Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
neutron diffractionZhou, Y.*; Song, W.*; Zhang, F.*; Wu, Y.*; Lei, Z.*; Jiao, M.*; Zhang, X.*; Dong, J.*; Zhang, Y.*; Yang, M.*; et al.
Journal of Alloys and Compounds, 971, p.172635_1 - 172635_7, 2024/01
被引用回数：0 パーセンタイル：0(Chemistry, Physical)The grain orientation-dependent lattice strain evolution of a (TiZrHfNb)
refractory high-entropy alloy (HEA) during tensile loading has been investigated using neutron diffraction. The equivalent strain-hardening rate of each of the primary 
-oriented grain families was found to be relatively low, manifesting the macroscopically weak work-hardening ability of such a body-centered cubic (BCC)-structured HEA. This finding is indicative of a dislocation planar slip mode that is confined in a few single-slip planes and leads to in-plane softening by high pile-up stresses.
Harjo, S.
日本結晶学会誌, 65(3), p.178 - 182, 2023/08
Observations of deformation behavior of high entropy alloys using neutron diffraction measurements during deformation at various temperatures are reviewed. Neutrons are used to investigate stresses and crystallographic microstructures inside engineering materials, taking advantage of their large penetrating power and the ability to see the arrangement of atoms by diffraction methods. The important structural details of high entropy alloys such as internal stresses, phase conditions, dislocations, texture etc. are discussed in relation to the deformation conditions. Some highlights are introduced: (a) Cooperative deformation in CrMnFeCoNi alloy at ultralow temperatures, (b) Stacking fault energies in CrFeCoNi and CrCoNi alloys, and (c) Load redistribution in eutectic high entropy alloy AlCoCrFeNi
during high temperature deformation.
Lam, T.-N.*; Chin, H.-H.*; Zhang, X.*; Feng, R.*; Wang, H.*; Chiang, C.-Y.*; Lee, S. Y.*; 川崎 卓郎; Harjo, S.; Liaw, P. K.*; et al.
Acta Materialia, 245, p.118585_1 - 118585_9, 2023/02
被引用回数：8 パーセンタイル：78.27(Materials Science, Multidisciplinary)The present study investigates the crystallographic-texture effects on the improved fatigue resistance in the CoCrFeMnNi high-entropy alloys (HEAs) with the full-size geometry of the ASTM Standards E647-99. We exploited X-ray nano-diffraction mapping to characterize the crystal-deformation levels ahead of the crack tip after stress unloading under both constant- and tensile overloaded-fatigue conditions. The crack-tip blunting-induced much higher deformation level was concentrated surrounding the crack-tip which delays the fatigue-crack growth immediately after a tensile overload. The predominant deformation texture orientation in the Paris regime was investigated, using electron backscatter diffraction and orientation distribution function analyses. The twinning formation-driven shear deformation gave rise to the development of the Goss-type texture within the plastic deformation regime under a tensile-overloaded-fatigue condition, which was attributed to enhance the crack deflection and thus the tensile induced crack-growth-retardation period in the CoCrFeMnNi HEA.
Naeem, M.*; He, H.*; Zhang, F.*; Huang, H.*; Harjo, S.; 川崎 卓郎; Wang, B.*; Lan, S.*; Wu, Z.*; Wang, F.*; et al.
Science Advances (Internet), 6(13), p.eaax4002_1 - eaax4002_8, 2020/03
被引用回数：147 パーセンタイル：99.05(Multidisciplinary Sciences)High-entropy alloys exhibit exceptional mechanical properties at cryogenic temperatures, due to the activation of twinning in addition to dislocation slip. The coexistence of multiple deformation pathways raises an important question regarding how individual deformation mechanisms compete or synergize during plastic deformation. Using in situ neutron diffraction, we demonstrate the interaction of a rich variety of deformation mechanisms in high-entropy alloys at 15 K, which began with dislocation slip, followed by stacking faults and twinning, before transitioning to inhomogeneous deformation by serrations. Quantitative analysis showed that the cooperation of these different deformation mechanisms led to extreme work hardening. The low stacking fault energy plus the stable face-centered cubic structure at ultralow temperatures, enabled by the high-entropy alloying, played a pivotal role bridging dislocation slip and serration.
Harjo, S.; Gong, W.; 川崎 卓郎; Naeem, M.*; He, H.*; Wang, X.-L.*
no journal, ,
5元系CrMnFeCoNi高エントロピー合金を77Kで引張変形させると強度増加のみでなく伸びが増加したことが発見されて以来、高エントロピー合金の低温変形挙動に関する研究が重要なトピックスの一つとなった。変形挙動を理解するためには、低温下での機械的特性試験を行うと同時に、内部組織変化も調べて機械的特性変化との関連性の理解が必要である。今までの内部組織観察は、変形試験の前・後において、もしくは、変形試験の途中に中断して、顕微鏡を用いて行われたことは多く、全体の機械的試験の範囲をカバーすることができなかったり、観察領域が狭く試験片全体を代表した情報が得られなかったりすることはしばしばある。J-PARCのTAKUMIは、15Kの温度領域下での変形試験が行える周辺環境装置を完備し、その場中性子回折実験を行うことで、低温下の機械的特性を得ながら回折測定で内部組織変化を同時に調べることができる。得られたCrMnFeCoNi、CrFeCoNi及びCrCoNiの高・中エントロピー合金の低温変形挙動について紹介・比較する。
