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Shigeharu Ukai - One of the best experts on this subject based on the ideXlab platform.
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diffusional mass flux accommodating two dimensional grain boundary sliding in ods Ferritic Steel
Acta Materialia, 2019Co-Authors: Hiroshi Masuda, Eiichi Sato, Hirobumi Tobe, Yoshito Sugino, Shigeharu UkaiAbstract:Abstract The interplay between grain boundary sliding (GBS) and atomic diffusion was studied for understanding the fundamental mechanisms of superplasticity and diffusion creep. Two-dimensional GBS was achieved during shear deformation at 900 °C with strain rates of 1.1 × 10−5–3.3 × 10−5 s−1 in oxide dispersion strengthened Ferritic Steel with an anisotropic grain structure, which was designed to minimize the free surface effects including floating grains. Microstructural development during the deformation was observed via electron backscatter diffraction and surface fiducial markers drawn by Ga+ focused ion beam. The plastic flow was predominantly mediated by the cooperative process of GBS and grain boundary diffusion, while other mechanisms including intragranular deformation was hardly recognized. The diffusional flux was typically triggered by local principal stress induced at grain boundaries; the matters flew from overlapping (compressive) to splitting (tensile) grain boundaries. In addition, grain boundary morphology changed from wavy to flat patterns via mass flux from convex to concave sides of grain boundaries to minimize the grain boundary energy. Two distinct interplays between GBS and atomic diffusion were confirmed; the most predominant mode was GBS along the shear strain (i.e. Rachinger sliding) and diffusional accommodation via grain boundaries, while a less amount of Coble diffusion creep along macroscopic principal stress was confirmed with GBS accommodation uncorrelated with the shear strain (i.e. Lifshitz sliding).
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transgranular dislocation activities and substructural evolutions accommodating two dimensional grain boundary sliding in ods Ferritic Steel
Acta Materialia, 2017Co-Authors: Eiichi Sato, Hiroshi Masuda, Hirobumi Tobe, Yoshito Sugino, Shigeharu UkaiAbstract:Abstract Two-dimensional (2D) grain boundary sliding (GBS), which is useful for phenomenological understanding of superplastic and near-superplastic deformation, was achieved during a high-temperature shear test in oxide-dispersion-strengthened Ferritic Steel exhibiting anisotropic microstructure with largely elongated and aligned grains. In this study, 2D GBS, dislocation slip and subsequent microstructural evolutions were examined using surface markers drawn by focused ion beam and electron back-scattered diffraction analysis. In the near-superplastic state (region III), GBS was accommodated by transgranular dislocation activities initiating from grain protrusions or triple junctions into core areas, as described by the Ball–Hutchison model. The accommodation mechanisms were determined by the microstructural correlation between GBS-triggered stress concentration and available slip orientation and were closely related to the angle θ between GBS and dislocation slippage. When θ was small, GBS tended to be accommodated by a group motion of dislocations belonging to {110} or {112} slip systems (slip-band type). When θ was large, GBS tended to be accommodated by intragranular dislocation accumulation, which led to the development of sub-boundaries along {110} planes via dynamic recovery (sub-boundary type); this would be the origin of continuous dynamic recrystallization.
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grain boundary sliding associated with low strain rate at 1000 c in recrystallized ods Ferritic Steel
Nuclear materials and energy, 2016Co-Authors: R Kamikawa, Shigeharu Ukai, Naoko Oono, Takeji Kaito, T Torimaru, A Kimura, Shigenari Hayashi, Hiroshi Masuda, Eiichi SatoAbstract:Abstract The high-temperature deformation process of the recrystallized 16CrODS Ferritic Steel was investigated at 1000 °C for the stress loading perpendicular to the elongated grain structure. The strain rate was varied in the range from 1.0 × 10−2 to 1.0 × 10−5 s−1. At the strain rate over 1.0 × 10−4 s−1, deformation is dominated by the conventional dislocation creep. Decreasing strain rate from 1.0 × 10−4 s−1, grain boundary sliding becomes prominent. Accommodation process for the localized stress induced by grain boundary sliding could be dislocation creep at 1.0 × 10−4 s−1, and by diffusional creep at 1.0 × 10−5 s−1 or less. These were verified through the observation of void formation and localized strain accumulation by KAM map.
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two dimensional grain boundary sliding and mantle dislocation accommodation in ods Ferritic Steel
Acta Materialia, 2016Co-Authors: Eiichi Sato, Hiroshi Masuda, Hirobumi Tobe, Yoshito Sugino, Shigeharu UkaiAbstract:Abstract The mechanism governing grain boundary sliding (GBS) accommodated by dislocation and microstructural evolution in regions II/III and III was studied to understand superplasticity. Two-dimensional GBS that occurred during high-temperature shear in oxide dispersion strengthened Ferritic Steel exhibiting an elongated and aligned grain structure was analyzed using surface markers drawn by focused ion beams. In addition, the accommodating dislocation structure was evaluated by electron back-scattered diffraction and electron channeling contrast imaging. In the initial stage of deformation, GBS triggered dislocation slippage in “mantle” areas near grain boundaries. These mantles tended to appear around GBS-resistant areas such as curved boundaries and grain protrusions. Next, the mantle dislocations generated dislocation walls before forming low-angle boundaries (LABs) along {110} crystallographic planes via dynamic recovery at the core/mantle boundaries. Finally, secondary GBS or rigid rotation occurred at the newly formed LABs to compensate for the initial GBS and resulted in continuous dynamic recrystallization. These mantle dislocation activities and substructural evolution mechanisms were graphically modeled and validated by comparison with previous studies.
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hardness and micro texture in friction stir welds of a nanostructured oxide dispersion strengthened Ferritic Steel
Materials Transactions, 2012Co-Authors: Shigeharu Ukai, Naoko Oono, Shigenari Hayashi, Bin Leng, Qingxin Tang, Yutaka S Sato, Hiroya Numata, Yoshito SuginoAbstract:The goal of this study is to characterize the hardness distribution and texture evolution in a friction stir welded oxide dispersion strengthened (ODS) Ferritic Steel. Hardness profiles were plotted by collecting data on the transverse cross section of the joint. The texture evolution and microstructure characteristics were studied by electron backscattering diffraction (EBSD). Results showed that regions near the bottom of the stir zone were the weak points in hardness, as those regions comprise coarser grains compared with the adjacent regions. EBSD results showed that the grain characterization (size, shape, and aspect ratio) varied within different regions and provided important insight into the material flow within the stir zone. EBSD results also revealed that textures within different regions presented some features of rotating coincidence. By suitable rotations of the poles figures, textures within different regions could superpose with each other almost exactly.
Hiroshi Masuda - One of the best experts on this subject based on the ideXlab platform.
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diffusional mass flux accommodating two dimensional grain boundary sliding in ods Ferritic Steel
Acta Materialia, 2019Co-Authors: Hiroshi Masuda, Eiichi Sato, Hirobumi Tobe, Yoshito Sugino, Shigeharu UkaiAbstract:Abstract The interplay between grain boundary sliding (GBS) and atomic diffusion was studied for understanding the fundamental mechanisms of superplasticity and diffusion creep. Two-dimensional GBS was achieved during shear deformation at 900 °C with strain rates of 1.1 × 10−5–3.3 × 10−5 s−1 in oxide dispersion strengthened Ferritic Steel with an anisotropic grain structure, which was designed to minimize the free surface effects including floating grains. Microstructural development during the deformation was observed via electron backscatter diffraction and surface fiducial markers drawn by Ga+ focused ion beam. The plastic flow was predominantly mediated by the cooperative process of GBS and grain boundary diffusion, while other mechanisms including intragranular deformation was hardly recognized. The diffusional flux was typically triggered by local principal stress induced at grain boundaries; the matters flew from overlapping (compressive) to splitting (tensile) grain boundaries. In addition, grain boundary morphology changed from wavy to flat patterns via mass flux from convex to concave sides of grain boundaries to minimize the grain boundary energy. Two distinct interplays between GBS and atomic diffusion were confirmed; the most predominant mode was GBS along the shear strain (i.e. Rachinger sliding) and diffusional accommodation via grain boundaries, while a less amount of Coble diffusion creep along macroscopic principal stress was confirmed with GBS accommodation uncorrelated with the shear strain (i.e. Lifshitz sliding).
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transgranular dislocation activities and substructural evolutions accommodating two dimensional grain boundary sliding in ods Ferritic Steel
Acta Materialia, 2017Co-Authors: Eiichi Sato, Hiroshi Masuda, Hirobumi Tobe, Yoshito Sugino, Shigeharu UkaiAbstract:Abstract Two-dimensional (2D) grain boundary sliding (GBS), which is useful for phenomenological understanding of superplastic and near-superplastic deformation, was achieved during a high-temperature shear test in oxide-dispersion-strengthened Ferritic Steel exhibiting anisotropic microstructure with largely elongated and aligned grains. In this study, 2D GBS, dislocation slip and subsequent microstructural evolutions were examined using surface markers drawn by focused ion beam and electron back-scattered diffraction analysis. In the near-superplastic state (region III), GBS was accommodated by transgranular dislocation activities initiating from grain protrusions or triple junctions into core areas, as described by the Ball–Hutchison model. The accommodation mechanisms were determined by the microstructural correlation between GBS-triggered stress concentration and available slip orientation and were closely related to the angle θ between GBS and dislocation slippage. When θ was small, GBS tended to be accommodated by a group motion of dislocations belonging to {110} or {112} slip systems (slip-band type). When θ was large, GBS tended to be accommodated by intragranular dislocation accumulation, which led to the development of sub-boundaries along {110} planes via dynamic recovery (sub-boundary type); this would be the origin of continuous dynamic recrystallization.
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grain boundary sliding associated with low strain rate at 1000 c in recrystallized ods Ferritic Steel
Nuclear materials and energy, 2016Co-Authors: R Kamikawa, Shigeharu Ukai, Naoko Oono, Takeji Kaito, T Torimaru, A Kimura, Shigenari Hayashi, Hiroshi Masuda, Eiichi SatoAbstract:Abstract The high-temperature deformation process of the recrystallized 16CrODS Ferritic Steel was investigated at 1000 °C for the stress loading perpendicular to the elongated grain structure. The strain rate was varied in the range from 1.0 × 10−2 to 1.0 × 10−5 s−1. At the strain rate over 1.0 × 10−4 s−1, deformation is dominated by the conventional dislocation creep. Decreasing strain rate from 1.0 × 10−4 s−1, grain boundary sliding becomes prominent. Accommodation process for the localized stress induced by grain boundary sliding could be dislocation creep at 1.0 × 10−4 s−1, and by diffusional creep at 1.0 × 10−5 s−1 or less. These were verified through the observation of void formation and localized strain accumulation by KAM map.
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two dimensional grain boundary sliding and mantle dislocation accommodation in ods Ferritic Steel
Acta Materialia, 2016Co-Authors: Eiichi Sato, Hiroshi Masuda, Hirobumi Tobe, Yoshito Sugino, Shigeharu UkaiAbstract:Abstract The mechanism governing grain boundary sliding (GBS) accommodated by dislocation and microstructural evolution in regions II/III and III was studied to understand superplasticity. Two-dimensional GBS that occurred during high-temperature shear in oxide dispersion strengthened Ferritic Steel exhibiting an elongated and aligned grain structure was analyzed using surface markers drawn by focused ion beams. In addition, the accommodating dislocation structure was evaluated by electron back-scattered diffraction and electron channeling contrast imaging. In the initial stage of deformation, GBS triggered dislocation slippage in “mantle” areas near grain boundaries. These mantles tended to appear around GBS-resistant areas such as curved boundaries and grain protrusions. Next, the mantle dislocations generated dislocation walls before forming low-angle boundaries (LABs) along {110} crystallographic planes via dynamic recovery at the core/mantle boundaries. Finally, secondary GBS or rigid rotation occurred at the newly formed LABs to compensate for the initial GBS and resulted in continuous dynamic recrystallization. These mantle dislocation activities and substructural evolution mechanisms were graphically modeled and validated by comparison with previous studies.
Akihiko Kimura - One of the best experts on this subject based on the ideXlab platform.
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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, Akihiko Kimura, Dongsheng Chen, 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, Akihiko Kimura, Dongsheng Chen, 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.
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ion irradiation hardening of brazed joints of tungsten and oxide dispersion strengthened ods Ferritic Steel
Materials Transactions, 2013Co-Authors: Y Himei, Ryuta Kasada, Takuya Nagasaka, H Noto, Kiyohiro Yabuuchi, S H Noh, Shuhei Nogami, Akihiko KimuraAbstract:Irradiation hardening and microstructural change of the brazed-joint of W and oxide dispersion strengthened Ferritic Steel (ODS-FS) was investigated by nano-indentation hardness test and transmission electron microscopy after ion irradiation with 6.4MeV Fe 3+ ions at 500°C up to 10dpa. Dual-beam irradiation of Fe 3+ ions and energy-degraded 1MeV He + ion was also carried out. A considerable irradiation hardening occurred in the W base metal where dislocation loops and nano-scaled voids or He-bubbles were observed. Dual-beam irradiation enhanced the hardening. No significant hardening was observed in ODS-FS. The hardness of insert material was reduced after irradiation, which is due to the recovery of dislocations generated during joining process. [doi:10.2320/matertrans.MG201212] (Received October 19, 2012; Accepted December 17, 2012; Published February 16, 2013)
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hrtem study of oxide nanoparticles in k3 ods Ferritic Steel developed for radiation tolerance
Journal of Nuclear Materials, 2011Co-Authors: L Hsiung, Akihiko Kimura, M J Fluss, Scott J Tumey, Joshua D Kuntz, Bassem S Eldasher, M A Wall, B Choi, F Willaime, Yves SerruysAbstract:Abstract Crystal and interfacial structures of oxide nanoparticles and radiation damage in 16Cr–4.5Al–0.3Ti–2W–0.37 Y2O3 ODS Ferritic Steel have been examined using high-resolution transmission electron microscopy (HRTEM) techniques. Oxide nanoparticles with a complex-oxide core and an amorphous shell were frequently observed. The crystal structure of complex-oxide core is identified to be mainly monoclinic Y4Al2O9 (YAM) oxide compound. Orientation relationships between the oxide and the matrix are found to be dependent on the particle size. Large particles (>20 nm) tend to be incoherent and have a spherical shape, whereas small particles (
Akira Kohyama - One of the best experts on this subject based on the ideXlab platform.
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effect of joining temperature on the microstructure and strength of tungsten Ferritic Steel joints diffusion bonded with a nickel interlayer
Journal of Materials Processing Technology, 2010Co-Authors: Zhihong Zhong, Hunchea Jung, Tatsuya Hinoki, Akira KohyamaAbstract:Abstract A diffusion bonding process, for joining of tungsten to Ferritic Steel using nickel as an interlayer, was developed for nuclear component application. The effect of joining temperature on the microstructure and tensile strength of the joint was investigated in this work. Metallographic analysis revealed that a good bonding was obtained at both the tungsten/nickel and nickel/Steel interfaces, and the diffusion products were identified in the diffusion zone. Nano-indentation test across the joining interfaces demonstrated the effect of solid solution hardening in the diffusion zone. Tensile test showed that the maximum average tensile strength of ∼200 MPa was obtained for the joint diffusion bonded at 900 °C. The results were discussed in terms of the joining temperature and of the residual stress generated during joining process.
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effect of holding time on the microstructure and strength of tungsten Ferritic Steel joints diffusion bonded with a nickel interlayer
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2009Co-Authors: Zhihong Zhong, Tatsuya Hinoki, Akira KohyamaAbstract:Abstract The microstructural development and mechanical properties of a tungsten/Ferritic Steel diffusion joint with a Ni interlayer, bonded at 900 °C under vacuum for 0.5–2 h, were investigated. Cross-sectional images of the W/Ni diffusion zone indicate the presence of a Ni-rich solid solution, Ni(W), for holding times up to 1.5 h. However, an intermetallic compound Ni4W grew as a distinguishable layer between the W and Ni(W) when the holding time was increased to 2 h. The growth behavior of diffusion layers and their growth mechanism is discussed. On the other hand, smooth changes in concentration of various elements across the Ni/Steel interface were observed for the joints annealed at the holding time studied. An average bond strength of 215 MPa was obtained for the joint bonded for 1 h; this bond strength decreased as holding time increased. Variations in the strength of the joints was significantly related to the microstructural development of the diffusion zone. The formation of Ni4W and a solid solution phase enhanced hardness at the interfaces but reduced strength of the joints.
Eiichi Sato - One of the best experts on this subject based on the ideXlab platform.
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diffusional mass flux accommodating two dimensional grain boundary sliding in ods Ferritic Steel
Acta Materialia, 2019Co-Authors: Hiroshi Masuda, Eiichi Sato, Hirobumi Tobe, Yoshito Sugino, Shigeharu UkaiAbstract:Abstract The interplay between grain boundary sliding (GBS) and atomic diffusion was studied for understanding the fundamental mechanisms of superplasticity and diffusion creep. Two-dimensional GBS was achieved during shear deformation at 900 °C with strain rates of 1.1 × 10−5–3.3 × 10−5 s−1 in oxide dispersion strengthened Ferritic Steel with an anisotropic grain structure, which was designed to minimize the free surface effects including floating grains. Microstructural development during the deformation was observed via electron backscatter diffraction and surface fiducial markers drawn by Ga+ focused ion beam. The plastic flow was predominantly mediated by the cooperative process of GBS and grain boundary diffusion, while other mechanisms including intragranular deformation was hardly recognized. The diffusional flux was typically triggered by local principal stress induced at grain boundaries; the matters flew from overlapping (compressive) to splitting (tensile) grain boundaries. In addition, grain boundary morphology changed from wavy to flat patterns via mass flux from convex to concave sides of grain boundaries to minimize the grain boundary energy. Two distinct interplays between GBS and atomic diffusion were confirmed; the most predominant mode was GBS along the shear strain (i.e. Rachinger sliding) and diffusional accommodation via grain boundaries, while a less amount of Coble diffusion creep along macroscopic principal stress was confirmed with GBS accommodation uncorrelated with the shear strain (i.e. Lifshitz sliding).
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transgranular dislocation activities and substructural evolutions accommodating two dimensional grain boundary sliding in ods Ferritic Steel
Acta Materialia, 2017Co-Authors: Eiichi Sato, Hiroshi Masuda, Hirobumi Tobe, Yoshito Sugino, Shigeharu UkaiAbstract:Abstract Two-dimensional (2D) grain boundary sliding (GBS), which is useful for phenomenological understanding of superplastic and near-superplastic deformation, was achieved during a high-temperature shear test in oxide-dispersion-strengthened Ferritic Steel exhibiting anisotropic microstructure with largely elongated and aligned grains. In this study, 2D GBS, dislocation slip and subsequent microstructural evolutions were examined using surface markers drawn by focused ion beam and electron back-scattered diffraction analysis. In the near-superplastic state (region III), GBS was accommodated by transgranular dislocation activities initiating from grain protrusions or triple junctions into core areas, as described by the Ball–Hutchison model. The accommodation mechanisms were determined by the microstructural correlation between GBS-triggered stress concentration and available slip orientation and were closely related to the angle θ between GBS and dislocation slippage. When θ was small, GBS tended to be accommodated by a group motion of dislocations belonging to {110} or {112} slip systems (slip-band type). When θ was large, GBS tended to be accommodated by intragranular dislocation accumulation, which led to the development of sub-boundaries along {110} planes via dynamic recovery (sub-boundary type); this would be the origin of continuous dynamic recrystallization.
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grain boundary sliding associated with low strain rate at 1000 c in recrystallized ods Ferritic Steel
Nuclear materials and energy, 2016Co-Authors: R Kamikawa, Shigeharu Ukai, Naoko Oono, Takeji Kaito, T Torimaru, A Kimura, Shigenari Hayashi, Hiroshi Masuda, Eiichi SatoAbstract:Abstract The high-temperature deformation process of the recrystallized 16CrODS Ferritic Steel was investigated at 1000 °C for the stress loading perpendicular to the elongated grain structure. The strain rate was varied in the range from 1.0 × 10−2 to 1.0 × 10−5 s−1. At the strain rate over 1.0 × 10−4 s−1, deformation is dominated by the conventional dislocation creep. Decreasing strain rate from 1.0 × 10−4 s−1, grain boundary sliding becomes prominent. Accommodation process for the localized stress induced by grain boundary sliding could be dislocation creep at 1.0 × 10−4 s−1, and by diffusional creep at 1.0 × 10−5 s−1 or less. These were verified through the observation of void formation and localized strain accumulation by KAM map.
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two dimensional grain boundary sliding and mantle dislocation accommodation in ods Ferritic Steel
Acta Materialia, 2016Co-Authors: Eiichi Sato, Hiroshi Masuda, Hirobumi Tobe, Yoshito Sugino, Shigeharu UkaiAbstract:Abstract The mechanism governing grain boundary sliding (GBS) accommodated by dislocation and microstructural evolution in regions II/III and III was studied to understand superplasticity. Two-dimensional GBS that occurred during high-temperature shear in oxide dispersion strengthened Ferritic Steel exhibiting an elongated and aligned grain structure was analyzed using surface markers drawn by focused ion beams. In addition, the accommodating dislocation structure was evaluated by electron back-scattered diffraction and electron channeling contrast imaging. In the initial stage of deformation, GBS triggered dislocation slippage in “mantle” areas near grain boundaries. These mantles tended to appear around GBS-resistant areas such as curved boundaries and grain protrusions. Next, the mantle dislocations generated dislocation walls before forming low-angle boundaries (LABs) along {110} crystallographic planes via dynamic recovery at the core/mantle boundaries. Finally, secondary GBS or rigid rotation occurred at the newly formed LABs to compensate for the initial GBS and resulted in continuous dynamic recrystallization. These mantle dislocation activities and substructural evolution mechanisms were graphically modeled and validated by comparison with previous studies.