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Gu, G. H.*; Jeong, S. G.*; Heo, Y.-U.*; Harjo, S.; Gong, W.; Cho, J.*; Kim, H. S.*; 他4名*
Journal of Materials Science & Technology, 223, p.308 - 324, 2025/07
被引用回数：0 パーセンタイル：0.00(Materials Science, Multidisciplinary)Face-centered cubic (FCC) equi-atomic multi-principal element alloys (MPEAs) exhibit excellent mechanical properties from cryogenic to room temperatures. At room temperature, deformation is dominated by dislocation slip, while at cryogenic temperatures (CTs), reduced stacking fault energy enhances strain hardening with twinning. This study uses in-situ neutron diffraction to analyze the temperature-dependent deformation behavior of Al
(CoNiV)
, a dual-phase (FCC/BCC) medium-entropy alloy (MEA). At liquid nitrogen temperature (LNT), deformation twinning in the FCC matrix leads to additional strain hardening through the dynamic Hall-Petch effect, giving the appearance of improved strengthening at LNT. In contrast, BCC precipitates show dislocation slip at both 77 K and 298 K, with temperature-dependent lattice friction stress playing a significant role in strengthening. The study enhances understanding of deformation behaviors and provides insights for future alloy design.
Wang, Y.*; Gong, W.; Harjo, S.; 他7名*
Acta Materialia, 288, p.120840_1 - 120840_14, 2025/04
被引用回数：0Low yield strength and the presence of Luders bands constitute principal impediments to the extensive applications of conventional medium Mn steels with a duplex microstructure of ferrite and austenite. Flash heating and the concept of chemical heterogeneity have been combined to engineer a duplex austenite-martensite microstructure in medium Mn steels, which has proven effective in augmenting the yield strength and mitigating the occurrence of Luders bands. However, the underlying mechanisms remain ambiguous. In the present work, the effect of austenite stability on yielding behavior was systematically investigated in an austenite-martensite duplex medium Mn steel. Austenite stability was identified as the critical factor governing yield strength, where reduced stability promotes early stage deformation induced martensite transformation, thereby decreasing yield strength. Diminished austenite stability may as well induce enhanced work hardening, thereby result in the inclination and eventual elimination of yield plateau, concomitant with the disappearance of Luders bands. These observations expand our current understanding of the yielding behavior in medium Mn steels and offer insights for the design of other advanced high strength steels.
neutron diffraction study伊東 達矢; 小川 祐平*; Gong, W.; Mao, W.*; 川崎 卓郎; 岡田 和歩*; 柴田 曉伸*; Harjo, S.
Acta Materialia, 287, p.120767_1 - 120767_16, 2025/04
被引用回数：0 パーセンタイル：0.00(Materials Science, Multidisciplinary)Incorporating solute hydrogen into Fe-Cr-Ni-based austenitic stainless steels enhances both strength and ductility, providing a promising solution to hydrogen embrittlement by causing solid-solution strengthening and assisting deformation twinning. However, its impacts on the relevant lattice defects evolution (
, dislocations, stacking faults, and twins) during deformation remains unclear. This study compared the tensile deformation behavior in an Fe-24Cr-19Ni (mass%) austenitic steel with 7600 atom ppm hydrogen-charged (H-charged) and without hydrogen-charged (non-charged) using neutron diffraction. Hydrogen effects on the lattice expansion, solid-solution strengthening, stacking fault probability, stacking fault energy, dislocation density, and strain/stress for twin evolution were quantitatively evaluated to link them with the macroscale mechanical properties. The H-charged sample showed improvements in yield stress, flow stress, and uniform elongation, consistent with earlier findings. However, solute hydrogen exhibited minimal influences on the evolution of dislocation and stacking fault. This fact contradicts the previous reports on hydrogen-enhanced dislocation and stacking fault evolutions, the latter of which can be responsible for the enhancement of twinning. The strain for twin evolution was smaller in the H-charged sample compared to the non-charged one. Nevertheless, when evaluated as the onset stress for twin evolution, there was minimal change between the two samples. These findings suggest that the increase in flow stress due to the solid-solution strengthening by hydrogen is a root cause of accelerated deformation twinning at a smaller strain, leading to an enhanced work-hardening rate and improved uniform elongation.
Pandian, K.*; Neikter, M.*; Ekh, M.*; Harjo, S.; 川崎 卓郎; Woracek, R.*; Hansson, T.*; Pederson, R.*
JOM, 77(4), p.1803 - 1815, 2025/04
To produce dense Ti-6Al-4V components, electron beam powder bed fusion is typically followed by post-heat treatment like hot isostatic pressing (HIP). Standard HIP at 920
C/100 MPa for 2 h coarsens the microstructure and reduces yield strength, while low-temp HIP at 800C/200 MPa for 2 h limits coarsening and retains strength comparable to as-built material. A coarser microstructure negatively affects tensile properties. Tensile tests at various temperatures suggest that thermally activated slip systems may influence elongation, requiring further study. In situ neutron time-of-flight diffraction during tensile loading enables analysis of strain evolution and slip plane activity. A two-phase elastic-plastic self-consistent model was used to compare with experiments. Results show basal slip {0002} activated at 20C, pyramidal slip {10-11} at 350C, and 
phase carrying higher stress than 
in the plastic regime.
川崎 卓郎; 福田 竜生; 山中 暁*; 村山 一郎*; 加藤 孝典*; 馬場 将亮*; 橋本 英樹*; Harjo, S.; 相澤 一也; 田中 裕久*; et al.
Journal of Applied Physics, 137(9), p.094101_1 - 094101_7, 2025/03
被引用回数：0Energy harvesting from waste heat can improve energy efficiency in society. This research investigated the structural behaviors of lead zirconate titanate-based ferroelectric ceramics using operando neutron diffraction measurements under the conditions of two energy-harvesting cycles that involve consideration of the temperature changes of automobile exhaust gas for achieving good harvesting efficiencies. Input and output electrical energies and neutron diffraction data were simultaneously collected. The obtained time-resolved neutron-diffraction intensity data indicate that the applied electric fields and temperature changes induced 90
domain rotation and lattice strain. These structural changes and their variations depending on cycle conditions, such as temperature changes, applied electric fields, and circuit switching, provide insight into the origins of the differences in the behaviors of electrical input/output energies in the cycles.
Naeem, M.*; Ma, Y.*; Tian, J.*; Kong, H.*; Romero-Resendiz, L.*; Fan, Z.*; Jiang, F.*; Gong, W.; Harjo, S.; Wu, Z.*; et al.
Materials Science & Engineering A, 924, p.147819_1 - 147819_10, 2025/02
被引用回数：0 パーセンタイル：0.00(Nanoscience & Nanotechnology)Face-centered cubic (fcc) medium-/high-entropy alloys (M/HEAs) typically enhance strength and ductility at cryogenic temperatures via stacking faults, twinning, or martensitic transformation. However, in-situ neutron diffraction on VCoNi MEA at 15 K reveals that strain hardening is driven solely by rapid dislocation accumulation, without these mechanisms. This results in increased yield strength, strain hardening, and fracture strain. The behavior, explained by the Orowan equation, challenges conventional views on cryogenic strengthening in fcc M/HEAs and highlights the role of dislocation-mediated plasticity at low temperatures.
Song, Y.*; Xu, S.*; 佐藤 駿介*; Lee, I.*; Xu, X.*; 大森 俊洋*; 長迫 実*; 川崎 卓郎; 鬼柳 亮嗣; Harjo, S.; et al.
Nature, 638, p.965 - 971, 2025/02
被引用回数：1In advanced applications like aerospace and space exploration, materials must balance lightness, functionality, and extreme thermal fluctuation resistance. Shape-memory alloys show promise with strength, toughness, and substantial strain recovery due to superelasticity, but maintaining low mass and effective operation at cryogenic temperatures is challenging. We hereby introduce a novel shape-memory alloy that adheres to these stringent criteria. Predominantly composed of Ti and Al with a chemical composition of Ti
Al
Cr
, this alloy 25 is characterized by a low density (4.36
10
kg/m) and a high specific strength (18510 Pa
m/kg) at room temperature, while exhibiting excellent superelasticity. The superelasticity, owing to a reversible stress-induced phase transformation from an ordered body-centered cubic parent phase to an ordered orthorhombic martensite, allows for a recoverable strain exceeding 7%. Remarkably, this functionality persists across a broad range of temperatures, from deep cryogenic 4.2 K to above room temperature, arising from an unconventional temperature dependence of transformation stresses. Below a certain threshold during cooling, the critical transformation stress inversely correlates with temperature. We interpret this behavior from the perspective of a temperature-dependent anomalous lattice instability of the parent phase. This alloy holds potential in everyday appliances requiring flexible strain accommodations, as well as components designed for extreme environmental conditions such as deep space and liquefied gases.
neutron diffraction measurement during tensile deformation山下 享介*; 諸岡 聡; Gong, W.; 川崎 卓郎; Harjo, S.; 北條 智彦*; 興津 貴隆*; 藤井 英俊*
ISIJ International, 64(14), p.2051 - 2060, 2024/12
An Fe-0.15C-5Mn-0.5Si-0.05Nb steel annealed at 660C and 685C showed L
ders deformation followed by high work hardening, with variations in Lders strain and hardening behavior. 
neutron diffraction during tensile tests analyzed phase stresses, strength contributions, and austenite orientation. Deformation-induced martensite contributed 
1000 MPa to strength near tensile failure, while austenite mainly enhanced ductility via transformation-induced plasticity. Austenite transformed to martensite during Lders deformation regardless of orientation, though 311-oriented grains tended to remain along the tensile direction.
Sn strands in ITER central solenoid conductors of short and long twist pitch諏訪 友音*; 礒野 高明*; Harjo, S.; 川崎 卓郎; 相澤 一也
Superconductor Science and Technology, 38(1), p.015008_1 - 015008_8, 2024/12
被引用回数：0 パーセンタイル：0.00(Physics, Applied)The ITER central solenoid (CS) conductors are composed of NbSn superconducting cables and stainless steel jackets. Approximately 60,000 electromagnetic loading cycles will be applied to the NbSn strands in the CS conductor over the course of ITER tokamak operation, and the CS conductor is required to maintain the current sharing temperature (
) for these electromagnetic loading cycles. However, in CS conductor prototypes, degradation of was observed after electromagnetic loading cycles. Visual inspections of the tested CS conductors revealed large bending and buckling of the NbSn strands. These strand deformations were considered to be the cause of degradation because even a small amount of strain markedly affects the critical current of NbSn strands. To prevent the strands from bending and buckling, the twist pitch of the cable was shortened to improve stiffness. The stiffer cables did prevent from degrading after electromagnetic loading cycles owing to the shortened twist pitch of the conductors, but a slight increase of was observed. Visual inspections revealed no significant bent or buckled strands, but small deformations cannot be investigated visually. Thus, internal strain was measured by neutron diffraction and the internal strain states of the prototype CS conductors having long twist pitches and the improved short-twist-pitch (STP) CS conductors were evaluated. The results indicated that, after electromagnetic loading cycles, bending of the strands in the STP CS conductor was limited and compressive strain was reduced. Therefore, we determined that this STP is not only effective to prevent degradation caused by bent strands but it also increases by reducing compressive strain.
neutron diffractionNaeem, M.*; Ma, Y.*; Knowles, A. J.*; Gong, W.; Harjo, S.; Wang, X.-L.*; Romero-Resendiz, L.*; 他6名*
Materials Science & Engineering A, 916, p.147374_1 - 147374_8, 2024/11
被引用回数：2 パーセンタイル：54.79(Nanoscience & Nanotechnology)Heterostructured materials (HSMs) improve the strength-ductility trade-off of alloys, but their cryogenic performance under real-time deformation is unclear. We studied heterostructured CrCoNi medium-entropy alloy via neutron diffraction at 77 K and 293 K. A significant mechanical mismatch between fine and coarse grains led to an exceptional yield strength of 918 MPa at 293 K, increasing to 1244 MPa at 77 K with a uniform elongation of 34%. This strength-ductility synergy at 77 K is attributed to high dislocation pile-up density, increased planar faults, and martensitic transformation. Compared to homogeneous alloys, HSMs show promise for enhancing cryogenic mechanical performance in medium-/high-entropy alloys.
neutron diffraction study to elucidate hydrogen effect on the deformation mechanism in Type 310S austenitic stainless steel伊東 達矢; 小川 祐平*; Gong, W.; Mao, W.*; 川崎 卓郎; 岡田 和歩*; 柴田 曉伸*; Harjo, S.
Proceedings of the 7th International Symposium on Steel Science (ISSS 2024), p.237 - 240, 2024/11
Hydrogen embrittlement has long been an obstacle to the development of safe infrastructure. However, in contrast to hydrogen's embrittling effect, recent research has revealed that the addition of hydrogen improves both the strength and uniform elongation of AISI Type 310S austenitic stainless steel. A detailed understanding of how hydrogen affects the deformation mechanism of this steel could pave the way for the development of more advanced materials with superior properties. In the present study, neutron diffraction experiments were conducted on Type 310S steel with and without hydrogen-charged to investigate the effect of hydrogen on the deformation mechanism. In addition to the effect of solid-solution strengthening by hydrogen, the q-value, a parameter representing the proportion of edge and screw dislocations in the accumulated dislocations, was quantitatively evaluated using CMWP analysis on neutron diffraction patterns. The comparison of q-values between the hydrogen-charged and non-charged samples reveals that hydrogen has minimal effect on dislocation character in Type 310S steel.
Harjo, S.; Mao, W.*; Gong, W.; 川崎 卓郎
Proceedings of the 7th International Symposium on Steel Science (ISSS 2024), p.205 - 208, 2024/11
This study aimed to elucidate the effect of grain size on the deformation behavior of TRIP steel. We prepared metastable austenitic Fe-24Ni-0.3C steel samples with average grain sizes of 35 
m (coarse grain: CG) and 0.5 m (ultrafine-grain: UFG) for in situ neutron diffraction studies during tensile deformation at room temperature. Our observations revealed increases in dislocation density in both samples prior to DIMT, indicating that plastic deformation precedes DIMT regardless of grain size. In the UFG sample, a significant rise in dislocation density occurred just around the yielding point with minimal increases in macroscopic plastic strain. Additionally, the dislocations exhibited strong dipole arrangements.
Mao, W.*; Gao, S.*; Gong, W.; 川崎 卓郎; 伊東 達矢; Harjo, S.; 辻 伸泰*
Acta Materialia, 278, p.120233_1 - 120233_13, 2024/10
被引用回数：5 パーセンタイル：73.35(Materials Science, Multidisciplinary)Using a hybrid method of in situ neutron diffraction and digital image correlation, we found that ultrafine-grained 304 stainless steel exhibits Luders deformation after yielding, in which the deformation behavior changes from a cooperation mechanism involving dislocation slip and martensitic transformation to one primarily governed by martensitic transformation, as the temperature decreases from 295 K to 77 K. Such martensitic transformation-governed Luders deformation delays the activation of plastic deformation in both the austenite parent and martensite product, resulting in delayed strain hardening. This preserves the strain-hardening capability for the later stage of deformation, thereby maintaining a remarkable elongation of 29% while achieving a high tensile strength of 1.87 GPa at 77 K.
Zhang, Y.-J.*; 梅田 岳昌*; 諸岡 聡; Harjo, S.; 宮本 吾郎*; 古原 忠*
Metallurgical and Materials Transactions A, 55(10), p.3921 - 3936, 2024/10
被引用回数：0 パーセンタイル：0.00(Materials Science, Multidisciplinary)In this study, a series of eutectoid steels with Mn addition up to 2 mass% were isothermally transformed at various temperatures from 873 K to 973 K to clarify the pearlite growth kinetics and the underlying thermodynamics at its growth front. The microscopic observation indicates the acceleration in pearlite growth rate and refinement in lamellar spacing by decreasing the transformation temperature or the amount of Mn addition. After analyzing the solute distribution at pearlite growth front via three-dimensional atom probe, no macroscopic Mn partitioning across pearlite/austenite interface is detected, whereas Mn segregation is only observed at ferrite/austenite interface. Furthermore, in-situ neutron diffraction measurements performed at elevated temperatures reveals that the magnitude of elastic strain generated during pearlite transformation is very small.
Zhu, L.*; He, H.*; Naeem, M.*; Sun, X.*; Qi, J.*; Liu, P.*; Harjo, S.; 中島 健次; Li, B.*; Wang, X.-L.*
Physical Review Letters, 133(12), p.126701_1 - 126701_6, 2024/09
被引用回数：1 パーセンタイル：58.36(Physics, Multidisciplinary)It has long been suspected that magnetism could play a vital role in the phase stability of multi- component high-entropy alloys. However, the nature of the magnetic order, if any, has remained elusive. Here, by using elastic and inelastic neutron scattering, we demonstrate evidence of antiferromagnetic order below 80 K and strong spin fluctuations persisting to room temperature in a single-phase face-centered cubic (fcc) CrMnFeCoNi high-entropy alloy. Despite the chemical complexity, the magnetic structure in CrMnFeCoNi can be described as 
-Mn-like, with the magnetic moments confined in alternating (001) planes and pointing toward the 
111
direction. Combined with first-principles calculation results, it is shown that the antiferromagnetic order and spin fluctuations help stabilized the fcc phase in CrMnFeCoNi high-entropy alloy.
Ying, H.*; Yang, X.*; He, H.*; Yan, A.*; An, K.*; Ke, Y.*; Wu, Z.*; Tang, S.*; Zhang, Z.*; Dong, H.*; et al.
Scripta Materialia, 250, p.116181_1 - 116181_7, 2024/09
被引用回数：1 パーセンタイル：54.79(Nanoscience & Nanotechnology)Nanoscale chemical fluctuations and their effect on the deformation behavior of CrFeCoNi-based high-entropy alloys (HEAs) were investigated using small-angle scattering and in situ neutron diffraction measurements. Small-angle scattering results demonstrated the presence of nano (
10 nm) chemical fluctuations in the as-prepared CrFeCoNiPd HEAs, which was attributed to the negative mixing of enthalpy and the significant atomic radius difference between Pd and the constituent elements in the CrFeCoNi-based alloys. Subsequent tensile tests demonstrated that the yield and tensile strengths of the as-prepared CrFeCoNiPd HEA surpass those of the as-prepared CrMnFeCoNi HEA. Neutron diffraction data analysis revealed an anomalous response of dislocation evolution with the strain.
Sn wires with and without Cu-Nb reinforcement中本 美緒*; 菅野 未知央*; 荻津 透*; 杉本 昌弘*; 谷口 諒*; 廣瀬 清慈*; 川崎 卓郎; Gong, W.; Harjo, S.; 淡路 智*; et al.
IEEE Transactions on Applied Superconductivity, 34(5), p.8400806_1 - 8400806_6, 2024/08
被引用回数：0 パーセンタイル：0.00(Engineering, Electrical & Electronic)For an accelerator magnet, a certain mechanical strength is required to sustain against a transverse compression stress due to Lorentz force. A bronze-route NbSn wire with Cu-Nb reinforcement was developed by Tohoku University and Furukawa Electric to enhance the strength against axial tension. The Cu-Nb reinforcement wire also exhibited some indication of strength improvement against transverse compression; however, the details of a reinforcement mechanism for the transverse compression stress have not been clarified. In this study, the internal strains of NbSn bronze-route wires with and without the Cu-Nb reinforcement under transverse compression stress were evaluated by neutron diffraction at BL19 (TAKUMI) in J-PARC. The samples were attached to jig with solder only at the ends and compression was applied at the center of the samples with 30-mm anvil with 5-mm wide and 8- to 15-mm high beam. Since a critical current, Ic of a superconducting wire depends on the three-dimensional strain, internal strain of NbSn along the axial and two orthogonal radial directions were evaluated at room temperature (RT). In the different setup, Ic measurements of the wires under transverse compression stresses were also performed at 4.2 K and 14.5 T. Using 3-mm wide anvil, the transverse compression was applied at 4.2 K or RT. The neutron diffraction results indicated no significant differences in the internal strains of NbSn under transverse compression between the samples with and without Cu-Nb reinforcement, while the Ic measurements showed potential increase in the irreversible stress (
) for Cu-Nb reinforced wires. The reason for this discrepancy was discussed based on the difference in the experimental setups for each measurement.
渡邊 未来*; 宮本 吾郎*; Zhang, Y.*; 諸岡 聡; Harjo, S.; 小林 康浩*; 古原 忠*
ISIJ International, 64(9), p.1464 - 1476, 2024/07
被引用回数：2 パーセンタイル：54.79(Metallurgy & Metallurgical Engineering)The mechanical properties of TRIP steels depend on heterogeneities of chemical composition and grain size in the retained structure, although these heterogeneities have not been characterized in detail. Therefore, in this study, we quantitatively investigate the inhomogeneous carbon concentration and grain size distribution, and its effects on the thermal stability of the retained in Fe-2Mn-1.5Si-0.4C (mass%) TRIP steel using FE-EPMA, EBSD, M
ssbauer spectroscopy, and in-situ neutron diffraction during bainitic transformation at 673 K. In-situ neutron diffraction experiments detects high-carbon evolving during bainite transformation, in addition to the original , and the time variation of the volume fraction of highcarbon agrees well with the fraction of retained at room temperature. Williamson-Hall analysis based on peak width suggests that heterogeneity of carbon content exists even within the high-carbon . Compositional analysis using FE-EPMA and three-dimensional atom probe directly revealed that fine filmy was highly enriched with carbon compared to larger blocky , and the carbon content in blocky decreases with increasing blocky size. DICTRA simulation qualitatively reproduces the size dependency of carbon enrichment into . It was also found that tends to be retained at higher carbon content and smaller grain size since the smaller grain size directly improves thermal stability and the smaller size further contributes to the thermal stability via enhanced carbon enrichment.
松下 慧*; 土田 紀之*; 石丸 詠一郎*; 平川 直樹*; Gong, W.; Harjo, S.
Journal of Materials Engineering and Performance, 33(13), p.6352 - 6361, 2024/07
被引用回数：0 パーセンタイル：0.00(Materials Science, Multidisciplinary)This study investigated the anisotropy of the tensile properties in a duplex stainless steel of 24Cr-5Ni-0.18N based on in situ neutron diffraction experiments. The 24Cr-5Ni-0.18N steel showed a better balance of tensile strength (TS) and uniform elongation (U.El) compared with 329J4L and 329J1 steels. The Lankford value (
-value) of the 24Cr-5Ni-0.18N steel was comparable to other duplex stainless steels while showing a larger TS. Regarding the anisotropy of the mechanical properties, the results for a test specimen oriented at 45 showed a low yield strength (YS) and TS, but a better U.El and -value. The neutron diffraction results are discussed to explain the mechanical properties.
Nguyen, T.-D.*; Singh, C.*; Kim, Y. S.*; Han, J. H. *; Lee, D.-H.*; Lee, K.*; Harjo, S.; Lee, S. Y.*
Journal of Materials Research and Technology, 31, p.1547 - 1556, 2024/07
被引用回数：1 パーセンタイル：0.00(Materials Science, Multidisciplinary)This study investigates the mechanical properties of a friction-stir-welded (FSW) AA6061-T6 aluminum alloy at ultra-low temperature (ULT) of 20 K. In-situ neutron diffraction and orientation imaging microscopy were employed to compare the tensile deformation behavior of the base metal (BM) and heat-affected zone (HAZ) in the FSW aluminum plate. The results demonstrate that compared to room-temperature (RT), ULT induces a significant improvement in tensile strength and ductility in both the BM and HAZ. The enhanced mechanical properties in BM at ULT result from a more homogeneous deformation than occurs at RT. On the other hand, HAZ at ULT exhibits an even lower yield strength than at RT, but the strain hardening rate (SHR) is the most significant among the alloys, leading to a tensile strength of 346 MPa and the highest ductility of 46.8%. The lowest yield strength corresponds to the lowest-hardness zones in HAZ, caused by dissolved/coarsened precipitates during the FSW process.
