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Jinsung Jang - One of the best experts on this subject based on the ideXlab platform.
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Microstructural investigation of oxide dispersion Strengthened Alloy 617 after creep rupture at high temperature
Materials Characterization, 2018Co-Authors: Man Wang, Heung Nam Han, Han Chang-hee, Woo-gon Kim, Jinsung JangAbstract:Abstract Oxide dispersion Strengthened (ODS) Alloys have been widely considered as candidate structural materials for advanced nuclear reactors because of their good high temperature properties and irradiation resistance. In this study, the creep properties of oxide dispersion Strengthened Alloy 617 (ODS-617) was examined at 950 °C under 25 MPa in the air. Conventional Alloy 617 tested under the same conditions was included for comparison. The ODS-617 exhibited superior creep resistance, including a much longer rupture life of 8533 h and a steady-state creep rate of 8.9 × 10−8 (1/s), which was two orders of magnitude lower than that of the conventional Alloy. The lower steady-state creep rate was related to the dispersion of nano-sized Y-Al-O particles, which may impede grain boundary diffusion. It seems that cracks preferentially developed near some large rod-like AlN particles, resulting in the brittle creep fracture mode.
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Precipitation behavior of oxide dispersion Strengthened Alloy 617
Journal of Materials Science, 2017Co-Authors: Mao Xiaodong, Young-bum Chun, Chang-hee Han, Jinsung JangAbstract:Oxide dispersion Strengthened Alloy 617 was prepared by mechanical Alloying and hot extrusion processes. Precipitation behavior during heat treatment was evaluated by XRD, SEM and TEM. It was revealed that the dominant precipitates in the solution-annealed sample were Cr-rich M₂₃C₆ and M₆C precipitates on grain boundaries, and Al–O, Y–Al–O and Y–Ti–O nano-particles in grain interior. Different from a conventional Alloy 617, TiN and TiC precipitates were not found. Aging at 760 °C for 100 h showed that γ′ were not formed, possibly due to the high affinity of O to Al and Ti, which suppressed the formation TiN, TiC and γ′. Heat treatment at high temperatures showed that M₂₃C₆ and Y₂Ti₂O₇ were stable up to 1300 °C, while most Al–O nano-particles evolved into Y–Al–O. The high thermal stability of fine Y₂Ti₂O₇ particles with a high number density is expected to contribute to a superior high temperature mechanical strength than γ′ precipitates .
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Microstructural evolution and tensile properties of oxide dispersion Strengthened Alloy 617 at elevated temperatures
Materials Science and Engineering: A, 2017Co-Authors: Young-bum Chun, Mao Xiaodong, Chang-hee Han, Jinsung JangAbstract:Abstract This study investigated evolution of the microstructure of oxide dispersion Strengthened Alloy 617 with annealing temperature. A mixture of preAlloyed Alloy 617 and Y2O3 powders was mechanically Alloyed and consolidated by hot-extrusion at 1100 °C. Hot extrusion developed a submicron-sized grain structure with M23C6 carbides and finely dispersed Al2O3 and Y2Ti2O7 oxides. The fine-grained structure was stable during subsequent annealing at temperatures up to 1250 °C. Further increase of annealing temperature to 1300 °C resulted in a significantly coarsened grain structure, which was coincident with the abrupt coarsening of oxides. M23C6 carbides in the as-extruded conditions were transformed to M7C3 carbides with complex shapes when annealed at 1200 °C, and their shapes changed to very coarse hexagonal prisms at 1250 °C, which was followed by the formation of eutectic M2C carbides at grain boundaries at 1300 °C. Tensile tests of the as-extruded ODS Alloy 617 showed that the yield strength decreased steeply at a transition temperature of around 600 °C, which can be attributed to diffusional creep along the grain boundaries.
E P George - One of the best experts on this subject based on the ideXlab platform.
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thermal activation parameters of plastic flow reveal deformation mechanisms in the crmnfeconi high entropy Alloy
Acta Materialia, 2018Co-Authors: Guillaume Laplanche, J. Bonneville, Céline Varvenne, William A. Curtin, E P GeorgeAbstract:Abstract To reveal the operating mechanisms of plastic deformation in an FCC high-entropy Alloy, the activation volumes in CrMnFeCoNi have been measured as a function of plastic strain and temperature between 77 K and 423 K using repeated load relaxation experiments. At the yield stress, σ y , the activation volume varies from ∼60 b3 at 77 K to ∼360 b3 at 293 K and scales inversely with yield stress. With increasing plastic strain, the activation volume decreases and the trends follow the Cottrell-Stokes law, according to which the inverse activation volume should increase linearly with σ − σ y (Haasen plot). This is consistent with the notion that hardening due to an increase in the density of forest dislocations is naturally associated with a decrease in the activation volume because the spacing between dislocations decreases. The values and trends in activation volume agree with theoretical predictions that treat the HEA as a high-concentration solid-solution-Strengthened Alloy. These results demonstrate that this HEA deforms by the mechanisms typical of solute strengthening in FCC Alloys, and thus indicate that the high compositional/structural complexity does not introduce any new intrinsic deformation mechanisms.
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Thermal activation parameters of plastic flow reveal deformation mechanisms in the CrMnFeCoNi high-entropy Alloy
Acta Materialia, 2018Co-Authors: Guillaume Laplanche, J. Bonneville, Céline Varvenne, William A. Curtin, E P GeorgeAbstract:To reveal the operating mechanisms of plastic deformation in an FCC high-entropy Alloy, the activation volumes in CrMnFeCoNi have been measured as a function of plastic strain and temperature between 77 K and 423 K using repeated load relaxation experiments. At the yield stress, sigma(y), the activation volume varies from similar to 60 b(3) at 77 K to similar to 360 b(3) at 293 K and scales inversely with yield stress. With increasing plastic strain, the activation volume decreases and the trends follow the Cottrell-Stokes law, according to which the inverse activation volume should increase linearly with sigma - sigma(y) (Haasen plot). This is consistent with the notion that hardening due to an increase in the density of forest dislocations is naturally associated with a decrease in the activation volume because the spacing between dislocations decreases. The values and trends in activation volume agree with theoretical predictions that treat the HEA as a high-concentration solid-solution-Strengthened Alloy. These results demonstrate that this HEA deforms by the mechanisms typical of solute strengthening in FCC Alloys, and thus indicate that the high compositional/structural complexity does not introduce any new intrinsic deformation mechanisms. (C) 2017 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Francis Wagner - One of the best experts on this subject based on the ideXlab platform.
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Static recrystallisation in an ODS FeAl Alloy: The effect of particles on texture and anisotropic grain growth developments
Intermetallics, 2008Co-Authors: Sofiane Guessasma, E. Suzon, Thierry Grosdidier, Francis WagnerAbstract:Abstract Microstructure modifications associated with static recrystallisation in an Oxide Dispersion Strengthened Alloy are investigated by using both experimental (Electron Back-scattered and X-ray Diffraction techniques) and simulation (Monte Carlo) approaches. The morphology of the grains issued from static recrystallisation is influenced significantly by the alignment of the oxide particles in the as-extruded starting material. Monte Carlo simulation is introduced to study the effect of particle distribution, particle alignment, initial grain size and shape on the morphological anisotropy developed in the recrystallised microstructure. Simulation results show significant correlation between grain shape anisotropy and particle availability in the alignment direction. The initial grain size criterion is associated with the separation length between aligned particles to obtain an efficient pinning effect. Grain shape anisotropy can be preserved if an efficient Zener pressure is coupled to an anisotropic grain growth.
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Static recrystallisation in an ODS FeAl Alloy: The effect of particles on texture and anisotropic grain growth developments
Intermetallics, 2008Co-Authors: Sofiane Guessasma, E. Suzon, Thierry Grosdidier, Francis WagnerAbstract:Microstructure modifications associated with static recrystallisation in an Oxide Dispersion Strengthened Alloy are investigated by using both experimental (Electron Back-scattered and X-ray Diffraction techniques) and simulation (Monte Carlo) approaches. The morphology of the grains issued from static recrystallisation is influenced significantly by the alignment of the oxide particles in the as-extruded starting material. Monte Carlo simulation is introduced to study the effect of particle distribution, particle alignment, initial grain size and shape on the morphological anisotropy developed in the recrystallised microstructure. Simulation results show significant correlation between grain shape anisotropy and particle availability in the alignment direction. The initial grain size criterion is associated with the separation length between aligned particles to obtain an efficient pinning effect. Grain shape anisotropy can be preserved if an efficient Zener pressure is cou! pled to an anisotropic grain growth.
K. Shinozaki - One of the best experts on this subject based on the ideXlab platform.
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Transient liquid phase diffusion bonding of iron base oxide dispersion Strengthened Alloy MA 956
Materials Science and Technology, 1995Co-Authors: Y. Nakao, K. ShinozakiAbstract:AbstractTo decrease the completion time during transient liquid phase (TLP) bonding, an Fe basedfiller metal (1M 7), comprising MA 956 base metal containing 7%Si and l%B (wt-%), was developed to join MA 956 base material. Transient liquid phase bonded joints free of microvoids and bondline intermetallic phases were obtained using a bonding temperature of 1563 K, a holding time of 2·16 ks, and an applied pressure of 7·0 MN m−2. The bondline region in the TLP bonded MA 956 base metal had a bamboolike microstructure which was considered to be peculiar to bonded oxide dispersion Strengthened Alloys. For this reason, the growth mechanism of the solid phase during isothermal solidification was evaluated. During tensile testing at 923 K, the joints TLP bonded at 1563 K for 2·16 ks fractured in the base metal zone and consequently the mechanical properties of the joint region and the base metal were similar. The creep rupture properties of the joint regions were close to the base metal properties in the transvers...
Young-bum Chun - One of the best experts on this subject based on the ideXlab platform.
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Precipitation behavior of oxide dispersion Strengthened Alloy 617
Journal of Materials Science, 2017Co-Authors: Mao Xiaodong, Young-bum Chun, Chang-hee Han, Jinsung JangAbstract:Oxide dispersion Strengthened Alloy 617 was prepared by mechanical Alloying and hot extrusion processes. Precipitation behavior during heat treatment was evaluated by XRD, SEM and TEM. It was revealed that the dominant precipitates in the solution-annealed sample were Cr-rich M₂₃C₆ and M₆C precipitates on grain boundaries, and Al–O, Y–Al–O and Y–Ti–O nano-particles in grain interior. Different from a conventional Alloy 617, TiN and TiC precipitates were not found. Aging at 760 °C for 100 h showed that γ′ were not formed, possibly due to the high affinity of O to Al and Ti, which suppressed the formation TiN, TiC and γ′. Heat treatment at high temperatures showed that M₂₃C₆ and Y₂Ti₂O₇ were stable up to 1300 °C, while most Al–O nano-particles evolved into Y–Al–O. The high thermal stability of fine Y₂Ti₂O₇ particles with a high number density is expected to contribute to a superior high temperature mechanical strength than γ′ precipitates .
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Microstructural evolution and tensile properties of oxide dispersion Strengthened Alloy 617 at elevated temperatures
Materials Science and Engineering: A, 2017Co-Authors: Young-bum Chun, Mao Xiaodong, Chang-hee Han, Jinsung JangAbstract:Abstract This study investigated evolution of the microstructure of oxide dispersion Strengthened Alloy 617 with annealing temperature. A mixture of preAlloyed Alloy 617 and Y2O3 powders was mechanically Alloyed and consolidated by hot-extrusion at 1100 °C. Hot extrusion developed a submicron-sized grain structure with M23C6 carbides and finely dispersed Al2O3 and Y2Ti2O7 oxides. The fine-grained structure was stable during subsequent annealing at temperatures up to 1250 °C. Further increase of annealing temperature to 1300 °C resulted in a significantly coarsened grain structure, which was coincident with the abrupt coarsening of oxides. M23C6 carbides in the as-extruded conditions were transformed to M7C3 carbides with complex shapes when annealed at 1200 °C, and their shapes changed to very coarse hexagonal prisms at 1250 °C, which was followed by the formation of eutectic M2C carbides at grain boundaries at 1300 °C. Tensile tests of the as-extruded ODS Alloy 617 showed that the yield strength decreased steeply at a transition temperature of around 600 °C, which can be attributed to diffusional creep along the grain boundaries.
