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Sample records for activation ferritic alloys

  1. Charpy impact test results for low activation ferritic alloys irradiated to 30 dpa

    Schubert, L.E.; Hamilton, M.L.; Gelles, D.S. [Pacific Northwest National Laboratory, Richland, WA (United States)

    1996-04-01

    Miniature specimens of six low activation ferritic alloys have been impact field tested following irradiation at 370{degrees}C to 30 dpa. Comparison of the results with those of control specimens and specimens irradiated to 10 dpa indicates that degradation in the impact behavior appears to have saturated by {approx}10 dpa in at least four of these alloys. The 7.5Cr-2W alloy referred to as GA3X appears most promising for further consideration as a candidate structural material in fusion reactor applications, although the 9Cr-1V alloy may also warrant further investigation.

  2. High strength ferritic alloy

    A high strength ferritic steel is specified in which the major alloying elements are chromium and molybdenum, with smaller quantities of niobium, vanadium, silicon, manganese and carbon. The maximum swelling is specified for various irradiation conditions. Rupture strength is also specified. (U.K.)

  3. Charpy impact test results of four low activation ferritic alloys irradiated at 370 degrees C to 15 DPA

    Miniature CVN specimens of four low activation ferritic alloys have been impact tested following irradiation at 370 degrees C to 15 dpa. Comparison of the results with those of control specimens indicates that degradation in the impact behavior occurs in each of these four alloys. The 9Cr-2W alloy referred to as GA3X and the similar alloy F82H with 7.8Cr-2W appear most promising for further consideration as candidate structural materials in fusion energy system applications. These two alloys exhibit a small DBTT shift to higher temperatures but show increased absorbed energy on the upper shelf

  4. Charpy impact test results of four low activation ferritic alloys irradiated at 370{degrees}C to 15 DPA

    Schubert, L.E.; Hamilton, M.L.; Gelles, D.S. [Pacific Northwest National Lab., Richland, WA (United States)

    1996-10-01

    Miniature CVN specimens of four low activation ferritic alloys have been impact tested following irradiation at 370{degrees}C to 15 dpa. Comparison of the results with those of control specimens indicates that degradation in the impact behavior occurs in each of these four alloys. The 9Cr-2W alloy referred to as GA3X and the similar alloy F82H with 7.8Cr-2W appear most promising for further consideration as candidate structural materials in fusion energy system applications. These two alloys exhibit a small DBTT shift to higher temperatures but show increased absorbed energy on the upper shelf.

  5. Carburisation of ferritic Fe-Cr alloys by low carbon activity gases

    Highlights: → Model Fe-Cr alloys are exposed to Ar-CO2 and Ar-CO2-H2O at 650 and 800 deg. C. → Alloy microstructures are extensively modified by carburisation. → Chromium carbides precipitate at both temperatures, and martensite forms at 800 deg. C. → Elevated carbon activities reflect local equilibrium at the scale/alloy interface. - Abstract: Model Fe-Cr alloys were exposed to Ar-CO2-H2O gas mixtures at 650 and 800 deg. C. At equilibrium, these atmospheres are oxidising to the alloys, but decarburising (aC ∼ 10-15 to 10-13). In addition to developing external oxide scales, however, the alloys also carburised. Carbon supersaturation at the scale/alloy interface relative to the gas reflects local equilibrium: a low oxygen potential corresponds to a high pCO/pCO2 ratio, and hence to a high carbon activity. Interfacial carbon activities calculated on the basis of scale-alloy equilibrium are shown to be in good agreement with measured carburisation rates and precipitate volume fractions, providing support for the validity of the thermodynamic model.

  6. Mechanical properties of a high-purity Fe-9Cr-2W-0.1C model alloy for low-activation ferritic steels for fusion reactors

    Reduced-activation ferritic steels, such as JLF-1 (Fe-9Cr-2W-0.1C-V-Ta-N) steel, are candidate structural materials for use in the next fusion device. It is essential to develop low-activation ferritic steels which have been purified in order to reduce the amount of radioactive impurity elements. It is important to clarify whether or not purification causes any significant changes in the mechanical properties of the ferritic steels, as they will be used as structural materials. In this study a high-purity Fe-9Cr-2W-0.1C model alloy was prepared from an ultra-high-purity iron. A significantly lower tensile strength was observed in the high-purity ferritic steel at room temperature and 573 K, as compared to that of JLF-1 steel. The difference in yield strength at room temperature is considered to be mainly due to a lower content of nitrogen and soluble impurities, a larger packet diameter and a larger lath length in the case of the high-purity steel. The hardness of the as-quenched high-purity steel and the recovery behavior below 823 K are not significantly different from those of conventional ferritic steel. (author)

  7. Plasticity of oxide dispersion strengthened ferritic alloys

    The object of this work is to study the plasticity mechanisms of two oxide dispersion strengthened ferritic alloys, DT and DY. Microstructural characterisation has been performed on DT and DY alloys by optical, scanning and transmission electron microscopy. These materials, strengthened by an oxide dispersion, contain an intermetallic χ phase precipitated on grain boundaries. The χ phase, stable up to 900 deg, can be dissolved into the matrix by heat treatment beyond 1 000 deg. Between 20 and 700 deg, according to tensile tests, the DY alloy which is strengthened by a fine dispersion of yttria particles is more resistant and less ductile than DT alloy, strengthened by titanium oxides. Tensile tests performed at room temperature, in the chamber of a SEM, have shown that micro-cracking of the χ phase coincides with the first stage of the macroscopic yielding. The cavities initiated by the χ phase micro-cracking induce a ductile fracture of the matrix. A dynamic strain ageing mechanism has been observed around 400 deg, which is attributed to the Mo contribution. Between 20 and 700 deg, comparison of tensile properties of alloys with or without χ phase has shown that the intermetallic phase has a detrimental effect on the ductility, but has no influence on the mechanical strength. Creep tests have been performed between 500 and 700 deg. Thermally activated plasticity mechanisms are observed in this temperature range. The χ phase, which is always micro-cracked after tensile testing, is not damaged after creep testing below a critical stress. This behaviour is explained by the influence of strain rate through the competition between strain hardening and relaxation of the matrix. (author)

  8. High hardness of alloyed ferrite after nitriding

    Detailed layer-by layer structure and phase analyses of the diffusion layer of nitrided binary alloys of iron with aluminium, chromium, vanadium and titanium have been carried out by means of a complex technique. Transition d-metals (chromium, vanadium and titanium) raise to a greater degree the solubility of nitrogen in the α solid solution, sharply increases the hardness of ferrite and decrease the depth of the layer. Nitrided binary alloys of iron with chromium, vanadium and titanium are strengthened through precipitation from the nitrogen-saturated α-solid solution of nitrides of alloying elements TiN, VN and CrN of a structure B1. A maximum hardness of ferrite alloyed by chromium, vanadium and titanium is observed after nitriding at 550 deg C when the precipitated special nitrides are fully coherent with the α matrix

  9. Delta ferrite in the weld metal of reduced activation ferritic martensitic steel

    Formation of delta(δ)-ferrite in the weld metal, during autogenous bead-on-plate welding of Reduced Activation Ferritic Martensitic (RAFM) steel using Gas Tungsten Arc Welding (GTAW) process, has been studied. Composition of the alloy is such that delta-ferrite is not expected in the alloy; but examination of the weld metal revealed presence of delta-ferrite in the weld metal. Volume fraction of delta-ferrite is found to be higher in the weld interface than in the rest of the fusion zone. Decrease in the volume fraction of delta-ferrite, with an increase in preheat temperature or with an increase in heat input, is observed. Results indicate that the cooling rate experienced during welding affects the volume fraction of delta-ferrite retained in the weld metal and variation in the delta-ferrite content with cooling rate is explained with variation in the time that the weld metal spends in various temperature regimes in which delta-ferrite is stable for the alloy during its cooling from the liquid metal to the ambient temperature. This manuscript will discuss the effect of welding parameters on formation of delta-ferrite and its retention in the weld metal of RAFM steel

  10. Delta ferrite in the weld metal of reduced activation ferritic martensitic steel

    Sam, Shiju, E-mail: shiju@ipr.res.in [Institute for Plasma Research, Gandhinagar, Gujarat 382 428 (India); Das, C.R.; Ramasubbu, V.; Albert, S.K.; Bhaduri, A.K.; Jayakumar, T. [Indira Gandhi Centre for Atomic Research, Kalpakkam 603 102 (India); Rajendra Kumar, E. [Institute for Plasma Research, Gandhinagar, Gujarat 382 428 (India)

    2014-12-15

    Formation of delta(δ)-ferrite in the weld metal, during autogenous bead-on-plate welding of Reduced Activation Ferritic Martensitic (RAFM) steel using Gas Tungsten Arc Welding (GTAW) process, has been studied. Composition of the alloy is such that delta-ferrite is not expected in the alloy; but examination of the weld metal revealed presence of delta-ferrite in the weld metal. Volume fraction of delta-ferrite is found to be higher in the weld interface than in the rest of the fusion zone. Decrease in the volume fraction of delta-ferrite, with an increase in preheat temperature or with an increase in heat input, is observed. Results indicate that the cooling rate experienced during welding affects the volume fraction of delta-ferrite retained in the weld metal and variation in the delta-ferrite content with cooling rate is explained with variation in the time that the weld metal spends in various temperature regimes in which delta-ferrite is stable for the alloy during its cooling from the liquid metal to the ambient temperature. This manuscript will discuss the effect of welding parameters on formation of delta-ferrite and its retention in the weld metal of RAFM steel.

  11. Gas- and plasma-driven hydrogen permeation through a reduced activation ferritic steel alloy F82H

    Zhou, Haishan, E-mail: zhou.haishan@LHD.nifs.ac.jp [The Graduate University for Advanced Studies, Toki 509-5292, Gifu (Japan); Hirooka, Yoshi; Ashikawa, Naoko; Muroga, Takeo; Sagara, Akio [The Graduate University for Advanced Studies, Toki 509-5292, Gifu (Japan); National Institute for Fusion Science, 322-6 Oroshi, Toki 509-5292, Gifu (Japan)

    2014-12-15

    The first wall of a magnetic fusion power reactor will be subjected to hydrogen isotope permeation by the two mechanisms: one is gas-driven and the other is plasma-driven. Hydrogen transport through a reduced activation ferritic steel alloy F82H has been investigated using a steady-state laboratory-scale plasma device. Permeation parameters including permeability, solubility and diffusivity have been measured in the temperature range from 150 to 520 °C. The surface recombination coefficient for hydrogen has also been estimated by a one-dimensional steady-state permeation model with the input data taken from experiments. Using these parameters, the hydrogen plasma-driven permeation flux and inventory for a 0.5 cm thick first wall around 500 °C are estimated to be ∼1.0 × 10{sup 13} atom cm{sup −2} s{sup −1} and ∼2 × 10{sup 16} atom cm{sup −3}, respectively. Also, the implications of all these data on reactor operation are discussed.

  12. Proeutectoid ferrite transformation in iron alloys. Tetsugokin no shoseki feraito hentai

    Enomoto, M. (Ibaraki Univ., Ibaraki (Japan). Faculty of Engineering)

    1994-02-20

    This article is not a comprehensive introduction of proeutectoid ferrite transformation, but is an arrangement of the research trends on ferrite transformation prepared by the author from the basic viewpoint on ferrite transformation centering around topics which he was involved. Concerning proeutectoid ferrite transformation, only the mother phase and the final equilibrium phase concern in it and since data of thermodynamics, crystallography and diffusion are outstandingly better organized than other fields, it is considered to be the transformation suitable for comparing the nucleus forming theory with the measured nucleus forming rate. In this article, with regard to proeutectoid ferrite transformation, nucleus forming from a solid phase to a solid phase is discussed, and it is pointed out that activating energy of formation of ferrite nucleus differs noticeably between the edge and surface of the grain boundary, thereby a big difference is made in its nucleus forming rate. Furthermore, the following items are mentioned; diffusion rate determining growth in a ternary alloy and diffusion via a grain boundary of an alloying element, a study on ferrite growth utilizing the fact that the movement of ledges on the side face of ferrite can be observed in situ, incomplete transformation of alloying elements and synergetic effects, etc. 39 refs., 16 figs.

  13. Radiation damage simulation studies of selected austenitic and ferritic alloys

    Results are presented of a study of the radiation damage structure of selected alloys following ion bombardment to simulate fusion-reactor exposures up to 40 dpa (approx. 3 MW-yr m-2) at temperatures from 4750C-6500C. Gas concentrations appropriate to fusion-reactor conditions were simulated using a mixed gas beam of 4 MeV He + 2 MeV H2. A beam of 46 MeV Ni ions was used in sequence with the gas beam to provide gas-to-damage ratios of 13 appm He/dpa and 52 appm H/dpa at a nickel-ion damage rate of approx. 1 dpa/hr. The materials investigated comprised three austenitic stainless steels (316L, modified 316-Ti and 316-Nb), a ferritic alloy (1.4914) and a commercial low-activation alloy containing Mn (TENELON). The results reveal that ferritic steels have good radiation damage resistance and are far superior to austenitic steels in respect of void-induced swelling. (author)

  14. Ferritic Alloys with Extreme Creep Resistance via Coherent Hierarchical Precipitates

    Song, Gian; Sun, Zhiqian; Li, Lin; Xu, Xiandong; Rawlings, Michael; Liebscher, Christian H.; Clausen, Bjørn; Poplawsky, Jonathan; Leonard, Donovan N.; Huang, Shenyan; Teng, Zhenke; Liu, Chain T.; Asta, Mark D.; Gao, Yanfei; Dunand, David C.; Ghosh, Gautam; Chen, Mingwei; Fine, Morris E.; Liaw, Peter K.

    2015-11-01

    There have been numerous efforts to develop creep-resistant materials strengthened by incoherent particles at high temperatures and stresses in response to future energy needs for steam turbines in thermal-power plants. However, the microstructural instability of the incoherent-particle-strengthened ferritic steels limits their application to temperatures below 900 K. Here, we report a novel ferritic alloy with the excellent creep resistance enhanced by coherent hierarchical precipitates, using the integrated experimental (transmission-electron microscopy/scanning-transmission-electron microscopy, in-situ neutron diffraction, and atom-probe tomography) and theoretical (crystal-plasticity finite-element modeling) approaches. This alloy is strengthened by nano-scaled L21-Ni2TiAl (Heusler phase)-based precipitates, which themselves contain coherent nano-scaled B2 zones. These coherent hierarchical precipitates are uniformly distributed within the Fe matrix. Our hierarchical structure material exhibits the superior creep resistance at 973 K in terms of the minimal creep rate, which is four orders of magnitude lower than that of conventional ferritic steels. These results provide a new alloy-design strategy using the novel concept of hierarchical precipitates and the fundamental science for developing creep-resistant ferritic alloys. The present research will broaden the applications of ferritic alloys to higher temperatures.

  15. The properties of silicon alloyed ferritic ductile irons

    Z. Glavas

    2016-07-01

    Full Text Available In this paper the influence of silicon content of 3,1 to 5,4 wt. % on the tensile properties, hardness and impact energy of ferritic ductile iron was analysed. It was found that silicon strengthens the ferrite, resulting in an increase in yield strength and tensile strength with increasing silicon content up to 4,22 wt. %. Elongation and impact energy decreases and the hardness increases with increasing silicon content. Since ferritic ductile irons alloyed and strengthened by silicon have a higher Rp0,2/Rm ratio and a higher elongation than conventional ferritic, ferritic/pearlitic and pearlitic ductile irons at the same level of tensile strength, we can expect an increased demand for these materials in applications where high resistance to impact load and low temperature impact properties are not required.

  16. The properties of silicon alloyed ferritic ductile irons

    Z. Glavas; A. Strkalj; A. Stojakovic

    2016-01-01

    In this paper the influence of silicon content of 3,1 to 5,4 wt. % on the tensile properties, hardness and impact energy of ferritic ductile iron was analysed. It was found that silicon strengthens the ferrite, resulting in an increase in yield strength and tensile strength with increasing silicon content up to 4,22 wt. %. Elongation and impact energy decreases and the hardness increases with increasing silicon content. Since ferritic ductile irons alloyed and strengthened by silicon have a h...

  17. High-coercivity ferrite magnets prepared by mechanical alloying

    Nanocrystalline hexaferrite (BaFe12O19 or SrFe12O19) and mixed Fe,Co-ferrite ((FexCo1-x)Fe2O4 with x=0-1) materials have been prepared by mechanical alloying and subsequent annealing. High coercivities were obtained in these nanocrystalline materials, 6-7 kOe for hexaferrite and ∝3 kOe for Co-ferrite. Hexaferrite powders prepared by mechanical alloying have been used as the starting material for high-coercivity bonded magnets. Hot-pressed anisotropic hexaferrite magnets have been produced with high values of coercivity and remanence. High magnetic performance was also achieved in some mixed Fe,Co-ferrites after magnetic annealing. (orig.)

  18. Alloys influence in ferritic steels with hydrogen attack

    Materials exposed to a corrosive environment and high temperatures, are associated with a decrease of their mechanical properties and embitterment.At room temperatures atomic hydrogen diffuses easily through metals structure, it accumulates in lattice defects forming molecular hydrogen and generating cracking due to internal stresses.Under high temperatures the phenomenon is more complex.The steels in these conditions present different structures of precipitates, that the change under creep conditions period.In this work it is determined the influence of Cr and V alloys, the changes of ferritic steel resistance in a corrosive environment and high temperatures.1.25 Cr 1 Mo 0.25 V and 2.25Cr 1 Mo under different loads and temperatures previously attacked by hydrogen environment.The hydrogen is induced by the electrolytic technique, optimizing the choice of temperatures, current density, electrolyte, etc. In order to control an adequate cathode charge, a follow up procedure is carried out by electronic barrier microscopy.After the attack, the material is settled at room temperatures for certain period of time, to allow the hydrogen to leave and evaluate the residual damage.Creep by torsion assays, under constant load and temperature is used as an experimental technique.With the outcome data curves are drawn in order to study the secondary creep rate, with the applied load and temperature, determining the value of stress exponent n and the activation energy Q.Comparing to equal assays to the same ferritic steels but non attacked by hydrogen, these values allows the prediction of microstructure changes present during these tests

  19. Activation analysis for different structural alloys considered for ITER

    Activation calculations have been made for the austentic steel 316SS, the ferritic alloy HT-9, the titanium alloy Ti6A14V, and the vanadium alloy V5Cr5Ti in a liquid metal (Na) design suggested recently for ITER. The calculations show that the vanadium alloy has the minimum short and long-term radioactivity and BHP. It also has the minimum decay heat at all the time. The titanium alloy has less radioactivity than the austenitic and this ferritic alloys. However, the decay heat of this alloy could exceed that of the conventional alloys

  20. Ferrite hardening response in a low alloy ferrite–martensite dual phase steel

    Highlights: • The ferrite hardening response varies with ferrite volume fraction. • A considerable variation in hardness was observed within a specific ferrite grain. • Finer ferrite grains were accompanied by more homogenized carbon content. • Coarser ferrite grains depicted a significant gradient of carbon content. • Ferrite hardness increased along the center to the peripheral regions of a grain. -- Abstract: This paper is concerned to investigate in details the variation of ferrite hardening response in conjunction with carbon partitioning developed within ferrite during austenite to ferrite phase transformation in a low alloy ferrite–martensite dual phase (DP) steel. For this purpose, a wide variety of ferrite–martensite DP microstructures consisting different volume fractions of ferrite and martensite have been prepared using step quenching heat treatment processes at isothermal temperature of 600 °C for various holding times. Nanoindentation measurements have been supplemented by energy dispersive X-ray and microprobe wavelength-dispersive spectroscopic analyses to follow the variation of ferrite hardening response and its relation to the carbon concentration of ferrite in the ferrite–martensite DP microstructures. The experimental results showed that the ferrite hardening response is quite variable depending on the progress of ferrite formation in the ferrite–martensite DP microstructures. For a specific ferrite grain in a specific ferrite martensite DP microstructure, the location nearer to the ferrite–martensite interfaces has been accompanied with a significant higher carbon concentration and simultaneously higher ferrite hardening response in comparison to that of central regions of ferrite grains. These results are rationalized with a higher concentration of carbon within ferrite developed as a consequence of higher carbon entrapment within defected ferrite area generated at early stage of austenite to ferrite phase transformation

  1. Ferrite hardening response in a low alloy ferrite–martensite dual phase steel

    Fereiduni, E., E-mail: e.fereiduni@yahoo.com; Ghasemi Banadkouki, S.S.

    2014-03-15

    Highlights: • The ferrite hardening response varies with ferrite volume fraction. • A considerable variation in hardness was observed within a specific ferrite grain. • Finer ferrite grains were accompanied by more homogenized carbon content. • Coarser ferrite grains depicted a significant gradient of carbon content. • Ferrite hardness increased along the center to the peripheral regions of a grain. -- Abstract: This paper is concerned to investigate in details the variation of ferrite hardening response in conjunction with carbon partitioning developed within ferrite during austenite to ferrite phase transformation in a low alloy ferrite–martensite dual phase (DP) steel. For this purpose, a wide variety of ferrite–martensite DP microstructures consisting different volume fractions of ferrite and martensite have been prepared using step quenching heat treatment processes at isothermal temperature of 600 °C for various holding times. Nanoindentation measurements have been supplemented by energy dispersive X-ray and microprobe wavelength-dispersive spectroscopic analyses to follow the variation of ferrite hardening response and its relation to the carbon concentration of ferrite in the ferrite–martensite DP microstructures. The experimental results showed that the ferrite hardening response is quite variable depending on the progress of ferrite formation in the ferrite–martensite DP microstructures. For a specific ferrite grain in a specific ferrite–martensite DP microstructure, the location nearer to the ferrite–martensite interfaces has been accompanied with a significant higher carbon concentration and simultaneously higher ferrite hardening response in comparison to that of central regions of ferrite grains. These results are rationalized with a higher concentration of carbon within ferrite developed as a consequence of higher carbon entrapment within defected ferrite area generated at early stage of austenite to ferrite phase

  2. Unusual thermal stability of nano-structured ferritic alloys

    Highlights: ► A nanostructured steel is examined by in situ small angle neutron scattering and high-temperature neutron diffraction. ► A bi-modal particle size distribution is identified by small angle neutron scattering. ► The nanometer sized clusters are thermally stable up to 1400 °C. ► The microstructure of the material is stable at high-temperatures, with no evidence of recrystallization or grain growth. - Abstract: A scientific question vitally important to the materials community is whether there exist “self-assembled” nanoclusters that are thermodynamically stable at elevated temperatures. Using in situ neutron scattering, we have characterized the structure and thermal stability of a nano-structured ferritic alloy. Nanometer sized nanoclusters were found to persist up to ∼1400 °C, providing direct evidence of a thermodynamically stable alloying state for the nanoclusters. High-temperature neutron diffraction measurements show a stable ferritic matrix, with little evidence of recrystallization or grain growth at temperatures up to 1300 °C. This result suggests that thermally stable nanoclusters and the oxygen-vacancy interaction limit the diffusion of Fe atoms and hence the mobility of grain boundaries, stabilizing the microstructure of the ferritic matrix at high temperatures.

  3. Effect of alloy content on microstructure and microchemistry of phases during short term thermal exposure of 9Cr–W–Ta–0.1C reduced activation ferritic/martensitic (RAFM) steels

    Ravikirana; R Mythili; S Raju; S Saroja; G Paneerselvam; T Jayakumar; E Rajendra Kumar

    2014-10-01

    This paper presents the results of an experimental study on the microstructural evolution in 9Cr reduced activation ferritic/martensitic steels during short term thermal exposures. Since the microstructure is strongly influenced by the alloying additions, mainly W, Ta and C contents, the effect of varying W and Ta contents on the martensite structure that forms during normalizing treatment and the subsequent changes during tempering of the martensite in the temperature regime of 923–1033 K have been studied. Microstructural changes like subgrain formation and nature of precipitates have been evaluated and correlated to hardness variations. The systematic change in size distribution and microchemistry of M23C6 carbide is studied with variation in W content at different temperatures.

  4. Processing and characterization of oxide dispersion strengthened 14YWT ferritic alloys

    West, Michael Keith

    Oxide dispersion strengthened (ODS) ferritic steels are currently being investigated as candidate materials for nuclear applications due to their increased high temperature strength and low activation characteristics. Recent studies have shown that ODS ferritic steels containing Ti exhibit enhanced high temperature properties due to the formation of a very fine dispersion of nanometer-sized oxide clusters based on Ti, Y, and O. Studies are currently underway to examine so called 14YWT alloys with nominal compositions of Fe-14Cr-3W-0.4Ti (wt. %) mechanically alloyed with 0.25 (wt.%) Y2O3. The focus of this study was to investigate how the early stages of processing of 14YWT alloys during mechanical milling, heat treatment, and consolidation affect the structure and properties of the alloys. The 14YWT alloys were milled at different times up to 80 hours, along with alloy powder compositions of Fe-14Cr + 0.25 wt.% Y2O 3 (14Y) and Fe-14Cr without Y2O3 (Fe-14Cr). The evolution of the microstructure and mechanical properties during milling was examined with a combination of optical metallography, x-ray diffraction, electron microscopy, atom probe tomography, and nanoindentation. Alloy powders were also heat treated and studied using high temperature x-ray diffraction and differential scanning calorimetry methods. Special attention was paid to milling parameters and temperature ranges which lead to the formation of nanosized oxide clusters in the alloys. Finally, the microstructure of consolidated alloys was examined and related to milling and heat treatment methods. Mechanical properties and microstructure during milling were similar in the three alloy powders examined regardless of dispersoid or alloy addition. Mechanical mixing of the alloy powders was inefficient after 40 hours of milling. Milling did not produce bulk amorphous phases but quickly reduced the crystallite size to ˜10-20 nm. Milling also resulted in relatively uniform dissolution of Y2O3. Thermal

  5. Deuterium Retention and Physical Sputtering of Low Activation Ferritic Steel

    T, Hino; K, Yamaguchi; Y, Yamauchi; Y, Hirohata; K, Tsuzuki; Y, Kusama

    2005-04-01

    Low activation materials have to be developed toward fusion demonstration reactors. Ferritic steel, vanadium alloy and SiC/SiC composite are candidate materials of the first wall, vacuum vessel and blanket components, respectively. Although changes of mechanical-thermal properties owing to neutron irradiation have been investigated so far, there is little data for the plasma material interactions, such as fuel hydrogen retention and erosion. In the present study, deuterium retention and physical sputtering of low activation ferritic steel, F82H, were investigated by using deuterium ion irradiation apparatus. After a ferritic steel sample was irradiated by 1.7 keV D+ ions, the weight loss was measured to obtain the physical sputtering yield. The sputtering yield was 0.04, comparable to that of stainless steel. In order to obtain the retained amount of deuterium, technique of thermal desorption spectroscopy (TDS) was employed to the irradiated sample. The retained deuterium desorbed at temperature ranging from 450 K to 700 K, in the forms of DHO, D2, D2O and hydrocarbons. Hence, the deuterium retained can be reduced by baking with a relatively low temperature. The fluence dependence of retained amount of deuterium was measured by changing the ion fluence. In the ferritic steel without mechanical polish, the retained amount was large even when the fluence was low. In such a case, a large amount of deuterium was trapped in the surface oxide layer containing O and C. When the fluence was large, the thickness of surface oxide layer was reduced by the ion sputtering, and then the retained amount in the oxide layer decreased. In the case of a high fluence, the retained amount of deuterium became comparable to that of ferritic steel with mechanical polish or SS 316L, and one order of magnitude smaller than that of graphite. When the ferritic steel is used, it is required to remove the surface oxide layer for reduction of fuel hydrogen retention. Ferritic steel sample was

  6. Discussion on the Alloying Element Partition and Growth Kinetics of Proeutectoid Ferrite in Fe-C-Mn-X Alloys

    Wei, R.; Enomoto, M.

    2011-12-01

    Experimental data on alloying element partition and growth kinetics of proeutectoid ferrite in quaternary Fe-C-Mn-Si, Ni, and Co alloys were reanalyzed using an approximate method, which permits a quick evaluation of alloy partitioning to be made. The method yielded results in good agreement with DICTRA and is applicable to Fe-C base multicomponent alloys. Differences of the predicted local condition at the α/ γ boundary from those previously presented in the alloys are noted.

  7. The properties and weldability of low activation ferritic steels

    A series of ferritic steels patterned on the chromium-molybdenum alloys, 2 1/4Cr--1Mo, 9Cr--1MoVNb and 12Cr--1MoVW, were tested for weldability. These steels are being developed as candidates for the first wall and blanket structures of fusion reactors. Use of these materials will minimize the long term radioactive hazards associated with disposal after service. In these low activation alloys, elements which become activated during irradiation with long half lives (Mo and Nb) are replaced. The major changes include the replacement of molybdenum with tungsten, the addition of vanadium in 2 1/4% Cr steels, and the replacement of niobium in the 9% Cr steel with tantalum. These replacement elements radically modify both the mechanical properties and weldability of the alloys. In this study, the effect of the alloy modifications on the microstructure and the mechanical properties of the welds are presented. Bainitic steels (2 1/4 Cr%) usually exhibit good weldability, while the martensitic steels (5, 9 and 12 Cr%) are suspectable to embrittlement in the heat affected zone (HAZ). The objective of this study was to characterize the welded microstructure and mechanical properties of these low activation alloys. Autogeneous bead-on-plate welds were produced using the gas tungsten arc welding (GTAW) process. Microstructure, microhardness, weld bend and tensile test results are reported for the base metal, heat affected zone and fusion zone of the weld. 46 refs., 36 figs., 14 tabs

  8. Investigation on the Behavior of Austenite and Ferrite Phases at Stagnation Region in the Turning of Duplex Stainless Steel Alloys

    Nomani, J.; Pramanik, A.; Hilditch, T.; Littlefair, G.

    2016-06-01

    This paper investigates the deformation mechanisms and plastic behavior of austenite and ferrite phases in duplex stainless steel alloys 2205 and 2507 under chip formation from a machine turning operation. SEM images and EBSD phase mapping of frozen chip root samples detected a build-up of ferrite bands in the stagnation region, and between 65 and 85 pct, more ferrite was identified in the stagnation region compared to austenite. SEM images detected micro-cracks developing in the ferrite phase, indicating ferritic build-up in the stagnation region as a potential triggering mechanism to the formation of built-up edge, as transgranular micro-cracks found in the stagnation region are similar to micro-cracks initiating built-up edge formation. Higher plasticity of austenite due to softening under high strain is seen responsible for the ferrite build-up. Flow lines indicate that austenite is plastically deforming at a greater rate into the chip, while ferrite shows to partition most of the strain during deformation. The loss of annealing twins and activation of multiple slip planes triggered at high strain may explain the highly plastic behavior shown by austenite.

  9. Investigation on the Behavior of Austenite and Ferrite Phases at Stagnation Region in the Turning of Duplex Stainless Steel Alloys

    Nomani, J.; Pramanik, A.; Hilditch, T.; Littlefair, G.

    2016-04-01

    This paper investigates the deformation mechanisms and plastic behavior of austenite and ferrite phases in duplex stainless steel alloys 2205 and 2507 under chip formation from a machine turning operation. SEM images and EBSD phase mapping of frozen chip root samples detected a build-up of ferrite bands in the stagnation region, and between 65 and 85 pct, more ferrite was identified in the stagnation region compared to austenite. SEM images detected micro-cracks developing in the ferrite phase, indicating ferritic build-up in the stagnation region as a potential triggering mechanism to the formation of built-up edge, as transgranular micro-cracks found in the stagnation region are similar to micro-cracks initiating built-up edge formation. Higher plasticity of austenite due to softening under high strain is seen responsible for the ferrite build-up. Flow lines indicate that austenite is plastically deforming at a greater rate into the chip, while ferrite shows to partition most of the strain during deformation. The loss of annealing twins and activation of multiple slip planes triggered at high strain may explain the highly plastic behavior shown by austenite.

  10. Characteristics of 14Cr-ODS ferritic alloy fabricated by mechanically alloying and microwave sintering

    Zhenhua, Yao [State Key Laboratory of Materia Processing and Die & Mould Technology, Huazhong University of Science and Technology, Wuhan 430074 (China); Weihao, Xiong, E-mail: whxiong@mail.hust.edu.cn [State Key Laboratory of Materia Processing and Die & Mould Technology, Huazhong University of Science and Technology, Wuhan 430074 (China); Bin, Huang; Qingqing, Yang [State Key Laboratory of Materia Processing and Die & Mould Technology, Huazhong University of Science and Technology, Wuhan 430074 (China); Jiang, Jianjun [School of Optical and Electronic Information, Huazhong University of Science and Technology, Wuhan 430074 (China)

    2015-06-15

    14Cr-ODS ferritic alloys were fabricated by microwave sintering and conventional vacuum sintering. The results showed that the sintering time could be reduced and the sintering temperature could be decreased effectively by adoption of microwave sintering. The tensile strength of the alloy microwave sintered at 1250 °C and the alloy vacuum sintered at 1350 °C were 691.4 MPa and 521.5 MPa respectively. The superior strength of microwave sintered one would be attributed to finer grain size, which was resulted from the shorter sintering time and lower sintering temperature. The elongation of microwave sintered alloy was worse than that of the vacuum sintering one. Nano-oxide precipitates were dispersed homogeneously in the Fe-based matrix, and their size was mostly ranged from several nm to more than 20 nm.

  11. Mapping of 475 oC embrittlement in ferritic Fe-Cr-Al alloys

    Embrittlement at 475 oC was mapped in ferritic ternary alloys with a wide composition range of Fe-(10-30)Cr-(0-20)Al (at.%) using a diffusion multiple technique. A large solid solution of Al suppresses the 475 oC embrittlement, while a small solid solution of Al promotes embrittlement. Transmission electron microscopy observations on aged samples suggest that suppression of the embrittlement due to Al addition can be attributed to the suppression of phase separation of the ferrite phase into the two phases Fe-rich ferrite and Cr-rich ferrite.

  12. The development of low-activation alloys at ORNL

    The objective of this program is to advance the technology of reduced-activation ferritic steels, austenitic stainless steels, and vanadium alloys to the point where these alloys could be considered as the structural material for fusion reactors in preference to the conventional high-activation alloys; and develop alloys to meet US Nuclear Regulatory Commission 10CFR61 guidelines for shallow land burial. 20 figs., 1 tab

  13. Detection and quantification of solute clusters in a nanostructured ferritic alloy

    Miller, M. K.; Reinhard, D.; Larson, D. J.

    2015-07-01

    A series of simulated atom probe datasets were examined with a friends-of-friends method to establish the detection efficiency required to resolve solute clusters in the ferrite phase of a 14YWT nanostructured ferritic alloy. The size and number densities of solute clusters in the ferrite of the as-milled mechanically-alloyed condition and the stir zone of a friction stir weld were estimated with a prototype high-detection-efficiency (∼80%) local electrode atom probe. High number densities, 1.8 × 1024 m-3 and 1.2 × 1024 m-3, respectively of solute clusters containing between 2 and 9 solute atoms of Ti, Y and O and were detected for these two conditions. These results support first principle calculations that predicted that vacancies stabilize these Ti-Y-O- clusters, which retard diffusion and contribute to the excellent high temperature stability of the microstructure and radiation tolerance of nanostructured ferritic alloys.

  14. Precipitation of Icosahedral Quasicrystalline Phase, R-phase and Laves Phase in Ferritic Alloys

    Keisuke Yamamoto; Yoshisato Kimura; Yoshinao Mishima

    2004-01-01

    Ferritic heat resistant steels involving precipitation of intermetallic phases have drawn a growing interest for the enhancement of creep strength, while the brittleness of the intermetallic phases may lower the toughness of the alloy.Therefore, it is necessary to optimize the dispersion characteristics of the intermetallics phase through microstructural control to minimize the trade-off between the strength and toughness. The effects of α-Fe matrix substructures on the precipitation sequence, morphology, dispersion characteristics, and the stability of the intermetallic phases are investigated in Fe-Cr-W-Co-Si system. The precipitates of the Si-free Fe-10Cr-1.4W-4.5Co (at%) alloy aged at 873K are the R-phase but those of the Si-added Fe-10Cr-1.4W-4.5Co-0.3Si (at%) alloy are the icosahedral quasicrystalline phase. The precipitates in both the Si-free and Si-added alloys aged at 973K are the Laves phase. Matrix of the alloys is controlled by heat treatments as to provide three types of matrix substructures; ferrite, ferrite/martensite mixture and martensite. The hardening behavior of the alloys depends on the matrix substructures and is independent of the kinds of precipitates. In the alloys with ferrite matrix, the peak of hardness during aging at 873K shifts to longer aging time in comparison with that in the alloys with lath martensite matrix which contain numbers of nucleation sites.

  15. Effects of consolidation temperature, strength and microstructure on fracture toughness of nanostructured ferritic alloys

    Fully consolidated nanostructured ferritic alloys (NFAs) were prepared by attritor milling pre-alloyed Fe-14Cr-3W-0.4Ti and 0.3 wt% Y2O3 powders, followed by hot isostatic pressing (HIPing) at 1000 oC or 1150 oC at 200 MPa for 4 h. Transmission electron microscopy (TEM) revealed similar bimodal distributions of fine and coarse ferrite grains in both cases. However, as expected, the alloy microhardness decreased with increasing in HIPing temperature. Three point bend tests on single edge notched specimens, with a nominal root radius ρ = 0.15 mm, were used to measure the notch fracture toughness, K ρ, as a function of test temperature. The K ρ curves were found to be similar for both processing conditions. It appears that the coarser ferrite grains control cleavage fracture, in a way that is independent of alloy strength and HIPing temperature

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

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

    1998-03-01

    Three ferritic alloys were irradiated in two fast reactors to doses of 50 dpa or more at temperatures near 400 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 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 {times} 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.

  17. Substrate integrated ferrite phase shifters and active frequency selective surfaces

    Cahill, B M

    2002-01-01

    There are two distinct parts to this thesis; the first investigates the use of ferrite tiles in the construction of printed phase shifting transmission lines, culminating in the design of two compact electromagnetic controlled beam steered patch and slot antenna arrays. The second part investigates the use of active frequency selective surfaces (AFSS), which are later used to cover a uPVC constructed enclosure. Field intensity measurements are taken from within the enclosure to determine the dynamic screening effectiveness. Trans Tech G-350 Ferrite is investigated to determine its application in printed microstrip and stripline phase shifting transmission lines. 50-Ohm transmission lines are constructed using the ferrite tile and interfaced to Rogers RT Duroid 5870 substrate. Scattering parameter measurements are made under the application of variable magnetic fields to the ferrite. Later, two types of planar microwave beam steering antennas are constructed. The first uses the ferrites integrated into the Dur...

  18. A comparison study of polymer/cobalt ferrite nano-composites synthesized by mechanical alloying route

    Sedigheh Rashidi; Abolghasem Ataie

    2015-01-01

    In this research, the effect of different biopolymers such as polyethylene glycol (PEG) and polyvinylalcohol (PVA) on synthesis and characterization of polymer/cobalt ferrite (CF) nano-composites bymechanical alloying method has been systematically investigated. The structural, morphological andmagnetic properties changes during mechanical milling were investigated by X-ray diffraction (XRD),Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), fieldemission ...

  19. Carburization of austenitic and ferritic alloys in hydrocarbon environments at high temperature

    Serna, A.

    2003-12-01

    Full Text Available The technical and industrial aspects of high temperature corrosion of materials exposed to a variety of aggressive environments have significant importance. These environments include combustion product gases and hydrocarbon gases with low oxygen potentials and high carbon potentials. In the refinery and petrochemical industries, austenitic and ferritic alloys are usually used for tubes in fired furnaces. The temperature range for exposure of austenitic alloys is 800-1100 °C, and for ferritic alloys 500-700 °C, with carbon activities ac > 1 in many cases. In both applications, the carburization process involves carbon (coke deposition on the inner diameter, carbon absorption at the metal surface, diffusion of carbon inside the alloy, and precipitation and transformation of carbides to a depth increasing with service. The overall kinetics of the internal carburization are approximately parabolic, controlled by carbon diffusion and carbide precipitation. Ferritic alloys exhibit gross but uniform carburization while non-uniform intragranular and grain-boundary carburization is observed in austenitic alloys.

    La corrosión a alta temperatura, tal como la carburación de materiales expuestos a una amplia variedad de ambientes agresivos, tiene especial importancia desde el punto de vista técnico e industrial. Estos ambientes incluyen productos de combustión, gases e hidrocarburos con bajo potencial de oxígeno y alto potencial de carbono. En las industrias de refinación y petroquímica, las aleaciones austeníticas y ferríticas se utilizan en tuberías de hornos. El rango de temperatura de exposición para aleaciones austeníticas está entre 800-1.100°C y para aleaciones ferríticas está entre 500-700°C, con actividades de carbono ac>1 en algunos casos. En tuberías con ambas aleaciones, el proceso de carburación incluye deposición de carbón (coque en el diámetro interno, absorción de carbono en la superficie

  20. A comparison study of polymer/cobalt ferrite nano-composites synthesized by mechanical alloying route

    Sedigheh Rashidi

    2015-12-01

    Full Text Available In this research, the effect of different biopolymers such as polyethylene glycol (PEG and polyvinylalcohol (PVA on synthesis and characterization of polymer/cobalt ferrite (CF nano-composites bymechanical alloying method has been systematically investigated. The structural, morphological andmagnetic properties changes during mechanical milling were investigated by X-ray diffraction (XRD,Fourier transform infrared spectroscopy (FTIR, transmission electron microscopy (TEM, fieldemission scanning electron microscopy (FESEM, and vibrating sample magnetometer techniques(VSM, respectively. The polymeric cobalt ferrite nano-composites were obtained by employing atwo-step procedure: the cobalt ferrite of 20 nm mean particle size was first synthesized by mechanicalalloying route and then was embedded in PEG or PVA biopolymer matrix by milling process. Theresults revealed that PEG melted due to the local temperature raise during milling. Despite thisphenomenon, cobalt ferrite nano-particles were entirely embedded in PEG matrix. It seems, PAV is anappropriate candidate for producing nano-composite samples due to its high melting point. InPVA/CF nano-composites, the mean crystallite size and milling induced strain decreased to 13 nm and0.48, respectively. Moreover, milling process resulted in well distribution of CF in PVA matrix eventhough the mean particle size of cobalt ferrite has not been significantly affecetd. FTIR resultconfirmed the attachment of PVA to the surface of nano-particles. Magnetic properties evaluationshowed that saturation magnetization and coercivity values decreased in nano-composite samplecomparing the pure cobalt ferrite.

  1. FERRITE STRUCTURE AND MECHANICAL PROPERTIES OF LOW ALLOY DUPLEX STEELS

    Hoel, R.H.; Thomas, G.

    1981-04-01

    The purpose of this communication is threefold. 1) To confirm the presence of and to characterize the precipitates in the ferrite phase of the base + Nb and base + Mo steels, 2) to study any possible variation in precipitate density as the martensitic volume fraction is changed and 3) to determine the level of precipitation strengthening.

  2. Detection and quantification of solute clusters in a nanostructured ferritic alloy

    Highlights: • Simulated APT data indicate that solute clusters can be resolved at 80% detection efficiency. • Solute clusters containing 2–9 atoms were detected in a prototype ∼80% detection efficiency LEAP. • High densities, 1.8 × 1024 m−3, of solute clusters were detected in as-milled flakes of 14YWT. • Lower densities, 1.2 × 1024 m−3, were detected in the stir zone of a FSW. • Vacancies stabilize the clusters, which retard diffusion and confers excellent stability. - Abstract: A series of simulated atom probe datasets were examined with a friends-of-friends method to establish the detection efficiency required to resolve solute clusters in the ferrite phase of a 14YWT nanostructured ferritic alloy. The size and number densities of solute clusters in the ferrite of the as-milled mechanically-alloyed condition and the stir zone of a friction stir weld were estimated with a prototype high-detection-efficiency (∼80%) local electrode atom probe. High number densities, 1.8 × 1024 m−3 and 1.2 × 1024 m−3, respectively of solute clusters containing between 2 and 9 solute atoms of Ti, Y and O and were detected for these two conditions. These results support first principle calculations that predicted that vacancies stabilize these Ti–Y–O– clusters, which retard diffusion and contribute to the excellent high temperature stability of the microstructure and radiation tolerance of nanostructured ferritic alloys

  3. Activation analyses for different fusion structural alloys

    The leading candidate structural materials, viz., the vanadium alloys, the nickel or the manganese stabilized austenitic steels, and the ferritic steels, are analysed in terms of their induced activation in the TPSS fusion power reactor. The TPSS reactor has 1950 MW fusion power and inboard and outboard average neutron wall loading of 3.75 and 5.35 MW/m2 respectively. The results shows that, after one year of continuous operation, the vanadium alloys have the least radioactivity at reactor shutdown. The maximum difference between the induced radioactivity in the vanadium alloys and in the other iron-based alloys occurs at about 10 years after reactor shutdown. At this time, the total reactor radioactivity, using the vanadium alloys, is about two orders of magnitude less than the total reactor radioactivity utilizing any other alloy. The difference is even larger in the first wall, the FW-vanadium activation is 3 orders of magnitude less than other alloys' FW activation. 2 refs., 7 figs

  4. Computational Design of Creep-Resistant Alloys and Experimental Validation in Ferritic Superalloys

    Liaw, Peter

    2014-12-31

    A new class of ferritic superalloys containing B2-type zones inside parent L21-type precipitates in a disordered solid-solution matrix, also known as a hierarchical-precipitate strengthened ferritic alloy (HPSFA), has been developed for high-temperature structural applications in fossil-energy power plants. These alloys were designed by the addition of the Ti element into a previously-studied NiAl-strengthened ferritic alloy (denoted as FBB8 in this study). In the present research, systematic investigations, including advanced experimental techniques, first-principles calculations, and numerical simulations, have been integrated and conducted to characterize the complex microstructures and excellent creep resistance of HPSFAs. The experimental techniques include transmission-electron microscopy, scanningtransmission- electron microscopy, neutron diffraction, and atom-probe tomography, which provide detailed microstructural information of HPSFAs. Systematic tension/compression creep tests revealed that HPSFAs exhibit the superior creep resistance, compared with the FBB8 and conventional ferritic steels (i.e., the creep rates of HPSFAs are about 4 orders of magnitude slower than the FBB8 and conventional ferritic steels.) First-principles calculations include interfacial free energies, anti-phase boundary (APB) free energies, elastic constants, and impurity diffusivities in Fe. Combined with kinetic Monte- Carlo simulations of interdiffusion coefficients, and the integration of computational thermodynamics and kinetics, these calculations provide great understanding of thermodynamic and mechanical properties of HPSFAs. In addition to the systematic experimental approach and first-principles calculations, a series of numerical tools and algorithms, which assist in the optimization of creep properties of ferritic superalloys, are utilized and developed. These numerical simulation results are compared with the available experimental data and previous first

  5. Studies on the activation energy from the ac conductivity measurements of rubber ferrite composites containing manganese zinc ferrite

    Manganese zinc ferrites (MZF) have resistivities between 0.01 and 10 Ω m. Making composite materials of ferrites with either natural rubber or plastics will modify the electrical properties of ferrites. The moldability and flexibility of these composites find wide use in industrial and other scientific applications. Mixed ferrites belonging to the series Mn(1-x)ZnxFe2O4 were synthesized for different ‘x’ values in steps of 0.2, and incorporated in natural rubber matrix (RFC). From the dielectric measurements of the ceramic manganese zinc ferrite and rubber ferrite composites, ac conductivity and activation energy were evaluated. A program was developed with the aid of the LabVIEW package to automate the measurements. The ac conductivity of RFC was then correlated with that of the magnetic filler and matrix by a mixture equation which helps to tailor properties of these composites.

  6. Studies on the activation energy from the ac conductivity measurements of rubber ferrite composites containing manganese zinc ferrite

    Hashim, Mohd.; Alimuddin; Kumar, Shalendra; Shirsath, Sagar E.; Mohammed, E. M.; Chung, Hanshik; Kumar, Ravi

    2012-11-01

    Manganese zinc ferrites (MZF) have resistivities between 0.01 and 10 Ω m. Making composite materials of ferrites with either natural rubber or plastics will modify the electrical properties of ferrites. The moldability and flexibility of these composites find wide use in industrial and other scientific applications. Mixed ferrites belonging to the series Mn(1-x)ZnxFe2O4 were synthesized for different ‘x’ values in steps of 0.2, and incorporated in natural rubber matrix (RFC). From the dielectric measurements of the ceramic manganese zinc ferrite and rubber ferrite composites, ac conductivity and activation energy were evaluated. A program was developed with the aid of the LabVIEW package to automate the measurements. The ac conductivity of RFC was then correlated with that of the magnetic filler and matrix by a mixture equation which helps to tailor properties of these composites.

  7. Temperature-dependent elastic anisotropy and mesoscale deformation in a nanostructured ferritic alloy.

    Stoica, G M; Stoica, A D; Miller, M K; Ma, D

    2014-01-01

    Nanostructured ferritic alloys are a new class of ultrafine-grained oxide dispersion-strengthened steels that have promising properties for service in extreme environments in future nuclear reactors. This is due to the remarkable stability of their complex microstructures containing numerous Y-Ti-O nanoclusters within grains and along grain boundaries. Although nanoclusters account primarily for the exceptional resistance to irradiation damage and high-temperature creep, little is known about the mechanical roles of the polycrystalline grains that constitute the ferritic matrix. Here we report an in situ mesoscale characterization of anisotropic responses of ultrafine ferrite grains to stresses using state-of-the-art neutron diffraction. We show the experimental determination of single-crystal elastic constants for a 14YWT alloy, and reveal a strong temperature-dependent elastic anisotropy that leads to elastic softening and instability of the ferrite. We also demonstrate, from anisotropy-induced intergranular strains, that a deformation crossover exists from low-temperature lattice hardening to high-temperature lattice softening in response to extensive plastic deformation. PMID:25300893

  8. SAW surfacing of low-alloyed steel with super-ferrite additional material

    Klimpel, A; T. Kik; J. Górka; A. Czupryński; P. Sitarz

    2009-01-01

    Purpose: of these researches was to investigate influence of heat input in SAW surfacing of low-alloyed steel with super-ferrite filler material on quality of deposits.Design/methodology/approach: the quality of single and multilayer, stringer beads was assessed by metallographic examinations, stresses measurements and hardness tests.Findings: due to the fact that it was used at automated surfacing stand, the analysis of properties of the deposits was performed for single and multilayer, str...

  9. The welding of austenitic-ferritic Mo-alloyed Cr-Ni-Steel

    This paper provides general information and guidance on the welding of austenitic-ferritic Mo-alloyed Cr-Ni stainless steel. Information is given on the various chemical compositions and on resistance to corrosion and on the mechanical and physical properties of commercially available steels. The effect of welding on the base metal and the selection of welding processes and welding consumables are described

  10. Precipitation behaviour of a ferritic FeNiAl alloy under irradiation

    Coarsening of coherent NiAl (β') precipitates in a ferritic Fe-8.3Al-3.ONi-O.1Nb (at.%) alloy was investigated during thermal annealing and during irradiation with 6.2 MeV protons at temperatures from 673 K to 973 K. The matrix concentration of Ni and Al was traced by resistivity measurements while the growth of the precipitates was studied quantitatively by transmission electron microscopy (TEM). Additional Vickershardness measurements gave information on precipitation strengthening in the alloy. (orig.)

  11. Development of ferritic steels for reduced activation: the US program

    The Cr-Mo ferritic (martensitic) steels are candidates for the structural components of fusion reactors. Irradiation of such steels in a fusion environment produces long-lived radioactive isotopes, which lead to difficult radioactive waste disposal problems once the structure is removed from service. Such problems could be reduced by using steels that contain only elements that produce radioactive isotopes that decay to low levels in a reasonable time (tens of years instead of hundreds or thousands of years). The US Department of Energy has a program to develop steels to meet the criteria for shallow land burial as opposed to deep geologic storage. A review of the alloy development programs indicates that ferritic steels that meet these criteria can be developed

  12. Development of new generation reduced activation ferritic-martensitic steels for advanced fusion reactors

    Tan, L.; Snead, L. L.; Katoh, Y.

    2016-09-01

    International development of reduced activation ferritic-martensitic (RAFM) steels has focused on 9 wt percentage Cr, which primarily contain M23C6 (M = Cr-rich) and small amounts of MX (M = Ta/V, X = C/N) precipitates, not adequate to maintain strength and creep resistance above ∼500 °C. To enable applications at higher temperatures for better thermal efficiency of fusion reactors, computational alloy thermodynamics coupled with strength modeling have been employed to explore a new generation RAFM steels. The new alloys are designed to significantly increase the amount of MX nanoprecipitates, which are manufacturable through standard and scalable industrial steelmaking methods. Preliminary experimental results of the developed new alloys demonstrated noticeably increased amount of MX, favoring significantly improved strength, creep resistance, and Charpy impact toughness as compared to current RAFM steels. The strength and creep resistance were comparable or approaching to the lower bound of, but impact toughness was noticeably superior to 9-20Cr oxide dispersion-strengthened ferritic alloys.

  13. Bismuth Ferrite for Active Control of Surface Plasmon Polariton Modes

    Babicheva, Viktoriia; Zhukovsky, Sergei; Lavrinenko, Andrei

    We propose and investigate several layouts of m etal-insulator-metal waveguide with active core which can be utilized for dynamic switching in photonic integrated circuits. The active material, bismuth ferrite (BiFeO3), is sandwiched between metal plates and changes i ts refractive index through ...

  14. Bismuth Ferrite for Active Control of Surface Plasmon Polariton Modes

    Babicheva, Viktoriia; Zhukovsky, Sergei; Lavrinenko, Andrei

    2014-01-01

    We propose and investigate several layouts of m etal-insulator-metal waveguide with active core which can be utilized for dynamic switching in photonic integrated circuits. The active material, bismuth ferrite (BiFeO3), is sandwiched between metal plates and changes i ts refractive index through...

  15. Development of new ferritic alloys reinforced by nano titanium nitrides

    Mathon, M.H., E-mail: marie-helene.mathon@cea.fr [Laboratoire Léon Brillouin, CEA-CNRS, CEA/Saclay, 91191 Gif-sur-Yvette (France); Perrut, M., E-mail: mikael.perrut@onera.fr [Laboratoire Léon Brillouin, CEA-CNRS, CEA/Saclay, 91191 Gif-sur-Yvette (France); Poirier, L., E-mail: poirier@nitruvid.com [Bodycote France and Belgium, 9 r Jean Poulmarch, 95100 Argenteuil (France); Ratti, M., E-mail: mathieu.ratti@snecma.fr [CEA, DEN, Service de Recherches Métallurgiques Appliquées, F91191 Gif-sur-Yvette (France); Hervé, N., E-mail: nicolas.herve@cea.fr [CEA, DRT, LITEN, F38054 Grenoble (France); Carlan, Y. de, E-mail: yann.decarlan@cea.fr [CEA, DEN, Service de Recherches Métallurgiques Appliquées, F91191 Gif-sur-Yvette (France)

    2015-01-15

    Nano-reinforced steels are considered for future nuclear reactors or for application at high temperature like the heat exchangers tubes or plates. Oxide Dispersion Strengthened (ODS) alloys are the most known of the nano-reinforced alloys. They exhibit high creep strength as well as high resistance to radiation damage. This article deals with the development of new nano reinforced alloys called Nitride Dispersed Strengthened (NDS). Those are also considered for nuclear applications and could exhibit higher ductility with a simplest fabrication way. Two main fabrication routes were studied: the co-milling of Fe–18Cr1W0.008N and TiH{sub 2} powders and the plasma nitration at low temperature of a Fe–18Cr1W0.8Ti powder. The materials were studied mainly by Small Angle Neutron Scattering. The feasibility of the reinforcement by nano-nitride particles is demonstrated. The final size of the nitrides can be similar (few nanometers) to the nano-oxides observed in ODS alloys. The mechanical properties of the new NDS show an amazing ductility at high temperature for a nano-reinforced alloy.

  16. Atom probe tomography of the austenite-ferrite interphase boundary composition in a model alloy Fe-C-Mn

    Thuillier, O. [Groupe de Physique des Materiaux, UMR CNRS 6634, Institut des Materiaux de Rouen, Universite de Rouen, 76 801 Saint Etienne du Rouvray Cedex (France)]. E-mail: olivier.thuillier@etu.univ-rouen.fr; Danoix, F. [Groupe de Physique des Materiaux, UMR CNRS 6634, Institut des Materiaux de Rouen, Universite de Rouen, 76 801 Saint Etienne du Rouvray Cedex (France); Goune, M. [Arcelor Research, Voie Romaine B.P. 320, 57214 Maizieres-Les-Metz (France); Blavette, D. [Groupe de Physique des Materiaux, UMR CNRS 6634, Institut des Materiaux de Rouen, Universite de Rouen, 76 801 Saint Etienne du Rouvray Cedex (France)

    2006-12-15

    A tomographic atom p analysis has been developed to study the interfacial conditions during isothermal austenite transformation to ferrite at 700 deg. C in an Fe-C-Mn model alloy. The interfacial conditions lead to different alloying element profiles across the interface, and a comparison is made between this experimental result and the DICTRA software predictions under the various conditions.

  17. Atom probe tomography of the austenite-ferrite interphase boundary composition in a model alloy Fe-C-Mn

    A tomographic atom probe analysis has been developed to study the interfacial conditions during isothermal austenite transformation to ferrite at 700 deg. C in an Fe-C-Mn model alloy. The interfacial conditions lead to different alloying element profiles across the interface, and a comparison is made between this experimental result and the DICTRA software predictions under the various conditions

  18. Postirradiation deformation behavior in ferritic Fe-Cr alloys

    It has been demonstrated that fast-neutron irradiation produces significant hardening in simple Fe-(3-18)Cr binary alloys irradiated to about 35 dpa in the temperature range 365 to 420 degrees C, whereas irradiation at 574 degrees C produces hardening only for 15% or more chromium. The irradiation-induced changes in tensile properties are discussed in terms of changes in the power law work-hardening exponent. The work-hardening exponent of the lower chromium alloys decreased significantly after low-temperature irradiation (≤ 420 degrees C) but increased after irradiation at 574 degrees C. The higher chromium alloys failed either in cleavage or in a mixed ductile/brittle fashion. Deformation microstructures are presented to support the tensile behavior

  19. Computational thermodynamics aided design of novel ferritic alloys

    Yang, Ying [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Chen, Tianyi [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Tan, Lizhen [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)

    2016-06-30

    With the aid of computational thermodynamics, Ni was identified to suppress the liquidus temperature of Fe2Zr and four Fe-Cr-Ni-Zr alloys were designed to study the Ni effect on the phase stability of Fe2Zr laves_phase. These alloys were fabricated through traditional arc-metling, followed by annealing at 1000 C for 336 hours and 700 C for 1275 hours. The microstructure were examined and characterized by SEM BSE image, EDS compositional mapping and point scan, XRD and TEM analysis. The major results were summarized below: 1)For investigated alloys with 12wt% Cr, 3~6wt% Zr and 3~9 wt%Ni, the phases in equilibrium with the BCC phase are C15_Laves phase, Fe23Zr6 phase. The volume fraction of intermetallic phases increases with Ni and Zr contents. 2)Instead of (Fe,Cr)2Zr C14_Laves phase, Ni stabilizes the C15_Laves structure in Fe-Cr-Ni-Zr alloys by substituting Fe and Cr atoms with Ni atoms in the first sublattice. 3)Fe23Zr6, that is metastable in the Fe-Cr-Zr ternary, is also stabilized by Ni addition. 4)Ni7Zr2 phase was observed in samples with high Ni/Zr ratio. Extensive solubility of Fe was identified in the phase. The microstructural and composition results obtained from this study will be incorportated into the the Fe-Cr-Ni-Zr database. The current samples will be subjected to ion irradiaition to be compared with those results for Fe-Cr-Zr alloys. Additional alloys will be designed to form (Fe,Cr,Ni)2Zr nanoprecipitates for further studies.

  20. Detection and quantification of solute clusters in a nanostructured ferritic alloy

    Miller, M.K., E-mail: millermk@ornl.gov [Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6139 (United States); Reinhard, D., E-mail: David.Reinhard@ametek.com [CAMECA Instruments, Inc., 5500 Nobel Drive, Madison, WI 53711 (United States); Larson, D.J., E-mail: David.Larson@ametek.com [CAMECA Instruments, Inc., 5500 Nobel Drive, Madison, WI 53711 (United States)

    2015-07-15

    Highlights: • Simulated APT data indicate that solute clusters can be resolved at 80% detection efficiency. • Solute clusters containing 2–9 atoms were detected in a prototype ∼80% detection efficiency LEAP. • High densities, 1.8 × 10{sup 24} m{sup −3}, of solute clusters were detected in as-milled flakes of 14YWT. • Lower densities, 1.2 × 10{sup 24} m{sup −3}, were detected in the stir zone of a FSW. • Vacancies stabilize the clusters, which retard diffusion and confers excellent stability. - Abstract: A series of simulated atom probe datasets were examined with a friends-of-friends method to establish the detection efficiency required to resolve solute clusters in the ferrite phase of a 14YWT nanostructured ferritic alloy. The size and number densities of solute clusters in the ferrite of the as-milled mechanically-alloyed condition and the stir zone of a friction stir weld were estimated with a prototype high-detection-efficiency (∼80%) local electrode atom probe. High number densities, 1.8 × 10{sup 24} m{sup −3} and 1.2 × 10{sup 24} m{sup −3}, respectively of solute clusters containing between 2 and 9 solute atoms of Ti, Y and O and were detected for these two conditions. These results support first principle calculations that predicted that vacancies stabilize these Ti–Y–O– clusters, which retard diffusion and contribute to the excellent high temperature stability of the microstructure and radiation tolerance of nanostructured ferritic alloys.

  1. The role of processing route on the microstructure of 14YWT nanostructured ferritic alloy

    Mazumder, B.; Parish, C. M.; Bei, H.; Miller, M. K.

    2015-10-01

    Nanostructured ferritic alloys have outstanding high temperature creep properties and enhanced tolerance to radiation damage over conventional ferritic alloys. To achieve these properties, NFAs are fabricated by mechanical alloying of metallic and yttria powders. Atom probe tomography has demonstrated that milling times of at least 40 h are required to produce a uniform distribution of solutes in the flakes. After milling and hot extrusion, the microstructure consists of α-Fe, high number densities of Ti-Y-O-vacancy-enriched nanoclusters, and coarse Y2Ti2O7 and Ti(O,C,N) precipitates on the grain boundaries. In contrast, the as-cast condition consists of α-Fe with 50-100 μm irregularly-shaped Y2Ti2O7 pyrochlore precipitates with smaller embedded precipitates with the Y3Al5O12 (yttrium-aluminum garnet) crystal structure indicating that this traditional processing route is not a viable approach to achieve the desired microstructure. The nano-hardnesses were also substantially different, i.e., 4 and 8 GPa for the as-cast and as-extruded conditions, respectively. These variances can be explained by the microstructural differences and the effects of the high vacancy content introduced by mechanical alloying, and the strong binding energy of vacancies with O, Ti, and Y atoms that retard diffusion.

  2. The microstructure and mechanical properties of Al-containing 9Cr ODS ferritic alloy

    In this study, a 9Cr oxide-dispersion strengthened (ODS) alloy with additional corrosion resistant element Al was fabricated by mechanical alloying (MA) and hot pressing (HP) to explore the impact of Al on the microstructure and mechanical property of a 9Cr ODS alloy. It is found that the Al completely dissolved into the Fe–Cr matrix after milling for 30 h. The minor phases in the Al-containing 9Cr ODS ferritic alloy were investigated by a high-energy X-ray, and were identified to be orthorhombic-YAlO3 (YAP), bcc-Y3Al5O12 (YAG), monoclinic-Al2Y4O9 (YAM), and hexagonal-YAlO3 (YAH). These phases were further confirmed by selected area diffraction pattern (SADP), energy dispersive spectroscopy (EDS), and high resolution transmission electron microscopy (HRTEM). In addition, their volume fractions were also calculated from the integrated intensities. According to the analysis of the particles and their formation sequences, the larger particles (greater than 100 nm) are identified as mainly YAG and Al2O3 particles, while the particles with small size (less than 30 nm) are likely primarily YAM, YAH, and YAP particles. The yielding strength (YS) and ultimate tensile strength (UTS) at RT are 563 MPa and 744 MPa, respectively, while the YS and UTS at 700 °C are 245 MPa and 276 MPa, respectively. Although the addition Al in ODS alloys decreases the strength at RT, the values at high temperature are similar to those obtained for 9Cr ODS alloys strengthened by fine Y–Ti–O particles. - Graphical abstract: Synchrotron X-ray diffraction line profile of the 9CrAl ODS alloy; (Ferrite matrix phases, along with minor phases, orthorhombic YAlO3 (yttrium aluminum perovskite, YAP), bcc Y3Al5O12 (yttrium aluminum garnet, YAG), monoclinic Al2Y4O9 (yttrium aluminum monoclinic, YAM), and hexagonal YAlO3 (yttium aluminum hexagonal, YAH) were recognized.). - Highlights: • The Al-containing 9Cr ODS ferritic alloy was firstly fabricated by MA and HP. • The precipitates were

  3. The microstructure and mechanical properties of Al-containing 9Cr ODS ferritic alloy

    Zhang, Guangming [School of Materials Science and Engineering, University of Science and Technology, Beijing, Beijing 100083 (China); Department of Nuclear, Plasma and Radiological Engineering, University of Illinois at Urbana-Champaign, IL 61801 (United States); Zhou, Zhangjian, E-mail: zhouzhj@mater.ustb.edu.cn [School of Materials Science and Engineering, University of Science and Technology, Beijing, Beijing 100083 (China); Mo, Kun [Nuclear Engineering Division, Argonne National Laboratory, Argonne, IL 60439 (United States); Wang, Pinghuai [Fusion Reactor & Materials Division, Southwestern Institute of Physics, Chengdu, Sichuan 610041 (China); Miao, Yinbin [Department of Nuclear, Plasma and Radiological Engineering, University of Illinois at Urbana-Champaign, IL 61801 (United States); Li, Shaofu; Wang, Man [School of Materials Science and Engineering, University of Science and Technology, Beijing, Beijing 100083 (China); Liu, Xiang [Department of Nuclear, Plasma and Radiological Engineering, University of Illinois at Urbana-Champaign, IL 61801 (United States); Gong, Mengqiang [School of Materials Science and Engineering, University of Science and Technology, Beijing, Beijing 100083 (China); Almer, Jonathan [X-ray Science Division, Argonne National Laboratory, Argonne, IL 60439 (United States); Stubbins, James F. [Department of Nuclear, Plasma and Radiological Engineering, University of Illinois at Urbana-Champaign, IL 61801 (United States)

    2015-11-05

    In this study, a 9Cr oxide-dispersion strengthened (ODS) alloy with additional corrosion resistant element Al was fabricated by mechanical alloying (MA) and hot pressing (HP) to explore the impact of Al on the microstructure and mechanical property of a 9Cr ODS alloy. It is found that the Al completely dissolved into the Fe–Cr matrix after milling for 30 h. The minor phases in the Al-containing 9Cr ODS ferritic alloy were investigated by a high-energy X-ray, and were identified to be orthorhombic-YAlO{sub 3} (YAP), bcc-Y{sub 3}Al{sub 5}O{sub 12} (YAG), monoclinic-Al{sub 2}Y{sub 4}O{sub 9} (YAM), and hexagonal-YAlO{sub 3} (YAH). These phases were further confirmed by selected area diffraction pattern (SADP), energy dispersive spectroscopy (EDS), and high resolution transmission electron microscopy (HRTEM). In addition, their volume fractions were also calculated from the integrated intensities. According to the analysis of the particles and their formation sequences, the larger particles (greater than 100 nm) are identified as mainly YAG and Al{sub 2}O{sub 3} particles, while the particles with small size (less than 30 nm) are likely primarily YAM, YAH, and YAP particles. The yielding strength (YS) and ultimate tensile strength (UTS) at RT are 563 MPa and 744 MPa, respectively, while the YS and UTS at 700 °C are 245 MPa and 276 MPa, respectively. Although the addition Al in ODS alloys decreases the strength at RT, the values at high temperature are similar to those obtained for 9Cr ODS alloys strengthened by fine Y–Ti–O particles. - Graphical abstract: Synchrotron X-ray diffraction line profile of the 9CrAl ODS alloy; (Ferrite matrix phases, along with minor phases, orthorhombic YAlO{sub 3} (yttrium aluminum perovskite, YAP), bcc Y{sub 3}Al{sub 5}O{sub 12} (yttrium aluminum garnet, YAG), monoclinic Al{sub 2}Y{sub 4}O{sub 9} (yttrium aluminum monoclinic, YAM), and hexagonal YAlO{sub 3} (yttium aluminum hexagonal, YAH) were recognized.). - Highlights: • The

  4. Ion-induced swelling of ODS ferritic alloy MA957 tubing to 500 dpa

    Toloczko, M.B., E-mail: mychailo.toloczko@pnnl.gov [Pacific Northwest National Laboratory, Richland, WA 99354 (United States); Garner, F.A. [Radiation Effects Consulting, Richland, WA 99354 (United States); Voyevodin, V.N.; Bryk, V.V.; Borodin, O.V.; Mel’nychenko, V.V.; Kalchenko, A.S. [Kharkov Institute of Physics and Technology, Kharkov (Ukraine)

    2014-10-15

    In order to study the potential swelling behavior of the ODS ferritic alloy MA957 at very high dpa levels, specimens were prepared from pressurized tubes that were unirradiated archives of tubes previously irradiated in FFTF to doses as high as 110 dpa. These unirradiated specimens were irradiated with 1.8 MeV Cr{sup +} ions to doses ranging from 100 to 500 dpa and examined by transmission electron microscopy. No co-injection of helium or hydrogen was employed. It was shown that compared to several tempered ferritic/martensitic steels irradiated in the same facility, these tubes were rather resistant to void swelling, reaching a maximum value of only 4.5% at 500 dpa and 450 °C. In this fine-grained material, the distribution of swelling was strongly influenced by the presence of void denuded zones along the grain boundaries.

  5. Ion-induced swelling of ODS ferritic alloy MA957 tubing to 500 dpa

    Toloczko, M. B.; Garner, F. A.; Voyevodin, V. N.; Bryk, V. V.; Borodin, O. V.; Mel'nychenko, V. V.; Kalchenko, A. S.

    2014-10-01

    In order to study the potential swelling behavior of the ODS ferritic alloy MA957 at very high dpa levels, specimens were prepared from pressurized tubes that were unirradiated archives of tubes previously irradiated in FFTF to doses as high as 110 dpa. These unirradiated specimens were irradiated with 1.8 MeV Cr+ ions to doses ranging from 100 to 500 dpa and examined by transmission electron microscopy. No co-injection of helium or hydrogen was employed. It was shown that compared to several tempered ferritic/martensitic steels irradiated in the same facility, these tubes were rather resistant to void swelling, reaching a maximum value of only 4.5% at 500 dpa and 450 °C. In this fine-grained material, the distribution of swelling was strongly influenced by the presence of void denuded zones along the grain boundaries.

  6. Reduced activation ferritic steel R and D in US/Japan collaborative research

    Material performance of reduced activation ferritic steels (RAFS) and their response to neutron irradiation, which have been investigated by utilizing fission reactors under the US/Japan collaborative research program (JUPITER), are summarized. Rather high resistance to neutron irradiation and helium was recognized for 9Cr-2W RAFS; irradiation hardening and helium embrittlement of RAFS were evaluated to be much less than for other candidate materials. Alloy design of high-temperature steels and the development of oxide dispersion-strengthened steels have been progressing. (author)

  7. System and method of forming nanostructured ferritic alloy

    Dial, Laura Cerully; DiDomizio, Richard; Alinger, Matthew Joseph; Huang, Shenyan

    2016-07-26

    A system for mechanical milling and a method of mechanical milling are disclosed. The system includes a container, a feedstock, and milling media. The container encloses a processing volume. The feedstock and the milling media are disposed in the processing volume of the container. The feedstock includes metal or alloy powder and a ceramic compound. The feedstock is mechanically milled in the processing volume using metallic milling media that includes a surface portion that has a carbon content less than about 0.4 weight percent.

  8. Effect of alloying on microstructure and precipitate evolution in ferritic weld metal

    Narayanan, Badri Kannan

    The effect of alloying on the microstructure of ferritic weld metal produced with an self-shielded flux cored arc welding process (FCAW-S) has been studied. The welding electrode has a flux core that is intentionally alloyed with strong deoxidizers and denitriding elements such as aluminum, titanium and zirconium in addition to austenite formers such as manganese and nickel. This results in formation of microstructure consisting of carbide free bainite, retained austenite and twinned martensite. The work focuses on characterization of the microstructures and the precipitates formed during solidification and the allotropic phase transformation of the weld metal. Aluminum, manganese and nickel have significant solubility in iron while aluminum, titanium and zirconium have very strong affinity for nitrogen and oxygen. The effect of these alloying elements on the phase transformation and precipitation of oxides and nitrides have been studied with various characterization techniques. In-situ X-ray synchrotron diffraction has been used to characterize the solidification path and the effect of heating and cooling rates on microstructure evolution. Scanning Transmission Electron Microscopy (STEM) in conjunction with Energy Dispersive Spectroscopy (EDS) and Electron energy loss spectroscopy (EELS) was used to study the effect of micro-alloying additions on inclusion evolution. The formation of core-shell structure of oxide/nitride is identified as being key to improvement in toughness of the weld metal. Electron Back Scattered Diffraction (EBSD) in combination with Orientation Imaging Microscopy (OIM) and Transmission electron microscopy (TEM) has been employed to study the effect of alloying on austenite to ferrite transformation modes. The prevention of twinned martensite has been identified to be key to improving ductility for achieving high strength weld metal.

  9. Some microstructural characterisations in a friction stir welded oxide dispersion strengthened ferritic steel alloy

    The goal of this study is to characterize microstructure of a friction stir welded oxide dispersion strengthened alloy. The welded material is constituted by two sheets of an yttria-dispersion-strengthened PM 2000 ferritic steel. Different areas of the friction stir welded product were analyzed using field emission gun secondary electron microscopy (FEG-SEM) and electron microprobe whereas nanoindentation was used to evaluate mechanical properties. The observed microstructural evolution, including distribution of the yttria dispersoids, after friction stir welding process is discussed and a correlation between the microstructure and the results of nanoindentation tests is established.

  10. Some microstructural characterisations in a friction stir welded oxide dispersion strengthened ferritic steel alloy

    Legendre, F. [CEA Saclay, DEN/DANS/DMN/SRMP, 91191 Gif-sur-Yvette cedex (France)], E-mail: flegendre@cea.fr; Poissonnet, S.; Bonnaillie, P.; Boulanger, L. [CEA Saclay, DEN/DANS/DMN/SRMP, 91191 Gif-sur-Yvette cedex (France); Forest, L. [CEA Saclay, DEN/DANS/DM2S/SEMT/LTA, 91191 Gif-sur-Yvette cedex (France)

    2009-04-30

    The goal of this study is to characterize microstructure of a friction stir welded oxide dispersion strengthened alloy. The welded material is constituted by two sheets of an yttria-dispersion-strengthened PM 2000 ferritic steel. Different areas of the friction stir welded product were analyzed using field emission gun secondary electron microscopy (FEG-SEM) and electron microprobe whereas nanoindentation was used to evaluate mechanical properties. The observed microstructural evolution, including distribution of the yttria dispersoids, after friction stir welding process is discussed and a correlation between the microstructure and the results of nanoindentation tests is established.

  11. Some microstructural characterisations in a friction stir welded oxide dispersion strengthened ferritic steel alloy

    Legendre, F.; Poissonnet, S.; Bonnaillie, P.; Boulanger, L.; Forest, L.

    2009-04-01

    The goal of this study is to characterize microstructure of a friction stir welded oxide dispersion strengthened alloy. The welded material is constituted by two sheets of an yttria-dispersion-strengthened PM 2000 ferritic steel. Different areas of the friction stir welded product were analyzed using field emission gun secondary electron microscopy (FEG-SEM) and electron microprobe whereas nanoindentation was used to evaluate mechanical properties. The observed microstructural evolution, including distribution of the yttria dispersoids, after friction stir welding process is discussed and a correlation between the microstructure and the results of nanoindentation tests is established.

  12. Radiation damage simulation studies of selected austenitic and ferritic/martensitic alloys for fusion reactor structural applications

    Results are given of an investigation of the radiation damage stability of selected austenitic and ferritic alloys following ion bombardment in the Harwell VEC to simulate fusion-reactor exposures up to 110 dpa at temperatures from 425 deg to 625 deg C. Gas production rates appropriate to CTR conditions were simulated using a mixed beam of (4 MeV He + 2 MeV H2) in the ratio 1:4 He:H. A beam of 46 MeV Ni or 20 MeV Cr ions was used in sequence with the mixed gas beam to provide a gas/damage ratio of 13 appm He/dpa at a damage rate of approx. 1 dpa/hr. The materials were investigated using TEM and comprised three austenitic alloys: European reference 316L, 316-Ti, 316-Nb; four high-nickel alloys: Fe/25 Ni/8Cr, Inconel 625, Inconel 706 and Nimonic PE16, and four ferritic/martensitic alloys: FV 448, FV 607, CRM 12 and FI. Some data were obtained for a non-magnetic structural alloy Nonmagne-30. The swelling behaviour is reported. The overall results of the study indicate that on a comparative basis the ferritic alloys are the most swelling-resistant, whilst the high-nickel alloys have an acceptable low swelling response up to 110 dpa. The 316 alloys tested have shown an unfavourable swelling response. (author)

  13. Corrosion of ferritic-martensitic steels and nickel-based alloys in supercritical water

    Ren, Xiaowei

    The corrosion behavior of ferritic/martensitic (F/M) steels and Ni-based alloys in supercritical water (SCW) has been studied due to their potential applications in future nuclear reactor systems, fossil fuel power plants and waste treatment processes. 9˜12% chromium ferritic/martensitic steels exhibit good radiation resistance and stress corrosion cracking resistance. Ni-based alloys with an austenitic face-centered cubic (FCC) structure are designed to retain good mechanical strength and corrosion/oxidation resistance at elevated temperatures. Corrosion tests were carried out at three temperatures, 360°C, 500°C and 600°C, with two dissolved oxygen contents, 25 ppb and 2 ppm for up to 3000 hours. Alloys modified by grain refinement and reactive element addition were also investigated to determine their ability to improve the corrosion resistance in SCW. A duplex oxide structure was observed in the F/M steels after exposure to 25 ppb oxygen SCW, including an outer oxide layer with columnar magnetite grains and an inner oxide layer constituted of a mixture of spinel and ferrite phases in an equiaxed grain structure. An additional outermost hematite layer formed in the SCW-exposed samples when the oxygen content was increased to 2 ppm. Weight gain in the F/M steels increased with exposure temperatures and times, and followed parabolic growth kinetics in most of the samples. In Ni-based alloys after exposure to SCW, general corrosion and pitting corrosion were observed, and intergranular corrosion was found when exposed at 600°C due to formation of a local healing layer. The general oxide structure on the Ni-based alloys was characterized as NiO/Spinel/(CrxFe 1-x)2O3/(Fe,Ni). No change in oxidation mechanism was observed in crossing the critical point despite the large change in water properties. Corrosion resistance of the F/M steels was significantly improved by plasma-based yttrium surface treatment because of restrained outward diffusion of iron by the

  14. Phase Field Modeling of Cyclic Austenite-Ferrite Transformations in Fe-C-Mn Alloys

    Chen, Hao; Zhu, Benqiang; Militzer, Matthias

    2016-08-01

    Three different approaches for considering the effect of Mn on the austenite-ferrite interface migration in an Fe-0.1C-0.5Mn alloy have been coupled with a phase field model (PFM). In the first approach (PFM-I), only long-range C diffusion is considered while Mn is assumed to be immobile during the phase transformations. Both long-range C and Mn diffusions are considered in the second approach (PFM-II). In the third approach (PFM-III), long-range C diffusion is considered in combination with the Gibbs energy dissipation due to Mn diffusion inside the interface instead of solving for long-range diffusion of Mn. The three PFM approaches are first benchmarked with isothermal austenite-to-ferrite transformation at 1058.15 K (785 °C) before considering cyclic phase transformations. It is found that PFM-II can predict the stagnant stage and growth retardation experimentally observed during cycling transformations, whereas PFM-III can only replicate the stagnant stage but not the growth retardation and PFM-I predicts neither the stagnant stage nor the growth retardation. The results of this study suggest a significant role of Mn redistribution near the interface on reducing transformation rates, which should, therefore, be considered in future simulations of austenite-ferrite transformations in steels, particularly at temperatures in the intercritical range and above.

  15. SAW surfacing of low-alloyed steel with super-ferrite additional material

    A. Klimpel

    2009-10-01

    Full Text Available Purpose: of these researches was to investigate influence of heat input in SAW surfacing of low-alloyed steel with super-ferrite filler material on quality of deposits.Design/methodology/approach: the quality of single and multilayer, stringer beads was assessed by metallographic examinations, stresses measurements and hardness tests.Findings: due to the fact that it was used at automated surfacing stand, the analysis of properties of the deposits was performed for single and multilayer, stringer beads.Research limitations/implications: for complete information about tested deposits it is needed to compare deposits properties with other technologies of super-ferrite deposits surfacing.Practical implications: results of this paper is an optimal range of parameters for surfacing of single and multilayer, stringer beads of super-ferrite layers.Originality/value: the researches (macro- and micro-observations, hardness tests, stresses distribution tests were provided for surfacing of single and multilayer, stringer beads, and the results were compared. The influence of heat input on layers properties and theirs structure was defined.

  16. Substrate integrated ferrite phase shifters and active frequency selective surfaces

    There are two distinct parts to this thesis; the first investigates the use of ferrite tiles in the construction of printed phase shifting transmission lines, culminating in the design of two compact electromagnetic controlled beam steered patch and slot antenna arrays. The second part investigates the use of active frequency selective surfaces (AFSS), which are later used to cover a uPVC constructed enclosure. Field intensity measurements are taken from within the enclosure to determine the dynamic screening effectiveness. Trans Tech G-350 Ferrite is investigated to determine its application in printed microstrip and stripline phase shifting transmission lines. 50-Ohm transmission lines are constructed using the ferrite tile and interfaced to Rogers RT Duroid 5870 substrate. Scattering parameter measurements are made under the application of variable magnetic fields to the ferrite. Later, two types of planar microwave beam steering antennas are constructed. The first uses the ferrites integrated into the Duroid as microstrip lines with 3 patch antennas as the radiating elements. The second uses stripline transmission lines, with slot antennas as the radiating sources etched into the ground plane of the triplate. Beam steering is achieved by the application of an external electromagnet. An AFSS is constructed by the interposition of PIN diodes into a dipole FSS array. Transmission response measurements are then made for various angles of electromagnetic wave incidence. Two states of operation exist: when a current is passed through the diodes and when the diodes are switched off. These two states form a high pass and band stop space filter respectively. An enclosure covered with the AFSS is constructed and externally illuminated in the range 2.0 - 2.8GHz. A probe antenna inside the enclosure positioned at various locations through out the volume is used to establish the effective screening action of the AFSS in 3 dimensional space. (author)

  17. The effect of fusion-relevant helium levels on the mechanical properties of isotopically tailored ferritic alloys

    The yield and maximum strengths of an irradiated series of isotopically tailored ferritic alloys were evaluated using the shear punch test. The composition of three of the alloys was Fe-12Cr-1.5Ni. Different balances of nickel isotopes were used in each alloy in order to produce different helium levels. A fourth alloy, which contained no nickel, was also irradiated. The addition of nickel at any isotopic balance to the Fe-12Cr base alloy significantly increased the shear yield and maximum strengths of the alloys, and as expected, the strength of the alloys decreased with increasing irradiation temperature. Helium itself, up to 75 appm over 7 dpa appears to have little effect on the mechanical properties of the alloys

  18. TEM examination of microstructural evolution during processing of 14CrYWTi nanostructured ferritic alloys

    A transmission electron microscopy (TEM) study was carried out on the co-evolution of the coarser-scale microstructural features in mechanically alloyed (MA) powders and hot isostatic press (HIP) consolidated Fe-14Cr-3W-0 and 0.4Ti-0.25Y2O3 nanostructured ferritic alloys (NFAs). The pancake shaped nanoscale grains in the as-MA powders are textured and elongated parallel to the particle surface. Powder annealing results in re-crystallization at 850 deg. C and grain growth at 1150 deg. C. The grains also recrystallize and may grow in the alloys HIPed at 850 deg. C, but appear to retain a polygonized sub-grain structure. The grains are larger and more distinct in the alloys HIPed at 1000 and 1150 deg. C. However, annealing resulted in bi-modal grain size distribution. Finer grains retained a significant dislocation density and populations of small precipitates with crystal structures distinct form the matrix. The grains and precipitates were much larger in alloys without Ti

  19. Thermodynamic and kinetic modeling of oxide precipitation in nanostructured ferritic alloys

    The mechanical properties and radiation tolerance of nanostructured ferritic alloys rely on a dense population of nanometer-scale Y–Ti oxides. The stability of these nano-oxides during extended service is critical in high temperature applications. Here, a model framework is developed for the thermodynamics and kinetics of Y–Ti oxide nucleation, growth and coarsening. The model, which is based upon available thermodynamic and kinetic data as well as key density functional theory calculations, shows that nano-oxide nucleation and growth are highly driven and that pipe diffusion is the dominant mode of their coarsening, in agreement with previous analyses of experimental high temperature data. The model predicts that the nano-oxides are thermally stable for 80 or more years below 1175 K. This analysis also provides insights into the effect of O and Ti on nano-oxide sizes, and on optimization of alloy microstructure

  20. Plasticity of oxide dispersion strengthened ferritic alloys; Plasticite des alliages ferritiques renforces par dispersion d`oxydes

    Zakine, C.

    1994-07-05

    The object of this work is to study the plasticity mechanisms of two oxide dispersion strengthened ferritic alloys, DT and DY. Microstructural characterisation has been performed on DT and DY alloys by optical, scanning and transmission electron microscopy. These materials, strengthened by an oxide dispersion, contain an intermetallic {chi} phase precipitated on grain boundaries. The {chi} phase, stable up to 900 deg, can be dissolved into the matrix by heat treatment beyond 1 000 deg. Between 20 and 700 deg, according to tensile tests, the DY alloy which is strengthened by a fine dispersion of yttria particles is more resistant and less ductile than DT alloy, strengthened by titanium oxides. Tensile tests performed at room temperature, in the chamber of a SEM, have shown that micro-cracking of the {chi} phase coincides with the first stage of the macroscopic yielding. The cavities initiated by the {chi} phase micro-cracking induce a ductile fracture of the matrix. A dynamic strain ageing mechanism has been observed around 400 deg, which is attributed to the Mo contribution. Between 20 and 700 deg, comparison of tensile properties of alloys with or without {chi} phase has shown that the intermetallic phase has a detrimental effect on the ductility, but has no influence on the mechanical strength. Creep tests have been performed between 500 and 700 deg. Thermally activated plasticity mechanisms are observed in this temperature range. The {chi} phase, which is always micro-cracked after tensile testing, is not damaged after creep testing below a critical stress. This behaviour is explained by the influence of strain rate through the competition between strain hardening and relaxation of the matrix. (author).

  1. Study of behaviour during a quench treatment of ferrite delta of binary and pseudo-binary alloys

    Focusing of Fe-Cr and Fe-Mo alloys (and extending results to different binary alloys like Fe-W, Fe-Al and Fe-Si, and even to some ternary systems such as Fe-Cr-Ni and Fe-Mo-Ni), and after having recalled some previous results and presented experimental materials and processes, this research thesis describes the behaviour of the considered alloys, reports a detailed study of Fe-Mo alloys (influence of carbon content), a bibliographical study of the gamma-to-delta transformation, the study of hybrid alloys (behaviour, partial transformations, diffusion), the study of other types of alloys (hyper-quench of delta ferrite of Fe-Mo alloys, adsorption and diffusion). It discusses the case of two-phase structures, and the mechanism and kinetics of the delta-to-gamma transformation

  2. Microstructure modelling of ferritic alloys under high flux 1 MeV electron irradiations

    Hardouin Duparc, A.; Moingeon, C.; Smetniansky-de-Grande, N.; Barbu, A. E-mail: alain.barbu@poly.polytechnique.fr

    2002-04-01

    The point-defect clustering is an important component of the hardening of low copper content pressure vessel steels. This study reports the first steps of a project devoted to the modelling of the nucleation and growth of point-defect clusters in ferritic alloys under irradiation at large fluence. A cluster-dynamics modelling based on rate equations giving the evolution of the population of interstitial loops up to some 0.1 {mu}m and of vacancy clusters is developed. It is applied to two alloys FeCu (0.13 wt%) and FeMn(1.5 wt%)Ni(0.8 wt%)Cu(0.13 wt%)P(0.01 wt%) the composition of which is close to the one of pressure vessel steels and to non-alloyed Fe for comparison. The model was calibrated by carrying out 1 MeV irradiations in a high voltage microscope on these three materials and by using the results of experiments and atomic simulations reported in the literature. It is shown that the presence of copper in iron stabilises the interstitial clusters and more important that the parameters relative to the interstitials in the complex alloys are totally different from those for iron: the migration energy must be increased from 0.3 to 1 eV and the binding energy of di-interstitials must be decrease from 0.9 to 0.2 eV.

  3. Controlling diffusion for a self-healing radiation tolerant nanostructured ferritic alloy

    Diffusion plays a major role in the stability of microstructures to extreme conditions of high temperature and high doses of irradiation. In nanostructured ferritic alloys, first principle calculations indicate that the binding energy of vacancies is reduced by the presence of oxygen, titanium and yttrium atoms. Therefore, the number of free vacancies available for diffusion can be greatly reduced. The mechanical properties of these alloys, compared to traditional wrought alloys of similar composition and grain structure, is distinctly different, and the ultrafine grained alloy is distinguished by a high number density of Ti–Y–O-enriched nanoclusters and solute clusters, which drives the mechanical response. When a displacement cascade interacts with a nanocluster, the solute atoms are locally dispersed into the matrix by ballistic collisions, but immediately a new nanocluster reforms due to the local supersaturation of solutes and vacancies until the excess vacancies are consumed. The result of these processes is a structural material for advanced energy systems with a microstructure that is self-healing and tolerant to high doses of radiation and high temperatures

  4. Controlling diffusion for a self-healing radiation tolerant nanostructured ferritic alloy

    Miller, M.K., E-mail: millermk@ornl.gov [Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, TN 37831 (United States); Parish, C.M.; Bei, H. [Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831 (United States)

    2015-07-15

    Diffusion plays a major role in the stability of microstructures to extreme conditions of high temperature and high doses of irradiation. In nanostructured ferritic alloys, first principle calculations indicate that the binding energy of vacancies is reduced by the presence of oxygen, titanium and yttrium atoms. Therefore, the number of free vacancies available for diffusion can be greatly reduced. The mechanical properties of these alloys, compared to traditional wrought alloys of similar composition and grain structure, is distinctly different, and the ultrafine grained alloy is distinguished by a high number density of Ti–Y–O-enriched nanoclusters and solute clusters, which drives the mechanical response. When a displacement cascade interacts with a nanocluster, the solute atoms are locally dispersed into the matrix by ballistic collisions, but immediately a new nanocluster reforms due to the local supersaturation of solutes and vacancies until the excess vacancies are consumed. The result of these processes is a structural material for advanced energy systems with a microstructure that is self-healing and tolerant to high doses of radiation and high temperatures.

  5. Microstructural characterization of a friction stir welded oxide dispersion strengthened ferritic steel alloy

    Full text of publication follows: The fusion and fission reactors are faced with important challenges, notably in the field of materials. A class of materials, susceptible to resist to the required severe environments, is the ODS family (Oxide Dispersion Strengthened), who are metallic alloys strengthened by a very fine oxide dispersion. An obstacle to the development of these materials is their weldability because conventional fusion welding methods can disturb the fine oxide dispersion in the alloy that leads to a degradation of the high temperature behavior. Consequently, the Friction Stir Welding (FSW), which is a solid-state joining process, could be an alternative way to weld ODS alloys while keeping the fine microstructure. In this framework, the goal of this study is to make a microstructural characterization of a friction stir welded ODS alloy. The welded material is constituted by two plates of a yttria dispersion-strengthened PM 2000 ferritic steel. Different areas (non welded, heat affected zone and nugget) of the FSW welded product are analyzed by using field emission gun secondary electron microscopy (FEG-SEM), electron microprobe and transmission electron microscopy (TEM). The observed evolution of the microstructure, as the modification of the size and the repartition of the yttria dispersoids, after friction stir welding process is discussed and a correlation between the microstructural examinations and the results of nano-indentation tests is established. (authors)

  6. The consequences of helium production on microstructural development in isotopically tailored ferritic alloys

    Gelles, D.S. [Pacific Northwest Lab., Richland, WA (United States)

    1996-10-01

    A series of alloys have been made adding various isotopes of nickel in order to vary the production of helium during irradiation by a two step nuclear reaction in a mixed spectrum reactor. The alloys use a base composition of Fe-12Cr with an addition of 1.5% nickel, either in the form of {sup 60}Ni which produces no helium, {sup 59}Ni which produces helium at a rate of about 10 appm He/dpa, or natural nickel ({sup Nat}Ni) which provides an intermediate level of helium due to delayed development of {sup 59}Ni. Specimens were irradiated in the HFIR at Oak Ridge, TN to {approx}7 dpa at 300 and 400{degrees}C. Microstructural examinations indicated that nickel additions promote precipitation in all alloys, but the effect appears to be much stronger at 400{degrees}C than at 300{degrees}C. There is sufficient dose by 7 dpa (and with 2 appm He) to initiate void swelling in ferritic/martensitic alloys. Little difference was found between response from {sup 59}Ni and {sup Nat}Ni. Also, helium bubble development for high helium generation conditions appeared to be very different at 300 and 400{degrees}C. At 300{degrees}C, it appeared that high densities of bubbles formed whereas at 400{degrees}C, bubbles could not be identified, possibly because of the complexity of the microstructure, but more likely because helium accumulated at precipitate interfaces.

  7. Controlling diffusion for a self-healing radiation tolerant nanostructured ferritic alloy

    Miller, M. K.; Parish, C. M.; Bei, H.

    2015-07-01

    Diffusion plays a major role in the stability of microstructures to extreme conditions of high temperature and high doses of irradiation. In nanostructured ferritic alloys, first principle calculations indicate that the binding energy of vacancies is reduced by the presence of oxygen, titanium and yttrium atoms. Therefore, the number of free vacancies available for diffusion can be greatly reduced. The mechanical properties of these alloys, compared to traditional wrought alloys of similar composition and grain structure, is distinctly different, and the ultrafine grained alloy is distinguished by a high number density of Ti-Y-O-enriched nanoclusters and solute clusters, which drives the mechanical response. When a displacement cascade interacts with a nanocluster, the solute atoms are locally dispersed into the matrix by ballistic collisions, but immediately a new nanocluster reforms due to the local supersaturation of solutes and vacancies until the excess vacancies are consumed. The result of these processes is a structural material for advanced energy systems with a microstructure that is self-healing and tolerant to high doses of radiation and high temperatures.

  8. The potential for using high chromium ferritic alloys for hydroprocessing reactors

    This paper outlines the development of hydroprocessing reactors and the parallel development of applicable steels for their high temperature and high pressure process environments. Trends in the development of newer processes for severe hydroprocessing applications have been increasing in operating hydrogen partial pressures and operating temperatures that require the development of new alloys to meet these more severe process environments. The paper outlines the properties of conventional hydroprocessing reactor materials and discusses the advantages of the advanced high chromium ferritic steel alloy Grade 91 (9Cr-1Mo-V) for high temperature hydroprocessing applications. Additionally, the alloys permitted for ASME Section I and Section VIII Division I construction, Grade 92 (Code Case 2179), and what will probably be called Grade 122 (Code Case 2180) are briefly introduced as possible future choices for hydroprocessing reactor construction. These three alloys contain 9-12% Cr and have time independent allowable stress values above 566 deg. C. These high, time independent, strength values provide materials that will in some cases permit extending hydroprocessing temperature limits by 112 deg. C. The paper provides room temperature and elevated temperature mechanical and toughness properties for the low chrome and Grade 91 materials and discusses the effects of hydrogen attack, and hydrogen and isothermal embrittlement. Fabrication aspects, including forming and welding are addressed. The paper discusses the environmental resistance of these alloys and investigates the possibility of utilizing excess wall metal thickness in these materials in less severe applications in lieu of the deposition of a higher chromium alloy weld overlay to overcome the corrosive effects of the process environment

  9. Ferritic Alloys as Accident Tolerant Fuel Cladding Material for Light Water Reactors

    Rebak, Raul B. [General Electric Global Research, Schnectady, NY (United States)

    2014-12-30

    provide hermetic seal. The replacement of a zirconium alloy using a ferritic material containing chromium and aluminum appears to be the most near term implementation for accident tolerant nuclear fuels.

  10. Effect of mechanical alloying atmosphere on the microstructure and Charpy impact properties of an ODS ferritic steel

    Two types of oxide dispersion strengthened (ODS) ferritic steels, with the composition of Fe-14Cr-2W-0.3Ti-0.3Y2O3 (in weight percent), have been produced by mechanically alloying elemental powders of Fe, Cr, W, and Ti with Y2O3 particles either in argon atmosphere or in hydrogen atmosphere, degassing at various temperatures, and compacting the mechanically alloyed powders by hot isostatic pressing. It was found in particular that mechanical alloying in hydrogen yields a significant reduction in oxygen content in the materials, a lower dislocation density, and a strong improvement in the fast fracture properties of the ODS ferritic steels, as measured by Charpy impact tests.

  11. Previsions of the microstructural evolution of ferritic alloys under irradiation by numerical atomic scale simulations

    In this work, we have improved a diffusion model for point defects (vacancies and self-interstitials) by introducing hetero-interstitials. The model has been used to simulate by Kinetic Monte Carlo (KMC) the formation of solute rich clusters that are observed experimentally in irradiated ferritic model alloys of type Fe - CuMnNiSiP - C.Electronic structure calculations have been used to characterize the interactions between self-interstitials and all solute atoms, and also carbon. P interacts with vacancies and strongly with self-interstitials. Mn also interacts with self-interstitials to form mixed dumbbells. C, with occupies octahedral sites, interacts strongly with vacancies and less with self-interstitials. Binding and migration energies, as well as others atomic scale properties, obtained by ab initio calculations, have been used as parameters for the KMC code. Firstly, these parameters have been optimized over isochronal annealing experiments, in the literature, of binary alloys that have been electron-irradiated. Isochronal annealing simulations, by reproducing experimental results, have allowed us to link each mechanism to a single evolution of the resistivity during annealing. Moreover, solubility limits of all the elements have been determined by Metropolis Monte Carlo. Secondly, we have simulated the evolution at 300 C of the microstructure under irradiation of different alloys of increasing complexity: pure Fe, binary alloys, ternaries, quaternaries, and finally complex alloys which compositions are close to those of pressure vessel steels. The results show that the model globally reproduces all the experimental tendencies, what has led us to propose mechanisms to explain the behaviours observed. (author)

  12. Evaluation of Microstructure and Mechanical Properties of Nano-Y2O3-Dispersed Ferritic Alloy Synthesized by Mechanical Alloying and Consolidated by High-Pressure Sintering

    Karak, Swapan Kumar; Dutta Majumdar, J.; Witczak, Zbigniew; Lojkowski, Witold; Ciupiński, Łukasz; Kurzydłowski, K. J.; Manna, Indranil

    2013-06-01

    In this study, an attempt has been made to synthesize 1.0 wt pct nano-Y2O3-dispersed ferritic alloys with nominal compositions: 83.0 Fe-13.5 Cr-2.0 Al-0.5 Ti (alloy A), 79.0 Fe-17.5 Cr-2.0 Al-0.5 Ti (alloy B), 75.0 Fe-21.5 Cr-2.0 Al-0.5 Ti (alloy C), and 71.0 Fe-25.5 Cr-2.0 Al-0.5 Ti (alloy D) steels (all in wt pct) by solid-state mechanical alloying route and consolidation the milled powder by high-pressure sintering at 873 K, 1073 K, and 1273 K (600°C, 800°C, and 1000°C) using 8 GPa uniaxial pressure for 3 minutes. Subsequently, an extensive effort has been undertaken to characterize the microstructural and phase evolution by X-ray diffraction, scanning and transmission electron microscopy, and energy dispersive spectroscopy. Mechanical properties including hardness, compressive strength, Young's modulus, and fracture toughness were determined using micro/nano-indentation unit and universal testing machine. The present ferritic alloys record extraordinary levels of compressive strength (from 1150 to 2550 MPa), Young's modulus (from 200 to 240 GPa), indentation fracture toughness (from 3.6 to 15.4 MPa√m), and hardness (from13.5 to 18.5 GPa) and measure up to 1.5 through 2 times greater strength but with a lower density (~7.4 Mg/m3) than other oxide dispersion-strengthened ferritic steels (ferritic matrix useful for grain boundary pinning and creep resistance.

  13. High-temperature oxidation behavior of nano-structured ferritic oxide dispersion-strengthened alloys

    Graphical abstract: - Highlights: • Oxidation behavior was studied avoiding chemical composition effect except yttrium. • Nano-particle effect was compared with yttrium addition effect. • Grain size effect in ODS alloy was investigated. - Abstract: The effect of yttrium and nanoclusters on the high-temperature oxidation behavior of Fe–14Cr–3W–0.4Ti nano-structured ferritic oxide dispersion-strengthened alloys was investigated. For comparison purposes, conventional stainless steels with the same chemical composition were studied as well. Long-term oxidation tests were conducted at 800 °C for up to 2000 h in atmospheric air. The mass-gain versus time curves were obtained and the microstructure and chemical elements distribution in different regions of the specimens after oxidation were then analyzed by SEM/EDS and XRD. The experimental results showed that an addition of yttrium to Fe–14C–3W–0.4Ti alloy sufficiently reduced the oxidation rate. However, ODS processing to precipitate nanoclusters is a more effective means of improving high-temperature oxidation rather than a simple yttrium addition

  14. Interaction of carbon–vacancy complex with minor alloying elements of ferritic steels

    Interstitial carbon, dissolved in bcc matrix of ferritic steels, plays an important role in the evolution of radiation-induced microstructure since it exhibits strong interaction with vacancies. Frequent formation and break-up of carbon–vacancy pairs, occurring in the course of irradiation, affect both kinetics of the accumulation of point defect clusters and carbon spatial distribution. The interaction of typical alloying elements (Mn, Ni, Cu, Si, Cr and P) in ferritic steels used as structural materials in nuclear reactors with a carbon–vacancy complex is analyzed using ab initio techniques. It is found that all the considered solutes form stable triple clusters resulting in the increase of the total binding energy by 0.2–0.3 eV. As a result of the formation of energetically favourable solute–carbon–vacancy triplets, the dissociation energy for vacancy/carbon emission is also increased by ∼0.2–0.3 eV, suggesting that the solutes enhance thermal stability of carbon–vacancy complex. Association of carbon–vacancy pairs with multiple solute clusters is found to be favorable for Ni, Cu and P. The energetic stability of solute(s)–carbon–vacancy complexes was rationalized on the basis of pairwise interaction data and by analyzing the variation of local magnetic moments on atoms constituting the clusters

  15. Interaction of carbon–vacancy complex with minor alloying elements of ferritic steels

    Bakaev, A., E-mail: abakaev@sckcen.be [SCK-CEN, Nuclear Materials Science Institute, Boeretang 200, Mol B2400 (Belgium); Center for Molecular Modeling, Department of Physics and Astronomy, Ghent University, Technologiepark 903, 9052 Zwijnaarde (Belgium); Department of Experimental Nuclear Physics K-89, Institute of Physics, Nanotechnology and Telecommunications, St. Petersburg State Polytechnical University, 29 Polytekhnicheskaya Str., 195251 St. Petersburg (Russian Federation); Terentyev, D. [SCK-CEN, Nuclear Materials Science Institute, Boeretang 200, Mol B2400 (Belgium); He, X. [China Institute of Atomic Energy, P.O. Box 275-51, 102413 Beijing (China); Zhurkin, E.E. [Department of Experimental Nuclear Physics K-89, Institute of Physics, Nanotechnology and Telecommunications, St. Petersburg State Polytechnical University, 29 Polytekhnicheskaya Str., 195251 St. Petersburg (Russian Federation); Van Neck, D. [Center for Molecular Modeling, Department of Physics and Astronomy, Ghent University, Technologiepark 903, 9052 Zwijnaarde (Belgium)

    2014-08-01

    Interstitial carbon, dissolved in bcc matrix of ferritic steels, plays an important role in the evolution of radiation-induced microstructure since it exhibits strong interaction with vacancies. Frequent formation and break-up of carbon–vacancy pairs, occurring in the course of irradiation, affect both kinetics of the accumulation of point defect clusters and carbon spatial distribution. The interaction of typical alloying elements (Mn, Ni, Cu, Si, Cr and P) in ferritic steels used as structural materials in nuclear reactors with a carbon–vacancy complex is analyzed using ab initio techniques. It is found that all the considered solutes form stable triple clusters resulting in the increase of the total binding energy by 0.2–0.3 eV. As a result of the formation of energetically favourable solute–carbon–vacancy triplets, the dissociation energy for vacancy/carbon emission is also increased by ∼0.2–0.3 eV, suggesting that the solutes enhance thermal stability of carbon–vacancy complex. Association of carbon–vacancy pairs with multiple solute clusters is found to be favorable for Ni, Cu and P. The energetic stability of solute(s)–carbon–vacancy complexes was rationalized on the basis of pairwise interaction data and by analyzing the variation of local magnetic moments on atoms constituting the clusters.

  16. Process development for 9Cr nanostructured ferritic alloy (NFA) with high fracture toughness

    Byun, Thak Sang; Yoon, Ji Hyun; Hoelzer, David T.; Lee, Yong Bok; Kang, Suk Hoon; Maloy, Stuart A.

    2014-06-01

    This article is to summarize the process development and key characterization results for the newly-developed Fe-9Cr based nanostructured ferritic alloys (NFAs) with high fracture toughness. One of the major drawbacks from pursuing ultra-high strength in the past development of NFAs is poor fracture toughness at high temperatures although a high fracture toughness is essential to prevent cracking during manufacturing and to mitigate or delay irradiation-induced embrittlement in irradiation environments. A study on fracture mechanism using the NFA 14YWT found that the low-energy grain boundary decohesion in fracture process at a high temperature (>200 °C) resulted in low fracture toughness. Lately, efforts have been devoted to explore an integrated process to enhance grain bonding. Two base materials were produced through mechanical milling and hot extrusion and designated as 9YWTV-PM1 and 9YWTV-PM2. Isothermal annealing (IA) and controlled rolling (CR) treatments in two phase region were used to enhance diffusion across the interfaces and boundaries. The PM2 alloy after CR treatments showed high fracture toughness (KJQ) at represented temperatures: 240-280 MPa √m at room temperature and 160-220 MPa √m at 500 °C, which indicates that the goal of 100 MPa √m over possible nuclear application temperature range has been well achieved. Furthermore, it is also confirmed by comparison that the CR treatments on 9YWTV-PM2 result in high fracture toughness similar to or higher than those of the conventional ferritic-martensitic steels such as HT9 and NF616.

  17. Low-chromium reduced-activation ferritic steels for fusion

    Klueh, R.L.; Alexander, D.J.; Kenik, E.A. [Oak Ridge National Laboratory, TN (United States)

    1996-04-01

    Development of reduced-activation ferritic steels has concentrated on high-chromium (8-10 wt% Cr) steels. However, there are advantages for a low-chromium steel, and initial ORNL studies on reduced-activation steels were on compositions with 2.25 to 12% Cr. Those studies showed an Fe-2.25Cr-2W-0.25V-0.1C (2 1/4Cr-2WV) steel to have the highest strenglth of the steels studied. Although this steel had the best strength, Charpy impact properties were inferior to those of an Fe-9Cr-2W-0.25V-0.07Ta-0.1C (9Cr-2WVTa) and an Fe-2.25Cr-2W-0.1C (2 1/4Cr-2W) steel. Therefore, further development of the low-chromium Cr-W steels was required. These results indicate that it is possible to develop low-chromium reduced-activation ferritic steels that have tensile and impact properties as good or better than those of high-chromium (7-9% Cr) steels. Further improvement of properties should be possible by optimizing the composition.

  18. The effect of ageing temperature and time on the mechanical properties of Fe-NiCrMo alloys with different contents of δ ferrite

    Laboratory cast alloys with 2-27% of δ ferrite were aged for up to 17,520 h in the temperature range 290-350 deg. C. Tensile and Charpy tests were performed at 22 and 290 deg. C on specimens aged for different times, and the microhardnesses of both constituents of the microstructure were determined for the alloy with 27% of δ ferrite. The effects of the content of δ ferrite, the ageing and testing temperature, and the ageing time on mechanical properties and notch toughness are presented and discussed

  19. Activating Flux Design for Laser Welding of Ferritic Stainless Steel

    马立; 胡绳荪; 胡宝; 申俊琦; 王勇慧

    2014-01-01

    The behaviors of YAG laser welding process of ferritic stainless steel with activating fluxes were investi-gated in this study. Some conventional oxides, halides and carbonates were applied in laser welding. The results showed that the effect of oxides on the penetration depth was more remarkable. Most activating fluxes improved the penetration more effectively at low power than that at high power. The uniform design was adopted to arrange the formula of multicomponent activating fluxes, showing that the optimal formula can make the penetration depth up to 2.23 times as large as that without flux, including 50%ZrO2, 12.09%CaCO3, 10.43%CaO and 27.48%MgO. Through the high-speed photographs of welding process, CaF2 can minimize the plasma volume but slightly improve the pene-tration capability.

  20. Reduced activation ODS ferritic steel - recent development in high speed hot extrusion processing

    Oksiuta, Zbigniew [Faculty of Mechanical Engineering, Bialystok Technical University (Poland); Lewandowska, Malgorzata; Kurzydlowski, Krzysztof [Faculty of Materials Science and Engineering, Warsaw University of Technology (Poland); Baluc, Nadine [Ecole Polytechnique Federale de Lausanne (EPFL), Centre de Recherches en Physique des Plasmas, Association Euratom-Confederation Suisse, Villigen PSI (Switzerland)

    2010-05-15

    The paper presents the microstructure and mechanical properties of an oxide dispersion strengthened (ODS), reduced activation, ferritic steel, namely the Fe-14Cr-2W-0.3Ti-0.3Y{sub 2}O{sub 3} alloy, which was fabricated by hot isostatic pressing followed by high speed hydrostatic extrusion (HSHE) and heat treatment HT at 1050 C. Transmission electron microscopy (TEM) observations revealed significant differences in the grain size and dislocation density between the as-HIPped and as-HSHE materials. It was also found that the microstructure of the steel is stable after HT. The HSHE process improves significantly the tensile and Charpy impact properties of the as-HIPped steel. The ultimate tensile strength at room temperature increases from 950 up to 1350 MPa, while the upper shelf energy increases from 3.0 up to 6.0 J. However, the ductile-to-brittle transition temperature (DBTT) remains relatively high (about 75 C).These results indicate that HSHE is a promising method for achieving grain refinement and thus improving the mechanical properties of ODS ferritic steels. (Abstract Copyright [2010], Wiley Periodicals, Inc.)

  1. Formation of Y2O3 nanoclusters in nano-structured ferritic alloys: Modeling of precipitation kinetics and yield strength

    The solubility product of Y2O3 in ferrite and the diffusion coefficient of yttrium in ferrite have been obtained by fitting a model based on the classical nucleation-growth-coarsening theory of precipitation, as adapted to an anisothermal heat treatment, to experimental small angle neutron scattering results of Y2O3 precipitate size distributions in a mechanically alloyed and consolidated Fe-15 at.%Cr-0.13 at.%Y-0.18 at.%O ferritic alloy. This precipitation model is coupled to a dispersed barrier model of structural hardening to predict the yield strength of the alloys as a function of heat treatment. The resulting model and thermodynamic/kinetic properties are then applied to better understand how the precipitation kinetics impact the yield stress in various anisothermal heat treatments, as compared to an isothermal heat treatment. The modeling results clearly indicate that the anisothermal heat treatments can be tailored to establish a higher density and a smaller size distribution of Y2O3 precipitates, which also increase the yield stress.

  2. Electronic Structures and Alloying Behaviors of Ferrite Phases in High Co-Ni Secondary Hardened Martensitic Steels

    2000-01-01

    @@The electronic structure of ferrite (tempered martensite phase) in high Co-Ni secondary hardened martensitic steel has been investigated. The local density of states (LDOS) of alloying elements in the steel displays the relationship between solid solubility and the shape of the LDOS. The bond order integral (BOI) between atoms in the steel shows that the directional bonding of the p orbital of Si or C leads to the brittleness of the steel. At last, ∑BOI between atoms demonstrate that C, Co, Mn, Cr, Mo, Si strengthen the alloyed steel through solid-solution effects.

  3. Study of the precipitation and of the hardening microscopic mechanisms under irradiation in dilute ferritic alloys

    The copper precipitation plays a significant role in the embrittlement process of reactor vessel steels under neutron irradiation at 300 deg C. In order to understand the copper precipitation mechanisms, we have studied model ferritic binary FeCu and ternary alloys FeCuX (X=Mn,Ni, Cr, P). These materials have been either Irradiated with 2.5 MeV electrons In the 175-360 deg C temperature range or thermal aged at 500 deg C. The evolution of materials has been followed by resistivity measurements under irradiation, by small angle neutron scattering and by Vickers microhardness measurements. We have shown the similarity of copper precipitation under thermally ageing at 500 deg C and electron Irradiation at 300 deg C, in FeCu1,34%. This result confirms that the main effect of electronic irradiation is to accelerate precipitation. Nevertheless, we have observed that irradiation induces an additional contribution to hardening attributed to point defect clusters. Concerning the ternary alloys, we observed that at 300 deg C the addition of a third element has no significant effect on the copper precipitation kinetic under irradiation but that at lower temperature manganese slows down precipitation kinetic. In order to reproduce the experimental results obtained on FeCu1,34% by using a cluster kinetics model, we have to suppose that the precipitation is heterogeneous and controlled by interface reactions for the small size clusters. In addition, neutron or electron irradiated industrial steels have been studied by small angle neutron scattering. The results revealed the presence of nano-metric solute clusters which contain few copper atoms and which are not linked to the formation of displacement cascades. (author)

  4. Effects of alloying elements on sticking occurring during hot rolling of ferritic stainless steels

    In this study, effects of alloying elements on the sticking occurring during hot rolling of five kinds of ferritic STS430J1L stainless steels were investigated by analyzing high-temperature hardness and oxidation behavior of the rolled steels. Hot-rolling simulation tests were conducted by a high-temperature wear tester which could simulate actual hot rolling. The simulation test results revealed that the sticking process proceeded with three stages, i.e., nucleation, growth, and saturation. Since the hardness continuously decreased as the test temperature increased, whereas the formation of Fe-Cr oxides in the rolled steel surface region increased, the sticking of five stainless steels was evaluated by considering both the high-temperature hardness and oxidation effects. The addition of Zr, Cu, or Si had a beneficial effect on the sticking resistance, while the Ni addition did not show any difference in the sticking. Particularly in the case of the Si addition, Si oxides formed first in the initial stage of high-temperature oxidation, worked as initiation sites for Fe-Cr oxides, accelerated the formation of Fe-Cr oxides, and thus raised the sticking resistance by about 10 times in comparison with the steel without Si content

  5. Design optimization of ferritic alloy LMFBR fuel assemblies as affected by in-reactor deformation

    Because of the relatively high resistance to irradiation-induced creep and swelling exhibited by the high strength ferritic alloy HT-9, it is a major structural material candidate for use in Liquid Metal Fast Breeder Reactor (LMFBR) fuel assembly hexagonal ducts, principally to minimize the duct dilation due to the nuclear environment. The design of a fuel assembly with an HT-9 duct can be performed as part of an overall plant performance optimization to achieve minimum plant operational costs. Such evaluations were performed to quantify the effect on fuel cycle costs of possible future changes to either the current estimates of HT-9 swelling and creep or to the uncertainty band widths of creep and swelling. The evaluations were conducted using a reactor system design computer code capable of implementing core design tradeoff studies to obtain a minimum cost optimization of the reactor system performance. The results of the study quantify the incentive for minimum creep and swelling and the incentive to obtain sufficient data to minimize the creep and swelling uncertainty band widths

  6. Thermal stability of nanoscale helium bubbles in a 14YWT nanostructured ferritic alloy

    Edmondson, P.D., E-mail: philip.edmondson@materials.ox.ac.uk; Parish, C.M.; Li, Q.; Miller, M.K.

    2014-02-01

    Highlights: • 14YWT NFA irradiated with 335keV He{sup +} to 6.75x10{sup 20} He m{sup -2} at 400 °C then thermally treated at 750 °C for up to 100 hr. • As-irradiated material displayed poly-disperse bubble size distribution that became more inhomogeneous with thermal treatment. • The bubbles were observed to coarsen following thermal treatment. • Coarsening behaviour exhibits characteristics of self-interstitial and dislocation loop punching, Brownian motion and coalescence and Ostwald ripening. - Abstract: A 14YWT nanostructured ferritic alloy has been irradiated with 335 keV He{sup +} to a total fluence of 6.75 × 10{sup 20} He m{sup −2} at a temperature of 400 °C and subsequently thermally treated at 750 °C for up to 100 h. Transmission electron microscopy has been used to characterize the size and distribution of the resultant helium bubbles. The results indicate that the bubbles generally increase in size and the distribution becomes more inhomogeneous during the thermal treatment. The results are discussed in terms of the helium supply and vacancy supersaturation, Brownian motion and coalescence, and Ostwald ripening mechanisms.

  7. Incidence of mechanical alloying contamination on oxides and carbides formation in ODS ferritic steels

    Ferritic ODS steels containing 14 or 18 wt.% Cr are produced by mechanical alloying (MA), hot consolidation and cold working. This study focuses on the evolution of interstitials such as oxygen, nitrogen and carbon at each stage of the fabrication route by comparing two MA methods: attrition milling or ball milling. The milling time required to obtain a homogenous distribution of yttrium at the micron scale in the ground powders is relatively short by using an attritor. But, in this case the carbon and nitrogen contamination is more pronounced considering powders which have reached a similar metastable stationary state. The presence of oxygen in excess results in the formation of large micron-sized oxides after extrusion. Most of them are identified as titanium-based or silicon oxides by EDS analysis. For attrition milling, a high density of aligned Ti(C,N) compounds and some FeCrW carbides (M23C6 type) mainly distributed at the grain boundaries are identified, correlated with the higher carbon contamination

  8. Dual-beam irradiation of friction stir spot welding of nanostructured ferritic oxide dispersion strengthened alloy

    Highlights: ► FSSW has been successfully applied to join two sheets of ODS material. ► Dynamic recrystallization occurs in the thermo mechanically affected zone, resulting in a decrease in hardness. ► After irradiation, a clear maximum is visible in all depth dependent hardness charts, which is caused by defects generated during ion bombardment. ► The material changes during FSSW are larger than the radiation induced hardness increase. - Abstract: Nanostructured ferritic oxide dispersion strengthened (ODS) alloys usually contain a high density of Y–Al–O and Y–Ti–O nanoparticles, high dislocation densities and fine grains. Friction stir spot welding (FSSW) is a very promising technique for the joining of ODS materials without oxide particle agglomeration and loss in mechanical properties in the weld zone. Heating and severe plastic deformation can significantly alter the originally as-received material. The local microstructure determines the weld mechanical properties, which are analyzed by nanoindentation. The FSSW region consists of three different zones: the base material, the thermo-mechanically affected zone and the heat affected zone. Irradiation of the FSSW area was performed with a Fe+/He+ dual ion beam. Hardness changes within the welding zones and variation with irradiation damage are discussed.

  9. Dual-beam irradiation of friction stir spot welding of nanostructured ferritic oxide dispersion strengthened alloy

    Chen, Chun-Liang, E-mail: chunliang@mail.ndhu.edu.tw [Department of Materials Science and Engineering, I-Shou University, Kaohsiung 840, Taiwan (China); Richter, Asta [Department of Engineering, Technical University of Applied Sciences, Wildau, Bahnhofstrasse 1, 15745 Wildau (Germany); Koegler, Reinhard [Institute of Ion Beam Physics and Materials Research, Helmholtz Center Dresden-Rossendorf (HZDR), Bautzner Landstrasse 400, 01328 Dresden (Germany); Wu, Lung-Tien [Metal Industries Research and Development Centre, Kaohsiung 811, Taiwan (China)

    2012-09-25

    Highlights: Black-Right-Pointing-Pointer FSSW has been successfully applied to join two sheets of ODS material. Black-Right-Pointing-Pointer Dynamic recrystallization occurs in the thermo mechanically affected zone, resulting in a decrease in hardness. Black-Right-Pointing-Pointer After irradiation, a clear maximum is visible in all depth dependent hardness charts, which is caused by defects generated during ion bombardment. Black-Right-Pointing-Pointer The material changes during FSSW are larger than the radiation induced hardness increase. - Abstract: Nanostructured ferritic oxide dispersion strengthened (ODS) alloys usually contain a high density of Y-Al-O and Y-Ti-O nanoparticles, high dislocation densities and fine grains. Friction stir spot welding (FSSW) is a very promising technique for the joining of ODS materials without oxide particle agglomeration and loss in mechanical properties in the weld zone. Heating and severe plastic deformation can significantly alter the originally as-received material. The local microstructure determines the weld mechanical properties, which are analyzed by nanoindentation. The FSSW region consists of three different zones: the base material, the thermo-mechanically affected zone and the heat affected zone. Irradiation of the FSSW area was performed with a Fe{sup +}/He{sup +} dual ion beam. Hardness changes within the welding zones and variation with irradiation damage are discussed.

  10. Effect of friction stir welding and post-weld heat treatment on a nanostructured ferritic alloy

    Mazumder, B.; Yu, X.; Edmondson, P. D.; Parish, C. M.; Miller, M. K.; Meyer, H. M.; Feng, Z.

    2016-02-01

    Nanostructured ferritic alloys (NFAs) are new generation materials for use in high temperature energy systems, such as nuclear fission or fusion reactors. However, joining these materials is a concern, as their unique microstructure is destroyed by traditional liquid-state welding methods. The microstructural evolution of a friction stir welded 14YWT NFA was investigated by atom probe tomography, before and after a post-weld heat treatment (PWHT) at 1123K. The particle size, number density, elemental composition, and morphology of the titanium-yttrium-oxygen-enriched nanoclusters (NCs) in the stir and thermally-affected zones were studied and compared with the base metal. No statistical difference in the size of the NCs was observed in any of these conditions. After the PWHT, increases in the number density and the oxygen enrichment in the NCs were observed. Therefore, these new results provide additional supporting evidence that friction stir welding appears to be a viable joining technique for NFAs, as the microstructural parameters of the NCs are not strongly affected, in contrast to traditional welding techniques.

  11. Effect of mechanical alloying parameters on irradiation damage in oxide dispersion strengthened ferritic steels

    Issues for developing oxide dispersion strengthened (ODS) steel are anisotropic mechanical properties due to the bamboo-like structure, impurity pick up during the mechanical alloying (MA) process, stability of oxide particles, heat-treatment condition and chemical composition. Several ODS steels were fabricated with a changing gas environment during MA, heat-treatment condition and chemical composition, and were electron-irradiated to 12 dpa at 673-748 K in a high-voltage electron microscope. An ODS martensitic steel (M-Ar) with high dislocation density showed very good swelling resistance. Swelling levels of ODS ferritic steels depended on the gas environment during MA and the recrystallization condition. These indicated that a helium gas environment during MA was more effective to suppress swelling than an argon gas environment and that cold working after recrystallization reduced void formation and swelling. The effect of MA parameters, such as the gas environment, heat-treat condition and cold working on the swelling behavior was evaluated

  12. Effects of austenite grain size and cooling rate on Widmanstaetten ferrite formation in low-alloy steels

    Bodnar, R.L.; Hansen, S.S. (Bethlehem Steel Corp., PA (United States). Hot Rolled Products Div.)

    1994-04-01

    Deformation dilatometry is used to simulate the hot rolling of 0.20 pct C-1.10 pct Mn steels over a product thickness range of 6 to 170 mm. In addition to a base steel, steels with additions of 0.02 pct Ti, 0.06 pct V, or 0.02 pct Nb are included in the study. The transformation behavior of each steel is explored for three different austenite grain sizes, nominally 30, 55, and 100 [mu]m. In general, the volume fraction of Widmanstaetten ferrite increases in all four steels with increasing austenite grain size and cooling rate, with austenite grain size having the more significant effect. The Nb steel has the lowest transformation temperature range and the greatest propensity for Widmanstaetten ferrite formation, while the amount of Widmanstaetten ferrite is minimized in the Ti steel (as a result of intragranular nucleation of polygonal ferrite on coarse TiN particles). The data emphasize the importance of a refined austenite grain size in minimizing the formation of a coarse Widmanstaetten structure. With a sufficiently fine prior austenite grain size (e.g., [le]30 [mu]m), significant amounts of Widmanstaetten structure can be avoided, even in a Nb-alloyed steel.

  13. A review of advantages of high-efficiency X-ray spectrum imaging for analysis of nanostructured ferritic alloys

    Nanostructured ferritic alloys (NFAs) exhibit complex microstructures consisting of 100–500 nm ferrite grains, grain boundary solute enrichment, and multiple populations of precipitates and nanoclusters (NCs). Understanding these materials’ excellent creep and radiation-tolerance properties requires a combination of multiple atomic-scale experimental techniques. Recent advances in scanning transmission electron microscopy (STEM) hardware and data analysis methods have the potential to revolutionize nanometer-to micrometer-scale materials analysis. Modern high-brightness, high-X-ray collection STEM instruments are capable of enabling advanced experiments, such as simultaneous energy dispersive X-ray spectroscopy and electron energy loss spectroscopy spectrum imaging at nm to sub-nm resolution, that are now well-established for the study of nuclear materials. In this paper, we review past results and present new results illustrating the effectiveness of latest-generation STEM instrumentation and data analysis

  14. A review of advantages of high-efficiency X-ray spectrum imaging for analysis of nanostructured ferritic alloys

    Parish, Chad M.; Miller, Michael K.

    2015-07-01

    Nanostructured ferritic alloys (NFAs) exhibit complex microstructures consisting of 100-500 nm ferrite grains, grain boundary solute enrichment, and multiple populations of precipitates and nanoclusters (NCs). Understanding these materials' excellent creep and radiation-tolerance properties requires a combination of multiple atomic-scale experimental techniques. Recent advances in scanning transmission electron microscopy (STEM) hardware and data analysis methods have the potential to revolutionize nanometer-to micrometer-scale materials analysis. Modern high-brightness, high-X-ray collection STEM instruments are capable of enabling advanced experiments, such as simultaneous energy dispersive X-ray spectroscopy and electron energy loss spectroscopy spectrum imaging at nm to sub-nm resolution, that are now well-established for the study of nuclear materials. In this paper, we review past results and present new results illustrating the effectiveness of latest-generation STEM instrumentation and data analysis.

  15. Formation Mechanisms of Alloying Element Nitrides in Recrystallized and Deformed Ferritic Fe-Cr-Al Alloy

    Akhlaghi, Maryam; Meka, Sai Ramudu; Jägle, Eric A.; Kurz, Silke J. B.; Bischoff, Ewald; Mittemeijer, Eric J.

    2016-09-01

    The effect of the initial microstructure (recrystallized or cold-rolled) on the nitride precipitation process upon gaseous nitriding of ternary Fe-4.3 at. pct Cr-8.1 at. pct Al alloy was investigated at 723 K (450 °C) employing X-ray diffraction (XRD) analyses, transmission electron microscopy (TEM), atom probe tomography (APT), and electron probe microanalysis (EPMA). In recrystallized Fe-Cr-Al specimens, one type of nitride develops: ternary, cubic, NaCl-type mixed Cr1- x Al x N. In cold-rolled Fe-Cr-Al specimens, precipitation of two types of nitrides occurs: ternary, cubic, NaCl-type mixed Cr1- x Al x N and binary, cubic, NaCl-type AlN. By theoretical analysis, it was shown that for the recrystallized specimens an energy barrier for the nucleation of mixed Cr1- x Al x N exists, whereas in the cold-rolled specimens no such energy barriers for the development of mixed Cr1- x Al x N and of binary, cubic AlN occur. The additional development of the cubic AlN in the cold-rolled microstructure could be ascribed to the preferred heterogeneous nucleation of cubic AlN on dislocations. The nitrogen concentration-depth profile of the cold-rolled specimen shows a stepped nature upon prolonged nitriding as a consequence of instantaneous nucleation of nitride upon arrival of nitrogen and nitride growth rate-limited by nitrogen transport through the thickening nitrided zone.

  16. Oxide dispersion strengthened ferritic alloys. 14/20% chromium: effects of processing on deformation texture, recrystallization and tensile properties

    The ferritic oxide dispersion strengthened alloys are promising candidates for high temperature application materials, in particular for long life core components of advanced nuclear reactors. The aim of this work is to control the microstructure, in order to optimise the mechanical properties. The two ferritic alloys examined here, MA956 and MA957, are obtained by Mechanical Alloying techniques. They are characterised by quite anisotropic microstructure and mechanical properties. We have investigated the influence of hot and cold working processes (hot extrusion, swaging and cold-drawing) and recrystallization heat treatments on deformation textures, microstructures and tensile properties. The aim was to control the size of the grains and their anisotropic shape, using recrystallization heat treatments. After consolidation and hot extrusion, as-received materials present a extremely fine microstructure with elongated grains and a very strong (110) deformation texture with single-crystal character. At that stage of processing, recrystallization temperature are very high (1450 degrees C for MA957 alloy and 1350 degrees C for MA956 alloy) and materials develop millimetric recrystallized grains. Additional hot extrusion induce a fibre texture. Cold-drawing maintains a fibre texture, but the intensity decreases with increasing cold-work level. For both materials, the decrease of texture intensities correspond to a decrease of the recrystallization temperatures (from 1350 degrees C for a low cold-work level to 750 degrees C for 60 % cold-deformation, case of MA956 alloy) and a refinement of the grain size (from a millimetric size to less than an hundred of micrometer). Swaging develop a cyclic component where the intensity increases with increasing deformation in this case, the recrystallization temperature remains always very high and the millimetric grain size is slightly modified, even though cold-work level increases. Technologically, cold-drawing is the only way

  17. Gas atomized precursor alloy powder for oxide dispersion strengthened ferritic stainless steel

    Rieken, Joel [Iowa State Univ., Ames, IA (United States)

    2011-12-13

    Gas atomization reaction synthesis (GARS) was employed as a simplified method for producing precursor powders for oxide dispersion strengthened (ODS) ferritic stainless steels (e.g., Fe-Cr-Y-(Ti,Hf)-O), departing from the conventional mechanical alloying (MA) process. During GARS processing a reactive atomization gas (i.e., Ar-O2) was used to oxidize the powder surfaces during primary break-up and rapid solidification of the molten alloy. This resulted in envelopment of the powders by an ultra-thin (t < 150 nm) metastable Cr-enriched oxide layer that was used as a vehicle for solid-state transport of O into the consolidated microstructure. In an attempt to better understand the kinetics of this GARS reaction, theoretical cooling curves for the atomized droplets were calculated and used to establish an oxidation model for this process. Subsequent elevated temperature heat treatments, which were derived from Rhines pack measurements using an internal oxidation model, were used to promote thermodynamically driven O exchange reactions between trapped films of the initial Cr-enriched surface oxide and internal Y-enriched intermetallic precipitates. This novel microstructural evolution process resulted in the successful formation of nano-metric Y-enriched dispersoids, as confirmed using high energy X-ray diffraction and transmission electron microscopy (TEM), equivalent to conventional ODS alloys from MA powders. The thermal stability of these Y-enriched dispersoids was evaluated using high temperature (1200°C) annealing treatments ranging from 2.5 to 1,000 hrs of exposure. In a further departure from current ODS practice, replacing Ti with additions of Hf appeared to improve the Y-enriched dispersoid thermal stability by means of crystal structure modification. Additionally, the spatial distribution of the dispersoids was found to depend strongly on the original rapidly solidified microstructure. To exploit this, ODS microstructures were engineered from

  18. Characterization and corrosion resistance of organically modified silicate-NiZn ferrite/polyaniline hybrid coatings on aluminum alloys

    Wu, K.H. [Department of Applied Chemistry and Materials Science, Chung Cheng Institute of Technology, National Defense University, Tahsi, Taoyuan 335, Taiwan (China)]. E-mail: khwu@ccit.edu.tw; Chao, C.M. [Department of Applied Chemistry and Materials Science, Chung Cheng Institute of Technology, National Defense University, Tahsi, Taoyuan 335, Taiwan (China); Liu, C.H. [Department of Applied Chemistry and Materials Science, Chung Cheng Institute of Technology, National Defense University, Tahsi, Taoyuan 335, Taiwan (China); Chang, T.C. [Department of Applied Chemistry and Materials Science, Chung Cheng Institute of Technology, National Defense University, Tahsi, Taoyuan 335, Taiwan (China)

    2007-07-15

    Hybrid coatings based on organically modified silicate (Ormosil)-NiZn ferrite/polyaniline (10-30 wt.%) were synthesized through a sol-gel technique. Tetraethylenepentamine, 3-glycidoxypropyltrimethoxysilane, tetraethoxysilane and Ni{sub 0.5}Zn{sub 0.5}Fe{sub 2}O{sub 4}/polyaniline were used as precursors for the hybrid coatings. These hybrid films were deposited via spin coating onto an aluminum alloy to improve the corrosion protection. The effects induced by the NiZn ferrite/polyaniline content on the chain dynamics, ferromagnetic behavior and corrosion performances of the coated samples were investigated. The rotating-frame spin-lattice relaxation times and scale of the spin-diffusion path length indicated that the configuration of the hybrid films was highly cross-linked, dense and adhered to the aluminum alloy substrates. The magnetic properties of the resulting hybrids showed super-paramagnetic behavior, such as zero coercive force (coercivity 0 G) and a low blocking temperatures (45 K). Potentio-dynamic and salt-spray analysis revealed that the hybrid films provided an exceptional barrier and corrosion protection in comparison with untreated aluminum alloy substrates.

  19. Characterization and corrosion resistance of organically modified silicate-NiZn ferrite/polyaniline hybrid coatings on aluminum alloys

    Hybrid coatings based on organically modified silicate (Ormosil)-NiZn ferrite/polyaniline (10-30 wt.%) were synthesized through a sol-gel technique. Tetraethylenepentamine, 3-glycidoxypropyltrimethoxysilane, tetraethoxysilane and Ni0.5Zn0.5Fe2O4/polyaniline were used as precursors for the hybrid coatings. These hybrid films were deposited via spin coating onto an aluminum alloy to improve the corrosion protection. The effects induced by the NiZn ferrite/polyaniline content on the chain dynamics, ferromagnetic behavior and corrosion performances of the coated samples were investigated. The rotating-frame spin-lattice relaxation times and scale of the spin-diffusion path length indicated that the configuration of the hybrid films was highly cross-linked, dense and adhered to the aluminum alloy substrates. The magnetic properties of the resulting hybrids showed super-paramagnetic behavior, such as zero coercive force (coercivity 0 G) and a low blocking temperatures (45 K). Potentio-dynamic and salt-spray analysis revealed that the hybrid films provided an exceptional barrier and corrosion protection in comparison with untreated aluminum alloy substrates

  20. The Kinetics of Dislocation Loop Formation in Ferritic Alloys Through the Aggregation of Irradiation Induced Defects

    Kohnert, Aaron Anthony

    The mechanical properties of materials are often degraded over time by exposure to irradiation environments, a phenomenon that has hindered the development of multiple nuclear reactor design concepts. Such property changes are the result of microstructural changes induced by the collision of high energy particles with the atoms in a material. The lattice defects generated in these recoil events migrate and interact to form extended damage structures. This study has used theoretical models based on the mean field chemical reaction rate theory to analyze the aggregation of isolated lattice defects into larger microstructural features that are responsible for long term property changes, focusing on the development of black dot damage in ferritic iron based alloys. The purpose of such endeavors is two-fold. Primarily, such models explain and quantify the processes through which these microstructures form. Additionally, models provide insight into the behavior and properties of the point defects and defect clusters which drive general microstructural evolution processes. The modeling effort presented in this work has focused on physical fidelity, drawing from a variety of sources of information to characterize the unobservable defect generation and agglomeration processes that give rise to the observable features reported in experimental data. As such, the models are based not solely on isolated point defect creation, as is the case with many older rate theory approaches, but instead on realistic estimates of the defect cluster population produced in high energy cascade damage events. Experimental assessments of the microstructural changes evident in transmission electron microscopy studies provide a means to measure the efficacy of the kinetic models. Using common assumptions of the mobility of defect clusters generated in cascade damage conditions, an unphysically high density of damage features develops at the temperatures of interest with a temperature dependence

  1. Low-chromium reduced-activation ferritic steels

    Steels are being developed for fusion-reactor applications that contain only elements that produce radioactive isotopes that decay to low levels in a reasonable time. These reduced-activation or fast induced-radioactivity decay ferritic steels are being developed to be analogous to the Cr-Mo steels presently in the fusion program, but with molybdenum replaced by tungsten. In this paper, steels with 2-1/4% Cr will be discussed. To determine the effect of tungsten and vanadium on these steels, heats were produced with 2% W, with 0.25% V, with 1% W and 0.25% V, and with 2% W and 0.25% V. Tempering and microstructural studies were made and tensile and impact tests were conducted. Preliminary results indicate that it should be possible to develop a low-chromium Cr-W steel without molybdenum or niobium. Such steels should have properties as good as or better than the three Cr-Mo steels presently being considered as candidates for fusion-reactor applications. 22 refs., 12 figs., 3 tabs

  2. Microstructure and Mechanical Propertiesof a Nitride-Strengthened Reduced ActivationFerritic/Martensitic Steel

    Zhou, Qiangguo; Zhang, Wenfeng; Yan, Wei; Wang, Wei; SHA, WEI; Shan, Yiyin; Yang, Ke

    2012-01-01

    Nitride-strengthened reduced activation ferritic/martensitic (RAFM) steels are developed taking advantage of the high thermal stability of nitrides. In the current study, the microstructure and mechanical properties of a nitride-strengthened RAFM steel with improved composition were investigated. Fully martensitic microstructure with fine nitrides dispersion was achieved in the steel. In all, 1.4 pct Mn is sufficient to suppress delta ferrite and assure the steel of the full martensitic micro...

  3. EBSD as a tool to identify and quantify bainite and ferrite in low-alloyed Al-TRIP steels.

    Zaefferer, S; Romano, P; Friedel, F

    2008-06-01

    Bainite is thought to play an important role for the chemical and mechanical stabilization of metastable austenite in low-alloyed TRIP steels. Therefore, in order to understand and improve the material properties, it is important to locate and quantify the bainitic phase. To this aim, electron backscatter diffraction-based orientation microscopy has been employed. The main difficulty herewith is to distinguish bainitic ferrite from ferrite because both have bcc crystal structure. The most important difference between them is the occurrence of transformation induced geometrically necessary dislocations in the bainitic phase. To determine the areas with larger geometrically necessary dislocation density, the following orientation microscopy maps were explored: pattern quality maps, grain reference orientation deviation maps and kernel average misorientation maps. We show that only the latter allow a reliable separation of the bainitic and ferritic phase. The kernel average misorientation threshold value that separates both constituents is determined by an algorithm that searches for the smoothness of the boundaries between them. PMID:18503676

  4. Simulation of Ferrite Formation in Fe-C Alloys Based on a Three-Dimensional Mixed-Mode Transformation Model

    van Bohemen, S. M. C.; Bos, C.; Sietsma, J.

    2011-09-01

    A three-dimensional mixed-mode (MM) transformation model accounting for both soft impingement and hard impingement was developed that calculates the growth kinetics of ferrite grains in an austenite matrix. The simulations are compared to the kinetics of ferrite formation in high-purity Fe-C alloys for which phase-transformation kinetics were measured isothermally by dilatometry at several temperatures in the range of 973 K to 1043 K (700 °C to 770 °C). The interface mobility is obtained from the best fit of the data at 1023 K (750 °C) for which the nucleus density N is estimated from the final microstructure. Subsequently, the experimental ferrite kinetics in Fe-0.36C at the other temperatures are simulated. The values of N extracted from the fits can be described with a nucleation model. The significance of the MM calculations is rationalized by comparing the results for Fe-0.17C with simulations assuming purely diffusion-controlled (DC) and purely interface-controlled (IC) growth. Comparison of simulated fraction curves for Fe-0.57C with the three models demonstrates that the transformation in high-carbon steels is essentially DC.

  5. A wear and corrosion resistant α-ferrite toughened Fe9Cr9Si2 ternary intermetallic alloy

    Mechanical moving components working under corrosion or elevated temperature aggressive service conditions demand tribological materials having excellent combinations of wear and corrosion resistance. Most conventional high-performance wear resistant materials such as high Cr cast irons lack adequate corrosion resistance, while most corrosion resistant materials such as stainless steels are poor in resisting wear. In this paper, a novel α-ferrite toughened Fe9Cr9Si2 wear and corrosion resistant ternary intermetallic alloy was developed with a microstructure consisting of small amount of dispersive α particles well distributed in the continuous matrix of Fe9Cr9Si2 (referred as α/Fe9Cr9Si2 alloy). Corrosion properties were evaluated using the anodic polarization methods in H2SO4 and NaCl water solutions. Wear resistance was tested under room-temperature block-on-wheel dry sliding wear test conditions. Due to the unique chemical composition of both the Cr and Si highly alloyed α and the σ-phase Fe9Cr9Si2, the α/Fe9Cr9Si2 alloy exhibited outstanding corrosion resistance. Due to the excellent combination of high hardness and the strong covalent-dominant atomic bonds of σ-Fe9Cr9Si2, the excellent toughness and ductility of α and the unique chemical composition induced oxidation wear, the α-toughened Fe9Cr9Si2 σ-based alloy exhibited outstanding dry sliding wear resistance

  6. Helium Retention and Desorption Behaviour of Reduced Activation Ferritic/Martenstic Steel

    WANG Pinghuai; NOBUTA Yuji; HINO Tomoaki; YAMAUCHI Yuji; CHEN Zilning; XU Zengyu; LI Xiongwei; LIU Shi

    2009-01-01

    The reduced activation ferritic/martenstic steel CLF-1 prepared by the Southwest-ern Institute of Physics in China was irradiated by helium ions with an energy of 5 keV at room temperature using an electron cyclotron resonance (ECR) ion irradiation apparatus. After the irradiation, the helium retention and desorption were investigated using a technique of thermal desorption spectroscopy (TDS). The experiment was conducted with both the normal and welded samples. Blisters were observed after the helium ion irradiation, and the surface density of blisters in the welded samples was lower than that in the non-welded samples. Three desorption peaks were observed in both the non-welded and welded samples. These desorption peaks corresponded to those of blister ruptures and the helium release from the inner bubbles and the defects. The amount of helium retained in the welded samples was approximately the same as that in the non-welded samples, which was much less than other reduced activation materials, such as vanadium alloy and SiC/SiC composites.

  7. Post extrusion heat treatment effects on microstructure and mechanical properties of 9Cr nano structured ferritic alloy

    Yoon, Jihyu; Kang, Sukhoon; Lee, Yongbok [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of); Byun, Thak S.; Hoelzer, David T. [Oak Ridge National Laboratory, Oak Ridge (United States)

    2012-10-15

    Nano structured ferritic alloys (NFAs) show enhanced high temperature strength by adding nano scale oxide particles into ferritic-martensitic (FM) steel. High Cr FM steels are under intense research as candidate materials for the components of next generation nuclear systems. The adequate mechanical and fract ural properties are prerequisites for core materials that are subjected to a rigorous environment at a high temperature of up to 650 .deg. C and neutron irradiation of 200 {approx} 400 dpa. A few recent researches have reported that the fracture toughness of NFAs is very low at above 300 .deg. C. To overcome this drawback of NFAs, post extrusion heat treatments that can evolve the partial phase transformations in a 9Cr-NFA were applied in this study. The objectives of this study are to improve the fracture toughness and ductility of NFA through a simple post-extrusion thermo-mechanical process, which can lead to changes in the microstructure of nano structured 9Cr alloy into a dual phase structure.

  8. Fe-Cr-V ternary alloy-based ferritic steels for high- and low-temperature applications

    The phase stability of alloys and steels developed for application in nuclear fission and fusion technology is one of the decisive factors determining the potential range of operating temperatures and radiation conditions that the core elements of a power plant can tolerate. In the case of ferritic and ferritic-martensitic steels, the choice of the chemical composition is dictated by the phase diagram for binary FeCr alloys where in the 0-9% range of Cr composition the alloy remains in the solid solution phase at and below the room temperature. For Cr concentrations exceeding 9% the steels operating at relatively low temperatures are therefore expected to exhibit the formation of α' Cr-rich precipitates. These precipitates form obstacles for the propagation of dislocations, impeding plastic deformation and embrittling the material. This sets the low temperature limit for the use of of high (14% to 20%) Cr steels, which for the 20% Cr steels is at approximately 600 deg. C. On the other hand, steels containing 12% or less Cr cannot be used at temperatures exceeding ∼600 deg. C due to the occurrence of the α-γ transition (912 deg. C in pure iron and 830 deg. C in 7% Cr alloy), which weakens the steel in the high temperature limit. In this study, we investigate the physical properties of a concentrated ternary alloy system that attracted relatively little attention so far. The phase diagram of ternary Fe-Cr-V alloy shows no phase boundaries within a certain broad range of Cr and V concentrations. This makes the alloy sufficiently resistant to corrosion and suggests that steels and dispersion strengthened materials based on this alloy composition may have better strength and stability at high temperatures. Experimental heats were produced on a laboratory scale by arc melting the material components to pellets, then by melting the pellets in an induction furnace and casting the melt into copper moulds. The compositions in weight percent (iron base) are 10Cr5V, 10Cr

  9. Microstructural developments in Fe-Cr-W low activation ferritic steels under dual beam charged particle irradiation

    Chromium-molybdenum ferritic steels have a better resistance to void swelling than austenitic steels and were considered for use as first wall structural materials in future fusion reactors. One of the major alloying elements, Mo, is deleterious for the reduction of radioactivity; reduced activation steels are under development, where Mo is replaced by W. In this work, four kinds of reduced activation steels were dual or single ion irradiated to 125 dpa. In the duel ion irradiated steels with a 7-12% Cr content, the dimensional stability of the martensite phase was superior to the other phases. The cavity microstructures of bainitic steels with 2.25% Cr content were affected by the He/dpa ratio (and by the He injection rate) even when they had a high damage level (up to 125 dpa.) Hitherto, the low activation steels developed by replacing Mo by W suggest excellent stability of microstructures and thus a high resistance to swelling. (orig.)

  10. Dispersoid Distribution and Microstructure in Fe-Cr-Al Ferritic Oxide Dispersion-Strengthened Alloy Prepared by Friction Consolidation

    Catalini, David; Kaoumi, Djamel; Reynolds, Anthony; Grant, Glenn J.

    2015-07-09

    INCOLOY® MA956 is a ferritic Oxide Dispersion Strengthened (ODS) alloy. Three different oxides, Y4Al2O9, YAlO3 and Y3Al5O12, have been observed in this alloy. The oxide particle sizes range from just a few up to hundreds of nm and these particles are responsible of the high temperature mechanical strength of this alloy. Mechanically alloyed MA956 powder was consolidated via Friction Consolidation using three different processing conditions. As a result, three small compacts of low porosity were produced. The compacts exhibited a refined equiaxed grain structure with grain sizes smaller than 10 µm and the desired oxide dispersion.YAlO3 and Y3Al5O12 were identified in the compacts by Scanning Electron Microscopy (SEM), Electron Dispersive Spectroscopy (EDS) and X-ray diffraction (XRD). The size distribution of precipitates above 50 nm showed a direct proportionality between average precipitate size and grain size. The total energy input during processing was correlated with the relative amount of each of the oxides in the disks: the higher the total processing energy input, the higher the relative amount of Y3Al5O12 precipitates. The elemental composition of the oxide precipitates was also probed individually by EDS showing an aluminum enrichment trend as precipitates grow in size.

  11. Transmutation of alloys in MFE facilities as calculated by REAC (a computer code system for activation and transmutation)

    A computer code system for fast calculation of activation and transmutation has been developed. The system consists of a driver code, cross-section libraries, flux libraries, a material library, and a decay library. The code is used to predict transmutations in a Ti-modified 316 stainless steel, a commercial ferritic alloy (HT9), and a V-15%Cr-5%Ti alloy in various magnetic fusion energy (MFE) test facilities and conceptual reactors

  12. Testing for compatibility of reduced activation ferritic steel with plasma on JFT-2M partial coverage of the vacuum vessel with ferritic steel

    The compatibility of reduced activation ferritic steel (F82H), which is a leading candidate material for the demo reactor (e.g. SSTR), with plasma has been investigated in the JFT-2M tokamak with 3 steps in an AMTEX (Advanced Material Tokamak EXperiment). In the first step, the reduction of fast ion losses was well demonstrated with the ferritic steel outside the vacuum vessel. In the second step, the ferritic steel was installed inside the vacuum vessel in order to perform a preliminary investigation of the effect of the ferromagnetism on plasma stability and control, and impurity release. For this purpose, ferritic steels of 7 mm thickness were installed to form 2 sets of toroidally uniform belts, which cover 20% of the vacuum vessel. No deteriorative effects were observed regarding mode locking, plasma control, and impurity desorption. The initial boron coating was applied in order to modify the surface of the ferritic steel. The impurity is remarkably reduced and high normalized-beta plasma was obtained. Thus encouraging results were obtained for the third step, where whole vacuum vessel wall will be covered with ferritic steel. (author)

  13. Alloying design of oxide dispersion strengthened ferritic steel for long life FBRs core materials

    Oxide dispersion strengthened (ODS) ferrite steels with excellent swelling resistance and superior high temperature strength are prospective cladding materials for advanced fast breeder reactors. The addition of Ti in 13Cr-3W ODS ferritic steels improved the high temperature strength remarkably by the formation of uniformly distributed ultra-fine oxide particles. ODS ferritic steels have a bamboo-like grain structure and a strong deformation texture. The decrease of creep rupture strength in the bi-axial direction compared to the uni-axial direction is attributed mainly to this unique bamboo grain structure. Nearly equivalent creep rutpure strength for both bi-axial and uni-axial direction was successfully attained by introducing the α to γ transformation in ODS martensitic steel. (orig.)

  14. Evaluation of mechanical properties in stainless alloy ferritic with 5 % molybdenum; Avaliacao das propriedades mecanicas em ligas inoxidaveis ferriticas com 5% de molibdenio

    Lima Filho, V.X.; Gomes, F.H.F.; Guimaraes, R.F.; Saboia, F.H.C.; Abreu, H.F.G. de [Instituto Federal de Educacao, Ciencia e Tecnologia do Ceara (IFCE). Campus Maracanau, CE (Brazil)], e-mail: venceslau@ifce.edu.br

    2010-07-01

    The deterioration of equipment in the oil industry is caused by high aggressiveness in processing the same. One solution to this problem would increase the content of molybdenum (Mo) alloys, since this improves the corrosion resistance. As the increase of Mo content causes changes in mechanical properties, we sought to evaluate the mechanical properties of alloys with 5% Mo and different levels of chromium (Cr). Were performed metallography and hardness measurement of the alloys in the annealed condition. Subsequent tests were performed tensile and Charpy-V, both at room temperature. The results showed that 2% difference in the content of Cr did not significantly alter the mechanical properties of alloys. The alloys studied had higher values in measured properties when compared to commercial ferritic alloys with similar percentages of Cr. The high content of Mo resulted in a brittle at room temperature but ductile at temperatures above 70 degree C. (author)

  15. Atom probe study of the microstructural evolution induced by irradiation in Fe-Cu ferritic alloys and pressure vessel steels

    Pressure vessel steels used in pressurized water reactors are low alloyed ferritic steels. They may be prone to hardening and embrittlement under neutron irradiation. The changes in mechanical properties are generally supposed to result from the formation of point defects, dislocation loops, voids and/or copper rich clusters. However, the real nature of the irradiation induced-damage in these steels has not been clearly identified yet. In order to improve our vision of this damage, we have characterized the microstructure of several steels and model alloys irradiated with electrons and neutrons. The study was performed with conventional and tomographic atom probes. The well known importance of the effects of copper upon pressure vessel steel embrittlement has led us to study Fe-Cu binary alloys. We have considered chemical aging as well as aging under electron and neutron irradiations. The resulting effects depend on whether electron or neutron irradiations ar used for thus. We carried out both kinds of irradiation concurrently so as to compare their effects. We have more particularly considered alloys with a low copper supersaturation representative of that met with the French vessel alloys (0.1% Cu). Then, we have examined steels used on French nuclear reactor pressure vessels. To characterize the microstructure of CHOOZ A steel and its evolution when exposed to neutrons, we have studied samples from the reactor surveillance program. The results achieved, especially the characterization of neutron-induced defects have been compared with those for another steel from the surveillance program of Dampierre 2. All the experiment results obtained on model and industrial steels have allowed us to consider an explanation of the way how the defects appear and grow, and to propose reasons for their influence upon steel embrittlement. (author). 3 appends

  16. Correlation of Fe/Cr phase decomposition process and age-hardening in Fe–15Cr ferritic alloys

    The effects of thermal aging on the microstructure and mechanical properties of Fe–15Cr ferritic model alloys were investigated by TEM examinations, micro-hardness measurements and tensile tests. The materials used in this work were Fe–15Cr, Fe–15Cr–C and Fe–15Cr–X alloys, where X refers to Si, Mn and Ni to simulate a pressure vessel steel. Specimens were isothermally aged at 475 °C up to 5000 h. Thermal aging causes a significant increase in the hardness and strength. An almost twice larger hardening is required for embrittlement of Fe–15Cr–X relative to Fe–15Cr. The age-hardening is mainly due to the formation of Cr-rich α′ precipitates, while the addition of minor elements has a small effect on the saturation level of age-hardening. The correlation of phase decomposition process and age-hardening in Fe–15Cr alloy was interpreted by dispersion strengthened models

  17. Correlation between chemical composition and size of very small oxide particles in the MA957 ODS ferritic alloy

    ODS (oxide dispersion strengthened) alloys have superior creep properties. As it is well known, these excellent creep properties result from very fine oxide particles dispersed with the matrix. However, there is no common understanding about the nature of the very small oxide particles. Two hypotheses arise from the literature, 1: non-stoichiometric Y-, Ti-, O-enriched clusters and 2: stoichiometric Y2Ti2O7. In this work, both chemically extracted residue method and extraction replica method were applied to the commercial ODS ferritic alloy, MA957. These samples were then observed using XRD (X-ray diffractometry) and FEG-STEM (field emission gun-scanning transmission electron microscopy) with EDS (energy dispersive X-ray spectrometer). From the results, it was concluded that the composition of small particles is related to the particle size. They exhibit at least two types of phase, 1: non-stoichiometric Y-, Ti-, O-enriched clusters from ∼2 to ∼15 nm (Y/Ti 2Ti2O7 from ∼15 to ∼35 nm. Based on the result, it is suggested that the appropriate increase of titanium content compared to yttrium content in oxide particles by modifying the chemical compositions of ODS alloys could be an effective way to obtain a finer dispersion of oxide particles

  18. Influence of scandium addition on the high-temperature grain size stabilization of oxide-dispersion-strengthened (ODS) ferritic alloy

    The influence of 1–4 at% Sc addition on the thermal stability of mechanically alloyed ODS ferritic alloy was studied in this work. Sc addition was found to significantly stabilize grain size and microhardness at high temperatures. Grain sizes of samples with 1 and 4 at% Sc was found maintained in the nanoscale range at temperatures up to 1000 °C with hardness maintained at 5.6 and 6.7 GPa, respectively. The detailed microstructure was also investigated from EDS elemental mapping, where nanofeatures [ScTiO] were observed, while nanosized [YTiO] particles were rarely seen. This is probably due to the concentration difference between Sc and Y, leading to the formation of [ScTiO] favoring that of [YTiO]. Precipitation was considered as the major source for the observed high temperature stabilization. In addition, 14YT–Sc alloys without large second phases such as Ti-oxide can exhibit better performance compared to conventional ODS materials

  19. Development of ultra high strength nano-Y2O3 dispersed ferritic steel by mechanical alloying and hot isostatic pressing

    Highlights: → Nano-Y2O3 dispersed FeCrTiAl ferritic alloys developed by mechanical alloying. → Over 99% density (7.32-7.38 Mg/m3) achieved by hot isostatic pressing. → Dispersion of nanometric Y2Ti2O7, Y2O3, Fe11TiY or Al9.22Cr2.78Y is uniform. → Extremely high compressive strength, modulus, fracture toughness, hardness achieved. → Compressive strength is 2-3 times higher with lower density than similar ODS steel. - Abstract: The present investigation aims to develop ultra high strength ferritic steels through consolidation of mechanically alloyed powders of 1.0 wt% nano-Y2O3 dispersed 83.0Fe-13.5Cr-2.0Al-0.5Ti (alloy A), 79.0Fe-17.5Cr-2.0Al-0.5Ti (alloy B), 75.0Fe-21.5Cr-2.0Al-0.5Ti (alloy C) and 71.0Fe-25.5Cr-2.0Al-0.5Ti (alloy D) alloys (all in wt%) by hot isostatic pressing (HIP) at 600, 800 and 1000 deg. C using 1.2 GPa pressure for 1 h. Following this mechano-chemical synthesis and consolidation, extensive effort has been undertaken to characterize the microstructural evolution by X-ray diffraction, scanning and transmission electron microscopy and energy dispersive spectroscopy. Mechanical properties including hardness, compressive strength, Young's modulus and fracture toughness were determined using nano-indentation and universal testing machine. The present ferritic alloys record extraordinary levels of compressive strength (2012-3325 MPa), Young's modulus (230-295 GPa), fracture toughness (4.6-21.8 MPa √m) and hardness (15.5-19.7 GPa), and measure up to 2-3 times greater strength with a lower density (∼7.4 Mg/m3) than that of other oxide dispersion strengthened ferritic steels (2O3 (ex situ) or Y2Ti2O7 (in situ) particles in higher volume fraction in high-Cr ferritic matrix.

  20. Ultra-fine ferrite grain refinement by static re-crystallization of hot rolled vanadium micro-alloyed steels

    The phenomenon of ultrafine-grain refinement of ferrite during transformational grain refinement (TGR) followed by static re-crystallization of vanadium micro-alloyed steels was studied. A substantial grain refinement (2.8 mu m) was attained during TGR process by rolling at 900 deg. C. Cold rolling with 70% of reduction introduced strain, utilized for re-crystallization during annealing at different temperatures. Electron Backscattered Diffraction (EBSD) technique was employed to quantify the low angle grain boundaries (LAGB) and high angle grain boundaries (HAGB) spacings and results were correlated with hardness drops during annealing process. At higher annealing times and temperatures the vanadium precipitates restricted the process of grain growth probably due to effective dispersion strengthening. The abnormal grain growth during annealing, predicted previously for niobium steels, found absent in the present vanadium microalloyed steels. (author)

  1. Journal of Nuclear Materials - Radiation-induced segregation and phase stability in ferritic-martensitic alloy T 91

    Jiao, Zhijie [ORNL; Busby, Jeremy T [ORNL; Was, Gary S [ORNL; Jiao, Zhijie [University of Michigan

    2010-01-01

    Radiation-induced segregation in ferritic martensitic alloy T 91 was studied to understand the behavior of solutes as a function of dose and temperature. Irradiations were conducted using 2 MeV protons to doses of 1, 3, 7 and 10 dpa at 400 C. Radiation-induced segregation at prior austenite grain boundaries was measured, and various features of the irradiated microstructure were characterized, including grain boundary carbide coverage, the dislocation microstructure, radiation-induced precipitation and irradiation hardening. Results showed that Cr, Ni and Si segregate to prior austenite grain boundaries at low dose, but segregation ceases and redistribution occurs above 3 dpa. Grain boundary carbide coverage mirrors radiation-induced segregation. Irradiation induces formation of Ni Si Mn and Cu-rich precipitates that account for the majority of irradiation hardening. Radiation-induced segregation behavior is likely linked to the evolution of the precipitate and dislocation microstructures. 2010 Elsevier B.V. All rights reserved

  2. Consideration of the growth mode in isochronal austenite-ferrite transformation of ultra-low-carbon Fe-C alloy

    Chen, Hao; Liu, Yongchang; Li, Yanli; Zhang, Lifang [Tianjin University, Tianjin Key Lab of Advanced Jointing Technology, School of Materials Science and Engineering, Tianjin (China); Yan, Zesheng [Tianjin Pipe (Group) Cooperation, Tianjin (China)

    2010-01-15

    The three cooling rates of 10, 100, 200 K/min dilatometry experiments are used to investigate the kinetics of the isochronal austenite ({gamma}) to ferrite ({alpha}) transformation of Fe-0.0036wt.%C alloy. ''Normal transformation'' and ''abnormal transformation'' have both been observed for transformations at different cooling rates. In accordance with the thermodynamic characteristics of the {gamma}{yields}{alpha} transformation investigated here and previous kinetic considerations, a JMAK-like approach for the kinetics of isochronal phase transformations was developed that incorporates three overlapping processes: site saturation nucleation, alternate growth modes (from interface-controlled to diffusion-controlled to interface-controlled growth), as well as impingement for random distribution nuclei. The JMAK-like approach has been employed to fit the experimental results, and the fitting results show that for the {gamma}{yields}{alpha} transformation of the Fe-C alloy at all applied cooling rates, the growth mode evolves in the corresponding order: from interface-controlled to diffusion-controlled growth; from interface-controlled to diffusion-controlled to interface-controlled growth; and interface-controlled growth. (orig.)

  3. Outgassing characteristics of F82H ferritic steel as a low activation material for fusion reactor

    Odaka, Kenji; Satou, Osamu [Hitachi Ltd., Tsuchiura, Ibaraki (Japan). Mechanical Engineering Research Lab.; Ootsuka, Michio; Abe, Tetsuya; Hara, Shigemitsu; Takatsu, Hideyuki; Enoeda, Mikio

    1997-09-01

    Outgassing characteristics of F82H ferritic steel as a low activation material for the blanket of fusion device were investigated. A test chamber was constructed by welding F82H ferritic steel plates. The inner surface of the chamber was buffed and electropolished. The test chamber was degassed by the prebaking at temperature of 350degC for 20 h in vacuum. Then outgassing rates of the test chamber were measured by the throughput method as a function of pumping time for the cases that the test chamber was baked and not baked. The typical outgassing rate after baking at 250degC for 24 h was 3 x 10{sup -9} Pa{center_dot}ms{sup -1} and it seems that this value is sufficiently small to produce pressures at least as low as 10{sup -9} Pa in the vacuum chamber made of F82H ferritic steel. In the pump-down of the test chamber without baking after exposure to air, the outgassing rate decreases with pumping time and reached 1 x 10{sup -7} Pa{center_dot}ms{sup -1} at t = 10{sup 5} s. The activation energy of hydrogen in bulk diffusion in the F82H ferritic steel was measured and found to be 7 kcal/mol. (author)

  4. Experimental study and Monte Carlo simulations of phase transformations in ferrite of duplex stainless steels and their model alloys

    Duplex stainless steels used in primary circuit of 2. generation nuclear power plant endure thermal ageing at service temperatures (285 C-323 C). This leads to an increase of their hardness and to a decrease of their Charpy toughness. The evolution of these properties is due to the phase transformations which occur in ferrite. Even if it is well known that the steel composition plays a role on the mechanical properties evolution (steels with low Ni and Mo contents are less sensitive to thermal ageing), the origin of this difference of behaviour has not been clearly identified yet. In this study, the kinetics of the phase transformations in the ferrite of a duplex stainless steel with low Ni and Mo contents and duplex model alloys with specific compositions have been studied by atom probe tomography.This work showed that: i) G phase precipitation is less intense and the kinetic of the spinodal decomposition is slower for this steel than for steels with higher Ni and Mo contents, ii) the synergy between spinodal decomposition and G phase precipitation is also observed in this steel, iii) the Mo does not affect the early stages of the G phase precipitation, iv) the formation mechanism of G phase precipitates is at least a two steps mechanism, v) when the number density of G phase precipitates is low, hardening is mainly controlled by the amplitude and the mean wavelength of the spinodal decomposition, vi) when the number density of G phase precipitates is high, the hardening due to G phase precipitates may not be negligible. A kinetic Monte Carlo model has been developed to explain the synergy observed experimentally between the spinodal decomposition and the G phase precipitation. This model allowed us to show that the coarsening of G phase precipitates is driven by a diffusion mechanism along a/a' interfaces, and not by a bulk diffusion mechanism. (author)

  5. Compatibility of reduced activation ferritic/martensitic steel specimens with liquid Na and NaK in irradiation rig of IFMIF

    In the high flux region of the International Fusion Materials Irradiation Facility (IFMIF), the neutron irradiation damage for iron-based alloys will exceed 20 dpa/year. An accurate specimen temperature measurement under a large amount of nuclear heating is a key issue but the change of heat transfer of gap between irradiation specimens and specimen holder during irradiation test is inevitable, if gap is filled with an inert gas and temperature is monitored by a thermocouple buried in the specimen holder. A solution to make heat transfer predictable is to fill the gap with a liquid metal (sodium or sodium-potassium alloy). An issue of compatibility between Reduced Activation Ferritic/Martensitic steels and the liquid metals is addressed in this paper, and some recommendations for designing irradiation rig are presented, such as a purification control before filling liquid metals, or a careful selection of material of rig to avoid carbon mass transfer. (author)

  6. (Ni, Zn, Sn) Ru and (Ni, Sn) Sn substituted barium ferrite prepared by mechanical alloying

    NiRu, ZnRu, SnRu and SnSn mixtures considerably improved the saturation magnetization, Ms with low substitution values; diminishing quickly at the same times the coercivity, Hci to suitable values for high-density magnetic recording applications. On the other hand, the NiSn mixture also decreased the coercivity rapidly however without enhancing the saturation magnetization. The shown differences on magnetic properties were mainly due both to magnetic nature of divalent ion and to secondary phase apparitions. The mixtures with Sn2+ as partner ion diminished markedly to Tc. The tetravalent Ru4+ ion has a special effect on magnetic properties of hexagonal ferrites (increases Ms and diminishes fast Hci with low substitutions).

  7. Load partitioning between the bcc-iron matrix and NiAl-type precipitates in a ferritic alloy on multiple length scales

    Sun, Zhiqian; Song, Gian; Sisneros, Thomas A.; Clausen, Bjørn; Pu, Chao; Li, Lin; Gao, Yanfei; Liaw, Peter K.

    2016-01-01

    An understanding of load sharing among constituent phases aids in designing mechanical properties of multiphase materials. Here we investigate load partitioning between the body-centered-cubic iron matrix and NiAl-type precipitates in a ferritic alloy during uniaxial tensile tests at 364 and 506 °C on multiple length scales by in situ neutron diffraction and crystal plasticity finite element modeling. Our findings show that the macroscopic load-transfer efficiency is not as high as that predicted by the Eshelby model; moreover, it depends on the matrix strain-hardening behavior. We explain the grain-level anisotropic load-partitioning behavior by considering the plastic anisotropy of the matrix and elastic anisotropy of precipitates. We further demonstrate that the partitioned load on NiAl-type precipitates relaxes at 506 °C, most likely through thermally-activated dislocation rearrangement on the microscopic scale. The study contributes to further understanding of load-partitioning characteristics in multiphase materials. PMID:26979660

  8. Preparation of ferritic 17%Cr ODS steel by mechanical alloying from prealloyed steel powder

    Hadraba, Hynek; Husák, Roman; Kuběna, Ivo; Bureš, R.; Fáberová, M.; Strečková, M.

    2014-01-01

    Roč. 14, č. 4 (2014), s. 222-227. ISSN 1335-8987 R&D Projects: GA ČR(CZ) GA14-25246S Institutional support: RVO:68081723 Keywords : ODS steel * mechanical alloying * hot rolling Subject RIV: JG - Metallurgy

  9. Development of High-Temperature Ferritic Alloys and Performance Prediction Methods for Advanced Fission Energy Systems

    G. RObert Odette; Takuya Yamamoto

    2009-08-14

    Reports the results of a comprehensive development and analysis of a database on irradiation hardening and embrittlement of tempered martensitic steels (TMS). Alloy specific quantitative semi-empirical models were derived for the dpa dose, irradiation temperature (ti) and test (Tt) temperature of yield stress hardening (or softening) .

  10. Effect of ferrite formation on abnormal austenite grain coarsening in low-alloy steels during the hot rolling process

    Asahi, Hitoshi; Yagi, Akira; Ueno, Masakatsu

    1998-05-01

    Abnormal coarsening of austenite (γ) grains occurred in low-alloy steels during a seamless pipe hotrolling process. Often, the grains became several hundred micrometers in diameter. This made it difficult to apply direct quenching to produce high-performance pipes. The phenomenon of grain coarsening was successfully reproduced using a thermomechanical simulator, and the factors which affected grain coarsening were clarified. The mechanism was found to be basically strain-induced grain rowth which occurred during reheating at around 930 °C. Furthermore, once a pipe temperature decreased to the dual-phase region after the minimal hot working and prior to the reheating process, the grain coarsening was more pronounced. It was understood that the formation of ferrite along grain boundaries had the role of reducing the migration of grain boundaries into neighboring grains, leaving a strain-free, recrystallized region behind. This abnormal grain coarsening was found to be effectively prevented by an addition of Nb, the content of which varied depending on the C content. The effect of the Nb addition was confirmed by an in-line test.

  11. Ab Initio Investigation of He Bubbles at the Y2Ti2O7-Fe Interface in Nanostructured Ferritic Alloys

    Danielson, Thomas; Tea, Eric; Hin, Celine

    Nanostructured ferritic alloys are promising materials candidates for the next generation of nuclear reactors due to their ability to withstand high temperatures, high pressures, high neutron flux and especially, the presence of high concentrations of transmutation product helium. As helium diffuses through the matrix, large number densities of complex oxide nanoclusters, namely Y2Ti2O7, Y2O3 and Y2TiO5, act as trapping sites for individual helium atoms and helium clusters. Consequently, there is a significant decrease in the amount of helium that reaches grain boundaries, mitigating the threat of pressurized bubble formation and embrittlement. In order to understand the helium trapping mechanisms of the oxides at a fundamental level, the interface between the nanoclusters and the iron matrix must be modeled. We present results obtained using density functional theory on the Y2Ti2O7-Fe interface where the structure has been modeled based on experimental observations. Helium has been added along the interface in order to investigate the influence of helium on the structure and to obtain thermodynamic and kinetic parameters of helium along the interface.

  12. Stress-corrosion and fatigue cracking behaviour of nitrogen-alloyed austenitic and ferritic-austenitic chrome-nickel-(molybdenum)steels

    Under unfavorable heat-exchanger conditions simulated with 3 % sodium chloride solutions of different rhoH-values and redox potentials there excists a close connection between the stress-corrosion and fatigue behavior and the results of electrochemical measurements for nitrogen-alloyed austenitic and ferritic-austenitic high-alloy stells. Elevated contents of chromium and molybdenum have a positive effect. With free corrosion the materials no. 1.4311 and 1.4406 as well as partly also 1.4439 and the corresponding weldings are not suited if there is a hazard of stress corrosion. For 1.4439 and 1.4462 and their weldings of the same type a lower-bound stress may be given for the hazard of stress corrosion. It is within the order of magnitude of the garanteed elevated temperature yield strength and is therefore distinctly higher for the ferritic-austenitic steel 1.4462 than for nitrogenous austenitic steels. For the nitrogenous austenitic steels mentioned the dynamic loading capacity with and without the action of corrosive media is marked by lower than for the steel 1.4462 with ferritic-austenitic structure and its welding of the same type. As the notch sensitivity for both groups of material can be taken as equal the steel 1.4462 appears suitable for being used under unfavorable heat-exchanger conditions if high resistance against stress-corrosion and fatigue cracking is taken into account. (orig.)

  13. Large zinc cation occupancy of octahedral sites in mechanically activated zinc ferrite powders

    The cation site occupancy of a mechanically activated nanocrystalline zinc ferrite powder was determined as (Zn0.552+Fe0.183+)tet[Zr0.452+Fe1.823+]octO4 through analysis of extended x-ray absorption fine structure measurements, showing a large redistribution of cations between sites compared to normal zinc ferrite samples. The overpopulation of cations in the octahedral sites was attributed to the ascendance in importance of the ionic radii over the crystal energy and bonding coordination in determining which interstitial sites are occupied in this structurally disordered powder. Slight changes are observed in the local atomic environment about the zinc cations, but not the iron cations, with respect to the spinel structure. The presence of Fe3+ on both sites is consistent with the measured room temperature magnetic properties. (c) 2000 American Institute of Physics

  14. Microstructure and Mechanical Properties of a Nitride-Strengthened Reduced Activation Ferritic/Martensitic Steel

    Zhou, Qiangguo; Zhang, Wenfeng; Yan, Wei; Wang, Wei; Sha, Wei; Shan, Yiyin; Yang, Ke

    2012-12-01

    Nitride-strengthened reduced activation ferritic/martensitic (RAFM) steels are developed taking advantage of the high thermal stability of nitrides. In the current study, the microstructure and mechanical properties of a nitride-strengthened RAFM steel with improved composition were investigated. Fully martensitic microstructure with fine nitrides dispersion was achieved in the steel. In all, 1.4 pct Mn is sufficient to suppress delta ferrite and assure the steel of the full martensitic microstructure. Compared to Eurofer97, the steel showed similar strength at room temperature but higher strength at 873 K (600 °C). The steel exhibited very high impact toughness and a low ductile-to-brittle transition temperature (DBTT) of 243 K (-30 °C), which could be further reduced by purification.

  15. ATR-A1 irradiation experiment on vanadium alloys and low activation steels

    Tasi, H.; Strain, R.V.; Gomes, I.; Hins, A.G.; Smith, D.L.

    1996-04-01

    To study the mechanical properties of vanadium alloys under neutron irradiation at low temperatures, an experiment was designed and constructed for irradiation in the Advanced Test Reactor (ATR). The experiment contained Charpy, tensile, compact tension, TEM, and creep specimens of vanadium alloys. It also contained limited low-activation ferritic steel specimens as part of the collaborative agreement with Monbusho of Japan. The design irradiation temperatures for the vanadium alloy specimens in the experiment are {approx}200 and 300{degrees}C, achieved with passive gap-gap sizing and fill gas blending. To mitigate vanadium-to-chromium transmutation from the thermal neutron flux, the test specimens are contained inside gadolinium flux filters. All specimens are lithium-bonded. The irradiation started in Cycle 108A (December 3, 1995) and is expected to have a duration of three ATR cycles and a peak influence of 4.4 dpa.

  16. Development and characterisation of 9Cr ODS and reduced activation ferritic/martensitic steels for fast fission and fusion reactors

    This paper presents the results of the indigenous efforts at IGCAR towards developing a 9Cr Oxide Dispersion Strengthened (ODS) and Reduced Activation Ferritic Martensitic (RAFM) steels for the Fast Breeder Reactors (FBR) and fusion program in India. The sodium cooled fast reactors require development of high temperature radiation resistant materials for achieving high fuel burn-up of 200GWd/t (∼160 dpa) or higher, which is one of the key factors for their efficient and economical operation. Ferritic/Martensitic steels (9-12% Cr) although exhibit higher void swelling resistance than austenitics, have poor high temperature creep strength, which limits the operating temperatures to ∼550 deg. C. Oxide dispersion strengthening (ODS) is a promising means of extending the creep resistance of F/M steels beyond 650 deg. C together with the advantages of high thermal conductivity and low swelling. Based on these well known principles, a developmental effort has been taken up to fabricate clad tubes using the yttria strengthened 9Cr ferritic steel. A small amount of Ti addition resulted in very fine mixed oxide particles of Y and Ti, thus improving creep rupture strength significantly. The process of clad tubes fabrication involved mechanical milling of alloy powders, consolidation by hot extrusion and tube formation by cold pilgering. Further, the particle size distribution studied using Analytical and High Resolution Electron Microscopy at intermediate stages and in the product showed a distribution of Y2O3 particles predominantly in the size range of 5-20nm. The process parameters have been optimized and tubes of outer diameter 6.6 mm, thickness 0.48 mm and length 1500mm have been produced. The RAFM steel for the test blanket module of International Thermonuclear Experimental Reactor (ITER) project has also been developed. The steel conforming to specifications has been achieved by replacement of Mo and Nb (elements that lead to high induced radioactivity) by W and Ta

  17. Numerical atomic scale simulations of the microstructural evolution of ferritic alloys under irradiation

    In this work, we have developed a model of point defect (vacancies and interstitials) diffusion whose aim is to simulate by kinetic Monte Carlo (KMC) the formation of solute rich clusters observed experimentally in irradiated FeCuNiMnSi model alloys and in pressure vessel steels. Electronic structure calculations have been used to characterize the interactions between point defects and the different solute atoms. Each of these solute atoms establishes an attractive bond with the vacancy. As for Mn, which is the element which has the weakest bond with the vacancy, it establishes more favourable bonds with interstitials. Binding energies, migration energies as well as other atomic scale properties, determined by ab initio calculations, have led to a parameter set for the KMC code. Firstly, these parameters have been optimised on thermal ageing experiments realised on the FeCu binary alloy and on complex alloys, described in the literature. The vacancy diffusion thermal annealing simulations show that when a vacancy is available, all the solutes migrate and form clusters, in agreement with the observed experimental tendencies. Secondly, to simulate the microstructural evolution under irradiation, we have introduced interstitials in the KMC code. Their presence leads to a more efficient transport of Mn. The first simulations of electron and neutron irradiations show that the model results are globally qualitatively coherent with the experimentally observed tendencies. (author)

  18. The microstructure and strength properties of MA957 nanostructured ferritic alloy joints produced by friction stir and electro-spark deposition welding

    The nanostructured ferritic alloy (NFA) MA957 was joined by friction stir welding (FSW) and electro-sparked deposition (ESD) welding. Transmission electron microscopy (TEM) and small angle neutron scattering (SANS) characterization studies showed a uniform fine-scale equiaxed ferrite structure with a high dislocation density and slightly coarsened nm-scale particles in the joint region of the FSW weld compared to the base metal. Microhardness and tensile measurements on the FSW showed a modest reduction in the strength of the joint compared to the as-processed MA957. In contrast, the ESD-welds contained considerable porosity and the nm-scale particles dissolved or coarsened significantly, resulting in a larger degradation of the joint region strength. Thus FSW is a promising method for joining NFAs

  19. The effect of Alloying elements on pitting resistance of ferritic and austenitic stainless steels in terms of pitting resistance equivalents (PRE)

    The alloying elements, such as Cr, Mo, and N of stainless steels play important roles in their resistances to pitting corrosion. The pitting resistances of stainless steels ha e long been characterized in terms of electrochemical parameters such as pitting potentials. however, in order to better understand the resistances to pitting of stainless steels, Pit Propagation Rate (PPR) and Critical Pitting Temperature (CPT) tests were carried out in deaerated 0.1N H2SO4 + 0.1N NaCl solution. The effect of Cr, Mo, and N alloying elements on the pitting corrosion resistances of both ferritic Fe-Cr, Fe-Cr-Mo stainless steels and austenitic stainless steels was examined by performing polarization, PPR, and CPT tests. The comparison between test results was made in terms of the Pitting Resistance Equivalent (PRE). Results showed that PRE values are the good parameters representing the extents of pitting corrosion resistance on a single scale regardless of both kinds of alloying elements and types of ferritic or austenitic stainless steels

  20. Comparison of fracture behavior for low-swelling ferritic and austenitic alloys irradiated in the Fast Flux Test Facility (FFTF) to 180 DPA

    Fracture toughness testing was conducted to investigate the radiation embrittlement of high-nickel superalloys, modified austenitic steels and ferritic steels. These materials have been experimentally proven to possess excellent resistance to void swelling after high neutron exposures. In addition to swelling resistance, post-irradiation fracture resistance is another important criterion for reactor material selection. By means of fracture mechanics techniques the fracture behavior of those highly irradiated alloys was characterized in terms of irradiation and test conditions. Precipitation-strengthened alloys failed by channel fracture with very low postirradiation ductility. The fracture toughness of titanium-modified austenitic stainless steel D9 deteriorates with increasing fluence to about 100 displacement per atom (dpa), the fluence level at which brittle fracture appears to occur. Ferritic steels such as HT9 are the most promising candidate materials for fast and fusion reactor applications. The upper-shelf fracture toughness of alloy HT9 remained adequate after irradiation to 180 dpa although its ductile- brittle transition temperature (DBTT) shift by low temperature irradiation rendered the material susceptible to brittle fracture at room temperature. Understanding the fracture characteristics under various irradiation and test conditions helps reduce the potential for brittle fracture by permitting appropriate measure to be taken

  1. Study of the formation of solute clusters under irradiation in model ferritic alloys

    Neutron irradiation results in the formation of a high number density (1023 to 1024 m-3) of ultrafine (2 nm in diameter) solute clusters in reactor vessel steels. These clusters contain a supersaturated element (copper), and some others solutes (Mn, Ni, Si and P) soluble at the temperature of irradiation (300 C). The aim of the work described in this report is to understand what are the basic processes at the origin of the formation of these clusters, and to obtain information about the effect of the different solutes. The microstructure of model alloys, after different irradiation experiments is characterised by atom probe. The comparison between experimental results and results obtained by mean field modelling (evolution of point defects under irradiation) suggests that the precipitation of the solute clusters is heterogeneous, on point defects clusters. Precipitation kinetic is slowed down by solutes other than copper. (author)

  2. Tensile properties of ODS-14%Cr ferritic alloy irradiated in a spallation environment

    The tensile properties of mechanically-alloyed oxide dispersion strengthened MA957 steel were measured at room temperature following irradiation in the SINQ spallation target up to almost 20 dpa corresponding to an accumulated helium content of about 1750 appm, with an average irradiation temperature range of 100-360 deg. C. In contrast to the behaviour of 9Cr-1Mo martensitic steel samples subjected to identical irradiation conditions and which were drastically embrittled at high dose, all tested MA957 specimens displayed a ductile fracture mode as shown by the measured values of uniform and total elongations and by the results of fracture surface examinations. This good mechanical behaviour is a new evidence that this type of material may be able to sustain high displacement damage and helium levels and is thus particularly well suited for fusion applications.

  3. High-temperature tensile properties of nano-oxide dispersion strengthened ferritic steels produced by mechanical alloying and spark plasma sintering

    Oxide-dispersion strengthened (ODS) ferritic steels were produced by mechanical alloying and subsequent spark plasma sintering. Very fast heating rates were used to minimize porosity when controlling grain size and precipitation of dispersoids within a compacted material. Sintering cycles performed at 1373 K (1100 C) induced heterogeneous, but fine grain size distribution and high density of nano-oxides. Yield strengths at room temperature and at 923 K (650 C) are 975 MPa and 298 MPa, respectively. Furthermore, high-temperature ductility is much increased: total strain of 28 pct at 923 K (650 C). (authors)

  4. Corrosion characteristics of low activation ferritic steel, JLF-1, in liquid lithium in static and thermal convection conditions

    The compatibility of JLF-1(Fe-9Cr-2W-0.1C), a reduced activation ferritec/martensitic (RAFM) steel with static and flowing lithium (Li) was investigated. The corrosion characteristics were studied by means of measurement of weight losses and scanning electron microscope (SEM)/energy dispersive X-ray spectrometer (EDS) analysis on the surfaces and cross-sections of the specimens. The weight losses of JLF-1 specimens showed saturation at the temperature of 500 deg. C and 600 deg. C. This is possibly due to the saturation of Fe, Cr in bulk Li or formation of saturated layer of dissolved elements in liquid Li near the specimen surface. In the corrosion test in a thermal convection loop, the corrosion rate at 500 deg. C for 250 h was significantly larger than that obtained in the static test in an identical condition. After Li exposure, the phase transformation from martensite to ferrite was found on the specimens. The chemical analysis results and the loss of carbides suggested that the phase change was caused by the depletion of carbon. At the same time, selective depletion of alloy elements, such as Cr and W was detected by EDS on the surface. The result of Vickers hardness test showed that obvious softening occurred on the surface of the specimens after Li exposure and the depth of the softened region was consistent with that of the phase transformation. The flowing Li enhanced the weight loss, phase change and hardness reduction due to the mass transfer

  5. Analysis of ferrite grain growth mechanisms during {gamma}-{alpha} transformation in a niobium alloyed steel using EBSD

    Novillo, E. [CEIT and TECNUN, P Manuel de Lardizabal 15, 20018 Donostia-San Sebastian (Spain); Hernandez, D. [CEIT and TECNUN, P Manuel de Lardizabal 15, 20018 Donostia-San Sebastian (Spain); Gutierrez, I. [CEIT and TECNUN, P Manuel de Lardizabal 15, 20018 Donostia-San Sebastian (Spain)]. E-mail: igutierrez@ceit.es; Lopez, B. [CEIT and TECNUN, P Manuel de Lardizabal 15, 20018 Donostia-San Sebastian (Spain)

    2004-11-15

    The austenite to ferrite phase transformation was studied in a C-Mn-Nb steel after different hot deformation schedules, leading to deformed and recrystallized austenite. The mechanisms of nucleation and growth of ferrite grains were investigated by means of the electron back scattered diffraction (EBSD) technique. The ferrite microstructures were characterised in terms of the misorientation angles between ferrite grains and the deviations from an ideal Kurdjumov-Sachs orientation relationship with the austenite. The results show that the grain refinement produced by the accumulation of the deformation in the austenite is limited to a certain extent by the ferrite grain coarsening taking place behind the transformation front. Both coalescence and normal grain growth have been observed to contribute to this coarsening. Coalescence is enhanced as a result of the variant selection taking place in transformation from a recrystallized austenite. The accumulation of the deformation in the austenite results in ferrite-ferrite boundaries of higher misorientation, causing coalescence in this case to be less favoured, as compared with normal grain growth.

  6. Irradiation-induced grain growth in nanocrystalline reduced activation ferrite/martensite steel

    In this work, we investigate the microstructure evolution of surface-nanocrystallized reduced activation ferrite/martensite steels upon high-dose helium ion irradiation (24.3 dpa). We report a significant irradiation-induced grain growth in the irradiated buried layer at a depth of 300–500 nm, rather than at the peak damage region (at a depth of ∼840 nm). This phenomenon can be explained by the thermal spike model: minimization of the grain boundary (GB) curvature resulting from atomic diffusion in the cascade center near GBs.

  7. Report of IEA workshop on reduced activation ferritic/martensitic steels

    IEA Workshop on Reduced Activation Ferritic/Martensitic Steels under implementing agreement for program of research and development on fusion materials was held at Tokyo Yayoi Kaikan and JAERI headquarter on November 2-3, 2000. The objective of this workshop was a review of the fusion material development programs, the progress of the collaboration and the irradiation effects studies on RAF/M steels in the collaborating parties (Europe, Russia the United States, and Japan). Moreover, the development of plans for future collaboration was discussed. The present report contains viewgraphs presented at the workshop. (author)

  8. Report of IEA workshop on reduced activation ferritic/martensitic steels

    NONE

    2001-03-01

    IEA Workshop on Reduced Activation Ferritic/Martensitic Steels under implementing agreement for program of research and development on fusion materials was held at Tokyo Yayoi Kaikan and JAERI headquarter on November 2-3, 2000. The objective of this workshop was a review of the fusion material development programs, the progress of the collaboration and the irradiation effects studies on RAF/M steels in the collaborating parties (Europe, Russia the United States, and Japan). Moreover, the development of plans for future collaboration was discussed. The present report contains viewgraphs presented at the workshop. (author)

  9. Absorption and Decomposition of CO2 by Active Ferrites Prepared by Atmospheric Plasma Spraying

    Li, Shaowei; He, Zhida; Zheng, Yanjun; Chen, Changfeng

    2015-12-01

    Active ferrites, which play an important role in the catalytic decomposition of CO2, have been fabricated by atmospheric plasma spraying to incorporate FeO and anoxic iron oxide [Fe3O4-δ (0 powder a greater ability to decompose CO2 when compared to hydrogen-reduced Fe3O4 or Fe2O3 particles. Spraying distance is found to play an important role in modulating the decomposition ability of the powders, while elevated temperatures can also enhance the catalytic decomposition of CO2.

  10. Hot-rolling of reduced activation 8CrODS ferritic steel

    Highlights: •Hot-rolling can induce a coarser ferrite grain in 8CrODS ferritic steel. •HR specimen consists of martensite, residual ferrite and transformed ferrite. •The coarsening of the transformed ferrite was analyzed by EBSD. •Hot-rolling can improve the strength of 8CrODS ferritic steel at 700 °C. -- Abstract: The 8CrODS ferritic steel is based on J1-lot developed for the advanced fusion blanket material to increase the coolant outlet temperature. A hot-rolling was conducted at the temperature above Ar3 of 716 °C, and its effect on the microstructure and tensile strength in 8CrODS ferritic steel was evaluated, comparing together with normalized and tempered specimen. It was confirmed that hot-rolling leads to slightly increased fraction of the ferrite and highly improved tensile strength. This ferrite was formed by transformation from the hot-rolled austenite during cooling due to fine austenite grains induced by hot-rolling. The coarsening of the transformed ferrite in hot-rolled specimen can be attributed to the crystalline rotation and coalescence of the similar oriented grains. The improved strength of hot-rolled specimen was ascribed to the high dislocation density and replacement of easily deformed martensite with the transformed coarse ferrite

  11. Hot-rolling of reduced activation 8CrODS ferritic steel

    Wu, Xiaochao, E-mail: chaoxiaowu_008@163.com [Hokkaido University, Graduate School of Engineering, Materials Science and Engineering, N13, W-8, Kita-ku, Sapporo 060-8628 (Japan); Ukai, Shigeharu [Hokkaido University, Faculty of Engineering, Materials Science and Engineering, N13, W-8, Kita-ku, Sapporo 060-8628 (Japan); Leng, Bin [Hokkaido University, Graduate School of Engineering, Materials Science and Engineering, N13, W-8, Kita-ku, Sapporo 060-8628 (Japan); Oono, Naoko; Hayashi, Shigenari [Hokkaido University, Faculty of Engineering, Materials Science and Engineering, N13, W-8, Kita-ku, Sapporo 060-8628 (Japan); Sakasegawa, Hideo; Tanigawa, Hiroyasu [Japan Atomic Energy Agency, 4002 Oarai, Ibaraki 311-1393 (Japan)

    2013-11-15

    Highlights: •Hot-rolling can induce a coarser ferrite grain in 8CrODS ferritic steel. •HR specimen consists of martensite, residual ferrite and transformed ferrite. •The coarsening of the transformed ferrite was analyzed by EBSD. •Hot-rolling can improve the strength of 8CrODS ferritic steel at 700 °C. -- Abstract: The 8CrODS ferritic steel is based on J1-lot developed for the advanced fusion blanket material to increase the coolant outlet temperature. A hot-rolling was conducted at the temperature above A{sub r3} of 716 °C, and its effect on the microstructure and tensile strength in 8CrODS ferritic steel was evaluated, comparing together with normalized and tempered specimen. It was confirmed that hot-rolling leads to slightly increased fraction of the ferrite and highly improved tensile strength. This ferrite was formed by transformation from the hot-rolled austenite during cooling due to fine austenite grains induced by hot-rolling. The coarsening of the transformed ferrite in hot-rolled specimen can be attributed to the crystalline rotation and coalescence of the similar oriented grains. The improved strength of hot-rolled specimen was ascribed to the high dislocation density and replacement of easily deformed martensite with the transformed coarse ferrite.

  12. Manufacturing development of low activation vanadium alloys

    General Atomics is developing manufacturing methods for vanadium alloys as part of a program to encourage the development of low activation alloys for fusion use. The culmination of the program is the fabrication and installation of a vanadium alloy structure in the DIII-D tokamak as part of the Radiative Divertor modification. Water-cooled vanadium alloy components will comprise a portion of the new upper divertor structure. The first step, procuring the material for this program has been completed. The largest heat of vanadium alloy made to date, 1200 kg of V-4Cr-4Ti, has been produced and is being converted into various product forms. Results of many tests on the material during the manufacturing process are reported. Research into potential fabrication methods has been and continues to be performed along with the assessment of manufacturing processes particularly in the area of joining. Joining of vanadium alloys has been identified as the most critical fabrication issue for their use in the Radiative Divertor Program. Joining processes under evaluation include resistance seam, electrodischarge (stud), friction and electron beam welding. Results of welding tests are reported. Metallography and mechanical tests are used to evaluate the weld samples. The need for a protective atmosphere during different welding processes is also being determined. General Atomics has also designed, manufactured, and will be testing a helium-cooled, high heat flux component to assess the use of helium cooled vanadium alloy components for advanced tokamak systems. The component is made from vanadium alloy tubing, machined to enhance the heat transfer characteristics, and joined to end flanges to allow connection to the helium supply. Results are reported

  13. Compatibility of graphite with a martensitic-ferritic steel, an austenitic stainless steel and a Ni-base alloy up to 1250 C

    To study the chemical interactions between graphite and a martensitic-ferritic steel (1.4914), an austenitic stainless steel (1.4919; AISI 316), and a Ni-base alloy (Hastelloy X) isothermal reaction experiments were performed in the temperature range between 900 and 1250 C. At higher temperatures a rapid and complete liquefaction of the components occurred as a result of eutectic interactions. The chemical interactions are diffusion-controlled processes and can be described by parabolic rate laws. The reaction behavior of the two steels is very similar. The chemical interactions of the steels with graphite are much faster above 1100 C than those for the Ni-base alloy. Below 1000 C the effect is opposite. (orig.)

  14. Development of oxide dispersion strengthened ferritic steels for fusion

    An oxide dispersion strengthened (ODS) ferritic steel with high temperature strength has been developed in line with low activation criteria for application in fusion power systems. The composition Fe-13.5Cr-2W-0.5Ti-0.25Y2O3 was chosen to provide a minimum chromium content to insure fully delta-ferrite stability. High temperature strength has been demonstrated by measuring creep response of the ODS alloy in uniaxial tension at 650 and 900 C in an inert atmosphere chamber. Results of tests at 900 C demonstrate that this alloy has creep properties similar to other alloys of similar design and can be considered for use in high temperature fusion power system designs. The alloy selection process, materials production, microstructural evaluation and creep testing are described

  15. Development of oxide dispersion strengthened ferritic steels for fusion

    Mukhopadhyay, D.K. [Vista Metals, Inc., McKeesport, PA (United States); Froes, F.H. [Univ. of Idaho, ID (United States); Gelles, D.S. [Pacific Northwest National Lab., Richland, WA (United States)

    1998-03-01

    An oxide dispersion strengthened (ODS) ferritic steel with high temperature strength has been developed in line with low activation criteria for application in fusion power systems. The composition Fe-13.5Cr-2W-0.5Ti-0.25Y{sub 2}O{sup 3} was chosen to provide a minimum chromium content to insure fully delta-ferrite stability. High temperature strength has been demonstrated by measuring creep response of the ODS alloy in uniaxial tension at 650 and 900 C in an inert atmosphere chamber. Results of tests at 900 C demonstrate that this alloy has creep properties similar to other alloys of similar design and can be considered for use in high temperature fusion power system designs. The alloy selection process, materials production, microstructural evaluation and creep testing are described.

  16. Microstructural stability of reduced activation ferritic/martensitic steels under high temperature and stress cycling

    Reduced activation ferritic/martensitic steels are leading candidates for blanket/first-wall structures of the D-T fusion reactors. In fusion application, structural materials will suffer cyclic stresses caused by repeated changes of temperature and electromagnetic forces according to reactor operation scenarios. Therefore, creep-fatigue behaviors are extremely important to qualify reduced activation steels as fusion structural materials. In this work, microstructural stability of reduced activation ferritic/martensitic steels under various external stresses, such as constant stress cyclic stress, was studied. The materials used are JLF-1 steel (9Cr-2W-V,Ta) and JLS-2 steel (9Cr-3W-V,Ta). The microstructure inspection by means of transmission electron microscopy (TEM) and scanning electron microscopy (SEM) was performed following creep rupture tests, fatigue and creep-fatigue tests at elevated temperatures. In order to examine precipitation morphology in detail, the improved extracted residue and extracted replica methods were applied. From the microstructural observation of creep rupture-tested specimen, intergranular precipitates such as M23C6 and Laves phase coarsened by applying the static stress

  17. High-temperature creep rupture of low alloy ferritic steel butt-welded pipes subjected to combined internal pressure and end loadings.

    Vakili-Tahami, F; Hayhurst, D R; Wong, M T

    2005-11-15

    Constitutive equations are reviewed and presented for low alloy ferritic steels which undergo creep deformation and damage at high temperatures; and, a thermodynamic framework is provided for the deformation rate potentials used in the equations. Finite element continuum damage mechanics studies have been carried out using these constitutive equations on butt-welded low alloy ferritic steel pipes subjected to combined internal pressure and axial loads at 590 and 620 degrees C. Two dominant modes of failure have been identified: firstly, fusion boundary failure at high stresses; and, secondly, Type IV failure at low stresses. The stress level at which the switch in failure mechanism takes place has been found to be associated with the relative creep resistance and lifetimes, over a wide range of uniaxial stresses, for parent, heat affected zone, Type IV and weld materials. The equi-biaxial stress loading condition (mean diameter stress equal to the axial stress) has been confirmed to be the worst loading condition. For this condition, simple design formulae are proposed for both 590 and 620 degrees C. PMID:16243708

  18. Underwater explosive welding of tungsten to reduced-activation ferritic steel F82H

    Mori, Daichi [Institute of Advanced Energy, Kyoto University, Gokasho, Uji, Kyoto 611-0011 (Japan); Kasada, Ryuta, E-mail: r-kasada@iae.kyoto-u.ac.jp [Institute of Advanced Energy, Kyoto University, Gokasho, Uji, Kyoto 611-0011 (Japan); Konishi, Satoshi [Institute of Advanced Energy, Kyoto University, Gokasho, Uji, Kyoto 611-0011 (Japan); Morizono, Yasuhiro [Graduate School of Science and Technology, Kumamoto University, 2-39-1 Kurokami, Kumamoto 860-8555 (Japan); Hokamoto, Kazuyuki [Institute of Pulsed Power Science, Kumamoto University, 2-39-1 Kurokami, Kumamoto 860-8555 (Japan)

    2014-10-15

    Highlights: • The underwater explosive welding was successfully applied in the joining of tungsten to F82H reduced activation ferritic steel. • Microstructure of the interface showed the formation of a wave-like interface with a thin mixed layer of tungsten and F82H. • Nanoindentation hardness results exhibited a gradual change away from the welded interface without hardened layer. • Small punch tests on the welded specimens resulted in the cracking at a center of tungsten followed by the interfacial cracking. - Abstract: The present study reports the underwater explosive welding of commercially pure tungsten onto the surface of a reduced-activation ferritic steel F82H plate. Cross-sectional observation revealed the formation of a wave-like interface, consisting of a thin mixed layer of W and F82H. The results of nanoindentation hardness testing identified a gradual progressive change in the interface, with no hardened or brittle layer being observed. Small punch tests on the welded specimens resulted in cracking at the center of the tungsten, followed by crack propagation toward both the tungsten surface and the tungsten/steel interface.

  19. A strong magneto-optical activity in rare-earth La3+ substituted M-type strontium ferrites

    M-type strontium ferrites with substitution of Sr2+ by rare-earth La3+ were prepared by conventional ceramic technology. The structure, magnetic properties, and magneto-optical Kerr activity of Sr1-xLaxFe12O19 (x = 0, 0.05, 0.10, 0.15, 0.20) were investigated by x-ray diffraction (XRD), vibrating sample magnetometer (VSM), and magneto-optical ellipsometry, respectively. X-ray diffraction showed that the samples sintered at 1290 deg. C for 3 h were single M-type hexagonal ferrites. The magnetic properties were remarkably changed due to the valence change of Fe ions induced by the substitution of La ions. Most significantly, an important magneto-optical activity was induced in the La3+ substituted M-type strontium ferrites around 3 eV.

  20. Interaction of minor alloying elements of high-Cr ferritic steels with lattice defects: An ab initio study

    Bakaev, A. [SCK-CEN, Nuclear Materials Science Institute, Boeretang 200, Mol B2400 (Belgium); Center for Molecular Modeling, Department of Physics and Astronomy, Ghent University, Technologiepark 903, 9052 Zwijnaarde (Belgium); Department of Experimental Nuclear Physics K-89, Faculty of Physics and Mechanics, St. Petersburg State Polytechnical University, 29 Polytekhnicheskaya str., 195251 St. Petersburg (Russian Federation); Terentyev, D., E-mail: dterenty@sckcen.be [SCK-CEN, Nuclear Materials Science Institute, Boeretang 200, Mol B2400 (Belgium); Bonny, G. [SCK-CEN, Nuclear Materials Science Institute, Boeretang 200, Mol B2400 (Belgium); Klaver, T.P.C. [Department of Materials Science and Engineering, Faculty of 3mE, TU Delft, Mekelweg 2, 2628 CD Delft (Netherlands); Olsson, P. [Department of Neutron Research, Angstrom Laboratory, Uppsala University, Box 525, SE-75120 Uppsala (Sweden); Van Neck, D. [Center for Molecular Modeling, Department of Physics and Astronomy, Ghent University, Technologiepark 903, 9052 Zwijnaarde (Belgium)

    2014-01-15

    Highlights: • The interaction of Mo, W, Nb, Ta, V, Mn, Si with point and extended defects is characterized. • Mn and Si exhibit peculiar interaction with both point and extended lattice defects. • The results for substitutional atoms of the refractory metals well follow one specific trend. -- Abstract: Basic properties of minor alloying elements, namely Mo, W, Nb, Ta, V, Mn, Si entering the conventional and reduced-activation structural Fe–(9–12)Cr steels have been analyzed using ab initio calculations. The electronic structure calculations were applied to study the interaction of minor alloying elements with a number of important and well defined lattice structures, such as point defects, the 1/2〈1 1 1〉 screw dislocation core, high angle symmetric grain boundaries and free surfaces. The studied elements were classified according to their similarities and discrepancies regarding the interaction with the above mentioned defects. The refractory alloying elements are found to follow the same trend whereas Mn and Si exhibit peculiar behavior with respect to the interaction with both point and extended lattice defects. The obtained results are discussed and compared with previously published ab initio and available experimental data.

  1. Investigation on different oxides as candidates for nano-sized ODS particles in reduced-activation ferritic (RAF) steels

    Future generation reactor concepts are based on materials that can stand higher temperatures and higher neutron doses in corrosive environments. Oxide dispersion strengthened steels with chromium contents ranging from 9 to 14 wt.% – produced by mechanical alloying – are typical candidate materials for future structural materials in fission and fusion power plants. Y2O3 has proven to be a good candidate for addition to ferritic steels during mechanical alloying to form nano-sized dispersion oxide particles during compacting of the material. These oxide particles have many positive effects on the material such as improved high-temperature properties and higher corrosion resistance. However, there is potential for improvements by choosing different oxides. In this present work, four different oxides (MgO, La2O3, Ce2O3 and ZrO2) are selected by looking at their thermal stabilities and Gibbs free enthalpies of various chemical compositions. These oxides are mixed and mechanically alloyed with ferritic steel powder (Fe13Cr1W0.3Ti) and compared to a reference material produced with Y2O3 (Fe13Cr1W0.3Ti + Y2O3). The materials were characterized in terms of their mechanical properties and detailed microstructural investigations by transmission electron microscopy and electron backscatter diffraction. All further results of the mechanical testing and microstructural characterizations are analyzed, compared, and discussed in this paper

  2. Compatibility of reduced activation ferritic/martensitic steels with liquid breeders

    The compatibility of Reduced Activation Ferritic/Martensitic Steel (RAFM) with liquid Li and molten-salt Flibe have been characterized and accessed. Static compatibility tests were carried out in which the specimens were immersed into liquid Li or Flibe in isothermal autoclaves. Also carried out were compatibility tests in flowing liquid Li by thermal convection loops. In the case of liquid Li, the corrosion rate increased with temperature significantly. The corrosion was almost one order larger for the loop tests than for the static tests. Chemical analysis showed that the corrosion was enhanced when the level of N in Li is increased. Transformation from martensitic to ferritic phase and the resulting softening were observed in near-surface area of Li-exposed specimens, which were shown to be induced by decarburization. In the case of Flibe, the corrosion loss was much larger in a Ni crucible than in a RAFM crucible. Both fluorides and oxides were observed on the surfaces. Thus, the key corrosion process of Flibe is the competing process of fluoridation and oxidation. Possible mechanism of the enhanced corrosion in Ni crucible is electrochemical circuit effect. It was suggested that the corrosion loss rate of RAFM by liquid Li and Flibe can be reduced by reducing the level of impurity N in Li and avoiding the use of dissimilar materials in Flibe, respectively. (author)

  3. Diffusive transport parameters of deuterium through China reduced activation ferritic-martensitic steels

    Wang, Bo; Liu, Lingbo; Xiang, Xin; Rao, Yongchu; Ye, Xiaoqiu; Chen, Chang An

    2016-03-01

    Reduced Activation Ferritic/Martensitic (RAFM) steels have been considered as the most promising candidate structure materials for a fusion reactor. In the recent decades, two new types of RAFM steels, called China Low Activation Martensitic (CLAM) steel and China Low-activation Ferritic (CLF-1) steel, have been developed. The gas evolution permeation technique has been used to investigate diffusive transport parameters of deuterium through CLAM and CLF-1 over the temperature range 623 ∼ 873 K at deuterium pressure of 105 Pa. The resultant transport parameters are: Φ (mol. m-1 s-1 Pa-1/2) = 5.40 × 10-8 exp (-46.8 (kJ. mol-1)/RT), D(m2 s-1) = 3.81 × 10-7 exp(-24.0(kJ. mol-1)/RT) and S (mol. m-3 Pa-1/2) = 1.42 × 10-1 exp(-22.8(kJ. mol-1)/RT) for CLAM; while Φ(mol m-1 s-1 Pa-1/2) = 1.76 × 10-8 exp(-43.9(kJ. mol-1)/RT), D(m2. s-1) = 1.02 × 10-7 exp(-16.9(kJ. mol-1)/RT) and S(mol. m-1 Pa-1/2) = 1.73 × 10-1 exp(-27.0(kJ. mol-1) /RT) for CLF-1. The results show that CLAM is more permeable than CLF-1, thus it is easier for hydrogen isotopes to transport and be removed.

  4. Thermo-mechanical fatigue behavior of reduced activation ferrite/martensite stainless steels

    The thermo-mechanical cycling fatigue (TMCF) behavior of reduced activation ferrite/martensite stainless steels is examined. The test rig consists of a stiff load frame, which is directly heated by the digitally controlled ohmic heating device. Cylindrical specimens are used with a wall thickness of 0.4 mm. Variable strain rates are applied at TMCF test mode, due to the constant heating rate of 5.8 K/s and variable temperature changes. TMCF results of as received EUROFER 97 in the temperature range between 100 and 500-600 deg. C show a reduction in life time (a factor of 2) compared to F82H mod. and OPTIFER IV. TMCF-experiments with hold times of 100 and 1000 s show dramatic reduction in life time for all three materials

  5. Nitriding treatment of reduced activation ferritic steel as functional layer for liquid breeder blanket

    The development of functional layers such as a tritium permeation barrier and an anti-corrosion layer is the essential technology for the development of a molten salt type self cooled fusion blanket. In the present study, the characteristics of a nitriding treatment on a reduced activation ferritic steel, JLF-1 (Fe-9Cr-2W-0.1C) as the functional layer were investigated. The steel surface was nitrided by an ion nitriding treatment or a radical nitriding treatment. The nitridation characteristic of the steel surface was made clear based on the thermodynamic stability. The thermal diffusivity, the hydrogen permeability and the chemical stability in the molten salt Flinak were investigated. The results indicated that the nitriding treatment can improve the compatibility in the Flinak without the decrease of the thermal diffusivity, though there was little improvement as the hydrogen permeation barrier. (author)

  6. Effect of mechanical restraint on weldability of reduced activation ferritic/martensitic steel thick plates

    Serizawa, Hisashi; Nakamura, Shinichiro; Tanaka, Manabu; Kawahito, Yousuke; Tanigawa, Hiroyasu; Katayama, Seiji

    2011-10-01

    As one of the reduced activation ferritic/martensitic steels, the weldability of thick F82H plate was experimentally examined using new heat sources in order to minimize the total heat input energy in comparison with TIG welding. A full penetration of 32 mm thick plate could be produced as a combination of a 12 mm deep first layer generated by a 10 kW fiber laser beam and upper layers deposited by a plasma MIG hybrid welding with Ar + 2%O shielding gas. Also, the effect of mechanical restraint on the weldability under EB welding of thick F82H plate was studied by using FEM to select an appropriate specimen size for the basic test. The appropriate and minimum size for the basic test of weldability under EB welding of 90 mm thick plate might be 200 mm in length and 400 mm in width where the welding length should be about 180 mm.

  7. Effect of mechanical restraint on weldability of reduced activation ferritic/martensitic steel thick plates

    As one of the reduced activation ferritic/martensitic steels, the weldability of thick F82H plate was experimentally examined using new heat sources in order to minimize the total heat input energy in comparison with TIG welding. A full penetration of 32 mm thick plate could be produced as a combination of a 12 mm deep first layer generated by a 10 kW fiber laser beam and upper layers deposited by a plasma MIG hybrid welding with Ar + 2%O shielding gas. Also, the effect of mechanical restraint on the weldability under EB welding of thick F82H plate was studied by using FEM to select an appropriate specimen size for the basic test. The appropriate and minimum size for the basic test of weldability under EB welding of 90 mm thick plate might be 200 mm in length and 400 mm in width where the welding length should be about 180 mm.

  8. Magnetic properties and adsorptive performance of manganese–zinc ferrites/activated carbon nanocomposites

    Owing to the unique microstructure and high specific surface area, activated carbon (AC) could act as an excellent adsorbent for wastewater treatment and good carrier for functional materials. In this paper, manganese–zinc ferrites (Mn0.5Zn0.5Fe2O4: MZF) were anchored into AC by hydrothermal method, resulting in the excellent magnetic response for AC nanocomposites in wastewater treatment. All results demonstrated the magnetic nanoparticles presented a spinel phase structure and existed in the pores of AC. The saturation magnetization (Ms) of MZF/AC nanocomposites increased with the ferrites content, while the pore volume and specific surface area declined. The Sample-5 possessed the specific surface area of 1129 m2 g−1 (close to 1243 m2 g−1 of AC) and Ms of 3.96 emu g−1. Furthermore, the adsorptive performance for organic dyes was studied and 99% methylene blue was adsorbed in 30 min. The magnetic AC nanocomposites could be separated easily from solution by magnetic separation technique. - Graphical abstract: The Sample-5 presented both good magnetic response and high BET surface area up to 1129 m2 g−1 (close to AC of 1243 m2 g−1), which could be separated completely for about 60 s. MZF/AC nanocomposites (Sample-3, 4, 5) in our work could be used as the magnetic absorbents, which could be separated easily by an outer magnet after the MB adsorption. - Highlights: • Mn0.5Zn0.5Fe2O4 (MZF) as few as possible was implanted into activated carbon (AC) for the higher surface area. • Sample-5 possessed the high specific surface area (1129 m2 g−1) and the suitable Ms (3.96 emu g−1). • Methylene blue was adsorbed almost completely by MZF/AC nanocomposites in 30 min. • MZF/AC nanocomposites were separated easily from solution by magnetic separation technique

  9. Development of Reduced Activation Ferritic-Martensitic Steels in South Korea

    In the mid-1980s research programs for development of low activation materials began. This is based on the US Nuclear Regulatory Commission Guidelines (10CFR part 61) that were developed to reduce longlived radioactive isotopes, which allows nuclear reactor waste to be disposed of by shallow land burial when removed from service. Development of low activation materials is also key issue in nuclear fusion systems, as the structural components can became radioactive due to nuclear transmutation caused by exposure to high dose neutron irradiation. Reduced-activation ferritic martensitic (RAFM) steels have been developed in the leading countries in nuclear fusion technology, and are now being considered as candidate structural material for the test blanket module (TBM) in the international thermonuclear experiment reactor (ITER). South Korea joined the ITER program in 2003 and since then extensive effort has been made for developing the helium-cooled solid-breeder (HCSB) TBM which is scheduled to be tested in the ITER program. However, there has been no research activity to develop RAFM steels in South Korea, while all the participants in the ITER program have developed their own RAFM steels. It is recently that the Korea Atomic Energy Research Institute (KAERI) started the Korean RAFM steel research program, aiming at an application for the HCSB-type TBM structure in ITER. In what follows, the current status of RAFM steels and the R and D program led by KAERI to develop Korean RAFM steels are summarized

  10. Manifestation of weak ferromagnetism and photocatalytic activity in bismuth ferrite nanoparticles

    Bismuth ferrite (BFO) nanoparticles were synthesized by auto-ignition technique with and without adding ignition fuel such as citric acid. The presence of citric acid in the reaction mixture yielded highly-magnetic BFO/γ-Fe2O3 nanocomposite. When this composite was annealed to 650°C, a single phase BFO was formed with average crystallite size of 50 nm and showed weak ferromagnetic behavior. Conversely, the phase pure BFO prepared without adding citric acid exhibited antiferromagnetism because of its larger crystallite size of around 70 nm. The visible-light driven photocatalytic activity of both the pure BFO and BFO/γ-Fe2O3 nanocomposite were examined by degrading methyl orange dye. The pure BFO showed a moderate photocatalytic activity; while BFO/γ-Fe2O3 nanocomposite showed enhanced activity. This could be probably due to the optimal band gap ratio between BFO and γ-Fe2O3 phases reduced the recombination of electron-hole pairs which aided in the enhancement of photocatalytic activity.

  11. Study on the activated laser welding of ferritic stainless steel with rare earth elements yttrium

    Wang, Yonghui; Hu, Shengsun; Shen, Junqi

    2015-10-01

    The ferritic stainless steel SUS430 was used in this work. Based on a multi-component activating flux, composed of 50% ZrO2, 12.09 % CaCO3, 10.43 % CaO, and 27.49 % MgO, a series of modified activating fluxes with 0.5%, 1%, 2%, 5%, 10%, 15%, and 20% of rare earth (RE) element yttrium (Y) respectively were produced, and their effects on the weld penetration (WP) and corrosion resistant (CR) property were studied. Results showed that RE element Y hardly had any effects on increasing the WP. In the FeCl3 spot corrosion experiment, the corrosion rates of almost all the samples cut from welded joints turned out to be greater than the parent metal (23.51 g/m2 h). However, there was an exception that the corrosion rate of the sample with 5% Y was only 21.96 g/m2 h, which was even better than parent metal. The further Energy Dispersive Spectrometer (EDS) test showed the existence of elements Zr, Ca, O, and Y in the molten slag near the weld seam while none of them were found in the weld metal, indicating the direct transition of element from activating fluxes to the welding seam did not exist. It was known that certain composition of activating fluxes effectively restrain the loss of Cr element in the process of laser welding, and as a result, the CR of welded joints was improved.

  12. Effect of water depth on the underwater wet welding of ferritic steels using austenitic Ni-based alloy electrodes.

    Sheakley, Brian J.

    2000-01-01

    Underwater welding using shielded metal arc welding (SMAW) on US naval Vessels is very attractive because of the ability to effect repairs without costly dry dock expenses. In the past the primary problems with underwater wet weldments on steels utilizing SMAW with ferritic electrodes, were underbead cracking in the heat affected zone (HAZ), slag inclusions, oxide inclusions, and porosity. To avoid underbead cracking three weld samples were made using an austenitic nickel weld metal with an O...

  13. TEM Study of the Orientation Relationship Between Cementite and Ferrite in a Bainitic Low Carbon High Strength Low Alloy Steel

    Illescas Fernandez, Silvia; Brown, A P; He, K.; Fernández, Javier; Guilemany Casadamon, Josep Maria

    2005-01-01

    Two different bainitic structures are observed in a steel depending on the sample heat treatment. The different types of bainitic structures exhibit different orientation relationships between cementite and the ferrite matrix. Upper bainite presents a Pitsch orientation relationship and lower bainite presents a Bagaryatski orientation relationship. Different heat treatments of low carbon HSLA steel samples have been studied using TEM in order to find the orientation relationshi...

  14. Investigation on different oxides as candidates for nano-sized ODS particles in reduced-activation ferritic (RAF) steels

    Hoffmann, Jan, E-mail: j.hoffmann@kit.edu [Karlsruhe Institute of Technology (KIT), Institute for Applied Materials (IAM-AWP), Karlsruhe (Germany); Rieth, Michael; Lindau, Rainer; Klimenkov, Michael; Möslang, Anton [Karlsruhe Institute of Technology (KIT), Institute for Applied Materials (IAM-AWP), Karlsruhe (Germany); Sandim, Hugo Ricardo Zschommler [Department of Materials Engineering, EEL, University of São Paulo, 12600-970 Lorena (Brazil)

    2013-11-15

    Future generation reactor concepts are based on materials that can stand higher temperatures and higher neutron doses in corrosive environments. Oxide dispersion strengthened steels with chromium contents ranging from 9 to 14 wt.% – produced by mechanical alloying – are typical candidate materials for future structural materials in fission and fusion power plants. Y{sub 2}O{sub 3} has proven to be a good candidate for addition to ferritic steels during mechanical alloying to form nano-sized dispersion oxide particles during compacting of the material. These oxide particles have many positive effects on the material such as improved high-temperature properties and higher corrosion resistance. However, there is potential for improvements by choosing different oxides. In this present work, four different oxides (MgO, La{sub 2}O{sub 3}, Ce{sub 2}O{sub 3} and ZrO{sub 2}) are selected by looking at their thermal stabilities and Gibbs free enthalpies of various chemical compositions. These oxides are mixed and mechanically alloyed with ferritic steel powder (Fe13Cr1W0.3Ti) and compared to a reference material produced with Y{sub 2}O{sub 3} (Fe13Cr1W0.3Ti + Y{sub 2}O{sub 3}). The materials were characterized in terms of their mechanical properties and detailed microstructural investigations by transmission electron microscopy and electron backscatter diffraction. All further results of the mechanical testing and microstructural characterizations are analyzed, compared, and discussed in this paper.

  15. Progress of reduced activation ferritic/martensitic steel development in Japan

    Recent accomplishment by the Japanese activity for the reduced activation ferritic/martensitic steel (RAF/M) development has been reviewed. Some of the results obtained in EU and US by international collaborative activities are also introduced. Effect of irradiation on the shift of ductile-to-brittle transition temperature (DBTT) has been evaluated to a dose of 20dpa. Results suggest that RAF/M appears to satisfy the requirement on DBTT-shift for the blanket application in the dose range up to several tens of dpa. Also, enhancement effect of DBTT-shift by transmutation produced helium (He) atoms was revealed to be smaller than has been suggested previously. Preliminary studies about the effect of irradiation on fatigue mechanism, the susceptibility to environmentally assisted cracking in water and flow stress-strain relation have been conducted for the specimens irradiated to several dpa, including the post irradiation tensile property examination of the joints by Hot-isostatic press (HIP) bonding method. The results also indicate that RAF/Ms exhibit suitable properties for ITER test blanket module. (author)

  16. Neutron activation analysis of zirconium niobium alloys

    Full text: One of the important problems in nuclear reactor projecting is the choice of constructional materials, which meet to the requirements concerned with function, technical characteristics and expected performance of the reactor construction. Also it is necessary to take into account change of their properties under the influence of intensive neutron radiation. Zirconium and zirconium-niobium alloys are used in nuclear engineering as a fuel cladding and both matrix and impurity composition have an influence on their performance capabilities.Under intensive neutron radiation high content of undesirable trace elements in constructional materials can cause forming long-lived radionuclides with high induced activity and hence severe problems may occur at service, control of the equipment and carrying out experiments. Therefore analytical control of component and impurity composition of these materials is an important problem.Neutron activation analysis (NAA) is one of multielemental and high sensitivity methods, which widely applied for the analysis of high purity materials. Prior experiments have shown that instrumental NAA is not suitable for analysis of Zr-Nb alloys due to strong induced matrix activity. Therefore we have developed radiochemical procedure for separation of impurities from matrix elements. Study of the literature data has shown that zirconium and niobium are good extracted from hydrochloric medium by 0 75 M solution of di-2-ethylhexylphosphoric acid (DEHPA) in ortho-xylene. Also this system good extracts hafnium which being accompanying element has high content and interferes with determining impurity elements. To improve separation efficiency we have used 'DEHPA - ZM HCl' chromatography system. On the basis of the carried out researches the radiochemical NAA technique for analysis of high purity zirconium and zirconium-niobium alloys has been developed. The technique is based on extraction-chromatographic separation of matrix radionuclides

  17. Characterization of low alloy ferritic steel–Ni base alloy dissimilar metal weld interface by SPM techniques, SEM/EDS, TEM/EDS and SVET

    The interface region of welded A508–Alloy 52 M is characterized by scanning probe microscope (SPM) techniques, scanning electron microscopy (SEM)/energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM)/Energy Dispersive Spectroscopy (EDS) and scanning vibrate electrode technique (SVET). The regions along the welded A508–Alloy 52 M interface can be categorized into two types according to their different microstructures. In the type-I interface region, A508 and Alloy 52 M are separated by the fusion boundary, while in the type-II interface region, A508 and Alloy 52 M are separated by a martensite zone. A508, martensite zone and grain boundaries in Alloy 52 M are ferromagnetic while the Alloy 52 M matrix is paramagnetic. The Volta potentials measured by scanning Kelvin probe force microscopy (SKPFM) of A508, martensite zone and Alloy 52 M follow the order: V52 M > VA508 > Vmartensite. The corrosion behavior of A508–Alloy 52 M interface region is galvanic corrosion, in which Alloy 52 M is cathode while A508 is anode. The martensite dissolves faster than Alloy 52 M, but slower than A508 in the test solution. - Highlights: • The A508–Alloy 52 M interface regions can be categorized into two types. • The chromium depleted region is observed along the Alloy 52 M grain boundary. • The Alloy 52 M grain boundaries which are close to the interface are ferromagnetic. • Martensite zone has lower Volta potential but higher corrosion resistance than A508

  18. Establishing a Scientific Basis for Optimizing Compositions, Process Paths and Fabrication Methods for Nanostructured Ferritic Alloys for Use in Advanced Fission Energy Systems

    Odette, G Robert; Cunningham, Nicholas J., Wu, Yuan; Etienne, Auriane; Stergar, Erich; Yamamoto, Takuya

    2012-02-21

    The broad objective of this NEUP was to further develop a class of 12-15Cr ferritic alloys that are dispersion strengthened and made radiation tolerant by an ultrahigh density of Y-Ti-O nanofeatures (NFs) in the size range of less than 5 nm. We call these potentially transformable materials nanostructured ferritic alloys (NFAs). NFAs are typically processed by ball milling pre-alloyed rapidly solidified powders and yttria (Y2O3) powders. Proper milling effectively dissolves the Ti, Y and O solutes that precipitate as NFs during hot consolidation. The tasks in the present study included examining alternative processing paths, characterizing and optimizing the NFs and investigating solid state joining. Alternative processing paths involved rapid solidification by gas atomization of Fe, 14% Cr, 3% W, and 0.4% Ti powders that are also pre-alloyed with 0.2% Y (14YWT), where the compositions are in wt.%. The focus is on exploring the possibility of minimizing, or even eliminating, the milling time, as well as producing alloys with more homogeneous distributions of NFs and a more uniform, fine grain size. Three atomization environments were explored: Ar, Ar plus O (Ar/O) and He. The characterization of powders and alloys occurred through each processing step: powder production by gas atomization; powder milling; and powder annealing or hot consolidation by hot isostatic pressing (HIPing) or hot extrusion. The characterization studies of the materials described here include various combinations of: a) bulk chemistry; b) electron probe microanalysis (EPMA); c) atom probe tomography (APT); d) small angle neutron scattering (SANS); e) various types of scanning and transmission electron microscopy (SEM and TEM); and f) microhardness testing. The bulk chemistry measurements show that preliminary batches of gas-atomized powders could be produced within specified composition ranges. However, EPMA and TEM showed that the Y is heterogeneously distributed and phase separated, but

  19. Effect of strain on ferrite transformation from super-cooled austenite in Fe-0. 5%C alloy. Fe-0. 5%C gokin no karei osutenaito/feraito hentai ni oyobosu kako no eikyo

    Matsuura, K.; Ito, Y.; Narita, T. (Hokkaido Univ., Sapporo (Japan). Faculty of Engineering)

    1993-08-01

    During the cooling of a steel, when austenite is applied by strain, the temperature of ferrite transformation would increase accompanied with decrease of its given temperature and increase of strain. In this study, the isothermal transformation behaviour from austenite to ferrite applied by strain in the super-cooled state was investigated, effect of strain on size of ferrite particles and increase of volume rate during transformation were explained by using the velocity theory. That is, concerning to the alloy of two-elemental system Fe-0.51%C cooled at 0.3[degree]C/s and applied by strain at 710[degree]C, at which austenite was super-cooled by 55[degree]C, its isothermal transformation behaviour was investigated. As a result, the following conclusions were obtained. Time required for the transformation remarkably decreased and the size of ferrite particles became ultra-fine subjected to strain. The nucleation rate of ferrite particles remarkably increased with increasing strain. 14 refs., 11 figs., 1 tab.

  20. Crystallization of -type hexagonal ferrites from mechanically activated mixtures of barium carbonate and goethite

    J Temuujin; M Aoyama; M Senna; T Masuko; C Ando; H Kishi; A Minjigmaa

    2006-10-01

    -type hexagonal ferrite precursor was prepared by a soft mechanochemical treatment of BaCO3 and -FeOOH mixtures. The effect of milling on its structure and thermal behaviour was examined by XRD, SEM and FTIR. Well crystallized -type hexagonal ferrite was formed from just 1 h milled precursors at 800°C. The beneficial effect of milling was explained in terms of increased homogeneity with simultaneous hetero bridging bond formation between powder constituents.

  1. Size effect of primary Y2O3 additions on the characteristics of the nanostructured ferritic ODS alloys: Comparing as-milled and as-milled/annealed alloys using S/TEM

    The need for providing S/TEM evidence to clarify the mechanisms of nano-scale precipitate formation was the motivation of this investigation. In this study, an Fe–14Cr–0.4Ti alloy was ball-milled with different amounts of Y2O3 content up to 10 wt.%, and then annealed at temperatures up to 1100 °C. Micron-size Y2O3 particles were substituted for the nano-size counterpart to elucidate the mechanism of oxide precipitate formation. The S/TEM studies revealed that the microstructure of the alloy with 10 wt.% yttria contained amorphous undissolved Y2O3 after ball milling, while a small part of the initial oxide particles were dissolved into the solid solution. Consequently, when the amount of yttria was reduced to 1 wt.%, the amorphous phase of the yttria vanished and the whole content of Y2O3 was dissolved into the BCC solid solution. Defect analysis of precipitates on the annealed samples via S/TEM and micro-hardness studies revealed that the use of micron-size primary oxide particles can produce nano-size precipitates, stable up to temperatures as high as 1100 °C, and uniformly distributed throughout the microstructure. This study indicates that the use of high energy ball milling along with micron-size primary oxide particles can lead to nanostructured ferritic ODS alloys without the use of nano-size primary oxide additions

  2. Deposition of La0.8Sr0.2Cr0.97V0.03O3 and MnCr2O4 thin films on ferritic alloy for solid oxide fuel cell application

    Mikkelsen, Lars; Chen, Ming; Hendriksen, Peter Vang;

    2007-01-01

    Single layer dense films of La0.8Sr0.2Cr0.97V0.03O3 (LSC) and MnCr2O4 with a thickness of 500 nm were deposited on a commercially available ferritic alloy (Crofer 22APU) by large-area Pulsed Laser Deposition. The deposited samples were subsequently oxidized at 1173 K for 500 h in humidified air...

  3. Weldability of reduced activation ferritic/martensitic steel under ultra power density fiber laser welding

    Full text of publication follows: Reduced activation ferritic/martensitic steels (RAFMs) are recognized as the primary candidate structural materials for fusion blanket systems as it has been developed based on massive industrial experience of ferritic/martensitic steel replacing Mo and Nb of high chromium heat resistant martensitic steels (such as modified 9Cr-1Mo) with W and Ta, respectively. As one of RAFMS, F82H, which has been developed and studied in Japan, is designed with emphasis on high temperature property and weldablility, and was provided and evaluated in various countries as a part of the collaboration of IEA fusion materials development. Although F82H is the well perceived RAFM as ITER Test Blanket Module (TBM) structural material, the weldability was proved though TIG, EB and YAG laser weld tests using only 15 and 25 mm thickness plate. In order to reduce the welding distortion, the residual stress and the area of the heat affected zone, it is necessary to decrease the total heat input under the welding. Recently, as a result of R and D efforts about the sources of laser beam, a high-power fiber laser beam has been developed as one of the desirable heat sources for high-speed and deep-penetration welding. Since the power density of the fiber laser beam is very large, it is possible to increase the welding speed more than 10 m/min. So, in this study, the weldability of 1.5 mm thickness F82H plate and pipe was examined by using a ultra power density fiber laser, in order to reveal the excellent weldability of F82H. As a basic study of the butt welding between 1.5 mm plate and 1.5 mm thickness pipe with 11 mm outer diameter, the focus position, the beam position and the laser power were varied using 25 mm square plate and 25 mm length pipe. Then, by using the fiber laser with 1.1 MW/mm2 peak power density under the appropriate welding condition obtained from the basic study, a full penetrated weld bead with narrow width was formed in the butt welding

  4. A proposal to alloy design for low activation high manganese austenitic stainless steel - role of carbon and nitrogen

    The role of carbon and nitrogen in high Mn-Cr-Fe base alloy has been investigated in order to propose a favorable starting composition for a low activation austenitic stainless steel. The base composition of Fe-12% Cr-15% Mn was selected by the results of our previous study, because of prevention of δ ferrite formation and retardation of σ phase. The combined addition of carbon and nitrogen is very beneficial in making a stable γ phase, preventing σ phase formation and increasing high-temperature strength at around 875 K. Cold work of 20% is also very useful in increasing creep rupture strength because of finely dispersed precipitation of carbide during creep. From the consideration of these results, an alloy system of Fe-12% Cr-15% Mn-0.2% C-0.2% N has been designed as one of the preferable primary low activation austenitic stainless steel. (orig.)

  5. Characterization of TiN, TiC and Ti(C,N) in titanium-alloyed ferritic chromium steels focusing on the significance of different particle morphologies

    Titanium-alloyed ferritic chromium steels are a competitive option to classical austenitic stainless steels owing to their similar corrosion resistance. The addition of titanium significantly influences their final steel cleanliness. The present contribution focuses on the detailed metallographic characterization of titanium nitrides, titanium carbides and titanium carbonitrides with regard to their size, morphology and composition. The methods used are manual and automated Scanning Electron Microscopy with Energy Dispersive X-ray Spectroscopy as well as optical microscopy. Additional thermodynamic calculations are performed to explain the precipitation procedure of the analyzed titanium nitrides. The analyses showed that homogeneous nucleation is decisive at an early process stage after the addition of titanium. Heterogeneous nucleation gets crucial with ongoing process time and essentially influences the final inclusion size of titanium nitrides. A detailed investigation of the nuclei for heterogeneous nucleation with automated Scanning Electron Microscopy proved to be difficult due to their small size. Manual Scanning Electron Microscopy and optical microscopy have to be applied. Furthermore, it was found that during solidification an additional layer around an existing titanium nitride can be formed which changes the final inclusion morphology significantly. These layers are also characterized in detail. Based on these different inclusion morphologies, in combination with thermodynamic results, tendencies regarding the formation and modification time of titanium containing inclusions in ferritic chromium steels are derived. - Graphical abstract: Display Omitted - Highlights: • The formation and modification of TiN in the steel 1.4520 was examined. • Heterogeneous nucleation essentially influences the final steel cleanliness. • In most cases heterogeneous nuclei in TiN inclusions are magnesium based. • Particle morphology provides important information

  6. Status of ATR-A1 irradiation experiment on vanadium alloys and low-activation steels

    Tsai, H.; Strain, R.V.; Gomes, I.; Smith, D.L. [Argonne National Lab., IL (United States); Matsui, H. [Tohoku Univ. (Japan)

    1996-10-01

    The ATR-A1 irradiation experiment was a collaborative U.S./Japan effort to study at low temperature the effects of neutron damage on vanadium alloys. The experiment also contained a limited quantity of low-activation ferritic steel specimens from Japan as part of the collaboration agreement. The irradiation started in the Advanced Test Reactor (ATR) on November 30, 1995, and ended as planned on May 5, 1996. Total exposure was 132.9 effective full power days (EFPDs) and estimated neutron damage in the vanadium was 4.7 dpa. The vehicle has been discharged from the ATR core and is scheduled to be disassembled in the next reporting period.

  7. Past research and fabrication conducted at SCK-CEN on ferritic ODS alloys used as cladding for FBR's fuel pins

    De Bremaecker, Anne, E-mail: adbremae@sckcen.be [Studiecentrum voor Kernenergie-Centre d' Etude de l' Energie Nucleaire (SCK-CEN), NMS, Mol (Belgium)

    2012-09-15

    In the 1960s in the frame of the sodium-cooled fast breeders, SCK-CEN decided to develop claddings made with ferritic stainless materials because of their specific properties, namely a higher thermal conductivity, a lower thermal expansion, a lower tendency to He-embrittlement, and a lower swelling than the austenitic stainless steels. To enhance their lower creep resistance at 650-700 Degree-Sign C arose the idea to strengthen the microstructure by oxide dispersions. This was the starting point of an ambitious programme where both the matrix and the dispersions were optimized. A purely ferritic 13 wt% Cr matrix was selected and its mechanical strength was improved through addition of ferritizing elements. Results of tensile and stress-rupture tests showed that Ti and Mo were the most beneficial elements, partly because of the chi-phase precipitation. In 1973 the optimized matrix composition was Fe-13Cr-3.5Ti-2Mo. To reach creep properties similar to those of AISI 316, different dispersions and methods were tested: internal oxidation (that was not conclusive), and the direct mixing of metallic and oxide powders (Al{sub 2}O{sub 3}, MgO, ZrO{sub 2}, TiO{sub 2}, ZrSiO{sub 4}) followed by pressing, sintering, and extrusion. The compression and extrusion parameters were determined: extrusion as hollow at 1050 Degree-Sign C, solution annealing at 1050 Degree-Sign C/15 min, cleaning, cold drawing to the final dimensions with intermediate annealings at 1050 Degree-Sign C, final annealing at 1050 Degree-Sign C, straightening and final aging at 800 Degree-Sign C. The choice of titania and yttria powders and their concentrations were finalized on the basis of their out-of-pile and in-pile creep and tensile strength. As soon as a resistance butt welding machine was developed and installed in a glove-box, fuel segments with PuO{sub 2} were loaded in Belgian MTR BR2. The fabrication parameters were continuously optimized: milling and beating, lubrication, cold drawing (partial

  8. Thermal and mechanical behaviour of the reduced-activation-ferritic-martensitic steel EUROFER

    Reduced activation ferritic/martensitic (RAFM) steels are being considered for structural application in potential fusion energy systems. Based on the substantial experience with RAFM developmental steels of OPTIFER type, an industrial 3.5 tons batch of a 9CrWVTa-RAFM steel, called EUROFER 97 had been specified and ordered. A characterisation programme has been launched to determine the relevant mechanical and physical-metallurgical properties in order to qualify the steel for fusion application. The hardening, tempering and transformation behaviour of EUROFER is in good agreement with that of other RAFM-steels like OPTIFER and the Japanese industrial scale heat F82H mod. Tensile tests, performed between RT and 750 deg. C, show comparable strength and ductility values that are not strongly affected by different heat treatments and ageing at 580 and 600 deg. C up to 3300 h. Impact bending tests indicate a superior ductile to brittle transition temperature (DBTT) of EUROFER in the as-received condition compared with that of F82H mod. Creep tests between 450 and 650 deg. C up to test times of 15000 h reveal a creep strength similar to other RAFM steels like OPTIFER and F82H mod. EUROFER shows a good low-cycle fatigue behaviour with longer lifetimes than F82H mod. The deformation and softening behaviour is similar

  9. Effect of silicon on the microstructure and mechanical properties of reduced activation ferritic/martensitic steel

    Chen, Shenghu; Rong, Lijian

    2015-04-01

    The effect of Si in the range of 0.05-0.77 wt.% on the microstructure, tensile properties and impact toughness of reduced activation ferritic/martensitic (RAFM) steels has been investigated. An increase in Si content affected the prior austenite grain size resulting in an increase in the tensile strength at room temperature. The tensile strength of steels tested above 773 K did not change significantly with the addition of Si, which was due to the diminished carbide hardening effect and boundary strengthening effect. Detailed fractographic analysis revealed that tear fractures occurred in the samples tensile tested at room temperature, while cup and cone fractures were found in samples tensile tested at temperatures above 773 K, which were induced by the easing of dislocation pile-ups. The ductile-to-brittle transition temperature (DBTT) decreased when the Si content increased to 0.22 wt.%. However, the DBTT increased when the Si content reached 0.77 wt.% and this was due to the precipitation of Laves phase. The RAFM steel with approximately 0.22 wt.% Si content was found to possess an optimized combination of microstructure, tensile properties and impact toughness.

  10. Influence of smelting processes on precipitation behaviors and mechanical properties of low activation ferrite steels

    Research highlights: → Creep properties could be improved dramatically by control of smelting process. → VIM + ESR smelting process could improve the W macrosegregation. → W could accelerate the transition of M7C3 to M23C6 in RAFM steel. → The synergetic effect of carbides and tungsten depletion of solid solution lead to the decrease in creep resistance. - Abstract: In this paper, the influence of smelting processes on precipitation behaviors and mechanical properties of CLF-1 (China low activation ferrite) steel was investigated. Mechanical properties of CLF-1 steels melted by vacuum induction melting (VIM, CS25 steel) and vacuum induction melting followed by consumable electrode remelting (VIM + ESR, CS350 steel) had been studied. The results indicated that the steels showed similar values of hardness and tensile strength, however, creep properties of CLF-1 steel were obviously improved by VIM + ESR process. M23C6 and M7C3 Carbides were precipitated in the CS25 steel, and M23C6 carbides were precipitated in CS350 steel after high-temperature tempering at 1013 K for 90 min. Creep properties of CS25 steel were shown to be dramatically deteriorated by the existence of rod M7C3 precipitates, which was due to W macrosegregation in the CS25 steel melted by VIM. M7C3 was replaced by M23C6 after ageing at 823 K for 5000 h.

  11. Long term high temperature oxidation characteristics of La and Cu alloyed ferritic stainless steels for solid oxide fuel cell interconnects

    Swaminathan, Srinivasan; Lee, Young-Su; Kim, Dong-Ik

    2016-09-01

    To ensure the best performance of solid oxide fuel cell metallic interconnects, the Fe-22 wt.% Cr ferritic stainless steels with various La contents (0.006-0.6 wt.%) and Cu addition (1.57 wt.%), are developed. Long-term isothermal oxidation behavior of these steels is investigated in air at 800 °C, for 2700 h. Chemistry, morphology, and microstructure of the thermally grown oxide scale are examined using XPS, SEM-EDX, and XRD techniques. Broadly, all the steels show a double layer consisting of an inner Cr2O3 and outer (Mn, Cr)3O4. Distinctly, in the La-added steels, binary oxides of Cr, Mn and Ti are found at the oxide scale surface together with (Mn, Cr)3O4. Furthermore, all La-varied steels possess the metallic Fe protrusions along with discontinuous (Mn, Cr)3O4 spinel zones at the oxide scale/metal interface and isolated precipitates of Ti-oxides in the underlying matrix. Increase of La content to 0.6 wt.% is detrimental to the oxidation resistance. For the Cu-added steel, Cu is found to segregate strongly at the oxide scale/metal interface which inhibits the ingress of oxygen thereby suppressing the subscale formation of (Mn, Cr)3O4. Thus, Cu addition to the Fe-22Cr ferritic stainless steels benefits the oxidation resistance.

  12. Catalysis by Oxidic Spinel Ferrites

    Darshane, V.; Lokegaonkar, S.; Oak, S.

    1997-01-01

    Mixed metal oxides viz. ferrites, ferrochromites and chromites have been studied with a view to investigating a correlation between bulk physical properties and catalytic performance over decomposition of alcohols. We could observe a satisfactory relationship between lattice parameter, electronic activation energy, nature and mobility of charge carriers and Curie temperature with reference to catalytic activity of various spinel ferrites.

  13. Harnessing microbial subsurface metal reduction activities to synthesise nanoscale cobalt ferrite with enhanced magnetic properties

    Coker, Victoria S.; Telling, Neil D.; van der Laan, Gerrit; Pattrick, Richard A.D.; Pearce, Carolyn I.; Arenholz, Elke; Tuna, Floriana; Winpenny, Richard E.P.; Lloyd, Jonathan R.

    2009-03-24

    Nanoscale ferrimagnetic particles have a diverse range of uses from directed cancer therapy and drug delivery systems to magnetic recording media and transducers. Such applications require the production of monodisperse nanoparticles with well-controlled size, composition, and magnetic properties. To fabricate these materials purely using synthetic methods is costly in both environmental and economical terms. However, metal-reducing microorganisms offer an untapped resource to produce these materials. Here, the Fe(III)-reducing bacterium Geobacter sulfurreducens is used to synthesize magnetic iron oxide nanoparticles. A combination of electron microscopy, soft X-ray spectroscopy, and magnetometry techniques was employed to show that this method of biosynthesis results in high yields of crystalline nanoparticles with a narrow size distribution and magnetic properties equal to the best chemically synthesized materials. In particular, it is demonstrated here that cobalt ferrite (CoFe{sub 2}O{sub 4}) nanoparticles with low temperature coercivity approaching 8 kOe and an effective anisotropy constant of {approx} 10{sup 6} erg cm{sup -3} can be manufactured through this biotechnological route. The dramatic enhancement in the magnetic properties of the nanoparticles by the introduction of high quantities of Co into the spinel structure represents a significant advance over previous biomineralization studies in this area using magnetotactic bacteria. The successful production of nanoparticulate ferrites achieved in this study at high yields could open up the way for the scaled-up industrial manufacture of nanoparticles using environmentally benign methodologies. Production of ferromagnetic nanoparticles for pioneering cancer therapy, drug delivery, chemical sensors, catalytic activity, photoconductive materials, as well as more traditional uses in data storage embodies a large area of inorganic synthesis research. In particular, the addition of transition metals other than

  14. Effect of heat treatment and irradiation temperature on impact behavior of irradiated reduced-activation ferritic steels

    Klueh, R.L.; Alexander, D.J. [Oak Ridge National Lab., TN (United States)

    1998-03-01

    Charpy tests were conducted on eight normalized-and-tempered reduced-activation ferritic steels irradiated in two different normalized conditions. Irradiation was conducted in the Fast Flux Test Facility at 393 C to {approx}14 dpa on steels with 2.25, 5, 9, and 12% Cr (0.1% C) with varying amounts of W, V, and Ta. The different normalization treatments involved changing the cooling rate after austenitization. The faster cooling rate produced 100% bainite in the 2.25 Cr steels, compared to duplex structures of bainite and polygonal ferrite for the slower cooling rate. For both cooling rates, martensite formed in the 5 and 9% Cr steels, and martensite with {approx}25% {delta}-ferrite formed in the 12% Cr steel. Irradiation caused an increase in the ductile-brittle transition temperature (DBTT) and a decrease in the upper-shelf energy. The difference in microstructure in the low-chromium steels due to the different heat treatments had little effect on properties. For the high-chromium martensitic steels, only the 5 Cr steel was affected by heat treatment. When the results at 393 C were compared with previous results at 365 C, all but a 5 Cr and a 9 Cr steel showed the expected decrease in the shift in DBTT with increasing temperature.

  15. Fractographic examination of reduced activation ferritic/martensitic steel charpy specimens irradiated to 30 dpa at 370{degrees}C

    Gelles, D.S.; Hamilton, M.L. [Pacific Northwest National Lab., Richland, WA (United States); Schubert, L.E. [Univ. of Missouri, Rolla, MO (United States)

    1996-10-01

    Fractographic examinations are reported for a series of reduced activation ferritic/Martensitic steel Charpy impact specimens tested following irradiation to 30 dpa at 370{degrees}C in FFTF. One-third size specimens of six low activation steels developed for potential application as structural materials in fusion reactors were examined. A shift in brittle fracture appearance from cleavage to grain boundary failure was noted with increasing manganese content. The results are interpreted in light of transmutation induced composition changes in a fusion environment.

  16. Research and Development of Reduced Activation Ferritic/Martensitic Steel CLF-1 in SWIP

    Full text: Because of the good industrial bases and the superior resistance for irradiation, reduced activation ferritic/martensitic (RAFM) steel is recognized as the primary structural material for ITER test blanket modules (TBM) and a DEMOnstration reactor. In China, one of the basic options of the blanket module concept to be tested in ITER is helium cooled solid breeder (HCSB) with the RAFM steel as the reference structural material. To provide material and property database for the design and fabrication of the ITER HCSB TBM, a new type of RAFM steel CLF-1 was developed and characterized by South Western Institute of Physics in China. In this paper, recent progress in SWIP research on RAFM steel CLF-1 R and D is reviewed with a focus on ITER-TBM design and fabrication. A new heat of 350 kg of CLF-1 steel was produced recently and different product forms (plates, rods and welding wires) were manufactured. Recent advances in the fields of steel development, mainly on the melting and processing techniques, composition optimization and thermo-mechanical treatment were addressed. The properties database and technical information required for blanket design and fabrication were derived. From the tensile and creep properties test, the design allowable stresses are derived. From the Charpy impact test, ductile to brittle transition temperature (DBTT) are evaluated. From the physical properties databases, density, modulus of elasticity, thermal conductivity, thermal diffusivity, specific heat, linear expansion coefficients are derived. The effect of thermal ageing on the microstructure and properties was investigated to study the stability under high temperature for long periods of time. In addition, the efforts to characterize the weldability of CLF-1 using tungsten-inert-gas (TIG) method for the fabrication of TBM were also introduced. (author)

  17. Optimization of production and properties of the nanoscaled ferritic ODS-alloy 13Cr-1W-0,3Y2O3-0,3TiH2 and characterization of structure and property correlations

    Fusion power reactors next to renewable energy sources shall form an important basis for a future energy scenario avoiding damaging emissions due to the lack of fossil primary energy carriers. An efficient operation of such reactors necessitate temperatures >700 C, which require new kinds of structural materials. Today only reduced activated oxide dispersion-strengthened (ODS-) materials based on iron, which have high strengths at elevated temperatures, offer the possibility to meet those criterias, which are developed in internationally coordinated programs. Therefore a nearly industrial production process based on the powdermetallurgical route is iteratively and systematically optimized to produce the ferritic ODS-alloy 13Cr-1W-0,3Y2O3-0,3TiH2. Through TEM elemental analyses of mechanically alloyed steel powder it is confirmed, that the additives Y2O3 and TiH2 dissolve completely in the powder and form the ODS-particles during the HIP-cycle. Detailed studies of powder contamination during mechanical alloying reveal correlations between the contamination behaviour of certain elements and the milling parameters. A specially designed procedure of powder encapsulation and sealing leads to a successful powder compaction to the ODS-material 13Cr-1W-0,3Y2O3-0,3TiH2. Detailed TEM studies show a bimodal grain size distribution within the material at first. The alloy's recrystallization behaviour is the main reason for this phenomenon and is therefore discussed in detail. A high dispersion of ODS-particles as the decisive material's component with particle sizes von 3-5nm within grains and 12-36nm at the grain boundaries is successfully reached and verified by numerous TEM-Elemental Mappings. By applying hot rolling as an additional step during production a more even grain structure by equally maintaining the fine nanoskaled particle dispersion is set up. The microstructure is highly stable, since no grain- or ODS-particle coarsening occurs during short term heat

  18. Cryomilling effect on the mechanical alloying behaviour of ferritic oxide dispersion strengthened powder with Y2O3

    Highlights: •Significant particle/grain size refinement of both Y2O3 and Fe-alloy powders by cryomilling. •Mechanisms of fragmentation/dissolution of Y2O3 during cryomilling were suggested. •The effect of cryomilling on residual microstrain was found. •Increased interstitial elements contamination during cryomilling was found. -- Abstract: Cryogenic cooling effect on mechanical alloying of the mixture of Fe–14Cr–3W–0.1Ti and Y2O3 powders was investigated. The powder mixtures were ball milled for 40 h at room-temperature and −150 °C. Cryomilling produced much finer particle/grain size than conventional room-temperature milling. XRD diffraction peak intensity was much lower under cryomilling conditions due to formation of nano-size grains and increased residual microstrain. Absorption amounts of interstitial elements were considerably higher under cryomilling conditions

  19. The effect of chelating/combustion agent on catalytic activity and magnetic properties of Dy doped Ni-Zn ferrite

    Samoila, P.; Slatineanu, T. [Faculty of Chemistry, Alexandru Ioan Cuza University of Iasi, 11 Carol I Boulevard 700506 (Romania); Postolache, P. [Faculty of Physics, Alexandru Ioan Cuza University of Iasi, 11 Carol I Boulevard 700506 (Romania); Iordan, A.R. [Faculty of Chemistry, Alexandru Ioan Cuza University of Iasi, 11 Carol I Boulevard 700506 (Romania); Palamaru, M.N., E-mail: palamaru@uaic.ro [Faculty of Chemistry, Alexandru Ioan Cuza University of Iasi, 11 Carol I Boulevard 700506 (Romania)

    2012-09-14

    The spinel ferrite Ni{sub 0.8}Zn{sub 0.2}Fe{sub 1.98}Dy{sub 0.02}O{sub 4} was prepared by sol-gel low temperature autocombustion method using four different chelating/combustion agents: citric acid, tartaric acid, urea and cellulose. Infrared spectroscopy (IR), X-ray diffraction (XRD), scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET) specific surface area measurement, the catalytic H{sub 2}O{sub 2} decomposition and the magnetic behavior were employed to investigate the influence of the combustion agents on structural characteristics, catalytic activity and magnetic properties. Spinel-type phase in the nano-scale domain was accomplished during sol-gel synthesis and was confirmed by XRD and IR. The best catalytic activity is belonging to the sample obtained using urea, which shows the smallest grain size (SEM), the highest specific surface area (BET measurements) and DyFeO{sub 3} phase (XRD), while ferrimagnetic behavior prevails for all the samples independently of fuel agent. Highlights: Black-Right-Pointing-Pointer Ni-Zn ferrite doped with Dy as catalyst and magnetic material. Black-Right-Pointing-Pointer Four chelating/combustion agents were used in sol-gel method. Black-Right-Pointing-Pointer Citric acid and cellulose allowed spinel monophase formation confirmed by XRD. Black-Right-Pointing-Pointer Catalytic activity of ferrite samples is affected by synthesis conditions. Black-Right-Pointing-Pointer Magnetic behavior is not changed significantly as a function of fuel agent.

  20. Effect of alloying elements on the electronic properties of thin passive films formed on carbon steel, ferritic and austenitic stainless steels in a highly concentrated LiBr solution

    The influence of alloying elements on the electrochemical and semiconducting properties of thin passive films formed on several steels (carbon steel, ferritic and austenitic stainless steels) has been studied in a highly concentrated lithium bromide (LiBr) solution at 25 °C, by means of potentiodynamic tests and Mott–Schottky analysis. The addition of Cr to carbon steel promoted the formation of a p-type semiconducting region in the passive film. A high Ni content modified the electronic behaviour of highly alloyed austenitic stainless steels. Mo did not modify the electronic structure of the passive films, but reduced the concentration of defects. - Highlights: • The addition of Cr to carbon steel promotes p-type semiconductivity. • Passive films formed on stainless steels are made up of complex spinel oxides. • Ni modifies the electronic behaviour of highly alloyed austenitic stainless steels

  1. The anti-microbial activity of titania-nickel ferrite composite nanoparticles

    Rana, S.; Misra, R. D. K.

    2005-12-01

    A novel approach to synthesize a new generation of composite nanoparticles consisting of a photocatalytic shell of anatase-titania and a magnetic core of nickel ferrite has been adopted combining reverse micelle and chemical hydrolysis techniques. Titania is an effective anti-microbial agent that can be directly sprayed on infected areas of the human body or environment. Unfortunately, titania is an electrical insulator and is difficult to extract from the sprayed surface after treatment. The titania photocatalytic shell provides good antimicrobial capability that renders the bacteria inactive and removes the organic pollutants, while the nickel ferrite magnetic core enables controlled delivery of composite nanoparticles through the application of a small magnetic field, encouraging their application as removable anti-microbial photocatalyst nanoparticles.

  2. Synthesis, characterization and catalytic activity of furosemide-functionalized ferrite on the sedimentation behavior of starch

    Palanikumar, S.; Meenarathi, B.; Kannammal, L.; Anbarasan, R.

    2015-01-01

    Furosemide-functionalized nanoferrite was synthesized and characterized by various analytical techniques. The furosemide-functionalized ferrite was used to settle down the starch particles under three different pH. Thus, obtained starch/Fe3O4 nanocomposites were characterized by Fourier transform infrared spectroscopy (FTIR), fluorescence spectroscopy, scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The sedimentation velocity of starch in the presence of furosemide-functionalized Fe3O4 was critically compared with the available literature value and the results are discussed in detail. The high sedimentation velocity of starch under the influence of gravitational force and the external magnetic force is studied. The starch-coated ferrites exhibited the lower vibrating sample magnetometer (VSM) value. This novel research work will bring out a new methodology in the field of starch materials.

  3. Impedance spectroscopy of the oxide films formed during high temperature oxidation of a cobalt-plated ferritic alloy

    Velraj, S.; Zhu, J. H.; Painter, A. S.; Du, S. W.; Li, Y. T.

    2014-02-01

    Impedance spectroscopy was used to evaluate the oxide films formed on cobalt-coated Crofer 22 APU ferritic stainless steel after thermal oxidation at 800 °C in air for different times (i.e. 2, 50, 100 and 500 h). Impedance spectra of the oxide films exhibited two or three semicircles depending on the oxidation time, which correspond to the presence of two or three individual oxide layers. Coupled with scanning electron microscopy/energy-dispersive spectroscopy (SEM/EDS) and X-ray diffraction (XRD), the individual oxide layer corresponding to each semicircle was determined unambiguously. Impedance spectrum analysis of the oxide films formed on the sample after thermal exposure at 800 °C in air for 2 h led to the identification of the low-frequency and high-frequency semicircles as being from Cr2O3 and Co3O4, respectively. SEM/EDS and XRD analysis of the 500-h sample clearly revealed the presence of three oxide layers, analyzed to be Co3-xCrxO4, CoCr2O4, and Cr2O3. Although the SEM images of the 50-h and 100-h samples did not clearly show the CoCr2O4 layer, impedance plots implied their presence. The oxide scales were assigned to their respective semicircles and the electrical properties of Co3-xCrxO4, CoCr2O4 and Cr2O3 were determined from the impedance data.

  4. Microstructural characterization of weld joints of 9Cr reduced activation ferritic martensitic steel fabricated by different joining methods

    Thomas Paul, V.; Saroja, S.; Albert, S.K.; Jayakumar, T.; Rajendra Kumar, E., E-mail: vtp@igcar.gov.in

    2014-10-15

    This paper presents a detailed electron microscopy study on the microstructure of various regions of weldment fabricated by three welding methods namely tungsten inert gas welding, electron beam welding and laser beam welding in an indigenously developed 9Cr reduced activation ferritic/martensitic steel. Electron back scatter diffraction studies showed a random micro-texture in all the three welds. Microstructural changes during thermal exposures were studied and corroborated with hardness and optimized conditions for the post weld heat treatment have been identified for this steel. Hollomon–Jaffe parameter has been used to estimate the extent of tempering. The activation energy for the tempering process has been evaluated and found to be corresponding to interstitial diffusion of carbon in ferrite matrix. The type and microchemistry of secondary phases in different regions of the weldment have been identified by analytical transmission electron microscopy. - Highlights: • Comparison of microstructural parameters in TIG, electron beam and laser welds of RAFM steel • EBSD studies to illustrate the absence of preferred orientation and identification of prior austenite grain size using phase identification map • Optimization of PWHT conditions for indigenous RAFM steel • Study of kinetics of tempering and estimation of apparent activation energy of the process.

  5. Ferrite stability in duplex austenitic stainless steel welds

    The presence of ferrite in austenitic stainless steel welds is known to be beneficial in avoiding hot cracking problems. In particular, the primary delta ferrite mode of solidification is important. For alloy compositions in which primary ferrite forms, it has been shown that up to approximately 40% ferrite may exist in the as-solidified structures. With further cooling, the ferrite becomes unstable, transforming to austenite. However, under typical welding conditions, the cooling rate is sufficiently high to suppress the complete transformation of ferrite and some residual ferrite is retained. For example, for Type 308 austenitic stainless steel filler metal, gas-tungsten arc welds contain 6 to 10% ferrite, although under equilibrium conditions at elevated temperatures, this same alloy can be homogenized into a fully austenitic structure. Thus, it is clear the retained ferrite in such duplex structure welds is unstable and transforms during elevated temperature applications. The stability of ferrite was investigated by measuring its composition after several different thermal treatments. The composition was measured by means of analytical electron microscopy of thinned foils, and only the major constituents, iron, chromium, and nickel, were analyzed. The composition of ferrite was measured as a function of aging time and temperature. It was found that, during aging, the ferrite composition changes and approaches a metastable equilibrium limit before eventually transforming to sigma phase or austenite. This limiting composition was determined as a function of temperature

  6. Electron Beam Welding of Reduced Activation Ferritic Martensitic ODS-EUROFER Steel for Application in Helium Cooled Modular Divertor Concepts

    For specific blanket and divertor applications in future fusion power reactors a replacement of presently considered Reduced Activation Ferritic Martensitic (RAFM) steels as structural material by suitable oxide dispersion strengthened (ODS) ferritic martensitic or ferritic steels would allow a substantial increase of the operating temperature from ∼ 550 oC to about 650 oC. In all cases appropriate joining technologies have to be developed. Diffusion welding techniques to perform similar and dissimilar joints have been studied successfully. Friction Stir Welding (FSW) has shown a good potential but application is limited due to geometrical restrictions and needs further development. For the advanced helium-cooled modular divertor concept various joining techniques are required for joining the complex structural parts made of different materials. First attempts have been made for joining the divertor structures of ODS EUROFER by means of the Electron beam welding process with its highly concentrated energy input. This welding is widely used to produce high quality-high integrity welded similar and dissimilar joints of a large variety of materials. For this purpose, samples of ODS-EUROFER steel were welded using a PTR 150 kV/15 kW EB welding facility. Two different post-weld heat treatments (PWHT) were applied to investigate their influence on the mechanical and microstructural properties of the welded joints. Miniaturised tensile specimens were used to determine the tensile behaviour in the temperature range between RT and 700 oC. KLST specimens were used for Charpy impact tests. The microstructure of the weld and heat affected zone was examined using optical and scanning electron microscopy. Transmission electron microscopical methods were applied to investigate the size and spatial distribution of the dispersed oxides and potential segregation phenomena. (author)

  7. Depth-dependent nanoindentation hardness of reduced-activation ferritic steels after MeV Fe-ion irradiation

    Highlights: • We investigate nanoindentation hardness of reduced-activation ferritic steels after ion irradiation. • We model the depth-dependent bulk-equivalent hardness with considering indentation size effect. • We examine a film/substrate model to explain softer substrate effect. • Damage gradient effect is terminated by the appearance of softer substrate effect. • The critical depth of softer substrate effect depends on the amount of irradiation hardening. - Abstract: The irradiation hardening behavior of F82H reduced-activation ferritic steels after MeV Fe-ion beam irradiation experiments was investigated with a nanoindentation test. Two sets of ion-irradiation experiments were conducted at 270 °C with 10.5 MeV Fe3+ ions up to 5 dpa at a 1000 nm depth at TIARA facility and at 290 °C with 6.4 MeV Fe3+ ions up to 3 dpa at a 600 nm depth at DuET facility, respectively. The measured nanoindentation hardness was converted to the depth-dependent bulk-equivalent hardness based on a combination of the Nix–Gao model to explain the indentation size effect and the film/substrate model to explain the damage gradient effect in the ion-irradiated region and softer substrate effect of the non-irradiated region beyond the irradiated depth range

  8. Effects of Grit Blasting and Annealing on the High-Temperature Oxidation Behavior of Austenitic and Ferritic Fe-Cr Alloys

    Proy, M.; Utrilla, M. V.; Otero, E.; Bouchaud, B.; Pedraza, F.

    2014-08-01

    Grit blasting (corundum) of an austenitic AISI 304 stainless steel (18Cr-8Ni) and of a low-alloy SA213 T22 ferritic steel (2.25Cr-1Mo) followed by annealing in argon resulted in enhanced outward diffusion of Cr, Mn, and Fe. Whereas 3 bar of blasting pressure allowed to grow more Cr2O3 and Mn x Cr3- x O4 spinel-rich scales, higher pressures gave rise to Fe2O3-enriched layers and were therefore disregarded. The effect of annealing pre-oxidation treatment on the isothermal oxidation resistance was subsequently evaluated for 48 h for both steels and the results were compared with their polished counterparts. The change of oxidation kinetics of the pre-oxidized 18Cr-8Ni samples at 850 °C was ascribed to the growth of a duplex Cr2O3/Mn x Cr3- x O4 scale that remained adherent to the substrate. Such a positive effect was less marked when considering the oxidation kinetics of the 2.25Cr-1Mo steel but a more compact and thinner Fe x Cr3- x O4 subscale grew at 650 °C compared to that of the polished samples. It appeared that the beneficial effect is very sensitive to the experimental blasting conditions. The input of Raman micro-spectroscopy was shown to be of ground importance in the precise identification of multiple oxide phases grown under the different conditions investigated in this study.

  9. Recent activities on the compatibility of the ferritic steel wall with the plasma in the JFT-2M tokamak

    Tsuzuki, K.; Sato, M.; Kawashima, H.; Isei, N.; Kimura, H.; Ogawa, H.; Miyachi, K.; Yamamoto, M.; Shibata, T.

    2002-12-01

    The compatibility of the low activation ferritic steel with a fusion plasma has been investigated in the JFT-2M tokamak. The program consists of three stages. In the first stage, the reduction of fast ion losses was well demonstrated by ferritic steel plates (FPs) outside the vacuum vessel (VV). In the second stage, 20% of the inner surface of the VV was covered by the FPs. The plasma control, stability, and impurity release were preliminary investigated. No deteriorative effect on the plasma was observed at least in the following conditions: partial covering of 20% and the normalized beta value less than 2.8. First boronization was applied to JFT-2M leading to a remarkable decrease of the oxygen impurity. After the boronization, plasmas with the highest normalized beta in JFT-2M were obtained. Thus encouraging results were gained for this stage. In the third stage, the VV was fully covered by FPs, where the ripple reduction and the plasma stability will be investigated as a full scale testing.

  10. Phase transformation and impact properties in the experimentally simulated weld heat-affected zone of a reduced activation ferritic/martensitic steel

    In this work, the phase transformation and impact properties in the weld heat-affected zone (HAZ) of a reduced activation ferritic/martensitic (RAFM) steel are investigated. The HAZs were experimentally simulated using a Gleeble simulator. The base steel consisted of tempered martensite through normalizing at 1000 °C and tempering at 750 °C, while the HAZs consisted of martensite, δ-ferrite and a small volume of autotempered martensite. The impact properties using a Charpy V-notch impact test revealed that the HAZs showed poor impact properties due to the formation of martensite and δ-ferrite as compared with the base steel. In addition, the impact properties of the HAZs further deteriorated with an increase in the δ-ferrite fraction caused by increasing the peak temperature. The impact properties of the HAZs could be improved through the formation of tempered martensite after post weld heat treatment (PWHT), but they remained lower than that of the base steel because the δ-ferrite remained in the tempered HAZs

  11. Articles comprising ferritic stainless steels

    Rakowski, James M.

    2016-06-28

    An article of manufacture comprises a ferritic stainless steel that includes a near-surface region depleted of silicon relative to a remainder of the ferritic stainless steel. The article has a reduced tendency to form an electrically resistive silica layer including silicon derived from the steel when the article is subjected to high temperature oxidizing conditions. The ferritic stainless steel is selected from the group comprising AISI Type 430 stainless steel, AISI Type 439 stainless steel, AISI Type 441 stainless steel, AISI Type 444 stainless steel, and E-BRITE.RTM. alloy, also known as UNS 44627 stainless steel. In certain embodiments, the article of manufacture is a fuel cell interconnect for a solid oxide fuel cell.

  12. Influence of Zr and nano-Y2O3 additions on thermal stability and improved hardness in mechanically alloyed Fe base ferritic alloys

    The motivation of this work was driven to improve the thermal stability in systems where polymorphic transformations can result in an additional driving force, upsetting the expected thermodynamic stability. In this study, Fe92Ni8 alloys with Zr and nano-Y2O3 additions were produced by ball milling and then annealed at high temperatures. Emphasis was placed on understanding the effects of dispersed nano-Y2O3 particle additions and their effect on microstructural stability at and above the bcc-to-fcc transformation occurring at 700 °C in Fe–Ni systems. Results reveal that microstructural stability and hardness can be promoted by a combination of Zr and Y2O3 additions, that being mostly effective for stability before and after phase transition, respectively. The mechanical strength of these alloys is achieved by a unique microstructure comprised a ultra-fine grain Fe base matrix, which contains dispersions of both nano-scale in-situ formed Zr base intermetallics and ex-situ added Y2O3 secondary oxide phases. Both of these were found to be essential for a combination of high thermal stability and high mechanical strength properties. - Highlights: • Polymorphic transformations can limit the processing of nanostructured powders. • It causes a rapid grain growth and impairs the improved mechanical properties. • We aim to improve the hardness and thermal stability above the phase transformation. • Thermal stability is achieved by a combination of Zr and Y2O3 additions. • Hardness is promoted by in-situ formed and ex-situ added secondary nano phases

  13. Experimental study on activating welding for aluminum alloys

    Huang Yong; Fan Ding

    2005-01-01

    TIG welding and EB welding for aluminum alloy 3003 were carried out to study the effects of activating flux on weld penetration of activating welding for aluminum alloys. SiO2 was used as the activating flux. It is found that, SiO2 can increase the weld penetration and decrease the weld width of FBTIG when the flux gap is small. For A-TIG welding and EB welding with focused mode, the weld penetrations and the weld widths increase simultaneously. SiO2 has little effect on the weld penetration and weld width of EB welding with defocused mode. It is believed that, change of surface tension temperature gradient is not the main mechanism of SiO2 improving weld penetration of activating welding for aluminum alloys.

  14. Experimental evidence and thermodynamics analysis of high magnetic field effects on the austenite to ferrite transformation temperature in Fe-C-Mn alloys

    The non-isothermal decomposition of austenite into ferrite and pearlite in Fe-xC-1.5 wt.% Mn steels with x = 0.1, 0.2 and 0.3 wt.% C is investigated by in situ dilatometry and microstructure characterization in magnetic fields up to 16 T. The global shift towards higher temperatures of the respective austenite, ferrite + austenite and ferrite + pearlite stability regions is experimentally quantified. A systematic increase in the ferrite area fraction and proportional reduction of the Vickers hardness values with the magnetic field intensity are also reported. Moreover, the steels' magnetizations, measured up to 3.5 T and 1100 K, are used to calculate the magnetic contribution to the free energy of the transformation and to account thermodynamically for the field dependence of the transformation temperature. The impact of magnetic field is found to be greater with increasing carbon content in the steels.

  15. Experimental evidence and thermodynamics analysis of high magnetic field effects on the austenite to ferrite transformation temperature in Fe-C-Mn alloys

    Garcin, T., E-mail: thomas.garcin@grenoble.cnrs.fr [CNRS/CRETA, 25 rue des martyrs BP166, 38042 Grenoble CEDEX 9 (France); Rivoirard, S. [CNRS/CRETA, 25 rue des martyrs BP166, 38042 Grenoble CEDEX 9 (France); Elgoyhen, C. [CRM Gent, Technologiepark 903c, B-9052 Zwijnaarde (Belgium); Beaugnon, E. [CNRS/CRETA, 25 rue des martyrs BP166, 38042 Grenoble CEDEX 9 (France)

    2010-04-15

    The non-isothermal decomposition of austenite into ferrite and pearlite in Fe-xC-1.5 wt.% Mn steels with x = 0.1, 0.2 and 0.3 wt.% C is investigated by in situ dilatometry and microstructure characterization in magnetic fields up to 16 T. The global shift towards higher temperatures of the respective austenite, ferrite + austenite and ferrite + pearlite stability regions is experimentally quantified. A systematic increase in the ferrite area fraction and proportional reduction of the Vickers hardness values with the magnetic field intensity are also reported. Moreover, the steels' magnetizations, measured up to 3.5 T and 1100 K, are used to calculate the magnetic contribution to the free energy of the transformation and to account thermodynamically for the field dependence of the transformation temperature. The impact of magnetic field is found to be greater with increasing carbon content in the steels.

  16. Superficial effects during the activation of zirconium AB2 alloys

    The activation of zirconium nickel alloys with and without the addition of chromium and titanium is investigated through electrochemical and optical techniques.These alloys show high hydrogen absorption capacity and are extensively used in metal hydride batteries.Recent investigations in aqueous 1 M KOH indicate oxide layer growth and occlusion of hydrogen species in the alloys during the application of different cathodic potential programmes currently used in the activation process.In this research several techniques such as voltammetry, ellipsometry, energy dispersive analysis of X-rays EDAX, and scanning electron microscopy SEM are applied on the polished massive alloy Zr1-xTix, x=0.36 y 0.43, and Zr1-xTixCrNi, x=0.1,0.2 y 0.4.Data analysis shows that the stability, compactness and structure of the passive layers are strongly dependent on the applied potential programme.The alloy activation depends on the formation of deepen crevices that remain after a new polishing. Microscopic observation shows increase in the crevices thickness after the cathodic sweep potential cycling, which produces fragmentation of the grains and oxide growth during the activation process.This indicates metal breaking and intergranular dissolution that take place together with oxide and hydride formation.In some cases the resultant crevice thickness is one or two orders higher than that of the superficial oxide growth indicating intergranular localised corrosion

  17. Evaluation of hardening behaviour of ion irradiated reduced activation ferritic/martensitic steels by an ultra-micro-indentation technique

    The evaluation of the temperature dependence of irradiation hardening in a reduced activation ferritic/martensitic steel (RAFs), F82H (Fe-8Cr-2W-V-Ta) and Ni-doped (1%, 2%) F82H, was performed using single/dual-beam ion irradiation and ultra-micro-indentation technique. In analyzing the load-displacement curve, it was assumed that the elastic modulus did not exceed the original value due to irradiation-induced damage because micro-hardness was defined as a function of composite elastic modulus. Secondly, micro-structural evolution was characterized for irradiation conditions where significant changes in micro-hardness in RAFs were found. Finally, based on these results, the plastic deformation behavior of F82H steels with the irradiation hardening was investigated

  18. HEAT INPUT AND POST WELD HEAT TREATMENT EFFECTS ON REDUCED-ACTIVATION FERRITIC/MARTENSITIC STEEL FRICTION STIR WELDS

    Tang, Wei [ORNL; Chen, Gaoqiang [ORNL; Chen, Jian [ORNL; Yu, Xinghua [ORNL; Frederick, David Alan [ORNL; Feng, Zhili [ORNL

    2015-01-01

    Reduced-activation ferritic/martensitic (RAFM) steels are an important class of structural materials for fusion reactor internals developed in recent years because of their improved irradiation resistance. However, they can suffer from welding induced property degradations. In this paper, a solid phase joining technology friction stir welding (FSW) was adopted to join a RAFM steel Eurofer 97 and different FSW parameters/heat input were chosen to produce welds. FSW response parameters, joint microstructures and microhardness were investigated to reveal relationships among welding heat input, weld structure characterization and mechanical properties. In general, FSW heat input results in high hardness inside the stir zone mostly due to a martensitic transformation. It is possible to produce friction stir welds similar to but not with exactly the same base metal hardness when using low power input because of other hardening mechanisms. Further, post weld heat treatment (PWHT) is a very effective way to reduce FSW stir zone hardness values.

  19. Effect of pre-strain on susceptibility of Indian Reduced Activation Ferritic Martensitic Steel to hydrogen embrittlement

    Sonak, Sagar; Tiwari, Abhishek; Jain, Uttam; Keskar, Nachiket; Kumar, Sanjay; Singh, Ram N.; Dey, Gautam K.

    2015-10-01

    The role of pre-strain on hydrogen embrittlement susceptibility of Indian Reduced Activation Ferritic Martensitic Steel was investigated using constant nominal strain-rate tension test. The samples were pre-strained to different levels of plastic strain and their mechanical behavior and mode of fracture under the influence of hydrogen was studied. The effect of plastic pre-strain in the range of 0.5-2% on the ductility of the samples was prominent. Compared to samples without any pre-straining, effect of hydrogen was more pronounced on pre-strained samples. Prior deformation reduced the material ductility under the influence of hydrogen. Up to 35% reduction in the total strain was observed under the influence of hydrogen in pre-strained samples. Hydrogen charging resulted in increased occurrence of brittle zones on the fracture surface. Hydrogen Enhanced Decohesion (HEDE) was found to be the dominant mechanism of fracture.

  20. Ferritic steels for French LMFBR steam generators

    Austenitic stainless steels have been widely used in many components of the French LMFBR. Up to now, ferritic steels have not been considered for these components, mainly due to their relatively low creep properties. Some ferritic steels are usable when the maximum temperatures in service do not exceed about 5300C. It is the case of the steam generators of the Phenix plant, where the exchange tubes of the evaporator are made of 2,25% Cr-1% Mo steel, stabilized or not by addition of niobium. These ferritic alloys have worked successfully since the first steam production in October 1973. For the SuperPhenix power plant, an ''all austenitic stainless alloy'' apparatus has been chosen. However, for the future, ferritic alloys offer potential for use as alternative materials in the evaporators: low alloys steels type 2,25% Cr-1% Mo (exchange tubes, tube-sheets, shells), or at higher chromium content type 9% Cr-2% Mo NbV (exchange tubes) or 12M Cr-1% Mo-V (tube-sheets). Most of these steels have already an industrial background, and are widely used in similar applications. The various potential applications of these steels are reviewed with regards to the French LMFBR steam generators, indicating that some points need an effort of clarification, for instance the properties of the heterogeneous ferritic/austenitic weldments

  1. On crystallochemical mechanism of small alloying addition effect on dissolution process of corrosion-resistant steels in active state

    Regularities of component dissolution and the changes of the surface layer composition of the Fe-Cr and Fe-Cr-Mo steels are studied. The investigations have been carried out taking as an example high-purity ferrite steels of the FeCr18 and FeCr26 type with Mo content from O to 1.7 and from 0 to 1.2 at. % in 1n H2SO4 respectively at room temperature. The notions of dissolution character of energetically heterogeneous alloy surface are developed. A conclusion is made on the mechanism of inhibitting effect of molybdenum on the anode process of steel dissolution in the active state and on the mechanism of its effect on steel passivation capacity

  2. Microstructure and toughness of Cr-W and Cr-V ferritic steels

    In order to obtain an optimum alloy composition of reduced-activation Cr-W-V ferritic steels, the microstructural evolution during thermal aging at 823-973 K and its effect on the toughness were investigated for simple Cr-W and Cr-V steels by means of transmission electron microscopy and Charpy impact testing. The microstructural evolution of the Cr-W steels was similar to that of the conventional Cr-Mo steels. Carbides precipitated in the martensite and the intermetallic compound Fe2W precipitated in the δ-ferrite of the Cr-W steels. On the other hand, only carbides precipitated in both the martensite and the δ-ferrite of the Cr-V steels. The effect of Cr, W and V on the thermal embrittlement is discussed by taking account of the precipitation behavior. (orig.)

  3. Alloy Design and Development of Cast Cr-W-V Ferritic Steels for Improved High-Temperature Strength for Power Generation Applications

    Klueh, R L; Maziasz, P J; Vitek, J M; Evans, N D; Hashimoto, N

    2006-09-23

    Economic and environmental concerns demand that the power-generation industry seek increased efficiency for gas turbines. Higher efficiency requires higher operating temperatures, with the objective temperature for the hottest sections of new systems {approx} 593 C, and increasing to {approx} 650 C. Because of their good thermal properties, Cr-Mo-V cast ferritic steels are currently used for components such as rotors, casings, pipes, etc., but new steels are required for the new operating conditions. The Oak Ridge National Laboratory (ORNL) has developed new wrought Cr-W-V steels with 3-9% Cr, 2-3% W, 0.25% V (compositions are in wt.%), and minor amounts of additional elements. These steels have the strength and toughness required for turbine applications. Since cast alloys are expected to behave differently from wrought material, work was pursued to develop new cast steels based on the ORNL wrought compositions. Nine casting test blocks with 3, 9, and 11% Cr were obtained. Eight were Cr-W-V-Ta-type steels based on the ORNL wrought steels; the ninth was COST CB2, a 9Cr-Mo-Co-V-Nb cast steel, which was the most promising cast steel developed in a European alloy-development program. The COST CB2 was used as a control to which the new compositions were compared, and this also provided a comparison between Cr-W-V-Ta and Cr-Mo-V-Nb compositions. Heat treatment studies were carried out on the nine castings to determine normalizing-and-tempering treatments. Microstructures were characterized by both optical and transmission electron microscopy (TEM). Tensile, impact, and creep tests were conducted. Test results on the first nine cast steel compositions indicated that properties of the 9Cr-Mo-Co-V-Nb composition of COST CB2 were better than those of the 3Cr-, 9Cr-, and 11Cr-W-V-Ta steels. Analysis of the results of this first iteration using computational thermodynamics raised the question of the effectiveness in cast steels of the Cr-W-V-Ta combination versus the Cr

  4. Microstructure and mechanical properties in the weld heat affected zone of 9Cr-2W-VTa reduced activation ferritic/martensitic steel for fusion

    Reduced activation ferritic/martensitic (RAFM) steel demonstrated excellent resistance to the neutron irradiation and mechanical properties. The investigation of weldability in company with the development of RAFM steel is essential for construction of the fusion reactor. Generally, the superior mechanical properties of the RAFM steel can be upset during welding process due to microstructural change by rapid heating and cooling in the weld heat affected zone (HAZ). The phase transformation and mechanical properties in the weld HAZ of RAFM steel were investigated. The base steel consisted of tempered martensite and two carbides. During rapid welding thermal cycle, the microstructure of the base steel was transformed into martensite and δ-ferrite. In addition, the volume fraction of δ-ferrite and grain size increased with increase in the peak temperature and heat input. The strength of the HAZs was higher than that of the base steel due to the formation of martensite, whereas the impact properties of the HAZs deteriorated as compared with the base steel due to the formation of δ-ferrite. The PWHT improved the impact properties of the HAZs, resulting from the formation of tempered martensite

  5. Microstructure and mechanical properties in the weld heat affected zone of 9Cr-2W-VTa reduced activation ferritic/martensitic steel for fusion

    Moon, Joonoh; Lee, Changhoon; Lee, Taeho; Jang, Minho; Park, Mingu [Korea Institute of Materials Science, Changwon (Korea, Republic of); Kim, Hyoung Chan [National Fusion Research Institute, Daejeon (Korea, Republic of)

    2014-05-15

    Reduced activation ferritic/martensitic (RAFM) steel demonstrated excellent resistance to the neutron irradiation and mechanical properties. The investigation of weldability in company with the development of RAFM steel is essential for construction of the fusion reactor. Generally, the superior mechanical properties of the RAFM steel can be upset during welding process due to microstructural change by rapid heating and cooling in the weld heat affected zone (HAZ). The phase transformation and mechanical properties in the weld HAZ of RAFM steel were investigated. The base steel consisted of tempered martensite and two carbides. During rapid welding thermal cycle, the microstructure of the base steel was transformed into martensite and δ-ferrite. In addition, the volume fraction of δ-ferrite and grain size increased with increase in the peak temperature and heat input. The strength of the HAZs was higher than that of the base steel due to the formation of martensite, whereas the impact properties of the HAZs deteriorated as compared with the base steel due to the formation of δ-ferrite. The PWHT improved the impact properties of the HAZs, resulting from the formation of tempered martensite.

  6. Hydrogen and helium effects on reduced activation Fe-Cr ferrite-martensite and ODS steels

    Malitckii, Evgenii

    2015-01-01

    Significant amounts of hydrogen and helium are generated in the structural materials of the nuclear reactor systems by the interaction of the alloying elements with both fast and thermal neutrons. Hydrogen can also be effectively absorbed by other environmental processes. Helium and hydrogen stabilize the small vacancy clusters and facilitate the further formation of the voids that causes the swelling of the structural steels. At the same time, hydrogen plays an important role in degradation ...

  7. One-step pickling-activation before magnesium alloy plating

    WANG Xin-juan; YU Gang; OUYANG Yue-jun; HE Xiao-mei; ZHANG Jun; YE Li-yuan

    2009-01-01

    A one-step pickling-activation process was proposed as an environmental friendly pretreatment method in phosphate-permanganate solution before electroplating on magnesium alloys. The effects of pickling-activation on qualities of coating were assessed by adhesion and porosity testing of copper plating. The interfacial reactions between specimen and solution were analyzed with SEM, EDX and XRD. The results show that the developed process of pickling-activation can equalize the potentials on substrate surface. The compacted zinc film can be obtained by zinc immersion after treating magnesium alloy in the pH 4-6 phosphate-permanganate solution for 3-5 min. The adhesion and corrosion resistance of copper plating are enhanced. The one-step pickling-activation can replace the existing two-step process of acid pickling and activation which contains a great deal of chromium and fluorine. The procedure of surface pretreatment is simplified and the production environment is improved.

  8. Effects of activating fluxes on the weld penetration and corrosion resistant property of laser welded joint of ferritic stainless steel

    Wang, Yonghui; Hu, Shengsun; Shen, Junqi

    2015-10-01

    This study was based on the ferritic stainless steel SUS430. Under the parallel welding conditions, the critical penetration power values (CPPV) of 3mm steel plates with different surface-coating activating fluxes were tested. Results showed that, after coating with activating fluxes, such as ZrO2, CaCO3, CaF2 and CaO, the CPPV could reduce 100~250 W, which indicating the increases of the weld penetrations (WP). Nevertheless, the variation range of WP with or without activating fluxes was less than 16.7%. Compared with single-component ones, a multi-component activating flux composed of 50% ZrO2, 12.09% CaCO3, 10.43% CaO, and 27.49% MgO was testified to be much more efficient, the WP of which was about 2.3-fold of that without any activating fluxes. Furthermore, a FeCl3 spot corrosion experiment was carried out with samples cut from weld zone to test the effects of different activating fluxes on the corrosion resistant (CR) property of the laser welded joints. It was found that all kinds of activating fluxes could improve the CR of the welded joints. And, it was interesting to find that the effect of the mixed activating fluxes was inferior to those single-component ones. Among all the activating fluxes, the single-component of CaCO3 seemed to be the best in resisting corrosion. By means of Energy Dispersive Spectrometer (EDS) testing, it was found that the use of activating fluxes could effectively restrain the loss of Cr element of weld zone in the process of laser welding, thus greatly improving the CR of welded joints.

  9. The effect of cooling rate and austenite grain size on the austenite to ferrite transformation temperature and different ferrite morphologies in microalloyed steels

    The effect of different austenite grain size and different cooling rates on the austenite to ferrite transformation temperature and different ferrite morphologies in one Nb-microalloyed high strength low alloy steel has been investigated. Three different austenite grain sizes were selected and cooled at two different cooling rates for obtaining austenite to ferrite transformation temperature. Moreover, samples with specific austenite grain size have been quenched, partially, for investigation on the microstructural evolution. In order to assess the influence of austenite grain size on the ferrite transformation temperature, a temperature differences method is established and found to be a good way for detection of austenite to ferrite, pearlite and sometimes other ferrite morphologies transformation temperatures. The results obtained in this way show that increasing of austenite grain size and cooling rate has a significant influence on decreasing of the ferrite transformation temperature. Micrographs of different ferrite morphologies show that at high temperatures, where diffusion rates are higher, grain boundary ferrite nucleates. As the temperature is lowered and the driving force for ferrite formation increases, intragranular sites inside the austenite grains become operative as nucleation sites and suppress the grain boundary ferrite growth. The results indicate that increasing the austenite grain size increases the rate and volume fraction of intragranular ferrite in two different cooling rates. Moreover, by increasing of cooling rate, the austenite to ferrite transformation temperature decreases and volume fraction of intragranular ferrite increases.

  10. Rapid solidification of candidate ferritic steels

    HT-9 and 9Cr-1Mo steels were rapidly solidified by the liquid dynamic compaction process and 2-1/4Cr-1Mo steel was prepared by the ultrasonic gas atomization process. The consolidation was performed in the ferritic temperature range in order to minimize segregation. These alloys will be tested at ORNL using 1/3 CVN test specimens and the results will be compared with those for conventially processed alloys