combinatorial experiments are achieved on periodically structured Ni-Ti thin film composition spreads by laser interference irradiation using a Nd:YAG laser. Continuous Ni-Ti compositional spreads covering almost the whole binary system are prepared by combining sputter mask, shutter and movement of substrate. The continuous compositional spread is subsequently micro-structured into a sample library consisting of well-defined lines of individual samples by laser interference irradiation. The composition and microstructure effects in continuous spread and sample libraries after laser structuring are explored by scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and white light interferometry (WLI) microscopy. The sample library consists of individual samples with a distance of about 5 μm and a composition resolution as high as 0.1 at.% in between. Although, there are certain difficulties so far in obtaining the optimized laser fluence for the spread, the laser interference irradiation provides an effective way to prepare thin film libraries with around 200 sample lines within 1 mm

Martensitic phase transformation in shape-memory alloys

International Nuclear Information System (INIS)

Golestaneh, A.A.

1979-01-01

Isothermal studies are described of the shape-recovery phenomenon, stress-strain behavior, electrical resistivity and thermo-electric power associated with the martensite-parent phase reaction in the Ni-Ti shape-memory alloys. The energy-balance equation that links the reaction kinetics with the strain energy change during the cooling-deforming and heating cycle is analyzed. The strain range in which the Clausius-Clapeyron equation satisfactorily describes this reaction is determined. A large change in the Young's modulus of the specimen is found to be associated with the M → P reaction. A hysteresis loop in the resistivity-temperature plot is found and related to the anomaly in the athermal resistivity changes during cyclic M → P → M transformation. An explanation for the resistivity anomaly is offered. The M structure is found to be electrically negative relative to the P structure. A thermal emf of greater than or equal to 0.12 mV is found at the M-P interface

Vacuum Arc Melting Processes for Biomedical Ni-Ti Shape Memory Alloy

OpenAIRE

Tsai De-Chang; Chiang Chen-Hsueh

2015-01-01

This study primarily involved using a vacuum arc remelting (VAR) process to prepare a nitinol shape-memory alloy with distinct ratios of alloy components (nitinol: 54.5 wt% to 57 wt%). An advantage of using the VAR process is the adoption of a water-cooled copper crucible, which effectively prevents crucible pollution and impurity infiltration. Optimising the melting production process enables control of the alloy component and facilitates a uniformly mixed compound during subsequent processi...

Endodontic shaping performance using nickel-titanium hand and motor ProTaper systems by novice dental students.

Science.gov (United States)

Tu, Ming-Gene; Chen, San-Yue; Huang, Heng-Li; Tsai, Chi-Cheng

2008-05-01

Preparing a continuous tapering conical shape and maintaining the original shape of a canal are obligatory in root canal preparation. The purpose of this study was to compare the shaping performance in simulated curved canal resin blocks of the same novice dental students using hand-prepared and engine-driven nickel-titanium (NiTi) rotary ProTaper instruments in an endodontic laboratory class. Twenty-three fourth-year dental students attending China Medical University Dental School prepared 46 simulated curved canals in resin blocks with two types of NiTi rotary systems: hand and motor ProTaper files. Composite images were prepared for estimation. Material removed, canal width and canal deviation were measured at five levels in the apical 4 mm of the simulated curved canals using AutoCAD 2004 software. Data were analyzed using Wilcoxon's rank-sum test. The hand ProTaper group cut significantly wider than the motor rotary ProTaper group in the outer wall, except for the apical 0 mm point. The total canal width was cut significantly larger in the hand group than in the motor group. There was no significant difference between the two groups in centering canal shape, except at the 3 mm level. These findings show that the novice students prepared the simulated curved canal that deviated more outwardly from apical 1 mm to 4 mm using the hand ProTaper. The ability to maintain the original curvature was better in the motor rotary ProTaper group than in the hand ProTaper group. Undergraduate students, if following the preparation sequence carefully, could successfully perform canal shaping by motor ProTaper files and achieve better root canal geometry than by using hand ProTaper files within the same teaching and practicing sessions.

Characterization of Transformation-Induced Defects in Nickel Titanium Shape Memory Alloys

Science.gov (United States)

Bowers, Matthew L.

Shape memory alloys have remarkable strain recovery properties that make them ideal candidates for many applications that include devices in the automotive, aerospace, medical, and MEMS industries. Although these materials are widely used today, their performance is hindered by poor dimensional stability resulting from cyclic degradation of the martensitic transformation behavior. This functional fatigue results in decreased work output and cyclic accumulation of permanent strain. To date, few studies have taken a fundamental approach to investigating the interaction between plasticity and martensite growth and propagation, which is vitally important to mitigating functional fatigue in future alloy development. The current work focuses on understanding the interplay of these deformation mechanisms in NiTi-based shape memory alloys under a variety of different thermomechanical test conditions. Micron-scale compression testing of NiTi shape memory alloy single crystals is undertaken in an effort to probe the mechanism of austenite dislocation generation. Mechanical testing is paired with post mortem defect analysis via diffraction contrast scanning transmission electron microscopy (STEM). Accompanied by micromechanics-based modeling of local stresses surrounding a martensite plate, these results demonstrate that the previously existing martensite and resulting austenite dislocation substructure are intimately related. A mechanism of transformation-induced dislocation generation is described in detail. A study of pure and load-biased thermal cycling of bulk polycrystalline NiTi is done for comparison of the transformation behavior and resultant defects to the stress-induced case. Post mortem and in situ STEM characterization demonstrate unique defect configurations in this test mode and STEM-based orientation mapping reveals local crystal rotation with increasing thermal cycles. Changes in both martensite and austenite microstructures are explored. The results for

Comparison of cyclic fatigue resistance of novel nickel-titanium rotary instruments.

Science.gov (United States)

Capar, Ismail Davut; Ertas, Huseyin; Arslan, Hakan

2015-04-01

New files (ProTaper Next/HyFlex/OneShape) are made from novel nickel-titanium (NiTi) alloys/treatments. The purpose of this study was to compare the cyclic fatigue resistance of these new instruments with that of Revo-S instruments. Four groups of 20 NiTi endodontic instruments were tested in steel canals with a 3 mm radius and a 60° angle of curvature. The cyclic fatigue of the following NiTi instruments with a tip size 25 and 0.06 taper that were manufactured with different alloys was tested: ProTaper Next X2 (M-Wire), OneShape (conventional NiTi), Revo-S Shaping Universal (conventional NiTi) and HyFlex 25/0.6 (controlled memory NiTi wire). A one-way anova and post-hoc Tukey's test (α = 0.05) revealed that the HyFlex files had the highest fatigue resistance and the Revo-S had the least fatigue resistance among the groups (P < 0.001). © 2014 Australian Society of Endodontology.

On the improved adhesion of NiTi wires embedded in polyester and vinylester resins

Directory of Open Access Journals (Sweden)

Mattia Merlin

2015-01-01

Full Text Available This paper discusses the effect of different surface treatments on shape memory alloy wires embedded in PolyEster (PE and VinylEster (VE polymeric matrices. In particular, two types of chemical etching and a chemical bonding with a silane coupling agent have been performed on the surfaces of the wires. Pull-out tests have been carried out on samples made from a specifically designed Teflon mould. Considering the best results of the pull-out tests obtained with PE resin, the debonding induced by strain recovery of 4%, 5% and 6% pre-strained NiTi wires has been evaluated with the wires being subjected to different surface treatment conditions and then being embedded in the PE matrix. The results prove that the wires functionalised and embedded in the PE resin show the maximum pull-out forces and the highest interfacial adhesion. Finally, it has been found that debonding induced by strain recovery is strongly related to the propagation towards the radial direction of sharp cracks at the debonding region.

Cyclic fatigue resistance of R-Pilot, HyFlex EDM and PathFile nickel-titanium glide path files in artificial canals with double (S-shaped) curvature.

Science.gov (United States)

Uslu, G; Özyürek, T; Yılmaz, K; Gündoğar, M

2018-05-01

To examine the cyclic fatigue resistances of R-Pilot, HyFlex EDM and PathFile NiTi glide path files in S-shaped artificial canals. Twenty R-Pilot (12.5/.04), 20 HyFlex EDM (10/.05) and 20 PathFile (19/.02) single-file glide path files were included. Sixty files (n: 20/each) were subjected to static cyclic fatigue testing using double-curved canals until fracture occurred (TF). The number of cycles to fracture (NCF) was calculated by multiplying the rpm value by the TF. The length of the fractured fragment (FL) was determined by a digital microcaliper. Six samples of fractured files (n: 2/each) were examined by SEM to determine the fracture mode. The NCF and the FL data were analysed using one-way anova, post hoc Tamhane and Kruskal-Wallis tests using SPPS 21 software. The significance level was set at 5%. In the double-curved canal, all the files fractured first in the apical curvature and then in the coronal curvature. The NCF values revealed that the R-Pilot had the greatest cyclic fatigue resistance, followed by the HyFlex EDM and PathFile in both the apical and coronal curvatures (P < 0.05). R-Pilot NiTi glide path files, used in a reciprocating motion, had the greatest cyclic fatigue resistance amongst the tested NiTi glide path files in an artificial S-shaped canal. © 2017 International Endodontic Journal. Published by John Wiley & Sons Ltd.

An innovative approach to achieve re-centering and ductility of cement mortar beams through randomly distributed pseudo-elastic shape memory alloy fibers

Science.gov (United States)

Shajil, N.; Srinivasan, S. M.; Santhanam, M.

2012-04-01

Fibers can play a major role in post cracking behavior of concrete members, because of their ability to bridge cracks and distribute the stress across the crack. Addition of steel fibers in mortar and concrete can improve toughness of the structural member and impart significant energy dissipation through slow pull out. However, steel fibers undergo plastic deformation at low strain levels, and cannot regain their shape upon unloading. This is a major disadvantage in strong cyclic loading conditions, such as those caused by earthquakes, where self-centering ability of the fibers is a desired characteristic in addition to ductility of the reinforced cement concrete. Fibers made from an alternative material such as shape memory alloy (SMA) could offer a scope for re-centering, thus improving performance especially after a severe loading has occurred. In this study, the load-deformation characteristics of SMA fiber reinforced cement mortar beams under cyclic loading conditions were investigated to assess the re-centering performance. This study involved experiments on prismatic members, and related analysis for the assessment and prediction of re-centering. The performances of NiTi fiber reinforced mortars are compared with mortars with same volume fraction of steel fibers. Since re-entrant corners and beam columns joints are prone to failure during a strong ground motion, a study was conducted to determine the behavior of these reinforced with NiTi fiber. Comparison is made with the results of steel fiber reinforced cases. NiTi fibers showed significantly improved re-centering and energy dissipation characteristics compared to the steel fibers.

Failure Analysis and Recovery of a 50 MM Highly Elastic Intermetallic NiTi Ball Bearing for an ISS Application

Science.gov (United States)

DellaCorte, Christopher; Howard, S. Adam; Moore, Lewis E., III

2016-01-01

The ISS Distillation Assembly centrifuge is the pathfinder application for 50mm bore, deep-groove ball bearings made from the highly elastic intermetallic material 60NiTi. Superior corrosion and shock resistance are required to withstand the acidic wastewater exposure and heavy spacecraft launch related loads that challenge conventional steel bearings. During early ground testing one bearing unexpectedly and catastrophically failed after operating for only 200 hours of run time. A second bearing running on the same shaft was completely unaffected. A thorough investigation into the root cause of the failure determined that an excessively tight press-fit of the bearing outer race coupled with NiTis relatively low elastic modulus were key contributing factors. The proposed failure mode was successfully duplicated by experiment. To further corroborate the root cause theory, a successful bearing life test using improved installation practices (selective fitting) was conducted. The results show that NiTi bearings are suitable for space applications provided that care is taken to accommodate their unique material characteristics.

Length-dependent corrosion behavior, Ni2+ release, cytocompatibility, and antibacterial ability of Ni-Ti-O nanopores anodically grown on biomedical NiTi alloy.

Science.gov (United States)

Hang, Ruiqiang; Liu, Yanlian; Bai, Long; Zhang, Xiangyu; Huang, Xiaobo; Jia, Husheng; Tang, Bin

2018-08-01

In the present work, nickel-titanium-oxygen nanopores with different length (0.55-114 μm) were anodically grown on nearly equiatomic nickel-titanium (NiTi) alloy. Length-dependent corrosion behavior, nickel ion (Ni 2+ ) release, cytocompatibility, and antibacterial ability were investigated by electrochemical, analytical chemistry, and biological methods. The results show constructing nanoporous structure on the NiTi alloy improve its corrosion resistance. However, the anodized samples release more Ni 2+ than that of the bare NiTi alloy, suggesting chemical dissolution of the nanopores rather than electrochemical corrosion governs the Ni 2+ release. In addition, the Ni 2+ release amount increases with nanopore length. The anodized samples show good cytocompatibility when the nanopore length is covers the one (1-11 μm) that the nanopores showing favorable antibacterial ability. Consequently, the nanopores with length in the range of 1-11 μm are promising as coatings of biomedical NiTi alloy for anti-infection, drug delivery, and other desirable applications. Copyright © 2018 Elsevier B.V. All rights reserved.

Surface analyses of electropolished niobium samples for superconducting radio frequency cavity

International Nuclear Information System (INIS)

Tyagi, P. V.; Nishiwaki, M.; Saeki, T.; Sawabe, M.; Hayano, H.; Noguchi, T.; Kato, S.

2010-01-01

The performance of superconducting radio frequency niobium cavities is sometimes limited by contaminations present on the cavity surface. In the recent years extensive research has been done to enhance the cavity performance by applying improved surface treatments such as mechanical grinding, electropolishing (EP), chemical polishing, tumbling, etc., followed by various rinsing methods such as ultrasonic pure water rinse, alcoholic rinse, high pressure water rinse, hydrogen per oxide rinse, etc. Although good cavity performance has been obtained lately by various post-EP cleaning methods, the detailed nature about the surface contaminants is still not fully characterized. Further efforts in this area are desired. Prior x-ray photoelectron spectroscopy (XPS) analyses of EPed niobium samples treated with fresh EP acid, demonstrated that the surfaces were covered mainly with the niobium oxide (Nb 2 O 5 ) along with carbon, in addition a small quantity of sulfur and fluorine were also found in secondary ion mass spectroscopy (SIMS) analysis. In this article, the authors present the analyses of surface contaminations for a series of EPed niobium samples located at various positions of a single cell niobium cavity followed by ultrapure water rinsing as well as our endeavor to understand the aging effect of EP acid solution in terms of contaminations presence at the inner surface of the cavity with the help of surface analytical tools such as XPS, SIMS, and scanning electron microscope at KEK.

Efficacy of NiTi rotary instruments in removing calcium hydroxide dressing residues from root canal walls

Directory of Open Access Journals (Sweden)

Milton Carlos Kuga

2012-02-01

Full Text Available The aim of this study was to evaluate the efficacy of three rotary instrument systems (K3, ProTaper and Twisted File in removing calcium hydroxide residues from root canal walls. Thirty-four human mandibular incisors were instrumented with the ProTaper System up to the F2 instrument, irrigated with 2.5% NaOCl followed by 17% EDTA, and filled with a calcium hydroxide intracanal dressing. After 7 days, the calcium hydroxide dressing was removed using the following rotary instruments: G1 - NiTi size 25, 0.06 taper, of the K3 System; G2 - NiTi F2, of the ProTaper System; or G3 - NiTi size 25, 0.06 taper, of the Twisted File System. The teeth were longitudinally grooved on the buccal and lingual root surfaces, split along their long axis, and their apical and cervical canal thirds were evaluated by SEM (×1000. The images were scored and the data were statistically analyzed using the Kruskall Wallis test. None of the instruments removed the calcium hydroxide dressing completely, either in the apical or cervical thirds, and no significant differences were observed among the rotary instruments tested (p > 0.05.

Investigation of the Dissolution-Reformation Cycle of the Passive Oxide Layer on NiTi Orthodontic Archwires

Science.gov (United States)

Uzer, B.; Birer, O.; Canadinc, D.

2017-09-01

Dissolution-reformation cycle of the passive oxide layer on the nickel-titanium (NiTi) orthodontic archwires was investigated, which has recently been recognized as one of the key parameters dictating the biocompatibility of archwires. Specifically, commercially available NiTi orthodontic archwires were immersed in artificial saliva solutions of different pH values (2.3, 3.3, and 4.3) for four different immersion periods: 1, 7, 14, and 30 days. Characterization of the virgin and tested samples revealed that the titanium oxide layer on the NiTi archwire surfaces exhibit a dissolution-reformation cycle within the first 14 days of the immersion period: the largest amount of Ni ion release occurred within the first week of immersion, while it significantly decreased during the reformation period from day 7 to day 14. Furthermore, the oxide layer reformation was catalyzed on the grooves within the peaks and valleys due to relatively larger surface energy of these regions, which eventually decreased the surface roughness significantly within the reformation period. Overall, the current results clearly demonstrate that the analyses of dissolution-reformation cycle of the oxide layer in orthodontic archwires, surface roughness, and ion release behavior constitute utmost importance in order to ensure both the highest degree of biocompatibility and an efficient medical treatment.

Production of hard hydrophilic Ni-B coatings on hydrophobic Ni-Ti and Ti-6Al-4V alloys by electroless deposition

Energy Technology Data Exchange (ETDEWEB)

Buelbuel, Ferhat; Karabudak, Filiz; Yesildal, Ruhi [Ataturk Univ., Erzurum (Turkey). Mechanical Engineering Dept.

2017-07-01

This paper is mainly focused on the wetting state of liquid droplets on Ni-Ti and Ti-6Al-4V hierarchical structured hydrophobic surfaces in micro/nanoscale. Electroless Ni-B deposition as a surface coating treatment has recently drawn considerable attention of researchers owing to remarkable advantages when compared with other techniques such as low price, conformal ability to coat substrates, good bath stability and relatively easier plating process control. The Ni-Ti and Ti-6Al-4V substrates were plated by electroless Ni-B plating process. The coated films were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), hardness testing and static contact angle measurement. Results obtained from the analyses show that electroless Ni-B deposition may improve the hardness and wettability of the Ni-Ti and Ti-6Al-4V alloy surfaces.

Improving the Performance of Electrically Activated NiTi Shape Memory Actuators by Pre-Aging

Science.gov (United States)

Rathmann1, Christian; Fleczok1, Benjamin; Otibar1, Dennis; Kuhlenkötter, Bernd

2017-06-01

Shape memory alloys possess an array of unique functional properties which are influenced by a complex interaction of different factors. Due to thermal sensitivity, slight changes in temperature may cause the properties to change significantly. This poses a huge challenge especially for the use of shape memory alloys as actuators. The displacement is the key performance indicator, which has to be of equal or better quality compared to conventional actuators. One problem of shape memory alloys is the change in functional fatigue in the first cycles, which makes it rather difficult to design the actuator. Therefore, the reduction of this shakedown effect is crucial. For this reason, this paper investigates the effect of electrical heat treatment as a method for pre-aging. This topic has so far been little investigated so that the investigations focus on identifying important factors and effects by using the design of experiments.

Crack-closing of cement mortar beams using NiTi cold-drawn SMA short fibers

Science.gov (United States)

Choi, Eunsoo; Kim, Dong Joo; Chung, Young-Soo; Kim, Hee Sun; Jung, Chungsung

2015-01-01

In this study, crack-closing tests of mortar beams reinforced by shape memory alloy (SMA) short fibers were performed. For this purpose, NiTi SMA fibers with a diameter of 0.965 mm and a length of 30 mm were made from SMA wires of 1.0 mm diameter by cold drawing. Four types of SMA fibers were prepared, namely, straight and dog-bone-shaped fiber and the two types of fibers with paper wrapping in the middle of the fibers. The paper provides an unbonded length of 15 mm. For bending tests, six types of mortar beams with the dimensions of 40 mm × 40 mm × 160 mm (B×H×L) were prepared. The SMA fibers were placed at the bottom center of the beams along with an artificial crack of 10 mm depth and 1 mm thickness. This study investigated the influence of SMA fibers on the flexural strength of the beams from the measured force- deflection curves. After cracking, the beams were heated at the bottom by fire to activate the SMA fibers. Then, the beams recovered the deflection, and the cracks were closed. This study evaluated crack-closing capacity using the degree of crack recovery and deflection-recovery factor. The first factor is estimated from the crack-width before and after crack-closing, and the second one is obtained from the downward deflection due to loading and the upward deflection due to the closing force of the SMA fibers.

Reactive Stresses in Ni49Fe18Ga27Co6 Shape-Memory-Alloy Single Crystals

Science.gov (United States)

Averkin, A. I.; Krymov, V. M.; Guzilova, L. I.; Timashov, R. B.; Soldatov, A. V.; Nikolaev, V. I.

2018-03-01

The reactive stresses induced in Ni49Fe18Ga27Co6-alloy single crystals during martensitic transformations with a limited possibility of shape-memory-strain recovery have been experimentally studied. The data on these crystals are compared with the results obtained previously for Cu-Al-Ni, Ni-Ti, and Ni‒Fe-Ga crystals. The potential of application of the Ni49Fe18Ga27Co6 single crystals in designing drives and power motors is demonstrated.

Influence of Electropolishing and Magnetoelectropolishing on Corrosion and Biocompatibility of Titanium Implants

Science.gov (United States)

Rahman, Zia ur; Pompa, Luis; Haider, Waseem

2014-11-01

Titanium alloys are playing a vital role in the field of biomaterials due to their excellent corrosion resistance and biocompatibility. These alloys enhance the quality and longevity of human life by replacing or treating various parts of the body. However, as these materials are in constant contact with the aggressive body fluids, corrosion of these alloys leads to metal ions release. These ions leach to the adjacent tissues and result in adverse biological reactions and mechanical failure of implant. Surface modifications are used to improve corrosion resistance and biological activity without changing their bulk properties. In this investigation, electropolishing and magnetoelectropolishing were carried out on commercially pure titanium, Ti6Al4V, and Ti6Al4V-ELI. These surface modifications are known to effect surface charge, chemistry, morphology; wettability, corrosion resistance, and biocompatibility of these materials. In vitro cyclic potentiodynamic polarization tests were conducted in phosphate buffer saline in compliance with ASTM standard F-2129-12. The surface morphology, roughness, and wettability of these alloys were studied using scanning electron microscope, atomic force microscope, and contact angle meter, respectively. Moreover, biocompatibility of titanium alloys was assessed by growing MC3T3 pre-osteoblast cells on them.

Mechanical and structural properties of sputtered Ni/Ti multilayers

Energy Technology Data Exchange (ETDEWEB)

Senthil Kumar, M.; Boeni, P.; Tixier, S.; Clemens, D.; Horisberger, M. [Paul Scherrer Inst. (PSI), Villigen (Switzerland)

1997-09-01

Ni/Ti bilayers have been prepared by dc-magnetron sputtering in order to study their mechanical and structural properties. A remarkable reduction of stress is observed when the Ni layers are sputtered reactively in argon with a high partial pressure of air. The high angle x-ray diffraction studies show a tendency towards amorphisation of the Ni layers with increasing air flow. The low angle measurements indicate a substantial reduction of interdiffusion resulting in smoother interfaces with increasing air content. (author) 2 figs., 2 refs.

Martensitic phase transformations in Ni–Ti-based shape memory alloys: The Landau theory

International Nuclear Information System (INIS)

Shchyglo, Oleg; Salman, Umut; Finel, Alphonse

2012-01-01

We present a simple Landau free energy functional for cubic-to-orthorhombic and cubic-to-monoclinic martensitic phase transformations. The functional is derived following group–subgroup relations between different martensitic phases – tetragonal, trigonal, orthorhombic and monoclinic – in order to fully capture the symmetry properties of the free energy of the austenite and martensite phases. The derived free energy functional is fitted to the elastic and thermodynamic properties of NiTi and NiTiCu shape memory alloys which exhibit cubic-to-monoclinic and cubic-to-orthorhombic martensitic phase transformations, respectively.

Precipitation Strengthenable NiTiPd High Temperature Shape Memory Alloys

Science.gov (United States)

Bigelow, Glen; Garg, Anita; Benafan, Othmane; Noebe, Ronald; Gaydosh, Darrell; Padula, Santo, II

2017-01-01

In binary NiTi alloys, it has long been known that Ni-rich alloys can be heat treated to produce precipitates which both strengthen the matrix against dislocations and improve the behavior of the material under thermal and mechanical cycling. Within recent years, the same effect has been observed in Ni-rich NiTiHf high temperature shape memory alloys and heat treatment regimens have been defined which will reliably produce improved properties. In NiTiPd alloys, precipitation has also been observed, but studies are still underway to define reliable heat treatments and compositions which will provide a balance of strengthening and good thermomechanical properties. For this study, a series of NiTi-32 at.Pd alloys was produced to determine the effect of changing nickeltitanium content on the transformation behavior and heat treatability of the material. Samples were aged at temperatures between 350C and 450C for times up to 100 hours. Actuation type behavior was evaluated using uniaxial constant force thermal cycling (UCFTC) to determine the effect of composition and aging on the material behavior. TEMSEM was used to evaluate the microstructure and determine the types of precipitates formed. The correlation between composition, heat treat, microstructure, and thermomechanical behavior will be addressed and discussed.

Effort towards symmetric removal and surface smoothening of 1.3-GHz niobium single-cell cavity in vertical electropolishing using a unique cathode

Science.gov (United States)

Chouhan, Vijay; Kato, Shigeki; Nii, Keisuke; Yamaguchi, Takanori; Sawabe, Motoaki; Hayano, Hitoshi; Ida, Yoshiaki

2017-08-01

A detailed study on vertical electropolishing (VEP) of a 1.3-GHz single-cell niobium coupon cavity, which contains six coupons and four viewports at different positions, is reported. The cavity was vertically electropolished using a conventional rod and three types of unique cathodes named as Ninja cathodes, which were designed to have four retractable blades made of either an insulator or a metal or a combination of both. This study reveals the effect of the cathodes and their rotation speed on uniformity in removal thickness and surface morphology at different positions inside the cavity. Removal thickness was measured at several positions of the cavity using an ultrasonic thickness gauge and the surface features of the coupons were examined by an optical microscope and a surface profiler. The Ninja cathode with partial metallic blades was found to be effective not only in reducing asymmetric removal, which is one of the major problems in VEP and might be caused by the accumulation of hydrogen (H2 ) gas bubbles on the top iris of the cavity, but also in yielding a smooth surface of the entire cavity. A higher rotation speed of the Ninja cathode prevents bubble accumulation on the upper iris, and might result in a viscous layer of similar thickness in the cavity cell. Moreover, a higher electric field at the equator owing to the proximity of partial metallic blades to the equator surface resulted in a smooth surface. The effects of H2 gas bubbles and stirring were also observed in lab EP experiments.

Effort towards symmetric removal and surface smoothening of 1.3-GHz niobium single-cell cavity in vertical electropolishing using a unique cathode

Directory of Open Access Journals (Sweden)

Vijay Chouhan

2017-08-01

Full Text Available A detailed study on vertical electropolishing (VEP of a 1.3-GHz single-cell niobium coupon cavity, which contains six coupons and four viewports at different positions, is reported. The cavity was vertically electropolished using a conventional rod and three types of unique cathodes named as Ninja cathodes, which were designed to have four retractable blades made of either an insulator or a metal or a combination of both. This study reveals the effect of the cathodes and their rotation speed on uniformity in removal thickness and surface morphology at different positions inside the cavity. Removal thickness was measured at several positions of the cavity using an ultrasonic thickness gauge and the surface features of the coupons were examined by an optical microscope and a surface profiler. The Ninja cathode with partial metallic blades was found to be effective not only in reducing asymmetric removal, which is one of the major problems in VEP and might be caused by the accumulation of hydrogen (H_{2} gas bubbles on the top iris of the cavity, but also in yielding a smooth surface of the entire cavity. A higher rotation speed of the Ninja cathode prevents bubble accumulation on the upper iris, and might result in a viscous layer of similar thickness in the cavity cell. Moreover, a higher electric field at the equator owing to the proximity of partial metallic blades to the equator surface resulted in a smooth surface. The effects of H_{2} gas bubbles and stirring were also observed in lab EP experiments.

Production and characterization of stainless steel based Fe-Cr-Ni-Mn-Si(-Co) shape memory alloys

International Nuclear Information System (INIS)

Otubo, J.

1995-01-01

It is well known that the Fe based alloys can exhibit shape memory effect due to the γ to ε martensitic transformation. The effect may not be as striking as observed in the NiTi alloy but it might become attractive from the practical point of view. In this work, two compositions of Fe-Cr-Ni-Mn-Si(-Co) stainless steel based shape memory alloy, prepared by the VIM technique, will be presented. The results are good with shape recovery of 95% for a pre-strain of 4% after some training cycles. In terms of workability the alloys produced are worse than the usual AISI304. However, adjusting the thermo-mechanical processing, it is perfectly possible to produce wire as thin as 1,20mm in dia. or down. (orig.)

Shape Memory Actuator: thermomechanical training and surface optimization of shape memory wires embedded in a polymeric matrix

OpenAIRE

Scoponi, Martina

2011-01-01

In the first part of my work I studied the mechanical and thermal behaviour of NiTi wires and strips in order to find the best training cycle to achieve a good compromise between transformation temperatures, recovery forces and phase reversibility. Other parameters such as the stress-rate and maximum recovery deformations, useful to realize smart composites, were evaluated. DSC and DMTA analyses were performed on NiTi thin strips that were cold rolled with different thickness r...

Management of long-term and reversible hysteroscopic sterilization: a novel device with nickel-titanium shape memory alloy

Science.gov (United States)

2014-01-01

Background Female sterilization is the second most commonly used method of contraception in the United States. Female sterilization can now be performed through laparoscopic, abdominal, or hysteroscopic approaches. The hysteroscopic sterilization may be a safer option than sterilization through laparoscopy or laparotomy because it avoids invading the abdominal cavity and undergoing general anaesthesia. Hysteroscopic sterilization mainly includes chemical agents and mechanical devices. Common issues related to the toxicity of the chemical agents used have raised concerns regarding this kind of contraception. The difficulty of the transcervical insertion of such mechanical devices into the fallopian tubes has increased the high incidence of device displacement or dislodgment. At present, Essure® is the only commercially available hysteroscopic sterilization device being used clinically. The system is irreversible and is not effective immediately. Presentation of the hypothesis Our new hysteroscopic sterility system consists of nickel-titanium (NiTi) shape memory alloy and a waterproof membrane. The NiTi alloy is covered with two coatings to avoid toxic Ni release and to prevent stimulation of epithelial tissue growth around the oviducts. Because of the shape memory effect of the NiTi alloy, the device works like an umbrella: it stays collapsed at low temperature before placement and opens by the force of shape memory activated by the body temperature after it is inserted hysteroscopically into the interstitial tubal lumen. The rim of the open device will incise into interstitial myometrium during the process of unfolding. Once the device is fixed, it blocks the tube completely. When the patient no longer wishes for sterilization, the device can be closed by perfusing liquid with low temperature into the uterine cavity, followed by prospective hysteroscopic removal. After the device removal, the fallopian tube will revert to its physiological functions. Testing the

Thermodynamic assessment of the stabilization effect in deformed shape memory alloy martensite

International Nuclear Information System (INIS)

Kato, Hiroyuki; Yasuda, Yohei; Sasaki, Kazuaki

2011-01-01

When a martensitic shape memory alloy is deformed, the reverse transformation occurs at higher temperature than that of undeformed martensite. This is a typical case of the stabilization effect of martensite that is commonly observed in shape memory alloys. Regarding previous results measured by electric resistance and/or dilatometoric methods in NiTi and CuAlNi shape memory alloys, this study has performed calorimetric measurement in these alloys in order to re-examine the stabilization effect in terms of thermodynamics. Experimental evidence for appreciable changes in the reverse transformation temperature due to variant change of the martensite is presented. The elastic energy stored in the deformed martensite and the irreversible energy dissipated during the reverse transformation are estimated from the transformation temperatures, the stress-strain curves of the martensite and the latent heat of transformation. The temperatures of the reverse martensitic transformation have been related to these energies in explicit form.

Cu-Al-Ni Shape Memory Single Crystal Wires with High Transformation Temperature

Science.gov (United States)

Hautcoeur, Alain; Fouché, Florian; Sicre, Jacques

2016-01-01

CN-250X is a new material with higher performance than Nickel-Titanium Shape Memory Alloy (SMA). For space mechanisms, the main disadvantage of Nickel-Titanium Shape Memory Alloy is the limited transformation temperature. The new CN-250X Nimesis alloy is a Cu-Al-Ni single crystal wire available in large quantity because of a new industrial process. The triggering of actuators made with this Cu-Al-Ni single crystal wire can range from ambient temperature to 200 C in cycling and even to 250 C in one-shot mode. Another advantage of CN-250X is a better shape recovery (8 to 10%) than Ni-Ti (6 to 7%). Nimesis is the first company able to produce this type of material with its new special industrial process. A characterization study is presented in this work, including the two main solicitation modes for this material: tensile and torsion. Different tests measure the shape recovery of Cu-Al-Ni single crystals wires during heating from room temperature to a temperature higher than temperature of end of martensitic transformation.

Microstructure of NiTi orthodontic wires observations using transmission electron microscopy

OpenAIRE

Ferčec, J.; Jenko, D.; Buchmeister, B.; Rojko, F.; Budič, B.; Kosec, B.; Rudolf, R.

2014-01-01

This work presents the results of the microstructure observation of six different types of NiTi orthodontic wires by using Transmission Electron Microscopy (TEM). Within these analyses the chemical compositions of each wire were observed in different places by applying the EDS detector. Namely, the chemical composition in the orthodontic wires is very important because it shows the dependence between the phase temperatures and mechanical properties. Microstructure observations showed that ort...

Vacuum Arc Melting Processes for Biomedical Ni-Ti Shape Memory Alloy

Directory of Open Access Journals (Sweden)

Tsai De-Chang

2015-01-01

Full Text Available This study primarily involved using a vacuum arc remelting (VAR process to prepare a nitinol shape-memory alloy with distinct ratios of alloy components (nitinol: 54.5 wt% to 57 wt%. An advantage of using the VAR process is the adoption of a water-cooled copper crucible, which effectively prevents crucible pollution and impurity infiltration. Optimising the melting production process enables control of the alloy component and facilitates a uniformly mixed compound during subsequent processing. This study involved purifying nickel and titanium and examining the characteristics of nitinol alloy after alloy melt, including its microstructure, mechanical properties, phase transition temperature, and chemical components.

Influence of the particle size on phase transformation temperatures of Ni-49at.%Ti shape memory alloy powders

International Nuclear Information System (INIS)

Anselmo, George Carlos. S.; Castro, Walman B. de; Araujo, Carlos Jose de

2009-01-01

It is important to control the martensitic transformation start temperature (Ms) of Ti-Ni alloys because it determines the temperature range over which the shape memory effect and superelasticity appear. Powder metallurgy (PM) is known to provide the possibility of material saving and automated fabrication of at least semi-finished products as well as net-shape components for NiTi alloys. In this study powder with different particle sizes was subjected by gas atomization. The evolution of the control the martensitic transformation start temperature (Ms) was studied by differential scanning calorimetry. The effect of the particle size of powders on the transformation temperatures behaviors was discussed. (author)

Niti CAR 27 Versus a Conventional End-to-End Anastomosis Stapler in a Laparoscopic Anterior Resection for Sigmoid Colon Cancer

Science.gov (United States)

Kwag, Seung-Jin; Kim, Jun-Gi; Kang, Won-Kyung; Lee, Jin-Kwon

2014-01-01

Purpose The Niti CAR 27 (ColonRing) uses compression to create an anastomosis. This study aimed to investigate the safety and the effectiveness of the anastomosis created with the Niti CAR 27 in a laparoscopic anterior resection for sigmoid colon cancer. Methods In a single-center study, 157 consecutive patients who received an operation between March 2010 and December 2011 were retrospectively assessed. The Niti CAR 27 (CAR group, 63 patients) colorectal anastomoses were compared with the conventional double-stapled (CDS group, 94 patients) colorectal anastomoses. Intraoperative, immediate postoperative and 6-month follow-up data were recorded. Results There were no statistically significant differences between the two groups in terms of age, gender, tumor location and other clinical characteristics. One patient (1.6%) in the CAR group and 2 patients (2.1%) in the CDS group experienced complications of anastomotic leakage (P = 0.647). These three patients underwent a diverting loop ileostomy. There were 2 cases (2.1%) of bleeding at the anastomosis site in the CDS group. All patients underwent a follow-up colonoscopy (median, 6 months). One patient in the CAR group experienced anastomotic stricture (1.6% vs. 0%; P = 0.401). This complication was solved by using balloon dilatation. Conclusion Anastomosis using the Niti CAR 27 device in a laparoscopic anterior resection for sigmoid colon cancer is safe and feasible. Its use is equivalent to that of the conventional double-stapler. PMID:24851217

Comparative analysis of torsional and bending behavior through finite-element models of 5 Ni-Ti endodontic instruments.

Science.gov (United States)

Arbab-Chirani, Reza; Chevalier, Valérie; Arbab-Chirani, Shabnam; Calloch, Sylvain

2011-01-01

The objectives of this study were to compare numerically the bending and torsional mechanical behavior of 5 endodontic rotary Ni-Ti instruments with equivalent size and various designs for tapers, pitch, and cutting blades.First, the geometries of Hero (20/0.06), HeroShaper (20/0.06), ProFile (20/0.06), Mtwo (20/0.06), and ProTaper F1 were generated by finite element code. Then, the 2 most representative clinical loadings, i.e., bending and torsion, were studied with an ad hoc model for the superelasticity of Ni-Ti. Bending was generated by tip deflection and torsion by a constant twist-angle of the tip. Mechanical behavior of these 5 endodontic rotary Ni-Ti instruments could be evaluated and compared. Protaper F1 presented the greatest level of bending stress and torque. Hero and HeroShaper were more rigid than ProFile and Mtwo. This numerical comparison evaluated the effects of the geometrical parameters on the instrumental mechanical behavior. The 5 endodontic instruments, investigated in the present study, do not have the same bending and torsional mechanical behavior. Each clinician must be aware of these behavior differences so as to use the adequate file according to the clinical situation and to the manufacturer's recommendations. Copyright © 2011 Mosby, Inc. All rights reserved.

Surface analyses of electropolished niobium samples for superconducting radio frequency cavity

Energy Technology Data Exchange (ETDEWEB)

Tyagi, P. V.; Nishiwaki, M.; Saeki, T.; Sawabe, M.; Hayano, H.; Noguchi, T.; Kato, S. [GUAS, Tsukuba, Ibaraki 305-0801 (Japan); KEK, Tsukuba, Ibaraki 305-0801 (Japan); KAKEN Inc., Hokota, Ibaraki 311-1416 (Japan); GUAS, Tsukuba, Ibaraki 305-0801 (Japan) and KEK, Tsukuba, Ibaraki 305-0801 (Japan)

2010-07-15

The performance of superconducting radio frequency niobium cavities is sometimes limited by contaminations present on the cavity surface. In the recent years extensive research has been done to enhance the cavity performance by applying improved surface treatments such as mechanical grinding, electropolishing (EP), chemical polishing, tumbling, etc., followed by various rinsing methods such as ultrasonic pure water rinse, alcoholic rinse, high pressure water rinse, hydrogen per oxide rinse, etc. Although good cavity performance has been obtained lately by various post-EP cleaning methods, the detailed nature about the surface contaminants is still not fully characterized. Further efforts in this area are desired. Prior x-ray photoelectron spectroscopy (XPS) analyses of EPed niobium samples treated with fresh EP acid, demonstrated that the surfaces were covered mainly with the niobium oxide (Nb{sub 2}O{sub 5}) along with carbon, in addition a small quantity of sulfur and fluorine were also found in secondary ion mass spectroscopy (SIMS) analysis. In this article, the authors present the analyses of surface contaminations for a series of EPed niobium samples located at various positions of a single cell niobium cavity followed by ultrapure water rinsing as well as our endeavor to understand the aging effect of EP acid solution in terms of contaminations presence at the inner surface of the cavity with the help of surface analytical tools such as XPS, SIMS, and scanning electron microscope at KEK.

On the effects of geometry, defects, and material asymmetry on the mechanical response of shape memory alloy cellular lattice structures

International Nuclear Information System (INIS)

Ravari, M R Karamooz; Kadkhodaei, M; Ghaei, A; Esfahani, S Nasr; Andani, M Taheri; Elahinia, M; Karaca, H

2016-01-01

Shape memory alloy (such as NiTi) cellular lattice structures are a new class of advanced materials with many potential applications. The cost of fabrication of these structures however is high. It is therefore necessary to develop modeling methods to predict the functional behavior of these alloys before fabrication. The main aim of the present study is to assess the effects of geometry, microstructural imperfections and material asymmetric response of dense shape memory alloys on the mechanical response of cellular structures. To this end, several cellular and dense NiTi samples are fabricated using a selective laser melting process. Both cellular and dense specimens were tested in compression in order to obtain their stress–strain response. For modeling purposes, a three -dimensional (3D) constitutive model based on microplane theory which is able to describe the material asymmetry was employed. Five finite element models based on unit cell and multi-cell methods were generated to predict the mechanical response of cellular lattices. The results show the considerable effects of the microstructural imperfections on the mechanical response of the cellular lattice structures. The asymmetric material response of the bulk material also affects the mechanical response of the corresponding cellular structure. (paper)

Construction of extracellular microenvironment to improve surface endothelialization of NiTi alloy substrate

Energy Technology Data Exchange (ETDEWEB)

Liu, Peng, E-mail: liupeng79@cqu.edu.cn [Key Laboratory of Biorheological Science and Technology of Ministry of Education, College of Bioengineering, Chongqing University, Chongqing 400044 (China); State Key Laboratory of Molecular Engineering of Polymers, Department of Macromolecular Science, Fudan University, Shanghai 200433 (China); Zhao, Yongchun; Yan, Ying; Hu, Yan; Yang, Weihu [Key Laboratory of Biorheological Science and Technology of Ministry of Education, College of Bioengineering, Chongqing University, Chongqing 400044 (China); Cai, Kaiyong, E-mail: kaiyong_cai@cqu.edu.cn [Key Laboratory of Biorheological Science and Technology of Ministry of Education, College of Bioengineering, Chongqing University, Chongqing 400044 (China)

2015-10-01

To mimic extracellular microenvironment of endothelial cell, a bioactive multilayered structure of gelatin/chitosan pair, embedding with vascular endothelial growth factor (VEGF), was constructed onto NiTi alloy substrate surface via a layer-by-layer assembly technique. The successful fabrication of the multilayered structure was demonstrated by scanning electron microscopy, atomic force microscopy, contact angle measurement, attenuated total reflection-fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy, respectively. The growth behaviors of endothelial cells on various NiTi alloy substrates were investigated in vitro. Cytoskeleton observation, MTT assay, and wound healing assay proved that the VEGF-embedded multilayer structure positively stimulated adhesion, proliferation and motogenic responses of endothelial cells. More importantly, the present system promoted the nitric oxide production of endothelial cells. The approach affords an alternative to construct extracellular microenvironment for improving surface endothelialization of a cardiovascular implant. - Highlights: • Biofunctional multilayer films mimicking extracellular microenvironment were successfully fabricated. • Multilayered structure stimulated the biological responses of endothelial cells. • The approach affords an efficient approach for surface endothelialization of stent implant.

A Constitutive Description for Shape Memory Alloys with the Growth of Martensite Band

Directory of Open Access Journals (Sweden)

Weiguo Li

2014-01-01

Full Text Available Based on the experimental results and the finite element analysis, a constitutive model is proposed for two phase shape memory alloys by introducing a compensative volumetric strain into a constrained relationship between the two phases, accounting for the reduced constraint due to the growth of martensite band. The pseudoelasticity of NiTi shape memory alloy micro-tube, subjected to pure tension, is analyzed and compared with the experimental results. It can be seen that the pseudoelastic behavior, especially the phenomena of a stress drop during tension processes, can be well described with the proposed model. The proposed model separates the complicated constitutive behavior of a shape memory alloy (SMA into simple responses arising respectively from its two phases, taking into account laminar microstructure, the thickness of martensite phase and the interaction between the two phases, and provides an easy but comprehensive method for the description of the constitutive behavior of SMAs under complex thermomechanical loading.

The effect of cold work, heat treatment, and composition on the austenite to R-phase transformation temperature of Ni-Ti shape memory alloys

International Nuclear Information System (INIS)

Thoma, P.E.; Angst, D.R.; Schachner, K.D.

1995-01-01

The influence of cold work (CW) and heat treatment (HT) on the austenite to R-Phase (A→R) transformation temperature (TT) of a near equiatomic and three other Ti rich NiTi SMA is examined. For the SMA having a near equiatomic composition, the A→R TT increases with increasing CW at low HT temperatures. For the SMA having the maximum possible Ti content, the A→R TT decreases with increasing CW at low HT temperatures. For all compositions, the A→R TT is not sensitive to CW at high HT temperatures. At a Ti content slightly below the maximum possible, the A→R TT is relatively insensitive to CW and HT temperature. For all of the SMA investigated, the A→R TT increases with increasing Ti content for a specific CW and HT temperature, and this effect is greatest at low CW and at high HT temperatures. (orig.)

Experimental Studies on Dynamic Vibration Absorber using Shape Memory Alloy (NiTi) Springs

International Nuclear Information System (INIS)

Kumar, V. Raj; Kumar, M. B. Bharathi Raj; Kumar, M. Senthil

2011-01-01

Shape memory alloy (SMA) springs have been used as actuators in many applications although their use in the vibration control area is very recent. Since shape memory alloys differ from conventional alloy materials in many ways, the traditional design approach for springs is not completely suitable for designing SMA springs. Some vibration control concepts utilizing unique characteristics of SMA's will be presented in this paper.A dynamic vibration absorber (DVA) using shape memory alloy (SMA) actuator is developed for attenuation of vibration in a cantilever beam. The design procedure of the DVA is presented. The system consists of a cantilever beam which is considered to generate the real-time vibration using shaker. A SMA spring is used with a mass attached to its end. The stiffness of the SMA spring is dynamically varied in such a way to attenuate the vibration. Both simulation and experimentation are carried out using PID controller. The experiments were carried out by interfacing the experimental setup with a computer using LabVIEW software, Data acquisition and control are implemented using a PCI data acquisition card. Standard PID controllers have been used to control the vibration of the beam. Experimental results are used to demonstrate the effectiveness of the controllers designed and the usefulness of the proposed test platform by exciting the structure at resonance. In experimental setup, an accelerometer is used to measure the vibration which is fed to computer and correspondingly the SMA spring is actuated to change its stiffness to control the vibration. The results obtained illustrate that the developed DVA using SMA actuator is very effective in reducing structural response and have great potential to be an active vibration control medium.

THE MICROSTRUCTURAL PROPERTIES OF EXPLOSION WELDED Ni/Ti JOINT

Directory of Open Access Journals (Sweden)

Kamila Zdrodowska

2014-06-01

Full Text Available Explosion welding is one of the ways of bonding materials. This method is used to bond metals which either cannot be joined or they are difficult to bond by other methods. The study investigates the metallographic characteristics of Ni/Ti joints in the form of a plate. Microstructures of the joints are examined and hardness measurements are carried out on the bonded materials and their interfaces. A detailed analysis of the distributions of wave length and width is presented. An average microhardness of the interface is found to be higher than that of the base materials.

An analytical mechanical model to describe the response of NiTi rotary endodontic files in a curved root canal.

Science.gov (United States)

Leroy, Agnès Marie Françoise; Bahia, Maria Guiomar de Azevedo; Ehrlacher, Alain; Buono, Vicente Tadeu Lopes

2012-08-01

To build a mathematical model describing the mechanical behavior of NiTi rotary files while they are rotating in a root canal. The file was seen as a beam undergoing large transformations. The instrument was assumed to be rotating steadily in the root canal, and the geometry of the canal was considered as a known parameter of the problem. The formulae of large transformations mechanics then allowed the calculation of the Green-Lagrange strain field in the file. The non-linear mechanical behavior of NiTi was modeled as a continuous piecewise linear function, assuming that the material did not reach plastic deformation. Criteria locating the changes of behavior of NiTi were established and the tension field in the file, and the external efforts applied on it were calculated. The unknown variable of torsion was deduced from the equilibrium equation system using a Coulomb contact law which solved the problem on a cycle of rotation. In order to verify that the model described well reality, three-point bending experiments were managed on superelastic NiTi wires, whose results were compared to the theoretical ones. It appeared that the model gave a good mentoring of the empirical results in the range of bending angles that interested us. Knowing the geometry of the root canal, one is now able to write the equations of the strain and stress fields in the endodontic instrument, and to quantify the impact of each macroscopic parameter of the problem on its response. This should be useful to predict failure of the files under rotating bending fatigue, and to optimize the geometry of the files. Copyright © 2012 Elsevier B.V. All rights reserved.

Recovery and residual stress of SMA wires and applications for concrete structures

International Nuclear Information System (INIS)

Choi, Eunsoo; Cho, Sung-Chul; Park, Taehyo; Hu, Jong Wan; Chung, Young-Soo

2010-01-01

In general, NiTi shape memory alloys are used for applications in civil structures. NiTi SMAs show good superelasticity and shape memory effect properties. However, for application of the shape memory effect, it is desirable for SMAs to show a wide temperature hysteresis, especially for civil structures which are exposed to severe environmental conditions. NiTiNb SMAs, in general, show a wider temperature hysteresis than NiTi SMAs and are more applicable for civil structures. This study examines the temperature hysteresis of NiTiNb and NiTi SMAs, and their recovery and residual stress are investigated. In addition, the tensile behaviors of SMA wires under residual stress are evaluated. This study explains the possible applications for concrete structures with the shape memory effect and illustrates two experimental results of concrete cylinders and reinforced concrete columns. For both tests, SMA wires of NiTiNb and NiTi are used to confine concrete using residual stress. The SMA wire jackets on the concrete cylinders increase the peak strength and the ductility compared to the plain concrete cylinders. In addition, the SMA wire jackets on reinforced concrete columns increase the ductility greatly without flexural strength degradation

Neutron diffraction investigation of hysteresis reduction and increase in linearity in the stress-strain response of superelastic NiTi

International Nuclear Information System (INIS)

Rathod, C.R.; Clausen, B.; Bourke, M.A.M.; Vaidyanathan, R.

2006-01-01

In situ neutron diffraction measurements during loading have been performed on plastically deformed superelastic NiTi samples. The measurements observed retained B19 ' phase in the unloaded state as a result of the plastic deformation in otherwise completely B2 phase samples. A reversible stress-induced B2-B19 ' transformation on application and removal of stress occurred in the presence of this retained B19 ' phase. The amount and orientation of this retained B19 ' phase changed with cycling. Such direct atomic scale observations in the bulk are used here for the first time to qualitatively elucidate the macroscopic stress-strain response in plastically deformed superelastic NiTi

Properties and medical applications of shape memory alloys.

Science.gov (United States)

Tarniţă, Daniela; Tarniţă, D N; Bîzdoacă, N; Mîndrilă, I; Vasilescu, Mirela

2009-01-01

One of the most known intelligent material is nitinol, which offers many functional advantages over conventional implantable alloys. Applications of SMA to the biomedical field have been successful because of their functional qualities, enhancing both the possibility and the execution of less invasive surgeries. The biocompatibility of these alloys is one of their most important features. Different applications exploit the shape memory effect (one-way or two-way) and the super elasticity, so that they can be employed in orthopedic and cardiovascular applications, as well as in the manufacture of new surgical tools. Therefore, one can say that smart materials, especially SMA, are becoming noticeable in the biomedical field. Super elastic NiTi has become a material of strategic importance as it allows to overcome a wide range of technical and design issues relating to the miniaturization of medical devices and the increasing trend for less invasive and therefore less traumatic procedures. This paper will consider just why the main properties of shape memory alloys hold so many opportunities for medical devices and will review a selection of current applications.

Fabrication of a smart air intake structure using shape memory alloy wire embedded composite

International Nuclear Information System (INIS)

Jung, Beom-Seok; Kim, Min-Saeng; Kim, Ji-Soo; Kim, Yun-Mi; Lee, Woo-Yong; Ahn, Sung-Hoon

2010-01-01

Shape memory alloys (SMAs) have been actively studied in many fields utilizing their high energy density. Applying SMA wire-embedded composite to aerospace structures, such as air intake of jet engines and guided missiles, is attracting significant attention because it could generate a comparatively large actuating force. In this research, a scaled structure of SMA wire-embedded composite was fabricated for the air intake of aircraft. The structure was composed of several prestrained Nitinol (Ni-Ti) SMA wires embedded in intersection -shape glass fabric reinforced plastic (GFRP), and it was cured at room temperature for 72 h. The SMA wire-embedded GFRP could be actuated by applying electric current through the embedded SMA wires. The activation angle generated from the composite structure was large enough to make a smart air intake structure.

Recoverable Wire-Shaped Supercapacitors with Ultrahigh Volumetric Energy Density for Multifunctional Portable and Wearable Electronics.

Science.gov (United States)

Shi, Minjie; Yang, Cheng; Song, Xuefeng; Liu, Jing; Zhao, Liping; Zhang, Peng; Gao, Lian

2017-05-24

Wire-shaped supercapacitors (SCs) based on shape memory materials are of considerable interest for next-generation portable and wearable electronics. However, the bottleneck in this field is how to develop the devices with excellent electrochemical performance while well-maintaining recoverability and flexibility. Herein, a unique asymmetric electrode concept is put forward to fabricate smart wire-shaped SCs with ultrahigh energy density, which is realized by using porous carbon dodecahedra coated on NiTi alloy wire and flexible graphene fiber as yarn electrodes. Notably, the wire-shaped SCs not only exhibit high flexibility that can be readily woven into real clothing but also represent the available recoverable ability. When irreversible plastic deformations happen, the deformed shape of the devices can automatically resume the initial predesigned shape in a warm environment (about 35 °C). More importantly, the wire-shaped SCs act as efficient energy storage devices, which display high volumetric energy density (8.9 mWh/cm 3 ), volumetric power density (1080 mW/cm 3 ), strong durability in multiple mechanical states, and steady electrochemical behavior after repeated shape recovery processes. Considering their relative facile fabrication technology and excellent electrochemical performance, this asymmetric electrode strategy produced smart wire-shaped supercapacitors desirable for multifunctional portable and wearable electronics.

Assessing the morphology of selective laser melted NiTi-scaffolds for a three-dimensional quantification of the one-way shape memory effect

Science.gov (United States)

Bormann, Therese; de Wild, Michael; Beckmann, Felix; Müller, Bert

2013-04-01

NiTi is promising for the use as bone scaffold, because the pseudoelasticity or the one- and two-way shape memory effect in the physiological window can mechanically stimulate the adherent cells. Such stimuli can enhance osseointegration and might reduce stress shielding associated with load bearing implants. The present study is based on the additive manufacturing technique of selective laser melting (SLM) to fabricate three-dimensional NiTi scaffolds. We demonstrate that the morphology of the scaffolds can be quantified using synchrotron radiation-based micro computed tomography (SRμCT) and sophisticated registration software. Comparing the CAD file with the SLM scaffolds, quality factors are derived. With respect to the CAD file, the overlap corresponds to (92.5 +/- 0.6) %. (7.4 +/- 0.42) % of material was missing and (48.9 +/- 2.3) % of excess material found. This means that the actual scaffold is less porous than expected, a fact that has to be considered for the scaffold design. In order to quantify the shape memory effect during the shape recovery process, we acquired radiographs rotating an initially deformed scaffold in angular steps of 0.2 degree during controlled heating. The continuously acquired radiographs were combined to tomography data, showing that the quality factors evolved with temperature as the scaffold height, measured by conventional thermo-mechanical analysis. Furthermore, the data comprise the presence of compressive and tensile local strains in the three-dimensional scaffolds to be compared with the physiological situation.

Synchrotron high energy X-ray diffraction study of microstructure evolution of severely cold drawn NiTi wire during annealing

International Nuclear Information System (INIS)

Yu, Cun; Aoun, Bachir; Cui, Lishan; Liu, Yinong; Yang, Hong; Jiang, Xiaohua; Cai, Song; Jiang, Daqiang; Liu, Zunping; Brown, Dennis E.; Ren, Yang

2016-01-01

Microstructure evolution of a cold-drawn NiTi shape memory alloy wire was investigated by means of in-situ synchrotron high-energy X-ray diffraction during continuous heating. The cold-drawn wire contained amorphous regions and nano-crystalline domains in its microstructure. Pair distribution function analysis revealed that the amorphous regions underwent structural relaxation via atomic rearrangement when heated above 100 °C. The nano-crystalline domains were found to exhibit a strong cold work induced lattice strain anisotropy along 〈111〉, which coincides with the crystallographic fiber orientation of the domains along the wire axial direction. The lattice strain anisotropy systematically decreased upon heating above 200 °C, implying a structural recovery. Crystallization of the amorphous phase led to a broadening of the angular distribution of 〈111〉 preferential orientations of grains along the axial direction as relative to the original 〈111〉 axial fiber texture of the nanocrystalline domains produced by the severe cold wire drawing deformation.

Vibrations Generated by Several Nickel-titanium Endodontic File Systems during Canal Shaping in an Ex Vivo Model.

Science.gov (United States)

Choi, Dong-Min; Kim, Jin-Woo; Park, Se-Hee; Cho, Kyung-Mo; Kwak, Sang Won; Kim, Hyeon-Cheol

2017-07-01

This study aimed to compare the vibration generated by several nickel-titanium (NiTi) file systems and transmitted to teeth under 2 different motions (continuous rotation motion and reciprocating motion). Sixty J-shaped resin blocks (Endo Training Bloc-J; Dentsply Maillefer, Ballaigues, Switzerland) were trimmed to a root-shaped form and divided into 2 groups according to the types of electric motors: WaveOne motor (WOM, Dentsply Maillefer) and X-Smart Plus motor (XSM, Dentsply Maillefer). Each group was further subdivided into 3 subgroups (n = 10 each) according to the designated file systems: ProTaper Next (PTN, Dentsply Maillefer), ProTaper Universal (PTU, Dentsply Maillefer), and WaveOne (WOP, Dentsply Maillefer) systems. Vibration was measured during the pecking motion using an accelerometer attached to a predetermined consistent position. The average vibration values were subjected to 2-way analysis of variance as well as the t test and Duncan test for post hoc comparison at the 95% confidence interval. Both motor types and instrument types produced significantly different ranges of average vibrations. Regardless of the instrument types, the WOM group generated greater vibration than the XSM group (P file system may generate greater vibration than the continuous rotation NiTi file systems. The motor type also has a significant effect to amplify the vibrations. Copyright © 2017 American Association of Endodontists. Published by Elsevier Inc. All rights reserved.

Relaxation peak near 200 K in NiTi alloy

Science.gov (United States)

Zhu, J. S.; Schaller, R.; Benoit, W.

1989-10-01

Internal friction (IF), frequency ( f), electrical resistance ( R) and zero point movement of the torsion pendulum (ɛ) have been measured in near equi-atomic NiTi alloy in order to clarify the mechanism for the relaxation peak near 200 K. The height of the relaxation peak decreases successively with thermal cycling and settles down to a lower stable value in running 15 cycles. However, the electrical resistance of the sample shows a variation in contrast with the internal friction. Both of them will return to the initial state after a single annealing at 773 K for 1 h. The probable mechanism of this relaxation peak was discussed.

Processing of Ni30Pt20Ti50 High-Temperature Shape-Memory Alloy Into Thin Rod Demonstrated

Science.gov (United States)

Noebe, Ronald D.; Draper, Susan L.; Biles, Tiffany A.; Leonhardt, Todd

2005-01-01

High-temperature shape-memory alloys (HTSMAs) based on nickel-titanium (NiTi) with significant ternary additions of palladium (Pd), platinum (Pt), gold (Au), or hafnium (Hf) have been identified as potential high-temperature actuator materials for use up to 500 C. These materials provide an enabling technology for the development of "smart structures" used to control the noise, emissions, or efficiency of gas turbine engines. The demand for these high-temperature versions of conventional shape-memory alloys also has been growing in the automotive, process control, and energy industries. However these materials, including the NiPtTi alloys being developed at the NASA Glenn Research Center, will never find widespread acceptance unless they can be readily processed into useable forms.

Finite element modeling of indentation-induced superelastic effect using a three-dimensional constitutive model for shape memory materials with plasticity

International Nuclear Information System (INIS)

Zhang, Yijun; Cheng, Yang-Tse; Grummon, David S.

2007-01-01

Indentation-induced shape memory and superelastic effects are recently discovered thermo-mechanical behaviors that may find important applications in many areas of science and engineering. Theoretical understanding of these phenomena is challenging because both martensitic phase transformation and slip plasticity exist under complex contact loading conditions. In this paper, we develop a three-dimensional constitutive model of shape memory alloys with plasticity. Spherical indentation-induced superelasticity in a NiTi shape memory alloy was simulated and compared to experimental results on load-displacement curves and recovery ratios. We show that shallow indents have complete recovery upon unloading, where the size of the phase transformation region is about two times the contact radius. Deep indents have only partial recovery when plastic deformation becomes more prevalent in the indent-affected zone

Dental students' perceptions about the endodontic treatments performed using NiTi rotary instruments and hand stainless steel files.

Science.gov (United States)

Martins, Renata Castro; Seijo, Marília Oliveira Saraiva; Ferreira, Efigênia Ferreira; Paiva, Saul Martins; Ribeiro Sobrinho, Antônio Paulino

2012-01-01

This study evaluated the perceptions of Brazilian undergraduate dental students about the endodontic treatments performed using NiTi rotary instruments and hand stainless steel. Data were collected using a questionnaire administered to undergraduate dental students enrolled in endodontic disciplines. The students were divided into 3 groups: G1, students who had treated straight canals with SS hand instruments; G2, students who had treated curved canals with SS hand instruments; and G3, students who had treated both straight and curved canals with NiTi rotary instruments. The number of endodontic treatments performed, types of treated teeth, students' learning, time spent, encountered difficulties, quality of endodontic treatment and characteristics of the employed technique were analyzed. There was a 91.3% rate of return for the questionnaires. Mandibular molars were the most frequently treated teeth, followed by maxillary incisors. The Kruskal-Wallis test showed no differences in learning (p=0.528) or in the characteristics of the technique employed (p=0.560) among the three groups. G3 students performed a greater number of endodontic treatments (pendodontic treatments differed only between G1 and G2 (p=0.045). The use of NiTi rotary instruments should be included in undergraduate dental curriculum, contributing to the increase of patients assisted and consequently to improve the clinical experience of the students.

Coating NiTi archwires with diamond-like carbon films: reducing fluoride-induced corrosion and improving frictional properties.

Science.gov (United States)

Huang, S Y; Huang, J J; Kang, T; Diao, D F; Duan, Y Z

2013-10-01

This study aims to coat diamond-like carbon (DLC) films onto nickel-titanium (NiTi) orthodontic archwires. The film protects against fluoride-induced corrosion and will improve orthodontic friction. 'Mirror-confinement-type electron cyclotron resonance plasma sputtering' was utilized to deposit DLC films onto NiTi archwires. The influence of a fluoride-containing environment on the surface topography and the friction force between the brackets and archwires were investigated. The results confirmed the superior nature of the DLC coating, with less surface roughness variation for DLC-coated archwires after immersion in a high fluoride ion environment. Friction tests also showed that applying a DLC coating significantly decreased the fretting wear and the coefficient of friction, both in ambient air and artificial saliva. Thus, DLC coatings are recommended to reduce fluoride-induced corrosion and improve orthodontic friction.

Welding shape memory alloys with NdYAG lasers Soldadura de ligas de memória de forma com laser Nd-YAG

Directory of Open Access Journals (Sweden)

Luisa Quintino

2012-09-01

Full Text Available The demand of emerging joining techniques for shape memory alloys (SMA has become of great importance, as their functional properties namely shape memory effect (SME and superelasticity (SE present unique solutions for state-of-the-art applications. Welding of SMAs is a challenge due to the risk of reduced mechanical performance after laser processing. The wider application of these alloys in various sectors as aerospace, medical or electronic industry is hindered by the limitations in its processing. The need to weld SMAs to other materials is pressing for applications in the above referred sectors. In dissimilar joints the need to understand materials behavior is even more challenging since base materials have different physical properties leading to different heat flow, convection processes and residual stress distribution. The chemical composition across the weld pool varies and intermetallic compounds are formed. Research detailing the effects of laser processing on NiTi is essential to overcome many of these challenges. The objectives of the current study are to analyze the effects of laser welding in the weld shape of both similar and dissimilar joints of NiTi to stainless steel and titanium alloys.A procura de técnicas de ligação para ligas de memória de forma tem-se revetido de importância crescente, devido ao desenvolvimento de aplicações deste material com particulares propriedades de memória de forma e superelasticidade. A soldadura de ligas de memória de forma é um desafio devido ao risco de emporbrecimento das propriedades mecânicas depois do processamento laser. A aplicação alargarda destas ligas em vários sectores como o aeroespacial, medico ou electrónico é prejudicado pelas limitações de processamento. A necessidade de soldar ligas de memória de forma a outros materiais é premente para estes sectores. Em juntas dissimilares, o entendimento do comportamento dos materaias é um desafio ainda maior uma vez que

Development of a flexible nanocomposite TiO{sub 2} film as a protective coating for bioapplications of superelastic NiTi alloys

Energy Technology Data Exchange (ETDEWEB)

Aun, Diego Pinheiro, E-mail: diegoaun@yahoo.com.br [Department of Metallurgical and Materials Engineering, Universidade Federal de Minas Gerais, Av. Antonio Carlos, 6627, 30270-901 Belo Horizonte, MG (Brazil); Houmard, Manuel, E-mail: mhoumard@ufmg.br [Department of Materials and Construction Engineering, Universidade Federal de Minas Gerais, Av. Antonio Carlos, 6627, 30270-901 Belo Horizonte, MG (Brazil); Mermoux, Michel, E-mail: michel.mermoux@lepmi.grenoble-inp.fr [LEPMI, Grenoble INP, rue de la Piscine—BP75 38402, Saint Martin d' Hères (France); Latu-Romain, Laurence, E-mail: laurence.latu-romain@simap.grenoble-inp.fr [SIR Team, Science et Ingénierie des Matériaux et Procédés, Grenoble INP, 1130, rue de la Piscine—BP75 38402, Saint Martin d' Hères (France); Joud, Jean-Charles, E-mail: jean-charles.joud@grenoble-inp.fr [SIR Team, Science et Ingénierie des Matériaux et Procédés, Grenoble INP, 1130, rue de la Piscine—BP75 38402, Saint Martin d' Hères (France); Berthomé, Gregory, E-mail: gregory.berthome@simap.grenoble-inp.fr [SIR Team, Science et Ingénierie des Matériaux et Procédés, Grenoble INP, 1130, rue de la Piscine—BP75 38402, Saint Martin d' Hères (France); Buono, Vicente Tadeu Lopes, E-mail: vbuono@demet.ufmg.br [Department of Metallurgical and Materials Engineering, Universidade Federal de Minas Gerais, Av. Antonio Carlos, 6627, 30270-901 Belo Horizonte, MG (Brazil)

2016-07-01

Highlights: • A NiTi alloy was coated with a flexible TiO{sub 2} protective layer via the sol–gel method. • Maximum flexibility was obtained with a nanocomposite crystalline/amorphous film. • The film reduces the Ni surface content, possibly improving the biocompatibility. - Abstract: An experimental procedure to coat superelastic NiTi alloys with flexible TiO{sub 2} protective nanocomposite films using sol–gel technology was developed in this work to improve the metal biocompatibility without deteriorating its superelastic mechanical properties. The coatings were characterized by scanning and transmission electron microscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, and glazing incidence X-ray diffraction. The elasticity of the film was tested in coated specimens submitted to three-point bending tests. A short densification by thermal treatment at 500 °C for 10 min yielded a bilayer film consisting of a 50 nm-thick crystallized TiO{sub 2} at the inner interface with another 50-nm-thick amorphous oxide film at the outer interface. This bilayer could sustain over 6.4% strain without cracking and could thus be used to coat biomedical instruments as well as other devices made with superelastic NiTi alloys.

Synthesis and electrical behavior of Ni-Ti substituted Y-type hexaferrites for high frequency application

Science.gov (United States)

Ahmad, Bashir; Ashiq, Muhammad Naeem; Mumtaz, Saleem; Ali, Irshad; Najam-Ul-Haq, Muhmmad; Sadiq, Imran

2018-04-01

This article reports the fabrication of Ni-Ti doped derivatives of Sr2Co2Fe12-2xO22 by economical Sol-gel method. At room temperature X-ray diffraction (XRD) pattern of powder was obtained after sintering at 1050 °C. The XRD analysis revealed the formation of pure Sr-Y hexaferrite phase. It was found that the observed values of dielectric parameters decreased with increasing Ni-Ti substitution. The higher values of dielectric constants and dielectric loss factor at lower frequency were owing to surface charge polarization. In all the samples the resonance peaks were also observed. The observed room temperature DC electrical resistivity found to increase from 1.8x106 to 4.9x109 ohm cm. The observed activation energies values of the fabricated materials are found in 0.52-0.82 eV range. The decrease in dielectric parameters and increase in resistivity of the fabricated samples with substituents suggest these materials have worth application in micro-wave devices as such devices required highly resistive materials.

Transformation behavior, chemical composition, surface topography and bending properties of five selected 0.016" x 0.022" NiTi archwires.

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Fischer-Brandies, Helge; Es-Souni, Mohammed; Kock, Norman; Raetzke, Klaus; Bock, Ole

2003-03-01

The aim of this study was to characterize five selected commercial NiTi archwires in terms of their transformation behavior, chemical composition, surface topography and mechanical properties (at temperatures of 22 degrees C, 37 degrees C and 60 degrees C). The rectangular orthodontic archwires investigated were Neo Sentalloy F80 (GAC, Central Islip, NY, USA), 35 degrees C Thermo-Active Copper NiTi (A-Company/Ormco, Glendora, CA, USA), Rematitan "Lite" (Dentaurum, Pforzheim, Germany), Titanol SE S (Forestadent, Pforzheim, Germany) and Titanal (Lancer, San Marcos, CA, USA) in size 0.016" x 0.022". The chemical composition and surface topography were analyzed by energy dispersive X-ray spectroscopy using an analytical scanning electron microscope (XL30, EDAX SUTW Saphire Detector; Philips, Eindhoven, Netherlands). The transition temperatures were measured by means of differential scanning calorimetry (DSC; Perkin-Elmer Pyris 1, Perkin-Elmer, Fremont, CA, USA) in a range of - 80 degrees C to + 80 degrees C. The mechanical properties and their dependence on temperature were determined by means of 3-point bending tests. The binary archwire materials were characterized by a two-phase structure (NiTi matrix and Ni3Ti4 precipitates). The SEM analyses revealed abradant residues in virtually all archwires, while DSC revealed complex transformation properties. In addition to the martensitic and austenitic transformations, an R-phase transformation was also detected. The bending tests showed pronounced loading and unloading plateaus. The martensitic archwires (Neo Sentalloy F80, 35 degrees C Thermo-Active Copper NiTi) were found to have a lower strength than the martensitic-austenitic (Rematitan "Lite") and the austenitic archwires (Titanol SE S, Titanal). With increasing temperature (in the range from 22 degrees C to 60 degrees C) a linear rise in the plateau forces was recorded. When assessing the quality of archwires, account should be taken of the surface quality, as it is

In-situ experimental evidence on R-phase related deformation processes in activated NiTi wires

Czech Academy of Sciences Publication Activity Database

Šittner, Petr; Sedlák, Petr; Landa, Michal; Novák, Václav; Lukáš, Petr

438-440, - (2006), s. 579-584 ISSN 0921-5107 R&D Projects: GA AV ČR IAA1048107; GA ČR GA202/04/2016 Institutional research plan: CEZ:AV0Z10100520; CEZ:AV0Z10480505; CEZ:AV0Z20760514 Keywords : memory alloys * NiTi wires * ultrasonics * neutron diffraction Subject RIV: BM - Solid Matter Physics ; Magnetism

Effect of Upper-Cycle Temperature on the Load-Biased, Strain-Temperature Response of NiTi

Science.gov (United States)

Padula, Santo, II; Noebe, Ronald; Bigelow, Glen; Qiu, Shipeng; Vaidyanathan, Raj; Gaydosh, Darrell; Garg, Anita

2011-01-01

Over the past decade, interest in shape memory alloy based actuators has increased as the primary benefits of these solid-state devices have become more apparent. However, much is still unknown about the characteristic behavior of these materials when used in actuator applications. Recently we have shown that the maximum temperature reached during thermal cycling under isobaric conditions could significantly affect the observed mechanical response of NiTi (55 wt% Ni), especially the amount of transformation strain available for actuation and thus work output. The investigation we report here extends that original work to ascertain whether further increases in the upper-cycle temperature would produce additional changes in the work output of the material, which has a stress-free austenite finish temperature of 113 C, and to determine the optimum cyclic conditions. Thus, isobaric, thermal-cycle experiments were conducted on the aforementioned alloy at various stresses from 50-300 MPa using upper-cycle temperatures of 165, 200, 230, 260, 290, 320 and 350 C. The data indicated that the amount of applied stress influenced the transformation strain, as would be expected. However, the maximum temperature reached during the thermal excursion also plays an equally significant role in determining the transformation strain, with the maximum transformation strain observed during thermal cycling to 290 C. In situ neutron diffraction at stress and temperature showed that the differences in transformation strain were mostly related to changes in martensite texture when cycling to different upper-cycle temperatures. Hence, understanding this effect is important to optimizing the operation of SMA-based actuators and could lead to new methods for processing and training shape memory alloys for optimal performance.

Laser surface treatment of polyamide and NiTi alloy and the effects on mesenchymal stem cell response

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Waugh, D. G.; Lawrence, J.; Shukla, P.; Chan, C.; Hussain, I.; Man, H. C.; Smith, G. C.

2015-07-01

Mesenchymal stem cells (MSCs) are known to play important roles in development, post-natal growth, repair, and regeneration of mesenchymal tissues. What is more, surface treatments are widely reported to affect the biomimetic nature of materials. This paper will detail, discuss and compare laser surface treatment of polyamide (Polyamide 6,6), using a 60 W CO2 laser, and NiTi alloy, using a 100 W fiber laser, and the effects of these treatments on mesenchymal stem cell response. The surface morphology and composition of the polyamide and NiTi alloy were studied by scanning electron microscopy (SEM) and X-ray photoemission spectroscopy (XPS), respectively. MSC cell morphology cell counting and viability measurements were done by employing a haemocytometer and MTT colorimetric assay. The success of enhanced adhesion and spreading of the MSCs on each of the laser surface treated samples, when compared to as-received samples, is evidenced in this work.

Elementary martensitic transformation processes in Ni-rich NiTi single crystals with Ni4Ti3 precipitates

International Nuclear Information System (INIS)

Michutta, J.; Somsen, Ch.; Yawny, A.; Dlouhy, A.; Eggeler, G.

2006-01-01

The present study shows that multiple-step martensitic transformations can be observed in aged Ni-rich NiTi single crystals. Ageing of solution-annealed and water-quenched Ni-rich NiTi single crystals results in a homogeneous precipitation of coherent Ni 4 Ti 3 particles. When the interparticle spacing reaches a critical value (order of magnitude: 200 nm), three distinct transformation processes are observed on cooling from the high-temperature phase using differential scanning calorimetry and in situ transmission electron microscopy. The transformation sequence begins with the formation of R-phase starting from all precipitate/matrix interfaces (first step). The transformation continues with the formation of B19' and its subsequent growth along all precipitate/matrix interfaces (second step). Finally, the matrix in between the precipitates transforms to B19' (third step). Elementary transformation mechanisms which account for two- and three-step transformations in a system with small-scale microstructural heterogeneities were identified

Angular distributions of sputtered particles from NiTi alloy

International Nuclear Information System (INIS)

Neshev, I.; Hamishkeev, V.; Chernysh, V.S.; Postnikov, S.; Mamaev, B.

1993-01-01

The angular distributions of sputtered Ni and Ti from a polycrystalline NiTi (50-50%) alloy are investigated by Auger electron spectroscopy and Rutherford backscattering spectroscopy. A difference in the angular distributions is observed with Ni being sputtered preferentially near the surface normal. A computer program for the calculation of the angular distributions of constituents sputtered from binary targets is created and used. The mechanisms responsible for the observed differences in the angular distributions are discussed. It is found that the collisional cascade theory is not directly applicable to the results of the constituents' angular distributions obtained in the presence of oxygen. The fitted coefficients of bombardment-induced segregation are found to be greater than the experimentally obtained ones. (author)

Effects of focused ion beam milling on the compressive behavior of directionally solidified micro-pillars and the nanoindentation response of an electro-polished surface

International Nuclear Information System (INIS)

Shim, Sang Hoon; Bei, Hongbin; Miller, Michael K; Pharr, George Mathews; George, Easo P

2009-01-01

Focused ion beam (FIB) milling is the typical way in which micro-pillars are fabricated to study small-scale plasticity and size effects in uniaxial compression. However, FIB milling can introduce defects into the milled pillars. To investigate the effects of FIB damage on mechanical behavior, we tested Mo-alloy micro-pillars that were FIB milled following directional solidification, and compared their compressive response to pillars that were not FIB milled. We also FIB milled at glancing incidence a Mo-alloy single-crystal surface, and compared its nanoindentation response to an electro-polished surface of the same crystal. Consequences for the interpretation of data obtained from FIB milled micro-pillars are discussed

Microstructural and Mechanical Properties of Porous 60NiTi Prepared by Conventional Press-and-sinter Method

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Khanlari Khashayar

2017-01-01

Full Text Available An intermetallic nickel-titanium alloy, 60NiTi, comprised of approximately 60 wt.% Ni and 40 wt.% Ti, contains a broad combination of physical and mechanical properties such as high hardness, low elastic modulus, resistance to aqueous corrosion and good biocompatibility. These unique combinations make this alloy an attractive candidate for medical components such as implants and prosthesis, where biocompatible materials with high hardness and low stiffness are typically used. The conventional press-and-sinter method which represents the least complex, most flexible and economic powder metallurgy method was used to produce porous 60NiTi parts suitable for biomedical applications. The effect of sintering holding time on the microstructure and mechanical properties is investigated. The structure of the as sintered parts is quite porous which is beneficial based on the medical point of view. The ultimate compressive strength of the samples is higher than that of the compact human bone and can, therefore, meet the strength demand of implants for general bone replacement applications.

Analysis of neutron diffraction spectra acquired in situ during stress-induced transformations in superelastic NiTi

International Nuclear Information System (INIS)

Vaidyanathan, R.; Bourke, M.A.; Dunand, D.C.

1999-01-01

Neutron diffraction spectra were obtained during various stages of a reversible stress-induced austenite to martensite phase transformation in superelastic NiTi. This was accomplished by neutron diffraction measurements on bulk polycrystalline NiTi samples simultaneously subjected to mechanical loading. Analysis of the data was carried out using individual lattice plane (hkl) reflections as well as by Rietveld refinement. In the Rietveld procedure, strains in austenite were described in terms of an isotropic (hkl independent) and an anisotropic (hkl dependent) component. At higher stresses, austenite lattice plane reflections exhibited nonlinear and dissimilar elastic responses which may be attributed to the transformation. The texture evolution is significant in both austenite and martensite phases during the transformation and two approaches were used to describe this evolving texture, i.e., an ellipsoidal model due to March - Dollase and a generalized spherical-harmonic approach. The respective predictions of the phase fraction evolution as a function of applied stress were compared. A methodology is thus established to quantify the discrete phase strains, phase volume fractions, and texture during such transformations. copyright 1999 American Institute of Physics

A novel approach to determine the effect of irrigation on temperature and failure of Ni-Ti endodontic rotary files

Science.gov (United States)

Mousavi, Sayed Ali; Kargar-Dehnavi, Vida; Mousavi, Sayed Amir

2012-01-01

Background: Nickel-titanium (Ni-Ti) rotary instrument files are important devices in Endodontics in root canal preparation. Ni-Ti file breakage is a critical and problematic issue and irrigation techniques were applied to decrease risk of file failure root. The aim of the present study was to compare the temperature gradient change of different irrigation solutions with Ni-Ti rotary instrument system during root canal preparation and also to define their effects on the file failure. Materials and Methods: A novel computerized instrumentation was utilized and thirty standard (ProFile #25/.04) files were divided into three groups and subjected to a filing in the root canal test. Changes in temperature on teeth under constant instrumental conditions with custom-designed computerized experimental apparatus were measured by using a temperature sensor bonded to the apical hole. A rotary instrument for canal preparation in three series of solution was used and the changes in temperature after each solution were compared. Finally, the file failure results were mentored according to each step of test. Comparisons were performed between group status clinically by using ANOVA (t) test, once the sample showed up normal and differences of Pinstruments, which were immersed in 5% NaOCl, when compared with the water group (Pinstruments immersed in water, when compared with the no solution group (Pinstruments. Conclusion: By immersing the file in 5% NaOCl, the temperature gradient decreased and instrument failure was reduced. PMID:23087732

Physical and mechanical properties of a thermomechanically treated NiTi wire used in the manufacture of rotary endodontic instruments.

Science.gov (United States)

Pereira, E S J; Peixoto, I F C; Viana, A C D; Oliveira, I I; Gonzalez, B M; Buono, V T L; Bahia, M G A

2012-05-01

To compare physical and mechanical properties of one conventional and one thermomechanically treated nickel-titanium (NiTi) wire used to manufacture rotary endodontic instruments. Two NiTi wires 1.0 mm in diameter were characterized; one of them, C-wire (CW), was processed in the conventional manner, and the other, termed M-Wire (MW), received an additional heat treatment according to the manufacturer. Chemical composition was determined by energy-dispersive X-ray spectroscopy, phase constitution by XRD and the transformation temperatures by DSC. Tensile loading/unloading tests and Vickers microhardness measurements were performed to assess the mechanical behaviour. Data were analysed using analysis of variance (α = 0.05). The two wires showed approximately the same chemical composition, close to the 1 : 1 atomic ratio, and the β-phase was the predominant phase present. B19' martensite and the R-phase were found in MW, in agreement with the higher transformation temperatures found in this wire compared with CW, whose transformation temperatures were below room temperature. Average Vickers microhardness values were similar for MW and CW (P = 0.91). The stress at the transformation plateau in the tensile load-unload curves was lower and more uniform in the M-Wire, which also showed the smallest stress hysteresis and apparent elastic modulus. The M-Wire had physical and mechanical properties that can render endodontic instruments more flexible and fatigue resistant than those made with conventionally processed NiTi wires. © 2011 International Endodontic Journal.

Comparison of two techniques for assessing the shaping efficacy of repeatedly used nickel-titanium rotary instruments.

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Ounsi, Hani F; Franciosi, Giovanni; Paragliola, Raffaele; Al-Hezaimi, Khalid; Salameh, Ziad; Tay, Franklin R; Ferrari, Marco; Grandini, Simone

2011-06-01

The shaping capacity of nickel-titanium (NiTi) rotary instruments is often assessed by photographic or micro-computed tomography (micro-CT) measurements, and these instruments are often used more than once clinically. This study was conducted to compare photographic and micro-CT measurements and to assess if the repeated use of NiTi instruments affected the shape of canal preparation. Ten new sets of ProTaper Universal instruments (Dentsply-Maillefer, Ballaigues, Switzerland) were used in 60 resin blocks simulating curved root canals. Groups 1 to 6 (n=10) represented the first to sixth use of the instrument, respectively. Digitized images of the prepared blocks were taken in both mesiodistal (MD) and buccolingual (BL) directions and area measurements (mm(2)) were calculated using AutoCAD (Autodesk Inc, San Rafael, CA). The volumes of the same prepared canals were measured using micro-CT (mm(3)). Statistical analysis was performed to detect differences between photographic and volumetric measurements and differences between uses. Two-way repeated-measures analysis of variance revealed significant differences between groups (P < .001). Regarding measurement type, there were no significant differences between BL and MD measurements, but there were significant differences between micro-CT and BL measurements (P < .001) and micro-CT and MD measurements (P=.001). Significant differences were also noted between uses. Within the limitations of the present study, micro-CT scanning is more discriminative of the changes in canal space associated with repeated instrument use than photographic measurements. Canal preparations are significantly smaller after the third use of the same instrument. Copyright © 2011 American Association of Endodontists. Published by Elsevier Inc. All rights reserved.

A bridge column with superelastic NiTi SMA and replaceable rubber hinge for earthquake damage mitigation

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Varela, Sebastian; ‘Saiid' Saiidi, M.

2016-07-01

This paper reports a unique concept for resilient bridge columns that can undergo intense earthquake loading and remain functional with minimal damage and residual drift. In this concept, the column is designed so that its components can be easily disassembled and reassembled to facilitate material recycling and component reuse. This is meant to foster sustainability of bridge systems while minimizing monetary losses from earthquakes. Self-centering and energy dissipation in the column were provided by unbonded superelastic nickel-titanium (NiTi) shape memory alloy bars placed inside a plastic hinge element made of rubber. This replaceable plastic hinge was in turn attached to a concrete-filled carbon fiber-reinforced polymer tube and a precast concrete footing that were designed to behave elastically. The proposed concept was evaluated experimentally by testing a ¼-scale column model under simulated near-fault earthquake motions on a shake table. After testing, the model was disassembled, reassembled and tested again. The seismic performance of the reassembled model was found to be comparable to that of the ‘virgin’ model. A relatively simple computational model of the column tested that was developed in OpenSees was able to match some of the key experimental response parameters.

Bioactivity and electrochemical behavior of hydroxyapatite-silicon-multi walled carbon nano-tubes composite coatings synthesized by EPD on NiTi alloys in simulated body fluid

Energy Technology Data Exchange (ETDEWEB)

Khalili, V., E-mail: V_khalili@sut.ac.ir [Department of Materials Engineering, Engineering Faculty, University of Bonab, Bonab (Iran, Islamic Republic of); Khalil-Allafi, J. [Research Center for Advanced Materials and Mineral Processing, Faculty of Materials Engineering, Sahand University of Technology, Tabriz (Iran, Islamic Republic of); Frenzel, J.; Eggeler, G. [Institute for Materials, Faculty of Mechanical Engineering, Ruhr-University Bochum, 44801 Bochum (Germany)

2017-02-01

In order to improve the surface bioactivity of NiTi bone implant and corrosion resistance, hydroxyapatite coating with addition of 20 wt% silicon, 1 wt% multi walled carbon nano-tubes and both of them were deposited on a NiTi substrate using a cathodic electrophoretic method. The apatite formation ability was estimated using immersion test in the simulated body fluid for 10 days. The SEM images of the surface of coatings after immersion in simulated body fluid show that the presence of silicon in the hydroxyapatite coatings accelerates in vitro growth of apatite layer on the coatings. The Open-circuit potential and electrochemical impedance spectroscopy were measured to evaluate the electrochemical behavior of the coatings in the simulated body fluid at 37 °C. The results indicate that the compact structure of hydroxyapatite-20 wt% silicon and hydroxyapatite-20 wt% silicon-1 wt% multi walled carbon nano-tubes coatings could efficiently increase the corrosion resistance of NiTi substrate. - Highlights: • The composite coatings of HA, Si and MWCNTs was prepared using electrophoretic deposition. • The presence of 1 wt.% MWCNTs in the HA coating provides more nucleation cites of apatite crystallites in SBF. • The presence of Si in HA coating increases the growth rate of apatite crystallites with the Ca/P atomic ratio of 1.67. • The EIS indicate the compact HA-20%Si and HA-20%Si-1%MWCNTs coatings efficiently increase corrosion resistance of NiTi. • The porous HA and HA-1%MWCNTs do not increase significantly corrosion resistance due to the easy diffusion path.

Active frequency tuning of the cantilever nanoresonator utilizing a phase transformation of NiTi thin film

Czech Academy of Sciences Publication Activity Database

Stachiv, Ivo; Šittner, Petr; Jeng, Y.-R.; Vokoun, David

2017-01-01

Roč. 19, č. 7 (2017), s. 5161-5169 ISSN 1392-8716 R&D Projects: GA ČR GC15-13174J Institutional support: RVO:68378271 Keywords : nanoresonator * resonant frequency * thin film * smart memory alloys * NiTi film Subject RIV: BM - Solid Matter Physics ; Magnetism OBOR OECD: Condensed matter physics (including formerly solid state physics, supercond.) Impact factor: 0.398, year: 2016

Characterization of mechanical properties of hydroxyapatite-silicon-multi walled carbon nano tubes composite coatings synthesized by EPD on NiTi alloys for biomedical application.

Science.gov (United States)

Khalili, Vida; Khalil-Allafi, Jafar; Sengstock, Christina; Motemani, Yahya; Paulsen, Alexander; Frenzel, Jan; Eggeler, Gunther; Köller, Manfred

2016-06-01

Release of Ni(1+) ions from NiTi alloy into tissue environment, biological response on the surface of NiTi and the allergic reaction of atopic people towards Ni are challengeable issues for biomedical application. In this study, composite coatings of hydroxyapatite-silicon multi walled carbon nano-tubes with 20wt% Silicon and 1wt% multi walled carbon nano-tubes of HA were deposited on a NiTi substrate using electrophoretic methods. The SEM images of coated samples exhibit a continuous and compact morphology for hydroxyapatite-silicon and hydroxyapatite-silicon-multi walled carbon nano-tubes coatings. Nano-indentation analysis on different locations of coatings represents the highest elastic modulus (45.8GPa) for HA-Si-MWCNTs which is between the elastic modulus of NiTi substrate (66.5GPa) and bone tissue (≈30GPa). This results in decrease of stress gradient on coating-substrate-bone interfaces during performance. The results of nano-scratch analysis show the highest critical distance of delamination (2.5mm) and normal load before failure (837mN) as well as highest critical contact pressure for hydroxyapatite-silicon-multi walled carbon nano-tubes coating. The cell culture results show that human mesenchymal stem cells are able to adhere and proliferate on the pure hydroxyapatite and composite coatings. The presence of both silicon and multi walled carbon nano-tubes (CS3) in the hydroxyapatite coating induce more adherence of viable human mesenchymal stem cells in contrast to the HA coated samples with only silicon (CS2). These results make hydroxyapatite-silicon-multi walled carbon nano-tubes a promising composite coating for future bone implant application. Copyright © 2016 Elsevier Ltd. All rights reserved.

Corrosion resistance of a laser spot-welded joint of NiTi wire in simulated human body fluids.

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Yan, Xiao-Jun; Yang, Da-Zhi

2006-04-01

The purpose of this study was to investigate corrosion resistance of a laser spot-welded joint of NiTi alloy wires using potentiodynamic tests in Hank's solution at different PH values and the PH 7.4 NaCl solution for different Cl- concentrations. Scanning electron microscope observations were carried out before and after potentiodynamic tests. The composition of a laser spot-welded joint and base metal were characterized by using an electron probe microanalyzer. The results of potentiodynamic tests showed that corrosion resistance of a laser spot-welded joint of NiTi alloy wire was better than that of base metal, which exhibited a little higher breakdown potential and passive range, and a little lower passive current density. Corrosion resistances of a laser spot-welded joint and base metal decreased with increasing of the Cl- concentration and PH value. The improvement of corrosion resistance of the laser spot-welded joint was due to the decrease of the surface defects and the increase of the Ti/Ni ratio. (c) 2005 Wiley Periodicals, Inc.

Endodontic management of C-shaped root canal system of mandibular first molar by using a modified technique of self-adjusting file system.

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