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Shigeharu Ukai - One of the best experts on this subject based on the ideXlab platform.
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Oxide dispersoid coherency of a ferritic martensitic 12cr Oxide Dispersion Strengthened alloy under self ion irradiation
Journal of Nuclear Materials, 2021Co-Authors: Hyosim Kim, Shigeharu Ukai, Jonathan Gigax, Francis A Garner, Lin ShaoAbstract:Abstract Ferritic-martensitic Oxide-Dispersion-Strengthened (ODS) alloy has shown excellent mechanical property and high radiation tolerance. However, the stability of dispersoids during displacive irradiation in the individual ferritic and martensitic phases is unclear. Here, the correlation among dispersoid coherency, size, density, and matrix phase are studied in dual-phase 12Cr ODS after 100 peak displacements-per-atom (dpa) irradiation at 475°C, using 3.5 MeV Fe2+ self-ions. The size and density changes of coherent and incoherent dispersoids were analyzed as a function of irradiation depth. The average dispersoid size decreased after irradiation in both phases, and the large incoherent dispersoids in the tempered martensite phase underwent a more dramatic change than those in the ferrite phase. The dispersoid density significantly increased in the ferrite phase within the irradiated region, mostly resulting in an increase in coherent dispersoid density. On the other hand, only a small change in density was observed in the tempered martensite phase for both coherent and incoherent dispersoids. This study shows that dispersoid evolution is dramatically different in ferrite and tempered martensite phases.
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Mechanical Behavior of Oxide Dispersion Strengthened Steels Irradiated in JOYO
2020Co-Authors: Shinichiro Yamashita, Shigeharu Ukai, T Yoshitake, Naoaki Akasaka, Akihiko KimuraAbstract:Oxide Dispersion Strengthened (ODS) steels, which are candidate materials for water-cooled solid breeder blankets, were fabricated with several manufacturing parameters, and then irradiated in the experimental fast reactor JOYO to evaluate their irradiation behavior. Engineering stress strain curves of ODS steels irradiated at 673 K exhibited superior material response, i.e., increased tensile strength due to irradiation hardening and no loss of total elongation. Also, their temperature dependence of tensile properties indicated that degradation of the tensile properties at elevated temperature, which is closely related to phase stability during irradiation, could be avoided due to optimal combination of manufacturing parameters, such as chemical composition, types of inert gas during mechanical alloying, heat-treatment temperature and initial phases of the matrix
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effect of helium on dispersoid evolution under self ion irradiation in a dual phase 12cr Oxide Dispersion Strengthened alloy
Materials, 2019Co-Authors: Hyosim Kim, Shigeharu Ukai, Jonathan Gigax, Francis A Garner, Tianyao Wang, Lin ShaoAbstract:As one candidate alloy for future Generation IV and fusion reactors, a dual-phase 12Cr Oxide-Dispersion-Strengthened (ODS) alloy was developed for high temperature strength and creep resistance and has shown good void swelling resistance under high damage self-ion irradiation at high temperature. However, the effect of helium and its combination with radiation damage on Oxide dispersoid stability needs to be investigated. In this study, 120 keV energy helium was preloaded into specimens at doses of 1 × 1015 and 1 × 1016 ions/cm2 at room temperature, and 3.5 MeV Fe self-ions were sequentially implanted to reach 100 peak displacement-per-atom at 475 °C. He implantation alone in the control sample did not affect the dispersoid morphology. After Fe ion irradiation, a dramatic increase in density of coherent Oxide dispersoids was observed at low He dose, but no such increase was observed at high He dose. The study suggests that helium bubbles act as sinks for nucleation of coherent Oxide dispersoids, but dispersoid growth may become difficult if too many sinks are introduced, suggesting that a critical mass of trapping is required for stable dispersoid growth.
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recrystallization of cold rolled Oxide Dispersion Strengthened copper during room temperature annealing
Journal of Alloys and Compounds, 2019Co-Authors: S M S Aghamiri, Shigeharu Ukai, Naoko Oono, Ryuta Kasada, H Noto, Yoshimitsu Hishinuma, T MurogaAbstract:Abstract Static discontinuous recrystallization was studied during room temperature annealing of a newly designed 80% room temperature rolled Oxide Dispersion Strengthened copper. At early stages of annealing, fine new oriented nanosized/submicron grains were recrystallized in the unique matrix of single brass-oriented deformed grain. Upon longer annealing time up to 14 months, the size, area fraction and number density of the recrystallized grains increased significantly along with changing the crystallographic textures. The analysis of misorientation angle distribution of boundaries indicated transformation of low angle boundaries to high angle boundaries results in nucleation of recrystallized grains by significant contribution of static recovery. Furthermore, the constant level of mechanical hardness after recrystallization was interpreted by the balance between grain size hardening, Oxide particle hardening and strain hardening.
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dispersoid stability in ion irradiated Oxide Dispersion Strengthened alloy
Journal of Nuclear Materials, 2018Co-Authors: Hyosim Kim, Shigeharu Ukai, Tianyi Chen, Jonathan Gigax, Francis A Garner, Lin ShaoAbstract:Abstract The radiation response of Oxide dispersoids in a Hf-doped Oxide-Dispersion-Strengthened (ODS) alloy was studied by using 3.5 MeV Fe2+ self-ion irradiation at 475 °C. The size changes of coherent and incoherent dispersoids were studied as a function of depth. Although there was up to 2.6 times difference in local displacements-per-atom (dpa) rate at different characterization depths, the sizes of coherent and incoherent dispersoids did not show a noticeable dependence on dpa rate at depths up to the peak dpa position. In order to explain the experimental observations, the diffusion of solute atoms (dissolved from dispersoids) must take into consideration defect-assisted-diffusion mechanisms. A high dpa rate results in enhanced dispersoid dissolution. On the other hand, dispersoid recovery is increased due to defect-assisted diffusion. Therefore, the two effects are balanced, leading to a relative insensitivity of dispersoid size to dpa rate. The study further shows that both coherent and incoherent dispersoids shrink during irradiation but the final equilibrium sizes of coherent dispersoids are smaller than that of incoherent dispersoids, arising primarily from a difference of their interfacial energies. Incoherent dispersoids undergo more significant volume reduction under irradiation than do coherent dispersoids.
Akihiko Kimura - One of the best experts on this subject based on the ideXlab platform.
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Mechanical Behavior of Oxide Dispersion Strengthened Steels Irradiated in JOYO
2020Co-Authors: Shinichiro Yamashita, Shigeharu Ukai, T Yoshitake, Naoaki Akasaka, Akihiko KimuraAbstract:Oxide Dispersion Strengthened (ODS) steels, which are candidate materials for water-cooled solid breeder blankets, were fabricated with several manufacturing parameters, and then irradiated in the experimental fast reactor JOYO to evaluate their irradiation behavior. Engineering stress strain curves of ODS steels irradiated at 673 K exhibited superior material response, i.e., increased tensile strength due to irradiation hardening and no loss of total elongation. Also, their temperature dependence of tensile properties indicated that degradation of the tensile properties at elevated temperature, which is closely related to phase stability during irradiation, could be avoided due to optimal combination of manufacturing parameters, such as chemical composition, types of inert gas during mechanical alloying, heat-treatment temperature and initial phases of the matrix
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effect of cr al contents on the 475oc age hardening in Oxide Dispersion Strengthened ferritic steels
Nuclear materials and energy, 2016Co-Authors: Shigeharu Ukai, Wentuo Han, Akihiko Kimura, Naoko Oono, Kiyohiro Yabuuchi, Takeji Kaito, T Torimaru, Shigenari HayashiAbstract:Abstract The age-hardening in Oxide Dispersion Strengthened (ODS) ferritic steels with various additions of Cr (12, 15 and 18 wt.%) and Al (0, 5, 7 and 9 wt.%) were investigated. After 5000 h aging at 475 o C, the hardness increases in all these ODS steels, while the increased level depends on the Cr/Al contents. In 12Cr-ODS steels, the more the Al, the higher the increased hardness is. However, in 18Cr-ODS steels, higher Al addition suppresses the age-hardening. TEM observations of 18Cr-ODS steels reveal that 9Al suppresses the formation of Cr-enriched α' phase, while the 18Cr-5Al-ODS steel comprises a plenty of α′ phases. Adding Zr in ODS steels appears to increase the age-hardening. The susceptibility to age-hardening is remarkably lower in the ODS ferritic steels than in the non-ODS ferritic steel with the similar concentration of Cr.
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modifications of grain boundary structure by friction stir welding in the joint of nano structured Oxide Dispersion Strengthened ferritic steel and reduced activation martensitic steel
Scripta Materialia, 2015Co-Authors: Wentuo Han, Dongsheng Chen, Akihiko Kimura, Hisashi Serizawa, Hidetoshi Fujii, Yoshiaki MorisadaAbstract:The joint of Oxide Dispersion Strengthened (ODS) ferritic steel and martensitic steel was produced by friction stir welding. The thermo-mechanical process during welding causes recrystallization in the ODS steel and phase transformation in the martensitic steel. In stir zones of both steels, low-angle boundaries significantly convert to high-angle boundaries. The recrystallization in ODS steel is characterized by the increase in the Σ3 twin boundary with an almost constant fraction of Σ5–Σ29 boundaries, while the martensitic steel shows an opposite trend.
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effects of mechanical force on grain structures of friction stir welded Oxide Dispersion Strengthened ferritic steel
Journal of Nuclear Materials, 2014Co-Authors: Wentuo Han, Yoshiaki Morisada, Dongsheng Chen, Akihiko Kimura, Hisashi Serizawa, Hidetoshi Fujii, Naoto Tsuda, Hiroyuki NotoAbstract:Abstract The weldability of Oxide Dispersion Strengthened (ODS) ferritic steels is a critical obstructive in the development and use of these steels. Friction stir welding has been considered to be a promising way to solve this problem. The main purpose of this work was to reveal the effects of mechanical force on grain structures of friction stir welded ODS ferritic steel. The grain appearances and the misorientation angles of grain boundaries in different welded zones were investigated by the electron backscatter diffraction (EBSD). Results showed that the mechanical force imposed by the stir tool can activate and promote the recrystallization characterized by the transformation of boundaries from LABs to HABs, and contribute to the grain refinement. The type of recrystallization in the stir zone can be classified as the continuous dynamic recrystallization (CDRX).
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stress corrosion cracking susceptibility of Oxide Dispersion Strengthened ferritic steel in supercritical pressurized water dissolved with different hydrogen and oxygen contents
Corrosion Science, 2014Co-Authors: Akihiko KimuraAbstract:Abstract Stress corrosion cracking (SCC) susceptibility was investigated by means of steady strain rate tests for a 15Cr–4Al–2W Oxide Dispersion Strengthened (ODS) ferritic steel in supercritical pressurized water (SCPW) dissolved with different hydrogen (DH) and dissolved oxygen (DO) contents. All the specimens exhibit ductile fracture mode, regardless of the strain rate. The effect of DH and DO on the fracture behavior is negligible. Small cracks were observed at necking region but most of the cracks were identified as “corrosion layer cracking” by cross-sectional observation. The ODS ferritic steel shows no susceptibility to SCC in SCPW at this experimental conditions.
Fujio Abe - One of the best experts on this subject based on the ideXlab platform.
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tem and hrtem study of Oxide particles in an al alloyed high cr Oxide Dispersion Strengthened steel with zr addition
Journal of Nuclear Materials, 2014Co-Authors: Peng Dou, Shigeharu Ukai, Takanari Okuda, Akihiko Kimura, Ryuta Kasada, Masaki Inoue, Somei Ohnuki, Toshiharu Fujisawa, Fujio AbeAbstract:Abstract The nanoparticles in an Al-alloyed high-Cr Oxide Dispersion Strengthened (ODS) ferritic steel with Hf addition, i.e., SOC-16 (Fe-15Cr-2W-0.1Ti-4Al-0.62Hf-0.35Y2O3), have been examined by transmission electron microscopy (TEM) and high resolution transmission electron microscopy (HRTEM). Relative to an Al-alloyed high-Cr ODS ferritic steel without Hf addition, i.e., SOC-9 (Fe-15.5Cr-2W-0.1Ti-4Al-0.35Y2O3), the Dispersion morphology and coherency of the Oxide nanoparticles in SOC-16 were significantly improved. Almost all the small nanoparticles (diameter 10 nm) were also mainly identified as cubic Y2Hf2O7 Oxides with the anion-deficient fluorite structure. The results presented here are compared with those of SOC-9 with a brief discussion of the underlying mechanisms of the unusual thermal and irradiation stabilities of the Oxides as well as the superior strength, excellent irradiation tolerance and extraordinary corrosion resistance of SOC-16.
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polymorphic and coherency transition of y al complex Oxide particles with extrusion temperature in an al alloyed high cr Oxide Dispersion Strengthened ferritic steel
Acta Materialia, 2011Co-Authors: Peng Dou, Shigeharu Ukai, Takanari Okuda, Akihiko Kimura, Masaki Inoue, Somei Ohnuki, Toshiharu Fujisawa, Fujio AbeAbstract:Abstract The phase and metal/Oxide interface structure of the nanometer-scale particles in an Al-alloyed high-Cr Oxide Dispersion Strengthened ferritic steel extruded at 1150 °C and 1050 °C were characterized by high-resolution transmission electron microscopy and diffraction contrast techniques, including weak beam electron microscopy. After extrusion at 1150 °C, yttrium–aluminum–hexagonal (YAH, YAlO3) and yttrium–aluminum–perovskite (YAP, YAlO3) Oxides (diameter ⩽10 nm) constitute ∼55% and 38% of the particles, respectively; ∼78% of the particles (4.5–10 nm in diameter), which include 40% YAH Oxide and 38% YAP phase with misfit (translational) moire fringe spacing of 2.15 nm and 1.65 nm, respectively, are semi-coherent with the matrix. After extrusion at 1050 °C, almost all the particles are YAH phase, and ∼86.5% (diameter
C Capdevila - One of the best experts on this subject based on the ideXlab platform.
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Role of strain heterogeneity on recrystallisation of Oxide Dispersion Strengthened Fe–Cr–Al alloys for high-temperature applications
Journal of Materials Science, 2012Co-Authors: G Pimentel, I. Toda-caraballo, J. Chao, C CapdevilaAbstract:Mechanically alloyed iron-based Oxide Dispersion-Strengthened alloys have the potential for application in heat exchangers for biomass power plants, with operating temperature and pressure at entry of the gas turbine working fluid being around 1,100 °C and 15–30 bar, respectively. The yttria Dispersion in such alloys improves the high-temperature creep and stress rupture life. The strength is further enhanced by the development of a coarse-grained microstructure during recrystallization. Factors controlling the evolution of this desirable microstructure are explored in this study, focusing specifically on PM 2000. The results can be interpreted if it is assumed that anything which makes the microstructure heterogeneous stimulates recrystallization. The combination of these results with finite element modelling is used to interpret the role of strain heterogeneity on the development of recrystallized grain structure. In this sense, larger strain gradients lead to more refined and more isotropic grain structures.
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influence of recrystallization on phase separation kinetics of Oxide Dispersion Strengthened fe cr al alloy
Scripta Materialia, 2012Co-Authors: C Capdevila, M K Miller, G Pimentel, Jesus ChaoAbstract:The effect of different starting microstructures on the kinetics of Fe-rich (α) and Cr-rich (α′) phase separation during aging of Fe–Cr–Al Oxide Dispersion Strengthened (ODS) alloys has been analyzed with a combination of atom probe tomography and thermoelectric power measurements. The results revealed that the high recrystallization temperature necessary to produce a coarse grained microstructure in Fe-base ODS alloys affects the randomness of Cr-atom distributions and defect density, which consequently affect the phase separation kinetics at low annealing temperatures.
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heterogeneous deformation and recrystallisation of iron base Oxide Dispersion Strengthened pm2000 alloy
Materials Science and Technology, 2001Co-Authors: C Capdevila, Y L Chen, Niels Christian Krieger Lassen, A R Jones, H K D H BhadeshiaAbstract:AbstractThe recrystallisation behaviour of PM2000 Oxide Dispersion Strengthened ferritic alloy has been investigated for tube specimens which had been cold deformed after extrusion. The evolution of the recrystallisation temperature, defined as the minimum temperature at which the specimen begins to recrystallise, has been studied in detail as a function of the level of deformation. The microstructure was characterised using optical and transmission electron microscopy, together with microhardness measurements, and local texture measurements obtained using the electron backscattering pattern technique. The results can be interpreted if it is assumed that any procedure that produces a heterogeneous microstructure, stimulates recrystallisation. In this sense, larger strain gradients lead to more refined and more isotropic grain structures. The way in which these results can be exploited for commercial applications is discussed.
Wentuo Han - One of the best experts on this subject based on the ideXlab platform.
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effect of cr al contents on the 475oc age hardening in Oxide Dispersion Strengthened ferritic steels
Nuclear materials and energy, 2016Co-Authors: Shigeharu Ukai, Wentuo Han, Akihiko Kimura, Naoko Oono, Kiyohiro Yabuuchi, Takeji Kaito, T Torimaru, Shigenari HayashiAbstract:Abstract The age-hardening in Oxide Dispersion Strengthened (ODS) ferritic steels with various additions of Cr (12, 15 and 18 wt.%) and Al (0, 5, 7 and 9 wt.%) were investigated. After 5000 h aging at 475 o C, the hardness increases in all these ODS steels, while the increased level depends on the Cr/Al contents. In 12Cr-ODS steels, the more the Al, the higher the increased hardness is. However, in 18Cr-ODS steels, higher Al addition suppresses the age-hardening. TEM observations of 18Cr-ODS steels reveal that 9Al suppresses the formation of Cr-enriched α' phase, while the 18Cr-5Al-ODS steel comprises a plenty of α′ phases. Adding Zr in ODS steels appears to increase the age-hardening. The susceptibility to age-hardening is remarkably lower in the ODS ferritic steels than in the non-ODS ferritic steel with the similar concentration of Cr.
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modifications of grain boundary structure by friction stir welding in the joint of nano structured Oxide Dispersion Strengthened ferritic steel and reduced activation martensitic steel
Scripta Materialia, 2015Co-Authors: Wentuo Han, Dongsheng Chen, Akihiko Kimura, Hisashi Serizawa, Hidetoshi Fujii, Yoshiaki MorisadaAbstract:The joint of Oxide Dispersion Strengthened (ODS) ferritic steel and martensitic steel was produced by friction stir welding. The thermo-mechanical process during welding causes recrystallization in the ODS steel and phase transformation in the martensitic steel. In stir zones of both steels, low-angle boundaries significantly convert to high-angle boundaries. The recrystallization in ODS steel is characterized by the increase in the Σ3 twin boundary with an almost constant fraction of Σ5–Σ29 boundaries, while the martensitic steel shows an opposite trend.
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effects of mechanical force on grain structures of friction stir welded Oxide Dispersion Strengthened ferritic steel
Journal of Nuclear Materials, 2014Co-Authors: Wentuo Han, Yoshiaki Morisada, Dongsheng Chen, Akihiko Kimura, Hisashi Serizawa, Hidetoshi Fujii, Naoto Tsuda, Hiroyuki NotoAbstract:Abstract The weldability of Oxide Dispersion Strengthened (ODS) ferritic steels is a critical obstructive in the development and use of these steels. Friction stir welding has been considered to be a promising way to solve this problem. The main purpose of this work was to reveal the effects of mechanical force on grain structures of friction stir welded ODS ferritic steel. The grain appearances and the misorientation angles of grain boundaries in different welded zones were investigated by the electron backscatter diffraction (EBSD). Results showed that the mechanical force imposed by the stir tool can activate and promote the recrystallization characterized by the transformation of boundaries from LABs to HABs, and contribute to the grain refinement. The type of recrystallization in the stir zone can be classified as the continuous dynamic recrystallization (CDRX).
