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Luo, M.-Y.*; Lam, T.-N.*; Wang, P.-T.*; Tsou, N.-T.*; Chang, Y.-J.*; Feng, R.*; 川崎 卓郎; Harjo, S.; Liaw, P. K.*; Yeh, A.-C.*; et al.
Scripta Materialia, 210, p.114459_1 - 114459_7, 2022/03
被引用回数：14 パーセンタイル：91.45(Nanoscience & Nanotechnology)The effect of grain size on strain-controlled low-cycle fatigue (LCF) properties in the CoCrFeMnNi high-entropy alloys (HEAs) was investigated towards the distinct microstructural developments during cyclic loading at a strain amplitude of 
1.0%. A much more prominent secondary cyclic hardening (SCH) behavior at the final deformation stage was observed in the fine-grained (FG) than in the coarse-grained (CG) CoCrFeMnNi. In-situ neutron-diffraction and microscopic examination, strongly corroborated by molecular dynamic (MD) simulations, indicated that dislocation activities from planar slip to wavy slip-driven subgrain structures within the grains acted as the primary cyclic-deformation behaviors in the FG CoCrFeMnNi. Differently observed in the cyclic behavior of the CG CoCrFeMnNi was due to a transition from the planar dislocation slip to twinning.
Lam, T.-N.*; Luo, M.-Y.*; 川崎 卓郎; Harjo, S.; Jain, J.*; Lee, S.-Y.*; Yeh, A.-C.*; Huang, E.-W.*
Crystals (Internet), 12(2), p.157_1 - 157_9, 2022/02
被引用回数：6 パーセンタイル：87.21(Crystallography)In this research, we systematically investigated equiatomic CoCrFeNi and CoCrFeMnNi high-entropy alloys (HEAs). Both of these HEA systems are single-phase, face-centered-cubic (FCC) structures. Specifically, we examined the tensile response in as-cast quaternary CoCrFeNi and quinary CoCrFeMnNi HEAs at room temperature. Compared to CoCrFeNi HEA, the elongation of CoCrFeMnNi HEA was 14% lower, but the yield strength and ultimate tensile strength were increased by 17% and 6%, respectively. The direct real-time evolution of structural defects during uniaxial straining was acquired via in situ neutron-diffraction measurements. The dominant microstructures underlying plastic deformation mechanisms at each deformation stage in as-cast CoCrFeNi and CoCrFeMnNi HEAs were revealed using the Convolutional Multiple Whole Profile (CMWP) software for peak-profile fitting. The possible mechanisms are reported.
Lam, T.-N.*; Lee, S. Y.*; Tsou, N.-T.*; Chou, H.-S.*; Lai, B.-H.*; Chang, Y.-J.*; Feng, R.*; 川崎 卓郎; Harjo, S.; Liaw, P. K.*; et al.
Acta Materialia, 201, p.412 - 424, 2020/12
被引用回数：33 パーセンタイル：91.53(Materials Science, Multidisciplinary)We examined fatigue-crack-growth behaviors of CoCrFeMnNi high-entropy alloys (HEAs) under as-fatigued and tensile-overloaded conditions using neutron-diffraction measurements coupled with diffraction peak-profile analyses. We applied both high-resolution transmission electron microscopy (HRTEM) and neutron-diffraction strain mapping for the complementary microstructure examinations. Immediately after a single tensile overload, the crack-growth-retardation period was obtained by enhancing the fatigue resistance, as compared to the as-fatigued condition. The combined mechanisms of the overload-induced larger plastic deformation, the enlarged compressive residual stresses and plastic-zone size, the crack-tip blunting ahead of the crack tip, and deformation twinning governed the pronounced macroscopic crack-growth-retardation behavior following the tensile overload.
Lam, T.-N.*; Chou, Y.-S.*; Chang, Y.-J.*; Sui, T.-R.*; Yeh, A.-C.*; Harjo, S.; Lee, S. Y.*; Jain, J.*; Lai, B.-H.*; Huang, E.-W.*
Crystals (Internet), 9(8), p.420_1 - 420_8, 2019/08
被引用回数：9 パーセンタイル：67.83(Crystallography)An equal-molar CoCrFeMnNi, face-centered-cubic (fcc) high-entropy alloy (HEA) and a nickel-based superalloy are studied using in situ neutron diffraction experiments. With continuous measurements, the evolution of diffraction peaks is collected for microscopic lattice strain analyses. Cyclic hardening and softening are found in both metallic systems. However, as obtained from the diffraction-peak-width evolution, the underneath deformation mechanisms are quite different. The CoCrFeMnNi HEA exhibits distinct lattice strain and microstructure responses under tension-compression cyclic loadings.
Illman, W. A.*; Liu, X.*; 竹内 真司; Yeh, T.-C. J.*; 安藤 賢一*; 三枝 博光
Water Resources Research, 45(1), p.W01406_1 - W01406_18, 2009/00
被引用回数：182 パーセンタイル：82.4(Environmental Sciences)瑞浪超深地層研究所周辺に分布する深層ボーリング孔を用いて、異なる2回の大規模孔間試験を実施した。その結果に基づいて、非定常水圧トモグラフィ(THT)の解析を実施し、透水係数(
)と比貯留係数(
)を不確実性の空間分布とともに求めた。さらに等価なとを求め、三次元逆解析モデルへの初期パラメータとして使用した。その結果、顕著に高いと低いのゾーンが数百メートルにわたって連続することがわかった。さらに、低いを示すゾーンが認識された。これは事前に遮水性と予測されたNNW断層に相当するゾーンである。以上の結果は、(1)水位変化、(2)予測されている断層の分布、(3)揚水に伴う最大水位低下量、(4)揚水に伴う水位変動の応答時間、そして(5)複数の大規模地震に同期した水位変動と整合的である。
Illman, W. A.*; Liu, X.*; Yeh, J.*; 安藤 賢一*; 竹内 真司; 三枝 博光
no journal, ,
瑞浪超深地層研究所において2回の孔間水理試験を実施した。その結果を非定常水理トモグラフィ(THT: Transient Hydraulic Tomography)コードを用いて解析を行い、透水係数と比貯留係数の3次元分布を比較した。その結果、高い透水係数と低い比貯留係数が550mから1200mの範囲にわたって分布し、これらが2つの断層帯を形成していることが示された。また透水係数と比貯留係数は負の相関を有し、このため水圧伝播が早いことが明らかとなった。さらにTHTコードによる解析により、低透水性ゾーンの存在が表現された。これは、既に予測している北北西走向の遮水性断層と整合している。解析結果の妥当性の確認については、地質学的な情報,揚水に伴う応答時間,伝播速度などにより実施した。
