On the microstructural factors affecting creep resistance of die-cast Mg–La-rare earth (Nd, Y or Gd) alloys

Energy Technology Data Exchange (ETDEWEB)

Gavras, S. [Magnesium Innovation Centre, Helmholtz-Zentrum Geesthacht, Max-Planck-Straße 1, Geesthacht (Germany); Zhu, S.M. [School of Aerospace, Mechanical and Manufacturing Engineering, RMIT University, Carlton, Victoria 3053 (Australia); Nie, J.F. [Department of Materials Science and Engineering, Monash University, Victoria 3800 (Australia); Gibson, M.A. [School of Aerospace, Mechanical and Manufacturing Engineering, RMIT University, Carlton, Victoria 3053 (Australia); Department of Materials Science and Engineering, Monash University, Victoria 3800 (Australia); CSIRO Manufacturing, Clayton, Victoria 3168 (Australia); Easton, M.A. [School of Aerospace, Mechanical and Manufacturing Engineering, RMIT University, Carlton, Victoria 3053 (Australia)

2016-10-15

Creep properties of high-pressure die-cast Mg–La-RE (Nd, Y or Gd) alloys, varying in ternary RE additions and in different heat treatment conditions, have been investigated. Through the use of short-term solution treatments (1 h at 520 °C) it was shown that the continuous intermetallic phase present in the eutectic at grain boundaries became discontinuous. This effect, in combination with the likely removal of the localised region of supersaturated solute in solid solution near grain boundaries, reduced the creep resistance. When relatively high concentrations of ternary alloying additions were used, solid solution strengthening and precipitation hardening appeared to compensate for the negative effect of reduced grain boundary reinforcement. Microstructural investigation revealed that Nd-containing alloys had fewer and larger dynamic precipitates present in the α-Mg matrix following creep testing at 177 °C and 90 MPa. It was concluded that grain boundary reinforcement in combination with the thermal stability of the precipitates formed, which is ultimately related to the diffusivity of solute in solid solution, are also contributing factors to creep resistance.

Numerical description of creep of highly creep resistant alloys

International Nuclear Information System (INIS)

Preussler, T.

1991-01-01

Fatigue tests have been performed with a series of highly creep resistant materials for gas turbines and related applications for gaining better creep data up to long-term behaviour. The investigations were performed with selected individual materials in the area of the main applications down to strains and stresses relevant to design, and have attained trial durations of 25000 to 60000 h. In continuing former research, creep equations for a selection of characterizing individual materials have been improved and partly newly developed on the basis of a differentiated evaluation. Concerning the single materials, there are: one melt each of the materials IN-738 LC, IN-939, IN-100, FSX-414 and Inconel 617. The applied differentiated evaluation is based on the elastoplastical behaviour from the hot-drawing test, the creep behaviour from the non interrupted or the interrupted fatigue test, and the contraction behaviour from the annealing test. The creep equations developed describe the high temperature deformation behaviour taking into account primary, secondary and partly the tertiary creep dependent of temperature, stress and time. These equations are valid for the whole application area of the respective material. (orig./MM) [de

Creep of titanium--silicon alloys

International Nuclear Information System (INIS)

Paton, N.E.; Mahoney, M.W.

1976-01-01

Operative creep mechanisms in laboratory melts of Ti-5Zr-0.5Si and Ti-5Zr-0.5Si have been investigated as a function of microstructure, creep stress, and temperature. From creep rate data and transmission electron microscopy results, it has been shown that an important creep strengthening mechanism at 811 0 K in Si-bearing Ti alloys is clustering of solute atoms on dislocations. All of the alloys investigated showed anomalously high apparent activation energies and areas for creep and a high exponent (n) in the Dorn equation. In addition, the effect of heat treatment was investigated and it is shown that the highest creep strength was obtained by using a heat treatment which retained the maximum amount of silicon in solution. This is consistent with the proposed creep strengthening mechanism. An investigation of the creep behavior of several other Si containing alloys including two commercial alloys, Ti-11 and IMI-685 indicated similar results. 12 fig., 6 tables

9-12% Cr heat resistant steels. Alloy design, TEM characterisation of microstructure evolution and creep response at 650 C

International Nuclear Information System (INIS)

Rojas Jara, David

2011-01-01

This work was carried out aiming to design and characterise 9-12% Cr steels with tailormade microstructures for applications in fossil fuel fired power plants. The investigations concentrated in the design and characterisation of heat resistant steels for applications in high oxidising atmospheres (12% Cr) and 9% Cr alloys for components such as rotors (P91). ThermoCalc calculations showed to be a reliable tool for alloy development. The modeling also provided valuable information for the adjustment of the processing parameters (austenisation and tempering temperatures). Two 12% Cr heat resistant steels with a fine dispersion of nano precipitates were designed and produced supported by thermodynamic modeling (ThermoCalc). A detailed characterisation of the microstructure evolution at different creep times (100 MPa / 650 C / 8000 h) was carried out by scanning transmission electron microscopy (STEM). The results of the microstructure analysis were correlated with the mechanical properties in order to investigate the influence of different precipitates (especially M 23 C 6 carbides) on the creep strength of the alloys. Precipitation of Laves phase and Z-phase was observed after several hundred hours creep time. Very few Z-phase of the type Cr(V,Ta)N nucleating from existing (V,Ta)(C,N) was observed. Both alloys show growth and coarsening of Laves phase, meanwhile the MX carbonitrides present a very slow growth and coarsening rate. Alloys containing Laves phase, MX and M 23 C 6 precipitates show best creep properties. The influence of hot-deformation and tempering temperature on the microstructure evolution on one of the designed 12% Cr alloys was studied during short-term creep at 80-250 MPa and 650 C. Quantitative determination of dislocation density and sub-grain size in the initial microstructure and after creep was investigated by STEM combined with the high-angle annular dark-field detector (HAADF). A correlation between microstructure evolution and creep

9-12% Cr heat resistant steels. Alloy design, TEM characterisation of microstructure evolution and creep response at 650 C

Energy Technology Data Exchange (ETDEWEB)

Rojas Jara, David

2011-03-21

This work was carried out aiming to design and characterise 9-12% Cr steels with tailormade microstructures for applications in fossil fuel fired power plants. The investigations concentrated in the design and characterisation of heat resistant steels for applications in high oxidising atmospheres (12% Cr) and 9% Cr alloys for components such as rotors (P91). ThermoCalc calculations showed to be a reliable tool for alloy development. The modeling also provided valuable information for the adjustment of the processing parameters (austenisation and tempering temperatures). Two 12% Cr heat resistant steels with a fine dispersion of nano precipitates were designed and produced supported by thermodynamic modeling (ThermoCalc). A detailed characterisation of the microstructure evolution at different creep times (100 MPa / 650 C / 8000 h) was carried out by scanning transmission electron microscopy (STEM). The results of the microstructure analysis were correlated with the mechanical properties in order to investigate the influence of different precipitates (especially M{sub 23}C{sub 6} carbides) on the creep strength of the alloys. Precipitation of Laves phase and Z-phase was observed after several hundred hours creep time. Very few Z-phase of the type Cr(V,Ta)N nucleating from existing (V,Ta)(C,N) was observed. Both alloys show growth and coarsening of Laves phase, meanwhile the MX carbonitrides present a very slow growth and coarsening rate. Alloys containing Laves phase, MX and M{sub 23}C{sub 6} precipitates show best creep properties. The influence of hot-deformation and tempering temperature on the microstructure evolution on one of the designed 12% Cr alloys was studied during short-term creep at 80-250 MPa and 650 C. Quantitative determination of dislocation density and sub-grain size in the initial microstructure and after creep was investigated by STEM combined with the high-angle annular dark-field detector (HAADF). A correlation between microstructure

Alloying effect on the room temperature creep characteristics of a Ti-Zr-Be bulk metallic glass

Science.gov (United States)

Gong, Pan; Wang, Sibo; Li, Fangwei; Wang, Xinyun

2018-02-01

The effect of alloying elements (e.g. Fe, Al, and Ni) on the room temperature creep behavior of a lightweight Ti41Zr25Be34 bulk metallic glass (BMG) was investigated via nanoindentation tests. The generalized Kelvin model was adopted to describe the creep curves. The strain rate sensitivity m has been derived as a measure of the creep resistance. The compliance spectrum and retardation spectrum were also derived. The results show that the creep resistance of Ti41Zr25Be34 alloy can be obviously improved with the addition of alloying elements, and the most effective element is found to be Al. The mechanism for enhancing the creep resistance was discussed in terms of the scale variation of the shear transformation zone induced by alloying.

The effect of aluminium on the creep behavior of titanium aluminide alloys

International Nuclear Information System (INIS)

Nandy, T.K.; Mishra, R.S.; Gogia, A.K.; Banerjee, D.

1995-01-01

Small increases in the Al content of Ti 3 Al-Nb alloys are known to improve creep resistance at the expense of the room temperature ductility. Though considerable work has been done on the creep behavior of titanium aluminide alloys, a systematic investigation involving the role of Al on the creep of aluminides is lacking. In the present study the authors have therefore carried out a complete investigation on stress and temperature effects on two alloys with differing Al contents, Ti-24Al-15Nb and Ti-26Al-15Nb (nominal composition in at%) in order to understand the effect of Al in terms of power law creep behavior. The following conclusions are made: (1) A strong Al effect on the creep resistance of O phase alloys in the Ti-Al-Nb systems has been confirmed, through a study of stress and temperature effects on the creep behavior of the Ti-24Al-15Nb and the Ti-26Al-15Nb compositions. (2) It has been shown, however, that the small differences in Al do not affect either the activation energies for creep (∼370 kJ/mole) or the creep mechanism (climb controlled creep with a stress exponent of 4). The activation energies and stress exponents are similar to that observed in single phase O alloys. (3) It is suggested that Al influences creep strength through an intrinsic effect on the pre-exponential term AD o in the power law creep equation. It is possible that this effect is related to a higher ordering energy of the O phase with increasing Al content

Development of Ultra-high Purity (UHP) Fe-Based Alloys with High Creep and Oxidation Resistance for A-USC Technology

Science.gov (United States)

Hamdani, Fethi; Das, Nishith K.; Shoji, Tetsuo

2018-06-01

The design of ultra-high purity (UHP) Fe-based model alloys for advanced ultra-supercritical (A-USC) technology is attempted in this work. Creep testing has been performed in air at 700 °C and a stress level of 150 MPa. Analysis of the fracture surface and cross section of the crept specimen was performed. To evaluate the oxidation resistance in A-USC conditions, oxidation testing was performed in supercritical water (SCW) at 700 °C and 25 MPa. Weight gain (WG) measurements and meticulous characterization of the oxide scale were carried out. Based on thermodynamics and density functional theory calculations, some reactive elements in the Fe-Cr-Ni system were designated to promote precipitation strengthening and to improve the hydrogen-accelerated oxidation resistance. The addition of a 2 wt pct Mo into Fe-22Cr-22Ni-0.6Nb wt pct-based matrix did not significantly improve the creep resistance. The addition of 0.26 wt pct Zr coupled with cold working was effective for improving creep properties. The Mo-modified model alloy showed almost the same WG value as SUS310, while the Zr-modified alloy showed a higher WG value. Meanwhile, a Cr-enriched continuous oxide layer was formed at the oxidation front of the Zr-modified alloy and SUS310S after exposure to SCW conditions.

Development of Ultra-high Purity (UHP) Fe-Based Alloys with High Creep and Oxidation Resistance for A-USC Technology

Science.gov (United States)

Hamdani, Fethi; Das, Nishith K.; Shoji, Tetsuo

2018-03-01

The design of ultra-high purity (UHP) Fe-based model alloys for advanced ultra-supercritical (A-USC) technology is attempted in this work. Creep testing has been performed in air at 700 °C and a stress level of 150 MPa. Analysis of the fracture surface and cross section of the crept specimen was performed. To evaluate the oxidation resistance in A-USC conditions, oxidation testing was performed in supercritical water (SCW) at 700 °C and 25 MPa. Weight gain (WG) measurements and meticulous characterization of the oxide scale were carried out. Based on thermodynamics and density functional theory calculations, some reactive elements in the Fe-Cr-Ni system were designated to promote precipitation strengthening and to improve the hydrogen-accelerated oxidation resistance. The addition of a 2 wt pct Mo into Fe-22Cr-22Ni-0.6Nb wt pct-based matrix did not significantly improve the creep resistance. The addition of 0.26 wt pct Zr coupled with cold working was effective for improving creep properties. The Mo-modified model alloy showed almost the same WG value as SUS310, while the Zr-modified alloy showed a higher WG value. Meanwhile, a Cr-enriched continuous oxide layer was formed at the oxidation front of the Zr-modified alloy and SUS310S after exposure to SCW conditions.

Creep property of carbon and nitrogen free high strength new alloys

Energy Technology Data Exchange (ETDEWEB)

Muneki, S., E-mail: ABE.Fujio@nims.go.j [Heat Resistant Design Group, Steel Research Center, National Institute for Materials Science (Japan); Okubo, H.; Abe, F. [Heat Resistant Design Group, Steel Research Center, National Institute for Materials Science (Japan)

2010-06-15

The carbon and nitrogen free new alloys which were composed of supersaturated martensitic microstructure with high dislocation density before the creep test have been investigated systematically. These alloys were produced from the new approach which raised creep strength by the utilization of the reverse transformed austenite phase as a matrix and intermetallic compounds such as Laves phase and mu-phase as precipitates during heating before the creep test. It is important that these alloys are independent of any carbides and nitrides as strengthening factors. The high temperature creep test over 700 {sup o}C exceeds 50,000 h, and the test is continuous. Creep behavior of the alloys is found to be different from that of the conventional high-Cr ferritic steels. The addition of boron to the alloy pulled the recrystallization temperature up in the high temperature, and it became a creep test in the un-recrystallization condition, and the creep property of high temperature over 700 {sup o}C was drastically improved. The minimum creep rates of Fe-Ni alloys at 700 {sup o}C are found to be much lower than those of the conventional high Cr ferritic heat resistant steels, which is due to fine dispersion strengthening useful even at 700 {sup o}C in these alloys. As a result it became clear that the value for 100,000 h was exceeded at 700 {sup o}C and 100 MPa calculated from the Larson-Miller parameter at C = 20.

The microstructure and impression creep behavior of cast Mg–4Sn–4Ca alloy

International Nuclear Information System (INIS)

Khalilpour, Hamid; Mahdi Miresmaeili, Seyed; Baghani, Amir

2016-01-01

Because of low creep properties of magnesium–aluminum alloys, magnesium–tin alloys have received much attention in applications where high mechanical properties in high temperatures required. In this study creep properties of Mg–4Sn–4Ca alloy were investigated by the aim of impression creep test, scanning electron microscopy, energy dispersion spectrometry and X-ray diffraction analysis. The impression creep tests were carried out under different shear modulus normalized stress at high temperatures. According to the measured stress exponent values and activation energies the climb-controlled dislocation creep was determined as the dominant mechanism. The creep resistance of this alloy was related to the presence of Ca–Mg–Sn and Mg_2Ca phases which are distributed uniformly in the matrix and exhibit high thermal stability.

Applicability of creep damage rules to a nickel-base heat-resistant alloy Hastelloy XR

International Nuclear Information System (INIS)

Tsuji, Hirokazu; Nakajima, Najime; Tanabe, Tatsuhiko; Nakasone, Yuji

1992-01-01

A series of constant load and temperature creep rupture tests and varying load and/or temperature creep rupture tests was carried out on a nickel-base heat-resistant alloy Hastelloy XR, which was developed for applications in the High-Temperature Engineering Test Reactor, at temperatures ranging from 850 to 1000deg C in order to examine the applicability of the conventional creep damage rules, i.e., the life fraction, the strain fraction and their mixed rules. The life fraction rule showed the best applicability of these three criteria. The good applicability of the rule was considered to result from the fact that the creep strength of Hastelloy XR was not strongly affected by the change of the chemical composition and/or the microstructure during exposure to the high-temperature simulated HTGR helium environment. In conclusion the life fraction rule is applicable in engineering design of high-temperature components made of Hastelloy XR. (orig.)

Effects of microstructures and creep conditions on the fractal dimension of grain boundary fracture in high-temperature creep of heat-resistant alloys

International Nuclear Information System (INIS)

Tanaka, Manabu

1993-01-01

The effects of microstructural aspects, such as grain size and grain boundary configuration, and creep conditions on the fractal dimension of the grain boundary fracture were examined using several heat-resistant alloys, principally in an analysis scale range between one grain boundary length and specimen size. Grain boundary fracture surface profiles in the heat-resistant alloys exhibited a fractal nature in the scale range between one grain boundary length and specimen size as well as in the scale range below one grain boundary length. The fractal dimension of the grain boundary fracture slightly increased with decreasing grain size and was generally a little larger in the specimens with serrated grain boundaries than in those with straight grain boundaries. The fractal dimension of the grain boundary and the number of grain boundary microcracks which affected the grain boundary fracture patterns were a little larger in the specimen with the smaller grain size, and were also larger in the specimen with serrated grain boundaries. The fractal dimension of the grain boundary fracture increased with decreasing creep stress in the temperature range from 973 to 1422 K in these alloys, since more grain boundary microcracks existed in the specimens ruptured under the lower stresses at the higher temperatures. (orig.) [de

The microstructure and impression creep behavior of cast Mg–4Sn–4Ca alloy

Energy Technology Data Exchange (ETDEWEB)

Khalilpour, Hamid, E-mail: Ha.Khalilpoorster@gmail.com [Shahid Rajaee Teacher Training University, Faculty of Mechanical Engineering, Lavizan, Tehran (Iran, Islamic Republic of); Mahdi Miresmaeili, Seyed, E-mail: s_m_miresmaeily@yahoo.com [Shahid Rajaee Teacher Training University, Faculty of Mechanical Engineering, Lavizan, Tehran (Iran, Islamic Republic of); Baghani, Amir, E-mail: amir-baghani@uiowa.edu [University of Iowa, Department of Mechanical and Industrial Engineering, Iowa City, IA (United States)

2016-01-15

Because of low creep properties of magnesium–aluminum alloys, magnesium–tin alloys have received much attention in applications where high mechanical properties in high temperatures required. In this study creep properties of Mg–4Sn–4Ca alloy were investigated by the aim of impression creep test, scanning electron microscopy, energy dispersion spectrometry and X-ray diffraction analysis. The impression creep tests were carried out under different shear modulus normalized stress at high temperatures. According to the measured stress exponent values and activation energies the climb-controlled dislocation creep was determined as the dominant mechanism. The creep resistance of this alloy was related to the presence of Ca–Mg–Sn and Mg{sub 2}Ca phases which are distributed uniformly in the matrix and exhibit high thermal stability.

Creep and creep-rupture behavior of Alloy 718

International Nuclear Information System (INIS)

Brinkman, C.R.; Booker, M.K.; Ding, J.L.

1991-01-01

Data obtained from creep and creep-rupture tests conducted on 18 heats of Alloy 718 were used to formulate models for predicting high temperature time dependent behavior of this alloy. Creep tests were conducted on specimens taken from a number of commercial product forms including plate, bar, and forgoing material that had been procured and heat treated in accordance with ASTM specifications B-670 or B-637. Data were obtained over the temperature range of 427 to 760 degree C ad at test times to about 87,000 h. Comparisons are given between experimental data and the analytical models. The analytical models for creep-rupture included one based on lot-centering regression analysis and two based on the Minimum Commitment Method. A ''master'' curve approach was used to develop and equation for estimating creep deformation up to the onset of tertiary creep. 11 refs., 13 figs

Corrosion and Creep Characteristics of the HANA-4 Alloy with the various Manufacturing Processes

International Nuclear Information System (INIS)

Kim, Hyun-Gil; Choi, Byung-Kwan; Park, Jeong-Yong; Jeong, Yong-Hwan

2008-01-01

Zirconium alloys have been used as a fuel cladding material for several decades, since these alloys have revealed a good corrosion resistance and mechanical properties in reactor operating conditions. The development of an advanced Zr-based alloy with an improved corrosion and creep resistance is necessary for the high burn-up operating conditions in PWRs. The alloying element effects of the Nb, Sn, Fe, Cr, Cu etc as well as an optimization of the manufacturing processes such as the reduction ratio and annealing temperatures have been studied to improve the corrosion and creep properties. A high Nb-containing Zr-based alloy named HANA-4 was designed at KAERI and its nominal composition is Zr-1.5Nb-0.4Sn-0.2Fe-0.1Cr in wt.%. For high Nb-containing Zr alloys, their corrosion resistance is very sensitive to their microstructural characteristics which are determined by a manufacturing process. In order to obtain the best manufacturing process for the HANA-4 alloy, various evaluations such as corrosion and creep tests, a microstructural analysis, and a texture analysis were performed on the HANA-4 alloy with various manufacturing processes

Creep and fatigue of alloy 800 in helium

International Nuclear Information System (INIS)

Cook, R.H.

1975-01-01

Proposals for use of Alloy 800 as a H.T.R. boiler material have prompted studies of its creep and high temperature fatigue properties in impure helium with comparative tests in air. In impure helium, as expected in a H.T.R., reactions of potential importance are selective oxidation (of chromium, aluminium and titanium) and possibly carburisation from carbon monoxide or methane. In air, general oxidation will occur, possibly accompanied by nitridation. The effects of these reactions will depend on specimen geometry and the nature of the deformation. Two important possibilities are: (i) that environment affects the structure and properties of a surface zone of material undegoing uniform deformation (this may modify creep rate and crack nucleation); and (ii) that environment affects behaviour of a small region (e.g. at the root of a notch or ahead of a crack) in a specimen undergoing non-uniform deformation (this will modify crack growth and hence rupture life or fatigue endurance). This paper summarises experimental work demonstrating an influence of the above reactions on mechanical properties of austenitic steels and nickel-based alloys, drawing examples where possible from the limited data available on Alloy 800. Whilst nitridation and carburisation may simply increase creep resistance at the expense of ductility (and possibly of fatigue resistance), the effects of oxidation are complex. A high oxygen pressures (as in air) oxygen may reduce creep and fatigue resistance by promoting cavitation but formation of oxide in cracks can reduce their propagation rate. At low oxygen pressures, as expected in H.T.R. helium, oxygen enhanced cavitation is less likely, but selective oxidation along grain boundaries can sometimes assist crack nucleation. (author)

Room temperature creep in metals and alloys

Energy Technology Data Exchange (ETDEWEB)

Deibler, Lisa Anne [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States). Materials Characterization and Performance

2014-09-01

Time dependent deformation in the form of creep and stress relaxation is not often considered a factor when designing structural alloy parts for use at room temperature. However, creep and stress relaxation do occur at room temperature (0.09-0.21 T_m for alloys in this report) in structural alloys. This report will summarize the available literature on room temperature creep, present creep data collected on various structural alloys, and finally compare the acquired data to equations used in the literature to model creep behavior. Based on evidence from the literature and fitting of various equations, the mechanism which causes room temperature creep is found to include dislocation generation as well as exhaustion.

Transformation-Induced Creep and Creep Recovery of Shape Memory Alloy.

Science.gov (United States)

Takeda, Kohei; Tobushi, Hisaaki; Pieczyska, Elzbieta A

2012-05-22

If the shape memory alloy is subjected to the subloop loading under the stress-controlled condition, creep and creep recovery can appear based on the martensitic transformation. In the design of shape memory alloy elements, these deformation properties are important since the deflection of shape memory alloy elements can change under constant stress. The conditions for the progress of the martensitic transformation are discussed based on the kinetics of the martensitic transformation for the shape memory alloy. During loading under constant stress rate, temperature increases due to the stress-induced martensitic transformation. If stress is held constant during the martensitic transformation stage in the loading process, temperature decreases and the condition for the progress of the martensitic transformation is satisfied, resulting in the transformation-induced creep deformation. If stress is held constant during the reverse transformation stage in the unloading process, creep recovery appears due to the reverse transformation. The details for these thermomechanical properties are investigated experimentally for TiNi shape memory alloy, which is most widely used in practical applications. The volume fraction of the martensitic phase increases in proportion to an increase in creep strain.

Impression creep properties of a semi-solid processed magnesium-aluminum alloy containing calcium and rare earth elements

International Nuclear Information System (INIS)

Nami, B.; Razavi, H.; Miresmaeili, S.M.; Mirdamadi, Sh.; Shabestari, S.G.

2011-01-01

The creep properties of a thixoformed magnesium-aluminum alloy containing calcium and rare earth elements were studied under shear modulus-normalized stresses ranging from 0.0225 to 0.035 at temperatures of 150-212 o C using the impression creep technique. Analysis of the creep mechanism based on a power-law equation indicated that pipe diffusion-controlled dislocation climb is the dominant mechanism during creep. The alloy has a better creep resistance than high-pressure die-cast magnesium-aluminum alloy.

Effect of solute segregation on thermal creep in dilute nanocyrstalline Cu alloys

International Nuclear Information System (INIS)

Schäfer, Jonathan; Ashkenazy, Yinon; Albe, Karsten; Averback, Robert S

2012-01-01

Highlights: ► Segregating solutes lower the grain boundary free volume in nanocrystalline Cu. ► Lower free volume leads to reduced atomic mobility and higher creep resistance. ► Increase in creep resistance scales with atomic size of segregating solutes. ► Atomic processes in boundaries are similar to the ones in amorphous material. - Abstract: The effect of solute segregation on thermal creep in dilute nanocrystalline alloys (Cu–Nb, Cu–Fe, Cu–Zr) was studied at elevated temperatures using molecular dynamics simulations. A combined Monte-Carlo and molecular dynamics simulation technique was first used to equilibrate the distribution of segregating solutes. Then the creep rates of the diluted Cu samples were measured as functions of temperature, composition, load and accumulated strain. In Cu–Nb samples, the creep rates were observed to increase initially with strain, but then saturate at a value close to that obtained for alloys prepared by randomly locating the solute in the grain boundaries. This behavior is attributed to an increase in grain boundary volume and energy with added chemical disorder. At high temperatures, the apparent activation energy for creep was anomalously high, 3 eV, but only 0.3 eV at lower temperatures. This temperature dependence is found to correlate with atomic mobilities in bulk Cu–Nb glasses. Calculations of creep in nanocrystalline Cu alloys containing other solutes, Fe and Zr, show that the suppression of creep rate scales with their atomic volumes when dissolved in Cu.

Creep and creep rupture properties of unalloyed vanadium and solid-solution-strengthened vanadium-base alloys

International Nuclear Information System (INIS)

Kainuma, T.; Iwao, N.; Suzuki, T.; Watanabe, R.

1982-01-01

The creep and creep rupture properties of vanadium and vanadium-base alloys were studied at 700 and 1000 0 C. The alloys were vanadium-base binary alloys containing about 5 - 21 at.% Al, Ti, Nb, Ta, Cr, Mo or Fe, three V-20wt.%Nb-base ternary alloys containing 5 or 10 wt.% Al, Cr or Mo, V-10wt.%Ta-10wt.%Al and V-25wt.%Cr-0.8wt.%Zr. The creep rupture stress of the binary alloys, except the V-Al and V-Ti alloys, increased linearly with increasing concentration of the alloying elements. The V-Nb alloy had the best properties with respect to the rupture stress and creep rate at 700 0 C and the rupture stress at 1000 0 C, but the V-Mo alloy appeared likely to have better creep properties at longer times and higher temperatures. Of the five ternary alloys, V-20wt.%Nb-5wt.%Cr and V-20wt.%Nb-10wt.%Mo showed the best creep properties. The creep properties of these two alloys were compared with those of other vanadium alloys and of type 316 stainless steel. (Auth.)

A combinatorial approach to the development of a creep resistant beta titanium alloy

Science.gov (United States)

Peterson, Benjamin H.

Timetal 21S has been selected as a baseline for the development of a new high temperature beta titanium alloy. A combinatorial approach employing directed laser deposition of elemental powders has been used to produce a number of test coupons with controlled variations of composition. In addition to the variation of the baseline elements (Ti, Mo, Nb, Al and Si), the alloys contain varying amounts of neutral elements (Zr and Sn), beta-stabilizers (W) and dispersoid formers (B, C and Ge). Subsequently, the creep properties, represented by their minimum creep rates, have been assessed using an Instron Electrothermal Mechanical Tester (ETMT). The microstructures of the test coupons have been characterized using a range of techniques and have been quantified using rigorous stereological techniques to populate databases and subsequently train and test Bayesian Neural Network models for the prediction of creep properties. Additionally, advanced characterization techniques and computation tools have been employed to aid in the identification of the creep rate-limiting microstructural features. For example, SEM and TEM studies show a critical dependence of the size of alpha-denuded beta regions on the creep properties in these beta-Ti alloys. The most important microstructural features (volume fraction alpha, alpha lath thickness and beta mean free path) and alloying additions (Sn and Ge) have been identified and are discussed. The ETMT, used to investigate creep properties in the work, has also been characterized and compared with traditional tensile and creep testing methods. Computational models incorporating heat transfer and electrostatics were used to investigate the temperature profiles that result from the interaction of joule heating, conductive cooling and radiative cooling in subscale Ti-6Al-4V samples at five current densities in the ETMT. The tensile properties, including YS, UTS, E and total elongation, of sub-scale specimens have been evaluated over a range

Creep Aging Behavior Characterization of 2219 Aluminum Alloy

Directory of Open Access Journals (Sweden)

Lingfeng Liu

2016-06-01

Full Text Available In order to characterize the creep behaviors of 2219 aluminum alloy at different temperatures and stress levels, a RWS-50 Electronic Creep Testing Machine (Zhuhai SUST Electrical Equipment Company, Zhuhai, China was used for creep experiment at temperatures of 353~458 k and experimental stresses of 130~170 MPa. It was discovered that this alloy displayed classical creep curve characteristics in its creep behaviors within the experimental parameters, and its creep value increased with temperature and stress. Based on the creep equation of hyperbolic sine function, regression analysis was conducted of experimental data to calculate stress exponent, creep activation energy, and other related variables, and a 2219 aluminum alloy creep constitutive equation was established. Results of further analysis of the creep mechanism of the alloy at different temperatures indicated that the creep mechanism of 2219 aluminum alloy differed at different temperatures; and creek characteristics were presented in three stages at different temperatures, i.e., the grain boundary sliding creep mechanism at a low temperature stage (T < 373 K, the dislocation glide creep mechanism at a medium temperature stage (373 K ≤ T < 418 K, and the dislocation climb creep mechanism at a high temperature stage (T ≥ 418 K. By comparative analysis of the fitting results and experiment data, they were found to be in agreement with the experimental data, revealing that the established creep constitutive equation is suitable for different temperatures and stresses.

Cast Steels for Creep-Resistant Parts Used in Heat Treatment Plants

Directory of Open Access Journals (Sweden)

Drotlew A.

2012-12-01

Full Text Available Creep-resistant parts of heat treatment furnaces are in most cases made from high-alloyed chromium-nickel and nickel-chromium iron alloys, both cast and wrought. This paper presents the types of casting alloys used for this particular purpose, since the majority of furnace components are made by the casting process. Standards were cited which give symbols of alloy grades used in technical specifications by the domestic industry. It has been indicated that castings made currently are based on a wider spectrum of the creep-resistant alloy grades than the number of alloys covered by the standards. Alloy grades recommended by the technical literature for individual parts of the furnace equipment were given. The recommendations reflect both the type of the technological process used and the technical tasks performed by individual parts of the furnace equipment. Comments were also made on the role of individual alloying elements in shaping the performance properties of castings.

Microstructures and creep properties of Mg–4Al–(1–4) La alloys produced by different casting techniques

International Nuclear Information System (INIS)

Bai Jing; Sun Yangshan; Xue Feng; Qiang Jing

2012-01-01

The microstructures, mechanical properties and creep resistance of Mg–4Al–(1–4) La alloys produced by permanent mold casting and high pressure die casting (HPDC) were investigated. In addition to solute atoms in α-Mg matrix, Al element may exist in the form of three different intermetallic phases in the present alloys depending on the experimental conditions. In both casting states, the increase of La addition results in a rise in the volume fraction of Al 11 La 3 eutectic, and simultaneously Mg 17 Al 12 phase, including divorced eutectic in as-cast state and discontinuous precipitation after creep, is suppressed until completely disappears. This leads to a gradual increase in creep resistance. The formation of more Mg 17 Al 12 phase in HPDC alloys is considered a major factor in causing their worse creep properties by comparison with that of the permanent mold casting alloys when La content is in a lower level below 2 wt.%. By contrast, the HPDC alloys show better creep resistance with La content added above 2 wt.% owing to the formation of denser network distribution of Al 11 La 3 phase along grain/dendrite boundaries as a result of more rapid solidification rate and higher solidification pressure. For the alloys studied, grain/dendrite boundary sliding is suggested to be a possible controlling mechanism responsible for creep deformation at elevated temperatures.

Cast Steels for Creep-resistant Parts Used in Heat Treatment Plants

Directory of Open Access Journals (Sweden)

A. Drotlew

2012-12-01

Full Text Available Creep-resistant parts of heat treatment furnaces are in most cases made from high-alloyed chromium-nickel and nickel-chromium ironalloys, both cast and wrought. This paper presents the types of casting alloys used for this particular purpose, since the majority of furnace components are made by the casting process. Standards were cited which give symbols of alloy grades used in technical specifications by the domestic industry. It has been indicated that castings made currently are based on a wider spectrum of the creep-resistant alloy grades than the number of alloys covered by the standards. Alloy grades recommended by the technical literature for individual parts of the furnace equipment were given. The recommendations reflect both the type of the technological process used and the technical tasks performed by individual parts of the furnace equipment. Comments were also made on the role of individual alloying elements in shaping the performance properties of castings.

Irradiation creep of dispersion strengthened copper alloy

Energy Technology Data Exchange (ETDEWEB)

Pokrovsky, A.S.; Barabash, V.R.; Fabritsiev, S.A. [and others

1997-04-01

Dispersion strengthened copper alloys are under consideration as reference materials for the ITER plasma facing components. Irradiation creep is one of the parameters which must be assessed because of its importance for the lifetime prediction of these components. In this study the irradiation creep of a dispersion strengthened copper (DS) alloy has been investigated. The alloy selected for evaluation, MAGT-0.2, which contains 0.2 wt.% Al{sub 2}O{sub 3}, is very similar to the GlidCop{trademark} alloy referred to as Al20. Irradiation creep was investigated using HE pressurized tubes. The tubes were machined from rod stock, then stainless steel caps were brazed onto the end of each tube. The creep specimens were pressurized by use of ultra-pure He and the stainless steel caps subsequently sealed by laser welding. These specimens were irradiated in reactor water in the core position of the SM-2 reactors to a fluence level of 4.5-7.1 x 10{sup 21} n/cm{sup 2} (E>0.1 MeV), which corresponds to {approx}3-5 dpa. The irradiation temperature ranged from 60-90{degrees}C, which yielded calculated hoop stresses from 39-117 MPa. A mechanical micrometer system was used to measure the outer diameter of the specimens before and after irradiation, with an accuracy of {+-}0.001 mm. The irradiation creep was calculated based on the change in the diameter. Comparison of pre- and post-irradiation diameter measurements indicates that irradiation induced creep is indeed observed in this alloy at low temperatures, with a creep rate as high as {approx}2 x 10{sup {minus}9}s{sup {minus}1}. These results are compared with available data for irradiation creep for stainless steels, pure copper, and for thermal creep of copper alloys.

Irradiation creep of dispersion strengthened copper alloy

International Nuclear Information System (INIS)

Pokrovsky, A.S.; Barabash, V.R.; Fabritsiev, S.A.

1997-01-01

Dispersion strengthened copper alloys are under consideration as reference materials for the ITER plasma facing components. Irradiation creep is one of the parameters which must be assessed because of its importance for the lifetime prediction of these components. In this study the irradiation creep of a dispersion strengthened copper (DS) alloy has been investigated. The alloy selected for evaluation, MAGT-0.2, which contains 0.2 wt.% Al 2 O 3 , is very similar to the GlidCop trademark alloy referred to as Al20. Irradiation creep was investigated using HE pressurized tubes. The tubes were machined from rod stock, then stainless steel caps were brazed onto the end of each tube. The creep specimens were pressurized by use of ultra-pure He and the stainless steel caps subsequently sealed by laser welding. These specimens were irradiated in reactor water in the core position of the SM-2 reactors to a fluence level of 4.5-7.1 x 10 21 n/cm 2 (E>0.1 MeV), which corresponds to ∼3-5 dpa. The irradiation temperature ranged from 60-90 degrees C, which yielded calculated hoop stresses from 39-117 MPa. A mechanical micrometer system was used to measure the outer diameter of the specimens before and after irradiation, with an accuracy of ±0.001 mm. The irradiation creep was calculated based on the change in the diameter. Comparison of pre- and post-irradiation diameter measurements indicates that irradiation induced creep is indeed observed in this alloy at low temperatures, with a creep rate as high as ∼2 x 10 -9 s -1 . These results are compared with available data for irradiation creep for stainless steels, pure copper, and for thermal creep of copper alloys

Oxidation resistant high creep strength austenitic stainless steel

Science.gov (United States)

Brady, Michael P.; Pint, Bruce A.; Liu, Chain-Tsuan; Maziasz, Philip J.; Yamamoto, Yukinori; Lu, Zhao P.

2010-06-29

An austenitic stainless steel displaying high temperature oxidation and creep resistance has a composition that includes in weight percent 15 to 21 Ni, 10 to 15 Cr, 2 to 3.5 Al, 0.1 to 1 Nb, and 0.05 to 0.15 C, and that is free of or has very low levels of N, Ti and V. The alloy forms an external continuous alumina protective scale to provide a high oxidation resistance at temperatures of 700 to 800.degree. C. and forms NbC nanocarbides and a stable essentially single phase fcc austenitic matrix microstructure to give high strength and high creep resistance at these temperatures.

Overview of Strategies for High-Temperature Creep and Oxidation Resistance of Alumina-Forming Austenitic Stainless Steels

Science.gov (United States)

Yamamoto, Y.; Brady, M. P.; Santella, M. L.; Bei, H.; Maziasz, P. J.; Pint, B. A.

2011-04-01

A family of creep-resistant, alumina-forming austenitic (AFA) stainless steel alloys is under development for structural use in fossil energy conversion and combustion system applications. The AFA alloys developed to date exhibit comparable creep-rupture lives to state-of-the-art advanced austenitic alloys, and superior oxidation resistance in the ~923 K to 1173 K (650 °C to 900 °C) temperature range due to the formation of a protective Al2O3 scale rather than the Cr2O3 scales that form on conventional stainless steel alloys. This article overviews the alloy design approaches used to obtain high-temperature creep strength in AFA alloys via considerations of phase equilibrium from thermodynamic calculations as well as microstructure characterization. Strengthening precipitates under evaluation include MC-type carbides or intermetallic phases such as NiAl-B2, Fe2(Mo,Nb)-Laves, Ni3Al-L12, etc. in the austenitic single-phase matrix. Creep, tensile, and oxidation properties of the AFA alloys are discussed relative to compositional and microstructural factors.

Irradiation creep in simple binary alloys

International Nuclear Information System (INIS)

Nagakawa, J.; Sethi, V.K.; Turner, A.P.L.

1981-07-01

Creep enhancement during 21-MeV deuteron irradiation was examined at 350 0 C for two simple binary alloys with representative microstructures, i.e., solid-solution (Ni - 4 at. % Si) and precipitation-hardened (Ni - 12.8 at. % Al) alloys. Coherent precipitates were found to be very effective in suppressing irradiation-enhanced creep. Si solute atoms depressed irradiation creep moderately and caused irradiation hardening via radiation-induced segregation. The stress-dependence of irradiation creep in Ni - 4 at. % Si should a transition, which seems to reflect a change of mechanism from dislocation climb due to stress-induced preferential absorption (SIPA) to climb-controlled dislocation glide enhanced by irradiation

Creep and rupture of an ODS alloy with high stress rupture ductility. [Oxide Dispersion Strengthened

Science.gov (United States)

Mcalarney, M. E.; Arsons, R. M.; Howson, T. E.; Tien, J. K.; Baranow, S.

1982-01-01

The creep and stress rupture properties of an oxide (Y2O3) dispersion strengthened nickel-base alloy, which also is strengthened by gamma-prime precipitates, was studied at 760 and 1093 C. At both temperatures, the alloy YDNiCrAl exhibits unusually high stress rupture ductility as measured by both elongation and reduction in area. Failure was transgranular, and different modes of failure were observed including crystallographic fracture at intermediate temperatures and tearing or necking almost to a chisel point at higher temperatures. While the rupture ductility was high, the creep strength of the alloy was low relative to conventional gamma prime strengthened superalloys in the intermediate temperature range and to ODS alloys in the higher temperature range. These findings are discussed with respect to the alloy composition; the strengthening oxide phases, which are inhomogeneously dispersed; the grain morphology, which is coarse and elongated and exhibits many included grains; and the second phase inclusion particles occurring at grain boundaries and in the matrix. The creep properties, in particular the high stress dependencies and high creep activation energies measured, are discussed with respect to the resisting stress model of creep in particle strengthened alloys.

Comparison between PIII superficial treatment and ceramic coating in creep test of Ti-6Al-4V alloy

International Nuclear Information System (INIS)

Reis, D.A.P.; Moura Neto, C.; Silva, M.M.; Ueda, M.; Oliveira, V.S.; Couto, A.A.

2009-01-01

The objective of this work was evaluating the creep resistance of the Ti-6Al-4V alloy with superficial treatment of PIII superficial treatment and ceramic coating in creep test of Ti-6Al-4V alloy. It was used Ti-6Al-4V alloy as cylindrical bars under forged and annealing of 190 deg C by 6 hours condition and cooled by air. The Ti-6Al-4V alloy after the superficial treatment of PIII and ceramic coating was submitted to creep tests at 600°C and 250 and 319 MPa under constant load mode. In the PIII treatment the samples was put in a vacuum reactor (76 x 10 -3 Pa) and implanted by nitrogen ions in time intervals between 15 and 120 minutes. Yttria (8 wt.%) stabilized zirconia (YSZ) with a CoNiCrAlY bond coat was atmospherically plasma sprayed on Ti-6Al-4V substrates by Sulzer Metco Type 9 MB. The obtained results suggest the ceramic coating on Ti-6Al-4V alloy improved its creep resistance. (author)

Study of creep of Ti-6Al-4V alloy using plasma immersion ion implantation (PIII)

International Nuclear Information System (INIS)

Zepka, Susana; Yogi, Lucila Mayumi; Silva, Maria Margareth da; Reis, Danieli Aparecida Pereira; Moura Neto, Carlos de; Oliveira, Vinicius Souza de; Ueda, Mario

2010-01-01

This study aims to investigate the creep resistance of the Ti-6Al-4V alloy after surface modification by plasma immersion ion implantation (PIII). For the PIII treatment it was used nitrogen gas (ion implantation) to the formation of plasma, the material was treated for 100 minutes. After PIII treatment the samples were analyzed using the techniques of X-ray diffraction, spectrometry energy dispersive X-ray and atomic force microscopy. The creep tests were realized at 600°C, at constant load of 250 and 319 MPa. After the creep tests the samples were analyzed by optical microscopy and scanning electron microscopy. By chemical analysis by X-ray and EDS it is possible to determinate the Ti 2 N on the surface. Through the study of the creep curves it is observed an increasing in creep resistance of the alloy after PIII treatment. (author)

Superior high creep resistance of in situ nano-sized TiCx/Al-Cu-Mg composite.

Science.gov (United States)

Wang, Lei; Qiu, Feng; Zhao, Qinglong; Zha, Min; Jiang, Qichuan

2017-07-03

The tensile creep behavior of Al-Cu-Mg alloy and its composite containing in situ nano-sized TiC x were explored at temperatures of 493 K, 533 K and 573 K with the applied stresses in the range of 40 to 100 MPa. The composite reinforced by nano-sized TiC x particles exhibited excellent creep resistance ability, which was about 4-15 times higher than those of the unreinforced matrix alloy. The stress exponent of 5 was noticed for both Al-Cu-Mg alloy and its composite, which suggested that their creep behavior was related to dislocation climb mechanism. During deformation at elevated temperatures, the enhanced creep resistance of the composite was mainly attributed to two aspects: (a) Orowan strengthening and grain boundary (GB) strengthening induced by nano-sized TiC x particles, (b) θ' and S' precipitates strengthening.

Effect of equal-channel angular pressing on the creep resistance of precipitation-strengthened alloys

Czech Academy of Sciences Publication Activity Database

Sklenička, Václav; Král, Petr; Dvořák, Jiří; Kvapilová, Marie; Kawasaki, M.; Langdon, T. G.

667-669, - (2011), s. 897-902 ISSN 0255-5476. [NanoSPD5 - International Conference on Nanomaterials by Severe Plastic Deformation /5./. Nanjing, 21.03.2011-25.03.2011] Institutional research plan: CEZ:AV0Z20410507 Keywords : creep * equal-channel angular pressing * precipitation- strength ened alloys * creep damage Subject RIV: JG - Metallurgy

Influence of loading path and precipitates on indentation creep behavior of wrought Mg–6 wt% Al–1 wt% Zn magnesium alloy

Energy Technology Data Exchange (ETDEWEB)

Nautiyal, Pranjal [Discipline of Mechanical Engineering, Indian Institute of Information Technology, Design & Manufacturing, Jabalpur, Madhya Pradesh 482005 (India); Department of Applied Mechanics, Indian Institute of Technology, Delhi 110016 (India); Jain, Jayant [Department of Applied Mechanics, Indian Institute of Technology, Delhi 110016 (India); Agarwal, Arvind, E-mail: agarwala@fiu.edu [Department of Mechanical and Materials Engineering, Florida International University, Miami, FL 33174 (United States)

2016-01-05

This study reports the effect of loading path and precipitates on indentation induced creep behavior of AZ61 magnesium alloy. Indentation creep tests were performed on solution-treated and peak-aged extruded AZ61 magnesium alloy, and Atomic Force Microscopy (AFM) investigations were carried out to study deformation mechanisms. Twinning is the dominant creep mechanism for indentation along the extrusion direction (ED) in solution-treated alloy. A combination of slip and twinning appears to be the prominent mechanisms for indentation creep perpendicular to ED. Creep flow is arrested for indentation perpendicular to ED, due to slip–twin interactions. Influence of precipitates on creep deformation was also studied. Aged specimen exhibited higher creep resistance than solution-treated specimen. Unlike solution-treated specimens, twinning was not observed in aged alloy. Creep in aged specimen was attributed to slip.

Evaluation of long-term creep behaviour on K-cladding tubes

International Nuclear Information System (INIS)

Bang, J. G.; Jeong, Y. H.; Jeong, Y. H.

2003-01-01

KAERI has developed new zirconium alloys for high burnup fuel cladding. To evaluate the performance of these alloys, various out-pile tests are conducting. At high burnup, the creep resistance as well as corrosion resistance is one of the major factors determining nuclear fuel performance. Long-term creep test was performed at 350 .deg. C and 400 .deg. C and 100, 120, 135, and 150 MPa of applied hoop stress to evaluate the creep properties. The creep resistance was strongly affected by the final heat treatment conditions, while there was no effect of intermediate heat treatment. The creep strain of the recrystallized alloys is higher than that of the stress-relieved alloys by a factor of 3. The alloying elements also influenced the creep behaviour. Increase of Sn content enhanced the creep resistance, while Nb decreased the creep resistance. As a result of texture analysis, basal pole was directed to normal direction, while prism pole was to rolling direction. The development of the deformation texture and the ammealing texture showed almost similar process to Zircaloy cladding

Microstructural analysis of the creep resistance of die-cast Mg-4Al-2RE alloy

Energy Technology Data Exchange (ETDEWEB)

Zhu, S.M. [CAST CRC, Department of Materials Engineering, Monash University, Victoria 3800 (Australia)], E-mail: suming.zhu@eng.monash.edu.au; Gibson, M.A. [CAST CRC, CSIRO Materials Science and Engineering, Private Bag 33, Clayton South MDC, Clayton, Victoria 3169 (Australia); Nie, J.F.; Easton, M.A. [CAST CRC, Department of Materials Engineering, Monash University, Victoria 3800 (Australia); Abbott, T.B. [Advanced Magnesium Technologies, Milton, Queensland 4064 (Australia)

2008-03-15

The microstructure and microstructural stability of die-cast AE42 (Mg-4Al-2RE) alloy were investigated by transmission electron microscopy. It is shown that the formation of Mg{sub 17}Al{sub 12} after ageing at 200 deg. C is not due to the decomposition of A1{sub 11}RE{sub 3} as reported in the literature, but, rather, is associated with the supersaturation of Al solute in the {alpha}-Mg matrix. The level of Al solute retained in the {alpha}-Mg matrix after die-casting is suggested to be an important factor in influencing creep resistance.

The creep properties of a low alloy ferritic steel containing an intermetallic precipitate dispersion

International Nuclear Information System (INIS)

Batte, A.D.; Murphy, M.C.; Edmonds, D.V.

1976-01-01

A good combination of creep rupture ductility and strength together with excellent long term thermal stability, has been obtained from a dispersion of intermetallic Laves phase precipitate in a non-transforming ferritic low alloy steel. The steel is without many of the problems currently associated with the heat affected zone microstructures of low alloy transformable ferritic steels, and can be used as a weld metal. Following suitable development to optimize the composition and heat treatment, such alloys may provide a useful range of weldable creep resistant steels for steam turbine and other high temperature applications. They would offer the unique possibility of easily achievable microstructural uniformity, giving good long term strength and ductility across the entire welded joint

Creep and stress rupture behaviour of zircaloy-2 and Zr-2.5% Nb alloy tubes at 573 K

International Nuclear Information System (INIS)

Laha, K.; Bhanu Sankara Rao, K.; Chandravathi, K.S.; Mannan, S.L.

1992-01-01

Zirconium alloys are extensively used for coolant tubes of pressurised heavy water reactors. The choice of these materials is based on their good corrosion resistance in water, low capture cross section for thermal neutrons and good mechanical properties. In this paper the results of an investigation performed on the creep and rupture behaviour of indigenously produced zircaloy-2 and Zr-2.5% Nb alloy are presented. Samples for creep testing were cut longitudinally from finished pressure tubes. Creep rupture tests were carried out in air under constant load conditions at 300 C employing five stress levels in the range 300-360 MPa. Zr-2.5% Nb alloy displayed higher rupture lives at all stress levels compared to zircaloy-2. Steady state creep rate of Zr-2.5%Nb was lower than that zircaloy-2 at identical stress levels. In the stress range of the experiments, the dependence of the steady state creep rate (ε s ) on applied stress (σ) for both the alloys could be represented by a power law, ε s =A σ n The stress sensitivity (n) for Zr-2.5% Nb was lower than that of zircaloy-2. For both the alloys the time to creep rupture t r was found related to the steady state creep rate through the modified Monkman-Grant relation (ε s ) α . t r = constant. Similar value of α was obtained for both the materials. Zr-2.5%Nb exhibited higher ductility (% elongation to rupture) compared to zircaloy-2 at stress levels ≥ 320 MPa. At lower stresses significant difference in ductility was not noticed. Percentage reduction in area was lower in Zr-2.5%Nb at all stress levels indicating better resistance for necking. The time for onset of tertiary was longer for Zr-2.5% Nb alloy. The proportion of life spent by Zr-2.5% Nb in steady state creep regime was higher compared to that of zircaloy-2. Metallographic investigations on longitudinal sections in both the alloys showed large number of intragranular pores close to the fracture surface. A few number of cracks which are characteristic of

High temperature creep strength of Advanced Radiation Resistant Oxide Dispersion Strengthened Steels

Energy Technology Data Exchange (ETDEWEB)

Noh, Sanghoon; Kim, Tae Kyu [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)

2014-05-15

Austenitic stainless steel may be one of the candidates because of good strength and corrosion resistance at the high temperatures, however irradiation swelling well occurred to 120dpa at high temperatures and this leads the decrease of the mechanical properties and dimensional stability. Compared to this, ferritic/martensitic steel is a good solution because of excellent thermal conductivity and good swelling resistance. Unfortunately, the available temperature range of ferritic/martensitic steel is limited up to 650 .deg. C. ODS steel is the most promising structural material because of excellent creep and irradiation resistance by uniformly distributed nano-oxide particles with a high density which is extremely stable at the high temperature in ferritic/martensitic matrix. In this study, high temperature strength of advanced radiation resistance ODS steel was investigated for the core structural material of next generation nuclear systems. ODS martensitic steel was designed to have high homogeneity, productivity and reproducibility. Mechanical alloying, hot isostactic pressing and hot rolling processes were employed to fabricate the ODS steels, and creep rupture test as well as tensile test were examined to investigate the behavior at high temperatures. ODS steels were fabricated by a mechanical alloying and hot consolidation processes. Mechanical properties at high temperatures were investigated. The creep resistance of advanced radiation resistant ODS steels was more superior than those of ferritic/ martensitic steel, austenitic stainless steel and even a conventional ODS steel.

Creep behavior of a nanocrystalline Fe-B-Si alloy

International Nuclear Information System (INIS)

Xiao, M.; Kong, Q.P.

1997-01-01

The research of nanocrystalline materials has attracted much attention in the world. In recent years, there have been several studies on their creep behavior. Among these, the authors have studied the tensile creep of a nanocrystalline Ni-P alloy (28 nm) at temperatures around 0.5 Tm (Tm is the melting point). The samples were prepared by the method of crystallization of amorphous ribbon. Based on the data of stress exponent and activation energy, they suggested that the creep was controlled by boundary diffusion; while the creep of the same alloy with a larger grain size (257 nm) was controlled by a different mechanism. In the present paper, the authors extend the research to the creep of a nanocrystalline Fe-B-Si alloy. The samples are also prepared by crystallization of amorphous ribbon. The samples such prepared have an advantage that the interfaces are naturally formed without artificial compaction and porosity

Research on high-temperature compression and creep behavior of porous Cu–Ni–Cr alloy for molten carbonate fuel cell anodes

Directory of Open Access Journals (Sweden)

Li W.

2015-06-01

Full Text Available The effect of porosity on high temperature compression and creep behavior of porous Cu alloy for the new molten carbonate fuel cell anodes was examined. Optical microscopy and scanning electron microscopy were used to investigate and analyze the details of the microstructure and surface deformation. Compression creep tests were utilized to evaluate the mechanical properties of the alloy at 650 °C. The compression strength, elastic modulus, and yield stress all increased with the decrease in porosity. Under the same creep stress, the materials with higher porosity exhibited inferior creep resistance and higher steadystate creep rate. The creep behavior has been classified in terms of two stages. The first stage relates to grain rearrangement which results from the destruction of large pores by the applied load. In the second stage, small pores are collapsed by a subsequent sintering process under the load. The main deformation mechanism consists in that several deformation bands generate sequentially under the perpendicular loading, and in these deformation bands the pores are deformed by flattering and collapsing sequentially. On the other hand, the shape of a pore has a severe influence on the creep resistance of the material, i.e. every increase of pore size corresponds to a decrease in creep resistance.

A study of creep behavior in refractory alloys for thermionic emitter applications

International Nuclear Information System (INIS)

Gao Hong; Zee, Ralph

1997-01-01

The creep behavior of HfC strengthened tungsten alloys was studied. An ultrahigh vacuum high precision creep test system was constructed for this purpose so that the samples could be heated up to 3000 K for heat treatment and creep strain could be measured from the creep sample inside the vacuum chamber. Creep tests were conducted in tungsten strengthened with 0.37 percent of HfC at temperatures between 2000 K to 2500 K for durations up to 8 weeks. To explain the creep behavior observed in this dispersion strengthened alloy, a creep model was proposed which accounted for the presence of HfC particles in the form of a back stress generated by these particles. This model was verified by the creep test data of a W-0.37HfC alloy tested under both extruded and recrystallized microstructural conditions. According to this model, the steady state creep of this type alloys was expected to increase with time due to the HfC particle coarsening and recrystallization under high temperatures. In contrast, conventional simple power law creep only predicts a constant steady state creep for these materials, which does not represent the microstructural evolution of the materials. In this study, the experimental study was designed to verify the semi-mechanistic phenomenological creep model developed for carbide particle strengthened tungsten alloys

Creep rupture strength and creep behavior of low-activation martensitic OPTIFER alloys. Final report

International Nuclear Information System (INIS)

Schirra, M.; Falkenstein, A.; Heger, S.; Lapena, J.

2001-07-01

The creep rupture strength and creep experiments performed on low-activation OPTIFER alloys in the temperature range of 450-700 C shall be summarized in the present report. Together with the reference alloy of the type 9.5Cr1W-Mn-V-Ta, W-free variants (+Ge) with a more favorable activation and decay behavior shall be studied. Their smaller strength values are compensated by far better toughness characteristics. Of each development line, several batches of slightly varying chemical composition have been investigated over service lives of up to 40,000 h. Apart from the impact of a reference thermal treatment at a hardening temperature of 1075 C and an annealing temperature of 750 C, the influence of reduced hardening temperatures (up to 950 C) has been determined. A long-term use at increased temperatures (max. 550 C-20,000 h) produces an aging effect with strength being decreased in the annealed state. To determine this aging effect quantitatively, creep rupture experiments have been performed using specimens that were subjected to variable types of T/t annealing (550 -650 C, 330-5000 h). Based on all test results, minimum values for the 1% time-strain limit and creep rupture in the T range of 400-600 C can be given as design curves for 20,000 h. The minimum creep rates obtained from the creep curves recorded as a function of the experimental stress yield the stress exponent n (n=Norton) for the individual test temperatures. Creep behavior as a function of the test temperature yields the values for the effective activation energy of creeping Q K . The influence of a preceding temperature transient up to 800 C (≤Ac 1b ) or 840 C (>Ac 1b ) with subsequent creep rupture tests at 500 C and 550 C, respectively, shall be described. The results obtained for the OPTIFER alloys shall be compared with the results achieved for the Japanese 2% W-containing F82H-mod. alloy. (orig.) [de

The role of cobalt on the creep of Waspaloy

Science.gov (United States)

Jarrett, R. N.; Chin, L.; Tien, J. K.

1984-01-01

Cobalt was systematically replaced with nickel in Waspaloy (which normally contains 13% Co) to determine the effects of cobalt on the creep behavior of this alloy. Effects of cobalt were found to be minimal on tensile strengths and microstructure. The creep resistance and the stress rupture resistance determined in the range from 704 to 760 C (1300 to 1400 C) were found to decrease as cobalt was removed from the standard alloy at all stresses and temperatures. Roughly a ten-fold drop in rupture life and a corresponding increase in minimum creep rate were found under all test conditions. Both the apparent creep activation energy and the matrix contribution to creep resistance were found to increase with cobalt. These creep effects are attributed to cobalt lowering the stacking fault energy of the alloy matrix. The creep resistance loss due to the removal of cobalt is shown to be restored by slightly increasing the gamma' volume fraction. Results are compared to a previous study on Udimet 700, a higher strength, higher gamma' volume fraction alloy with similar phase chemistry, in which cobalt did not affect creep resistance. An explanation for this difference in behavior based on interparticle spacing and cross-slip is presented.

Comparison between pulsed Nd:YAG laser superficial treatment and ceramic coating in creep test of Ti-6Al-4V alloy

International Nuclear Information System (INIS)

Reis, A.G.; Reis, D.A.P.; Moura Neto, C.; Oliveira, H.S.; Couto, A.A.

2009-01-01

The objective of this work was evaluating the creep resistance of the Ti-6Al-4V alloy with superficial treatment of pulsed Nd:YAG laser and ceramic coating in creep test of Ti-6Al-4V alloy. It was used Ti-6Al-4V alloy as cylindrical bars under forged and annealing of 190 deg C by 6 hours condition and cooled by air. The Ti-6Al-4V alloy after the superficial treatment of pulsed Nd:YAG laser and ceramic coating was submitted to creep tests at 600°C and 125 at 319 MPa, under constant load mode. In the Nd:YAG pulsed laser treatment was used an environment of 40 % N and 60 % Ar, with 2.1 W of power and 10 m/s of speed. Yttria (8 wt.%) stabilized zirconia (YSZ) with a CoNiCrAlY bond coat was atmospherically plasma sprayed on Ti-6Al-4V substrates by Sulzer Metco Type 9 MB. The obtained results suggest the laser treatment on Ti-6Al-4V alloy improved its creep resistance. (author)

Creep-Data Analysis of Alloy 617 for High Temperature Reactor Intermediate Heat Exchanger

International Nuclear Information System (INIS)

Kim, Woo Gon; Ryu, Woo Seog; Kim, Yong Wan; Yin, Song Nan

2006-01-01

The design of the metallic components such as hot gas ducts, intermediate heat exchanger (IHX) tube, and steam reformer tubes of very high temperature reactor (VHTR) is principally determined by the creep properties, because an integrity of the components should be preserved during a design life over 30 year life at the maximum operating temperature up to 1000 .deg. C. For designing the time dependent creep of the components, a material database is needed, and an allowable design stress at temperature should be determined by using the material database. Alloy 617, a nicked based superalloy with chromium, molybdenum and cobalt additions, is considered as a prospective candidate material for the IHX because it has the highest design temperature. The alloy 617 is approved to 982 .deg. C (1800 .deg. F) and other alloys approved to 898 .deg. C (1650 .deg. C), such as alloy 556, alloy 230, alloy HX, alloy 800. Also, the alloy 617 exhibits the highest level of creep strength at high temperatures. Therefore, it is needed to collect the creep data for the alloy 617 and the creep-rupture life at the given conditions of temperature and stress should be predicted for the IHX construction. In this paper, the creep data for the alloy 617 was collected through literature survey. Using the collected data, the creep life for the alloy 617 was predicted based on the Larson-Miller parameter. Creep master curves with standard deviations were presented for a safety design, and failure probability for the alloy 617 was obtained with a time coefficient

Creep Damage Evaluation of Titanium Alloy Using Nonlinear Ultrasonic Lamb Waves

International Nuclear Information System (INIS)

Xiang Yan-Xun; Xuan Fu-Zhen; Deng Ming-Xi; Chen Hu; Chen Ding-Yue

2012-01-01

The creep damage in high temperature resistant titanium alloys Ti60 is measured using the nonlinear effect of an ultrasonic Lamb wave. The results show that the normalised acoustic nonlinearity of a Lamb wave exhibits a variation of the 'increase-decrease' tendency as a function of the creep damage. The influence of microstructure evolution on the nonlinear Lamb wave propagation has been analyzed based on metallographic studies, which reveal that the normalised acoustic nonlinearity increases due to a rising of the precipitation volume fraction and the dislocation density in the early stage, and it decreases as a combined result of dislocation change and micro-void initiation in the material. The nonlinear Lamb wave exhibits the potential for the assessment of the remaining creep life in metals

High-throughput design of low-activation, high-strength creep-resistant steels for nuclear-reactor applications

Energy Technology Data Exchange (ETDEWEB)

Lu, Qi; Zwaag, Sybrand van der [Novel Aerospace Materials Group, Faculty of Aerospace Engineering, Delft University of Technology, Kluyverweg 1, 2629 HS, Delft (Netherlands); Xu, Wei, E-mail: xuwei@ral.neu.edu.cn [State Key Laboratory of Rolling and Automation, Northeastern University, 110819, Shenyang (China); Novel Aerospace Materials Group, Faculty of Aerospace Engineering, Delft University of Technology, Kluyverweg 1, 2629 HS, Delft (Netherlands)

2016-02-15

Reduced-activation ferritic/martensitic steels are prime candidate materials for structural applications in nuclear power reactors. However, their creep strength is much lower than that of creep-resistant steel developed for conventional fossil-fired power plants as alloying elements with a high neutron activation cannot be used. To improve the creep strength and to maintain a low activation, a high-throughput computational alloy design model coupling thermodynamics, precipitate-coarsening kinetics and an optimization genetic algorithm, is developed. Twelve relevant alloying elements with either low or high activation are considered simultaneously. The activity levels at 0–10 year after the end of irradiation are taken as optimization parameter. The creep-strength values (after exposure for 10 years at 650 °C) are estimated on the basis of the solid-solution strengthening and the precipitation hardening (taking into account precipitate coarsening). Potential alloy compositions leading to a high austenite fraction or a high percentage of undesirable second phase particles are rejected automatically in the optimization cycle. The newly identified alloys have a much higher precipitation hardening and solid-solution strengthening at the same activity level as existing reduced-activation ferritic/martensitic steels.

Study of oxide layers in creep of Ti alloy

International Nuclear Information System (INIS)

Reis, D.A.P.; Moura Neto, C.; Machado, J.P.B.; Martins, G.V.; Barboza, M.J.R.

2009-01-01

The present study is about the effect of oxide layers in creep of Ti-6Al-4V alloy, in different atmospheres (air, nitrogen and argon). Ti-6Al-4V alloy was treated during 24 hours in a thermal treatment furnace at 600°C in different atmospheres (argon, nitrogen and air). The samples were analyzed by High Resolution X-Ray Diffraction, Scanning Electronic Microscopy (SEM), Atomic Force Microscopy (AFM) and microhardness test. The polished samples of Ti-6Al-4V alloy were treated during 24 hours at 600°C and the oxidation behavior in each case using argon, nitrogen and air atmospheres was observed. The oxidation was more aggressive in air atmosphere, forming TiO 2 film in the surface. The oxidation produced a weight gain through the oxide layer growth and hardening by oxygen dissolution. Ti-6Al-4V alloy specimens also were produced in order to test them in creep, at 250 MPa and 600 deg C, with argon, nitrogen and air atmospheres. When the Ti-6Al-4V alloy was tested under argon and nitrogen atmospheres oxidation effects are smaller and the behavior of the creep curves shows that the creep life time was better in atmospheres not so oxidant. It is observed a decreasing of steady state creep in function of the oxidation process reduction. It is shown that, for the Ti-6Al-4V alloy, their useful life is strongly affected by the atmosphere that is submitted, on account of the oxidation suffered by the material. (author)

Thermal creep behavior of N36 zirconium alloy cladding tube

International Nuclear Information System (INIS)

Wang, P.; Zhao, W.; Dai, X.

2015-01-01

N36 is an alloy containing Zr, Sn, Nb and Fe that is developed by China as a superior cladding material to meet the performance of PWR fuel assembly at the maximum fuel rod burn-up. The creep characteristics of N36 zirconium alloy cladding tube were investigated at temperature from 593 K to 723 K with stress ranging from 20 MPa to 160 MPa. Transitions in creep mechanisms were noted, showing the distinct three rate-controlled creep mechanisms for the alloy at test conditions. In the region of low stresses with stress exponent n ∼ 1 and activation energy Q ∼ (104±4) kJ.mol -1 , Coble creep, based on diffusion of materials through grain boundaries, is the dominant rate-controlling mechanism, which contributes to the creep deformation. The formation of slip bands acts as an accommodation mechanism. In the region of middle stress with stress exponent n ∼ 3 and activation energy Q ∼ (195±7) kJ.mol -1 , micro-creep, caused by viscous gliding of dislocations due to the interaction of O atoms with dislocations, controls the deformation. In the high stress region with stress exponent n ∼ 5-6 and activation energy Q ∼ (210±10) kJ.mol -1 , two mechanisms of the climb of edge dislocations (EDC) and the motion of jogged screw dislocation (MJS) contribute to rate controlling process. In test conditions N36 alloy cladding tube behaves a type of creep similar to that noted in class-I (A) alloys

Effect of heat treatment on elevated temperature tensile and creep properties of the extruded Mg–6Gd–4Y–Nd–0.7Zr alloy

Energy Technology Data Exchange (ETDEWEB)

Yuan, Lin, E-mail: yuanlin@hit.edu.cn; Shi, Wenchao; Jiang, WenMao; Zhao, Zhe; Shan, Debin

2016-03-21

The light and heavy rare earth elements are added to the magnesium alloys to improve the strengths and the creep resistance. The age hardening behaviors of the extruded Mg–6Gd–4Y–Nd–0.7Zr alloy aged at 200, 225 and 250 °C were investigated. Tensile tests and creep tests of the extruded and extruded-T5 Mg–6Gd–4Y–Nd–0.7Zr were carried out at 150–300 °C. The relationship between the microstructure and the properties of the extruded-T5 Mg–6Gd–4Y–Nd–0.7Zr alloy was studied. The result shows that the extruded Mg–6Gd–4Y–Nd–0.7Zr (contained less than 10 wt% Gd) peak aged at 225 °C for 72 h has the excellent creep resistance and high strengths with the UTS more than 350 MPa from room temperature to 200 °C, which are correlative with the precipitates. The high dense and uniform distribution of β′ phase with good heat stability precipitates inhibiting the dislocation motion contributes to age hardening, accelerates the ageing hardening response and increases the creep resistance. The artificially aged (T5) at low temperature further creep tested and tensile tested at higher temperatures decreases the resistance to the dislocation motion and the grain boundary sliding, resulting in the reduction in creep properties and strengths of the extruded-T5 Mg–6Gd–4Y–Nd–0.7Zr alloy above 225 °C.

Fatigue and creep-fatigue deformation of an ultra-fine precipitate strengthened advanced austenitic alloy

Energy Technology Data Exchange (ETDEWEB)

Carroll, M.C., E-mail: Mark.Carroll@INL.gov [Idaho National Laboratory, 1955 Fremont, PO Box 1625, Idaho Falls, ID 83415-2218 (United States); Carroll, L.J. [Idaho National Laboratory, 1955 Fremont, PO Box 1625, Idaho Falls, ID 83415-2218 (United States)

2012-10-30

An advanced austenitic alloy, HT-UPS (high-temperature ultrafine-precipitation-strengthened), has been identified as an ideal candidate material for the structural components of fast reactors and energy-conversion systems. HT-UPS alloys demonstrate improved creep resistance relative to 316 stainless steel (SS) through additions of Ti and Nb, which precipitate to form a widespread dispersion of stable nanoscale metallic carbide (MC) particles in the austenitic matrix. To investigate the behavior in more representative conditions than are offered by uniaxial creep tests, the low-cycle continuous fatigue and combined creep-fatigue response of an HT-UPS alloy have been investigated at 650 Degree-Sign C and 1.0% total strain, with an R-ratio of -1 and hold times at peak tensile strain of up to 150 min. The cyclic deformation response of HT-UPS is directly compared to that of standard 316 SS. The measured values for total cycles to failure between the two alloys are similar, despite differences in peak stress profiles and in qualitative observations of the deformed microstructures. Crack propagation is primarily transgranular in both fatigue and creep-fatigue of each alloy at the investigated conditions. Internal grain boundary damage in the form of fine cracks resulting from the tensile hold is present following the application of hold times of 60 min and longer, and considerably more internal cracks are quantifiable in 316 SS than in HT-UPS. The dislocation substructures observed in the deformed material differ substantially; an equiaxed cellular structure is observed in the microstructure of 316 SS, whereas HT-UPS exhibits widespread and relatively homogenous tangles of dislocations pinned by the nanoscale MC precipitates. The significant effect of the fine distribution of precipitates on observed fatigue and creep-fatigue response is described in three distinct behavioral regions as the microstructure evolves with continued cycling.

Creep properties and precipitate evolution in Al-Li alloys microalloyed with Sc and Yb

Energy Technology Data Exchange (ETDEWEB)

Krug, Matthew E. [Department of Materials Science and Engineering, Northwestern University, 2220 Campus Drive, Evanston, IL 60208 (United States); Seidman, David N. [Department of Materials Science and Engineering, Northwestern University, 2220 Campus Drive, Evanston, IL 60208 (United States); Northwestern Center for Atom Probe Tomography, Northwestern University, 2220 Campus Drive, Evanston, IL 60208 (United States); Dunand, David C., E-mail: dunand@northwestern.edu [Department of Materials Science and Engineering, Northwestern University, 2220 Campus Drive, Evanston, IL 60208 (United States)

2012-07-30

Highlights: Black-Right-Pointing-Pointer We examine the creep behavior of Al-alloys with Li and rare earth element additions. Black-Right-Pointing-Pointer These alloys exhibit threshold stresses below which no measurable creep occurs. Black-Right-Pointing-Pointer Larger precipitate size and lattice parameter mismatch increase creep resistance. Black-Right-Pointing-Pointer A simple parameter describes the threshold stress behavior in ternary Al-Sc-X alloys. Black-Right-Pointing-Pointer The findings are explained by a recent model of dislocation-precipitate interactions. - Abstract: A dilute Al-Sc alloy (Al-0.12 Sc, at.%, Al-Sc), its counterpart with a Li addition (Al-2.9 Li-0.11 Sc, at.%, Al-Li-Sc), as well as a quaternary alloy (Al-5.53 Li-0.048 Sc-0.009 Yb, at.%, Al-Li-Sc-Yb) were isothermally aged at 325 Degree-Sign C, and in some cases isochronally aged to 450 Degree-Sign C. As the {alpha} Prime -Al{sub 3}(Li,Sc) and Al{sub 3}(Li,Sc,Yb) precipitates, with L1{sub 2} structure, coarsen in the two Li-containing alloys, their Li and Yb concentrations decrease and their Sc concentration increases. A significant interfacial excess of Li also segregates at the {alpha}-Al matrix/{alpha} Prime -Al{sub 3}Sc(Li,Sc,Yb) precipitate interface: 5.99 {+-} 0.05 atoms nm{sup -2} in Al-Li-Sc and 13.2 {+-} 0.4 atoms nm{sup -2} in Al-Li-Sc-Yb after aging isochronally to 450 Degree-Sign C. During compression creep at 300 Degree-Sign C, the aged alloys exhibit threshold stresses between 8 and 22 MPa. A recent threshold stress model based on elastic interactions between dislocations and precipitates predicts correctly that Li additions in the Al-Li-Sc alloy reduce the threshold stress, while Yb in the Al-Li-Sc-Yb alloy increases it. The model is also in agreement with the threshold stresses of all Al-Sc-X alloys published to date.

Creep Rupture Properties for Base and Weld Metals of Alloy 617

International Nuclear Information System (INIS)

Kim, Woo-Gon; Kim, Min-Hwan; Park, Jae-Young; Ekaputra, I. M. W.

2015-01-01

The allowable deformation in the welds is also restricted to half the deformation permitted for the base metal, since the ductility of the welds at elevated temperatures is generally low. For a design use, the data of the tensile and creep properties for Alloy 617 WM should be sufficiently provided, and in particular, to develop a design code of Alloy 617 WM. However, the data for the WM are very rare and limited until now, although the data for the BM are available in the ASME draft code case, which was suspended at the end of the 1980s owing to a lack of support and interes. In this report, the creep data for Alloy 617 WM, which was fabricated by a gas tungsten arc welding (GTAW) procedure, were obtained by a series of creep tests at 800 .deg. C, and the creep properties of the WM were compared with those of the BM. The high-temperature creep properties for Alloy 617 WM, fabricated by a gas tungsten arc welding (GTAW) procedure, were investigated by a series of creep tests with different stress levels at 800 .deg. C, and the creep test data for the WM were compared with those of the BM. From the results, it was found that the WM had a slightly longer creep rupture life and lower creep rate than the BM, and a particularly lower rupture elongation. The lower creep rate in the WM was due to the lower rupture elongation than the BM

Evaluation of creep and relaxation data for hastelloy alloy x sheet

International Nuclear Information System (INIS)

Booker, M.K.

1979-02-01

Hastelloy alloy X has been a successful high-temperature structural material for more than two decades. Recently, Hastelloy alloy X sheet has been selected as a prime structural material for the proposed Brayton Isotope Power System (BIPS). The material also sees extensive application in the High-Temperature Gas-Cooled Reactor (HTGR). Design of these systems requires a detailed consideration of the high-temperature creep properties of this material. Therefore, available creep, creep-rupture, and relaxation data for Hastelloy alloy X were collected and analyzed to yield mathematical representations of the behavior for design use

Thermal isocreep curves obtained during multi-axial creep tests on recrystallized Zircaloy-4 and M5™ alloy

International Nuclear Information System (INIS)

Rautenberg, M.; Poquillon, D.; Pilvin, P.; Grosjean, C.; Cloué, J.M.; Feaugas, X.

2014-01-01

Zirconium alloys are widely used in the nuclear industry. Several components, such as cladding or guide tubes, undergo strong mechanical loading during and after their use inside the pressurized water reactors. The current requirements on higher fuel performances lead to the developing on new Zr based alloys exhibiting better mechanical properties. In this framework, creep behaviors of recrystallized Zircaloy-4 and M5™, have been investigated and then compared. In order to give a better understanding of the thermal creep anisotropy of Zr-based alloys, multi-axial creep tests have been carried out at 673 K. Using a specific device, creep conditions have been set using different values of β = σ zz /σ θθ , σ zz and σ θθ being respectively the axial and hoop creep stresses. Both axial and hoop strains are measured during each test which is carried out until stationary creep is stabilized. The steady-state strain rates are then used to build isocreep curves. Considering the isocreep curves, the M5™ alloy shows a largely improved creep resistance compared to the recrystallized Zircaloy-4, especially for tubes under high hoop loadings (0 < β < 1). The isocreep curves are then compared with simulations performed using two different mechanical models. Model 1 uses a von Mises yield criterion, the model 2 is based on a Hill yield criterion. For both models, a coefficient derived from Norton law is used to assess the stress dependence

Studies on neutron irradiation effects of iron alloys and nickel-base heat resistant alloys

International Nuclear Information System (INIS)

Watanabe, Katsutoshi

1987-09-01

The present paper describes the results of neutron irradiation effects on iron alloys and nickel-base heat resistant alloys. As for the iron alloys, irradiation hardening and embrittlement were investigated using internal friction measurement, electron microscopy and tensile testings. The role of alloying elements was also investigated to understand the irradiation behavior of iron alloys. The essential factors affecting irradiation hardening and embrittlement were thus clarified. On the other hand, postirradiation tensile and creep properties were measured of Hastelloy X alloy. Irradiation behavior at elevated temperatures is discussed. (author)

Cyclic creep-rupture behavior of three high-temperature alloys.

Science.gov (United States)

Halford, G. R.

1972-01-01

Study of some important characteristics of the cyclic creep-rupture curves for the titanium alloy 6Al-2Sn-4Zr-2Mo at 900 and 1100 F (755 and 865 K), the cobalt-base alloy L-605 at 1180 F (910 K), and for two hardness levels of 316 stainless steel at 1300 F (980 K). The cyclic creep-rupture curve relates tensile stress and tensile time-to-rupture for strain-limited cyclic loading and has been found to be independent of the total strain range and the level of compressive stress employed in the cyclic creep-rupture tests. The cyclic creep-rupture curve was always found to be above and to the right of the conventional (constant load) monotonic creep-rupture curve by factors ranging from 2 to 10 in time-to-rupture. This factor tends to be greatest when the creep ductility is large. Cyclic creep acceleration was observed in every cyclic creep-rupture test conducted. The phenomenon was most pronounced at the highest stress levels and when the tensile and compressive stresses were completely reversed. In general, creep rates were found to be lower in compression than in tension for equal true stresses. The differences, however, were strongly material-dependent.

Irradiation enhanced diffusion and irradiation creep tests in stainless steel alloys

International Nuclear Information System (INIS)

Loelgen, R.H.; Cundy, M.R.; Schuele, W.

1977-01-01

A review is given of investigations on the rate of phase changes during neutron and electron irradiation in many different fcc alloys showing either precipitation or ordering. The diffusion rate was determined as a function of the irradiation flux, the irradiation temperature and the irradiation dose. It was found that the radiation enhanced diffusion in all the investigated alloys is nearly temperature independent and linearly dependent on the flux. From these results conclusions were drawn concerning the properties of point defects and diffusion mechanisms rate determining during irradiation, which appears to be of a common nature for fcc alloys having a similar structure to those investigated. It has been recognized that the same dependencies which are found for the diffusion rate were also observed for the irradiation creep rate in stainless steels, as reported in literature. On the basis of this obervation a combination of measurements is suggested, of radiation enhanced diffusion and radiation enhanced creep in stainless steel alloys. Measurements of radiation enhanced diffusion are less time consuming and expensive than irradiation creep tests and information on this property can be obtained rather quickly, prior to the selection of stainless steel alloys for creep tests. In order to investigate irradiation creep on many samples at a time two special rigs were developed which are distinguished only by the mode of stress applied to the steel specimens. Finally, a few uniaxial tensile creep tests will be performed in fully instrumented rigs. (Auth.)

Progress Report on Long Hold Time Creep Fatigue of Alloy 617 at 850°C

International Nuclear Information System (INIS)

Carroll, Laura Jill

2015-01-01

Alloy 617 is the leading candidate material for an intermediate heat exchanger for the very high temperature reactor. To evaluate the behavior of this material in the expected service conditions, strain-controlled cyclic tests that include long hold times up to 240 minutes at maximum tensile strain were conducted at 850°C. In terms of the total number of cycles to failure, the fatigue resistance decreased when a hold time was added at peak tensile strain. Increases in the tensile hold duration degraded the creep-fatigue resistance, at least to the investigated strain controlled hold time of up to 60 minutes at the 0.3% strain range and 240 minutes at the 1.0% strain range. The creep-fatigue deformation mode is considered relative to the lack of saturation, or continually decreasing number of cycles to failure with increasing hold times. Additionally, preliminary values from the 850°C creep-fatigue data are calculated for the creep-fatigue damage diagram and have higher values of creep damage than those from tests at 950°C.

Creep deformation behaviour and microstructural changes in Zr-2.5% Nb alloy

International Nuclear Information System (INIS)

Chaudhuri, S.; Singh, R.; Ghosh, R.N.; Sinha, T.K.; Banerjee, S.

2002-01-01

Cold worked and stress relieved Zr-2.5% Nb alloy is a well-known material used as pressure tubes in Pressurised Heavy Water Reactors. The pressure tubes, made of a typical Zr-alloy, consisting of 2.54% Nb, 0.1175% oxygen and less than 100 ppm impurities, are expected to withstand 9.5 MPa to 12.5 MPa pressure at 250 degC to 310 degC under fast neutron fluxes of 3.5 x 10 17 nm -2 s -1 . These tubes are made by hot extrusion at 780 degC with an extrusion ratio 8.3:1 and 40% cold pilgering followed by annealing at 550 degC for 3 hours and subsequently by 20-30% cold pilgering and stress relieving at 400 degC for 24 hours. The microstructure of such cold worked and stress relieved alloy consists of Β-Zr precipitates in the matrix of elongated Α-Zr grains. Although various factors such as irradiation creep, thermal creep, irradiation growth etc are responsible for limiting the life of pressure tubes; the thermal creep contributes significantly in overall creep deformation. Keeping this in view as well as due to non-availability of adequate published information including creep database on this alloy, an extensive investigation on the thermal creep behaviour of indigenously produced Zr-2.5% Nb alloy was undertaken. The creep tests in air using Mayes' creep testing machines were carried out in the temperature range of 300 degC to 450 degC under stresses in the range of 50 to 550 MPa. Analysis of data revealed that the mechanism of creep deformation remains the same in this range

Novel experiments to characterise creep-fatigue degradation in VHTR alloys

International Nuclear Information System (INIS)

Simpson, J.A.; Wright, J.K.; Wright, R.N.

2015-01-01

It is well known in energy systems that the creep lifetime of high temperature alloys is significantly degraded when a cyclic load is superimposed on components operating in the creep regime. A test method has been developed in an attempt to characterise creep-fatigue behaviour of alloys at high temperature. The test imposes a hold time during the tensile phase of a fully reversed strain-controlled low cycle fatigue test. Stress relaxation occurs during the strain-controlled hold period. This type of fatigue stress relaxation test tends to emphasise the fatigue portion of the total damage and does not necessarily represent the behaviour of a component in-service well. Several different approaches to laboratory testing of creep-fatigue at 950 deg. C have been investigated for Alloy 617, the primary candidate for application in VHTR heat exchangers. The potential for mode switching in a cyclic test from strain control to load control, to allow specimen extension by creep, has been investigated to further emphasise the creep damage. In addition, tests with a lower strain rate during loading have been conducted to examine the influence of creep damage occurring during loading. Very short constant strain hold time tests have also been conducted to examine the influence of the rapid stress relaxation that occurs at the beginning of strain holds. (authors)

Creep rupture properties under varying load/temperature conditions on a nickel-base heat-resistant alloy strengthened by boron addition

International Nuclear Information System (INIS)

Tsuji, Hirokazu; Tanabe, Tatsuhiko; Nakajima, Hajime

1994-01-01

A series of constant load and temperature creep rupture tests and varying load and temperature creep rupture tests was carried out on Hastelloy XR whose boron content level is 60 mass ppm at 900 and 1000 C in order to examine the behavior of the alloy under varying load and temperature conditions. The life fraction rule completely fails in the prediction of the creep rupture life under varying load and temperature conditions though the rule shows good applicability for Hastelloy XR whose boron content level is below 10 mass ppm. The modified life fraction rule has been proposed based on the dependence of the creep rupture strength on the boron content level of the alloy. The modified rule successfully predicts the creep rupture life under the test conditions from 1000 to 900 C. The trend observed in the tests from 900 to 1000 C can be qualitatively explained by the mechanism that the oxide film which is formed during the prior exposure to 900 C plays the role of the protective barrier against the boron dissipation into the environment. (orig.)

Creep and residual mechanical properties of cast superalloys and oxide dispersion strengthened alloys

Science.gov (United States)

Whittenberger, J. D.

1981-01-01

Tensile, stress-rupture, creep, and residual tensile properties after creep testing were determined for two typical cast superalloys and four advanced oxide dispersion strengthened (ODS) alloys. The superalloys examined included the nickel-base alloy B-1900 and the cobalt-base alloy MAR-M509. The nickel-base ODS MA-757 (Ni-16CR-4Al-0.6Y2O3 and the iron-base ODS alloy MA-956 (Fe-20Cr-5Al-0.8Y2O3) were extensively studied, while limited testing was conducted on the ODS nickel-base alloys STCA (Ni-16Cr-4.5Al-2Y2O3) with a without Ta and YD-NiCrAl (Ni-16Cr-5Al-2Y2O3). Elevated temperature testing was conducted from 114 to 1477 K except for STCA and YD-NiCrAl alloys, which were only tested at 1366 K. The residual tensile properties of B-1900 and MAR-M509 are not reduced by prior creep testing (strains at least up to 1 percent), while the room temperature tensile properties of ODS nickel-base alloys can be reduced by small amounts of prior creep strain (less than 0.5 percent). The iron-base ODS alloy MA-956 does not appear to be susceptible to creep degradation at least up to strains of about 0.25 percent. However, MA-956 exhibits unusual creep behavior which apparently involves crack nucleation and growth.

Optimization of Thermo-Mechanical Processing for Forging of Newly Developed Creep-Resistant Magnesium Alloy ABaX633

Directory of Open Access Journals (Sweden)

Kamineni Pitcheswara Rao

2017-11-01

Full Text Available The compressive strength and creep resistance of cast Mg-6Al-3Ba-3Ca (ABaX633 alloy has been measured in the temperature range of 25 to 250 °C, and compared with that of its predecessor ABaX422. The alloy is stronger and more creep-resistant than ABaX422, and exhibits only a small decrease of yield stress with temperature. The higher strength of ABaX633 is attributed to a larger volume fraction of intermetallic particles (Al, Mg2Ca and Mg21Al3Ba2 in its microstructure. Hot deformation mechanisms in ABaX633 have been characterized by developing a processing map in the temperature and strain rate ranges of 300 to 500 °C and 0.0003 to 10 s−1. The processing map exhibits two workability domains in the temperature and strain rate ranges of: (1 380 to 475 °C and 0.0003 to 0.003 s−1, and (2 480–500 °C and 0.003 to 0.5 s−1. The apparent activation energy values estimated in the above two domains (204 and 216 kJ/mol are higher than that for lattice self-diffusion of Mg, which is attributed to the large back-stress that is caused by the intermetallic particles. Optimum condition for bulk working is 500 °C and 0.01 s−1 at which hot workability will be maximum. Flow instability is exhibited at lower temperatures and higher strain rates, as well as at higher temperatures and higher strain rates. The predictions of the processing map on the workability domains, as well as the instability regimes are fully validated by the forging of a rib-web (cup shaped component under optimized conditions.

Creep strength and rupture ductility of creep strength enhanced ferritic steels

Energy Technology Data Exchange (ETDEWEB)

Kushima, Hideaki; Sawada, Kota; Kimura, Kazuhiro [National Inst. for Materials Science, Tsukuba, Ibaraki (Japan)

2010-07-01

Creep strength and rupture ductility of Creep Strength Enhanced Ferritic (CSEF) steels were investigated from a viewpoint of stress dependence in comparison with conventional low alloy ferritic creep resistant steels. Inflection of stress vs. time to rupture curve was observed at 50% of 0.2% offset yield stress for both CSEF and conventional ferritic steels. Creep rupture ductility tends to decrease with increase in creep exposure time, however, those of conventional low alloy steels indicate increase in the long-term. Creep rupture ductility of the ASME Grades 92 and 122 steels indicates drastic decrease with decrease in stress at 50% of 0.2% offset yield stress. Stress dependence of creep rupture ductility of the ASME Grades 92 and 122 steels is well described by stress ratio to 0.2% offset yield stress, regardless of temperature. Drop of creep rupture ductility is caused by inhomogeneous recovery at the vicinity of prior austenite grain boundary, and remarkable drop of creep rupture ductility of CSEF steels should be derived from those stabilized microstructure. (orig.)

Creep strength and microstructure in 23Cr-45Ni-7W Alloy (HR6W) and Ni-base superalloys for advanced USC boilers

Energy Technology Data Exchange (ETDEWEB)

Semba, Hiroyuki; Okada, Hirokazu; Yonemura, Mitsuharu; Igarashi, Masaaki [Sumitomo metal Industries, Ltd., Hyogo (Japan). Corporate Research and Development Labs.

2008-07-01

Establishment of materials technologies on piping and tubing for advanced ultra super critical (A-USC) plants operated at steam temperatures above 700 C is a critical issue to achieve its hard target. 23Cr-45Ni-7W alloy (HR6W) has been developed in Japan, originally as a high strength tubing material for 650 C USC boilers. In order to clarify the capability of HR6W as a material applied to A-USC plants, creep strength and microstructure of HR6W were investigated in comparison with {gamma}'-strengthened Alloy 617 and other Ni-base superalloys, such as Alloy 263. It has been revealed that the amount of added W is intimately correlated with precipitation amount of Laves phase and thus it is a crucial factor controlling creep strength. Stability of long term creep strength and superior creep rupture ductility have been proved by creep rupture tests at 650-800 C up to 60000h. The 10{sup 5}h extrapolated creep rupture strengths are estimated to be 88MPa at 700 C and 64MPa at 750 C. Microstructural stability closely related with long term creep strength and toughness has also been confirmed by microstructural observations after creep tests and aging. Creep rupture strength of Alloy 617 has been found to be much higher than that of HR6W at 700 and 750 C, while comparable at 800 C. A thermodynamic calculation along with microstructural observation indicates that the amount of Laves phase in HR6W gradually decreases with increasing temperature, while that of {gamma}' in Alloy 617 rapidly decreases with increasing temperature and {gamma}' almost dissolves at 800 C. This may lead to an abrupt drop in creep strength of Alloy 617 above 750 C. Alloy 263, in which more {gamma}' precipitates than Alloy 617, shows much higher creep strength. However, it is suggested that inhomogeneous creep deformation is enhanced compared with HR6W and Alloy 617. Capability of HR6W as a material for A-USC plants was discussed in terms of creep properties, microstructural stability and other

Creep-fatigue of low cobalt superalloys

Science.gov (United States)

Halford, G. R.

1982-01-01

Testing for the low cycle fatigue and creep fatigue resistance of superalloys containing reduced amounts of cobalt is described. The test matrix employed involves a single high temperature appropriate for each alloy. A single total strain range, again appropriate to each alloy, is used in conducting strain controlled, low cycle, creep fatigue tests. The total strain range is based upon the level of straining that results in about 10,000 cycles to failure in a high frequency (0.5 Hz) continuous strain-cycling fatigue test. No creep is expected to occur in such a test. To bracket the influence of creep on the cyclic strain resistance, strain hold time tests with ore minute hold periods are introduced. One test per composition is conducted with the hold period in tension only, one in compression only, and one in both tension and compression. The test temperatures, alloys, and their cobalt compositions that are under study are given.

Low cycle fatigue and creep fatigue behavior of alloy 617 at high temperature

International Nuclear Information System (INIS)

Cabet, Celine; Carroll, Laura; Wright, Richard

2013-01-01

Alloy 617 is the leading candidate material for an intermediate heat exchanger (IHX) application of the very high temperature nuclear reactor (VHTR), expected to have an outlet temperature as high as 950 C. Acceptance of Alloy 617 in Section III of the ASME Code for nuclear construction requires a detailed understanding of the creep-fatigue behavior. Initial creep-fatigue work on Alloy 617 suggests a more dominant role of environment with increasing temperature and/or hold times evidenced through changes in creep-fatigue crack growth mechanisms and failure life. Continuous cycle fatigue and creep-fatigue testing of Alloy 617 was conducted at 950 C and 0.3% and 0.6% total strain in air to simulate damage modes expected in a VHTR application. Continuous cycle fatigue specimens exhibited transgranular cracking. Intergranular cracking was observed in the creep-fatigue specimens and the addition of a hold time at peak tensile strain degraded the cycle life. This suggests that creep-fatigue interaction occurs and that the environment may be partially responsible for accelerating failure. (authors)

Microstructural evolution and creep of Fe-Al-Ta alloys

Energy Technology Data Exchange (ETDEWEB)

Prokopcakova, Petra; Svec, Martin [Technical University of Liberec (Czech Republic). Dept. of Material Science; Palm, Martin [Max-Planck-Institut fuer Eisenforschung GmbH, Duesseldorf (Germany). Structure and Nano-/Micromechanics of Materials

2016-05-15

The microstructural evolution in Fe-Al-Ta alloys containing 23 - 31 at.% Al and 1.5 - 2.2 at.% Ta has been studied in the temperature range 650 - 750 C by annealing for 1, 10, 100 and 1 000 h. The experiments confirm that in this temperature range the precipitation of the stable hexagonal C14 Laves phase is preceded by formation of coherent, metastable L2{sub 1} Heusler phase precipitates within the Fe-Al matrix. However, precipitates of C14 are observed after much shorter annealing times than previously assumed. Creep strength increases substantially with increasing Al content of the alloys because the solid solubility for Ta in the Fe-Al matrix increases with increasing Al content and solid-solution hardening contributes substantially to the observed high creep strength. It may therefore be that the microstructural changes during creep have no noticeable effect on creep strength.

Microstructural evolution and creep of Fe-Al-Ta alloys

International Nuclear Information System (INIS)

Prokopcakova, Petra; Svec, Martin; Palm, Martin

2016-01-01

The microstructural evolution in Fe-Al-Ta alloys containing 23 - 31 at.% Al and 1.5 - 2.2 at.% Ta has been studied in the temperature range 650 - 750 C by annealing for 1, 10, 100 and 1 000 h. The experiments confirm that in this temperature range the precipitation of the stable hexagonal C14 Laves phase is preceded by formation of coherent, metastable L2 1 Heusler phase precipitates within the Fe-Al matrix. However, precipitates of C14 are observed after much shorter annealing times than previously assumed. Creep strength increases substantially with increasing Al content of the alloys because the solid solubility for Ta in the Fe-Al matrix increases with increasing Al content and solid-solution hardening contributes substantially to the observed high creep strength. It may therefore be that the microstructural changes during creep have no noticeable effect on creep strength.

Creep rupture properties under varying load/temperature conditions on a nickel-base heat-resistant alloy strengthened by boron addition

International Nuclear Information System (INIS)

Tsuji, Hirokazu; Nakajima, Hajime; Tanabe, Tatsuhiko.

1993-09-01

A series of constant load and temperature creep rupture tests and varying load and temperature creep rupture tests was carried out on Hastelloy XR whose boron content level is 60 mass ppm at 900 and 1000degC in order to examine the behavior of the alloy under varying load and temperature conditions. The life fraction rule completely fails in the prediction of the creep rupture life under varying load and temperature conditions though the rule shows good applicability for Hastelloy XR whose boron content level is below 10 mass ppm. The modified life fraction rule has been proposed based on the dependence of the creep rupture strength on the born content level of the alloy. The modified rule successfully predicts the creep rupture life under the test conditions from 1000degC to 900degC. The trend observed in the tests from 900degC to 1000degC can be qualitatively explained by the mechanism that the oxide film which is formed during the prior exposure to 900degC plays the role of the protective barrier against the boron dissipation into the environment. (author)

Indentation creep behaviors of amorphous Cu-based composite alloys

Science.gov (United States)

Song, Defeng; Ma, Xiangdong; Qian, Linfang

2018-04-01

This work reports the indentation creep behaviors of two Si2Zr3/amorphous Cu-based composite alloys utilizing nanoindentation technique. By analysis with Kelvin model, the retardation spectra of alloys at different positions, detached and attached regions to the intermetallics, were deduced. For the indentation of detached regions to Si2Zr3 intermetallics in both alloys, very similarity in creep displacement can be observed and retardation spectra show a distinct disparity in the second retardation peak. For the indentation of detached regions, the second retardation spectra also display distinct disparity. At both positions, the retardation spectra suggest that Si elements may lead to the relatively dense structure in the amorphous matrix and to form excessive Si2Zr3 intermetallics which may deteriorate the plastic deformation of current Cu-based composite alloys.

Investigation of creep rupture properties in air and He environments of alloy 617 at 800 °C

Energy Technology Data Exchange (ETDEWEB)

Kim, Woo-Gon, E-mail: wgkim@kaeri.re.k [Korea Atomic Energy Research Institute, 989-111 Daedeok-daero, Yuseong-gu, Daejeon 305-353 (Korea, Republic of); Ekaputra, I.M.W.; Park, Jae-Young [Pukyong National University, Busan 608-739 (Korea, Republic of); Kim, Min-Hwan; Kim, Yong-Wan [Korea Atomic Energy Research Institute, 989-111 Daedeok-daero, Yuseong-gu, Daejeon 305-353 (Korea, Republic of)

2016-09-15

Creep rupture properties for Alloy 617 were investigated by a series of creep tests under different applied stresses in air and He environments at 800 °C. The creep rupture time in air and He environments exhibited almost similar life in a short rupture time. However, when the creep rupture time reaches above 3000 h, the creep life in the He environment reduced compared with those of the air environment. The creep strain rate in the He environment was a little faster than that in the air environment above 3000 h. The reduction of creep life in the He environment was due to the difference of various microstructure features such as the carbide depleted zone, oxidation structures, surface cracking, voids below the surface, and voids in the matrix in air and He environments. Alloy 617 followed Norton’s power law and the Monkman–Grant relationship well. As the stress decreased, the creep ductility decreased slightly. The thickness of the outer and internal oxide layers presented the trend of a parabolic increase with an increase in creep rupture time in both the air and He environments. The thickness in the He environment was found to be thicker than in the air environment, although pure helium gas of 99.999% was used in the present investigation. The differences in the oxide-layer thickness caused detrimental effects on the creep resistance, even in a low oxygen-containing He agent.

Investigation of creep rupture properties in air and He environments of alloy 617 at 800 °C

International Nuclear Information System (INIS)

Kim, Woo-Gon; Ekaputra, I.M.W.; Park, Jae-Young; Kim, Min-Hwan; Kim, Yong-Wan

2016-01-01

Creep rupture properties for Alloy 617 were investigated by a series of creep tests under different applied stresses in air and He environments at 800 °C. The creep rupture time in air and He environments exhibited almost similar life in a short rupture time. However, when the creep rupture time reaches above 3000 h, the creep life in the He environment reduced compared with those of the air environment. The creep strain rate in the He environment was a little faster than that in the air environment above 3000 h. The reduction of creep life in the He environment was due to the difference of various microstructure features such as the carbide depleted zone, oxidation structures, surface cracking, voids below the surface, and voids in the matrix in air and He environments. Alloy 617 followed Norton’s power law and the Monkman–Grant relationship well. As the stress decreased, the creep ductility decreased slightly. The thickness of the outer and internal oxide layers presented the trend of a parabolic increase with an increase in creep rupture time in both the air and He environments. The thickness in the He environment was found to be thicker than in the air environment, although pure helium gas of 99.999% was used in the present investigation. The differences in the oxide-layer thickness caused detrimental effects on the creep resistance, even in a low oxygen-containing He agent.

The Effect of Creep Aging on the Fatigue Fracture Behavior of 2524 Aluminum Alloy

Directory of Open Access Journals (Sweden)

Wenke Li

2016-09-01

Full Text Available Normal temperature tensile and fatigue tests were adopted to test the mechanical performance and fatigue life of 2524 aluminum alloy under the three states of T3, artificial aging, and creep aging, and scanning electron microscope and transmission electron microscope were also used to observe the fatigue fracture morphology and aging precipitation features of the alloy under the above three states. Results showed that the alloy treated by creep aging can obtain higher fatigue life, but that treated by artificial aging is lower than T3; T3 alloy is mainly dominated by GPB region. Meanwhile, the crystal boundary displays continuously distributed fine precipitated phases; after artificial aging and creep aging treatment, a large amount of needle-shaped S′ phases precipitate inside the alloy, while there are wide precipitated phases at the crystal boundary. Wide precipitation free zones appear at the crystal boundary of artificial-aging samples, but precipitation free zones at the alloy crystal boundary of creep aging become narrower and even disappear. It can be seen that creep aging can change the precipitation features of the alloy and improve its fatigue life.

Microstructural evolution in a Ti-Ta high-temperature shape memory alloy during creep

International Nuclear Information System (INIS)

Rynko, Ramona; Marquardt, Axel; Pauksen, Alexander; Frenzel, Jan; Somsen, Christoph; Eggeler, Gunther

2015-01-01

Alloys based on the titanium-tantalum system are considered for application as high-temperature shape memory alloys due to their martensite start temperatures, which can surpass 200 C. In the present work we study the evolution of microstructure and the influence of creep on the phase transformation behavior of a Ti 70 Ta 30 (at.%) high-temperature shape memory alloy. Creep tests were performed in a temperature range from 470 to 530 C at stresses between 90 and 150 MPa. The activation energy for creep was found to be 307 kJ mol -1 and the stress exponent n was determined as 3.7. Scanning and transmission electron microscopy investigations were carried out to characterize the microstructure before and after creep. It was found that the microstructural evolution during creep suppresses subsequent martensitic phase transformations.

Effect of creep-aging on precipitates of 7075 aluminum alloy

Energy Technology Data Exchange (ETDEWEB)

Lin, Y.C., E-mail: yclin@csu.edu.cn [School of Mechanical and Electrical Engineering, Central South University, Changsha 410083 (China); State Key Laboratory of High Performance Complex Manufacturing, Changsha 410083 (China); State Key Laboratory of Material Processing and Die and Mould Technology, Wuhan 430074 (China); Jiang, Yu-Qiang; Chen, Xiao-Min; Wen, Dong-Xu [School of Mechanical and Electrical Engineering, Central South University, Changsha 410083 (China); State Key Laboratory of High Performance Complex Manufacturing, Changsha 410083 (China); Zhou, Hua-Min [State Key Laboratory of Material Processing and Die and Mould Technology, Wuhan 430074 (China)

2013-12-20

The creep-aging behaviors of 7075 aluminum alloy are studied by uniaxial tensile creep experiments under elevated temperatures. The effects of creep-aging temperature and applied stress on the precipitates of 7075-T651 aluminum alloy are investigated using a scanning electron microscope (SEM) and a transmission electron microscope (TEM). Results show that (1) coarse insoluble precipitates (Al{sub 7}Cu{sub 2}Fe and Mg{sub 2}Si) and intermediate precipitates (Al{sub 18}Mg{sub 3}Cr{sub 2} and Al{sub 3}Zr) are found in the aluminum matrix, and the effects of creep-aging treatment on these precipitates are not obvious; (2) the main aging precipitates are η′ and η phases, and the amount of aging precipitates increase with the increase of creep-aging temperature and applied stress; (3) with the increase of creep-aging temperature and applied stress, the precipitates are discontinuously distributed on the grain boundary, and the width of precipitate free zone increases with the increase of creep-aging temperature and applied stress and (4) compared with the microstructure in the traditional stress-free aged sample, the creep-aging process can refine the precipitates and narrow the width of the precipitate free zone.

Microstructural Evolution and Creep-Rupture Behavior of A-USC Alloy Fusion Welds

Science.gov (United States)

Bechetti, Daniel H.; DuPont, John N.; Siefert, John A.; Shingledecker, John P.

2016-09-01

Characterization of the microstructural evolution of fusion welds in alloys slated for use in advanced ultrasupercritical (A-USC) boilers during creep has been performed. Creep-rupture specimens involving INCONEL® 740, NIMONIC® 263 (INCONEL and NIMONIC are registered trademarks of Special Metals Corporation), and Haynes® 282® (Haynes and 282 are registered trademarks of Haynes International) have been analyzed via light optical microscopy, scanning electron microscopy, X-ray diffraction, and thermodynamic and kinetic modeling. Focus has been given to the microstructures that develop along the grain boundaries in these alloys during creep at temperatures relevant to the A-USC process cycle, and particular attention has been paid to any evidence of the formation of local γ'-denuded or γ'-free zones. This work has been performed in an effort to understand the microstructural changes that lead to a weld strength reduction factor (WSRF) in these alloys as compared to solution annealed and aged alloy 740 base metal. γ' precipitate-free zones have been identified in alloy 740 base metal, solution annealed alloy 740 weld metal, and alloy 263 weld metal after creep. Their development during long-term thermal exposure is correlated with the stabilization of phases that are rich in γ'-forming elements ( e.g., η and G) and is suppressed by precipitation of phases that do not contain the γ' formers ( e.g., M23C6 and μ). The location of failure and creep performance in terms of rupture life and WSRF for each welded joint is presented and discussed.

Mechanisms Governing the Creep Behavior of High Temperature Alloys for Generation IV Nuclear Energy Systems

Energy Technology Data Exchange (ETDEWEB)

Vasudevan, Vijay [Univ. of Cincinnati, OH (United States); Carroll, Laura [Idaho National Lab. (INL), Idaho Falls, ID (United States); Sham, Sam [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)

2015-04-06

This research project, which includes collaborators from INL and ORNL, focuses on the study of alloy 617 and alloy 800H that are candidates for applications as intermediate heat exchangers in GEN IV nuclear reactors, with an emphasis on the effects of grain size, grain boundaries and second phases on the creep properties; the mechanisms of dislocation creep, diffusional creep and cavitation; the onset of tertiary creep; and theoretical modeling for long-term predictions of materials behavior and for high temperature alloy design.

Mechanisms Governing the Creep Behavior of High Temperature Alloys for Generation IV Nuclear Energy Systems

International Nuclear Information System (INIS)

Vasudevan, Vijay; Carroll, Laura; Sham, Sam

2015-01-01

This research project, which includes collaborators from INL and ORNL, focuses on the study of alloy 617 and alloy 800H that are candidates for applications as intermediate heat exchangers in GEN IV nuclear reactors, with an emphasis on the effects of grain size, grain boundaries and second phases on the creep properties; the mechanisms of dislocation creep, diffusional creep and cavitation; the onset of tertiary creep; and theoretical modeling for long-term predictions of materials behavior and for high temperature alloy design.

Modeling creep deformation of a two-phase TiAI/Ti3Al alloy with a lamellar microstructure

Science.gov (United States)

Bartholomeusz, Michael F.; Wert, John A.

1994-10-01

A two-phase TiAl/Ti3Al alloy with a lamellar microstructure has been previously shown to exhibit a lower minimum creep rate than the minimum creep rates of the constituent TiAl and Ti3Al single-phase alloys. Fiducial-line experiments described in the present article demonstrate that the creep rates of the constituent phases within the two-phase TiAl/Ti3Al lamellar alloy tested in compression are more than an order of magnitude lower than the creep rates of single-phase TiAl and Ti3Al alloys tested in compression at the same stress and temperature. Additionally, the fiducial-line experiments show that no interfacial sliding of the phases in the TiAl/Ti3Al lamellar alloy occurs during creep. The lower creep rate of the lamellar alloy is attributed to enhanced hardening of the constituent phases within the lamellar microstructure. A composite-strength model has been formulated to predict the creep rate of the lamellar alloy, taking into account the lower creep rates of the constituent phases within the lamellar micro-structure. Application of the model yields a very good correlation between predicted and experimentally observed minimum creep rates over moderate stress and temperature ranges.

The effect of sheet processing on the microstructure, tensile, and creep behavior of INCONEL alloy 718

Science.gov (United States)

Boehlert, C. J.; Dickmann, D. S.; Eisinger, Ny. N. C.

2006-01-01

The grain size, grain boundary character distribution (GBCD), creep, and tensile behavior of INCONEL alloy 718 (IN 718) were characterized to identify processing-microstructure-property relationships. The alloy was sequentially cold rolled (CR) to 0, 10, 20, 30, 40, 60, and 80 pct followed by annealing at temperatures between 954 °C and 1050 °C and the traditional aging schedule used for this alloy. In addition, this alloy can be superplastically formed (IN 718SPF) to a significantly finer grain size and the corresponding microstructure and mechanical behavior were evaluated. The creep behavior was evaluated in the applied stress (σ a ) range of 300 to 758 MPa and the temperature range of 638 °C to 670 °C. Constant-load tensile creep experiments were used to measure the values of the steady-state creep rate and the consecutive load reduction method was used to determine the values of backstress (σ0). The values for the effective stress exponent and activation energy suggested that the transition between the rate-controlling creep mechanisms was dependent on effective stresses (σ e =σ a σ0) and the transition occurred at σ e ≅ 135 MPa. The 10 to 40 pct CR samples exhibited the greatest 650 °C strength, while IN 718SPF exhibited the greatest room-temperature (RT) tensile strength (>1550 MPa) and ductility (ɛ f >16 pct). After the 954 °C annealing treatment, the 20 pct CR and 30 pct CR microstructures exhibited the most attractive combination of elevated-temperature tensile and creep strength, while the most severely cold-rolled materials exhibited the poorest elevated-temperature properties. After the 1050 °C annealing treatment, the IN 718SPF material exhibited the greatest backstress and best creep resistance. Electron backscattered diffraction was performed to identify the GBCD as a function of CR and annealing. The data indicated that annealing above 1010 °C increased the grain size and resulted in a greater fraction of twin boundaries, which in

Primary and secondary creep in aluminum alloys as a solid state transformation

Science.gov (United States)

Fernández, R.; Bruno, G.; González-Doncel, G.

2016-08-01

Despite the massive literature and the efforts devoted to understand the creep behavior of aluminum alloys, a full description of this phenomenon on the basis of microstructural parameters and experimental conditions is, at present, still missing. The analysis of creep is typically carried out in terms of the so-called steady or secondary creep regime. The present work offers an alternative view of the creep behavior based on the Orowan dislocation dynamics. Our approach considers primary and secondary creep together as solid state isothermal transformations, similar to recrystallization or precipitation phenomena. In this frame, it is shown that the Johnson-Mehl-Avrami-Kolmogorov equation, typically used to analyze these transformations, can also be employed to explain creep deformation. The description is fully compatible with present (empirical) models of steady state creep. We used creep curves of commercially pure Al and ingot AA6061 alloy at different temperatures and stresses to validate the proposed model.

Dislocation analysis of die-cast Mg-Al-Ca alloy after creep deformation

International Nuclear Information System (INIS)

Terada, Yoshihiro; Itoh, Daigo; Sato, Tatsuo

2009-01-01

Tensile creep tests were combined with detailed transmission electron microscopy in order to characterize the dislocation movements during creep and to explain the creep properties of the Mg-Al-Ca AX52 die-cast alloy at 473 K and stresses from 15 to 70 MPa. TEM observations indicate that dislocations are generated within the primary α-Mg grain in the die-casting process, which consist of both the basal and non-basal segments. The basal segments of dislocations are able to bow out and glide on the basal planes under the influence of a stress, and the jogs follow the basal segments with the help of climb during creep. The creep mechanism for the alloy is deduced as dislocation climb due to the formation of sub-boundaries during creep, while the easy glide of the basal segments of dislocations is controlling the creep rates immediately after the stress application of creep tests.

Creep characteristics of a hypoeutectic Mg-Ca binary alloy with a near-fully lamellar microstructure

International Nuclear Information System (INIS)

Terada, Yoshihiro; Tsukahara, Masashi; Shibayama, Atsushi; Murata, Yoshinori; Morinaga, Masahiko

2011-01-01

Highlights: → We develop a hypoeutectic Mg-Ca cast alloy with a near-fully lamellar microstructure. → Dislocations are introduced within the lamellar microstructure during casting. → The dislocation segments in the α-Mg plates are located on the basal planes. → Creep of the alloy is ascribed to the easy glide of the introduced dislocations. -- The creep behavior of a hypoeutectic Mg-14.8 mass% Ca cast alloy with an α-Mg/C14-Mg 2 Ca near-fully lamellar microstructure was investigated at 473 K. Transmission electron microscopy shows that dislocations are introduced within the lamellar microstructure of the alloy during casting; the dislocation segments in the α-Mg plates are located on basal planes. The stress exponent of the creep rate is unity in the early stage of transient creep. Creep deformation of the alloy is ascribed to the easy glide of the introduced dislocations.

Long term creep strength of silver alloyed copper

International Nuclear Information System (INIS)

Auerkari, P.; Sandlin, S.

1988-12-01

The long term creep strength of silver alloyed copper has been estimated using literature creep data for materials with less than 0.1% Ag. The available data was very limited, and it was necessary to test the differences between various data sets and extrapolation methods. Assuming constant stress level and constant or changing temperature, the creep behaviour has been assessed using mainly Larson-Miller and theta-projection approaches. The calculations indicate that the different extrapolation methods and data sources can yield strongly different life estimates. With the available incomplete data the theta projection method may give the conservative life predictions, whereas the Larson-Miller approach grossly overestimates creep life. It is recommended that supplementary data is acquired to better assess the long term creep properties of canisters in repository conditions

Design basis for creep of zirconium alloy components in a fast neutron flux

International Nuclear Information System (INIS)

Ross-Ross, P.A.; Fidleris, V.

1975-01-01

The chalk River Nuclear Laboratory's experience with the creep of zirconium alloys in a neutron flux is described. Fast neutron flux changes the creep behaviour of zirconium alloys and new design criteria for in-reactor applications are needed. From experimental results empirical relations describing the effects of neutron flux, stress, temperature, time and anisotropy on creep rate were established. The relations are applied to the design of pressure tubes. (author)

Design basis for creep of zirconium alloy components in a fast neutron flux

International Nuclear Information System (INIS)

Ross-Ross, P.A.; Fidleris, V.

1974-01-01

The Chalk River Nuclear Laboratory's experience with the creep of zirconium alloys in a neutron flux is described. Fast neutron flux changes the creep behavior of zirconium alloys and new design criteria for in-reactor applications are needed. From experimental results empirical relations describing the effects of neutron flux, stress, temperature, time, and anisotropy on creep rate were established. The relations are applied to the design of pressure tubes. (author)

Heat resistance of Fe-Al intermetallics in the context of selected heat-resistant and hihg-temperature creep resistant steels

Directory of Open Access Journals (Sweden)

P. Baranowski

2009-04-01

Full Text Available Results are hereby presented of heat-resistance tests of two Fe3Al and FeAl intermetallic phase-based alloys in the context of St41k-typeboiler steel and 50H21G9N4 high-temperature creep resistant steel. It has been ascertained that heat resistance of the 50H21G9N4 steeland of the Fe3Al and FeAl intermetallic phase-based alloys significantly exceeds that of the boiler steel tested in the air atmosphere and the atmosphere of a flue gas with CO, CO2, SiO2 content alike. Improvement of these properties depends of exposure conditions. The largest differences have been observed when the tests were carried out in temperature 1023 K and in the flue gas atmosphere. The differences have been more and more noticeable as the exposition duration extended. A tendency has been also recorded of smaller mass decrements of the Fe3Al and FeAl intermetallic phase-based alloys as compared to the 50H21G9N4 steel.

Some factors influencing the creep behaviour of alloy 800

International Nuclear Information System (INIS)

Asbury, F.E.; Willoughby, G.

1975-01-01

Studies have been made of the stability of the creep behaviour of two commercial casts of Incoloy 800, one high carbon and the other low carbon. The effects of pre-ageing, of prolonged creep up to 10 4 hours duration, and of grain size were investigated. Three factors were found to excercise a major influence on creep behaviour. Firstly, when the high carbon alloy was heat treated at 1150degC super-saturation effects, ascribed principally to carbon, gave some initial strengthening which would not, however, persist for the duration of service life in nuclear power plant applications above 600degC. Secondly, a gamma-dash type phase precipitated readily at 550 to 600degC, giving a marked increase in creep strength. Nucleation was sluggish at higher temperatures but once established, this form of strengthening could persist up to at least 650degC. Creep under non-isothermal conditions at 600 to 700degC would be complex on account of the behaviour of this phase. The hardening associated with its precipitation was greater in the low carbon alloy. Finally it was demonstrated that, in spite of gamma-dash precipitation, fine grained low carbon material was weak in creep at low stresses and temperatures. This was ascribed to the occurrence of grain boundary diffusion creep. It appears that this source of weakening would persist in service, and severely restrict the maximum temperature of usage for fined grained high tensile material. (author)

Fatigue and creep deformed microstructures of aged alloys based on Al-4% Cu-0.3% Mg

International Nuclear Information System (INIS)

Reddy, A. Somi

2008-01-01

The addition of 0.4 wt.% of silver or cadmium to the alloy Al-4% Cu-0.3% Mg which has a high Cu:Mg ratio, changes the nature, morphology and dispersion of the precipitates that forms on age hardening at medium temperatures such as 150-200 o C. Fatigue and creep tests were carried out on alloys aged to peak strength at 170 o C. The tensile properties of the alloys aged at 170 o C increased in the order Al-4% Cu, Al-4% Cu-0.3% Mg, Al-4% Cu-0.3% Mg-0.4% Cd, and Al-4% Cu-0.3% Mg-0.4% Ag. Despite differences in their microstructures and tensile properties, the fatigue performance of the alloys was relatively unaffected. Fatigue behaviour was similar in each case and the alloys showed identical fatigue limits. Major differences were observed in the creep performance of the alloys creep tested at 150 o C in the peak strength condition age hardened at 170 o C. Creep performance of the alloys increased in the order of their tensile properties. The purpose of the present work was to discuss the fatigue and creep deformed microstructure of these alloys

Creep-Fatigue Behavior of Alloy 617 at 850 and 950°C, Revision 2

Energy Technology Data Exchange (ETDEWEB)

Carroll, L. [Idaho National Lab. (INL), Idaho Falls, ID (United States); Carroll, M. [Idaho National Lab. (INL), Idaho Falls, ID (United States)

2015-05-01

Alloy 617 is the leading candidate material for an Intermediate Heat Exchanger (IHX) of the Very High Temperature Reactor (VHTR). To evaluate the behavior of this material in the expected service conditions, strain-controlled cyclic tests including hold times up to 9000 s at maximum tensile strain were conducted at 850 and 950 degrees C. At both temperatures, the fatigue resistance decreased when a hold time was added at peak tensile strain. The magnitude of this effect depended on the specific mechanisms and whether they resulted in a change in fracture mode from transgranular in pure fatigue to intergranular in creep-fatigue for a particular temperature and strain range combination. Increases in the tensile hold duration beyond an initial value were not detrimental to the creep-fatigue resistance at 950 degrees C but did continue to degrade the lifetimes at 850 degrees C.

Biaxial thermal creep of Inconel 617 and Haynes 230 at 850 and 950 °C

International Nuclear Information System (INIS)

Tung, Hsiao-Ming; Mo, Kun; Stubbins, James F.

2014-01-01

The biaxial thermal creep behavior of Inconel 617 and Haynes 230 at 850 and 950 °C was investigated. Biaxial stresses were generated using the pressurized tube technique. The detailed creep deformation and fracture mechanism have been studied. Creep curves for both alloys showed that tertiary creep accounts for a greater portion of the materials’ life, while secondary creep only accounts for a small portion. Fractographic examinations of the two alloys indicated that nucleation, growth, and coalescence of creep voids are the dominant micro-mechanisms for creep fracture. At 850 °C, alloy 230 has better creep resistance than alloy 617. When subjected to the biaxial stress state, the creep rupture life of the two alloys was considerably reduced when compared to the results obtained by uniaxial tensile creep tests. The Monkman–Grant relation proves to be a promising method for estimating the long-term creep life for alloy 617, whereas alloy 230 does not follow the relation. This might be associated with the significant changes in the microstructure of alloy 230 at high temperatures

Constitutive modelling of creep-ageing behaviour of peak-aged aluminium alloy 7050

Directory of Open Access Journals (Sweden)

Yang Yo-Lun

2015-01-01

Full Text Available The creep-ageing behaviour of a peak-aged aluminium alloy 7050 was investigated under different stress levels at 174 ∘C for up to 8 h. Interrupted creep tests and tensile tests were performed to investigate the influences of creep-ageing time and applied stress on yield strength. The mechanical testing results indicate that the material exhibits an over-ageing behaviour which increases with the applied stress level during creep-ageing. As creep-ageing time approaches 8 h, the material's yield strength under different stress levels gradually converge, which suggests that the difference in mechanical properties under different stress conditions can be minimised. This feature can be advantageous in creep-age forming to the formed components such that uniformed mechanical properties across part area can be achieved. A set of constitutive equations was calibrated using the mechanical test results and the alloy-specific material constants were obtained. A good agreement is observed between the experimental and calibrated results.

Modelling of creep damage development in ferritic steels

Energy Technology Data Exchange (ETDEWEB)

Sandstroem, R [Swedish Institute for Metals Research, Stockholm (Sweden)

1999-12-31

The physical creep damage, which is observed in fossil-fired power plants, is mainly due to the formation of cavities and their interaction. It has previously been demonstrated that both the nucleation and growth of creep cavities can be described by power functions in strain for low alloy and 12 % CrMoV creep resistant steels. It possible to show that the physical creep damage is proportional to the product of the number of cavities and their area. Hence, the physical creep damage can also be expressed in terms of the creep strain. In the presentation this physical creep damage is connected to the empirical creep damage classes (1-5). A creep strain-time function, which is known to be applicable to low alloy and 12 % CrMoV creep resistant steels, is used to describe tertiary creep. With this creep strain - time model the residual lifetime can be predicted from the observed damage. For a given damage class the remaining life is directly proportional to the service time. An expression for the time to the next inspection is proposed. This expression is a function of fraction of the total allowed damage, which is consumed till the next inspection. (orig.) 10 refs.

Modelling of creep damage development in ferritic steels

Energy Technology Data Exchange (ETDEWEB)

Sandstroem, R. [Swedish Institute for Metals Research, Stockholm (Sweden)

1998-12-31

The physical creep damage, which is observed in fossil-fired power plants, is mainly due to the formation of cavities and their interaction. It has previously been demonstrated that both the nucleation and growth of creep cavities can be described by power functions in strain for low alloy and 12 % CrMoV creep resistant steels. It possible to show that the physical creep damage is proportional to the product of the number of cavities and their area. Hence, the physical creep damage can also be expressed in terms of the creep strain. In the presentation this physical creep damage is connected to the empirical creep damage classes (1-5). A creep strain-time function, which is known to be applicable to low alloy and 12 % CrMoV creep resistant steels, is used to describe tertiary creep. With this creep strain - time model the residual lifetime can be predicted from the observed damage. For a given damage class the remaining life is directly proportional to the service time. An expression for the time to the next inspection is proposed. This expression is a function of fraction of the total allowed damage, which is consumed till the next inspection. (orig.) 10 refs.

Creep properties of 20% cold-worked Hastelloy XR

International Nuclear Information System (INIS)

Kurata, Y.

1996-01-01

The creep properties of Hastelloy XR, in solution-treated and in 20% cold-worked conditions, were studied at 800, 900 and 1000 C. At 800 C, the steady-state creep rate and rupture ductility decrease, while rupture life increases after cold work to 20%. Although the steady-state creep rate and ductility also decrease at 900 C, the beneficial effect on rupture life disappears. Cold work to 20% enhan ces creep resistance of this alloy at 800 and 900 C due to a high density of dislocations introduced by the cold work. Rupture life of the 20% cold-worked alloy becomes shorter and the steady-state creep rate larger at 1000 C during creep of the 20% cold-worked alloy. It is emphasized that these cold work effects should be taken into consideration in design and operation of high-temperature structural components of high-temperature gas-cooled reactors. (orig.)

Creep damage evaluation of low alloy steel weld joint by small punch creep testing

International Nuclear Information System (INIS)

Nishioka, Tomoya; Sawaragi, Yoshiatsu; Uemura, Hiromi

2013-01-01

The effect of sampling location on SPC (Small Punch Creep) tests were investigated for weld joints to establish evaluation method of Type IV creep behavior. The SPC specimen shape was 10mm diameter and 0.5mm thick round disc prepared from weld joints of 2.25Cr-1Mo low alloy steel. It was found that the center of SPC specimen should be 2mm apart from the weld interface as the recommended sampling location. Creep damage was imposed for large weld joint specimens by axial creep loading at 620degC, 52MPa with the interrupted time fraction of 0.34, 0.45, 0.64 and 0.82.SPC samples were prepared from those damaged specimens following the recommended way described in this paper. Among the various SPC tests conducted, good relationships were found for the test condition of 625degC, 200N. Namely, good relationships were obtained both between minimum deflection rate and creep life fraction, and between rupture time and creep life fraction. Consequently, creep life assessment of Type IV fracture by SPC tests could be well conducted using the sampling location and the test condition recommended in this paper. (author)

Creep deformation in near-γ TiAl. Part 1: The influence of microstructure on creep deformation in Ti-49Al-1V

International Nuclear Information System (INIS)

Worth, B.D.; Jones, J.W.; Allison, J.E.

1995-01-01

The influence of microstructure on creep deformation was examine in the e near-γ TiAl alloy Ti-49Al-1V. Specifically, microstructures with varying volume fractions of lamellar constituent were produced through thermomechanical processing. Creep studies were conducted on these various microstructures under constant load in air at temperatures between 760 C and 870 C and at stresses ranging from 50 to 200 MPa. Microstructure significantly influences the creep behavior of this alloy, with a fully lamellar microstructure yielding the highest creep resistance of the microstructures examined. Creep resistance is dependent on the volume fraction of lamellar constituent, with the lowest creep resistance observed at intermediate lamellar volume fractions. Examination of the creep deformation structure revealed planar slip of dislocations in the equiaxed γ microstructure, while sub-boundary formation was observed in the duplex microstructure. The decrease in creep resistance of the duplex microstructure, compared with the equiaxed γ microstructure, is attributed to an increase in dislocation mobility within the equiaxed γ constituent, that results from partitioning of oxygen from the γ phase to the α 2 phase. Dislocation motion in the fully lamellar microstructure was confined to the individual lamellae, with no evidence of shearing of γ/γ or γ/α 2 interfaces. This suggests that the high creep resistance of the fully lamellar microstructure is a result of the fine spacing of the lamellar structure, which results in a decreased effective slip length for dislocation motion over that found in duplex and equiaxed γ microstructures

Crack growth under combined creep and fatigue conditions in alloy 800

International Nuclear Information System (INIS)

Pfaffelhuber, M.; Roedig, M.; Schubert, F.; Nickel, H.

1989-08-01

To investigate the crack growth behaviour under combined creep-fatigue loading, CT 25 mm-specimens of X10NiCrAlTi 32 20 (Alloy 800) have been tested in experiments with cyclic loadings and hold times, with static loadings and short stress rekief interrupts, with ramp type loadings and with sequences of separate fatigue and creep crack growth periods. The test temperature of 700deg C was selected because only in this temperature range this alloy provides similar amounts of crack growth under creep and fatigue conditions due to equivalent stress levels. For the estimation of crack growth under combined loading conditions a linear accumulation of increase in crack length was proved using the crack growth laws of pure creep and fatigue crack growth. Hold time and ramp loadings lead to a higher crack growth rate compared with pure creep or pure fatigue crack growth tests. In hold time experiments the crack growth rate is higher than ramp tests of the same period time. The results of hold time tests can be fairly enough predicted by linear damage accumulation rules. (orig.) [de

Study of the growth of cavities during creep of Mg base alloys

International Nuclear Information System (INIS)

Henckes-viatte, Marguerite.

1975-12-01

Nucleation and growth of intergranular cavities during tensile creep of magnesium base alloys, especially a MgAlSi alloy with 0,8% aluminium and 0,2% silicium, have been investigated. Cavities have been found to nucleate preferentially on precipitates. Their number follows a nearly linear law in function of time and elongation. The cavity nucleation model suggested by Smith and Barnby, by grain boundary sliding with precipitates acting as barriers, explains best our experimental results. Cavity growth during the major part of tensile creep tests performed at 350 deg C, can be accounted for by Hull and Rimmer grain boundary diffusion model, modified so as to include continuous cavity nucleation. At the end of the tertiary creep stage, other mechanisms such as plastic instability as well as mechanical growth seem to be operating. Cavities observed in areas denuded of precipitates formed during high temperature creep in a hydrided MgZr alloy, have also been investigated. Nucleation and growth of these cavities explain by mechanisms similar to the above ones [fr

High-Temperature Creep-Fatigue Behavior of Alloy 617

Directory of Open Access Journals (Sweden)

Rando Tungga Dewa

2018-02-01

Full Text Available This paper presents the high-temperature creep-fatigue testing of a Ni-based superalloy of Alloy 617 base metal and weldments at 900 °C. Creep-fatigue tests were conducted with fully reversed axial strain control at a total strain range of 0.6%, 1.2%, and 1.5%, and peak tensile hold time of 60, 180, and 300 s. The effects of different constituents on the combined creep-fatigue endurance such as hold time, strain range, and stress relaxation behavior are discussed. Under all creep-fatigue tests, weldments’ creep-fatigue life was less than base metal. In comparison with the low-cycle fatigue condition, the introduction of hold time decreased the cycle number of both base metal and weldments. Creep-fatigue lifetime in the base metal was continually decreased by increasing the tension hold time, except for weldments under longer hold time (>180 s. In all creep-fatigue tests, intergranular brittle cracks near the crack tip and thick oxide scales at the surface were formed, which were linked to the mixed-mode creep and fatigue cracks. Creep-fatigue interaction in the damage-diagram (D-Diagram (i.e., linear damage summation was evaluated from the experimental results. The linear damage summation was found to be suitable for the current limited test conditions, and one can enclose all the data points within the proposed scatter band.

Non-isothermal irradiation creep of nickel alloys Inconel 706 and PE-16

International Nuclear Information System (INIS)

Gilbert, E.R.; Chin, B.A.

1984-06-01

The results of in-reactor step temperature change experiments conducted on two nickel alloys, PE-16 and Inconel 706, were evaluated to determine the creep behavior under nonisothermal conditions. The effect of the temperature changes was found to be significantly different for the two alloys. Following a step temperature change, the creep rate of PE-16 adjusted to the rate found in isothermal tests at the new temperature. In contrast for Inconel 706, a reduction in temperature from 540 to 425 0 C produced a 300% increase in creep above that measured at 540 0 C in isothermal tests. The response of in-reactor creep in Inconel 706 to temperature changes was attributed to the dissolution of the gamma double-prime phase and subsequent loss of precipitation-strengthening at temperatures below 500 C

Spectral analysis of creep recovery process in finemet type amorphous alloy

NARCIS (Netherlands)

Jurikova, A; Csach, K; Miskuf, J; Bengus, VZ; Ocelik, Vaclav

2002-01-01

The creep recovery process in Finemet type amorphous alloy leas been analyzed using the method for calculating the relaxation tithe spectra. The influence of structural relaxation and temperature on the spectra shape lags been studied. The creep recovery spectrum of the anelastic deformation of the

Tensile and Creep Behavior of Extruded AA6063/SiCp Al MMCs

International Nuclear Information System (INIS)

Khalifa, Tarek A.; Mahmoud, Tamer S.

2010-01-01

Composites of AA6063 Al alloy reinforced with SiC particles (SiC p ) were prepared by the vortex method. Hot extrusion was carried out for the as cast composites with a reduction in area of 25%. Tensile and creep behavior of as-cast and extruded composites were studied at elevated temperatures. Tensile tests carried out at room temperature showed that for the as-cast composites, the addition of SiC p up to 10% by weight improves the strength but reduces ductility. Further addition of SiC p reduces the strength and ductility of the composites. At 150 and 300 deg. C the matrix alloy exhibits higher strength than the composites. Extrusion generally raised the strength of the composites at both room and elevated temperatures. Time rupture creep tests carried out at 300 deg. C showed that the composites exhibit higher creep resistance as compared to the matrix alloy except at relatively low stresses where the matrix has a better creep resistance. Extrusion improved the resistance of composites to creep rupture.

Comparative study on the high-temperature tensile and creep properties of Alloy 617 base and weld metals

International Nuclear Information System (INIS)

Kim, Woo Gon; Hong, Sung Deok; Kim, Yong Wan; Kim, Seon Jin; Park, Jae Young; Ekaputra, I. M. W.

2013-01-01

This paper presents a comparative investigation on the high-temperature tensile and creep properties of Alloy 617 base metal (BM) and weld metal (WM) fabricated by a gas tungsten arc weld process. The WM had higher yield strength and lower ultimate tensile strength than the BM does; however, its elongation was significantly lower than that of the BM. The creep curve of the BM and WM was somewhat different from that of typical heat-resistance steel, and did not show a textbook creep. The WM exhibited a longer creep rupture life, lower creep rate, and lower rupture ductility than the BM. However, as the creep rupture time reached approximately 36,800 h, the creep life of the WM was expected to be almost similar to that of the BM; and after 36,800 h, its creep life was expected to be worse than the BM. Loner creep tests is needed to investigate the long-term creep life of the WM. The creep failure mode of the BM and WM was obviously an intergranular cracking of the cavity formation and growth mechanisms, although it was more evident in the WM. The BM had a more ductile fracture surface than the WM

Creep behavior of plasma carburized Ti-6Al-4V alloy

International Nuclear Information System (INIS)

Oliveira, Veronica Mara Cortez Alves de; Barboza, Miguel Justino Ribeiro; Silva, Mariane Capellari Leite da; Pinto, Catia Gisele; Suzuki, Paulo Atsushi; Machado, Joao Paulo B.

2010-01-01

This paper aims to evaluate the effect of plasma carburizing on the Ti-6Al-4V alloy submitted to creep tests. The results showed that the alloy Ti-6Al-4V had a hardness of 334 ± 18 HV. After treatment thermochemical by plasma, was observed the formation of a layer of average thickness of 1,5 μm and hardness of 809 ± 79 HV due to the presence of TiC phase identified by X-ray diffraction. The treatment increased the values of average roughness of 1,28 to 2,02 μm. The creep properties of carburized specimens were improved in comparison with those of the uncarburized Ti-6Al-4V alloy. (author)

Model-based Approach for Long-term Creep Curves of Alloy 617 for a High Temperature Gas-cooled Reactor

International Nuclear Information System (INIS)

Kim, Woo Gon; Yin, Song Nan; Kim, Yong Wan

2008-01-01

Alloy 617 is a principal candidate alloy for the high temperature gas-cooled reactor (HTGR) components, because of its high creep rupture strength coupled with its good corrosion behavior in simulated HTGR-helium and its sufficient workability. To describe a creep strain-time curve well, various constitutive equations have been proposed by Kachanov-Rabotnov, Andrade, Garofalo, Evans and Maruyama, et al.. Among them, the K-R model has been used frequently, because a secondary creep resulting from a balance between a softening and a hardening of materials and a tertiary creep resulting from an appearance and acceleration of the internal or external damage processes are adequately considered. In the case of nickel-base alloys, it has been reported that a tertiary creep at a low strain range may be generated, and this tertiary stage may govern the total creep deformation. Therefore, a creep curve for nickel-based Alloy 617 will be predicted appropriately by using the K-R model that can reflect a tertiary creep. In this paper, the long-term creep curves for Alloy 617 were predicted by using the nonlinear least square fitting (NLSF) method in the K-R model. The modified K-R model was introduced to fit the full creep curves well. The values for the λ and K parameters in the modified K-R model were obtained with stresses

Application of neutron diffraction in characterization of texture evolution during high-temperature creep in magnesium alloys

International Nuclear Information System (INIS)

Sediako, A.; Shook, S.; Vogel, S.; Sediako, D.

2010-01-01

A good combination of room-temperature and elevated temperature strength and ductility, good salt-spray corrosion resistance and excellent diecastability are frequently among the main considerations in development of a new magnesium alloy for automotive industry. Unfortunately, there has been much lesser effort in development of wrought-stock alloys for high temperature applications. Extrudability and high temperature performance of wrought material become important factors in an effort to develop new wrought alloys and processing technologies. This paper shows some results received in creep testing and studies of in-creep texture evolution for several wrought magnesium alloys developed for use in elevated- temperature applications. Along with others 'traditional' characterization techniques of metals' performance in high- temperature creep, neutron diffraction was employed in this study to analyze evolution of crystallographic texture during creep deformation. The paper compares two methods of texture analysis in neutron diffraction studies: based on monochromatic (reactor-source) beam and white neutron beam (time-of-flight method, synchrotron). The time-of-flight (TOF) spectrometer illuminates the sample with a non-filtered beam of neutrons and captures the readings with an encircled detector array. This provides a very fast and detailed picture of the crystallographic texture for the bulk of the sample. As the white beam retains all neutron wavelengths, it takes much less time to collect statistically-valid dataset for the diffraction pattern. On the other hand, the monochromatic beam setup includes a monochromatic crystal that filters out a specific wavelength. The diffracted beam is then captured by a much simpler neutron detector. This setup is more flexible, allowing for choosing various wavelengths (depending on the sample material) but obviously requiring more time for statistically viable data collection. These studies were performed using E3 neutron

Creep-resistant, cobalt-free alloys for high temperature, liquid-salt heat exchanger systems

Science.gov (United States)

Holcomb, David E; Muralidharan, Govindarajan; Wilson, Dane F.

2016-09-06

An essentially Fe- and Co-free alloy is composed essentially of, in terms of weight percent: 6.0 to 7.5 Cr, 0 to 0.15 Al, 0.5 to 0.85 Mn, 11 to 19.5 Mo, 0.03 to 4.5 Ta, 0.01 to 9 W, 0.03 to 0.08 C, 0 to 1 Re, 0 to 1 Ru, 0 to 0.001 B, 0.0005 to 0.005 N, balance Ni, the alloy being characterized by, at 850.degree. C., a yield strength of at least 25 Ksi, a tensile strength of at least 38 Ksi, a creep rupture life at 12 Ksi of at least 25 hours, and a corrosion rate, expressed in weight loss [g/(cm.sup.2 sec)]10.sup.-11 during a 1000 hour immersion in liquid FLiNaK at 850.degree. C., in the range of 3 to 10.

Development status und future possibilities for martensitic creep resistant steels

Energy Technology Data Exchange (ETDEWEB)

Hald, J. [Technical Univ. Denmark, Lyngby (Denmark). Dept. of Mechanical Engineering

2010-07-01

In the last four decades new stronger modified 9%Cr martensitic creep resistant steels have been introduced in power plants, which has enabled increases in maximum achievable steam conditions from the previous 250 bar and 540-560 C up to the values of 300 bar and 600-620 C currently being introduced all over the world. In order to further increase the steam parameters of steel based power plants up to a target value of 650 C/325 bar it is necessary to double the creep strength of the martensitic steels. At the same time the resistance against steam oxidation must be improved by an increase of the chromium content in the steels from 9% to 12%. However, so far all attempts to make stronger 12%Cr steels have led to breakdowns in long-term creep strength. Significant progress has been achieved in the understanding of microstructure stability of the martensitic 9-12%Cr steels: Observed microstructure instabilities in 11-12%Cr steels are explained by Z-phase precipitation, which dissolves fine MN nitrides. Improved understanding of effects of B and N on long-term creep properties has formed the basis of a series of new stronger 9%Cr test alloys with improved creep strength. In parallel 9%Cr test steels with low C content show very promising behavior in long-term tests. However, the 9%Cr steels must be surface coated to protect against steam oxidation at high temperature applications above 620%C. A possibility to use fine Z-phases for strengthening of the martensitic steels has been identified, and this opens a new pathway for development of stable strong 12%Cr steels. There are still good prospects for the realization of a 325 bar / 650 C steam power plant all based on steel. (orig.)

The thermal fatigue behaviour of creep-resistant Ni-Cr cast steel

Directory of Open Access Journals (Sweden)

B. Piekarski

2007-12-01

Full Text Available The study gives a summary of the results of industrial and laboratory investigations regarding an assessment of the thermal fatigue behaviour of creep-resistant austenitic cast steel. The first part of the study was devoted to the problem of textural stresses forming in castings during service, indicating them as a cause of crack formation and propagation. Stresses are forming in carbides and in matrix surrounding these carbides due to considerable differences in the values of the coefficients of thermal expansion of these phases. The second part of the study shows the results of investigations carried out to assess the effect of carbon, chromium and nickel on crack resistance of austenitic cast steel. As a criterion of assessment the amount and propagation rate of cracks forming in the specimens as a result of rapid heating followed by cooling in running water was adopted. Tests were carried out on specimens made from 11 alloys. The chemical composition of these alloys was comprised in a range of the following values: (wt-%: 18-40 %Ni, 17-30 %Cr, 1.2-1.6%Si and 0.05-0.6 %C. The specimens were subjected to 75 cycles of heating to a temperature of 900oC followed by cooling in running water. After every 15 cycles the number of the cracks was counted and their length was measured. The results of the measurements were mathematically processed. It has been proved that the main factor responsible for an increase in the number of cracks is carbon content in the alloy. In general assessment of the results of investigations, the predominant role of carbon and of chromium in the next place in shaping the crack behaviour of creep-resistant austenitic cast steel should be stressed. Attention was also drawn to the effect of high-temperature corrosion as a factor definitely deteriorating the cast steel resistance to thermal fatigue.

Microstructure and creep behavior of an orthorhombic Ti-25Al-17Nb-1Mo alloy

International Nuclear Information System (INIS)

Zhang, J.W.; Zou, D.X.; Li, S.Q.; Lee, C.S.; Lai, J.K.L.

1998-01-01

Microstructural evolution during three heat-treatment schedules and the terminal microstructures in an orthorhombic alloy of Ti-25Al-17Nb-1Mo were observed and analyzed with optical microscopy, transmission electron microscopy (TEM), scanning electron microscopy (SEM), and X-ray diffraction (XRD). The creep behavior of the alloy with three different microstructures (a coarse-lath, fine-lath, and fine equiaxed microstructure) was studied over a temperature range of 600 C to 750 C and over a stress range of 150 to 400 MPa in air. The steady-state creep rates, apparent stress exponents, and apparent creep activation energies of the various samples have been determined. The results show that creep behaviors in the alloy are strongly influenced by microstructure. The effect on creep by some of the microstructural features, such as the multivariants within the coarse laths and the interfaces of the laths and the equiaxed grains, is also discussed

Report on FY15 Alloy 617 SMT Creep-Fatigue Test Results

Energy Technology Data Exchange (ETDEWEB)

Wang, Yanli [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Jetter, Robert I. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Baird, Seth T. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Pu, Chao [Univ. of Tennessee, Knoxville, TN (United States); Sham, Sam [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)

2015-06-22

For the temperature range of 990-950C, Alloy 617 is a candidate IHX structural material for high temperature gas reactors (HTGRs) because of its high temperature creep properties. Also, its superior strength over a broad temperature range also offers advantages for certain component applications. In order for the designers to be able to use Alloy 617 for these high temperature components, Alloy 617 has to be approved for use in Section III (the nuclear section) of the ASME (American Society of Mechanical Engineers) Boiler and Pressure Vessel Code. A plan has been developed to propose a Code Case for use of Alloy 617 at elevated temperature in Section III of the ASME Code by September 2015. There has not been a new high temperature material approved for use in Section III for almost 20 years. The Alloy 617 Code Case effort would lead the way to establish a path for Code qualification of new high temperature materials of interest to other advanced SMRs. Creep-fatigue at elevated temperatures is the most damaging structural failure mode. In the past 40 years significant efforts have been devoted to the elevated temperature Code rule development in Section III, Subsection NH* of the ASME Boiler and Pressure Vessel Code, to ascertain conservative structural designs to prevent creep-fatigue failure. The current Subsection NH creep-fatigue procedure was established by the steps of (1) analytically obtaining a detailed stress-strain history, (2) comparing the stress and strain components to cyclic test results deconstructed into stress and strain quantities, and (3) recombining the results to obtain a damage function in the form of the so-called creep-fatigue damage-diagram. The deconstruction and recombination present difficulties in evaluation of test data and determination of cyclic damage in design. The uncertainties in these steps lead to the use of overly conservative design factors in the current creep-fatigue procedure. In addition, and of major significance to the

Hydrogen diffusion and effect on degradation in welded microstructures of creep-resistant low-alloyed steels

International Nuclear Information System (INIS)

Rhode, Michael

2016-01-01

The main challenge for the future is to further increase the power plant thermal efficiency independent of the type of power plant concept, i.e. fossil-fired or nuclear power plant, where the material selection can directly affect reduction of CO 2 emissions. In power plant design, welding is the most applied manufacturing technique in component construction. The necessary weld heat input causes metallurgical changes and phase transitions in the heat affected zone (HAZ) of the base materials and in the deposited weld metal. The weld joint can absorb hydrogen during welding or in later service - This absorption can cause degradation of mechanical properties of the materials, and in certain loading conditions, hydrogen-assisted cold cracks can occur. This cracking phenomenon can appear time delayed due to the temperature dependency of the hydrogen diffusion and the presence of a ''critical'' hydrogen concentration. Additionally, each specific weld microstructure shows a certain hydrogen diffusion and solubility that contribute to susceptibility of the cracking phenomenon. Therefore hydrogen cannot be neglected as possible failure effect, which was identified recently in the case of T24 creep-resistant tube-to-tube weld joints. It is necessary to identify and assess the hydrogen effect in weld joints of low-alloyed steel grades for to improve further early detection of possible failures. For each specific weld joint microstructure, it is necessary to separate the interdependencies between mechanical load and the hydrogen concentration. The diffusivity and solubility must be considered to identify hydrogen quantities in the material at any given time. In this case, the effects of mechanical loading were dealt with independently. For the characterization of the mechanical properties, hydrogen charged tensile specimens were investigated for the base materials and thermally simulated HAZ microstructures. The hydrogen diffusion was characterized with

Hydrogen diffusion and effect on degradation in welded microstructures of creep-resistant low-alloyed steels

Energy Technology Data Exchange (ETDEWEB)

Rhode, Michael

2016-04-04

The main challenge for the future is to further increase the power plant thermal efficiency independent of the type of power plant concept, i.e. fossil-fired or nuclear power plant, where the material selection can directly affect reduction of CO{sub 2} emissions. In power plant design, welding is the most applied manufacturing technique in component construction. The necessary weld heat input causes metallurgical changes and phase transitions in the heat affected zone (HAZ) of the base materials and in the deposited weld metal. The weld joint can absorb hydrogen during welding or in later service - This absorption can cause degradation of mechanical properties of the materials, and in certain loading conditions, hydrogen-assisted cold cracks can occur. This cracking phenomenon can appear time delayed due to the temperature dependency of the hydrogen diffusion and the presence of a ''critical'' hydrogen concentration. Additionally, each specific weld microstructure shows a certain hydrogen diffusion and solubility that contribute to susceptibility of the cracking phenomenon. Therefore hydrogen cannot be neglected as possible failure effect, which was identified recently in the case of T24 creep-resistant tube-to-tube weld joints. It is necessary to identify and assess the hydrogen effect in weld joints of low-alloyed steel grades for to improve further early detection of possible failures. For each specific weld joint microstructure, it is necessary to separate the interdependencies between mechanical load and the hydrogen concentration. The diffusivity and solubility must be considered to identify hydrogen quantities in the material at any given time. In this case, the effects of mechanical loading were dealt with independently. For the characterization of the mechanical properties, hydrogen charged tensile specimens were investigated for the base materials and thermally simulated HAZ microstructures. The hydrogen diffusion was characterized

Uniaxial creep behavior of V-4Cr-4Ti alloy

International Nuclear Information System (INIS)

Natesan, K.; Soppet, W.K.; Purohit, A.

2002-01-01

We are undertaking a systematic study at Argonne National Laboratory to evaluate the uniaxial creep behavior of V-Cr-Ti alloys in a vacuum environment as a function of temperature in the range of 650-800 deg. C and at applied stress levels of 75-380 MPa. Creep strain in the specimens is measured by a linear-variable-differential transducer, which is attached between the fixed and movable pull rods of the creep assembly. Strain is measured at sufficiently frequent intervals during testing to define the creep strain/time curve. A linear least-squares analysis function is used to ensure consistent extraction of minimum creep rate, onset of tertiary creep and creep strain at the onset of tertiary creep. Creep test data, obtained at 650, 700, 725 and 800 deg. C, showed power-law creep behavior. Extensive analysis of the tested specimens is conducted to establish hardness profiles, oxygen content and microstructural characteristics. The data are also quantified by the Larson-Miller approach, and correlations are developed to relate time to rupture, onset of tertiary creep, times for 1% and 2% strain, exposure temperature and applied stress

Effect of stacking fault energy on high-temperature creep parameters of nickel-cobalt alloys

International Nuclear Information System (INIS)

Nerodenko, L.M.; Dabizha, E.V.

1982-01-01

Results of creep investigation are discussed for two alloys of the Ni-Co system. In terms of the structural creep model an analysis is made for the effect of stacking fault energy on averaged parameters of the dislocation structure: inovable dislocation density subgrain size, activation volume. The rate of steady-state creep is determined by the process of dislocation passing through the subgrain boundaries with activation energy of 171.0 and 211.5 kJ/mol for the Ni-25% Co and Ni-65% Co alloys, respectively

The Effect of Creep Aging on the Fatigue Fracture Behavior of 2524 Aluminum Alloy

OpenAIRE

Wenke Li; Lihua Zhan; Lingfeng Liu; Yongqian Xu

2016-01-01

Normal temperature tensile and fatigue tests were adopted to test the mechanical performance and fatigue life of 2524 aluminum alloy under the three states of T3, artificial aging, and creep aging, and scanning electron microscope and transmission electron microscope were also used to observe the fatigue fracture morphology and aging precipitation features of the alloy under the above three states. Results showed that the alloy treated by creep aging can obtain higher fatigue life, but that t...

Creep characterization of Al alloy thin films for use in RF-MEMS switches

NARCIS (Netherlands)

Modlinski, R.; Witvrouw, A.; Ratchev, P.; Puers, R.; Toonder, den J.M.J.; Wolf, I.C.D.Y.M.

2004-01-01

Creep is expected to be a major reliability problem in some MEMS, as for example RF-MEMS switches, especially at high RF powers. For this reason it should be avoided to use creep sensitive materials in these devices. In this paper we report on creep studies on Al-alloys, materials that are often

Thermal creep properties of alloy D9 stainless steel and 316 stainless steel fuel clad tubes

International Nuclear Information System (INIS)

Latha, S.; Mathew, M.D.; Parameswaran, P.; Bhanu Sankara Rao, K.; Mannan, S.L.

2008-01-01

Uniaxial thermal creep rupture properties of 20% cold worked alloy D9 stainless steel (alloy D9 SS) fuel clad tubes for fast breeder reactors have been evaluated at 973 K in the stress range 125-250 MPa. The rupture lives were in the range 90-8100 h. The results are compared with the properties of 20% cold worked type 316 stainless steel (316 SS) clad tubes. Alloy D9 SS were found to have higher creep rupture strengths, lower creep rates and lower rupture ductility than 316 SS. The deformation and damage processes were related through Monkman Grant relationship and modified Monkman Grant relationship. The creep damage tolerance parameter indicates that creep fracture takes place by intergranular cavitation. Precipitation of titanium carbides in the matrix and chromium carbides on the grain boundaries, dislocation substructure and twins were observed in transmission electron microscopic investigations of alloy D9 SS. The improvement in strength is attributed to the precipitation of fine titanium carbides in the matrix which prevents the recovery and recrystallisation of the cold worked microstructure

Thermo-physical Properties and Mechanical Properties of Burn-resistant Titanium Alloy Ti40

Directory of Open Access Journals (Sweden)

LAI Yunjin

2017-10-01

Full Text Available As a functional material of burn-resistant titanium alloy, the physical properties of Ti40 alloy were first reported. The chemical compositions of Ti40 alloy ingots by VAR were uniform. The microstructures of Ti40 alloy slab manufactured by HEFF+WPF were uniform. The results show that the room temperature tensile strength of Ti40 alloy is 950 MPa degree. The properties of high temperature heat exposure, creep resistance and lasting time are good at 500 ℃. In the range from room temperature to 600 ℃, Young's modulus and shear modulus are decreased linearly with increasing the temperature, Poisson's ratio is increases slowly as the temperature rises, and linear thermal expansion coefficient and average linear expansion coefficient is increase as the temperature rises.

Effect of preparation techniques on creep characteristics of the Zr-2. 5% Nb alloy at temperatures of 673 to 823 K

Energy Technology Data Exchange (ETDEWEB)

Pahutova, M; Kreici, J; Polesna, M [Ceskoslovenska Akademie Ved, Brno. Ustav Fyzikalni Metalurgie

1976-01-01

The effect of the initial raw material - zirconium sponge or zirconium iodide - on some creep and stres-strain properties was studied on Zr-2.5%Nb alloy by a stress-strain test at constant crosshead speed and by strain-rate sensitivity testing. Dependence of the creep characteristics on cooling conditions after solution treatment was examined. Alloy made from Zr-sponge was used for measurement of steady-state creep rate on time to fracture dependence and steady-state creep rate on time to fracture with respect to the angle between rolling direction of alloy sheets and tensile axis. Transmission electron microscopy was used for structure study of both alloys after different heat treatment. Higher creep strength of the alloy made from iodide zirconium (after respective heat treatment) than that of the alloy made from Zr-sponge is discussed. Oxygen content and its effect on structural changes during heat treatment seems to be responsible for higher creep strength of the first alloy. On the other hand the difference of respective creep strengths is not so significant as to justify production of Zr-2.5%Nb alloy and perhaps of future high-strength Zr alloys (for applications in structural components in reactors in the temperature range of 673 to 773 K) from iodide zirconium. Results of creep and stress-strain (short time) testing are briefly discussed.

Analysis of the creep behaviour of die-cast Mg–3Al–1Si alloy

Energy Technology Data Exchange (ETDEWEB)

Zhu, S.M., E-mail: suming.zhu@monash.edu [CAST Cooperative Research Centre, Department of Materials Engineering, Monash University, Victoria 3800 (Australia); ARC Centre of Excellence for Design in Light Metals, Department of Materials Engineering, Monash University, Victoria 3800 (Australia); Easton, M.A. [CAST Cooperative Research Centre, Department of Materials Engineering, Monash University, Victoria 3800 (Australia); Gibson, M.A. [CAST Cooperative Research Centre, CSIRO Process Science and Engineering, Clayton, Victoria 3169 (Australia); Dargusch, M.S. [Centre for Advanced Materials Processing and Manufacturing, School of Mechanical and Mining Engineering, The University of Queensland, Queensland 4075 (Australia); Defence Materials Technology Centre, The University of Queensland, Queensland 4075 (Australia); Nie, J.F. [ARC Centre of Excellence for Design in Light Metals, Department of Materials Engineering, Monash University, Victoria 3800 (Australia)

2013-08-20

The creep behaviour of die-cast Mg–3Al–1Si (AS31) alloy has been studied at 125 °C, 150 °C and 175 °C with stresses ranging 50–110 MPa. The alloy exhibits anomalously high stress exponents, i.e. 14.4 at 125 °C, 11.6 at 150 °C and 9.5 at 175 °C. Contrary to work reported previously, these high stress exponents cannot be rationalised using the threshold stress approach that is commonly adopted in analysing creep behaviour of dispersion strengthened alloys or metal matrix composites. It is shown that the observed high stress exponents are associated with the dominance of power-law breakdown creep in this study, and the stress dependence can be well described by the Garofalo sinh relationship with the natural exponent of 5. Transmission electron microscopy (TEM) observations reveal that cross-slip of 〈a〉 type dislocations is probably the controlling creep mechanism.

Analysis of the creep behaviour of die-cast Mg–3Al–1Si alloy

International Nuclear Information System (INIS)

Zhu, S.M.; Easton, M.A.; Gibson, M.A.; Dargusch, M.S.; Nie, J.F.

2013-01-01

The creep behaviour of die-cast Mg–3Al–1Si (AS31) alloy has been studied at 125 °C, 150 °C and 175 °C with stresses ranging 50–110 MPa. The alloy exhibits anomalously high stress exponents, i.e. 14.4 at 125 °C, 11.6 at 150 °C and 9.5 at 175 °C. Contrary to work reported previously, these high stress exponents cannot be rationalised using the threshold stress approach that is commonly adopted in analysing creep behaviour of dispersion strengthened alloys or metal matrix composites. It is shown that the observed high stress exponents are associated with the dominance of power-law breakdown creep in this study, and the stress dependence can be well described by the Garofalo sinh relationship with the natural exponent of 5. Transmission electron microscopy (TEM) observations reveal that cross-slip of 〈a〉 type dislocations is probably the controlling creep mechanism

Microstructural effects on the creep and crack propagation behaviors of γ-Ti aluminide alloy

International Nuclear Information System (INIS)

Lupinc, V.; Onofrio, G.; Nazmy, M.; Staubli, M.

1999-01-01

Gamma titanium aluminides class of materials possess several unique physical and mechanical properties. These characteristics can be attractive for specific industrial applications. By applying different heat treatment schedules one can change the microstructural features of this class of materials. In the present investigation, two heat treatment schedules were used to produce two different microstructures, duplex (D) and nearly lamellar (NL) in the cast and HIP'ed Ti-47Al-2W-0.5Si alloy. The tensile strength and creep behavior, in the 700--850 C temperature range, of this alloy have been determined and correlated to the corresponding microstructures. In addition, the fatigue crack propagation behavior in this alloy has been studied at different temperatures. The results on the creep behavior showed that the alloy with nearly lamellar microstructure has a strongly improved creep strength as compared with that of the duplex microstructure

Creep-Rupture Behavior of Ni-Based Alloy Tube Bends for A-USC Boilers

Science.gov (United States)

Shingledecker, John

Advanced ultrasupercritical (A-USC) boiler designs will require the use of nickel-based alloys for superheaters and reheaters and thus tube bending will be required. The American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code Section II PG-19 limits the amount of cold-strain for boiler tube bends for austenitic materials. In this summary and analysis of research conducted to date, a number of candidate nickel-based A-USC alloys were evaluated. These alloys include alloy 230, alloy 617, and Inconel 740/740H. Uniaxial creep and novel structural tests and corresponding post-test analysis, which included physical measurements, simplified analytical analysis, and detailed microscopy, showed that different damage mechanisms may operate based on test conditions, alloy, and cold-strain levels. Overall, creep strength and ductility were reduced in all the alloys, but the degree of degradation varied substantially. The results support the current cold-strain limits now incorporated in ASME for these alloys for long-term A-USC boiler service.

Reliability Evaluation on Creep Life Prediction of Alloy 617 for a Very High Temperature Reactor

International Nuclear Information System (INIS)

Kim, Woo-Gon; Hong, Sung-Deok; Kim, Yong-Wan; Park, Jae-Young; Kim, Seon-Jin

2012-01-01

This paper evaluates the reliability of creep rupture life under service conditions of Alloy 617, which is considered as one of the candidate materials for use in a very high temperature reactor (VHTR) system. A Z-parameter, which represents the deviation of creep rupture data from the master curve, was used for the reliability analysis of the creep rupture data of Alloy 617. A Service-condition Creep Rupture Interference (SCRI) model, which can consider both the scattering of the creep rupture data and the fluctuations of temperature and stress under any service conditions, was also used for evaluating the reliability of creep rupture life. The statistical analysis showed that the scattering of creep rupture data based on Z-parameter was supported by normal distribution. The values of reliability decreased rapidly with increasing amplitudes of temperature and stress fluctuations. The results established that the reliability decreased with an increasing service time.

In situ monitored in-pile creep testing of zirconium alloys

Science.gov (United States)

Kozar, R. W.; Jaworski, A. W.; Webb, T. W.; Smith, R. W.

2014-01-01

The experiments described herein were designed to investigate the detailed irradiation creep behavior of zirconium based alloys in the HALDEN Reactor spectrum. The HALDEN Test Reactor has the unique capability to control both applied stress and temperature independently and externally for each specimen while the specimen is in-reactor and under fast neutron flux. The ability to monitor in situ the creep rates following a stress and temperature change made possible the characterization of creep behavior over a wide stress-strain-rate-temperature design space for two model experimental heats, Zircaloy-2 and Zircaloy-2 + 1 wt%Nb, with only 12 test specimens in a 100-day in-pile creep test program. Zircaloy-2 specimens with and without 1 wt% Nb additions were tested at irradiation temperatures of 561 K and 616 K and stresses ranging from 69 MPa to 455 MPa. Various steady state creep models were evaluated against the experimental results. The irradiation creep model proposed by Nichols that separates creep behavior into low, intermediate, and high stress regimes was the best model for predicting steady-state creep rates. Dislocation-based primary creep, rather than diffusion-based transient irradiation creep, was identified as the mechanism controlling deformation during the transitional period of evolving creep rate following a step change to different test conditions.

Effect of texture on creep deformation behavior of Zr-2.5Nb alloy

International Nuclear Information System (INIS)

Guguloth, Krishna; Swaminathan, J.; Mitra, Rahul; Ghosh, R.N.; Singh, R.N.; Chakravartty, J.K.

2016-01-01

Zr-2.5%Nb alloys are extensively used as high temperature pressure tubes in nuclear reactor. Therefore creep behavior of this alloy is of considerable importance. The paper presents creep strain-time plots on two sets of specimens made from two as received pressure tubes having different diameters. These tubes were reported to have undergone different processing routes; both tubes were autoclaved at the same temperature in the steam atmosphere. A comparison of the creep strain-time plots of the two sets of specimen under identical test conditions showed a marked difference. The chemical composition and the microstructure of the two sets of samples were also found to be similar. Therefore X-ray diffraction patterns were taken from the two tubes. The ratio of intensity of two prominent reflections from 0002 and 1120 planes of alpha Zr in the case of 90mm tube was found to be 1.79; whereas that from the 110mm tube was 0.25. This suggests that in the case of 110mm tube most of the basal planes were less favorably oriented with respect to the loading axis. This is the reason why creep strength of 110mm tube was found to be higher. The paper also describes how the effect of texture can be incorporated in evaluating the creep behavior of Zr-Nb alloy. This suggests that a relatively larger volume of creep test data on Zr-2.5Nb pressure tube is necessary to account for the effect texture so that a reliable estimate of its creep life could be obtained. (author)

Multiaxial creep of tubes of Alloy 800 and Alloy 617 at high temperature

International Nuclear Information System (INIS)

Penkalla, H.J.; Schubert, F.; Nickel, H.

1989-01-01

The deformation behaviour under multiaxial loading at temperature higher than 800 deg. C is strongly controlled by creep. For dimensioning and inelastic analysis the use of v. Mises theory and Norton's creep law for stationary creep are demonstrated for different combination of internal pressure and axial or torsional stress or strains. The experimental results are in satisfactory agreement with the theoretical predicted deformation behaviour if values for the coefficient k and n in Norton's creep law are used, which are close to the real creep resistance in the component. (author). 11 refs, 12 figs, 2 tabs

Influence of pretreatment on creep-rupture-strength and creep-behaviour of a matrix-hardening Ni-base-alloy

International Nuclear Information System (INIS)

Schirra, M.

1982-01-01

The creep and time-to-rupture behaviour of the matrix hardening Nickel base alloy Inconel 625 was investigated in the temperature range 650-800 0 C. Three different thermo-mechanical pretreatment were used: I = Hot rolled finish; II = 870 0 C annealed; III = Sol. treatment 1150 0 C 1 h. The temperature range of this study is for samples which have undergone treatment I and II well above the temperatures normally used. The results show an anomalous stress dependence of creep and time-to-rupture at around 750 0 C. The reason is to be found in the very complex precipitation processes occurring while the stress is applied. The results are explained according to findings about precipitation in this type of alloy. (orig.) [de

Irradiation enhanced diffusion and irradiation creep tests in stainless steel alloys

International Nuclear Information System (INIS)

Loelgen, R.H.; Cundy, M.R.; Schuele, W.

1977-01-01

A review is given of investigations on the rate of phase changes during neutron and electron irradiation in many different fcc alloys showing either precipitation or ordering. The diffusion rate was determined as a function of the irradiation flux, the irradiation temperature and the irradiation dose. It was found that the radiation enhanced diffusion in all the investigated alloys is nearly temperature independent and linearly dependent on the flux. From these results conclusions were drawn concerning the properties of point defects and diffusion mechanisms rate determining during irradiation, which appears to be of a common nature for fcc alloys having a similar structure to those investigated. It has been recognized that the same dependencies which are found for the diffusion rate were also observed for the irradiation creep rate in stainless steels, as reported in literature. On the basis of this observation a combination of measurements is suggested, of radiation enhanced diffusion and radiation enhanced creep in stainless steel alloys. The diffusion tests will be performed at the Euratom Joint Research Centre in Ispra, Italy, and the irradiation creep tests will be carried out in the High Flux Reactor /9/ of the Euratom Joint Research Centre in Petten, The Netherlands. In order to investigate irradiation creep on many samples at a time two special rigs were developed which are distinguished only by the mode of stress applied to the steel specimens. In the first type of rig about 50 samples can be tested uniaxially under tension with various combinations of irradiation temperature and stress. The second type of rig holds up to 70 samples which are tested in bending, again with various combinations of irradiation temperature and stress

Exceptional increase in the creep life of magnesium rare-earth alloys due to localized bond stiffening.

Science.gov (United States)

Choudhuri, Deep; Srinivasan, Srivilliputhur G; Gibson, Mark A; Zheng, Yufeng; Jaeger, David L; Fraser, Hamish L; Banerjee, Rajarshi

2017-12-08

Several recent papers report spectacular, and unexpected, order of magnitude improvement in creep life of alloys upon adding small amounts of elements like zinc. This microalloying effect raises fundamental questions regarding creep deformation mechanisms. Here, using atomic-scale characterization and first principles calculations, we attribute the 600% increase in creep life in a prototypical Mg-rare earth (RE)-Zn alloy to multiple mechanisms caused by RE-Zn bonding-stabilization of a large volume fraction of strengthening precipitates on slip planes, increase in vacancy diffusion barrier, reduction in activated cross-slip, and enhancement of covalent character and bond strength around Zn solutes along the c-axis of Mg. We report that increased vacancy diffusion barrier, which correlates with the observed 25% increase in interplanar bond stiffness, primarily enhances the high-temperature creep life. Thus, we demonstrate that an approach of local, randomized tailoring of bond stiffness via microalloying enhances creep performance of alloys.

The effect of preparation techniques on creep characteristics of the Zr-2.5% Nb alloy at temperatures of 673 to 823 K

International Nuclear Information System (INIS)

Pahutova, M.; Krejci, J.; Polesna, M.

1976-01-01

The effect of the initial raw material - zirconium sponge or zirconium iodide - on some creep and stres-strain properties was studied on Zr-2.5%Nb alloy by a stress-strain test at constant crosshead speed and by strain-rate sensitivity testing. Dependence of the creep characteristics on cooling conditions after solution treatment was examined. Alloy made from Zr-sponge was used for measurement of steady-state creep rate on time to fracture dependence and steady-state creep rate on time to fracture with respect to the angle between rolling direction of alloy sheets and tensile axis. Transmission electron microscopy was used for structure study of both alloys after different heat treatment. Higher creep strength of the alloy made from iodide zirconium (after respective heat treatment) than that of the alloy made from Zr-sponge is discussed. Oxygen content and its effect on structural changes during heat treatment seems to be responsible for higher creep strength of the first alloy. On the other hand the difference of respective creep strengths is not so significant as to justify production of Zr-2.5%Nb alloy and perhaps of future high-strength Zr alloys (for applications in structural components in reactors in the temperature range of 673 to 773 K) from iodide zirconium. Results of creep and stress-strain (short time) testing are briefly discussed. (author)

Some aspects of anelastic and microplastic creep of pure Al and two Al-alloys

Energy Technology Data Exchange (ETDEWEB)

Sgobba, S. (Lab. de Metallurgie Mecanique, Dept. des Materiaux, Ecole Polytechnique Federale de Lausanne (Switzerland)); Kuenzi, H.U. (Lab. de Metallurgie Mecanique, Dept. des Materiaux, Ecole Polytechnique Federale de Lausanne (Switzerland)); Ilschner, B. (Lab. de Metallurgie Mecanique, Dept. des Materiaux, Ecole Polytechnique Federale de Lausanne (Switzerland))

1993-11-01

Anelastic creep of pure Al, commercial Al-Cu and a binary Al-Cu alloy has been measured at room temperature by means of a high resolution laser interferometer. The irreversible component of the deformation was also quantified from measurements of the anelastic creep recovery. The dependence of the deformation-time curves on thermal treatment and cold work is analyzed. The mechanisms responsible for the room temperature anelastic creep are discussed. Materials loaded below their elastic limit can present either a pure anelastic behavior (commercial Al-Cu) or additional viscoelastic creep (pure Al, high purity Al-Cu). For commercial Al-Cu, the presence of an irreversible deformation appears to be mainly related to the state of the surface. A viscoelastic after effect has been measured for this alloy after a Cu-electroplating treatment. As a typical result for room temperature creep, the irreversible deformation depends logarithmically on load time. (orig.).

Some aspects of anelastic and microplastic creep of pure Al and two Al-alloys

International Nuclear Information System (INIS)

Sgobba, S.; Kuenzi, H.U.; Ilschner, B.

1993-01-01

Anelastic creep of pure Al, commercial Al-Cu and a binary Al-Cu alloy has been measured at room temperature by means of a high resolution laser interferometer. The irreversible component of the deformation was also quantified from measurements of the anelastic creep recovery. The dependence of the deformation-time curves on thermal treatment and cold work is analyzed. The mechanisms responsible for the room temperature anelastic creep are discussed. Materials loaded below their elastic limit can present either a pure anelastic behavior (commercial Al-Cu) or additional viscoelastic creep (pure Al, high purity Al-Cu). For commercial Al-Cu, the presence of an irreversible deformation appears to be mainly related to the state of the surface. A viscoelastic after effect has been measured for this alloy after a Cu-electroplating treatment. As a typical result for room temperature creep, the irreversible deformation depends logarithmically on load time. (orig.)

Creep properties of heat-resistant superalloys for nuclear plants in helium

International Nuclear Information System (INIS)

Shimizu, Shigeki; Satoh, Keisuke; Matsuda, Shozo; Murase, Hirokazu; Fujioka, Junzo.

1979-01-01

In order to estimate the creep and rupture strengths of candidate alloys for the intermediate heat exchanger of VHTR, creep and stress rupture tests in impure helium were conducted on Hastelloy X, Inconel 617, Inconel 625, Incoloy 800 and Incoloy 807 at 900 0 C. The results were discussed in comparison with those in air and the alloys were examined from the point of view of the elevated temperature structural design. The main results obtained are summarized as follows: (1) No appreciable decrease in creep and rupture strengths in helium as compared with those in air is observed on Hastelloy X and Inconel 625. On the contrary, the creep and rupture strengths of Inconel 617 in helium decrease slightly as compared with those in air. In the case of Incoloy 807, the creep strength to cause 1 percent total strain and that to initiate secondary creep increase remarkably in helium as compared with those in air. However, the creep strength to cause initiation of tertiary creep and the rupture strength in helium remarkably decrease as compared with those in air. (2) The order of magnitude of the S 0 value for each material in helium is as follows; Hastelloy X > Inconel 617 > Incoloy 807 > Inconel 625 > Incoloy 800 Meanwhile, that of the S sub(t) value in helium is; Inconel 617 > Hastelloy X > Incoloy 807 > Inconel 625 > Incoloy 800. (author)

Compressive Creep Behaviour of Extruded Mg Alloys at 150 °C

Science.gov (United States)

Fletcher, M.; Bichler, L.; Sediako, D.; Klassen, R.

Wrought magnesium alloy bars, sections and tubes have been extensively used in the aerospace, electronics and automotive industries, where component weight is of concern. The operating temperature of these components is typically limited to below 100°C, since appreciable creep relaxation of the wrought alloys takes place above this temperature.

Creep behavior and wear resistance of Al 5083 based hybrid composites reinforced with carbon nanotubes (CNTs) and boron carbide (B{sub 4}C)

Energy Technology Data Exchange (ETDEWEB)

Alizadeh, Ali [Faculty of Materials & Manufacturing Processes, Malek-e-Ashtar University of Technology, Tehran (Iran, Islamic Republic of); Abdollahi, Alireza, E-mail: alirezaabdollahi1366@gmail.com [Faculty of Materials & Manufacturing Processes, Malek-e-Ashtar University of Technology, Tehran (Iran, Islamic Republic of); Biukani, Hootan [Faculty of Engineering, South Tehran Branch, Islamic Azad University, Tehran (Iran, Islamic Republic of)

2015-11-25

In the current research, aluminum based hybrid composite reinforced with boron carbide (B{sub 4}C) and carbon nanotubes (CNTs) was produced by powder metallurgy method. creep behavior, wear resistance, surface roughness, and hardness of the samples were investigated. To prepare the samples, Al 5083 powder was milled with boron carbide particles and carbon nanotubes using planetary ball mill under argon atmosphere with ball-to-powder weight ratio of 10:1 for 5 h. Afterwards, the milled powders were formed by hot press process at 380{sup °}C and then were sintered at 585{sup °}C under argon atmosphere for 2 h. There was shown to be an increase in hardness values of composite with an increase in B{sub 4}C content. The micrograph of worn surfaces indicate a delamination mechanism due to the presence of CNTs and abrasion mechanism in composite containing 10 vol.%B{sub 4}C. Moreover, it was shown that increasing B{sub 4}C content increases the wear resistance by 3 times under a load of 20 N and 10 times under a load of 10 N compared to CNTs-reinforced composite. surface roughness of the composite containing 5 vol.%CNT has shown to be more than other samples. The results of creep test showed that adding carbon nanotubes increases creep rate of Al 5083 alloy; however, adding B{sub 4}C decreases its creep rate. - Highlights: • Al 5083/(CNTs + B{sub 4}C) hybrid composite was produced by powder metallurgy method. • Creep behavior, wear resistance, surface roughness, and Hardness of samples were investigated. • Addition of CNTs to Al 5083 matrix reduces alloy hardness, wear resistance and creep strength. • By addition of B{sub 4}C and composite hybridization, creep strength and wear resistance increased. • Surface roughness of Al-5 vol.%CNT has shown to be more than other samples.

A life evaluation under creep-fatigue-environment interaction of Ni-base wrought alloys

International Nuclear Information System (INIS)

Hattori, Hiroshi; Kitagawa, Masaki; Ohtomo, Akira; Itoh, Mitsuyoshi

1986-01-01

In order to determine a failure criteria under cyclic loading and affective environment for HTGR systems, a series of strain controlled low-cycle fatigue tests were carried out at HTGR maximum gas temperatures in air, in vacuum and in HTGR helium environments on two nickel-base wrought alloys, namely Inconel 617 and Hastelloy XR. This paper first describes the creep-fatigue-environment properties of these alloys followed by a proposal of an evaluation method of creep-fatigue-environment interaction based on the experimental data to define the more reasonable design criteria, which is a modification of the linear damage summation rule. Second, the creep-fatigue properties of Hastelloy XR at 900 deg C and the result evaluated by this proposed method are shown. This criterion is successfully applied to the life prediction at 900 deg C. In addition, the creep-fatigue properties of Hastelloy XR-II are discussed. (author)

Damage in Creep Aging Process of an Al-Zn-Mg-Cu Alloy: Experiments and Modeling

Directory of Open Access Journals (Sweden)

Chao Lei

2018-04-01

Full Text Available In creep age forming (CAF, large integral panel components of high-strength aluminum alloy can be shaped and strengthened under external elastic loading at an elevated temperature through creep deformation and age hardening, simultaneously. However, the high ribbed structure on panel may induce stress concentration, inhomogeneous plastic deformation and even damage evolution on the bending rib, leading to the difficulty in controlling forming precision and material properties. Therefore, the generation and evolution of damage are necessary to be considered in the design of CAF. Taking 7050 aluminum alloy as the case material, the continuous and interrupted creep aging tests at 165 °C and three stress levels (300, 325, and 350 MPa were conducted, and the corresponding material properties, precipitate, and damage microstructures were studied by mechanical properties tests, transmission electron microscope (TEM and scanning electron microscope (SEM characterizations. With the increase of stress level, the creep deformation occurs easier, the precipitates grow up faster, the creep damage occurs earlier, the growth rate and the size of microvoids increase, the mechanical properties decrease more rapidly, and the dominant mechanism of creep fracture changes from shear to microvoid coalescence. To simulate creep aging behavior with damage, a continuum damage mechanics (CDM based model is calibrated and numerically implemented into ABAQUS solver via CREEP subroutine. The CAF of 7050 aluminum alloy panels with different height ribs were conducted by experiment and FE simulation. The forming process presents a typical stress relaxation phenomenon. The creep damage mainly occurs on the bending rib due to the severe stress concentration. With the increase of rib height, the creep strain and damage degree increase, but the springback decreases.

Interfacial structures and energetics of the strengthening precipitate phase in creep-resistant Mg-Nd-based alloys.

Science.gov (United States)

Choudhuri, D; Banerjee, R; Srinivasan, S G

2017-01-17

The extraordinary creep-resistance of Mg-Nd-based alloys can be correlated to the formation of nanoscale-platelets of β 1 -Mg 3 Nd precipitates, that grow along 〈110〉 Mg in bulk hcp-Mg and on dislocation lines. The growth kinetics of β 1 is sluggish even at high temperatures, and presumably occurs via vacancy migration. However, the rationale for the high-temperature stability of precipitate-matrix interfaces and observed growth direction is unknown, and may likely be related to the interfacial structure and excess energy. Therefore, we study two interfaces- {112} β1 /{100} Mg and {111} β1 /{110} Mg - that are commensurate with β 1 /hcp-Mg orientation relationship via first principles calculations. We find that β 1 acquires plate-like morphology to reduce small lattice strain via the formation of energetically favorable {112} β1 /{100} Mg interfaces, and predict that β 1 grows along 〈110〉 Mg on dislocation lines due to the migration of metastable {111} β1 /{110} Mg . Furthermore, electronic charge distribution of the two interfaces studied here indicated that interfacial-energy of coherent precipitates is sensitive to the population of distorted lattice sites, and their spatial extent in the vicinity of interfaces. Our results have implications for alloy design as they suggest that formation of β 1 -like precipitates in the hcp-Mg matrix will require well-bonded coherent interface along precipitate broad-faces, while simultaneously destabilizing other interfaces.

Taylor Series-Based Long-Term Creep-Life Prediction of Alloy 617

International Nuclear Information System (INIS)

Yin, Song Nan; Kim, Woo Gon; Kim, Yong Wan; Park, Jae Young; Kim, Soen Jin

2010-01-01

In this study, a Taylor series (T-S) model based on the Arrhenius, McVetty, and Monkman-Grant equations was developed using a mathematical analysis. In order to reduce fitting errors, the McVetty equation was transformed by considering the first three terms of the Taylor series equation. The model parameters were accurately determined by a statistical technique of maximum likelihood estimation, and this model was applied to the creep data of alloy 617. The T-S model results showed better agreement with the experimental data than other models such as the Eno, exponential, and L-M models. In particular, the T-S model was converted into an isothermal Taylor series (IT-S) model that can predict the creep strength at a given temperature. It was identified that the estimations obtained using the converted ITS model was better than that obtained using the T-S model for predicting the long-term creep life of alloy 617

Creep crack growth verification testing in alloy 800H tubular components

International Nuclear Information System (INIS)

Hunter, C.P.; Hurst, R.C.

1992-01-01

A method for determining the creep crack growth, CCG, and stress rupture behaviour of Alloy 800H tubular components containing longitudinal notches at 800deg C is described. The presence of the notch is found to systematically weaken the tube, the degree of weaking dependent upon the notch length and depth. The creep crack growth rates, determined from a specially adapted potential drop technique are compared with those obtained from conventional compact tension type specimens. Using the stress intensity factor, K 1 , and the C * parameter as the basis of comparison it is found that the latter gives excellent correlation between the specimen and component behaviour. Finally attention is drawn to the potential dangers of predicting the component creep crack growth behaviour from the data obtained using conventional specimens for a structure sensitive material such as Alloy 800H and conversely to the advantages of the component type CCG tests developed in the present work. (orig.)

Effects of stacking fault energy on the creep behaviors of Ni-base superalloy

International Nuclear Information System (INIS)

Tian, Chenggang; Han, Guoming; Cui, Chuanyong; Sun, Xiaofeng

2014-01-01

Highlights: • The decrease of SFE could promote the dislocation dissociation. • The creep mechanisms were significantly affected by the SFE of the alloys. • The creep properties of the alloys improved with the decrease of SFE by facilitating the microtwinning process. - Abstract: Cobalt in a 23 wt.% Co containing Ni-base superalloys was systematically substituted by Ni in order to study the effects of stacking fault energy (SFE) on the creep mechanisms. The deformation microstructures of the alloys during different creep stages at 725 °C and 630 MPa were investigated by transmission electron microscopy (TEM). The results showed that the creep life increased as the SFE decreased corresponding to the increase of Co content in the alloys. At primary creep stage, the dislocation was difficult to dissociate independent of SFE. In contrast, at secondary and tertiary creep stages the dislocations dissociated at γ/γ′ interface and the partial dislocation started to shear γ′ precipitates, leaving isolated faults (IFs) in high SFE alloy, while the dislocations dissociated in the matrix and the partials swept out the matrix and γ′ precipitates creating extended stacking faults (ESFs) or deformation microtwins which were involved in diffusion-mediated reordering in low SFE alloy. It is suggested that the deformation microtwinning process should be favorable with the decrease of SFE, which could enhance the creep resistance and improve the creep properties of the alloys

Creep of Two-Phase Microstructures for Microelectronic Applications

Energy Technology Data Exchange (ETDEWEB)

Reynolds, Heidi Linch [Univ. of California, Berkeley, CA (United States)

1998-12-01

The mechanical properties of low-melting temperature alloys are highly influenced by their creep behavior. This study investigates the dominant mechanisms that control creep behavior of two-phase, low-melting temperature alloys as a function of microstructure. The alloy systems selected for study were In-Ag and Sn-Bi because their eutectic compositions represent distinctly different microstructure.” The In-Ag eutectic contains a discontinuous phase while the Sn-Bi eutectic consists of two continuous phases. In addition, this work generates useful engineering data on Pb-free alloys with a joint specimen geometry that simulates microstructure found in microelectronic applications. The use of joint test specimens allows for observations regarding the practical attainability of superplastic microstructure in real solder joints by varying the cooling rate. Steady-state creep properties of In-Ag eutectic, Sn-Bi eutectic, Sn-xBi solid-solution and pure Bi joints have been measured using constant load tests at temperatures ranging from O°C to 90°C. Constitutive equations are derived to describe the steady-state creep behavior for In-Ageutectic solder joints and Sn-xBi solid-solution joints. The data are well represented by an equation of the form proposed by Dom: a power-law equation applies to each independent creep mechanism. Rate-controlling creep mechanisms, as a function of applied shear stress, test temperature, and joint microstructure, are discussed. Literature data on the steady-state creep properties of Sn-Bi eutectic are reviewed and compared with the Sn-xBi solid-solution and pure Bi joint data measured in the current study. The role of constituent phases in controlling eutectic creep behavior is discussed for both alloy systems. In general, for continuous, two-phase microstructure, where each phase exhibits significantly different creep behavior, the harder or more creep resistant phase will dominate the creep behavior in a lamellar microstructure. If a

Microstructural Evolution and Creep-Rupture Behavior of Fusion Welds Involving Alloys for Advanced Ultrasupercritical Power Generation

Science.gov (United States)

Bechetti, Daniel H., Jr.

Projections for large increases in the global demand for electric power produced by the burning of fossil fuels, in combination with growing environmental concerns surrounding these fuel sources, have sparked initiatives in the United States, Europe, and Asia aimed at developing a new generation of coal fired power plant, termed Advanced Ultrasupercritical (A-USC). These plants are slated to operate at higher steam temperatures and pressures than current generation plants, and in so doing will offer increased process cycle efficiency and reduced greenhouse gas emissions. Several gamma' precipitation strengthened Ni-based superalloys have been identified as candidates for the hottest sections of these plants, but the microstructural instability and poor creep behavior (compared to wrought products) of fusion welds involving these alloys present significant hurdles to their implementation and a gap in knowledge that must be addressed. In this work, creep testing and in-depth microstructural characterization have been used to provide insight into the long-term performance of these alloys. First, an investigation of the weld metal microstructural evolution as it relates to creep strength reductions in A-USC alloys INCONELRTM 740, NIMONICRTM 263 (INCONEL and NIMONIC are registered trademarks of Special Metals Corporation), and HaynesRTM 282RTM (Haynes and 282 are registered trademarks of Haynes International) was performed. gamma'-precipitate free zones were identified in two of these three alloys, and their development was linked to the evolution of phases that precipitate at the expense of gamma'. Alloy 282 was shown to avoid precipitate free zone formation because the precipitates that form during long term aging in this alloy are poor in the gamma'-forming elements. Next, the microstructural evolution of INCONELRTM 740H (a compositional variant of alloy 740) during creep was investigated. Gleeble-based interrupted creep and creep-rupture testing was used to

Effect of carburizing helium environment on creep behavior of Ni-base heat-resistant alloys for high-temperature gas-cooled reactors

International Nuclear Information System (INIS)

Kurata, Yuji; Ogawa, Yutaka; Nakajima, Hajime

1988-01-01

Creep tests were conducted on Ni-base heat-resistant alloys Hastelloy XR and XR-II, i.e. versions of Hastelloy X modified for nuclear applications, at 950degC using four types of helium environment with different impurity compositions, and mainly the effect of carburization was examined. For all the materials tested, the values of creep rupture time obtained under the carburizing conditions were similar to or longer than those in the commonly used, standard test environment (JAERI Type B helium). The difference among the results was interpreted by the counterbalancing effects of the strengthening due to carburization and possible weakening caused under very low oxidizing potential. In the corrosion monitoring specimens pronounced carbon pick-up was observed in the environment with high carbon activity and very low oxidizing potential. Based on the results obtained in the present and the previous works, it is suggested that a moderate control of the impurity chemistry is important rather than simple purification of the coolant in protecting the material from the environment-enhanced degradation. Either condition with high or low extremes in the oxidizing and carburizing potentials may cause enhanced degradation and thus are desirable to be avoided at the elevated temperatures. (author)

Creep-rupture Behaviors of a Diffusionally Aluminized Alloy 617

Energy Technology Data Exchange (ETDEWEB)

Sah, Injin [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of); Kim, Sung Hwan; Jang, Chang Heui [KAIST, Daejeon (Korea, Republic of)

2015-05-15

In light of the surface reaction, a sufficient Cr content in the matrix leads to an external chromia (Cr{sub 2}O{sub 3}) layer on the surface with the occurrence of internal oxides (Al{sub 2}O{sub 3}) into the matrix. It is well known that the internal oxides will reduce the effective cross-sectional area and/or be a notch under the loading condition. Thus, there have been extensive efforts to improve the oxidation resistance by imposing an aluminized layer (βNiAl or γ-Ni{sub 3}Al) for Ni-Cr alloys. In particular, the extensively formed carbide free zone below the affected substrate will reduce the creep-rupture strengths because the inter-granular carbides present along the grain boundaries effectively impede the grain boundary sliding under high-temperature tensile loading conditions.

Recovery of creep properties of alloy 625 after long term service

International Nuclear Information System (INIS)

Mathew, M.D.; Bhanu Sankara Rao, K.; Mannan, S.L.; Paknikar, K.

2000-01-01

Creep rupture properties of alloy 625, that has been in service for 60000 h at 993 K, have been evaluated between 923 and 1173 K, after subjecting the service exposed material to resolution annealing treatment at 1433 K for one hour. The isostress and Larson-Miller parameter methods were employed to estimate the residual life of the service exposed material. Creep rupture strength and rupture ductility recovered substantially following re-solution annealing. The variations in rupture life and rupture ductility with creep test variables have been rationalised on the basis of the microstructural changes that occurred in the material. (orig.)

Irradiation creep of various ferritic alloys irradiated at {approximately}400{degrees}C in the PFR and FFTF reactors

Energy Technology Data Exchange (ETDEWEB)

Toloczko, M.B.; Garner, F.A. [Pacific Northwest National Lab., Richland, WA (United States); Eiholzer, C.R. [Westinghouse Hanford Company, Richland, WA (United States)

1997-04-01

Three ferritic alloys were irradiated in two fast reactors to doses of 50 dpa or more at temperatures near 400{degrees}C. One martensitic alloy, HT9, was irradiated in both the FFTF and PFR reactors. PFR is the Prototype Fast Reactor in Dourneay, Scotland, and FFTF is the Fast Flux Test Facility in Richland, WA. D57 is a developmental alloy that was irradiated in PFR only, and MA957 is a Y{sub 2}O{sub 3} dispersion-hardened ferritic alloy that was irradiated only in FFTF. These alloys exhibited little or no void swelling at {approximately}400{degrees}C. Depending on the alloy starting condition, these steels develop a variety of non-creep strains early in the irradiation that are associated with phase changes. Each of these alloys creeps at a rate that is significantly lower than that of austenitic steels irradiated in the same experiments. The creep compliance for ferritic alloys in general appears to be {approximately}0.5 x 10{sup {minus}6} MPa{sup {minus}1} dpa{sup {minus}1}, independent of both composition and starting state. The addition of Y{sub 2}O{sub 3} as a dispersoid does not appear to change the creep behavior.

Properties of aluminum alloys tensile, creep, and fatigue data at high and low temperatures

CERN Document Server

1999-01-01

This book compiles more than 300 tables listing typical average properties of a wide range of aluminum alloys. The individual test results were compiled, plotted in various ways, and analyzed. The average values from the tensile and creep tests were then normalized to the published typical room-temperature tensile properties of the respective alloys for easy comparison. This extensive project was done by Alcoa Laboratories over a period of several years. The types of data presented include: Typical Mechanical Properties of Wrought and Cast Aluminum Alloys at Various Temperatures, including tensile properties at subzero temperatures, at temperature after various holding times at the test temperature, and at room temperature after exposure at various temperatures for various holding times; creep rupture strengths for various times at various temperatures; stresses required to generate various amounts of creep in various lengths of time; rotating-beam fatigue strengths; modulus of elasticity as a function of t...

Creep rupture properties of laves phase strengthened Fe--Ta--Cr--W and Fe--Ta--Cr--W--Mo alloys

International Nuclear Information System (INIS)

Singh, S.

1975-12-01

A small addition of tungsten (0.5 at. percent) was shown to have an effect similar to that of molybdenum on the phase transformation characteristics of alloy Ta7Cr (with a nominal composition of 1 at. percent Ta, 7 at. percent Cr, balance Fe). The existence of time-temperature dependent transformation behavior in alloy Ta7Cr0.5W was confirmed. The effect of spheroidization time and temperature on creep strength was determined. In addition, effect of mechanical processing prior to aging, on creep strength was also determined. It was also shown that by suitable modifications of composition, the grain boundary film can be broken during the aging treatment without the use of spheroidization treatment. Microhardness, tensile and creep properties have been determined. Optical metallography and scanning electron microscopy have been used to follow the microstructural changes and mode of fracture. The creep rupture strength of alloy Ta7CrW alloy was found to be superior to many of the best commercially available ferritic alloys at 1200 0 F. (21 fig., 8 tables)

Study of Creep of Alumina-Forming Austenitic Stainless Steel for High-Temperature Energy Applications

Science.gov (United States)

Afonina, Natalie Petrovna

To withstand the high temperature (>700°C) and pressure demands of steam turbines and boilers used for energy applications, metal alloys must be economically viable and have the necessary material properties, such as high-temperature creep strength, oxidation and corrosion resistance, to withstand such conditions. One promising class of alloys potentially capable of withstanding the rigors of aggressive environments, are alumina-forming austenitic stainless steels (AFAs) alloyed with aluminum to improve corrosion and oxidation resistance. The effect of aging on the microstructure, high temperature constant-stress creep behavior and mechanical properties of the AFA-type alloy Fe-20Cr-30Ni-2Nb-5Al (at.%) were investigated in this study. The alloy's microstructural evolution with increased aging time was observed prior to creep testing. As aging time increased, the alloy exhibited increasing quantities of fine Fe2Nb Laves phase dispersions, with a precipitate-free zone appearing in samples with higher aging times. The presence of the L1 2 phase gamma'-Ni3Al precipitate was detected in the alloy's matrix at 760°C. A constant-stress creep rig was designed, built and its operation validated. Constant-stress creep tests were performed at 760°C and 35MPa, and the effects of different aging conditions on creep rate were investigated. Specimens aged for 240 h exhibited the highest creep rate by a factor of 5, with the homogenized sample having the second highest rate. Samples aged for 2.4 h and 24 h exhibited similar low secondary creep rates. Creep tests conducted at 700oC exhibited a significantly lower creep rate compared to those at 760oC. Microstructural analysis was performed on crept samples to explore high temperature straining properties. The quantity and size of Fe2Nb Laves phase and NiAl particles increased in the matrix and on grain boundaries with longer aging time. High temperature tensile tests were performed and compared to room temperature results. The

Creep curve modeling of hastelloy-X alloy by using the theta projection method

International Nuclear Information System (INIS)

Woo Gon, Kim; Woo-Seog, Ryu; Jong-Hwa, Chang; Song-Nan, Yin

2007-01-01

To model the creep curves of the Hastelloy-X alloy which is being considered as a candidate material for the VHTR (Very High Temperature gas-cooled Reactor) components, full creep curves were obtained by constant-load creep tests for different stress levels at 950 C degrees. Using the experimental creep data, the creep curves were modeled by applying the Theta projection method. A number of computing processes of a nonlinear least square fitting (NLSF) analysis was carried out to establish the suitably of the four Theta parameters. The results showed that the Θ 1 and Θ 2 parameters could not be optimized well with a large error during the fitting of the full creep curves. On the other hand, the Θ 3 and Θ 4 parameters were optimized well without an error. For this result, to find a suitable cutoff strain criterion, the NLSF analysis was performed with various cutoff strains for all the creep curves. An optimum cutoff strain range for defining the four Theta parameters accurately was found to be a 3% cutoff strain. At the 3% cutoff strain, the predicted curves coincided well with the experimental ones. The variation of the four Theta parameters as the function of a stress showed a good linearity, and the creep curves were modeled well for the low stress levels. Predicted minimum creep rate showed a good agreement with the experimental data. Also, for a design usage of the Hastelloy-X alloy, the plot of the log stress versus log the time to a 1% strain was predicted, and the creep rate curves with time and a cutoff strain at 950 C degrees were constructed numerically for a wide rang of stresses by using the Theta projection method. (authors)

Indentation Creep Behavior of Nugget Zone of Friction Stir Welded 2014 Aluminum Alloy

Science.gov (United States)

Das, Jayashree; Robi, P. S.; Sankar, M. Ravi

2018-04-01

The present study is aimed at evaluating the creep behavior of the nugget zone of friction welded 2014 Aluminum alloy by indentation creep tests. Impression creep testing was carried out at different temperatures of 300°C, 350°C and 400 °C with stress 124.77MPa, 187.16MPa, 249.55 MPa using a 1.0 mm diameter WC indenter. Experiments were conducted till the curve enters the steady state creep region. Constitutive modeling of creep behavior was carried out considering the temperature, stress and steady state creep rate. Microstructural investigation of the crept specimen at 400°C temperature and 187.16 MPa load was carried out and found that the small precipitates accumulate along the grain boundaries at the favorable conditions of the creep temperature and stress, new precipitates evolve due to the ageing. The grains are broken and deformed due to the creep phenomena.

Tensile and Creep-Rupture Evaluation of a New Heat of Haynes Alloy 25

International Nuclear Information System (INIS)

Shingledecker, J.P.; Glanton, D.B.; Martin, R.L.; Sparks, B.L.; Swindeman, R.W.

2007-01-01

From 1999 to 2006, a program was undertaken within the Materials Science and Technology Division, formerly the Metals and Ceramics Division, of Oak Ridge National Laboratory to characterize the tensile and creep-rupture properties of a newly produced heat of Haynes alloy 25 (L-605). Tensile properties from room temperature to 1100 C were evaluated for base material and welded joints aged up to 12,000 hours at 675 C. Creep and creep-rupture tests were conducted on base metal and cross-weldments from 650 to 950 C. Pressurized tubular creep tests were conducted to evaluate multiaxial creep-rupture response of the material. Over 800,000 hours of creep test data were generated during the test program with the longest rupture tests extending beyond 38,000 hours, and the longest creep-rate experiments exceeding 40,000 hours

Mechanism-based modeling of solute strengthening: application to thermal creep in Zr alloy

Energy Technology Data Exchange (ETDEWEB)

Tome, Carlos [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Wen, Wei [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Capolungo, Laurent [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

2017-08-01

This report focuses on the development of a physics-based thermal creep model aiming to predict the behavior of Zr alloy under reactor accident condition. The current models used for this kind of simulations are mostly empirical in nature, based generally on fits to the experimental steady-state creep rates under different temperature and stress conditions, which has the following limitations. First, reactor accident conditions, such as RIA and LOCA, usually take place in short times and involve only the primary, not the steady-state creep behavior stage. Moreover, the empirical models cannot cover the conditions from normal operation to accident environments. For example, Kombaiah and Murty [1,2] recently reported a transition between the low (n~4) and high (n~9) power law creep regimes in Zr alloys depending on the applied stress. Capturing such a behavior requires an accurate description of the mechanisms involved in the process. Therefore, a mechanism-based model that accounts for the evolution with time of microstructure is more appropriate and reliable for this kind of simulation.

Effect of Gd–Ca combined additions on the microstructure and creep properties of Mg–7Al–1Si alloys

International Nuclear Information System (INIS)

Liu, Jian; Wang, Wuxiao; Zhang, Sha; Zhang, Dongjie; Zhang, Haiyan

2015-01-01

Highlights: • The effect of compound addition of Ca and Gd on the microstructure and creep properties of Mg–7Al–1Si alloys was investigated. • After adding 1 wt.% of (Ca + Gd), the creep strain and steady-state creep rate were reduced by about 80% and 84%, respectively. • After adding 1 wt.% of (Ca + Gd), the creep properties of Mg–7Al–1Si alloys were superior to that containing single Gd additive. • The improvement of creep properties after compound addition of Gd and Ca is a result of multiple factors. - Abstract: The microstructure and creep properties of Mg–7Al–1Si alloys with combined additions of alkaline earth element Ca and rare earth element (RE) Gd were investigated using scanning electron microscope (SEM), optical microscope, energy dispersive spectrometer (EDS), X-ray diffraction (XRD), and compressive creep tests. It was found that the combined additions of Ca and Gd contributed to grain refinement, modification of the morphology of coarse Chinese script Mg 2 Si phase, and reduction of β-Mg 17 Al 12 content. Mg–7Al–1Si alloys containing 1 wt.% compound modifier (0.5 wt.% Gd + 0.5 wt.% Ca) exhibited the minimal steady-state creep rate, and were even superior to Mg–7Al–1Si alloys containing single Gd addition. The great improvement of creep properties is mainly attributed to the reduction in the amount and continuity of eutectic β-Mg 17 Al 12 phase, morphology modification of Mg 2 Si phase, solution strengthening of Gd, as well as the formation of thermally stable intermetallic Al 2 Gd, which acted as an effective barrier against grain boundary sliding and dislocation movement

"A New Class of Creep Resistant Oxide/Oxide Ceramic Matrix Composites"

Energy Technology Data Exchange (ETDEWEB)

Dr. Mohit Jain, Dr. Ganesh Skandan, Prof. Roger Cannon, Rutgers University

2007-03-30

Despite recent progress in the development of SiC-SiC ceramic matrix composites (CMCs), their application in industrial gas turbines for distributed energy (DE) systems has been limited. The poor oxidation resistance of the non-oxide ceramics warrants the use of envrionmental barrier coatings (EBCs), which in turn lead to issues pertaining to life expectancy of the coatings. On the other hand, oxide/oxide CMCs are potential replacements, but their use has been limited until now due to the poor creep resistance at high temperatures, particularly above 1200 oC: the lack of a creep resistant matrix has been a major limiting factor. Using yttrium aluminum garnet (YAG) as the matrix material system, we have advanced the state-of-the-art in oxide/oxide CMCs by introducing innovations in both the structure and composition of the matrix material, thereby leading to high temperature matrix creep properties not achieved until now. An array of YAG-based powders with a unique set of particle characteristics were produced in-house and sintered to full density and compressive creep data was obtained. Aided in part by the composition and the microstructure, the creep rates were found to be two orders of magnitude smaller than the most creep resistant oxide fiber available commercially. Even after accounting for porosity and a smaller matrix grain size in a practical CMC component, the YAG-based matrix material was found to creep slower than the most creep resistant oxide fiber available commercially.

Influence of multi-step heat treatments in creep age forming of 7075 aluminum alloy: Optimization for springback, strength and exfoliation corrosion

Energy Technology Data Exchange (ETDEWEB)

Arabi Jeshvaghani, R.; Zohdi, H. [Department of Materials Engineering, Tarbiat Modares University, P.O. Box 14115-143, Tehran (Iran, Islamic Republic of); Shahverdi, H.R., E-mail: shahverdi@modares.ac.ir [Department of Materials Engineering, Tarbiat Modares University, P.O. Box 14115-143, Tehran (Iran, Islamic Republic of); Bozorg, M. [Department of Materials Engineering, Tarbiat Modares University, P.O. Box 14115-143, Tehran (Iran, Islamic Republic of); Hadavi, S.M.M. [School of Materials Science and Engineering, MA University of Technology, P.O. Box 16765-3197, Tehran (Iran, Islamic Republic of)

2012-11-15

Multi-step heat treatments comprise of high temperature forming (150 Degree-Sign C/24 h plus 190 Degree-Sign C for several minutes) and subsequent low temperature forming (120 Degree-Sign C for 24 h) is developed in creep age forming of 7075 aluminum alloy to decrease springback and exfoliation corrosion susceptibility without reduction in tensile properties. The results show that the multi-step heat treatment gives the low springback and the best combination of exfoliation corrosion resistance and tensile strength. The lower springback is attributed to the dislocation recovery and more stress relaxation at higher temperature. Transmission electron microscopy observations show that corrosion resistance is improved due to the enlargement in the size and the inter-particle distance of the grain boundaries precipitates. Furthermore, the achievement of the high strength is related to the uniform distribution of ultrafine {eta} Prime precipitates within grains. - Highlights: Black-Right-Pointing-Pointer Creep age forming developed for manufacturing of aircraft wing panels by aluminum alloy. Black-Right-Pointing-Pointer A good combination of properties with minimal springback is required in this component. Black-Right-Pointing-Pointer This requirement can be improved through the appropriate heat treatments. Black-Right-Pointing-Pointer Multi-step cycles developed in creep age forming of AA7075 for improving of springback and properties. Black-Right-Pointing-Pointer Results indicate simultaneous enhancing the properties and shape accuracy (lower springback).

Electrical Resistance Alloys and Low-Expansion Alloys

DEFF Research Database (Denmark)

Kjer, Torben

1996-01-01

The article gives an overview of electrical resistance alloys and alloys with low thermal expansion. The electrical resistance alloys comprise resistance alloys, heating alloys and thermostat alloys. The low expansion alloys comprise alloys with very low expansion coefficients, alloys with very low...... thermoelastic coefficients and age hardenable low expansion alloys....

Creep deformation, creep damage accumulation and residual life prediction for three low alloyed CrMo-steels

International Nuclear Information System (INIS)

Kondyr, A.; Sandstroem, R.; Samuelsson, A.

1979-02-01

A detailed analysis of creep strain results for three low alloyed steels of type 0.5 Mo, 1 Cr-0.5 Mo and 2.25 Cr-1 Mo has been undertaken. The results show that, excluding the primary stage, the true strain rate can be described by a simple analytical expression dE/dt = Aexp(B.E) where A and B are constants at constant stress and temperature. A is approximately equal to the minimum strain rate and B inversly proportional to the fracture strain. Furthermore, 1/AB equals the time t sub(r) to rupture. The residual life fraction in creep can be expressed as exp(-B.E) = 1-t/t sub(r) and a creep damage function μ is introduced as μ = 1-ABt. The expressions for strain rate and damage are shown to be a special case of the Rabotnov-Kachanov equations. The analysis has been generalized to account for multiaxial stress states, and as an example creep in a tube with internal pressure is considered. (author)

Creep properties of superalloys for the HTGR in impure helium environments

International Nuclear Information System (INIS)

Kawakami, H.; Nakanishi, T.

1981-01-01

This paper describes creep behaviors of two heat resistant alloys, Hastelloy X and Incoloy 800, in helium environments of the HTGR. In impure helium environments, these alloys are susceptible to carburization and oxidization. We have investigated these effects separately, and related them to the creep behaviors of the alloys. Experiments were carried out at 900 0 C both in helium and in air. Carburization results in decrease of secondary creep strain rate and delay of tertiary creep initiation. Oxidization caused decrease in tertiary creep strain rate of Hastelloy X, but did not that of Incoloy 800. Enhancement in tertiary creep strain rate of Hastelloy X in a very weakly oxidizing environment was confirmed in creep crack growth experiment using notched plate specimens. The rupture time of Hastelloy X in helium was short when compared with in air. Stress versus rupture time curves for both environments were parallel up to 5000 hours test, and a ratio of rupture stress in helium to that in air was about 0.9. In case of Incoloy 800, rupture time in helium was markedly prolonged as compared with that in air. (orig.)

Microstructure-sensitive modelling of dislocation creep in polycrystalline FCC alloys: Orowan theory revisited

Energy Technology Data Exchange (ETDEWEB)

Galindo-Nava, E.I., E-mail: eg375@cam.ac.uk; Rae, C.M.F.

2016-01-10

A new approach for modelling dislocation creep during primary and secondary creep in FCC metals is proposed. The Orowan equation and dislocation behaviour at the grain scale are revisited to include the effects of different microstructures such as the grain size and solute atoms. Dislocation activity is proposed to follow a jog-diffusion law. It is shown that the activation energy for cross-slip E{sub cs} controls dislocation mobility and the strain increments during secondary creep. This is confirmed by successfully comparing E{sub cs} with the experimentally determined activation energy during secondary creep in 5 FCC metals. It is shown that the inverse relationship between the grain size and dislocation creep is attributed to the higher number of strain increments at the grain level dominating their magnitude as the grain size decreases. An alternative approach describing solid solution strengthening effects in nickel alloys is presented, where the dislocation mobility is reduced by dislocation pinning around solute atoms. An analysis on the solid solution strengthening effects of typical elements employed in Ni-base superalloys is also discussed. The model results are validated against measurements of Cu, Ni, Ti and 4 Ni-base alloys for wide deformation conditions and different grain sizes.

Critical survey of the neutron-induced creep behaviour of steel alloys for the fusion reactor materials programme

International Nuclear Information System (INIS)

Hausen, H.

1985-01-01

The differences between the irradiation environment of a fission reactor and that of a fusion reactor are respectively described in relation to the radiation damage found and expected in the two types of nuclear reactor. It is shown that the microstructure developing for instance in stainless steel alloys is almost invariant to whether the production rate of helium is high or low. The finding is valid up to neutron doses corresponding to about 60 dpa. For this reason, irradiation creep data obtained in fission reactors may be used, with caution, for predicting creep behaviour in fusion reactors.It was further recognized that irradiation creep performed with high energy particles from an accelerator, yields results which are comparable to those obtained in fission reactors. For this reason, simulation creep experiments are found to be valuable for the development of irradiation creep resistant materials using, for example, high energy electrons or protons. Such kind of experiments are performed in many laboratories. For irradiation doses larger than 60 dpa, predictions with respect to creep rates in fission and fusion reactors are difficult. In end-of-life tests, which concern swelling, ductility, tensile properties, rupture, fatigue and embrittlement, the presence of helium, due to its production rate being much higher in most materials exposed to 14 MeV neutrons than to fission neutrons, may be of great importance

INVESTIGATION ON NEW CREEP- AND OXIDATION-RESISTANT MATERIALS

Czech Academy of Sciences Publication Activity Database

Khalaj, O.; Mašek, B.; Jirková, H.; Ronešová, A.; Svoboda, Jiří

2015-01-01

Roč. 49, č. 4 (2015), s. 645-651 ISSN 1580-2949 R&D Projects: GA ČR(CZ) GA14-24252S Institutional support: RVO:68081723 Keywords : ODS steel * alloys * composite * creep * Fe-Al Subject RIV: JI - Composite Material s Impact factor: 0.439, year: 2015

Phase Transformation and Creep Behavior in Ti50Pd30Ni20 High Temperature Shape Memory Alloy in Compression

Science.gov (United States)

Kumar, Parikshith K.; Desai, Uri; Monroe, James; Lagoudas, Dimitris C.; Karaman, Ibrahim; Noebe, Ron; Bigelow, Glenn

2010-01-01

The creep behavior and the phase transformation of Ti50Pd30Ni20 High Temperature Shape Memory Alloy (HTSMA) is investigated by standard creep tests and thermomechanical tests. Ingots of the alloy are induction melted, extruded at high temperature, from which cylindrical specimens are cut and surface polished. A custom high temperature test setup is assembled to conduct the thermomechanical tests. Following preliminary monotonic tests, standard creep tests and thermally induced phase transformation tests are conducted on the specimen. The creep test results suggest that over the operating temperatures and stresses of this alloy, the microstructural mechanisms responsible for creep change. At lower stresses and temperatures, the primary creep mechanism is a mixture of dislocation glide and dislocation creep. As the stress and temperature increase, the mechanism shifts to predominantly dislocation creep. If the operational stress or temperature is raised even further, the mechanism shifts to diffusion creep. The thermally induced phase transformation tests show that actuator performance can be affected by rate independent irrecoverable strain (transformation induced plasticity + retained martensite) as well as creep. The rate of heating and cooling can adversely impact the actuators performance. While the rate independent irrecoverable strain is readily apparent early in the actuators life, viscoplastic strain continues to accumulate over the lifespan of the HTSMA. Thus, in order to get full actuation out of the HTSMA, the heating and cooling rates must be sufficiently high enough to avoid creep.

Effect of Process Parameters on Fatigue and Fracture Behavior of Al-Cu-Mg Alloy after Creep Aging

Directory of Open Access Journals (Sweden)

Lihua Zhan

2018-04-01

Full Text Available A set of creep aging tests at different aging temperatures and stress levels were carried out for Al-Cu-Mg alloy, and the effects of creep aging on strength and fatigue fracture behavior were studied through tensile tests and fatigue crack propagation tests. The microstructures were further analyzed by using scanning electron microscopy (SEM and transmission electron microscopy (TEM. The results show that temperature and stress can obviously affect the creep behavior, mechanical properties, and fatigue life of Al-Cu-Mg alloy. As the aging temperature increases, the fatigue life of alloy first increases, and then decreases. The microstructure also displays a transition from the Guinier-Preston-Bagaryatsky (GPB zones to the precipitation of S phase in the grain interior. However, the precipitation phases grow up and become coarse at excessive temperatures. Increasing stress can narrow the precipitation-free zone (PFZ at the grain boundary and improve the fatigue life, but overhigh stress can produce the opposite result. In summary, the fatigue life of Al-Cu-Mg alloy can be improved by fine-dispersive precipitation phases and a narrow PFZ in a suitable creep aging process.

Modelling of degradation processes in creep resistant steels through accelerated creep tests after long-term isothermal ageing

Energy Technology Data Exchange (ETDEWEB)

Sklenicka, V.; Kucharova, K.; Svoboda, M.; Kroupa, A.; Kloc, L. [Academy of Sciences of the Czech Republic, Brno (Czech Republic). Inst. of Physics of Materials; Cmakal, J. [UJP PRAHA a.s., Praha-Zbraslav (Czech Republic)

2010-07-01

Creep behaviour and degradation of creep properties of creep resistant materials are phenomena of major practical relevance, often limiting the lives of components and structures designed to operate for long periods under stress at elevated and/or high temperatures. Since life expectancy is, in reality, based on the ability of the material to retain its high-temperature creep strength for the projected designed life, methods of creep properties assessment based on microstructural evolution in the material during creep rather than simple parametric extrapolation of short-term creep tests are necessary. In this paper we will try to further clarify the creep-strength degradation of selected advanced creep resistant steels. In order to accelerate some microstructural changes and thus to simulate degradation processes in long-term service, isothermal ageing at 650 C for 10 000 h was applied to P91 and P23 steels in their as-received states. The accelerated tensile creep tests were performed at temperature 600 C in argon atmosphere on all steels both in the as-received state and after long-term isothermal ageing, in an effort to obtain a more complete description of the role of microstructural stability in high temperature creep of these steels. Creep tests were followed by microstructural investigations by means of both transmission and scanning electron microscopy and by the thermodynamic calculations. The applicability of the accelerated creep tests was verified by the theoretical modelling of the phase equilibria at different temperatures. It is suggested that under restructed oxidation due to argon atmosphere microstructural instability is the main detrimental process in the long-term degradation of the creep rupture strength of these steels. (orig.)

Multi Resolution In-Situ Testing and Multiscale Simulation for Creep Fatigue Damage Analysis of Alloy 617

Energy Technology Data Exchange (ETDEWEB)

Liu, Yongming [Arizona State Univ., Tempe, AZ (United States). School for Engineering of Matter, Transport and Energy; Oskay, Caglar [Vanderbilt Univ., Nashville, TN (United States). Dept. of Civil and Environmental Engineering

2017-04-30

This report outlines the research activities that were carried out for the integrated experimental and simulation investigation of creep-fatigue damage mechanism and life prediction of Nickel-based alloy, Inconel 617 at high temperatures (950° and 850°). First, a novel experimental design using a hybrid control technique is proposed. The newly developed experimental technique can generate different combinations of creep and fatigue damage by changing the experimental design parameters. Next, detailed imaging analysis and statistical data analysis are performed to quantify the failure mechanisms of the creep fatigue of alloy 617 at high temperatures. It is observed that the creep damage is directly associated with the internal voids at the grain boundaries and the fatigue damage is directly related to the surface cracking. It is also observed that the classical time fraction approach does not has a good correlation with the experimental observed damage features. An effective time fraction parameter is seen to have an excellent correlation with the material microstructural damage. Thus, a new empirical damage interaction diagram is proposed based on the experimental observations. Following this, a macro level viscoplastic model coupled with damage is developed to simulate the stress/strain response under creep fatigue loadings. A damage rate function based on the hysteresis energy and creep energy is proposed to capture the softening behavior of the material and a good correlation with life prediction and material hysteresis behavior is observed. The simulation work is extended to include the microstructural heterogeneity. A crystal plasticity finite element model considering isothermal and large deformation conditions at the microstructural scale has been developed for fatigue, creep-fatigue as well as creep deformation and rupture at high temperature. The model considers collective dislocation glide and climb of the grains and progressive damage accumulation of

Multiaxial Creep-Fatigue and Creep-Ratcheting Failures of Grade 91 and Haynes 230 Alloys Toward Addressing Design Issues of Gen IV Nuclear Power Plants

Energy Technology Data Exchange (ETDEWEB)

Hassan, Tasnim [North Carolina State Univ., Raleigh, NC (United States); Lissenden, Cliff [Penn State Univ., University Park, PA (United States); Carroll, Laura [Idaho National Lab. (INL), Idaho Falls, ID (United States)

2015-04-01

The proposed research will develop systematic sets of uniaxial and multiaxial experimental data at a very high temperature (850-950°C) for Alloy 617. The loading histories to be prescribed in the experiments will induce creep-fatigue and creep-ratcheting failure mechanisms. These experimental responses will be scrutinized in order to quantify the influences of temperature and creep on fatigue and ratcheting failures. A unified constitutive model (UCM) will be developed and validated against these experimental responses. The improved UCM will be incorporated into the widely used finite element commercial software packages ANSYS. The modified ANSYS will be validated so that it can be used for evaluating the very high temperature ASME-NH design-by-analysis methodology for Alloy 617 and thereby addressing the ASME-NH design code issues.

Multiaxial Creep-Fatigue and Creep-Ratcheting Failures of Grade 91 and Haynes 230 Alloys Toward Addressing Design Issues of Gen IV Nuclear Power Plants

International Nuclear Information System (INIS)

Hassan, Tasnim; Lissenden, Cliff; Carroll, Laura

2015-01-01

The proposed research will develop systematic sets of uniaxial and multiaxial experimental data at a very high temperature (850-950°C) for Alloy 617. The loading histories to be prescribed in the experiments will induce creep-fatigue and creep-ratcheting failure mechanisms. These experimental responses will be scrutinized in order to quantify the influences of temperature and creep on fatigue and ratcheting failures. A unified constitutive model (UCM) will be developed and validated against these experimental responses. The improved UCM will be incorporated into the widely used finite element commercial software packages ANSYS. The modified ANSYS will be validated so that it can be used for evaluating the very high temperature ASME-NH design-by-analysis methodology for Alloy 617 and thereby addressing the ASME-NH design code issues.

Influence of Z-phase on long-term creep stability of martensitic 9-12% Cr steels

Energy Technology Data Exchange (ETDEWEB)

Danielsen, Hilmar K. [Technical Univ. of Denmark, Lyngby (Denmark). Dept. of Mechanical Engineering; Hald, John [DONG Energy A/S (Denmark); Vattenfall (Denmark)

2010-07-01

The long-term creep strength of the new generation of martensitic creep resistant 9-12%Cr steels since the well-known steel Grade 91 relies strongly on particle strengthening by fine Mn nitrides based on V and Nb. During long-term high-temperature exposures the Mn nitrides may be replaced by the thermodynamically more stable Z-phases (Cr(V,Nb)N) causing a breakdown in creep strength. Cr contents above 10.5% strongly accelerate Z-phase precipitation, which explains the lack of success for all attempts to develop martensitic creep resistant steels with high Cr content for oxidation protection. However 9%Cr steels do not seem to be affected by the Z-phase. Careful control of the Z-phase precipitation process has led to the design of experimental 12%Cr martensitic steels strengthened by fine Z-phase nitrides based on Nb or Ta. Such steels may again enable the combination of high strength and oxidation resistance in the same alloy. This opens a new pathway for further alloy development of the heat resistant martensitic steels. (orig.)

Degradation of mechanical properties of CrMo creep resistant steel operating under conditions of creep

Directory of Open Access Journals (Sweden)

J. Michel

2012-01-01

Full Text Available Mechanical properties of a steam tube made of CrMo creep resistant steel are analysed in this contribution after up to 2,6•105 hours service life in creep conditions at temperature 530 °C and calculated stress level in the tube wall 46,5 MPa. During service life there were in the steel gradual micro structure changes, fi rst pearlite spheroidization, precipitation, coaugulation and precipitate coarsening. Nevertheless the strength and deformation properties of the steel (Re, Rm, A5, Z, and the resistance to brittle fracture and the creep strength limit, were near to unchanged after 2,1•105 hours in service. The steam tube is now in service more than 2,6•105 h.

Oxidation and creep failure of alloy 617 foils at high temperature

Energy Technology Data Exchange (ETDEWEB)

Sharma, S.K.; Ko, G.D.; Li, F.X. [Department of Mechanical Engineering, Chonnam National University, Gwangju 500 757 (Korea, Republic of); Kang, K.J. [Department of Mechanical Engineering, Chonnam National University, Gwangju 500 757 (Korea, Republic of)], E-mail: kjkang@chonnam.ac.kr

2008-08-31

The microstructure of thermally grown oxides (TGO) and the creep properties of alloy 617 were investigated. Oxidation and creep tests were performed on 100 {mu}m thick foils at 800-1000 deg. C in air environment, while the thickness of TGO was monitored in situ. According to energy dispersive X-ray (EDX) mapping micrographs observation, superficial dense oxides, chromia (Cr{sub 2}O{sub 3}), which was thermodynamically unstable at 1000 deg. C, and discrete internal oxides, alumina ({alpha}-Al{sub 2}O{sub 3}), were found. Consequently, the weight of the foil specimen decreased due to the spalling and volatilization of the Cr{sub 2}O{sub 3} oxide layer after an initial weight-gaining. Secondary and tertiary creeps were observed at 800 deg. C, while the primary, secondary and tertiary creeps were observed at 1000 deg. C. Dynamic recrystallization occurred at 800 deg. C and 900 deg. C, while partial dynamic recrystallization at 1000 deg. C. The apparent activation energy, Q{sub app}, for the creep deformation was 271 kJ/mol, which was independent of the applied stress.

Elevated temperature creep behavior of Inconel alloy 625

International Nuclear Information System (INIS)

Purohit, A.; Burke, W.F.

1984-07-01

Inconel 625 in the solution-annealed condition has been selected as the clad material for the fuel and control rod housing assemblies of the Upgraded Transient Reactor Test Facility (TREAT Upgrade or TU). The clad is expected to be subjected to temperatures up to about 1100 0 C. Creep behavior for the temperature range of 800 0 C to 1100 0 C of Inconel alloy 625, in four distinct heat treated conditions, was experimentally evaluated

Creep deformation mechanisms in a γ titanium aluminide

Energy Technology Data Exchange (ETDEWEB)

Abdallah, Zakaria [Institute of Structural Materials, College of Engineering, Bay Campus, Swansea University, Swansea SA18EN (United Kingdom); Ding, Rengen [School of Metallurgy and Materials, University of Birmingham, Edgbaston, Birmingham B152TT (United Kingdom); Martin, Nigel; Dixon, Mark [Rolls-Royce plc, P.O. Box 31, Derby DE248BJ (United Kingdom); Bache, Martin [Institute of Structural Materials, College of Engineering, Bay Campus, Swansea University, Swansea SA18EN (United Kingdom)

2016-09-15

Titanium aluminides (TiAl) are considered as potential alternatives to replace nickel-based alloys of greater density for selected components within future gas turbine aero-engines. This is attributed to the high specific strength as well as the good oxidation resistance at elevated temperatures. The gamma (γ) titanium aluminide system Ti-45Al-2Mn-2Nb has previously demonstrated promising performance in terms of its physical and mechanical properties. The main aim of the current study, which is a continuation of a previously published paper, aims at evaluating the performance of this titanium aluminide system under high temperature creep conditions. Of particular interest, the paper is strongly demonstrating the precise capability of the Wilshire Equations technique in predicting the long-term creep behaviour of this alloy. Moreover, it presents a physically meaningful understanding of the various creep mechanisms expected under various testing conditions. To achieve this, two creep specimens, tested under distinctly different stress levels at 700 °C have been extensively examined. Detailed microstructural investigations and supporting transmission electron microscopy (TEM) have explored the differences in creep mechanisms active under the two stress regimes, with the deformation mechanisms correlated to Wilshire creep life prediction curves.

Applicability of the θ projection method to creep curves of Ni-22Cr-18Fe-9Mo alloy

International Nuclear Information System (INIS)

Kurata, Yuji; Utsumi, Hirokazu

1998-01-01

Applicability of the θ projection method has been examined for constant-load creep test results at 800 and 1000degC on Ni-22Cr-18Fe-9Mo alloy in the solution-treated and aged conditions. The results obtained are as follows: (1) Normal type creep curves obtained at 1000degC for aged Ni-22Cr-18Fe-9Mo alloy are fitted using the θ projection method with four θ parameters. Stress dependence of θ parameters can be expressed in terms of simple equations. (2) The θ projection method with four θ parameters cannot be applied to the remaining creep curves where most of the life is occupied by a tertiary creep stage. Therefore, the θ projection method consisting of only the tertiary creep component with two θ parameters was applied. The creep curves can be fitted using this method. (3) If the θ projection method with four θ or two θ parameters is applied to creep curves in accordance with creep curve shapes, creep rupture time can be predicted in terms of formulation of stress and/or temperature dependence of θ parameters. (author)

Creep-rupture behavior of 2-1/4 Cr-1 Mo steel, Alloy 800H and Hastelloy Alloy X in a simulated HTGR helium environment

International Nuclear Information System (INIS)

Lai, G.Y.; Wolwowicz, R.J.

1979-12-01

Creep-rupture testing was conducted on 1 1/4 Cr-1 Mo steel, Alloy 800H and Hastelloy Alloy X in flowing helium containing nominal concentration of following gases: 1500 μatm H 2 , 450 μatm CO, 50 μatm CH 4 , 50 μatm H 2 O and 5 μatm CO 2 . This environment is believed to represent maximum permissible levels of impurities in the primary coolant for the steam-cycle system of a high-temperature gas-cooled reactor (HTGR) when it is operating continuously with a water and/or steam leak at technical specification limits. Two or three heats of material for each alloy were investigated. Tests were conducted at 482 0 C and 760 0 C (1200 0 F and 1400 0 F) for Alloy 800H, and at 760 0 C and 871 0 C (1400 0 F and 1600 0 F) for Hastelloy Alloy X for times up to 10,000 h. Selected tests were performed on same heat of material in both air and helium environments to make a direct comparison of creep-rupture behaviors between two environments. Metallurgical evaluation was performed on selected post test specimens with respect to gas-metal interactions which included oxidation, carburization and/or decarburization. Correlation between gaseous corrosion and creep-rupture behavior was attempted. Limited tests were also performed to investigate the specimen size effects on creep-rupture behavior in the helium environment

Monitoring microstructural evolution of alloy 617 with non-linear acoustics for remaining useful life prediction; multiaxial creep-fatigue and creep-ratcheting

International Nuclear Information System (INIS)

Lissenden, Cliff; Hassan, Tasnin; Rangari, Vijaya

2014-01-01

The research built upon a prior investigation to develop a unified constitutive model for design-@by-@analysis of the intermediate heat exchanger (IHX) for a very high temperature reactor (VHTR) design of next generation nuclear plants (NGNPs). Model development requires a set of failure data from complex mechanical experiments to characterize the material behavior. Therefore uniaxial and multiaxial creep-@fatigue and creep-@ratcheting tests were conducted on the nickel base Alloy 617 at 850 and 950°C. The time dependence of material behavior, and the interaction of time dependent behavior (e.g., creep) with ratcheting, which is an increase in the cyclic mean strain under load-@controlled cycling, are major concerns for NGNP design. This research project aimed at characterizing the microstructure evolution mechanisms activated in Alloy 617 by mechanical loading and dwell times at elevated temperature. The acoustic harmonic generation method was researched for microstructural characterization. It is a nonlinear acoustics method with excellent potential for nondestructive evaluation, and even online continuous monitoring once high temperature sensors become available. It is unique because it has the ability to quantitatively characterize microstructural features well before macroscale defects (e.g., cracks) form. The nonlinear acoustics beta parameter was shown to correlate with microstructural evolution using a systematic approach to handle the complexity of multiaxial creep-@fatigue and creep-@ratcheting deformation. Mechanical testing was conducted to provide a full spectrum of data for: thermal aging, tensile creep, uniaxial fatigue, uniaxial creep-@fatigue, uniaxial creep-ratcheting, multiaxial creep-fatigue, and multiaxial creep-@ratcheting. Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM), and Optical Microscopy were conducted to correlate the beta parameter with individual microstructure mechanisms. We researched application of the

The creep and intergranular cracking behavior of Ni-Cr-Fe-C alloys in 360 degree C water

International Nuclear Information System (INIS)

Angeliu, T.M.; Paraventi, D.J.; Was, G.S.

1995-01-01

Mechanical testing of controlled-purity Ni-xCr-9Fe-yC alloys at 360 C revealed an environmental enhancement in IG cracking and time-dependent deformation in high purity and primary water over that exhibited in argon. Dimples on the IG facets indicate a creep void nucleation and growth failure mode. IG cracking was primarily located at the interior of the specimen and not necessarily linked to direct contact with the environment. Controlled potential CERT experiments showed increases in IG cracking as the applied potential decreased, suggesting that hydrogen is detrimental to the mechanical properties. It is proposed that the environment, through the presence of hydrogen, enhances IG cracking by enhancing the matrix dislocation mobility. This is based on observations that dislocation-controlled creep controls the IG cracking of controlled-purity Ni-xCr-9Fe-yC in argon at 360 C and grain boundary cavitation and sliding results that show the environmental enhancement of the creep rate is primarily due to an increase in matrix plastic deformation. However, controlled potential CLT experiments did not exhibit a change in the creep rate as the applied potential decreased. While this does not clearly support hydrogen assisted creep, the material may already be saturated with hydrogen at these applied potentials and thus no effect was realized. Chromium and carbon decrease the IG cracking in high purity and primary water by increasing the creep resistance. The surface film does not play a significant role in the creep or IG cracking behavior under the conditions investigated

Properties of super alloys for high temperature gas cooled reactor

International Nuclear Information System (INIS)

Izaki, Takashi; Nakai, Yasuo; Shimizu, Shigeki; Murakami, Takashi

1975-01-01

The existing data on the properties at high temperature in helium gas of iron base super alloys. Incoloy-800, -802 and -807, nickel base super alloys, Hastelloy-X, Inconel-600, -617 and -625, and a casting alloy HK-40 were collectively evaluated from the viewpoint of the selection of material for HTGRs. These properties include corrosion resistance, strength and toughness, weldability, tube making, formability, radioactivation, etc. Creep strength was specially studied, taking into consideration the data on the creep characteristics in the actual helium gas atmosphere. The necessity of further long run creep data is suggested. Hastelloy-X has completely stable corrosion resistance at high temperature in helium gas. Incoloy 800 and 807 and Inconel 617 are not preferable in view of corrosion resistance. The creep strength of Inconel 617 extraporated to 1,000 deg C for 100,000 hours in air was the greatest rupture strength of 0.6 kg/mm 2 in all above alloys. However, its strength in helium gas began to fall during a relatively short time, so that its creep strength must be re-evaluated in the use for long time. The radioactivation and separation of oxide film in primary construction materials came into question, Inconel 617 and Incoloy 807 showed high induced radioactivity intensity. Generally speaking, in case of nickel base alloys such as Hastelloy-X, oxide film is difficult to break away. (Iwakiri, K.)

Evaluation on materials performance of Hastelloy Alloy XR for HTTR uses-5 (Creep properties of base metal and weldment in air)

International Nuclear Information System (INIS)

Watanabe, Katsutoshi; Nakajima, Hajime; Koikegami, Hajime; Higuchi, Makoto; Nakanishi, Tsuneo; Saitoh, Teiichiro; Takatsu, Tamao.

1994-01-01

Creep properties of weldment made from Hastelloy Alloy XR base metals and filler metals for the High Temperature Engineering Test Reactor (HTTR) components were examined by means of creep and creep rupture tests at 900 and 950degC in air. The results obtained are as follows: creep rupture strength was nearly equal or higher than that of Hastelloy Alloy XR master curve and was much higher than design creep rupture strength [S R ]. Furthermore, creep rupture strength and ductility of the present filler metal was in the data band in comparison with those of the previous filler metals. It is concluded from these reasons that this filler metal has fully favorable properties for HTTR uses. (author)

Effect of silver and indium addition on mechanical properties and indentation creep behavior of rapidly solidified Bi–Sn based lead-free solder alloys

International Nuclear Information System (INIS)

Shalaby, Rizk Mostafa

2013-01-01

Mechanical properties and indentation creep of the melt-spun process Bi–42 wt%Sn, Bi–40 wt%Sn–2 wt%In, Bi–40 wt%Sn–2 wt%Ag and Bi–38 wt%Sn–2 wt%In–2 wt%Ag were studied by dynamic resonance technique and Vickers indentation testing at room temperature and compared to that of the traditional Sn–37 wt%Pb eutectic alloy. The results show that the structure of Bi–42 wt%Sn alloy is characterized by the presence of rhombohedral Bi and body centered tetragonal β-Sn. The two ternary alloys exhibit additional constituent phases of intermetallic compounds SnIn 19 for Bi–40 wt%Sn–2 wt%In and ε-Ag 3 Sn for Bi–40 wt%Sn–2 wt%Ag alloys. Attention has been paid to the role of intermetallic compounds on mechanical and creep behavior. The In and Ag containing solder alloy exhibited a good combination of higher creep resistance, good mechanical properties and lower melting temperature as compared with Pb–Sn eutectic solder alloy. This was attributed to the strengthening effect of Bi as a strong solid solution element in the Sn matrix and formation of intermetallic compounds β-SnBi, ε-Ag 3 Sn and InSn 19 which act as both strengthening agent and grain refiner in the matrix of the material. Addition of In and Ag decreased the melting temperature of Bi–Sn lead-free solder from 143 °C to 133 °C which was possible mainly due to the existence of InSn 19 and Ag 3 Sn intermetallic compounds. Elastic constants, internal friction and thermal properties of Bi–Sn based alloys have been studied and analyzed.

Development of Creep-Resistant and Oxidation-Resistant Austenitic Stainless Steels for High Temperature Applications

Science.gov (United States)

Maziasz, Philip J.

2018-01-01

Austenitic stainless steels are cost-effective materials for high-temperature applications if they have the oxidation and creep resistance to withstand prolonged exposure at such conditions. Since 1990, Oak Ridge National Laboratory (ORNL) has developed advanced austenitic stainless steels with creep resistance comparable to Ni-based superalloy 617 at 800-900°C based on specially designed "engineered microstructures" utilizing a microstructure/composition database derived from about 20 years of radiation effect data on steels. The wrought high temperature-ultrafine precipitate strengthened (HT-UPS) steels with outstanding creep resistance at 700-800°C were developed for supercritical boiler and superheater tubing for fossil power plants in the early 1990s, the cast CF8C-Plus steels were developed in 1999-2001 for land-based gas turbine casing and diesel engine exhaust manifold and turbocharger applications at 700-900°C, and, in 2015-2017, new Al-modified cast stainless steels with oxidation and creep resistance capabilities up to 950-1000°C were developed for automotive exhaust manifold and turbocharger applications. This article reviews and summarizes their development and their properties and applications.

Influence of stress on creep deformation properties of 9-12Cr ferritic creep resistant steels

Energy Technology Data Exchange (ETDEWEB)

Kimura, K.; Sawada, K.; Kushima, H. [National Institute for Materials Science (Japan)

2008-07-01

Creep deformation property of 9-12Cr ferritic creep resistant steels was investigated. With decrease in stress, a magnitude of creep strain at the onset of accelerating creep stage decreased from about 2% in the short-term to less than 1% in the longterm. A time to 1% total strain was observed in the transient creep stage in the short term regime, however, it shifted to the accelerating creep stage in the long-term regime. Life fraction of the times to 1% creep strain and 1% total strain tended to increase with decrease in stress. Difference in stress dependence of the minimum creep rate was observed in the high- and low-stress regimes with a boundary condition of 50% of 0.2% offset yield stress. Stress dependence of the minimum creep rate in the high stress regime was equivalent to a strain rate dependence of the flow stress evaluated by tensile test, and a magnitude of stress exponent, n, in the high stress regime decreased with increase in temperature from 20 at 550 C to 10 at 700 C. On the other hand, n value in the low stress regime was about 5, and creep deformation in the low stress regime was considered to be controlled by dislocation climb. Creep rupture life was accurately predicted by a region splitting method by considering a change in stress dependence of creep deformation. (orig.)

Fission induced swelling and creep of U–Mo alloy fuel

Energy Technology Data Exchange (ETDEWEB)

Kim, Yeon Soo, E-mail: yskim@anl.gov [Argonne National Laboratory, 9700 South Cass Avenue, Argonne, IL 60439 (United States); Hofman, G.L. [Argonne National Laboratory, 9700 South Cass Avenue, Argonne, IL 60439 (United States); Cheon, J.S. [Korea Atomic Energy Research Institute, 989-111 Daedeok-daero, Yuseong, Daejeon 305-353 (Korea, Republic of); Robinson, A.B.; Wachs, D.M. [Idaho National Laboratory, P.O. Box 1625, Idaho Falls, ID 83415 (United States)

2013-06-15

Tapering of U–Mo alloy fuel at the end of plates is attributed to lateral mass transfer by fission induced creep, by which fuel mass is relocated away from the fuel end region where fission product induced fuel swelling is in fact the highest. This mechanism permits U–Mo fuel to achieve high burnup by effectively relieving stresses at the fuel end region, where peak stresses are otherwise expected because peak fission product induced fuel swelling occurs there. ABAQUS FEA was employed to examine whether the observed phenomenon can be simulated using physical–mechanical data available in the literature. The simulation results obtained for several plates with different fuel fabrication and loading scheme showed that the measured data were able to be simulated with a reasonable creep rate coefficient. The obtained creep rate constant lies between values for pure uranium and MOX, and is greater than all other ceramic uranium fuels.

Creep curve formularization at 950degC for Hastelloy XR

International Nuclear Information System (INIS)

Kaji, Yoshiyuki; Muto, Yasushi

1991-03-01

Creep tests under constant stress were conducted on a nickel-base heat-resistant alloy, Hastelloy XR, in air at 950degC. Minimum creep strain rate, time to the onset of tertiary creep and time to rupture were obtained as a function of applied stress. Then, a creep constitutive equation was made based on the Garofalo formula for primary and secondary creep and based on the Kachanov-Rabotnov formula for tertiary creep, which could represent fairly well the experimental creep deformation curves under the constant stress conditions. The creep deformation under the constant load condition corresponding to the stress increment was analysed using the creep constitutive equation and strain hardening law. Then the calculated creep strain showed slightly higher value than the experimental creep strain, and the calculated life was shorter than the experimental one. (author)

Microstructure and elevated temperature mechanical and creep properties of Mg–4Y–3Nd–0.5Zr alloy in the product form of a large structural casting

International Nuclear Information System (INIS)

Ning, Z.L.; Yi, J.Y.; Qian, M.; Sun, H.C.; Cao, F.Y.; Liu, H.H.; Sun, J.F.

2014-01-01

Highlights: • A modified WE43 alloy, free of heavy rare earth elements, has been assessed. • The new alloy, Mg–4Y–3Nd–0.5Zr (wt.%), is stronger than WE43 up to 573 K. • The new alloy is more creep resistant than WE43 alloy at 473 K under 40–80 MPa. • It is promising to use neodymium to replace heavy rare earth elements in WE43. - Abstract: In order to save the invaluable heavy rare earth (HRE) elements for important functional applications, a modified version of the WE43 magnesium alloy, Mg–4Y–3Nd–0.5Zr (wt.%), free of the HRE elements, has been designed. As part of the alloy development program, a large complex component of the alloy (net product weight: 80 kg) was made via differential pressure casting. The large component was then subjected to the T6 treatment (solid solution and ageing) following established commercial practice for the T6 treatment of the WE43 alloy. A significant number of samples were prepared from the thickest section (58 mm) of the T6-treated component for both microstructural characterization and detailed property assessment. The alloy showed noticeably higher tensile strengths than did the HRE-containing WE43 alloy over the temperature range of 473–573 K. The creep resistance of the alloy was superior to that of the WE43 alloy at 473 K while being similar at 523 K. The microstructures of the alloy in the as-cast, solution treated and then aged states were characterized. The component-based detailed assessment suggests that the idea of using neodymium (Nd) to replace the HRE elements in the WE43 alloy is promising for structural applications at elevated temperatures

The role of particle ripening on the creep acceleration of Nimonic 263 superalloy

Directory of Open Access Journals (Sweden)

Angella Giuliano

2014-01-01

Full Text Available Physically based constitutive equations need to incorporate the most relevant microstructural features of materials to adequately describe their mechanical behaviour. To accurately model the creep behaviour of precipitation hardened alloys, the value and the evolution of strengthening particle size are important parameters to be taken into account. In the present work, creep tests have been run on virgin and overaged (up to 3500 h at 800 ∘C Nimonic 263, a polycrystalline nickel base superalloy used for combustion chambers of gas turbines. The experimental results suggest that the reinforcing particle evolution is not the main reason for the creep acceleration that seems to be better described by a strain correlated damage, such as the accumulation of mobile dislocations or the grain boundary cavitation. The coarsened microstructure, obtained by overageing the alloy at high temperature before creep testing, mainly influences the initial stage of the creep, resulting in a higher minimum creep rate and a corresponding reduction of the creep resistance.

Interfacial failure in dissimilar weld joint of high boron 9% chromium steel and nickel-based alloy under high-temperature creep condition

Energy Technology Data Exchange (ETDEWEB)

Matsunaga, Tetsuya, E-mail: MATSUNAGA.Tetsuya@nims.go.jp; Hongo, Hiromichi, E-mail: HONGO.Hiromichi@nims.go.jp; Tabuchi, Masaaki, E-mail: TABUCHI.Masaaki@nims.go.jp

2017-05-17

The advanced ultra-supercritical (A-USC) power generation system is expected to become the next-generation base-load power station in Japan. Dissimilar weld joints between high-Cr heat-resistant steels and nickel-based alloys with a nickel-based filler metal (Alloy 82) will need to be adopted for this purpose. However, interfacial failure between the steels and weld metal has been observed under high-temperature creep conditions. Fractography and microstructure observations showed the failure initiated in a brittle manner by an oxide notch at the bottom of the U-groove. The fracture then proceeded along the bond line in a ductile manner with shallow dimples, where micro-Vickers hardness tests showed remarkable softening in the steel next to the bond line. In addition, the steel showed a much larger total elongation and reduction of area than the weld metal at low stresses under long-term creep conditions, leading to mismatch deformation at the interface. According to the results, it can be concluded that the interfacial failure between the 9Cr steels and Alloy 82 weld metal is initiated by an oxide notch and promoted by softening and the difference in the plasticity of the steels and weld metal.

Principal physical mechanisms of material creep resistance and rupture at elevated temperatures

International Nuclear Information System (INIS)

Krishtal, M.A.

1977-01-01

Mechanisms of creep and long-term failure of refractory materials at different temperatures and stress levels are considered. At high temperatures and low stresses the diffusion (vacancial) mechanism is observed. Temperatures being low and stresses sufficiently high, dislocation mechanism involving avalanche dislocation break-off is manifested. Intermediate conditions provide other mechanisms, i.e. dislocation glide, dislocation climbing, grain-boundary and sub-grain-boundary mechanisms. Quantitative relationships between creep rate and some structural and kinetic parameters are discussed. Account of the creep mechanism is necessary when selecting methods for strengthening of alloys

Creep behavior and threshold stress of an extruded Al-6Mg-2Sc-1Zr alloy

International Nuclear Information System (INIS)

Deshmukh, S.P.; Mishra, R.S.; Kendig, K.L.

2004-01-01

Creep experiments were performed on extruded Al-6Mg-2Sc-1Zr (wt.%) alloy in a temperature range of 423-533 K. A threshold type creep behavior was measured and explained by observed dislocation-particle interactions. The experimental threshold stress values at various temperatures were compared with existing theoretical models. None of the available models could account for the decrease in threshold creep strength with increasing temperature

Influence of Z-phase on long-term creep stability of martensitic 9-12%Cr steels

Energy Technology Data Exchange (ETDEWEB)

Hald, J. [DONG Energy (Denmark)]|[Vattenfall Europe AG, Berlin (Germany)]|[DTU Mechanical Engineering (Denmark); Danielsen, H.K. [DTU Mechanical Engineering (Denmark)

2008-07-01

The long-term creep strength of the new generation of martensitic creep resistant 9- 12% Cr steels since the well-known steel Grade 91 relies strongly on particle strengthening by fine MN nitrides based on V and Nb. During long-term hightemperature exposures the MN nitrides may be replaced by the thermodynamically more stable Z-phases (Cr(V,Nb)N) causing a breakdown in creep strength. Cr contents above 10.5% strongly accelerate Z-phase precipitation, which explains the lack of success for all attempts to develop martensitic creep resistant steels with high Cr content for oxidation protection. The Z-phase nucleation process by Cr-diffusion into pre-existing MN nitrides is rate controlling for the Z-phase transformation. More work is needed before effects of chemical composition on the nucleation process can be reliably modeled. Careful control of the Z-phase precipitation process has led to the design of experimental 12%Cr martensitic steels strengthened by Z-phase. Such steels may again enable the combination of high strength and oxidation resistance in the same alloy. This opens a new pathway for further alloy development of the heat resistant martensitic steels. (orig.)

Monitoring microstructural evolution of alloy 617 with non-linear acoustics for remaining useful life prediction; multiaxial creep-fatigue and creep-ratcheting

Energy Technology Data Exchange (ETDEWEB)

Lissenden, Cliff [Pennsylvania State Univ., State College, PA (United States); Hassan, Tasnin [North Carolina State Univ., Raleigh, NC (United States); Rangari, Vijaya [Tuskegee Univ., Tuskegee, AL (United States)

2014-10-30

The research built upon a prior investigation to develop a unified constitutive model for design-­by-­analysis of the intermediate heat exchanger (IHX) for a very high temperature reactor (VHTR) design of next generation nuclear plants (NGNPs). Model development requires a set of failure data from complex mechanical experiments to characterize the material behavior. Therefore uniaxial and multiaxial creep-­fatigue and creep-­ratcheting tests were conducted on the nickel-­base Alloy 617 at 850 and 950°C. The time dependence of material behavior, and the interaction of time dependent behavior (e.g., creep) with ratcheting, which is an increase in the cyclic mean strain under load-­controlled cycling, are major concerns for NGNP design. This research project aimed at characterizing the microstructure evolution mechanisms activated in Alloy 617 by mechanical loading and dwell times at elevated temperature. The acoustic harmonic generation method was researched for microstructural characterization. It is a nonlinear acoustics method with excellent potential for nondestructive evaluation, and even online continuous monitoring once high temperature sensors become available. It is unique because it has the ability to quantitatively characterize microstructural features well before macroscale defects (e.g., cracks) form. The nonlinear acoustics beta parameter was shown to correlate with microstructural evolution using a systematic approach to handle the complexity of multiaxial creep-­fatigue and creep-­ratcheting deformation. Mechanical testing was conducted to provide a full spectrum of data for: thermal aging, tensile creep, uniaxial fatigue, uniaxial creep-­fatigue, uniaxial creep-ratcheting, multiaxial creep-fatigue, and multiaxial creep-­ratcheting. Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM), and Optical Microscopy were conducted to correlate the beta parameter with individual microstructure mechanisms. We researched

Development of Cast Alumina-forming Austenitic Stainless Steel Alloys for use in High Temperature Process Environments

Energy Technology Data Exchange (ETDEWEB)

Muralidharan, Govindarajan [ORNL; Yamamoto, Yukinori [ORNL; Brady, Michael P [ORNL; Pint, Bruce A [ORNL; Pankiw, Roman [Duraloy Technologies Inc; Voke, Don [Duraloy Technologies Inc

2015-01-01

There is significant interest in the development of alumina-forming, creep resistant alloys for use in various industrial process environments. It is expected that these alloys can be fabricated into components for use in these environments through centrifugal casting and welding. Based on the successful earlier studies on the development of wrought versions of Alumina-Forming Austenitic (AFA) alloys, new alloy compositions have been developed for cast products. These alloys achieve good high-temperature oxidation resistance due to the formation of protective Al₂O₃ scales while multiple second-phase precipitation strengthening contributes to excellent creep resistance. This work will summarize the results on the development and properties of a centrifugally cast AFA alloy. This paper highlights the strength, oxidation resistance in air and water vapor containing environments, and creep properties in the as-cast condition over the temperature range of 750°C to 900°C in a centrifugally cast heat. Preliminary results for a laboratory cast AFA composition with good oxidation resistance at 1100°C are also presented.

Comparison of creep behavior under varying load/temperature conditions between Hastelloy XR alloys with different boron content levels

International Nuclear Information System (INIS)

Tsuji, Hirokazu; Nakajima, Hajime; Shindo, Masami; Tanabe, Tatsuhiko; Nakasone, Yuji.

1996-01-01

In the design of the high-temperature components, it is often required to predict the creep rupture life under the conditions in which the stress and/or temperature may vary by using the data obtained with the constant load and temperature creep rupture tests. Some conventional creep damage rules have been proposed to meet the above-mentioned requirement. Currently only limited data are available on the behavior of Hastelloy XR, which is a developed alloy as the structural material for high-temperature components of the High-Temperature Engineering Test Reactor (HTTR), under varying stress and/or temperature creep conditions. Hence a series of constant load and temperature creep rupture tests as well as varying load and temperature creep rupture tests was carried out on two kinds of Hastelloy XR alloys whose boron content levels are different, i.e., below 10 and 60 mass ppm. The life fraction rule completely fails in the prediction of the creep rupture life of Hastelloy XR with 60 mass ppm boron under varying load and temperature conditions though the rule shows good applicability for Hastelloy XR with below 10 mass ppm boron. The change of boron content level of the material during the tests is the most probable source of impairing the applicability of the life fraction rule to Hastelloy XR whose boron content level is 60 mass ppm. The modified life fraction rule has been proposed based on the dependence of the creep rupture strength on the boron content level of the alloy. The modified rule successfully predicts the creep rupture life under the two stage creep test conditions from 1000 to 900degC. The trend observed in the two stage creep tests from 900 to 1000degC can be qualitatively explained by the mechanism that the oxide film which is formed during the prior exposure to 900degC plays the role of the protective barrier against the boron dissipation into the environment. (J.P.N.)

Report on fundamental modeling of irradiation-induced swelling and creep in FeCrAl alloys

Energy Technology Data Exchange (ETDEWEB)

Kohnert, Aaron A. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Dasgupta, Dwaipayan [Univ. of Tennessee, Knoxville, TN (United States); Wirth, Brian [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Linton, Kory D. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)

2016-09-23

In order to improve the accident tolerance of light water reactor (LWR) fuel, alternative cladding materials have been proposed to replace zirconium (Zr)-based alloys. Of these materials, there is a particular focus on iron-chromium-aluminum (FeCrAl) alloys due to much slower oxidation kinetics in high-temperature steam than Zr-alloys. This should decrease the energy release due to oxidation and allow the cladding to remain integral longer in the presence of high temperature steam, making accident mitigation more likely. As a continuation of the development for these alloys, the material response must be demonstrated to provide suitable radiation stability, in order to ensure that there will not be significant dimensional changes (e.g., swelling), as well as quantifying the radiation hardening and radiation creep behavior. In this report, we describe the use of cluster dynamics modeling to evaluate the defect physics and damage accumulation behavior of FeCrAl alloys subjected to neutron irradiation, with a particular focus on irradiation-induced swelling and defect fluxes to dislocations that are required to model irradiation creep behavior.

Dual Microstructure Heat Treatment of a Nickel-Base Disk Alloy

Science.gov (United States)

Gayda, John

2001-01-01

Existing Dual Microstructure Heat Treat (DMHT) technology was successfully applied to Alloy 10, a high strength, nickel-base disk alloy, to produce a disk with a fine grain bore and coarse grain rim. Specimens were extracted from the DMHT disk and tested in tension, creep, fatigue, and crack growth using conditions pertinent to disk applications. These data were then compared with data from "traditional" subsolvus and supersolvus heat treatments for Alloy 10. The results showed the DMHT disk to have a high strength, fatigue resistant bore comparable to that of subsolvus Alloy 10. Further, creep resistance of the DMHT rim was comparable to that of supersolvus Alloy 10. Crack growth resistance in the DMHT rim, while better than that for subsolvus, was inferior to that of supersolvus Alloy 10. The slow cool at the end of the DMHT conversion and/or the subsolvus resolution step are thought to be responsible for degrading rim DMHT crack growth resistance.

Long-term creep rupture strength of weldment of Fe-Ni based alloy as candidate tube and pipe for advanced USC boilers

Energy Technology Data Exchange (ETDEWEB)

Bao, Gang; Sato, Takashi [Babcok-Hitachi K.K., Hiroshima (Japan). Kure Research Laboratory; Marumoto, Yoshihide [Babcok-Hitachi K.K., Hiroshima (Japan). Kure Div.

2010-07-01

A lot of works have been going to develop 700C USC power plant in Europe and Japan. High strength Ni based alloys such as Alloy 617, Alloy 740 and Alloy 263 were the candidates for boiler tube and pipe in Europe, and Fe-Ni based alloy HR6W (45Ni-24Fe-23Cr-7W-Ti) is also a candidate for tube and pipe in Japan. One of the Key issues to achieve 700 C boilers is the welding process of these alloys. Authors investigated the weldability and the long-term creep rupture strength of HR6W tube. The weldments were investigated metallurgically to find proper welding procedure and creep rupture tests are ongoing exceed 38,000 hours. The long-term creep rupture strengths of the HST weld joints are similar to those of parent metals and integrity of the weldments was confirmed based on with other mechanical testing results. (orig.)

Phase Evolution in and Creep Properties of Nb-Rich Nb-Si-Cr Eutectics

Science.gov (United States)

Gang, Florian; Kauffmann, Alexander; Heilmaier, Martin

2018-03-01

In this work, the Nb-rich ternary eutectic in the Nb-Si-Cr system has been experimentally determined to be Nb-10.9Si-28.4Cr (in at. pct). The eutectic is composed of three main phases: Nb solid solution (Nbss), β-Cr2Nb, and Nb9(Si,Cr)5. The ternary eutectic microstructure remains stable for several hundred hours at a temperature up to 1473 K (1200 °C). At 1573 K (1300 °C) and above, the silicide phase Nb9(Si,Cr)5 decomposes into α-Nb5Si3, Nbss, and β-Cr2Nb. Under creep conditions at 1473 K (1200 °C), the alloy deforms by dislocation creep while the major creep resistance is provided by the silicide matrix. If the silicide phase is fragmented and, thus, its matrix character is destroyed by prior heat treatment [ e.g., at 1773 K (1500 °C) for 100 hours], creep is mainly controlled by the Laves phase β-Cr2Nb, resulting in increased minimum strain rates. Compared to state of the art Ni-based superalloys, the creep resistance of this three-phase eutectic alloy is significantly higher.

Correlation between microstructure and the creep behaviour at high temperature of Alloy 800 H

International Nuclear Information System (INIS)

Spiradek, K.; Degischer, H.P.; Lahodny, H.

1989-01-01

A systematic metallographic study was performed to identify the nature of the microstructural changes occurring during high temperature creep deformation of Alloy 800 H. Creep tests were carried out at 800 deg. C under constant load conditions corresponding to the initial stresses between 25 and 80 MPa. Some tests were interrupted after certain elongations to provide the samples for electron microscopy. Emphasis was put on the creep periods relevant to design where only a few per cent of deformation are tolerable. The influence of the initial material conditions on the creep behaviour was examined. Variations of the initial microstructures were achieved by different solution treatments (980/1250) deg. C, preageing at 800 deg. C (0/6400) h and cold deformation up to 10% followed by ageing at 800 deg. C. The results of the microstructural examinations were correlated with the creep curves that provide a basis for identification of the creep mechanisms operating at the test conditions. (author). 14 refs, 17 figs

Fatigue and Creep Crack Propagation behaviour of Alloy 617 in the Annealed and Aged Conditions

Energy Technology Data Exchange (ETDEWEB)

Julian K. Benz; Richard N. Wright

2013-10-01

The crack propagation behaviour of Alloy 617 was studied under various conditions. Elevated temperature fatigue and creep-fatigue crack growth experiments were conducted at 650 and 800 degrees C under constant stress intensity (triangle K) conditions and triangular or trapezoidal waveforms at various frequencies on as-received, aged, and carburized material. Environmental conditions included both laboratory air and characteristic VHTR impure helium. As-received Alloy 617 displayed an increase in the crack growth rate (da/dN) as the frequency was decreased in air which indicated a time-dependent contribution component in fatigue crack propagation. Material aged at 650°C did not display any influence on the fatigue crack growth rates nor the increasing trend of crack growth rate with decreasing frequency even though significant microstructural evolution, including y’ (Ni3Al) after short times, occurred during aging. In contrast, carburized Alloy 617 showed an increase in crack growth rates at all frequencies tested compared to the material in the standard annealed condition. Crack growth studies under quasi-constant K (i.e. creep) conditions were also completed at 650 degrees C and a stress intensity of K = 40 MPa9 (square root)m. The results indicate that crack growth is primarily intergranular and increased creep crack growth rates exist in the impure helium environment when compared to the results in laboratory air. Furthermore, the propagation rates (da/dt) continually increased for the duration of the creep crack growth either due to material aging or evolution of a crack tip creep zone. Finally, fatigue crack propagation tests at 800 degrees C on annealed Alloy 617 indicated that crack propagation rates were higher in air than impure helium at the largest frequencies and lowest stress intensities. The rates in helium, however, eventually surpass the rates in air as the frequency is reduced and the stress intensity is decreased which was not observed at 650

Plasticity of oxide dispersion strengthened ferritic alloys

International Nuclear Information System (INIS)

Zakine, C.; Prioul, C.; Alamo, A.; Francois, D.

1993-01-01

Two 13%Cr oxide dispersion strengthened (ODS) ferritic alloys, DT and DY, exhibiting different oxide particle size distribution and a χ phase precipitation were studied. Their tensile properties have been tested from 20 to 700 C. Experimental observations during room temperature tensile tests performed in a scanning electronic microscope have shown that the main damage mechanism consists in microcracking of the χ phase precipitates on grain boundaries. These alloys are high tensile and creep resistant between 500 and 700 C. Their strongly stress-sensitive creep behaviour can be described by usual creep laws and incorporating a threshold stress below which the creep rate is negligible. (orig.)

Experimental approach and micro-mechanical modeling of the creep behavior of irradiated zirconium alloys

International Nuclear Information System (INIS)

Ribis, J.

2007-12-01

The fuel rod cladding, strongly affected by microstructural changes due to irradiation such as high density of dislocation loops, is strained by the end-of-life fuel rod internal pressure and the potential release of fission gases and helium during dry storage. Within the temperature range that is expected during dry interim storage, cladding undergoes long term creep under over-pressure. So, in order to have a predictive approach of the behavior of zirconium alloys cladding in dry storage conditions it is essential to take into account: initial dislocation loops, thermal annealing of loops and creep straining due to over pressure. Specific experiments and modelling for irradiated samples have been developed to improve our knowledge in that field. A Zr-1%Nb-O alloy was studied using fine microstructural investigations and mechanical testing. The observations conducted by transmission electron microscopy show that the high density of loops disappears during a heat treatment. The loop size becomes higher and higher while their density falls. The microhardness tests reveal that the fall of loop density leads to the softening of the irradiated material. During a creep test, both temperature and applied stress are responsible of the disappearance of loops. The loops could be swept by the activation of the basal slip system while the prism slip system is inhibited. Once deprived of loops, the creep properties of the irradiated materials are closed to the non irradiated state, a result whose consequence is a sudden acceleration of the creep rate. Finally, a micro-mechanical modeling based on microscopic deformation mechanisms taking into account experimental dislocation loop analyses and creep test, was used for a predictive approach by constructing a deformation mechanism map of the creep behavior of the irradiated material. (author)

Creep properties of heat-resistant superalloys for nuclear plants in helium

International Nuclear Information System (INIS)

Shimizu, Shigeki; Satoh, Keisuke; Honda, Yoshio; Matsuda, Shozo; Murase, Hirokazu

1979-01-01

Creep properties of candidate superalloys for VHTR components in a helium environment at both temperatures of 800 0 C and 900 0 C were compared with those of the same alloys in the atmospheric condition, and the superalloys were contrasted with each other from the viewpoint of high temperature structural design. At 800 0 C, no significant effect of a helium environment on creep properties of the superalloys is observed. At 900 0 C, however, creep strength of Inconel 617, Incoloy 800 and Incoloy 807 in the helium environment decrease more than in the atmospheric environment. In Hastelloy X and Inconel 625, there is no significant difference between creep strengths in helium and those in the atmospheric condition. Concerning So and St values in helium at 900 0 C, Inconel 617 and Hastelloy X are clearly superior to other superalloys. (author)

Strengthening mechanisms, creep, and fatigue processes in dispersion-hardened niobium alloy. Final scientific report, 1 Feb 89-31 Jan 92

Energy Technology Data Exchange (ETDEWEB)

Mukherjee, A.K.; Gibeling, J.C.

1992-04-20

The creep and fatigue properties of pure Nb and Nb-l%Zr alloy were investigated. A model was developed based on the migration of subgrain boundary that can explain the anomalous primary creep transients found in Nb-l%Zr alloy, due to coarsening of subgrain structure. TEM investigations confirmed that such subgrain coarsening occurs during primary creep of Nb-l%Zr. Baseline low cycle fatigue studies of Nb and Nb-l%Zr were completed. Cyclic hardening is observed and there is a microplastic plateau in Nb. The Nb-1%Zr is stronger in cyclic deformation than Nb, with little influence of strain rate. The deformation in the alloy at both high and low strain rates is controlled by the interaction between gliding edge dislocation and solute atoms.

Microstructure Stability During Creep of Friction Stir Welded AA2024-T3 Alloy

Science.gov (United States)

Regev, Michael; Rashkovsky, Tal; Cabibbo, Marcello; Spigarelli, Stefano

2018-01-01

The poor weldability of the AA2024 aluminum alloy limits its use in industrial applications. Because friction stir welding (FSW) is a non-fusion welding process, it seems to be a promising solution for welding this alloy. In the current study, FSW was applied to butt weld AA2024-T3 aluminum alloy plates. Creep tests were conducted at 250 and at 315 °C on both the parent material and the friction stir welded specimens. The microstructures of the welded and non-welded AA2024-T3 specimens before and after the creep tests were studied and compared. A comprehensive transmission electron microscopy study together with a high-resolution scanning electron microscopy study and energy-dispersive x-ray spectroscopy analysis was conducted to investigate the microstructure stability. The parent material seems to contain two kinds of Cu-rich precipitates—coarse precipitates of a few microns each and uniformly dispersed fine nanosized precipitates. Unlike the parent material, the crept specimens were found to contain the two kinds of precipitates mentioned above together with platelet-like precipitates. In addition, extensive decoration of the grain boundaries with precipitates was clearly observed in the crept specimens. Controlled aging experiments for up to 280 h at the relevant temperatures were conducted on both the parent material and the welded specimens in order to isolate the contribution of exposure to high temperatures to the microstructure changes. TEM study showed the development of dislocation networks into a cellular dislocation structure in the case of the parent metal. Changes in the dislocation structure as a function of the creep strain and the FSW process were recorded. A detailed creep data analysis was conducted, taking into account the instability of the microstructure.

Image-based creep-fatigue damage mechanism investigation of Alloy 617 at 950 °C

Energy Technology Data Exchange (ETDEWEB)

Tahir, Fraaz; Dahire, Sonam; Liu, Yongming, E-mail: yongming.liu@asu.edu

2017-01-02

Alloy 617 is a primary candidate material to be used in the next generation of nuclear power plants. Structural materials for these plants are expected to undergo creep and fatigue at temperatures as high as 950 °C. This study uses a hybrid-control creep-fatigue loading profile, as opposed to the traditional strain-controlled loading, to generate creep dominated failure. Qualitative and quantitative image analysis through SEM, EDS, and EBSD, is used to show that hybrid control testing is capable of producing creep dominated failure and that time fraction approach is not a valid indicator of creep or fatigue dominated damage. The focus of image analysis is on surface fatigue cracks and internal creep voids. A creep-fatigue damage interaction diagram based on these micro-scale features is plotted. It is shown that the classical time fraction approach suggested by the ASME code does not agree with the experimental findings and has a poor correlation with observed microscale damage features. A new definition of creep damage fraction based on an effective hold time is found to correlate well with the micro-scale image analysis.

Creep laws for refractory tungsten alloys between 900 and 1100 oC under low stress

International Nuclear Information System (INIS)

Gallet, D.; Dhers, J.; Levoy, R.; Polcik, P.

2001-01-01

Refractory metals and alloys with melting point above 2500 o C, are commonly used at temperature well above 1000 o C. Very few creep data exist at low temperature and low stress. In the present work, we studied the micro-creep deformation and the structure stability of different W and W alloys, W-B, W-La 2 O 3 , W-K, W-Re, in the temperature range 900-1100 o C and stress range 10-50 MPa, up to 500 hours. A Norton type law has been established for those materials. Stress exponents around 1.0 have been obtained. Activation energies have been determined, and are much lower than self diffusion energies for all materials tested. The main mechanism involved has been identified as Harper-Dorn creep, implying some dislocation rearrangement. The dopants are classified according to their efficiency in creep reduction and boron at 100 ppm has been found to be the most efficient, whereas at 10 ppm, it degrades the behavior of stress relieved tungsten. Furthermore, we have found that the addition of some elements may have an efficient effect as recrystallization inhibitor. (author)

Summary on out-of-pile and in-pile properties of M5 alloy

International Nuclear Information System (INIS)

Zhao Wenjin

2001-01-01

The out-of-pile and in-pile corrosion, mechanical properties, microstructure,hydrogen absorption, creep and growth resistances of M5 alloy using as PWR fuel rod cladding materials developed by FRAMATOME in France has been summarized with reference to the literatures. The results obtained from in-pile irradiation tests show that the corrosion and hydrogen absorption resistances, creep and irradiation growth resistances of M5 alloy cladding are superior to that of the optimized Zircaloy-4. It could be estimated that the M5 alloy enables rod burnups close to 65GWd/tU to be reached

The effect of microstructural stability on long-term creep behaviour of 11 %Cr steels for steam power plants with operating steam temperatures up to 650 C

Energy Technology Data Exchange (ETDEWEB)

Wang, Y.; Scholz, A.; Berger, C. [Technische Univ. Darmstadt (DE). Inst. fuer Werkstoffkunde (IFW); Kauffmann, F.; Maile, K. [Stuttgart Univ. (DE). Materialpruefungsanstalt (MPA); Mayer, K.H. [Alstom Power, Nuernberg (Germany)

2010-07-01

The investigations of advanced ferritic/martensitic steels for 650 C power plant components focus on the improvement of high-temperature creep properties with respect to chemical composition. This study deals with the development of new heat resistant 11-12%Cr ferritic-martensitic steels with sufficient creep and oxidation resistance up to 650 application by using basic principles and concepts of physical metallurgy. The highest creep strength could be achieved with a 0.04% Nb alloyed 11%CrWCoMoVB melt, which is in addition alloyed with a higher C and B content as well as with lower W and Co portions. The microstructure evolution during creep of this newly developed steel was investigated in comparison to a sister alloy which comprises 0.06% Ta instead of the Nb. (orig.)

Designing Nanoscale Precipitates in Novel Cobalt-based Superalloys to Improve Creep Resistance and Operating Temperature

Energy Technology Data Exchange (ETDEWEB)

Dunand, David C. [Northwestern Univ., Evanston, IL (United States); Seidman, David N. [Northwestern Univ., Evanston, IL (United States); Wolverton, Christopher [Northwestern Univ., Evanston, IL (United States); Saal, James E. [Northwestern Univ., Evanston, IL (United States); Bocchini, Peter J. [Northwestern Univ., Evanston, IL (United States); Sauza, Daniel J. [Northwestern Univ., Evanston, IL (United States)

2014-10-01

High-temperature structural alloys for aerospace and energy applications have long been dominated by Ni-base superalloys, whose strength and creep resistance can be attributed to microstructures consisting of a large volume fraction of ordered (L1₂) γ'-precipitates embedded in a disordered’(f.c.c.) γ-matrix. These alloys exhibit excellent mechanical behavior and thermal stability, but after decades of incremental improvement are nearing the theoretical limit of their operating temperatures. Conventional Co-base superalloys are solid-solution or carbide strengthened; although they see industrial use, these alloys are restricted to lower-stress applications because the absence of an ordered intermetallic phase places an upper limit on their mechanical performance. In 2006, a γ+γ' microstructure with ordered precipitates analogous to (L1₂) Ni₃Al was first identified in the Co-Al-W ternary system, allowing, for the first time, the development of Co-base alloys with the potential to meet or even exceed the elevated-temperature performance of their Ni-base counterparts. The potential design space for these alloys is complex: the most advanced Ni-base superalloys may contain as many as 8-10 minor alloying additions, each with a specified purpose such as raising the γ' solvus temperature or improving creep strength. Our work has focused on assessing the effects of alloying additions on microstructure and mechanical behavior of γ'-strengthened Co-base alloys in an effort to lay the foundations for understanding this emerging alloy system. Investigation of the size, morphology, and composition of γ' and other relevant phases is investigated utilizing scanning electron microscopy (SEM) and 3-D picosecond ultraviolet local electrode atom probe tomography (APT). Microhardness, compressive yield stress at ambient and elevated temperatures, and compressive high-temperature creep measurements are employed to

Probability based high temperature engineering creep and structural fire resistance

CERN Document Server

Razdolsky, Leo

2017-01-01

This volume on structural fire resistance is for aerospace, structural, and fire prevention engineers; architects, and educators. It bridges the gap between prescriptive- and performance-based methods and simplifies very complex and comprehensive computer analyses to the point that the structural fire resistance and high temperature creep deformations will have a simple, approximate analytical expression that can be used in structural analysis and design. The book emphasizes methods of the theory of engineering creep (stress-strain diagrams) and mathematical operations quite distinct from those of solid mechanics absent high-temperature creep deformations, in particular the classical theory of elasticity and structural engineering. Dr. Razdolsky’s previous books focused on methods of computing the ultimate structural design load to the different fire scenarios. The current work is devoted to the computing of the estimated ultimate resistance of the structure taking into account the effect of high temperatur...

Improved creep strength of nickel-base superalloys by optimized γ/γ′ partitioning behavior of solid solution strengthening elements

International Nuclear Information System (INIS)

Pröbstle, M.; Neumeier, S.; Feldner, P.; Rettig, R.; Helmer, H.E.; Singer, R.F.; Göken, M.

2016-01-01

Solid solution strengthening of the γ matrix is one key factor for improving the creep strength of single crystal nickel-base superalloys at high temperatures. Therefore a strong partitioning of solid solution hardening elements to the matrix is beneficial for high temperature creep strength. Different Rhenium-free alloys which are derived from CMSX-4 are investigated. The alloys have been characterized regarding microstructure, phase compositions as well as creep strength. It is found that increasing the Titanium (Ti) as well as the Tungsten (W) content causes a stronger partitioning of the solid solution strengtheners, in particular W, to the γ phase. As a result the creep resistance is significantly improved. Based on these ideas, a Rhenium-free alloy with an optimized chemistry regarding the partitioning behavior of W is developed and validated in the present study. It shows comparable creep strength to the Rhenium containing second generation alloy CMSX-4 in the high temperature / low stress creep regime and is less prone to the formation of deleterious topologically close packed (TCP) phases. This more effective usage of solid solution strengtheners can enhance the creep properties of nickel-base superalloys while reducing the content of strategic elements like Rhenium.

Creep crack growth in phosphorus alloyed oxygen free copper

Energy Technology Data Exchange (ETDEWEB)

Wu, Rui; Seitisleam, Facredin (Swerea KIMAB (Sweden)); Sandstroem, Rolf; Jin, Lai-Zhe (Materials Science and Engineering, Royal Inst. of Technology (Sweden))

2011-01-15

Using standard compact tension (CT) specimens taken from a pierce and draw cylinder, creep crack growth (CCG) has been studied in phosphorus-alloyed oxygen-free copper (Cu-OFP) parent metal at 22, 75, 175, and 215 deg C. Pre- and post-test metallography are performed. At higher temperatures the rupture time of CCG is shorter by a factor up of 65 than that of uniaxial at same stress/reference stress. At 175 and 215 deg C, crack does grow by creep about 10 mm before final instantaneous failure. In contrast, there is hardly any visible crack growth at 22 and 75 deg C. The tests were interrupted after 5000 to 13000 hours. For ruptured tests at 175 and 215 deg C, strongly elongated and deformed grains are observed adjacent to crack. Extensive and intergranular creep cavities and microcracks are found several mm around crack. For interrupted tests at 22 and 75 deg C, strongly elongated and deformed grains, creep cavities, as well as microcracks are observed close to crack tip. Surface cracks from both sides have initiated and grown about 45 deg to the load direction towards inside. For the interrupted tests, hardness adjacent to crack tip has more than doubled because of work hardening, or heavy deformation. This is consistent with large crack tip opening. The true strain at the crack tip is estimated to 10 and 4 for the tests at 22 and 75 deg C, respectively. The stress state behind the crack tip has been modelled with FEM. Stress relaxation after loading has also been taken into account. A model for the creep damage based on the creep strain rate has been formulated that can describe the uniaxial creep rupture data without fitting parameters. Based on the formulation for the creep damage, a model for the crack propagation has been set up. When the creep damage has reached the value unity in front of the crack tip, the crack is assumed to propagate. Taking multiaxial effects into account the observed life times of the CT specimens can be well described. The multiaxial

Creep crack growth in phosphorus alloyed oxygen free copper

International Nuclear Information System (INIS)

Wu, Rui; Seitisleam, Facredin; Sandstroem, Rolf; Jin, Lai-Zhe

2011-01-01

Using standard compact tension (CT) specimens taken from a pierce and draw cylinder, creep crack growth (CCG) has been studied in phosphorus-alloyed oxygen-free copper (Cu-OFP) parent metal at 22, 75, 175, and 215 deg C. Pre- and post-test metallography are performed. At higher temperatures the rupture time of CCG is shorter by a factor up of 65 than that of uniaxial at same stress/reference stress. At 175 and 215 deg C, crack does grow by creep about 10 mm before final instantaneous failure. In contrast, there is hardly any visible crack growth at 22 and 75 deg C. The tests were interrupted after 5000 to 13000 hours. For ruptured tests at 175 and 215 deg C, strongly elongated and deformed grains are observed adjacent to crack. Extensive and intergranular creep cavities and microcracks are found several mm around crack. For interrupted tests at 22 and 75 deg C, strongly elongated and deformed grains, creep cavities, as well as microcracks are observed close to crack tip. Surface cracks from both sides have initiated and grown about 45 deg to the load direction towards inside. For the interrupted tests, hardness adjacent to crack tip has more than doubled because of work hardening, or heavy deformation. This is consistent with large crack tip opening. The true strain at the crack tip is estimated to 10 and 4 for the tests at 22 and 75 deg C, respectively. The stress state behind the crack tip has been modelled with FEM. Stress relaxation after loading has also been taken into account. A model for the creep damage based on the creep strain rate has been formulated that can describe the uniaxial creep rupture data without fitting parameters. Based on the formulation for the creep damage, a model for the crack propagation has been set up. When the creep damage has reached the value unity in front of the crack tip, the crack is assumed to propagate. Taking multiaxial effects into account the observed life times of the CT specimens can be well described. The multiaxial

Final report on in-reactor creep-fatigue deformation behaviour of a CuCrZr alloy: COFAT 1

DEFF Research Database (Denmark)

Singh, Bachu Narain; Tähtinen, S.; Moilanen, P.

CrZr(HT1) alloy exposed concurrently to flux of neutrons and creep-fatigue cyclic loading directly in a fission reactor. Special experimental facilities were designed and fabricated for this purpose. A number of in-reactor creep-fatigue experiments were successfully carried out in the BR-2 reactor at Mol...

Thermal and Irradiation Creep Behavior of a Titanium Aluminide in Advanced Nuclear Plant Environments

Science.gov (United States)

Magnusson, Per; Chen, Jiachao; Hoffelner, Wolfgang

2009-12-01

Titanium aluminides are well-accepted elevated temperature materials. In conventional applications, their poor oxidation resistance limits the maximum operating temperature. Advanced reactors operate in nonoxidizing environments. This could enlarge the applicability of these materials to higher temperatures. The behavior of a cast gamma-alpha-2 TiAl was investigated under thermal and irradiation conditions. Irradiation creep was studied in beam using helium implantation. Dog-bone samples of dimensions 10 × 2 × 0.2 mm3 were investigated in a temperature range of 300 °C to 500 °C under irradiation, and significant creep strains were detected. At temperatures above 500 °C, thermal creep becomes the predominant mechanism. Thermal creep was investigated at temperatures up to 900 °C without irradiation with samples of the same geometry. The results are compared with other materials considered for advanced fission applications. These are a ferritic oxide-dispersion-strengthened material (PM2000) and the nickel-base superalloy IN617. A better thermal creep behavior than IN617 was found in the entire temperature range. Up to 900 °C, the expected 104 hour stress rupture properties exceeded even those of the ODS alloy. The irradiation creep performance of the titanium aluminide was comparable with the ODS steels. For IN617, no irradiation creep experiments were performed due to the expected low irradiation resistance (swelling, helium embrittlement) of nickel-base alloys.

Grain boundary precipitation strengthening mechanism in W containing advanced creep resistant ferritic steels

Energy Technology Data Exchange (ETDEWEB)

Shibata, T.; Hasegawa, Y. [Tohoku Univ., Sendai (Japan)

2010-07-01

Grain boundary precipitation strengthening is expected to be a decisive factor in developing ferritic creep resistant steels. This study examined the grain boundary precipitation strengthening mechanism extracting the effect of the tempered martensitic microstructure and precipitates on the high angle grain boundary in M{sub 23}C4{sub 6} type carbide and the Fe{sub 2}W type Laves phase effect of the creep deformation fixing the grain boundary according to transmission electron microscope (TEM) observation. A creep test was carried out at high temperature in order to evaluate the high angle boundary strengthening effect simulating the long-term creep deformation microstructure by the lath structure disappearance. The correlation of the creep rupture time and the grain boundary shielding ratio were found to be independent of precipitate type. The creep deformation model represents block boundary shielding by precipitates as the decisive factor for W containing ferritic creep resistant steels. (orig.)

Stress-assisted discontinuous precipitation during creep of Ti3Al-Nb alloys

International Nuclear Information System (INIS)

Rowe, R.G.; Hall, E.L.

1991-01-01

Stress-assisted discontinuous precipitation was observed during creep of Ti-25Al-12.5Nb at. pct and associated with microstructures in which large primary creep strains were observed earlier. It was found that a large shift between the equilibrium beta(0) (B2) phase composition at the heat treatment temperature and disordered beta (bcc) phase at the creep temperature provided a driving force for discontinuous precipitation of disordered beta phase. Applied stress accelerated the growth of discontinuous beta phase at grain boundaries perpendicular to the principal stress axis, but did not produce a significant shift in composition. The difference between beta and ordered beta phase boundaries in the Ti-Al-Nb system at 650 C and 1040 C suggests that discontinuous precipitation or related dissolution should occur in all Ti3Al-Nb alloys. 11 refs

The High Temperature Tensile and Creep Behaviors of High Entropy Superalloy.

Science.gov (United States)

Tsao, Te-Kang; Yeh, An-Chou; Kuo, Chen-Ming; Kakehi, Koji; Murakami, Hideyuki; Yeh, Jien-Wei; Jian, Sheng-Rui

2017-10-04

This article presents the high temperature tensile and creep behaviors of a novel high entropy alloy (HEA). The microstructure of this HEA resembles that of advanced superalloys with a high entropy FCC matrix and L1 2 ordered precipitates, so it is also named as "high entropy superalloy (HESA)". The tensile yield strengths of HESA surpass those of the reported HEAs from room temperature to elevated temperatures; furthermore, its creep resistance at 982 °C can be compared to those of some Ni-based superalloys. Analysis on experimental results indicate that HESA could be strengthened by the low stacking-fault energy of the matrix, high anti-phase boundary energy of the strengthening precipitate, and thermally stable microstructure. Positive misfit between FCC matrix and precipitate has yielded parallel raft microstructure during creep at 982 °C, and the creep curves of HESA were dominated by tertiary creep behavior. To the best of authors' knowledge, this article is the first to present the elevated temperature tensile creep study on full scale specimens of a high entropy alloy, and the potential of HESA for high temperature structural application is discussed.

Pt-Rh alloys. Investigation of creep rate and rupture time at high temperatures

Energy Technology Data Exchange (ETDEWEB)

Trumic, Biserka; Gomidzelovic, Lidija; Marjanovic, Sasa; Ivanovic, Aleksandra; Dimitrijevic, Silvana [Belgrade Univ., Bor (Serbia). Inst. of Mining and Metallurgy; Krstic, Vesna

2013-02-01

The results of experimental investigation of creep rate and rupture time of the alloys of Pt-Rh system are presented in this paper. Selected alloys with 7-40 wt.-% Rh content were examined using a universal device for tensile testing of materials at high temperatures, and monitoring structure changes of the samples by electron microscopy. Investigations were performed in the temperature range between 1200 C and 1700 C at a stress between 2 MPa and 15 MPa. (orig.)

Long-term behaviour of heat-resistant steels and high-temperature materials

International Nuclear Information System (INIS)

1987-01-01

This book contains 10 lectures with the following subjects: On the effect of thermal pretreatment on the structure and creep behaviour of the alloy 800 H (V. Guttmann, J. Timm); Material properties of heat resistant ferritic and austenitic steels after cold forming (W. Bendick, H. Weber); Investigations for judging the working behaviour of components made of alloy 800 and alloy 617 under creep stress (H.J. Penkalla, F. Schubert); Creep behaviour of gas turbine materials in hot gas (K.H. Kloos et al.); Effect of small cold forming on the creep beahviour of gas turbine blades made of Nimonic 90 (K.H. Keienburg et al.); Investigations on creep fatigue alternating load strength of nickel alloys (G. Raule); Change of structure, creep fatigue behaviour and life of X20 Cr Mo V 12 1 (by G. Eggeler et al.); Investigations on thermal fatigue behaviour (K.H. Mayer et al.); Creep behaviour of similar welds of the steels 13 Cr Mo 4 4, 14 MoV 6 3, 10 Cr Mo 910 and GS-17 Cr Mo V 5 11 (K. Niel et al.); Determining the creep crack behaviour of heat resistant steels with samples of different geometry (K. Maile, R. Tscheuschner). (orig.,/MM) [de

Influence of microstructure on the thermal creep behaviour of zirconium alloys: experimental analysis and implementation of homogenization approaches

International Nuclear Information System (INIS)

Brenner, R.

2001-01-01

Zirconium alloys widely used in the nuclear industry can present thermomechanical variability of their behavior (especially for thermal creep) as a function of their microstructure. To have a better control of the mechanical behavior of these alloys and also to take into account the possible evolution of their fabrication process (chemical composition, thermal treatments,... ), it is important to have a modeling tool which help us to describe the relationship between the microstructure and the macroscopic behavior. This study contributes to establish a predictive modelling, based on an experimental analysis coupled with a homogenization approach of the thermal creep behavior of Zr alloys. The experimental analysis of the crystallographic texture effect for Zircaloy-4 alloys shows how the strain rate and stress exponent of the different glide systems are anisotropic. Transmission Electronic Microscopy analysis have been undertaken in order to determine the link between the texture and the activated slip system considering various mechanical tests (Ioading paths). The experimental analysis for Zr-Nb-1%-O bring to evidence the solid solution effect of Nb on the hardening of this alloy and the weak effect of the precipitates distribution on thermal creep behavior. An elasto-viscoplastic micromechanical modelling has been developed taking into account the microstructure effects on the macroscopic behavior of Zr alloys. The 'quasi-elastic' approximate of the self consistent scheme based on the affine formulation is proposed and compared with others and earlier formulations. The accuracy of this formulation for our study is demonstrated, as well as the from the scale transition point of view and the simple numerical resolution. A good agreement is found for the description of thermal creep behavior of Zircaloy-4 and Zr-Nb-1%-O alloys. The analysis of the results at a local scale (especially slip system secondary activities) gives the current limit for the description of

Development of a Novel, Bicombinatorial Approach to Alloy Development, and Application to Rapid Screening of Creep Resistant Titanium Alloys

Science.gov (United States)

Martin, Brian

Combinatorial approaches have proven useful for rapid alloy fabrication and optimization. A new method of producing controlled isothermal gradients using the Gleeble Thermomechanical simulator has been developed, and demonstrated on the metastable beta-Ti alloy beta-21S, achieving a thermal gradient of 525-700 °C. This thermal gradient method has subsequently been coupled with existing combinatorial methods of producing composition gradients using the LENS(TM) additive manufacturing system, through the use of elemental blended powders. This has been demonstrated with a binary Ti-(0-15) wt% Cr build, which has subsequently been characterized with optical and electron microscopy, with special attention to the precipitate of TiCr2 Laves phases. The TiCr2 phase has been explored for its high temperature mechanical properties in a new oxidation resistant beta-Ti alloy, which serves as a demonstration of the new bicombinatorial methods developed as applied to a multicomponent alloy system.

The compositional dependence of irradiation creep of austenitic alloys irradiated in PFR at 420{degrees}C

Energy Technology Data Exchange (ETDEWEB)

Toloczko, M.B.; Garner, F.A. [Pacific Northwest National Lab., Richland, WA (United States); Munro, B. [AEA Technology, Dounreay (United Kingdom)] [and others

1997-04-01

Irradiation creep data are expensive and often difficult to obtain, especially when compared to swelling data. This requires that maximum use be made of available data sources in order to elucidate the parametric dependencies of irradiation creep for application to new alloys and to new environments such as those of proposed fusion environments. One previously untapped source of creep data is that of a joint U.S./U.K. experiment conducted in the Prototype Fast Reactor (PFR) in Dounreay, Scotland. In this experiment, five austenitic steels were irradiated in a variety of starting conditions. In particular, these steels spanned a large range (15-40%) of nickel contents, and contained strong variations in Mo, Ti, Al, and Nb. Some alloys were solution-strengthened and some were precipitation-strengthened. Several were cold-worked. These previously unanalyzed data show that at 420{degrees}C all austenitic steels have a creep compliance that is roughly independent of the composition of the steel at 2{+-}1 x 10{sup {minus}6}MPa{sup {minus}1} dpa{sup {minus}1}. The variation within this range may arise from the inability to completely separate the non-creep strains arising from precipitation reactions and the stress-enhancement of swelling. Each of these can be very sensitive to the composition and starting treatment of a steel.

Shakedown Tests for Refurbished and Upgraded Frames and Initiation of Alloy 709 Creep Rupture Tests

Energy Technology Data Exchange (ETDEWEB)

Wang, Hong [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Moser, Jeremy L. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Hawkins, Charles S. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Lara-Curzio, Edgar [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)

2017-09-01

This report describes the shakedown tests conducted on the upgraded frames, and initiation of creep rupture tests on refurbished frames. SS316H, a reference material for Alloy 709, was used in shakedown tests, and the tests were conducted at 816 degree C under three stress levels to accumulate 1% creep strain. 1/4” gage diameter specimen design was used. The creep rupture tests on Alloy 709 were initiated at 600 degree C under 330 MPa to target 1,500 h rupture time. 12 specimens with 3/8” gage diameter were prepared from the materials with 6 heat treatment conditions, 2 from each. The required mechanical load under 330MPa was calculated to be 5,286 lb for the 3/8” gage diameter specimen. Among the ART frames, 7 frames are equipped with 10,000 lb load cell including #5 to 8 and #88 to 90, and can be used. 7 tests were thus started in this stage of project, and remaining 5 will be continued whenever any of the 7 tests is completed.

Creep Strength of Nb-1Zr for SP-100 Applications

Science.gov (United States)

Horak, James A.; Egner, Larry K.

1994-07-01

Power systems that are used to provide electrical power in space are designed to optimize conversion of thermal energy to electrical energy and to minimize the mass and volume that must be launched. Only refractory metals and their alloys have sufficient long-term strength for several years of uninterrupted operation at the required temperatures of 1200 K and above. The high power densities and temperatures at which these reactors must operate require the use of liquid-metal coolants. The alloy Nb-1 wt % Zr (Nb-lZr), which exhibits excellent corrosion resistance to alkali liquid-metals at high temperatures, is being considered for the fuel cladding, reactor structural, and heat-transport systems for the SP-100 reactor system. Useful lifetime of this system is limited by creep deformation in the reactor core. Nb-lZr sheet procured to American Society for Testing and Materials (ASTM) specifications for reactor grade and commercial grade has been processed by several different cold work and annealing treatments to attempt to produce the grain structure (size, shape, and distribution of sizes) that provides the maximum creep strength of this alloy at temperatures from 1250 to 1450 K. The effects of grain size, differences in oxygen concentrations, tungsten concentrations, and electron beam and gas tungsten arc weldments on creep strength were studied. Grain size has a large effect on creep strength at 1450 K but only material with a very large grain size (150 μm) exhibits significantly higher creep strength at 1350 K. Differences in oxygen or tungsten concentrations did not affect creep strength, and the creep strengths of weldments were equal to, or greater than, those for base metal.

Evaluation of Creep Strength of Heterogeneous Welded Joint in HR6W Alloy and Sanicro 25 Steel

Directory of Open Access Journals (Sweden)

Zieliński A.

2017-12-01

Full Text Available This article presents the results of investigations on HR6W alloy and Sanicro 25 steel and the dissimilar welded joint made of them. The characteristic images of microstructure of the investigated materials in the as-received condition and following the creep test, observed with a scanning electron microscope (SEM, are shown. The X-ray analysis of phase composition of the existing precipitates was carried out. The method for evaluation of creep strength based on abridged creep tests carried out at a temperature higher than the design one is presented. The obtained results do not deviate from the values of creep strength determined in long-term creep tests. The maximum difference in creep strength of the investigated materials is ±20%, which is in compliance with the acceptable scatter band. The methodology presented can be used for verification of creep strength (life time of the material of finished components to be operated under creep conditions.

Fatigue and creep cracking of nickel alloys for 700 C steam turbines

International Nuclear Information System (INIS)

Berger, C.; Granacher, J.; Thoma, A.; Roesler, J.; Del Genovese, D.

2001-01-01

Four materials of the types Inconel 706 (two heat treatment states), Inconel 617, and Waspaloy were tested as shaft materials for 700 to 720 C steam turbines. At an extrapolation time ratio of 10, Waspaloy was expected to have the highest creep strength (about 270 MPa at 700 C), with values of about 140 MPa at 700 C for Inconel 617. A preliminary evaluation of the 700 C creep rupture tests showed the highest creep rupture resistance for Inconel 617, followed by Waspaloy and Inconel 706 [de

Boron effects on creep rupture strength of W containing advanced ferritic creep resistant steels

Energy Technology Data Exchange (ETDEWEB)

Mito, N.; Hasegawa, Y. [Tohoku Univ., Sendai (Japan)

2010-07-01

The creep strength in ferritic creep resistant steels is increased by boron addition. However, the strengthening mechanisms have not yet been studied. This study clarifies the strengthening mechanism of 9% chromium steels with 10{proportional_to}100ppm boron and 0.5{proportional_to}2.0mass% tungsten in the laboratory. The strengthening effect of simultaneous addition of boron and tungsten was analyzed by hardenability, room-temperature strength and creep tests at 650 C. Changes in the microstructure as a result of the addition of boron and tungsten were also examined by optical microscope and transmission electron microscope (TEM). In addition, Alpha-ray Track Etching (ATE) method was used to detect the boron distribution and analyze the mechanisms change in the mechanical properties. Boron addition did not affect room-temperature strength, however, simultaneous addition of boron and tungsten increased room-temperature and high-temperature strength. According to ATE analysis, boron exists at the grain boundary. Therefore, synergistic effects of boron and tungsten on the creep strength suggest the tungsten precipitates stabilization by boron at the grain boundary. (orig.)

Transitions in creep mechanisms and creep anisotropy in Zr-1Nb-1Sn-0.2Fe sheet

International Nuclear Information System (INIS)

Murty, K.L.; Ravi, J.; Wiratmo

1995-01-01

The creep characteristics of a Zr-1Nb-1Sn-0.2Fe alloy sheet were investigated at temperatures from 773 to 923K and at stresses ranging from 9 to 150MPa along both the rolling and transverse directions. Transitions in creep mechansims are noted, with diffusional viscous creep at low stresses, viscous-glide-controlled microcreep in the intermediate stress regime and the climb of edge dislocations at high stresses. The creep anisotropy decreases with a decrease in the stress exponent and the creep rates differ by only 30% in the viscous creep regime, while an order-of-magnitude difference is noted at high stresses. The solute-strengthening effect of Nb addition is evident in the stress regime where appropriate data are available. These transitions in creep mechansims clearly reveal the dangers in blind extrapolation of short-term high stress data to low stresses and long times relevant to in-reactor conditions. The creep behavior of these materials is similar to that noted in Class I alloys, while the transitions in deformation mechanisms in Zircaloy-4 resemble those found in pure metals or Class II alloys with no viscous glide mechanism. ((orig.))

Small ring testing of a creep resistant material

International Nuclear Information System (INIS)

Hyde, C.J.; Hyde, T.H.; Sun, W.; Nardone, S.; De Bruycker, E.

2013-01-01

Many components in conventional and nuclear power plant, aero-engines, chemical plant etc., operate at temperatures which are high enough for creep to occur. These include steam pipes, pipe branches, gas and steam turbine blades, etc. The manufacture of such components may also require welds to be part of them. In most cases, only nominal operating conditions (i.e. pressure, temperatures, system load, etc.) are known and hence precise life predictions for these components are not possible. Also, the proportion of life consumed will vary from position to position within a component. Hence, non-destructive techniques are adopted to assist in making decisions on whether to repair, continue operating or replace certain components. One such approach is to test a small sample removed from the component to make small creep test specimens which can be tested to give information on the remaining creep life of the component. When such a small sample cannot be removed from the operating component, e.g. in the case of small components, the component can be taken out of operation in order to make small creep test specimens, the results from which can then be used to assist with making decisions regarding similar or future components. This paper presents a small creep test specimen which can be used for the testing of particularly strong and creep resistant materials, such as nickel-based superalloys

Creep strength and microstructural evolution of 9-12% Cr heat resistant steels during creep exposure at 600 C and 650 C

Energy Technology Data Exchange (ETDEWEB)

Mendez Martin, Francisca [Graz Univ. of Technology (Austria). Inst. for Materials Science and Welding; Panait, Clara Gabriela [MINES ParisTech, UMR CNRS, Evry (France). Centre des Materiaux; V et M France CEV, Aulnoye-Aymeries (France); Bendick, Walter [Salzgitter Mannesmann Forschung GmbH (SZMF), Duisburg (DE)] (and others)

2010-07-01

9-12% Cr heat resistant steels are used for applications at high temperatures and pressures in steam power plants. 12% Cr steels show higher creep strength and higher corrosion resistance compared to 9% Cr steels for short term creep exposure. However, the higher creep strength of 12 %Cr steels drops increasingly after 10,000-20,000 h of creep. This is probably due to a microstructural instability such as the precipitation of new phases (e.g. Laves phases and Z-phases), the growth of the precipitates and the recovery of the matrix. 9% Cr and 12% Cr tempered martensitic steels that have been creep tested for times up to 50,000 h at 600 C and 650 C were investigated using Transmission Electron Microscopy (TEM) on extractive replicas and thin foils together with Backscatter Scanning Electron Microscopy (BSE-SEM) to better understand the different creep behaviour of the two different steels. A significant precipitation of Laves phase and low amounts of Z-phase was observed in the 9% Cr steels after long-term creep exposure. The size distribution of Laves phases was measured by image analysis of SEM-BSE images. In the 12% Cr steel two new phases were identified, Laves phase and Z-phase after almost 30,000 h of creep test. The quantification of the different precipitated phases was studied. (orig.)

Creep properties of phosphorus alloyed oxygen free copper under multiaxial stress state

International Nuclear Information System (INIS)

Rui Wu; Sandstroem, Rolf; Seitisleam, Facredin

2009-10-01

Phosphorus alloyed oxygen free copper (Cu-OFP) canisters are planned to be used for spent nuclear fuel in Sweden. The copper canisters will be subjected to creep under multiaxial stress states in the repository. Creep tests have therefore been carried out at 75 deg C using double notch specimens with notch acuities of 0.5, 2, 5, and 18.8, respectively. The creep lifetime for notched specimens is considerably longer than that for the smooth one at a given net section stress, indicating that the investigated Cu-OFP is notch insensitive (notch strengthening). The notch strengthening factor in time is, for instance, greater than 70 at 180 MPa for the bluntest notch (notch acuity = 0.5). The creep lifetime is notch acuity dependent. The sharper the notch, the longer the creep lifetime is. The creep deformation is to a significant extent concentrated to the region around the notches. Different deformation on the two notches is observed. Both axial and radial strains on the failed notch are several times larger than those on the unbroken one. Linear relation between the axial and the radial strains on the notches is found. Transgranular failure is predominant, independent of stress, rupture time, and notch acuity. Adjacent to fracture, elongated grains along the stress direction, separate pores and cavities are often visible. On the unbroken notch, fewer separate cavities and cracks are only seen intergranularly for the sharper notches (notch acuity > 2). To interpret the tests for the notched creep specimens, finite element computations have been performed. A fundamental model for primary and secondary creep without fitting parameters has been used as constitutive equation. The FEM-modelling could represent the creep strain versus time curves for the notched specimens in a satisfactory way. In these curves the strain on loading is included. From the FEM-computations a stationary creep stress could be assessed, which is close to the reference stress. For a given

A Model for Creep and Creep Damage in the γ-Titanium Aluminide Ti-45Al-2Mn-2Nb.

Science.gov (United States)

Harrison, William; Abdallah, Zakaria; Whittaker, Mark

2014-03-14

Gamma titanium aluminides (γ-TiAl) display significantly improved high temperature mechanical properties over conventional titanium alloys. Due to their low densities, these alloys are increasingly becoming strong candidates to replace nickel-base superalloys in future gas turbine aeroengine components. To determine the safe operating life of such components, a good understanding of their creep properties is essential. Of particular importance to gas turbine component design is the ability to accurately predict the rate of accumulation of creep strain to ensure that excessive deformation does not occur during the component's service life and to quantify the effects of creep on fatigue life. The theta (θ) projection technique is an illustrative example of a creep curve method which has, in this paper, been utilised to accurately represent the creep behaviour of the γ-TiAl alloy Ti -45Al-2Mn-2Nb. Furthermore, a continuum damage approach based on the θ-projection method has also been used to represent tertiary creep damage and accurately predict creep rupture.

The metallurgy of high temperature alloys

Science.gov (United States)

Tien, J. K.; Purushothaman, S.

1976-01-01

Nickel-base, cobalt-base, and high nickel and chromium iron-base alloys are dissected, and their microstructural and chemical components are assessed with respect to the various functions expected of high temperature structural materials. These functions include the maintenance of mechanical integrity over the strain-rate spectrum from creep resistance through fatigue crack growth resistance, and such alloy stability expectations as microstructural coarsening resistance, phase instability resistance and oxidation and corrosion resistance. Special attention will be given to the perennial conflict and trade-off between strength, ductility and corrosion and oxidation resistance. The newest developments in the constitution of high temperature alloys will also be discussed, including aspects relating to materials conservation.

Creep behavior of the titanium alloy with zirconia plasma sprayed coating

International Nuclear Information System (INIS)

Reis, D.A.P.; Moura Neto, C.; Couto, A.A.

2009-01-01

The proposal of this research has been the study of the plasma spayed coating on creep of the Ti-6Al-4V, focusing on the determination of the experimental parameters related to the first and second creep stages. Yttria (8 wt %) stabilized zirconia (YSZ) (Metco 204B-NS) with CoNiCrAlY ( AMDRY 995C) has been plasma sprayed coated on Ti-6Al-4V substrate. Creep tests with constant load had been done on Ti-6Al-4V coated samples, the stress level was from 250 to 319 MPa at 600 deg C. Highest values of t p and the decrease of the second stage rate had shown a better creep resistance on coated sample. Results indicate that the coated sample was greater than uncoated sample, thus the plasma sprayed coating prevent the sample oxidation efficiently. (author)

Finite strain transient creep of D16T alloy: identification and validation employing heterogeneous tests

Science.gov (United States)

Shutov, A. V.; Larichkin, A. Yu

2017-10-01

A cyclic creep damage model, previously proposed by the authors, is modified for a better description of the transient creep of D16T alloy observed in the finite strain range under rapidly changing stresses. The new model encompasses the concept of kinematic hardening, which allows us to account for the creep-induced anisotropy. The model kinematics is based on the nested multiplicative split of the deformation gradient, proposed by Lion. The damage evolution is accounted for by the classical Kachanov-Rabotnov approach. The material parameters are identified using experimental data on cyclic torsion of thick-walled samples with different holding times between load reversals. For the validation of the proposed material model, an additional experiment is analyzed. Although this additional test is not involved in the identification procedure, the proposed cyclic creep damage model describes it accurately.

Study on creep damage behaviors of Ni-based alloy C276

International Nuclear Information System (INIS)

Mao Xueping; Guo Qi; Zhang Shengyuan; Hu Suyang; Lu Daogang; Xu Hong

2013-01-01

High temperature creep tests were carried out for Ni-based alloy C276 at 650℃, 700℃ and 750℃, which is one of the candidate materials for the fuel cladding of the supercritical water reactor. Methods of damage mechanics were adopted to calculate and analyze these data. Damage factors calculated by Kachanov formula and Norton formula based on θ projection method were compared. The results show that the damage factors about the material are similar at the three temperatures according to Kachanov formula. The predicted creep curves calculated by θ projection method have a close agreement with the experimental data. The damages calculated by Norton formula start at about 0.3 - 0.4 lifetime, and the damage factors calculated by Kachanov formula are relatively conservative. (authors)

Review of creep resistant alloys for power plant applications

Directory of Open Access Journals (Sweden)

A. Nagode

2011-01-01

Full Text Available A paper describes the most popular alloys for power plant application as well as the most promising alloys for future application in that technology. The components in power plants operate in severe conditions (high temperatures and pressures and they are expected reliable service for 30 years and more. The correct choice of the material is, thus, of a very importance. The paper describes the development as well as advantages and disadvantages of convenient ferritic/martensitic steels, ferritic/bainitic steels, austenitic stainless steels and the new alloys for the application at temperatures of 650°C and more.

Fractal nature of aluminum alloys substructures under creep and its implications

Science.gov (United States)

Fernández, R.; Bruno, G.; González-Doncel, G.

2018-04-01

The present work offers an explanation for the variation of the power-law stress exponent, n, with the stress σ normalized to the shear modulus G in aluminum alloys. The approach is based on the assumption that the dislocation structure generated with deformation has a fractal nature. It fully explains the evolution of n with σ/G even beyond the so-called power law breakdown region. Creep data from commercially pure Al99.8%, Al-3.85%Mg, and ingot AA6061 alloy tested at different temperatures and stresses are used to validate the proposed ideas. Finally, it is also shown that the fractal description of the dislocation structure agrees well with current knowledge.

Effect of 1.0% Ni on high-temperature impression creep and hardness of recycled aluminium alloy with high Fe content

Science.gov (United States)

Faisal, M.; Mazni, Noor; Prasada Rao, A. K.

2018-03-01

Reported work focusses on the effect of 1.0% Ni addition on the microstructure, high- temperature impression creep and thereby the hardness of recycled Al-alloy containing >2wt% Fe, obtained from automotive scrap. Present studies have shown that the addition of 1.0% Ni have supress the formation of α-phase (Al5FeSi) by supressing the peritectic transformation of β-phase (Al8Fe2Si). Such suppression is found to improve the hardness and high-temperature impression creep of the recycled aluminium alloy.

Evaluation of creep-fatigue/ environment interaction in Ni-base wrought alloys for HTGR application

International Nuclear Information System (INIS)

Hattori, Hiroshi; Kitagawa, Masaki; Ohtomo, Akira

1986-01-01

High Temperature Gas-cooled Reactor (HTGR) systems should be designed based on the high temperature structural strength design procedures. On the development of design code, the determination of failure criteria under cyclic loading and severe environments is one of the most important items. By using the previous experimental data for Ni-base wrought alloys, Inconel 617 and Hastelloy XR, several evaluation methods for creep-fatigue interaction were examined for their capability to predict their cyclic loading behavior for HTGR application. At first, the strainrange partitioning method, the frequency modified damage function and the linear damage summation rule were discussed. However, these methods were not satisfactory with the above experimental results. Thus, in this paper, a new fracture criterion, which is a modification of the linear damage summation rule, is proposed based on the experimental data. In this criterion, fracture is considered to occur when the sum of the fatigue damage, which is the function of the applied cyclic strain magnitude, and the modified creep damage, which is the function of the applied cyclic stress magnitude (determined as time devided by cyclic creep rupture time reflecting difference of creep damages by tensile creep and compressive creep), reaches a constant value. This criterion was successfully applied to the life prediction of materials at HTGR temperatures. (author)

Strain change and creep behavior of STACIR/AW power line with heat exposure

Energy Technology Data Exchange (ETDEWEB)

Kim, B.G.; Park, S.D.; Kim, S.S.; Lee, H.W. [Overhead Conductor Research Lab., Korea Electrotechnology Research Inst., Changwon (Korea)

2005-07-01

As a way to expand electric capacity in power line with hovering of electric power demand, STACIR/AW (super thermal-resistant Al alloy conductors Al-clad Invar-reinforced) overhead conductor which cans double ampacity has been developed. The STACIR/AW power line is mechanically composite stranded wire composed of INVAR/AW stranded wire as core for sag control and heat-resistant aluminum alloy for delivering doubled electric current. Recently, in order to ensure stable line operation and to predict its span of life, the changes of thermal properties for STACIR/AW have been investigated. In the present work, the changes of strain with temperature and the creep behavior as important factors in sag control will be presented. The transition temperature of STACIR/AW 410 sqmm was estimated approximately 130 C and the creep rates were decreased with temperatures. (orig.)

Relaxation resistance of heat resisting alloys with cobalt

International Nuclear Information System (INIS)

Borzdyka, A.M.

1977-01-01

Relaxation resistance of refractory nickel-chromium alloys containing 5 to 14 % cobalt is under study. The tests involve the use of circular samples at 800 deg to 850 deg C. It is shown that an alloy containing 14% cobalt possesses the best relaxation resistance exceeding that of nickel-chromium alloys without any cobalt by a factor of 1.5 to 2. The relaxation resistance of an alloy with 5% cobalt can be increased by hardening at repeated loading

The effect of carbon distribution on deformation and cracking of Ni-16Cr-9Fe-C alloys

International Nuclear Information System (INIS)

Hertzberg, J.L.; Was, G.S.

1995-01-01

Constant extension rate tensile (CERT) tests and constant load tensile (CLT) tests were conducted on controlled purity Ni-16Cr-9Fe-C alloys. The amount and form of carbon were varied in order to investigate the roles of carbon in solution and as intergranular (IG) carbides in the deformation and IG cracking behavior in 360 C argon and primary water environments. Results show that the strength, ductility and creep resistance of these alloys are increased with carbon present in solid solution, while IG cracking on the fracture surface is suppressed. Alloys containing carbon in the form of IG carbides, however, exhibit reduced strength and ductility relative to carbon in solution, while maintaining high IG cracking resistance with respect to carbon-free alloys. CERT results of commercial alloy 600 and controlled purity, carbon containing alloys yield comparable failure strains and IG cracking amounts. CLT comparisons with creep tests of alloy 600 suggest that alloys containing IG carbides are more susceptible to creep than those containing all carbon in solid solution

Titanium and titanium alloy creep (a bibliography with abstracts). Report for 1964--Jun 1976

International Nuclear Information System (INIS)

Smith, M.F.

1976-08-01

Research is cited on creep of titanium and its alloys with regard to composition, stress corrosion, fracture, microstructure and tests. Many reports deal with applications to aircraft, spacecraft, and nuclear reactors. (This updated bibliography contains 133 abstracts, 24 of which are new entries to the previous edition.)

Novel Interpretation of High Temperature Creep in an ODS Cu-ZrO2 Alloy

Czech Academy of Sciences Publication Activity Database

Čadek, Josef; Kuchařová, Květa

2002-01-01

Roč. 40, č. 3 (2002), s. 133-145 ISSN 0023-432X R&D Projects: GA AV ČR IBS2041001 Institutional research plan: CEZ:AV0Z2041904 Keywords : ODS Cu Alloy s * Creep Subject RIV: JI - Composite Materials Impact factor: 0.493, year: 2002

Strengthening behavior of beta phase in lamellar microstructure of TiAl alloys

Science.gov (United States)

Zhu, Hanliang; Seo, D. Y.; Maruyama, K.

2010-01-01

β phase can be introduced to TiAl alloys by the additions of β stabilizing elements such as Cr, Nb, W, and Mo. The β phase has a body-centered cubic lattice structure and is softer than the α2 and γ phases in TiAl alloys at elevated temperatures, and hence is thought to have a detrimental effect on creep strength. However, fine β precipitates can be formed at lamellar interfaces by proper heat treatment conditions and the β interfacial precipitate improves the creep resistance of fully lamellar TiAl alloys, since the phase interface of γ/β retards the motion of dislocations during creep. This paper reviews recent research on high-temperature strengthening behavior of the β phase in fully lamellar TiAl alloys.

Effects of microstructure on creep of Ti-24Al-11Nb polycrystals

International Nuclear Information System (INIS)

Albert, D.E.

1991-01-01

The purpose was to determine the steady-state creep rate (CRSS) of various microstructures of Ti-24Al-11Nb (a/o). This alloy is a two-phase (β + α 2 ) Ti 3 Al-based aluminide with niobium added to stabilize β. The microstructure of the heat-treated alloy is lath α 2 surrounded by a thin film of β arranged in a basketweave morphology, while the as-received microstructure consists of equiaxed α 2 plus a small amount of β. SSCR vs. stress and vs. temperature curves were determined to find Q a , apparent creep activation energy, and n, power law stress exponent. At low stresses, Q a s determined for all microstructures were found to be between 106 kJ/mol and 145 kJ/mol, which agrees fairly well with the value of 121 kJ/mol previously obtained for grain boundary diffusional creep in titanium at low stresses. Mechanical-test results show that microstructures with a coarse α 2 lath size in general display improved creep resistance over fine-lathed structures. Specimens with an equiaxed α 2 phase microstructure exhibit much greater creep rates at all stresses and temperatures

The effect of alloying elements on the creep and impact properties of high Cr steels

International Nuclear Information System (INIS)

Kim, S. H.; Song, B. J.; Ryu, W. S.

2000-01-01

The effect of minor alloying elements on the creep and impact properties in high Cr steels has been studied. The addition of W and N in creased the creep rupture strength without the decrease of the impact toughness. During deformation, growth of lath width and agglomeration of precipitates and precipitation of Laves phase occurred. These microstructural changes made the steels soften. The degree of softening was delayed by the addition of W and N. In W added steel, the Laves phase had a important role in increasing the creep rupture strength. But the impact toughness was rapidly degraded by the addition of W after aging at 600 .deg. C for 5000 hours. So it needs to evaluate more accurately the effect of Laves phase on creep and impact properties. In N added steel, V(C,N) was precipitated in lath boundary and interior of lath. The size of the precipitates was 20-50nm. The increase of creep rupture strength in N added steel may be due to the precipitate of the V(C,N). So it needs more test to clarify the effect of N on the creep and impact properties

In-reactor creep of zirconium alloys by thermal spikes

International Nuclear Information System (INIS)

Ibrahim, E.F.

1975-01-01

The size and duration of thermal spikes from fast neutrons have been calculated for zirconium alloys, showing that spikes up to 1.8 nm radius may exist for 2 x 10 -11 s at greater than melting point, at 570K ambient temperature. Creep rates have been calculated assuming that the elastic strain from the applied stress relaxes in the volume of the spikes (by preferential loop alignment or modification of an existing dislocation network). The calculated rates are consistent with strain rates observed in long term tests-in-reactor, if spike lifetimes are 2 to 2.5 x 10 -11 s. (Auth.)

Structural characteristics and elevated temperature mechanical properties of AJ62 Mg alloy

Energy Technology Data Exchange (ETDEWEB)

Kubásek, J., E-mail: Jiri.Kubasek@vscht.cz; Vojtěch, D.; Martínek, M.

2013-12-15

Structure and mechanical properties of the novel casting AJ62 (Mg–6Al–2Sr) alloy developed for elevated temperature applications were studied. The AJ62 alloy was compared to commercial casting AZ91 (Mg–9Al–1Zn) and WE43 (Mg–4Y–3RE) alloys. The structure was examined by scanning electron microscopy, x-ray diffraction and energy dispersive spectrometry. Mechanical properties were characterized by Viskers hardness measurements in the as-cast state and after a long-term heat treatment at 250 °C/150 hours. Compressive mechanical tests were also carried out both at room and elevated temperatures. Compressive creep tests were conducted at a temperature of 250 °C and compressive stresses of 60, 100 and 140 MPa. The structure of the AJ62 alloy consisted of primary α-Mg dendrites and interdendritic nework of the Al{sub 4}Sr and massive Al{sub 3}Mg{sub 13}Sr phases. By increasing the cooling rate during solidification from 10 and 120 K/s the average dendrite arm thickness decreased from 18 to 5 μm and the total volume fraction of the interdendritic phases from 20% to 30%. Both factors slightly increased hardness and compressive strength. The room temperature compressive strength and hardness of the alloy solidified at 30 K/s were 298 MPa and 50 HV 5, i.e. similar to those of the as-cast WE43 alloy and lower than those of the AZ91 alloy. At 250 °C the compressive strength of the AJ62 alloy decreased by 50 MPa, whereas those of the AZ91 and WE43 alloys by 100 and 20 MPa, respectively. The creep rate of the AJ62 alloy was higher than that of the WE43 alloy, but significantly lower in comparison with the AZ91 alloy. Different thermal stabilities of the alloys were discussed and related to structural changes during elevated temperature expositions. - Highlights: • Small effect of cooling rate on the compressive strength and hardness of AJ 62 • A bit lower compressive strength of AJ 62 compared to AZ91 at room temperature • Higher resistance of the AJ 62

Effect of substituting cerium-rich mischmetal with lanthanum on high temperature properties of die-cast Mg-Zn-Al-Ca-RE alloys

International Nuclear Information System (INIS)

Anyanwu, Ifeanyi A.; Gokan, Yasuhiro; Suzuki, Atsuya; Kamado, Shigeharu; Kojima, Yo; Takeda, Suguru; Ishida, Taketoshi

2004-01-01

Mg-Zn-Al-Ca-RE alloys have been found to be promising materials for substituting aluminum alloys used for automatic transmission case applications in the automobile industry. Particularly, Mg-0.5%Zn-6%Al-1%Ca-3%RE (ZAXE05613) alloy exhibits comparable creep resistance as ADC12 die-casting aluminum alloy that is currently used for automatic transmission case applications. Changing the rare earth (RE) content of the alloy from mischmetal to lanthanum gives a further improvement in the creep properties of the alloy. Lanthanum addition results in the crystallization of a large amount of acicular Al 11 RE 3 (Al 11 La 3 ) compound along the grain boundaries as well as across the grain boundaries and this effectively controls grain boundary sliding and dislocation motion in the vicinity of the grain boundaries. As a result, die-cast ZAXLa05613 alloy exhibits a higher creep resistance than that of ZAXE05613 alloy

Effects of grain size on high temperature creep of fine grained, solution and dispersion hardened V-1.6Y-8W-0.8TiC

Energy Technology Data Exchange (ETDEWEB)

Furuno, T. [Ehime Univerisity, 3 Bunkyo-cho, Matsuyama 790-8577 (Japan); Kurishita, H., E-mail: kurishi@imr.tohoku.ac.jp [International Research Center for Nuclear Materials Science, Institute for Materials Research (IMR), Tohoku University, Oarai, Ibaraki 311-1313 (Japan); Nagasaka, T.; Nishimura, A.; Muroga, T. [Fusion Engineering Research Center, National Institute for Fusion Science (NIFS), Oroshi-cho 322-6, Tok, Gifu 292 (Japan); Sakamoto, T.; Kobayashi, S.; Nakai, K. [Department of Materials Science and Biotechnology, Ehime Univerisity, 3 Bunkyo-cho, Matsuyama 790-8577 (Japan); Matsuo, S.; Arakawa, H. [International Research Center for Nuclear Materials Science, Institute for Materials Research (IMR), Tohoku University, Oarai, Ibaraki 311-1313 (Japan)

2011-10-01

Creep resistance is the major concern of vanadium and its alloys for fusion reactor structural applications. In order to elucidate the effects of grain size on the creep behavior of solution and dispersion strengthened vanadium alloys, V-1.6Y-8W-0.8TiC specimens with fine grain sizes from 0.58 to 1.45 {mu}m were prepared by mechanical alloying and HIP without any plastic working and tested at 1073 K and 250 MPa in vacuum. It is shown that the creep resistance of V-1.6Y-8W-0.8TiC depends strongly on grain size and increases with increasing grain size: The creep life for the grain size of 1.45 {mu}m is almost one order longer than that of 0.58 {mu}m, and about two orders longer than that of V-4Cr-4Ti (NIFS-Heat 2) although the grain size of V-4Cr-4Ti is as large as 17.8 {mu}m. The observed creep behavior is discussed in terms of grain size effects on dislocation glide and grain boundary sliding.

Creep behavior under internal pressure of zirconium alloy cladding oxidized in steam at high temperature

International Nuclear Information System (INIS)

Chosson, Raphael

2014-01-01

During hypothetical Loss-Of-Coolant-Accident (LOCA) scenarios, zirconium alloy fuel cladding tubes creep under internal pressure and are oxidized on their outer surface at high temperature (HT). Claddings become stratified materials: zirconia and oxygen-stabilized α phase, called α(O), are formed on the outer surface of the cladding whereas the inner part remains in the β domain. The strengthening effect of oxidation on the cladding creep behavior under internal pressure has been highlighted at HT. In order to model this effect, the creep behavior of each layer had to be determined. This study focused on the characterization of the creep behavior of the α(O) phase at HT, through axial creep tests performed under vacuum on model materials, containing from 2 to 7 wt.% of oxygen and representative of the α(O) phase. For the first time, two creep flow regimes have been observed in this phase. Underlying physical mechanisms and relevant microstructural parameters have been discussed for each regime. The strengthening effect due to oxygen on the α(O) phase creep behavior at HT has been quantified and creep flow equations have been identified. A ductile to brittle transition criterion has been also suggested as a function of temperature and oxygen content. Relevance of the creep flow equations for each layer, identified in this study or from the literature, has been discussed. Then, a finite element model, describing the oxidized cladding as a stratified material, has been built. Based on this model, a fraction of the experimental strengthening during creep is predicted. (author) [fr

In-pile creep test technique for zirconium alloys examination in BR-10 reactor channels

International Nuclear Information System (INIS)

Pevchikh, Yu.M.; Kruglov, A.S.; Troyanov, V.M.

2002-01-01

The irradiation enhanced creep phenomenon was discovered in stainless steels as a specific physical process accompanying high-intensity neutron flux irradiation in fast reactors. IPPE is also experienced in irradiation creep test activities, studying different types of materials under irradiation in BR-10 fast reactor. Series of in-channel type test facilities were constructed and tested in BR-10 reactor's 'dry' channels in order to carry out full-scale instrumented examination regarded to in-pile creep behaviour of different reactor materials. As a result, a specific test technique, named 'Tensometric method', has been developed and experimentally proved to be power enough in order to investigate irradiation creep of materials right in situ under neutron irradiation. The main peculiarity of test facility, which is constructed to apply the tensometric method, consists in absence of any special deformation-measurement cell at all. The in-pile creep strain measurement technique developed at IPPE is based on the non-direct measurement of specimen's deformation (either linear tensile strain or angular twisting one), which directly affects the loaded draws' tension parameters. Starting from 1993, in-pile creep experiments to investigate in-reactor creep behaviour of E110 and E635 zirconium alloys were carried out in BR-10. Experimental results and data collected during more than 20-year of BR-10 in-reactor creep test experience can be assumed as a strong evidence that the tensometric technique is a powerful instrument, which can give a chance to study different irradiation effects on reactor materials directly under irradiation. (author)

Creep-rupture behavior of iron superalloys in high-pressure hydrogen

Science.gov (United States)

Bhattacharyya, S.; Peterman, W.

1984-01-01

The creep-rupture properties of five iron-base and one cobalt-base high temperature alloys were investigated to assess the feasibility of using the alloys as construction materials in a Stirling engine. The alloys were heat treated and hardness measurements were taken. Typical microstructures of the alloys are shown. The creep-rupture properties of the alloys were determined at 760 and 815 C in 15.0 MPa H2 for 200 to 1000 hours. Plots of rupture life versus stress for the six superalloys are presented along with creep strain-time plots.

Properties and application of new bainitic and martensitic creep resistance steels

International Nuclear Information System (INIS)

Pasternak, J.; Dobrzanski, J.

2008-01-01

Supercritical operating parameters of lower emission power units, require novel creep resisting steels to be applied for boiler and pipe systems. Among them are T23 bainitic steels for water walls of boiler combustion chamber and martensitic VM12 steels for superheater coils were tested. RAFAKO S.A. has been co-operating with the Silesian Technical University in Katowice, the Institute of Welding and the Institute for Ferrous Metallurgy in Gliwice for several years now, initiating research and development programmes, implementing the new creep-resistant steels and actively participating in European programmes COST522 and COST536. This paper contains selected information and test results before implementation of the new creep-resistant steels, including: evaluation of working parameters, temperature conditions of main boiler components, which influence reliability and safety, selection of steels for furnace chamber components (approx. 2.5 % Cr) and steam superheater components (9-12 % Cr) destination, evaluation of the requested level of welded joints technological and strength properties, measurements and non-destructive examinations, evaluation of welded joints and HAZ structure by means of LM, TEM and SEM methods in the welding technology implementation process, evaluation of corrosion mechanisms and creep-resistance results - loss of service life - for selected evaporator and steam superheater components, as crucial elements in evaluation of reliability and safety of boiler equipment. Such an examination program includes assessment of steel structure stability during operation period in actual operational conditions. It was clearly shown that operation period have little impact on changes occurring in microstructure and other properties of examined steel grades. (author)

Heat-resistant materials

CERN Document Server

1997-01-01

This handbook covers the complete spectrum of technology dealing with heat-resistant materials, including high-temperature characteristics, effects of processing and microstructure on high-temperature properties, materials selection guidelines for industrial applications, and life-assessment methods. Also included is information on comparative properties that allows the ranking of alloy performance, effects of processing and microstructure on high-temperature properties, high-temperature oxidation and corrosion-resistant coatings for superalloys, and design guidelines for applications involving creep and/or oxidation. Contents: General introduction (high-temperature materials characteristics, and mechanical and corrosion properties, and industrial applications); Properties of Ferrous Heat-Resistant Alloys (carbon, alloy, and stainless steels; alloy cast irons; and high alloy cast steels); Properties of superalloys (metallurgy and processing, mechanical and corrosion properties, degradation, and protective coa...

Neutron irradiation creep in stainless steel alloys

Energy Technology Data Exchange (ETDEWEB)

Schuele, Wolfgang (Commission of the European Union, Institute for Advanced Materials, I-21020 Ispra (Vatican City State, Holy See) (Italy)); Hausen, Hermann (Commission of the European Union, Institute for Advanced Materials, I-21020 Ispra (Vatican City State, Holy See) (Italy))

1994-09-01

Irradiation creep elongations were measured in the HFR at Petten on AMCR steels, on 316 CE-reference steels, and on US-316 and US-PCA steels varying the irradiation temperature between 300 C and 500 C and the stress between 25 and 300 MPa. At the beginning of an irradiation a type of primary'' creep stage is observed for doses up to 3-5 dpa after which dose the secondary'' creep stage begins. The primary'' creep strain decreases in cold-worked steel materials with decreasing stress and decreasing irradiation temperature achieving also negative creep strains depending also on the pre-treatment of the materials. These primary'' creep strains are mainly attributed to volume changes due to the formation of radiation-induced phases, e.g. to the formation of [alpha]-ferrite below about 400 C and of carbides below about 700 C, and not to irradiation creep. The secondary'' creep stage is found for doses larger than 3 to 5 dpa and is attributed mainly to irradiation creep. The irradiation creep rate is almost independent of the irradiation temperature (Q[sub irr]=0.132 eV) and linearly dependent on the stress. The total creep elongations normalized to about 8 dpa are equal for almost every type of steel irradiated in the HFR at Petten or in ORR or in EBR II. The negative creep elongations are more pronounced in PCA- and in AMCR-steels and for this reason the total creep elongation is slightly smaller at 8 dpa for these two steels than for the other steels. ((orig.))

Prediction of creep-fatigue life by use of creep rupture ductility

International Nuclear Information System (INIS)

Yamaguchi, Koji; Suzuki, Naoyuki; Ijima, Kiyoshi; Kanazawa, Kenji

1985-01-01

It was clarified that tension strain hold reduced creep-fatigue life of many engineering materials in different degrees depending on material, temperature and test duration. However the reduction in the life due to holding for various durations could be correlated to the fraction of intergranular facets on fracture surfaces which was considered to be an index of the damage introduced during strain hold. This fraction of intergranular facets by creep-fatigue failure exhibited a direct relation to the creep rupture ductility of the material tested at the same temperature and for the same creep-fatigue life-time. From these results an empirical equation has been derived as follow; (Δ sub(epsilonsub(i)))/Dsub(c).(N sub(h sup(α))) = C, where Δ sub(epsilonsub(i)) is inelastic strain range, Dsub(c) is the creep rupture ductility for the same duration as creep-fatigue life time, Nsub(h) is the creep-fatigue life under tension strain hold conditions, and α and C are constants depending on the material and testing temperature. From the equation the life prediction is possible for a given inelastic strain range Δ sub(epsilonsub(i)) if the constants α and C, and Dsub(c) are known. The value of α was found to be 0.62 and 0.74 for various austenitic stainless steels and NCF800 at 600 0 C and 700 0 C, respectively, and 0.69 for 1 1/4Cr-1/2Mo steel at 600 0 C. The value of C was found to be 0.50 and 0.59 for various austenitic stainless steels and NCF800 at 600 0 C and 700 0 C, respectively, and 0.49 for 1 1/4Cr-1/2Mo steel at 600 0 C. The creep rupture ductility Dsub(c) is available in the NRIM Creep Data Sheets up to 10 5 h for multi-heats of many kinds of heat resistant alloys. (author)

Investigation on Long-term Creep Rupture Properties and Microstructure Stability of Fe-Ni based Alloy Ni-23Cr-7W at 700°C

DEFF Research Database (Denmark)

Tokairin, Tsuyoshi; Dahl, Kristian Vinter; Danielsen, Hilmar Kjartansson

2013-01-01

Long-term creep rupture properties and microstructural stability of Fe–Ni based alloy Ni–23Cr–7W (HR6W, ASME Code Case 2684) were experimentally investigated. Crept specimens at 700 °C for durations up to 37,667 h were chosen, the microstructure evolution during creep was characterized. Besides...... for the main strengthening precipitate, Laves phase. The alloy was proven to have good microstructural stability without observable coarsening of strengthening precipitates during long-term creep up to around 37,667 h. It was also verified that the growth kinetics of Laves phase can be well described...

Properties of thick welded joints on superheater collectors made from new generation high alloy martensitic creep-resisting steels for supercritical parameters

Energy Technology Data Exchange (ETDEWEB)

Dobrzanski, Janusz; Zielinski, Adam [Institute for Ferrous Metallurgy, Gliwice (Poland); Pasternak, Jerzy [Boiler Engineering Company RAFAKO S.A., Raciborz (Poland)

2010-07-01

The continuously developing power generation sector, including boilers with supercritical parameters, requires applications of new creep-resistant steel grades for construction of boilers steam superheater components. This paper presents selected information, experience within the field of research and implementation of a new group of creep-resistant as X10CrMoVNb9-1(P91), X10CrWMoVNb9-2(P92) and X12CrCoWVNb12-2-2(VM12) grades, containing 9-12%Cr. During welding and examination process the results of mechanical properties, requested level for base material and welded joints, as well as: tensile strength, impact strength and technological properties have been evaluated. Additional destructive examinations, with evaluation of structure stability, hardness distribution, for base material and welded joints after welding, heat treatment, again process have been determined. Recommendations due to the implementation influence of operating parameters of the main boiler components are part of this paper. (orig.)

Microstructural characterisation and constitutive behaviour of alloy RR1000 under fatigue and creep-fatigue loading conditions

International Nuclear Information System (INIS)

Stoecker, C.; Zimmermann, M.; Christ, H.-J.; Zhan, Z.-L.; Cornet, C.; Zhao, L.G.; Hardy, M.C.; Tong, J.

2009-01-01

Mechanical behaviour of a nickel-based superalloy, RR1000, has been investigated at 650 deg. C under cyclic and dwell loading conditions. The microstructural characteristics of the alloy have been studied using scanning electron microscopy (SEM) and transmission electron microscopy (TEM), and the distribution patterns of the dislocations and slip planes have been compared between samples tested under fatigue and creep-fatigue loading conditions. Constitutive behaviour of the alloy was described by a unified constitutive model, where both cyclic plastic and viscoplastic strains were represented by one inelastic strain. The results show that the precipitation state is very stable at 650 deg. C and only minor differences exist in the dislocation arrangements formed under pure fatigue and combined creep and fatigue conditions. Hence, a unified constitutive model seems to be justified in describing and predicting the constitutive behaviour in both cases.

Mechanical behavior and related microstructural aspects of a nano-lamellar TiAl alloy at elevated temperatures

International Nuclear Information System (INIS)

Klein, T.; Usategui, L.; Rashkova, B.; Nó, M.L.; San Juan, J.; Clemens, H.; Mayer, S.

2017-01-01

Advanced intermetallic γ-TiAl based alloys, which solidify via the disordered β phase, such as the TNM"+ alloy, are considered as most promising candidates for structural applications at high temperatures in aero and automotive industries, where they are applied increasingly. Particularly creep resistant microstructures required for high-temperature application, i.e. fine fully lamellar microstructures, can be attained via two-step heat-treatments. Thereby, an increasing creep resistance is observed with decreasing lamellar interface spacing. Once lamellar structures reach nano-scaled dimensions, deformation mechanisms are altered dramatically. Hence, this study deals with a detailed characterization of the elevated temperature deformation phenomena prevailing in nano-lamellar TiAl alloys by the use of tensile creep experiments and mechanical spectroscopy. Upon creep exposure, microstructural changes occur in the lamellar structure, which are analyzed by the comparative utilization of X-ray diffraction, scanning and transmission electron microscopy as well as atom probe tomography. Creep activation parameters determined by mechanical characterization suggest the dominance of dislocation climb by a jog-pair formation process. The dislocations involved in deformation are, in nano-lamellar TiAl alloys, situated at the lamellar interfaces. During creep exposure the precipitation of β_o phase and ζ-silicide particles is observed emanating from the α_2 phase, which is due to the accumulation of Mo and Si at lamellar interfaces.

Creep properties and simulation of weld repaired low alloy heat resistant CrMo and Mo steels at 540 deg C. Sub project 1 - Ex-serviced parent metal and virgin weld metals

Energy Technology Data Exchange (ETDEWEB)

Rui Wu; Storesund, Jan; Borggreen, Kjeld; Weilin Zang

2006-10-15

Many existing power generating and process plants, where low alloy heat resistant CrMo(V) steels are extensively used for critical components, have exceeded their design lifetime of usually 100,000 hours. Assessment of residual lifetime and extension of economic life by weld repair have become increasingly important and attractive. This project aims at i) performing weld repair and determining the degree of mismatching, ii) evaluating the creep properties of weld repairs, iii) analysing creep behaviour of weld repair and providing necessary data for further reliable simulations of weld repair creep behaviour in long term service, and iv), simulating and assessing lifetime and creep damage evolution of weld repair. Weld repair using 10 CrMo 9 10, 13 CrMo 4 4 and 15 Mo 3 consumables has been carried out in a service-exposed 10 CrMo 9 10 pipe. Creep specimens have been extracted from the service-exposed 10 CrMo 9 10 parent metal (PM), from the virgin 10 CrMo 9 10 weld metal (WM), from the virgin 13 CrMo 4 4 WM as well as from the virgin 15 Mo 3 WM. Iso-thermal uniaxial creep tests have been performed at 540 deg C in air. Pre- and post-metallography are carried out on the selected samples. FEM simulations using obtained creep data are executed. Pre-test metallography shows normal and acceptable weld repairs at given welding conditions. Creep tests demonstrate that the virgin 10 CrMo 9 10, 13 CrMo 4 4 and 15 Mo 3 WMs have apparently longer creep lifetime than the service-exposed CrMo 9 10 PM at higher stresses than 110 MPa. Among the weld metals, the longest creep lifetime is found in 10 CrMo 9 10. Higher creep strength and lower creep strain rate in the weld metals indicate an overmatch weld. At 95 MPa, however, lifetime of 13 CrMo 4 4 WM is surprisingly short (factors which may shorten lifetime are discussed and one more test will start to verify creep strength at low stress) and tests are still running for other two weld metals. More results regarding low stress

Creep behaviour of a casting titanium carbide reinforced AlSi12CuNiMg piston alloy at elevated temperatures; Hochtemperaturkriechverhalten der schmelzmetallurgisch hergestellten dispersionsverstaerkten Kolbenlegierung AlSi12CuNiMg

Energy Technology Data Exchange (ETDEWEB)

Michel, S.; Scholz, A. [Zentrum fuer Konstruktionswerkstoffe, TU Darmstadt (Germany); Tonn, B. [Institut fuer Metallurgie, TU Clausthal (Germany); Zak, H.

2012-03-15

This paper deals with the creep behaviour of the titanium carbide reinforced AlSi12CuNiMg piston alloy at 350 C and its comparison to the conventional AlSi12Cu4Ni2MgTiZr piston alloy. With only 0,02 vol-% TiC reinforcement the creep strength and creep rupture strength of the AlSi12CuNiMg piston alloy are significantly improved and reach the level of the expensive AlSi12Cu4Ni2MgTiZr alloy. (Copyright copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

Microstructure and mechanical properties in cast magnesium-neodymium binary alloys

International Nuclear Information System (INIS)

Yan Jingli; Sun Yangshan; Xue Feng; Xue Shan; Tao Weijian

2008-01-01

The microstructure, tensile properties and creep behavior of three binary magnesium-neodymium (Mg-Nd) based alloys were investigated. The microstructure of all the alloys consists of the dendritic α-Mg matrix and a divorced eutectic Mg 12 Nd. With the increase of neodymium addition, the volume fraction of the Mg 12 Nd phase increases and an interphase network is visible with 4 wt% of neodymium addition. The addition of Nd to Mg causes significant improvement of creep properties and the creep resistance increases with the increase of Nd addition, which is account for by the combination of precipitation and solid solution hardening. For the Mg-2 wt%Nd alloy, a stress exponent of 4.5 and an apparent activation energy of 151.8 kJ/mol were obtained at 175 deg. C/50-90 MPa and 150-225 deg. C/70 MPa, respectively, suggesting that the mechanism responsible for creep in the present investigation is dislocation climb

Stabilization effect of Zr and Ti additions on the ageing characteristics of Al-1 wt% Si alloy through a creep study

Energy Technology Data Exchange (ETDEWEB)

Deaf, G.H.; Beshai, M.H.N.; Abd El Khalek, A.M.; Graiss, G. [Ain Shams Univ., Cairo (Egypt). Dept. of Physics; Kenawy, M.A. [Ain Shams Univ., Cairo (Egypt). Womens Coll.

1997-12-31

Al-1 wt% Si and Al-1 wt% Si-0.1 wt% Zr-0.1 wt% Ti alloys were used to trace the effect of Zr and Ti additions on the behaviour of the steady state creep. After solid solution treatment specimens of both alloys were aged at 623, 673, 723 and 773 K and creep tests were performed at room temperature by applying stresses of 60.0, 62.4, 64.7 and 67.1 MPa. The results showed a sound stabilization effect of Zr and Ti on the ageing characteristics of binary Al-1 wt% Si alloy. Values of the applied stress sensitivity parameter, m, obtained were in the range of (20-34) for Al-Si alloy and (14-19) for Al-Si-Zr-Ti alloy. Time to rupture was found to be strongly increased by Zr and Ti additions. The activation energies of the precipitation process involved were found to be 81.9 kJ/mole and 33.7 kJ/mole of the Al-Si and Al-Si-Zr-Ti alloys respectively. (orig.) 17 refs.

Correlation of creep rate with microstructural changes during high temperature creep

Science.gov (United States)

Young, C. T.; Sommers, B. R.; Lytton, J. L.

1977-01-01

Creep tests were conducted on Haynes 188 cobalt-base alloy and alpha titanium. The tests on Haynes 188 were conducted at 1600 F and 1800 F for stresses from 3 to 20 ksi, and the as-received, mill-annealed results were compared to specimens given 5%, 10%, and 15% room temperature prestrains and then annealed one hour at 1800 F. The tests on alpha titanium were performed at 7,250 and 10,000 psi at 500 C. One creep test was done at 527 C and 10,000 psi to provide information on kinetics. Results for annealed titanium were compared to specimens given 10% and 20% room temperature prestrains followed by 100 hours recovery at 550 C. Electron microscopy was used to relate dislocation and precipitate structure to the creep behavior of the two materials. The results on Haynes 188 alloy reveal that the time to reach 0.5% creep strain at 1600 F increases with increasing prestrain for exposure times less than 1,000 hours, the increase at 15% prestrain being more than a factor of ten.

High temperature creep behavior in the (α + β) phase temperature range of M5 alloy

International Nuclear Information System (INIS)

Trego, G.

2011-01-01

The isothermal steady-state creep behavior of a M5 thin sheet alloy in a vacuum environment was investigated in the (α + β) temperature, low-stress (1-10 MPa) range. To this aim, the simplest approach consists in identifying α and β creep flow rules in their respective single-phase temperature ranges and extrapolating them in the two-phase domain. However, the (α + β) experimental behavior may fall outside any bounds calculated using such creep flow data. Here, the model was improved for each phase by considering two microstructural effects: (i) Grain size: Thermo-mechanical treatments applied on the material yielded various controlled grain size distributions. Creep tests in near-α and near-β ranges evidenced a strong grain-size effect, especially in the diffusional creep regime. (ii) Chemical contrast between the two phases in the (α + β) range: From thermodynamic calculations and microstructural investigations, the β phase is enriched in Nb and depleted in O (the reverse being true for the α phase). Thus, creep tests were performed on model Zr-Nb-O thin sheets with Nb and O concentrations representative of each phase in the considered temperature range. New α and β creep flow equations were developed from this extended experimental database and used to compute, via a finite element model, the creep rates of the two-phase material. The 3D morphology of phases (β grains nucleated at α grain boundaries) was explicitly introduced in the computations. The effect of phase morphology on the macroscopic creep flow was shown using this specific morphology, compared to other typical morphologies and to experimental data. (author) [fr

Biaxial Creep Specimen Fabrication

Energy Technology Data Exchange (ETDEWEB)

JL Bump; RF Luther

2006-02-09

This report documents the results of the weld development and abbreviated weld qualification efforts performed by Pacific Northwest National Laboratory (PNNL) for refractory metal and superalloy biaxial creep specimens. Biaxial creep specimens were to be assembled, electron beam welded, laser-seal welded, and pressurized at PNNL for both in-pile (JOYO reactor, O-arai, Japan) and out-of-pile creep testing. The objective of this test campaign was to evaluate the creep behavior of primary cladding and structural alloys under consideration for the Prometheus space reactor. PNNL successfully developed electron beam weld parameters for six of these materials prior to the termination of the Naval Reactors program effort to deliver a space reactor for Project Prometheus. These materials were FS-85, ASTAR-811C, T-111, Alloy 617, Haynes 230, and Nirnonic PE16. Early termination of the NR space program precluded the development of laser welding parameters for post-pressurization seal weldments.

Biaxial Creep Specimen Fabrication

International Nuclear Information System (INIS)

JL Bump; RF Luther

2006-01-01

This report documents the results of the weld development and abbreviated weld qualification efforts performed by Pacific Northwest National Laboratory (PNNL) for refractory metal and superalloy biaxial creep specimens. Biaxial creep specimens were to be assembled, electron beam welded, laser-seal welded, and pressurized at PNNL for both in-pile (JOYO reactor, O-arai, Japan) and out-of-pile creep testing. The objective of this test campaign was to evaluate the creep behavior of primary cladding and structural alloys under consideration for the Prometheus space reactor. PNNL successfully developed electron beam weld parameters for six of these materials prior to the termination of the Naval Reactors program effort to deliver a space reactor for Project Prometheus. These materials were FS-85, ASTAR-811C, T-111, Alloy 617, Haynes 230, and Nirnonic PE16. Early termination of the NR space program precluded the development of laser welding parameters for post-pressurization seal weldments

Mathematic modeling of reactor fuel radiation creep at example of uranium and its alloys

International Nuclear Information System (INIS)

Tarasov, V.A.

2001-01-01

The model of a radiation creep is explained within the framework of the mechanism of gliding and climbing dislocations based on the conception of a dislocation as not ideal sink for point radiation defects (PRD). The offered model is efficient for installed concentration PRD, considerably exceeding thermally steady state concentration. The gliding of dislocation are describing as due to moving dislocation kinks in Peierl's relief. The climbing of dislocation are describing as due to moving dislocation jogs. The mathematical model for the computer program simulating the offered model of radiation creep is developed. The complex of the computer programs simulating the radiation creep is developed. The computer simulation researches are conducted and the outcomes of a research of a kinetics of a flexible sliding and climbing dislocation interacting to obstacles of a various type (spherical centre of extension, dislocation prismatic loop and their spatially random distributions) for various installed concentration PRD, external loadings and temperatures are represented. The curves of installed rate of a radiation creep from temperature for uranium and its alloys with small additions of molybdenum (from 0,9 to 1,3 %) are obtained

Hydrogen in titanium alloys

International Nuclear Information System (INIS)

Wille, G.W.; Davis, J.W.

1981-04-01

The titanium alloys that offer properties worthy of consideration for fusion reactors are Ti-6Al-4V, Ti-6Al-2Sn-4Zr-2Mo-Si (Ti-6242S) and Ti-5Al-6Sn-2Zr-1Mo-Si (Ti-5621S). The Ti-6242S and Ti-5621S are being considered because of their high creep resistance at elevated temperatures of 500 0 C. Also, irradiation tests on these alloys have shown irradiation creep properties comparable to 20% cold worked 316 stainless steel. These alloys would be susceptible to slow strain rate embrittlement if sufficient hydrogen concentrations are obtained. Concentrations greater than 250 to 500 wppm hydrogen and temperatures lower than 100 to 150 0 C are approximate threshold conditions for detrimental effects on tensile properties. Indications are that at the elevated temperature - low hydrogen pressure conditions of the reactors, there would be negligible hydrogen embrittlement

Micromechanical Modeling of Grain Boundaries Damage in a Copper Alloy Under Creep

International Nuclear Information System (INIS)

Voese, Markus

2015-01-01

In order to include the processes on the scale of the grain structure into the description of the creep behaviour of polycrystalline materials, the damage development of a single grain boundary has been initially investigated in the present work. For this purpose, a special simulationmethod has been used, whose resolution procedure based on holomorphic functions. The mechanisms taken into account for the simulations include nucleation, growth by grain boundary diffusion, coalescence and shrinkage until complete sintering of grain boundary cavities. These studies have then been used to develop a simplified cavitation model, which describes the grain boundary damage by two state variables and the time-dependent development by a mechanism-oriented rate formulation. To include the influence of grain boundaries within continuum mechanical considerations of polycrystals, an interface model has been developed, that incorporates both damage according to the simplified cavitation model and grain boundary sliding in dependence of a phenomenological grain boundary viscosity. Furthermore a micromechanical model of a polycrystal has been developed that allows to include a material's grain structure into the simulation of the creep behaviour by means of finite element simulations. Thereby, the deformations of individual grains are expressed by a viscoplastic single crystal model and the grain boundaries are described by the proposed interface model. The grain structure is represented by a finite element model, in which the grain boundaries are modelled by cohesive elements. From the evaluation of experimental creep data, the micromechanical model of a polycrystal has been calibrated for a copper-antimony alloy at a temperature of 823 K. Thereby, the adjustment of the single crystal model has been carried out on the basis of creep rates of pure copper single crystal specimens. The experimental determination of grain boundary sliding and grain boundary porosity for coarse

Influenced prior loading on the creep fatigue damage accumulation of heat resistant steels

International Nuclear Information System (INIS)

Kloos, K.H.; Granacher, J.; Scholz, A.

1990-01-01

On two heat resistant power plant steels the influence of prior strain cycling on the creep rupture behaviour and the influence of prior creep loading on the strain cycling behaviour is investigated. These influences concern the number of cycles to failure and the rupture time being the reference values of the generalized damage accumulation rule and they are used for a creep fatigue analysis of the results of long term service-type strain cycling tests. (orig.) [de

Processing, Microstructure and Creep Behavior of Mo-Si-B-Based Intermetallic Alloys for Very High Temperature Structural Applications

Energy Technology Data Exchange (ETDEWEB)

Vijay Vasudevan

2008-03-31

This research project is concerned with developing a fundamental understanding of the effects of processing and microstructure on the creep behavior of refractory intermetallic alloys based on the Mo-Si-B system. In the first part of this project, the compression creep behavior of a Mo-8.9Si-7.71B (in at.%) alloy, at 1100 and 1200 C was studied, whereas in the second part of the project, the constant strain rate compression behavior at 1200, 1300 and 1400 C of a nominally Mo-20Si-10B (in at.%) alloy, processed such as to yield five different {alpha}-Mo volume fractions ranging from 5 to 46%, was studied. In order to determine the deformation and damage mechanisms and rationalize the creep/high temperature deformation data and parameters, the microstructure of both undeformed and deformed samples was characterized in detail using x-ray diffraction, scanning electron microscopy (SEM) with back scattered electron imaging (BSE) and energy dispersive x-ray spectroscopy (EDS), electron back scattered diffraction (EBSD)/orientation electron microscopy in the SEM and transmission electron microscopy (TEM). The microstructure of both alloys was three-phase, being composed of {alpha}-Mo, Mo{sub 3}Si and T2-Mo{sub 5}SiB{sub 2} phases. The values of stress exponents and activation energies, and their dependence on microstructure were determined. The data suggested the operation of both dislocation as well as diffusional mechanisms, depending on alloy, test temperature, stress level and microstructure. Microstructural observations of post-crept/deformed samples indicated the presence of many voids in the {alpha}-Mo grains and few cracks in the intermetallic particles and along their interfaces with the {alpha}-Mo matrix. TEM observations revealed the presence of recrystallized {alpha}-Mo grains and sub-grain boundaries composed of dislocation arrays within the grains (in Mo-8.9Si-7.71B) or fine sub-grains with a high density of b = 1/2<111> dislocations (in Mo-20Si-10B), which

Influence of S, P, C on grain boundary diffusion and creep properties of Alloy 800; Einfluss von S, P, C auf die Korngrenzendiffusion und Kriecheigenschaften von Alloy 800

Energy Technology Data Exchange (ETDEWEB)

Lindemann, J.; Hannesen, K.; Mast, R.; Viefhaus, H. [Max-Planck-Institut fuer Eisenforschung GmbH, Duesseldorf (Germany); Grabke, H.J.

1998-12-31

The paper reports examinations of Alloy 800 and specific commercially available variants known under the names of 800H, 800HT, and 800LC, differing in their concentrations of C, Al, and Ti. In addition, melts also containing phosphorus (0.09 wt-%) or sulfur (0.04 wt-%) as additional alloying materials have been prepared for the experiments. The volume diffusion and the grain boundary diffusion of {sup 59}Fe in those alloys was measured at temperatures between 800 and 1000 C by means of a radioactive tracer method combined with residual activity measurements. It was found that accompanying elements like phosphorus and sulfur increase the activation energy of the grain boundary diffusion of the iron and thus delay the grain boundary self-diffusion in Alloy 800. Creep curves were measured of the same materials after age-hardening treatment for 100 hours at 800 C, measurements performed at constant temperature but at three different, constant creep stress loads. The results showed that addition of phosphorus markedly increases the lifetime of Alloy 800, and reduces the creep rupture strain. The minimum strain rate in Alloy 800 containing 0.09 wt-% of phosphorus was found to be lower by a factor of 100, as compared to the other Alloy 800 materials used. (orig./CB) [Deutsch] Alloy 800 ist ein austenitischer Fe-Ni-Cr Stahl, der relativ geringe, aber wichtige Konzentrationen von Kohlenstoff, Aluminium und Titan enthaelt. Besondere Varianten von Alloy 800, bekannt als 800H, 800HT und 800LC, unterscheiden sich in den Konzentrationen dieser Elemente. Diese kommerziellen Legierungen wurden untersucht, und zusaetzlich wurden Schmelzen mit zulegiertem Phosphor (0,09 Gew-%) bzw. Schwefel (0,04 Gew-%) hergestellt. Mittels einer radioaktiven Tracermethode in Verbindung mit Restaktivitaetsmessungen wurde die Volumen- und Korngrenzendiffusion von {sup 59}Fe in diesen Legierungen im Temperaturbereich 800-1000 C gemessen. Es wurde gefunden, dass Begleitelemente wie Phosphor und

Optimum tungsten content in high strength 9 to 12% chromium containing creep resistant steels

International Nuclear Information System (INIS)

Hasegawa, Y.; Muraki, T.; Mimura, H.

2000-01-01

Tungsten containing ferritic creep resistant steels are the candidate materials for ultra-super-critical fossil power plant because of their high creep rupture strength. But the strengthening mechanisms by tungsten addition have not yet been completely studied. In this report, creep rupture time and creep strain rate measurement decided the optimum tungsten content in 9 to 12% chromium ferritic steels. The precipitation behavior of Laves phase and the precise discussion of creep strain rate analyses explain the contribution of Laves phase at the lath boundary and the contribution of tungsten in solid solution. P92 contains the optimum amount of tungsten and chromium, 1.8 mass% and 9 mass% respectively judging from the creep rupture strength point of view. (orig.)

Study on creep behavior of Grade 91 heat-resistant steel using theta projection method

Science.gov (United States)

Ren, Facai; Tang, Xiaoying

2017-10-01

Creep behavior of Grade 91 heat-resistant steel used for steam cooler was characterized using the theta projection method. Creep tests were conducted at the temperature of 923K under the stress ranging from 100-150MPa. Based on the creep curve results, four theta parameters were established using a nonlinear least square fitting method. Four theta parameters showed a good linearity as a function of stress. The predicted curves coincided well with the experimental data and creep curves were also modeled to the low stress level of 60MPa.

Preliminary application of the draft code case for alloy 617 for a high temperature component

International Nuclear Information System (INIS)

Lee, Hyeong Yeon; Kim, Yong Wan; Song, Kee Nam

2008-01-01

The ASME draft Code Case for Alloy 617 was developed in the late 1980s for the design of very-high-temperature gas cooled reactors. The draft Code Case was patterned after the ASME Code Section III Subsection NH and was intended to cover Ni-Cr-Co-Mo Alloy 617 to 982 .deg. C (1800 .deg. F). But the draft Code Case is still in an incomplete status, lacking necessary material properties and design data. In this study, a preliminary evaluation on the creep-fatigue damage for a high temperature hot duct pipe structure has been carried out according to the draft Code Case. The evaluation procedures and results according to the draft Code Case for Alloy 617 material were compared with those of the ASME Subsection NH and RCC-MR for Alloy 800H material. It was shown that many data including material properties, fatigue and creep data should be supplemented for the draft Code Case. However, when the evaluation results on the creep-fatigue damage according to the draft Code Case, ASME-NH and RCC-MR were compared based on the preliminary evaluation, it was shown that the Alloy 617 results from the draft Code Case tended to be more resistant to the creep damage while less resistant to the fatigue damage than those from the ASME-NH and RCC-MR

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.

Low-cycle fatigue of heat-resistant alloys in high-temperature gas-cooled reactor helium

International Nuclear Information System (INIS)

Tsuji, H.; Kondo, T.

1984-01-01

Strain controlled low-cycle fatigue tests were conducted on four nickel-base heat-resistant alloys at 900 0 C in simulated high-temperature gas-cooled reactor (HTGR) environments and high vacuums of about 10 -6 Pa. The observed behaviors of the materials were different and divided into two groups when tests were made in simulated HTGR helium, while all materials behaved similarly in vacuums. The materials that have relatively high ductility and compatibility with impure helium at test temperature showed considerable resistance to the fatigue damage in impure helium. On the other hand, the alloys qualified with their high creep strength were seen to suffer from the adverse effects of impure helium and the trend of intergranular cracking as well. The results were analyzed in terms of their susceptibility to the environmentenhanced fatigue damage by examining the ratios of the performance in impure helium to in vacuum. The materials that showed rather unsatisfactory resistance were considered to be characterized by their limited ductility partly due to their coarse grain structure and susceptibility to intergranular oxidation. Moderate carburization was commonly noted in all materials, particularly at the cracked portions, indicating that carbon intrusion had occurred during the crack growth stage

Alloying principles for magnesium base heat resisting alloys

International Nuclear Information System (INIS)

Drits, M.E.; Rokhlin, L.L.; Oreshkina, A.A.; Nikitina, N.I.

1982-01-01

Some binary systems of magnesium-base alloys in which solid solutions are formed, are considered for prospecting heat resistant alloys. It is shown that elements having essential solubility in solid magnesium strongly decreasing with temperature should be used for alloying maqnesium base alloys with high strength properties at increased temperatures. The strengthening phases in these alloys should comprise essential quantity of magnesium and be rather refractory

Improved creep and oxidation behavior of a martensitic 9Cr steel by the controlled addition of boron and nitrogen

Energy Technology Data Exchange (ETDEWEB)

Mayr, Peter [Massachusetts Institute of Technology, Cambridge, MA (United States). Dept. of Materials Science; Graz Univ. of Technology (Austria). Inst. of Material Science and Welding; Holzer, Ivan; Mendez-Martin, Francisca [Graz Univ. of Technology (Austria). Inst. of Material Science and Welding; Albu, Mihaela; Mitsche, Stefan [Graz Univ. of Technology (Austria). Inst. for Electron Microscopy; Gonzalez, Vanessa; Agueero, Alina [Instituto Nacional de Tecnica Aeroespacial, Torrejon de Ardoz (Spain)

2010-07-01

This manuscript gives an overview on recent developments of a martensitic steel grade based on 9Cr3W3CoVNb with controlled additions of boron and nitrogen. Alloy design by thermodynamic equilibrium calculations and calculation of boron-nitrogen solubility is discussed. Out of this alloy design process, two melts of a 9Cr3W3CoVNbBN steel were produced. The investigation focused on microstructural evolution during high temperature exposure, creep properties and oxidation resistance in steam at 650 C. Microstructural characterization of ''as-received'' and creep exposed material was carried out using conventional optical as well as advanced electron microscopic methods. Creep data at 650 was obtained at various stress levels. Longest-running specimens have reached more than 20,000 hours of testing time. In parallel, long-term oxidation resistance has been studied at 650 C in steam atmosphere up to 5,000 hours. Preliminary results of the extensive testing program on a 9Cr3W3CoVNbBN steel show significant improvement in respect to creep strength and oxidation resistance compared to the state-of-the-art 9 wt. % Cr martensitic steel grades. Up to current testing times, the creep strength is significantly beyond the +20% scatterband of standard grade P92 material. Despite the chromium content of 9 wt % the material exhibits excellent oxidation resistance. Steam exposed plain base material shows comparable oxidation behavior to coated material, and the corrosion rate of the boron-nitrogen controlled steel is much lower compared to standard 9 wt % Cr steel grades, P91 and P92. (orig.)

Development of Fe-Ni and Ni-base alloys without {gamma}' strengthening for advanced USC boilers

Energy Technology Data Exchange (ETDEWEB)

Semba, Hiroyuki; Okada, Hirokazu; Igarashi, Masaaki; Hirata, Hiroyuki [Sumitomo Metal Industries, Ltd., Amagasaki, Hyogo (Japan). Corporate Research and Development Labs.; Yoshizawa, Mitsuru [Sumitomo Metal Industries Ltd., Amagasaki, Hyogo (Japan). Steel Tube Works

2010-07-01

An Fe-Ni base alloy, 23Cr-45Ni-7W alloy (HR6W) strengthened by Fe{sub 2}W-type Laves phase is one of the candidate materials for the piping application. Stability of long-term creep strength and superior creep rupture ductility have been proved by creep rupture tests up to 60000h at 650-800 C. The 10{sup 5}h extrapolated creep rupture strength at 700 C approved by TUV is 85MPa. It has also been confirmed that HR6W has excellent microstructural stability by means of microstructural observations after term creep tests and aging. A thick wall pipe of HR6W, which is 457mm in diameter and 60mm in wall thickness, has successfully been manufactured by the Erhart Push Bench press method. This trial production has shown that hot workability of HR6W is sufficient for manufacturing thick wall piping for A-USC plants. A new Ni-base alloy, 30r-50Ni-4W alloy (HR35) has been proposed for piping application having comparable creep rupture strength with Alloy 617 at 700 C. This alloy is not strengthened by {gamma}' phase but mainly by {alpha}-Cr phase. The 10{sup 5}h extrapolated creep rupture strength is estimated to be 114 MPa at 700 C. It has sufficient creep rupture ductility compared with Alloy 617. A thick wall pipe of HR35 has also been successfully manufactured. Capability of HR6W and HR35 as structural materials for A-USC plants has been examined in detail. They have high resistance to relaxation cracking after welding. It is, therefore, concluded that both the alloys are promising candidates especially for thick wall piping in A-USC power plants. (orig.)

Dispersoid reinforced alloy powder and method of making

Energy Technology Data Exchange (ETDEWEB)

Anderson, Iver E.; Terpstra, Robert L.

2017-12-05

A method of making dispersion-strengthened alloy particles involves melting an alloy having a corrosion and/or oxidation resistance-imparting alloying element, a dispersoid-forming element, and a matrix metal wherein the dispersoid-forming element exhibits a greater tendency to react with a reactive species acquired from an atomizing gas than does the alloying element. The melted alloy is atomized with the atomizing gas including the reactive species to form atomized particles so that the reactive species is (a) dissolved in solid solution to a depth below the surface of atomized particles and/or (b) reacted with the dispersoid-forming element to form dispersoids in the atomized particles to a depth below the surface of said atomized particles. The atomized alloy particles are solidified as solidified alloy particles or as a solidified deposit of alloy particles. Bodies made from the dispersion strengthened alloy particles, deposit thereof, exhibit enhanced fatigue and creep resistance and reduced wear as well as enhanced corrosion and/or oxidation resistance at high temperatures by virtue of the presence of the corrosion and/or oxidation resistance imparting alloying element in solid solution in the particle alloy matrix.

Dispersoid reinforced alloy powder and method of making

Energy Technology Data Exchange (ETDEWEB)

Anderson, Iver E.; Terpstra, Robert L.

2017-10-10

A method of making dispersion-strengthened alloy particles involves melting an alloy having a corrosion and/or oxidation resistance-imparting alloying element, a dispersoid-forming element, and a matrix metal wherein the dispersoid-forming element exhibits a greater tendency to react with a reactive species acquired from an atomizing gas than does the alloying element. The melted alloy is atomized with the atomizing gas including the reactive species to form atomized particles so that the reactive species is (a) dissolved in solid solution to a depth below the surface of atomized particles and/or (b) reacted with the dispersoid-forming element to form dispersoids in the atomized particles to a depth below the surface of said atomized particles. The atomized alloy particles are solidified as solidified alloy particles or as a solidified deposit of alloy particles. Bodies made from the dispersion strengthened alloy particles, deposit thereof, exhibit enhanced fatigue and creep resistance and reduced wear as well as enhanced corrosion and/or oxidation resistance at high temperatures by virtue of the presence of the corrosion and/or oxidation resistance imparting alloying element in solid solution in the particle alloy matrix.

Grain-boundary sliding in a TiAl alloy with fine-grained duplex microstructure during 750 deg. C creep

Energy Technology Data Exchange (ETDEWEB)

Peter, D. [Ruhr University Bochum, Institute for Materials, D-44780 Bochum (Germany); Viswanathan, G.B., E-mail: Viswanathan.11@osu.edu [Ruhr University Bochum, Institute for Materials, D-44780 Bochum (Germany) and Department of Materials Science and Engineering, Ohio State University, Columbus, OH 43210 (United States); Wagner, M.F.-X.; Eggeler, G. [Ruhr University Bochum, Institute for Materials, D-44780 Bochum (Germany)

2009-06-15

Constant-load creep experiments at a temperature of 750 deg. C and a nominal stress of 300 MPa were conducted on a fine-grained Ti-45Al-5Nb-0.2B-0.2C (in at.%) alloy with a duplex microstructure. Microstructures before and after creep (accumulated strain: 9.6%) were analyzed using scanning and transmission electron microscopy (SEM and TEM). TEM analysis after creep indicates that the individual microstructural constituents of the fine duplex microstructure, namely, the equiaxed {gamma} and the lamellar {alpha}{sub 2}/{gamma} colonies, undergo varying degrees of deformation and develop various substructures. Lamellar grains deform by dislocation creep. They show clear evidence for dislocation and twin activity. In contrast, only few dislocations are found in the equiaxed grains. We show that the regions with small equiaxed {gamma} grains, representing 65-75 vol.% of the microstructure, deform by grain-boundary sliding.

Grain-boundary sliding in a TiAl alloy with fine-grained duplex microstructure during 750 deg. C creep

International Nuclear Information System (INIS)

Peter, D.; Viswanathan, G.B.; Wagner, M.F.-X.; Eggeler, G.

2009-01-01

Constant-load creep experiments at a temperature of 750 deg. C and a nominal stress of 300 MPa were conducted on a fine-grained Ti-45Al-5Nb-0.2B-0.2C (in at.%) alloy with a duplex microstructure. Microstructures before and after creep (accumulated strain: 9.6%) were analyzed using scanning and transmission electron microscopy (SEM and TEM). TEM analysis after creep indicates that the individual microstructural constituents of the fine duplex microstructure, namely, the equiaxed γ and the lamellar α 2 /γ colonies, undergo varying degrees of deformation and develop various substructures. Lamellar grains deform by dislocation creep. They show clear evidence for dislocation and twin activity. In contrast, only few dislocations are found in the equiaxed grains. We show that the regions with small equiaxed γ grains, representing 65-75 vol.% of the microstructure, deform by grain-boundary sliding.

TEM characterization of microstructure evolution of 12%Cr heat resistant steels

Energy Technology Data Exchange (ETDEWEB)

Rojas, D.; Prat, O.; Sauthoff, G. [Max-Planck-Institut fuer Eisenforschung GmbH, Duesseldorf (Germany); Garcia, J. [Helmholtz-Zentrum Berlin fuer Materialien und Energie GmbH, Berlin (Germany); Kaysser-Pyzalla, A.R. [Helmholtz-Zentrum Berlin fuer Materialien und Energie GmbH, Berlin (Germany); Bochum Univ. (Germany)

2010-07-01

A detailed characterization of the microstructure evolution of 12%Cr heat resistant steels at different creep times (100 MPa / 650 C / 8000 h) were carried out by scanning transmission electron microscopy (STEM). The results of the microstructure analysis are correlated with the mechanical properties in order to investigate the influence of different precipitates (especially M{sub 23}C{sub 6}) on the creep strength of the alloys. Precipitation of Laves phase and Z-phase was observed after several hours creep time. Very few Z-phase of the type Cr(V,Ta)N nucleating from existing (V,Ta)(C,N) was observed. Both alloys show growth and coarsening of Laves phase, meanwhile the MX carbonitrides present a very slow growth and coarsening rate. Alloys containing Laves phase, MX and M{sub 23}C{sub 6} precipitates show best creep properties. (orig.)

Development and testing ov danadium alloys for fusion applications

Energy Technology Data Exchange (ETDEWEB)

Chung, H.M.; Loomis, B.A.; Smith, D.L.

1996-10-01

V base alloys have advantages for fusion reactor first-wall and blanket structure. To screen candidate alloys and optimize a V-base alloy, physical and mechanical properties of V-Ti, V-Cr-Ti, and V-Ti- Si alloys were studied before and after irradiation in Li environment in fast fission reactors. V-4Cr-4Ti containing 500-1000 wppM Si and <1000 wppM O+N+C was investigated as the most promising alloy, and more testing is being done. Major results of the work are presented in this paper. The reference V-4Cr-4Ti had the most attractive combination of the mechanical and physical properties that are prerequisite for first-wall and blanket structures: good thermal creep, good tensile strength/ductility, high impact energy, excellent resistance to swelling, and very low ductile-brittle transition temperature before and after irradiation. The alloy was highly resistant to irradiation-induced embrittlement in Li at 420-600 C, and the effects of dynamically charged He on swelling and mechanical properties were insignificant. However, several important issues remain unresolved: welding, low-temperature irradiation, He effect at high dose and high He concentration, irradiation creep, and irradiation performance in air or He. Initial results of investigation of some of these issues are also given.

Creep and low cycles fatigue behaviour of inconel 617 and alloy 800H in the temperature range 1073-1223

International Nuclear Information System (INIS)

Yun, H.M.

1984-01-01

The creep rupture properties of high temperature alloys are being determined as part of the materials programme for the development of the high temperature, gas-cooled reactor (HTGR) as a source of nuclear process heat, especially for the gasification of lignite and coal. INCOLOY 800H AND INCONEL 617 have been tested in the temperature range from 1073 K to 1223 K in air as well as in helium with HTGR specific impurities. The static and dynamic creep behaviour of INCONEL 617 have been determined in constant load creep tests, relaxation tests and stress reduction tests. The results have been interpreted using the internal stress on the applied stress and test temperature was determined. In a few experiments the influence of cold deformation prior to the creep test on the magnitude of the internal stress was also investigated. (Author)

Effect of Bi-content on hardness and micro-creep behavior of Sn-3.5Ag rapidly solidified alloy

Energy Technology Data Exchange (ETDEWEB)

Kamal, M. [Metal Physics Laboratory, Faculty of Science, Mansoura University (Egypt); Gouda, El Said [Metal Physics Laboratory, Department of Solid State Physics, Physics Division, National Research Center, Dokki, Giza (Egypt); Marei, L.K. [Faculty of Petroleum and Mining Engineering, Suez Canal University, Suez (Egypt)

2009-12-15

In the present paper, the influence of 1, 3, 5 and 10 % Bi (weight %) as ternary additions on structure, melting and mechanical properties of rapidly solidified Sn-3.5Ag alloy has been investigated. The effect of Bi was discussed based on the experimental results. The experimental results showed that the alloys of Sn-3.5Ag, Sn-3.5Ag-1Bi and Sn-3.5Ag-3Bi are composed of two phases; Ag{sub 3}Sn IMC embedded in Sn matrix phase, which indicated that the solubility of Bi phase in Sn-matrix was extended to 3 % as a result of rapid solidification. Bi precipitation in Sn matrix was only observed in Sn-3.5Ag-5Bi and Sn-3.5Ag-10Bi alloys. Also, addition of Bi decreased continuously the melting point of the eutectic Sn-3.5Ag alloy to 202.6 C at 10 % Bi. Vickers hardness of Sn-3.5Ag rapidly solidified alloy increased with increasing Bi content up to 3 % due to supersaturated solid solution strengthening hardening mechanism of Bi phase in Sn matrix, while the alloys contain 5 and 10 % Bi exhibited lower values of Vickers hardness. The lower values can be attributed to the precipitation of Bi as a secondary phase which may form strained regions due to the embrittlement of Bi atom. In addition, the effect of Bi addition on the micro-creep behavior of Sn-3.5Ag alloy as well as the creep rate have been described and has been calculated at room temperature. (copyright 2009 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Irradiation creep experiments on fusion reactor candidate structural materials

International Nuclear Information System (INIS)

Hausen, H.; Cundy, M.R.; Schuele, W.

1991-01-01

Irradiation creep rates were determined for annealed and cold-worked AMCR- and 316-type steel alloys in the high flux reactor at Petten, for various irradiation temperatures, stresses and for neutron doses up to 4 dpa. Primary creep elongations were found in all annealed materials. A negative creep elongation was found in cold-worked materials for stresses equal to or below about 100 MPa. An increase of the negative creep elongation is found for decreasing irradiation temperatures and decreasing applied stresses. The stress exponent of the irradiation creep rate in annealed and cold-worked AMCR alloys is n = 1.85 and n = 1.1, respectively. The creep rates of cold-worked AMCR alloys are almost temperature independent over the range investigated (573-693 K). The results obtained in the HFR at Petten are compared with those obtained in ORR and EBR II. The smallest creep rates are found for cold-worked materials of AMCR- and US-PCA-type at Petten which are about a factor two smaller than the creep rates obtained of US-316 at Petten or for US-PCA at ORR or for 316L at EBR II. The scatter band factor for US-PCA, 316L, US-316 irradiated in ORR and EBR II is about 1.5 after a temperature and damage rate normalization

Manufacturing and performance tests of in-pile creep measuring machine of zirconium alloys

International Nuclear Information System (INIS)

Choi, Y.; Kim, B. G.; Kang, Y. H.

2000-01-01

A mock-up of the in-pile creep test machine of zirconium alloys for HANARO was designed and manufactured, which performance tests were carried. The dimension of the in-pile creep machine is 55 mm in diameter and 700 mm in length for HANARO, respectively. Load is transferred to specimen by through the working mechanisms in which the contraction of bellows by gas pressure moves a yoke and an upper grip connected to a specimen, simultaneously. It was observed that the extension of the specimen mounted in grips was transferred to a linear voltage differential transformer perfectly by a yoke and a push rod in a bearing. The displacement of specimen with applied pressure was determined with the LVDT and a pressure gauge, respectively. Resultant stress-strain behaviors of the specimen was determined by the displacement-applied gas pressure curve, which showed similar values obtained with a standard tensile test machine

The Evaluation of the Corrosion Resistance of the Al-Si Alloys Antimony Alloyed

Directory of Open Access Journals (Sweden)

Svobodova J.

2014-06-01

Full Text Available This paper deals with the evaluation of the corrosion resistance of the Al-Si alloys alloyed with the different amount of antimony. Specifically it goes about the alloy AlSi7Mg0,3 which is antimony alloyed in the concentrations 0; 0,001; 0,005; 0,01 a 0,05 wt. % of antimony. The introduction of the paper is dedicated to the theory of the aluminium alloys corrosion resistance, testing and evaluation of the corrosion resistance. The influence of the antimony to the Al-Si alloys properties is described further in the introduction. The experimental part describes the experimental samples which were prepared for the experiment and further they were exposed to the loading in the atmospheric conditions for a period of the 3 months. The experimental samples were evaluated macroscopically and microscopically. The results of the experiment were documented and the conclusions in terms of the antimony impact to the corrosion resistance of the Al-Si alloy were concluded. There was compared the corrosion resistance of the Al-Si alloy antimony alloyed (with the different antimony content with the results of the Al-Si alloy without the alloying after the corrosion load in the atmospheric conditions in the experiment.

Creep rupture behavior of Stirling engine materials

Science.gov (United States)

Titran, R. H.; Scheuerman, C. M.; Stephens, J. R.

1985-01-01

The automotive Stirling engine, being investigated jointly by the Department of Energy and NASA Lewis as an alternate to the internal combustion engine, uses high-pressure hydrogen as the working fluid. The long-term effects of hydrogen on the high temperature strength properties of materials is relatively unknown. This is especially true for the newly developed low-cost iron base alloy NASAUT 4G-A1. This iron-base alloy when tested in air has creep-rupture strengths in the directionally solidified condition comparable to the cobalt base alloy HS-31. The equiaxed (investment cast) NASAUT 4G-A1 has superior creep-rupture to the equiaxed iron-base alloy XF-818 both in air and 15 MPa hydrogen.

Preliminary Development of a Unified Viscoplastic Constitutive Model for Alloy 617 with Special Reference to Long Term Creep Behavior

International Nuclear Information System (INIS)

Sham, Sam; Walker, Kevin P.

2008-01-01

The expected service life of the Next Generation Nuclear Plant is 60 years. Structural analyses of the Intermediate Heat Exchanger (IHX) will require the development of unified viscoplastic constitutive models that address the material behavior of Alloy 617, a construction material of choice, over a wide range of strain rates. Many unified constitutive models employ a yield stress state variable which is used to account for cyclic hardening and softening of the material. For low stress values below the yield stress state variable these constitutive models predict that no inelastic deformation takes place which is contrary to experimental results. The ability to model creep deformation at low stresses for the IHX application is very important as the IHX operational stresses are restricted to very small values due to the low creep strengths at elevated temperatures and long design lifetime. This paper presents some preliminary work in modeling the unified viscoplastic constitutive behavior of Alloy 617 which accounts for the long term, low stress, creep behavior and the hysteretic behavior of the material at elevated temperatures. The preliminary model is presented in one-dimensional form for ease of understanding, but the intent of the present work is to produce a three-dimensional model suitable for inclusion in the user subroutines UMAT and USERPL of the ABAQUS and ANSYS nonlinear finite element codes. Further experiments and constitutive modeling efforts are planned to model the material behavior of Alloy 617 in more detail

Creep in sodium

International Nuclear Information System (INIS)

Charnock, W.; Cordwell, J.E.

1978-03-01

Available information on the creep of austenitic, ferritic and Alloy-800 type steels in liquid sodium is critically reviewed. Creep properties of stainless steels can be affected by element transfer and corrosion. At reactor structural component temperatures environmental effects are likely to be less important than changes due to thermal ageing. At high clad temperatures (700 0 C) decarburisation may cause the loss of strength and ductility in unstabilised steels while cavity formation may cause embrittlement in stabilised steels. The properties of Alloy 800 are, in some experiments, found to deteriorate while in others they are enhanced. This may be a consequence of the metallurgical complexity of the material or arise from the nature of the various techniques employed. Low alloy ferritic steels tend to decarburise in sodium at temperatures greater than 500 0 C and this leads to loss of strength and an increase in ductility. High alloy ferritics are immune to this effect and appear to be able to tolerate a degree of carburisation. Although intergranular cracking may be enhanced in liquid sodium the mechanical consequences are not significant and evidence for the existence of an embrittlement effect not associated with element transfer or corrosion is weak. Stress and strain may enhance element transfer at crack tips. However in real cracks the gettering or supply action of the crack faces conditions the chemistry of the cracks in sodium and protects the crack tip from element transfer. Thus creep crack extension rates should be independent of changes in bulk coolant chemistry. (author)

High Temperature Creep of an Al-8,5Fe-1,3V-1,7Si Alloy

Czech Academy of Sciences Publication Activity Database

Kuchařová, Květa; Zhu, S. J.; Čadek, Josef

2002-01-01

Roč. 40, č. 2 (2002), s. 69-84 ISSN 0023-432X R&D Projects: GA AV ČR IBS2041001 Institutional research plan: CEZ:AV0Z2041904 Keywords : Al-8,5Fe 1,3V 1,7Si alloy * creep behavior , true threshold stress Subject RIV: JI - Composite Materials Impact factor: 0.493, year: 2002

Creep damage development in welded X20 and P91

Energy Technology Data Exchange (ETDEWEB)

Brett, Steve; Holmstrom, Stefan; Hald, John; Borg, Ulrik; Aakjaer Jensen, Soeren; Vulpen, Rijk Van; Degnan, Craig; Vinter Dahl, Kristian; Vilhelmsen, Tommy

2011-03-15

The Martensitic steel X20CrMoV121 (hereinafter called X20) and the modified 9Cr1Mo steel (hereinafter called P91) have been used for a number of years in high temperature applications since they posses superior creep strength compared to low alloyed steels. Due to the simple fact that very few failures were observed, almost no knowledge as to the evolution of creep damage in welds were available despite long operation times exceeding well over 100.000 hours. It has been suggested that X20 will develop creep damage in a different manner compared to low alloyed steel, i.e damage initiation should be slow followed by accelerated growth. The research work presented in this report included systematic investigations of the first components of X20, which has developed creep during long-term operation. All of the investigated components showed creep damage evolution similar to low alloy steels

Corrosion resistance of titanium alloys for dentistry

International Nuclear Information System (INIS)

Laskawiec, J.; Michalik, R.

2001-01-01

Titanium and its alloys belong to biomaterials which the application scope in medicine increases. Some properties of the alloys, such as high mechanical strength, low density, low Young's modulus, high corrosion resistance and good biotolerance decide about it. The main areas of the application of titanium and its alloys are: orthopedics and traumatology, cardiosurgery, faciomaxillary surgery and dentistry. The results of investigations concerning the corrosion resistance of the technical titanium and Ti6Al14V alloy and comparatively a cobalt alloy of the Vitallium type in the artificial saliva is presented in the work. Significantly better corrosion resistance of titanium and the Ti6Al14V than the Co-Cr-Mo alloy was found. (author)

Creep in single crystals of γ single phase Ni-20Cr alloy and evolution of dynamic recrystallization

International Nuclear Information System (INIS)

Matsuo, T.; Terada, Y.; Takahashi, S.; Ishiwari, Y.

2000-01-01

The creep rate - time and the creep rate - strain curves of the single crystals of γ single phase Ni-20 mass%Cr alloy have been investigated at 1173 K under the wide stress range of 19.6 to 98 MPa, and compared with those of polycrystals. The orientation corresponding to the stress axis of the single crystals were chosen within the standard stereographic triangle. The creep curve in the Ni-20 mass%Cr single crystal consists of a transient stage and an accelerating stage without a steady state stage. The transient stage has two steps. In the first step, the creep rate slightly decreases, and in the second step, the decrease in creep rate becomes prominent with increasing the testing time. With decreasing the stress, the extension of transient stage becomes prominent, and by this extension, the decreasing ratio of the creep rate in transient stage is enlarged. At the lowest stress of 19.6 MPa, the most prominent extension of transient stage and the more than two order decrease in creep rate in transient stage are detected. The creep interrupting tests have been conducted at the stress of 29.4 MPa in the strain range of 0.1 to 0.6 to examine the appearance of dynamically recrystallized grains. At the strain of 0.1 corresponding to the end of the first step in transient stage, a straight subboundary parallel to slip plane appears in a wide distance of a few hundreds micrometers. With increasing the strain, the straight subboundary turns to waved one. At the strain showing the minimum creep rate, a lot of evolved subgrains appear. At the strain corresponding to the early stage of accelerating creep, dynamically recrystallized grains appear. It is confirmed that the onset of accelerating creep well corresponds to the appearance of dynamically recrystallized grains. In the single crystal creep ruptured, the whole gage portion turns to polycrystal with equiaxed grains having a diameter of 150 μm. (orig.)

Effect of creep and oxidation on reduced fatigue life of Ni-based alloy 617 at 850 °C

Energy Technology Data Exchange (ETDEWEB)

Chen, Xiang, E-mail: chenx@ornl.gov [Department of Nuclear, Plasma, and Radiological Engineering, University of Illinois at Urbana-Champaign, 104 South Wright Street, Urbana, IL 61801 (United States); Oak Ridge National Laboratory, 1 Bethel Valley Road, Oak Ridge, TN 37831 (United States); Yang, Zhiqing [Oak Ridge National Laboratory, 1 Bethel Valley Road, Oak Ridge, TN 37831 (United States); Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016 (China); Sokolov, Mikhail A.; Erdman, Donald L. [Oak Ridge National Laboratory, 1 Bethel Valley Road, Oak Ridge, TN 37831 (United States); Mo, Kun; Stubbins, James F. [Department of Nuclear, Plasma, and Radiological Engineering, University of Illinois at Urbana-Champaign, 104 South Wright Street, Urbana, IL 61801 (United States)

2014-01-15

Low cycle fatigue (LCF) and creep–fatigue testing of Ni-based alloy 617 was carried out at 850 °C. Compared with its LCF life, the material’s creep–fatigue life decreases to different extents depending on test conditions. To elucidate the microstructure-fatigue property relationship for alloy 617 and the effect of creep and oxidation on its fatigue life, systematic microstructural investigations were carried out using scanning electron microscopy, energy-dispersive X-ray spectroscopy, and electron backscatter diffraction (EBSD). In LCF tests, as the total strain range increased, deformations concentrated near high angle grain boundaries (HAGBs). The strain hold period in the creep–fatigue tests introduced additional creep damage to the material, which revealed the detrimental effect of the strain hold time on the material fatigue life in two ways. First, the strain hold time enhanced the localized deformation near HAGBs, resulting in the promotion of intergranular cracking of alloy 617. Second, the strain hold time encouraged grain boundary sliding, which resulted in interior intergranular cracking of the material. Oxidation accelerated the initiation of intergranular cracking in alloy 617. In the crack propagation stage, if oxidation was promoted and the cyclic oxidation damage was greater than the fatigue damage, oxidation-assisted intergranular crack growth resulted in a significant reduction in the material’s fatigue life.

Study of tertiary creep instability in several elevated-temperature structural materials

International Nuclear Information System (INIS)

Booker, M.K.; Sikka, V.K.

1978-01-01

Data for a number of common elevated temperature structural materials have been analyzed to yield mathematical predictions for the time and strain to tertiary creep at various rupture lives and temperatures. Materials examined include types 304 and 316 stainless steel, 2 1/4 Cr-1 Mo steel, alloy 800H, alloy 718, Hastelloy alloy X, and ERNiCr--3 weld metal. Data were typically examined over a range of creep temperatures for rupture lives ranging from less than 100 to greater than 10,000 hours. Within a given material, trends in these quantities can be consistently described, but it is difficult to directly relate the onset of tertiary creep to failure-inducing instabilities. A series of discontinued tests for alloy 718 at 649 and 620 0 C showed that the material fails by intergranular cracking but that no significant intergranular cracking occurs until well after the onset of tertiary creep

Evolution of microstructure and hardness of AE42 alloy after heat treatments

DEFF Research Database (Denmark)

Huang, Y.D.; Dieringa, H.; Hort, N.

2008-01-01

properties even further. It is shown that the microstructure of the squeeze-cast AE42 alloy is stable at high temperature 450 degrees C. The subsequent solution and ageing treatments have a limited effect on the hardness. The weak age-hardening is attributed to the precipitation of small amount Of Mg17Al12......The AE42 magnesium alloy was developed for high pressure die casting (HPDC) from low-aluminum magnesium alloys. In this alloy the rare earth (RE) elements were shown to increase creep resistance by forming AlxREy intermetallics along the grain boundaries. The present work investigates...... the microstructure of squeeze cast AE42 magnesium alloy and evaluates its hardness before and after heat treatments. The change in hardness is discussed based on the microstructural observations. Some suggestions are given concerning future design of alloy compositions in order to improve high temperature creep...

Influence of microstructure modification on the circumferential creep of Zr–Nb–Sn–Fe cladding tubes

International Nuclear Information System (INIS)

Jeong, Gu Beom; Kim, In Won; Hong, Sun Ig

2016-01-01

Out-of-reactor, non-irradiated thermal creep performances and lives of annealed and stress-relieved Zr-1.02Nb-0.69Sn-0.12Fe cladding tubes were studied and compared. The creep rates of annealed Zr-1.02Nb-0.69Sn-0.12Fe cladding tubes were appreciably slower than those of stress-relieved annealed counterpart. The stress exponent increased slightly from 5.1 to 6.1 in the stress-relieved cladding to 5.3–6.3 in the annealed cladding. The creep activation energy of the annealed Zr-1.02Nb-0.69Sn-0.12Fe alloy (300–330 kJ/mol) was larger compared to that of the stress-relieved alloy (210–260 kJ/mol). The creep activation energy of annealed alloy is close to that of self-diffusion in α-Zr (336 kJ/mol). The smaller activation energy in the stress-relieved alloy is attributed to the increasing contribution of faster diffusion path such as grain boundaries and dislocations. The presence of dislocation arrays with higher dislocation density and smaller grain size in the stress-relived alloy was confirmed by TEM analysis. The creep rupture time increased dramatically in the annealed Zr–1Nb- 0.7Sn-0.1Fe alloy compared to that of stress-relieved alloy, supporting the decrease of creep rate by annealing. The creep life of Zr-1.02Nb-0.69Sn-0.12Fe claddings can be extended through microstructure modification by annealing at intermediate temperatures in which dislocation creep dominates. - Highlights: • Effect of microstructure modification on creep in Zr–Nb–Sn–Fe tubes was studied. • Creep activation energy in annealed tubes was larger than in stress-relieved tubes. • Lower dislocation density in lager grains was observed after creep in annealed tubes. • Larson–Miller parameter of annealed tube was larger than that of stress-relieved one. • Creep life of tubes was extended through microstructure modification by annealing.

Simulation of precipitation and strengthening in MG-RE alloys

OpenAIRE

Liu, Hong

2017-01-01

Magnesium - rare earth (Mg-RE) alloys have received considerable attention in the past decades for wider applications in the aerospace industry due to their relatively high strength and excellent creep resistance. Most rare-earth containing magnesium alloys, such as Mg-Y, Mg-Gd, and Mg-Y-Nd, are precipitation hardenable. A technical barrier to the wider applications of such alloys is the lack of a sufficiently large age hardening response. To further improve this response, an improved underst...

Effects of product form and boron addition on the creep damage in the modified Hastelloy X alloys in a simulated HTGR helium gas environment

International Nuclear Information System (INIS)

Nakasone, Yuji; Tanabe, Tatsuhiko; Tsuji, Hirokazu; Nakajima, Hajime.

1992-01-01

The present paper investigates early-stage-creep damage of Hastelloy XR and XR-II alloys, modified versions of Hastelloy X alloy, which have been developed in Japan as most promising candidate structural alloys for Japanese high-temperature gas-cooled reactors (HTGRs). Creep tests were made on Hastelloy XR forging, tube and XR-II tube at 1,123 to 1,273 K in a simulated HTGR helium gas environment. The tests were interrupted at different strain levels of up to 5 % in order to evaluate creep damage via intergranular voids. The void sizes along grain boundaries and the A-parameter, the ratio of the number of damaged grain boundaries, on which one or more voids are found, to that of the total grain boundaries observed are used in order to evaluate creep damage. Statistical analysis of the A-parameter as well as the void sizes reveals that the values of the parameter show wide variations and follow the Weibull distribution, reflecting spatial randomness of the voids. The void sizes along grain boundaries, on the other hand, follow the log-normal distribution. The maximum void size d max and the mean value of the A-parameter A m are calculated and plotted against interruption creep strain ε int . The resultant d max vs. ε int and A m vs. ε int diagrams show that Hastelloy XR forging had suffered more damage than Hastelloy XR tube; nevertheless, the forging has longer interruption life, or the time to reach a given interruption creep strain. The result indicates that grains may have been deformed more easily in Hastelloy XR in the form of tube than in the form of forging. The diagrams also imply that the addition of boron has suppressed the nucleation as well as the growth of voids and thus has brought about longer interruption life of Hastelloy XR-II. (author)

Experiment and Modeling of Simultaneous Creep, Plasticity and Transformation of High Temperature Shape Memory Alloys During Cyclic Actuation

Science.gov (United States)

Kumar, Parikshith K.; Desai, Uri; Chatzigeorgiou, George; Lagoudas, Dimitris C.; Monroe, James; Karaman, Ibrahim; Noebe, Ron; Bigelow, Glen

2010-01-01

The present work is focused on studying the cycling actuation behavior of HTSMAs undergoing simultaneous creep and transformation. For the thermomechanical testing, a high temperature test setup was assembled on a MTS frame with the capability to test up to temperatures of 600 C. Constant stress thermal cycling tests were conducted to establish the actuation characteristics and the phase diagram for the chosen HTSMA. Additionally, creep tests were conducted at constant stress levels at different test temperatures to characterize the creep behavior of the alloy over the operational range. A thermodynamic constitutive model is developed and extended to take into account a) the effect of multiple thermal cycling on the generation of plastic strains due to transformation (TRIP strains) and b) both primary and secondary creep effects. The model calibration is based on the test results. The creep tests and the uniaxial tests are used to identify the viscoplastic behavior of the material. The parameters for the SMA properties, regarding the transformation and transformation induced plastic strain evolutions, are obtained from the material phase diagram and the thermomechanical tests. The model is validated by predicting the material behavior at different thermomechanical test conditions.

Advanced ordered intermetallic alloy deployment

Energy Technology Data Exchange (ETDEWEB)

Liu, C.T.; Maziasz, P.J.; Easton, D.S. [Oak Ridge National Lab., TN (United States)

1997-04-01

The need for high-strength, high-temperature, and light-weight materials for structural applications has generated a great deal of interest in ordered intermetallic alloys, particularly in {gamma}-based titanium aluminides {gamma}-based TiAl alloys offer an attractive mix of low density ({approximately}4g/cm{sup 3}), good creep resistance, and high-temperature strength and oxidation resistance. For rotating or high-speed components. TiAl also has a high damping coefficient which minimizes vibrations and noise. These alloys generally contain two phases. {alpha}{sub 2} (DO{sub 19} structure) and {gamma} (L 1{sub 0}), at temperatures below 1120{degrees}C, the euticoid temperature. The mechanical properties of TiAl-based alloys are sensitive to both alloy compositions and microstructure. Depending on heat-treatment and thermomechanical processing, microstructures with near equiaxed {gamma}, a duplex structure (a mix of the {gamma} and {alpha}{sub 2} phases) can be developed in TiAl alloys containing 45 to 50 at. % Al. The major concern for structural use of TiAl alloys is their low ductility and poor fracture resistance at ambient temperatures. The purpose of this project is to improve the fracture toughness of TiAl-based alloys by controlling alloy composition, microstructure and thermomechanical treatment. This work is expected to lead to the development of TiAl alloys with significantly improved fracture toughness and tensile ductility for structural use.

Oxidation resistance of nickel alloys at high temperature

International Nuclear Information System (INIS)

Tyuvin, Yu.D.; Rogel'berg, I.L.; Ryabkina, M.M.; Plakushchaya, A.F.

1977-01-01

The heat resistance properties of nickel alloys Ni-Cr-Si, Ni-Si-Al, Ni-Si-Mn and Ni-Al-Mn have been studied by the weight method during oxidation in air at 1000 deg and 1200 deg C. It is demonstrated that manganese reduces the heat resistance properties of Ni-Si and Ni-Al alloys, whilst the addition of over 3% aluminium enhances the heat resistance properties of Ni-Si (over 1.5%) alloys. The maximum heat resistance properties are shown by Ni-Si-Al and Ni-Cr-Si alloys with over 2% Si. These alloys offer 3 to 4 times better oxidation resistance as compared with pure nickel at 1000 deg C and 10 times at 1200 deg C

Microstructural Evolution of Advanced Radiation-Resistant ODS Steel with Different Lengths of Mechanical Alloying Time

Energy Technology Data Exchange (ETDEWEB)

Noh, Sanghoon; Kim, Ga Eon; Kang, Suk Hoon; Kim, Tae Kyu [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)

2015-05-15

Austenitic stainless steel may be one of the candidates because of good strength and corrosion resistance at the high temperatures, however irradiation swelling well occurred to 120dpa at high temperatures and this leads the decrease of the mechanical properties and dimensional stability. Compared to this, ferritic/ martensitic steel is a good solution because of excellent thermal conductivity and good swelling resistance. Unfortunately, the available temperature range of ferritic/martensitic steel is limited up to 650 .deg. C. ODS steel is the most promising structural material because of excellent creep and irradiation resistance by uniformly distributed nano-oxide particles with a high density which is extremely stable at the high temperature in ferritic/martensitic matrix. In this study, powder properties and microstructures of the ODS steel with different length of mechanical alloying time was investigated. The ODS steel milled 5h showed homogeneous grain structure with the highest hardness.

Microstructural Evolution of Advanced Radiation-Resistant ODS Steel with Different Lengths of Mechanical Alloying Time

International Nuclear Information System (INIS)

Noh, Sanghoon; Kim, Ga Eon; Kang, Suk Hoon; Kim, Tae Kyu

2015-01-01

Austenitic stainless steel may be one of the candidates because of good strength and corrosion resistance at the high temperatures, however irradiation swelling well occurred to 120dpa at high temperatures and this leads the decrease of the mechanical properties and dimensional stability. Compared to this, ferritic/ martensitic steel is a good solution because of excellent thermal conductivity and good swelling resistance. Unfortunately, the available temperature range of ferritic/martensitic steel is limited up to 650 .deg. C. ODS steel is the most promising structural material because of excellent creep and irradiation resistance by uniformly distributed nano-oxide particles with a high density which is extremely stable at the high temperature in ferritic/martensitic matrix. In this study, powder properties and microstructures of the ODS steel with different length of mechanical alloying time was investigated. The ODS steel milled 5h showed homogeneous grain structure with the highest hardness

Creep-fatigue behaviour of the titanium alloy IMI 834 at 600 C

International Nuclear Information System (INIS)

Nowack, H.; Kordisch, T.

1998-01-01

In the present study the creep-fatigue behaviour of the titanium alloy IMI 834 at 600 C was investigated. A comparison of the crack initiation life behaviour and of the crack propagation as caused by different types of complex creep-fatigue cycles (with hold times into tension and/or into compression direction and with different loading rates into tension and/or into compression direction) showed, that a slow increase of the loadings into tension reduced the life and increased the crack velocity more than hold times at the maximum load. Furthermore, there existed environmental influences. On the basis of the experimental investigations the prediction capability of convenient crack initiation life prediction methods was evaluated. It turned out that the prediction capability of the strain range partitioning method could be improved if it was frequency modified. The prediction capability of the frequency modification method could also be improved, if mean stresses in the cycles were explicitely accounted for. In the short and long crack stage the propagation behaviour could be correlated well if the effective cyclic J-integral was used. This is of importance for damage tolerance considerations. Because the strains and the stresses at the crack tip are most important for the crack propagation behaviour, they were analysed on the basis of the finite element method. It was found that the strains and stresses differed for different types of creep-fatigue cycles. (orig.)

Microstructural evolution during creep deformation of an 11CrMoVNb ferritic heat resistant steel

Energy Technology Data Exchange (ETDEWEB)

Lee, Kyu-Ho; Park, Dae-Bum [Korea Institute of Science and Technology, Seoul (Korea, Republic of). Materials and Devices Div.; Korea Univ., Seoul (Korea, Republic of). Dept. of Materials Science; Kwun, S.I. [Korea Univ., Seoul (Korea, Republic of). Dept. of Materials Science; Suh, Jin-Yoo; Jung, Woo-Sang [Korea Institute of Science and Technology, Seoul (Korea, Republic of). Materials and Devices Div.

2010-07-01

The effect of creep deformation on the microstructural development of an 11CrMoVNb ferritic heat resistant steel during high temperature creep test is investigated. Coarsening behavior of the precipitates, M{sub 23}C{sub 6} and MX, and growth behavior of martensite laths of crept specimens are carefully observed from both gage and grip parts of the specimens in order to discuss the effect of deformation. Particle coarsening and martensite lath widening are pronounced in the gage part due to the creep deformation. (orig.)

A Unified Physical Model for Creep and Hot Working of Al-Mg Solid Solution Alloys

Directory of Open Access Journals (Sweden)

Stefano Spigarelli

2017-12-01

Full Text Available The description of the dependence of steady-state creep rate on applied stress and temperature is almost invariably based on the Norton equation or on derived power-law relationships. In hot working, the Norton equation does not work, and is therefore usually replaced with the Garofalo (sinh equation. Both of these equations are phenomenological in nature and can be seldom unambiguously related to microstructural parameters, such as dislocation density, although early efforts in this sense led to the introduction of the “natural power law” with exponent 3. In an attempt to overcome this deficiency, a recent model with sound physical basis has been successfully used to describe the creep response of fcc metals, such as copper. The main advantage of this model is that it does not require any data fitting to predict the strain rate dependence on applied stress and temperature, which is a particularly attractive peculiarity when studying the hot workability of metals. Thus, the model, properly modified to take into account solid solution strengthening effects, has been here applied to the study of the creep and hot-working of simple Al-Mg single phase alloys. The model demonstrated an excellent accuracy in describing both creep and hot working regimes, still maintaining its most important feature, that is, it does not require any fitting of the experimental data.

Application of stress relaxation testing in evaluation of creep strength of a tungsten-alloyed 10% Cr cast steel

International Nuclear Information System (INIS)

Raghavender Rao, G.; Gupta, O.P.; Pradhan, B.

2011-01-01

Uniaxial isothermal stress relaxation tests (SRT) were performed on a tungsten-alloyed 10% Cr cast steel (G-X12Cr Mo W V Nb N 10 1 1) at temperatures of 580, 600 and 620 o C and initial strain levels of 0.2, 0.5 and 0.8%. Inelastic strain rates for different stresses were estimated from the stress versus time data generated from the tests. Conventional creep tests were also conducted on the same material at 580, 600 and 620 o C and at different stress levels. The strain rate data estimated from SRT were compared with minimum creep rates derived from the creep tests; the strain rates estimated from SRT with 0.8% initial strain level are in better agreement than those estimated from SRT with 0.2 and 0.5% initial strain levels. In order to ascertain the technique, stress relaxation behaviour was estimated from creep test data and compared with the stress relaxation curves obtained from SRT at corresponding temperatures. The stress relaxation curves obtained from SRT with 0.8% initial strain level are in good agreement with the stress relaxation curves estimated from the creep tests. It is concluded that the stress relaxation test with initial strain level of 0.8% could be considered as an appropriate short-term test technique for estimation of creep strength of newly developed materials.

Degradation of creep properties in a long-term thermally exposed nickel base superalloy

International Nuclear Information System (INIS)

Zrnik, J.; Strunz, P.; Vrchovinsky, V.; Muransky, O.; Novy, Z.; Wiedenmann, A.

2004-01-01

When exposed for long time at elevated temperatures of 430 and 650 deg. C the nickel base superalloy EI 698 VD can experience a significant decrease in creep resistance. The cause of the creep degradation of nickel base superalloy is generally attributed to the microstructural instability at prolonged high temperature exposure. In this article, the creep-life data, generated on long thermally exposed nickel base superalloy EI698 VD were related to the local microstructural changes observed using SEM and TEM analysing techniques. While structure analysis provided supporting evidence concerning the changes associated with grain boundary carbide precipitation, no persuasive evidence of a morphological and/or dimensional gamma prime change was showed. For clarifying of the role of gamma prime precipitates on alloy on creep degradation, the SANS (small angle neutron scattering) experiment was crucial in the characterization of the bulk-averaged gamma prime morphology and its size distribution with respect to the period of thermal exposure

The effect of environment on the creep crack growth behavior of several structural alloys

International Nuclear Information System (INIS)

Sadananda, K.; Shahinian, P.

1980-01-01

The creep crack growth behaviors of alloy 718, Inconel X-750, Udimet 700 and cold-worked type 304 and annealed and cold-worked type 316 austenitic stainless steels were determined in vacuum at elevated temperatures and the results were compared with those previously obtained in air. Alloy 718 and Inconel X-750 were found to be significantly sensitive to air with crack growth rates one to two orders of magnitude greater than those in vacuum. Udimet 700 is less sensitive to the environment and it is more sensitive to small changes in microstructure than to the environment per se. The austenitic stainless steels are least sensitive of all. Since the environmental sensitivity varies significantly for different materials, the service environment should be considered in the selection of materials for high temperature components. (Auth.)

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.

Detection of creep damage in a nickel base superalloy using NDE techniques

International Nuclear Information System (INIS)

Carreon, H.; Mora, B.; Barrera, G.

2009-10-01

Due to elevated temperatures, excessive stresses and severed corrosion conditions, turbine engine components are subject to creep processes that limit the components life such as a turbine bucket. The failure mechanism of a turbine bucket is related primarily to creep and corrosion and secondarily to thermal fatigue. As a result, it is desirable to assess the current conditions of such turbine component. This study uses the eddy current nondestructive evaluation technique in an effort to monitor the creep damage in a nickel base super-alloy, turbine bucket after service. The experimental results show an important electrical conductivity variation in eddy current images on the creep damage zone of nickel base super-alloy samples cut from a turbine bucket. Thermoelectric power measurements were also conducted in order to obtain a direct correlation between the presence of material changes due to creep damage and the electrical conductivity measurements. This research work shows an alternative non-destructive method in order to detect creep damage in a nickel base super-alloy turbine bucket. (Author)

Creep Rupture Life Prediction Based on Analysis of Large Creep Deformation

Directory of Open Access Journals (Sweden)

YE Wenming

2016-08-01

Full Text Available A creep rupture life prediction method for high temperature component was proposed. The method was based on a true stress-strain elastoplastic creep constitutive model and the large deformation finite element analysis method. This method firstly used the high-temperature tensile stress-strain curve expressed by true stress and strain and the creep curve to build materials' elastoplastic and creep constitutive model respectively, then used the large deformation finite element method to calculate the deformation response of high temperature component under a given load curve, finally the creep rupture life was determined according to the change trend of the responsive curve.The method was verified by durable test of TC11 titanium alloy notched specimens under 500 ℃, and was compared with the three creep rupture life prediction methods based on the small deformation analysis. Results show that the proposed method can accurately predict the high temperature creep response and long-term life of TC11 notched specimens, and the accuracy is better than that of the methods based on the average effective stress of notch ligament, the bone point stress and the fracture strain of the key point, which are all based on small deformation finite element analysis.

NASA-UVA Light Aerospace Alloy and Structures Technology Program (LA2ST). Supplement: Research on Materials for the High Speed Civil Transport

Science.gov (United States)

Gangloff, Richard P.; Starke, Edgar A., Jr.

1997-01-01

is no longer included in the NASA-UVA LAST program. Research on the Creep Behavior and Microstructural stability of Al-Cu-Mg-Ag and Al-Cu-Li-Mg-Ag showed that the creep resistance of three candidate aluminum alloys (C415, C416 and ML377) was much superior compared to that of the current Concorde alloy, AA2618. Creep induced change in precipitates at grain boundaries was observed in the alloy which exhibits the highest creep strain of the three examined. The other two alloys developed no detectable microstructural changes at grain boundaries under the creep conditions tested.

Investigations on diffusion-controlled transformations in creep resistant steels and graded cemented carbides

International Nuclear Information System (INIS)

Prat Borquez, Orlando

2011-01-01

The objective of this work was to simulate diffusion-controlled transformations on engineering alloys designed by the author and his colleagues. The main challenge of the work is to adapt the existing DICTRA models to the experimental processing and working conditions investigated, as well as to find the adequate boundary conditions for the description of the diffusion-controlled transformations governing the microstructure formation and evolution, in order to obtain reliable simulation results. The simulations were compared with experimental results of the microstructure evolution by scanning electron microscopy and scanning transmission electron microscopy (STEM). Two groups of materials were investigated. The first group was 9-12% Cr heat resistant alloys. These alloys are particularly interesting because the microstructure evolves during working conditions. Different compositions were designed in order to form different kinds and amounts of precipitates. For the designed 9-12% Cr creep steels the coarsening of MX and M 23 C 6 particles was modeled by applying the coarsening model implemented in DICTRA. The cell method of DICTRA was applied to investigate the kinetics of the Laves phase growth on 9-12% Cr alloys. The particular objectives of these investigations were: a) to determine the coarsening rate of precipitates, b) to investigate the influence of alloying element on the growth rate of the Laves phase, c) to determine the influence of the M 23 C 6 formation on the growth kinetics of the Laves phase, d) to determine the growth mechanism at the interface of the Laves phase (i.e. up-hill diffusion), e) to investigate the effect of the cell size on the simulation kinetics of Laves phase. The second group of materials was cemented carbides. They are used as cutting tools or wear parts in the automotive, aircraft and mining industry among others. The wear performance of cemented carbides (hardmetals and cermets) can be largely improved by applying wear

Phenomenological approach to precise creep life prediction by means of quantitative evaluation of strain rate acceleration in secondary creep

International Nuclear Information System (INIS)

Sato, Hiroyuki; Miyano, Takaya

2010-01-01

A method of creep life prediction by means of Strain-Acceleration-Parameter (SAP), α, is presented. The authors show that the shape of creep curve can be characterized by SAP that reflects magnitude of strain-rate change in secondary creep. The SAP-values, α are evaluated on magnesium-aluminium solution hardened alloys. Reconstruction of creep curves by combinations of SAP and minimum-creep rates are successfully performed, and the curves reasonably agree with experiments. The advantage of the proposed method is that the required parameters evaluated from individual creep curves are directly connected with the minimum creep rate. The predicted times-to-failure agree well with that obtained by experiments, and possibility of precise life time prediction by SAP is pronounced.

Microstructural Evolution of Thor™ 115 Creep-Strength Enhanced Ferritic Steel

Science.gov (United States)

Ortolani, Matteo; D'Incau, Mirco; Ciancio, Regina; Scardi, Paolo

2017-12-01

A new ferritic steel branded as Thor™ 115 has been developed to enhance high-temperature resistance. The steel design combines an improved oxidation resistance with long-term microstructural stability. The new alloy, cast to different product forms such as plates and tubes, was extensively tested to assess the high-temperature time-dependent mechanical behavior (creep). The main strengthening mechanism is precipitation hardening by finely dispersed carbide and nitride phases. Information on the evolution of secondary phases and time-temperature-precipitation behavior of the alloy, essential to ensure long-term property stability, was obtained by scanning transmission electron microscopy with energy dispersive spectroscopy, and by X-ray Powder Diffraction on specimens aged up to 50,000 hours. A thermodynamic modeling supports presentation and evaluation of the experimental results. The evolution of precipitates in the new alloy confirms the retention of the strengthening by secondary phases, even after long-term exposure at high temperature. The deleterious conversion of nitrides into Z phase is shown to be in line with, or even slower than that of the comparable ASME grade 91 steel.

Argon-arc welding of heat resisting aluminium alloys

International Nuclear Information System (INIS)

Ryazantsev, V.I.; Fedoseev, V.A.

1997-01-01

Welding of aluminium heat resisting alloys of the Al-Cu-Mg system is studied. The hot-shortness of heat-resistant alloys M40, 1150 and 1151 are at the level of aluminium alloys 1201 and by 2-3 times lower as compared to the aluminium alloy AMg6. The M40, 1150 and 1151 alloys have unquestionable advantages against other know aluminium alloys only at temperatures of welded structures operation, beginning with 150-2000 deg C and especially at 250 deg C