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伊東 達矢; 小川 祐平*; Gong, W.; 川崎 卓郎; 柴田 曉伸*; Harjo, S.
Scripta Materialia, 273, p.117084_1 - 117084_6, 2026/03
被引用回数：0 パーセンタイル：0.00(Nanoscience & Nanotechnology)The effect of solute hydrogen on stacking fault evolution in austenitic steels remains debated. In this study, the changes in stacking fault probability in the 
111
//loading direction grains family (
) of hydrogen-charged and non-charged Fe-24Cr-19Ni austenitic steels were evaluated using 
neutron diffraction during tensile deformation at 223 and 177 K. When values were plotted against macroscopic strain, hydrogen apparently enhanced stacking fault evolution. However, when identical data were translated into the form of versus stress, the superficial hydrogen-effect on notably disappeared. Rather, deformation temperature played more predominant role - lower temperature led to higher regardless of hydrogen-charging, reflecting the reduction of stacking fault energy with decreasing temperature. These findings demonstrate that hydrogen has a minor effect on stacking fault evolution compared with temperature and applied stress.
Li, H.*; Gong, W.; 川崎 卓郎; Harjo, S.; Zheng, R.*; 他6名*
Acta Materialia, 305, p.121884_1 - 121884_10, 2026/02
被引用回数：0 パーセンタイル：0.00(Materials Science, Multidisciplinary)The quest for lightweight and highly formable magnesium (Mg) alloys has drawn significant attention due to the growing demand for energy-efficient structural materials. Achieving high ductility in Mg at room temperature, which is critical for mass production of structural components, remains a formidable challenge despite decades of research. In this study, we demonstrate super-ductility in an ultrafine-grained (UFG) Mg alloy at room temperature. By microalloying with trace manganese (Mn) and reducing the grain size to sub-micron scale, Mg-0.3Mn binary alloy achieves an exceptional room temperature tensile elongation of 135% at a quasi-static strain rate. Detailed microstructural analysis reveals that grain boundary (GB) sliding, rather than intragranular dislocation slip, is the dominant deformation mechanism in the UFG Mg-0.3Mn alloy. Unlike conventional alloying strategies that lead to GB pinning, the segregation of Mn element along GBs in a manner of nano-clusters could reduce interfacial bonding strength, acting as a lubricant to facilitate GB sliding and thus dramatically boost the ductility. This innovative GB engineering approach unlocks unprecedentedly remarkable deformability of Mg-based alloys at room temperature, paving the way for next-generation lightweight structural applications.
Zhu, L.*; Dong, W.*; Naeem, M.*; Kong, H.*; Hu, C.*; Fan, Z.*; Gong, W.; Harjo, S.; Lan, S.*; Wu, Y.*; et al.
Acta Materialia, 303, p.121734_1 - 121734_10, 2026/01
被引用回数：1 パーセンタイル：0.00(Materials Science, Multidisciplinary)Body-centered cubic (BCC) metals typically exhibit high yield strength but limited work hardening and uniform elongation, especially at low temperatures. High-entropy alloys (HEAs) offer opportunities to overcome these limitations, though their deformation mechanisms remain unclear. Using in situ neutron diffraction and microstructural analysis, this study identifies the origin of the exceptionally large uniform elongation at liquid nitrogen temperature in a single-phase BCC (TiZrHf)
Al
Nb
HEA. Initial plastic deformation is governed by a BCC-to-orthorhombic (
") transformation, followed by " twinning and deformation-induced amorphization at later stages. The cooperation of these mechanisms suppresses work softening from dislocation plasticity, enabling high yield strength with large uniform elongation and providing a viable strategy for designing cryogenic structural materials.
Cho, K.*; 山下 葵平*; 角谷 心之輔*; 齊藤 拓馬*; 佐々木 泰祐*; 澤泉 克彦*; 奥川 将行*; 小泉 雄一郎*; 眞山 剛*; 菊川 泰地*; et al.
Acta Materialia, 303, p.121696_1 - 121696_18, 2026/01
被引用回数：3 パーセンタイル：0.00(Materials Science, Multidisciplinary)The deformation behavior and strengthening mechanism of Inconel 718 with a hierarchical structure composed of microscale crystallographic lamellar microstructure (CLM) and nanoscale cellular structure, fabricated by laser powder bed fusion, were clarified via nanoscale microstructural and in-situ neutron diffraction analyses. The CLM is a layered structure parallel to the building direction (BD) and consists of relatively wide main and narrow sub-layers with 110 and 100 orientations, respectively, with respect to BD. This is the first study to demonstrate that the yield stress of the alloys depends strongly on deformation stresses of the sub-layers, even though Schmid factors of the primary slip system for both layers are the same. The sub-layer continues to deform elastically even beyond the micro-yield point of the main layer, which results in the macroscopic strengthening at an early stage of deformation. On the other hand, the cellular structure is formed in both layers, associated with a dendritic cell growth along 100 direction, Nb segregation between the cells and an accumulation of dislocations to decrease a residual stress. The cell boundaries with numerous dislocations and Nb segregation act as a strong barrier to dislocation motion resulting in a stress increase through the Hall-Petch law, even though they are low-angle grain boundaries. The spacing and morphology of the cell boundary depend strongly on fabrication conditions. The optimized cellular structure provides significant strengthening comparable to or greater than that caused by large-angle grain boundaries, thereby increasing the macroscopic strength of the alloys through hardening of the sub-layer.
Su, Y. H.; 篠原 武尚; Parker, J. D.*; 及川 健一; 甲斐 哲也; Gong, W.; 伊東 達矢; Harjo, S.; 相澤 一也; 鬼柳 善明*; et al.
Materials Science & Engineering A, 951, p.149607_1 - 149607_16, 2026/01
被引用回数：0 パーセンタイル：0.00(Nanoscience & Nanotechnology)Local variations in residual stress/strain and microstructure during fatigue crack growth in compact tension specimens of SUS304 austenitic stainless steel were investigated using complementary methods: pulsed neutron Bragg-edge imaging (NBEI), neutron diffraction (ND), digital image correlation (DIC) and electron backscatter diffraction (EBSD). Surface strain fields were evaluated using DIC and EBSD. NBEI provided two-dimensional averaged microstructure information, whereas ND yielded detailed three-dimensional distributions of residual lattice (elastic) strain and stress. This study particularly focused on how NBEI is helpful in understanding overall damage characteristics in the vicinity of a crack tip two-dimensionally. Distribution of microstructural parameters associated with crack growth, such as lattice constant, crystallite size, and texture, across the entire specimen was considered using Bragg-edge spectral analysis. The plastic zone in front of the crack tip, characterized by reduced crystallite size, was observed during crack propagation. After final fracture, two distinct zones with reduced crystallite size were identified: one caused by localized plastic deformation near the crack tip, and the other by bending at the back end of the specimen. This paper introduces the four experimental techniques and describes their respective features. Each method has its own advantages and limitations; However, by integrating their results, a more comprehensive understanding of the overall stress/strain field can be achieved.
neutron diffraction analysis染川 英俊*; Gong, W.; 川崎 卓郎; Harjo, S.; Singh, A.*; 友田 陽*
Scripta Materialia, 269, p.116921_1 - 116921_6, 2025/12
被引用回数：0 パーセンタイル：0.00(Nanoscience & Nanotechnology)Deformation mechanism at room-temperature of fine-grained Pure Mg, AZ31 and Mg-Mn alloys is examined through in-situ neutron diffraction method and postmortem microstructural observations. Extension twins do not form in any of the specimens. In the AZ31 alloy, lattice strain and integrated intensity of individual planes change differently with progression of tensile tests, indicating large plastic anisotropy. This is due to large number of dislocation slips on not only basal but also prismatic planes. Whereas, Pure Mg and Mg-Mn alloy show a small difference in lattice strain and integrated intensity between diffraction peaks, because grain boundary sliding plays a role in relaxation of stress accumulations at grain boundaries, with less dependence on crystallographic orientation. Neutron diffraction analysis in Pure Mg and Mg-Mn alloy reveals that dislocation slips (on mainly basal plane) are generated by mechanisms associated with both accommodation process for grain boundary sliding and general intragranular plastic deformation.
山下 享介*; 柳樂 知也*; Gong, W.; 川崎 卓郎; Harjo, S.; 潮田 浩作*; 藤井 英俊*
鉄と鋼, 111(17), p.1057 - 1071, 2025/12
Neutron diffraction mapping was conducted on linear friction welded joints of 12 mm thick high-phosphorus weathering steel (SPA-H) to evaluate residual stress, dislocation density, and crystallographic orientation. Welding was performed at 100 MPa and 250 MPa. The weld interface mainly comprised refined ferrite with retained austenite and martensite, indicating temperatures exceeded A1 and induced reverse transformation. The 250 MPa joint showed a lower welding temperature. Elongated grains formed near the surface along the oscillation direction (OD), while equiaxed grains appeared at the center. High tensile residual stresses were found at the weld center, with compressive stress near the surface perpendicular to the weld. Pressure had little effect on overall stress trends. Dislocation density increased with pressure due to suppressed dynamic recovery. Strong texture developed at the interface, with limited pressure dependence.
Jeong, S. G.*; Kwon, J.*; Kim, E. S.*; Prasad, K.*; Harjo, S.; Gong, W.; 川崎 卓郎; Estrin, Y.*; Bouaziz, O.*; Hong, S. I.*; et al.
Materials Science & Engineering A, 942, p.148712_1 - 148712_11, 2025/10
被引用回数：1 パーセンタイル：46.46(Nanoscience & Nanotechnology)The cellular structure plays a key role in determining the mechanical properties of metal additive manufacturing (MAM) components. This study presents in situ neutron diffraction and dislocation density-based modeling for a CoCrFeMnNi high-entropy alloy (HEA) made via directed energy deposition (DED). A constitutive model based on the Kocks-Mecking-Estrin framework was used to represent the cellular structure. Parametric analysis showed lower dislocation accumulation and annihilation rates in the as-built sample (with cellular structure) than in the heat-treated one. These differences are linked to dislocation forest networks and local stacking fault energy variations. Dislocation density across cell interiors and walls was also compared with deformation-induced dislocation cells.
neutron diffractionLiu, Y.*; Yan, Z.*; Gao, Y.*; Li, Y.*; Gan, B.*; Harjo, S.; Gong, W.; 川崎 卓郎; Li, S.*; Wang, Y.-D.*
Microstructures (Internet), 5(4), p.2025096_1 - 2025096_15, 2025/10
The micromechanical behaviors and dislocation evolution in a polycrystalline Ni-Co-based superalloy were systematically investigated by neutron diffraction tensile testing combined with line profile analysis. The results reveal the sequential activation of 
' shearing and Orowan looping mechanisms, with interphase load partitioning governed by strain-dependent interactions of dislocation and precipitate. During the initial plastic deformation, the and ' phases undergo co-deformation through dislocation shearing without load transfer, while the Orowan looping facilitates the load transfer from to ' phase at a higher strain level. Furthermore, the low stacking fault energy leads to a rising fraction of screw dislocations by suppressing cross-slip. Crucially, the pinning effect of ' precipitates hinders the rearrangement of these dislocations into low-energy structures, resulting in the formation of high-energy, weakly screened dislocation configurations. These findings provide new evidence for the planar slip dominance in Ni-Co-based superalloys, enabling quantitative assessment of microstructural evolution and micromechanical responses.
Cao, T.*; Wei, D.*; Gong, W.; 川崎 卓郎; Harjo, S.; 他10名*
Materials Science & Engineering A, 940, p.148534_1 - 148534_16, 2025/09
被引用回数：2 パーセンタイル：46.46(Nanoscience & Nanotechnology)The thermal stability of microstructure and mechanical performance is crucial for the industrial application of laser powder bed fusion (LPBF) superalloy components in gas turbines and jet engines. This work investigated the microstructural evolution and strengthening mechanism of LPBF Mar-M509 cobalt-based superalloy before and after thermal exposure at 1200 
C using multi-scale microstructural characterization and in situ neutron diffraction tensile testing. The as-built Mar-M509 superalloy exhibited a heterogeneous microstructural features with coarse columnar and fine equiaxed grains, both containing dendritic and cellular substructures enriched with nanoscale carbides and high-density dislocations. The ultra high strength of the as-built sample was primarily attributed to dislocation-precipitation synergistic strengthening. After thermal exposure at 1200 C for 4 h, the dendritic and cellular substructures disappeared and the dislocation density decreased significantly. This study reveals the microstructural evolution and instability of LPBF Mar-M509 superalloy under high-temperature exposure and the impacts on mechanical properties, which provides critical support for the development of cobalt-based superalloys in high-temperature application fields.
neutron diffraction study山下 享介*; 古賀 紀光*; Mao, W.*; Gong, W.; 川崎 卓郎; Harjo, S.; 藤井 英俊*; 梅澤 修*
Materials Science & Engineering A, 941, p.148602_1 - 148602_11, 2025/09
被引用回数：1 パーセンタイル：0.00(Nanoscience & Nanotechnology)Ferrite-austenite duplex stainless steels offer excellent strength and ductility, making them suitable for extreme environments. In this study, neutron diffraction during tensile testing at 293 K and 200 K was used to investigate stress partitioning and phase-specific deformation. Phase stress was calculated using a texture-compensated method. At both temperatures, ferrite showed higher phase stress than austenite, acting as the harder phase. At 200 K, both phases exhibited increased strength and work hardening. Austenite showed significant stacking fault formation alongside dislocation migration, while ferrite retained its dislocation-based deformation mode, becoming more effective. Stress contributions from both phases were comparable. No martensitic transformation occurred. Strengthening and enhanced work hardening in both phases led to high strength at 200 K, with ductility similar to that at 293 K.
neutron diffraction and digital image correlation strain analysis川崎 卓郎; Harjo, S.; Gong, W.; Mao, W.*; 山下 享介*; 伊東 達矢; 相澤 一也
Review of Scientific Instruments, 96(9), p.093901_1 - 093901_6, 2025/09
被引用回数：3 パーセンタイル：84.81(Instruments & Instrumentation)A cryogenic tensile testing system for neutron diffraction measurement, incorporating macroscopic strain distribution measurement through the Digital Image Correlation (DIC) method, was developed. By integrating this system with a versatile horizontal load frame, tensile tests can be conducted within the temperature range from room temperature to 20 K. A tentative measurement combining neutron diffraction and the DIC technique was performed on an ultrafine-grained 304 stainless steel during tensile deformation at 77 K. It revealed that the deformation-induced martensitic transformation can be characterized more accurately by considering the local macroscopic strain in the neutron-irradiated gauge region, as determined by the DIC method, rather than the overall sample strain. The developed system enables accurate measurement of macroscopic strain, particularly in cases of non-uniform deformation, while simultaneously capturing associated crystallographic structure changes, thereby enhancing the effectiveness of neutron data for materials research.
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.
波紋, 35(3), p.129 - 133, 2025/08
Recent studies have shown that the addition of hydrogen to SUS310S stainless steel (Fe-24Cr-19Ni, mass%) simultaneously enhances both strength and ductility, indicating a phenomenon contrary to the conventional understanding of hydrogen embrittlement. In this study, we investigated the underlying mechanism through neutron diffraction experiments during tensile deformation using TAKUMI at the MLF of J-PARC. The results revealed that solid-solution strengthening by hydrogen plays the most significant role in improving the mechanical properties. Solute hydrogen atoms distort the lattice to suppress dislocation motion, thereby increasing the strength. The raised stress in the hydrogen charged sample enables the onset of deformation twinning at a smaller strain compared to the non-hydrogen charged sample. Consequently, the twinning-induced plasticity effect contributes more significantly to work hardening and the improvement of uniform elongation due to the solid-solution strengthening by hydrogen. These findings suggest a new pathway for the effective utilization of hydrogen in austenitic steels.
Peng, S. Y.*; Gong, W.; Tian, Y. Z.*; Harjo, S.; 他5名*
International Journal of Plasticity, 191, p.104401_1 - 104401_15, 2025/08
被引用回数：14 パーセンタイル：97.42(Engineering, Mechanical)Quantifying the contributions of various strengthening mechanisms is essential for manipulating these mechanisms and designing novel alloys. Although CoCrNi alloys demonstrate exceptional mechanical properties, their strengthening characteristics remain to be investigated. In this work, we conducted in situ neutron diffraction tensile tests and characterized deformation microstructures for CoCrNi alloys with different stacking fault energies (SFEs). The dislocation strengthening characteristics and the role of planar faults were systematically investigated. A reduction in SFE restricts cross slip, thereby increasing the dislocation multiplication rate while decreasing the dislocation strengthening coefficient . Additionally, a lower SFE facilitates the simultaneous activation of dislocations and planar faults, with dislocation strengthening consistently playing a dominant role. This work quantifies reasonable values for CoCrNi alloys and identifies cross slip as a critical factor potentially influencing value in face-centered cubic (FCC) alloys.
Zheng, R.*; Gong, W.; 他6名*
Acta Materialia, 293, p.121098_1 - 121098_12, 2025/07
被引用回数：4 パーセンタイル：77.86(Materials Science, Multidisciplinary)Hall-Petch law fails when grains smaller than a critical size, due to grain boundary (GB) kinetics-dominated plasticity. To enhance strength, improving GB stability is a consideration. However, this often requires a significant amount of alloying elements, posing resource challenges. Additionally, practical fabrication of extremely fine grains is still an issue. In our study, we firstly demonstrate a remarkable hardening-by-annealing phenomenon in magnesium (Mg) with relatively large grain sizes of 0.2-0.5 
m, even with ultra-low yttrium (Y) addition. We reveal that annealing induces GB segregation/relaxation, effectively limiting the GB kinetics and promoting dislocation-dominated plasticity. Furthermore, the accompanying dislocation annihilation hinders deformation due to dislocation scarcity. As a result, we discovered extraordinary hardening in bulk ultrafine grained Mg-Y ultra-dilute alloy. This work offers a promising avenue for developing energy- and resource-efficient sustainable Mg alloys with superior mechanical properties.
ders band-assisted high uniform ductility in ultrastrong ferrous medium-entropy alloy via hierarchical microstructureKwon, H.*; Lee, J. H.*; Zargaran, A.*; Harjo, S.; Gong, W.; Wang, J.*; Gu, G. H.*; Lee, B.-J.*; Bae, J. W.*; Kim, H. S.*
International Journal of Plasticity, 190, p.104378_1 - 104378_18, 2025/07
被引用回数：9 パーセンタイル：93.16(Engineering, Mechanical)In this work, we harness a hierarchical microstructure to simultaneously tailor strengthening and deformation mechanisms in a Co
Cr
Fe
Ni
Mo
(at%) ferrous medium-entropy alloy (MEA). A simple thermomechanical process (cold rolling and 90 s annealing) produces ultrafine recrystallized grains, non-recrystallized grains with substructures, and intragranular nanoprecipitates. This structure, with high dislocation density and fine grains, yields a high strength of 
1.60 GPa but can risk premature fracture. To overcome this, Lders deformation, enabled by ultrafine grain boundaries and stress-induced martensitic transformation at pre-existing nucleation sites, is employed. Stable Lders band propagation delays strain hardening and enables large uniform ductility. As a result, a tensile strength of 1.84 GPa and uniform elongation of 20% are achieved, matching the best tensile properties among reported multi-principal element alloys.
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：7 パーセンタイル：91.77(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.
Chen, Z.*; Gong, W.; Harjo, S.; 川崎 卓郎; Chen, G.*; 他14名*
Nature Communications (Internet), 16, p.6480_1 - 6480_13, 2025/07
被引用回数：6 パーセンタイル：81.66(Multidisciplinary Sciences)Developing alloys with both ultrahigh strength and ductility remains a for- midable scientific challenge, primarily due to the inherent strength-ductility tradeoff. Here, we present an approach to enhance the ductility and strength of a medium-entropy alloy (MEA) featuring a fully recrystallized face-centered cubic/hexagonal close-packed dual-phase ultrafine-grained architecture. This is achieved by activating unusual non-basal slips in the ordered hexagonal close-packed superlattice nanoprecipitates, resulting in this MEA that exhibits remarkable uniform elongation (
) and ultrahigh yield strength (
) across a wide temperature range, particularly at cryogenic temperatures ( 2100 MPa, 15%). The non-basal slips in the secondary phase are activated at ultrahigh stress levels, which are compatible with the increased yield strength of the MEA attained through multiple strengthening mechanisms, including grain boundaries, lattice friction, and second-phase nanoprecipitates provided by the multi-principal elements of the entropy alloy. The deformation mechanism elucidated in this work not only leverages the significant strengthening and strain hardening effects of brittle nanoprecipitates but also enables the ductilization of the alloy through sequential non-basal slip during ongoing deformation.
Mao, W.*; Gong, W.; 川崎 卓郎; Gao, S.*; 伊東 達矢; 山下 享介*; Harjo, S.; Zhao, L.*; Wang, Q.*
Scripta Materialia, 264, p.116726_1 - 116726_6, 2025/07
被引用回数：2 パーセンタイル：0.00(Nanoscience & Nanotechnology)An ultrafine-grained 304 austenitic stainless steel exhibited pronounced serrated Luders deformation at 20 K, with stress and temperature oscillations reaching 200 MPa and 20 K. 
neutron diffraction and digital image correlation revealed discontinuous Luders band propagation and burst martensite formation. During deformation, austenite phase stress remained lower than at upper yielding, indicating elastic behavior. Notably, martensite phase stress stayed lower than austenite until fracture, likely due to stress relaxation from burst martensitic transformation at 20 K. The low martensite stress delayed brittle fracture until austenite plastically yielded during uniform deformation.
Kim, Y. S.*; Kang, T.*; Hong, S.-K.*; Brechtl, J.*; Lebyodkin, M.*; Cheng, Y.-H.*; Huang, E.-W.*; Liaw, P. K.*; Harjo, S.; Gong, W.; et al.
Acta Materialia, 292, p.120970_1 - 120970_16, 2025/06
被引用回数：8 パーセンタイル：91.77(Materials Science, Multidisciplinary)Metallic materials can exhibit low-temperature serrated deformation (LTSD) at cryogenic temperatures, potentially causing sudden failures. Understanding LTSD is thus crucial for ensuring material reliability in such environments. LTSD has been explained by two main mechanisms: (i) dislocation-based mechanical instability and (ii) thermomechanical instability, but each has limitations when considered alone. To address this, we propose a new LTSD mechanism, a thermally induced dislocation dynamics model, based on cryogenic experimental evidence. This model accounts for dislocation avalanches and localized heating, leading to hierarchical dislocation networks and transitions in deformation modes. A modified deformation-mechanism map for SS316L is also presented. Our findings highlight the rate-dependent nature of LTSD and negative strain-rate sensitivity, including the first observation of links between small stress fluctuations and large serrations.
