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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.
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.
友田 陽*; Harjo, S.; 徐 平光; 諸岡 聡; Gong, W.; Wang, Y.*
Metals, 15(6), p.610_1 - 610_19, 2025/05
被引用回数：2 パーセンタイル：48.13(Materials Science, Multidisciplinary)Lattice parameters of product and matrix phases in steels have been measured using in situ X-ray and neutron diffraction during forward and reverse transformations. These parameters are influenced by temperature, transformation-induced internal stresses, alloying element partitioning, crystal defects, and magnetic strains. Disentangling these contributions is essential for understanding lattice behavior. This review explores internal strain (stress) associated with ferrite, pearlite, bainite, martensite, and reverse austenite transformations, emphasizing the distinction between diffusional and displacive mechanisms. It also examines how plastic deformation of austenite affects subsequent bainite or martensite formation. The roles of dislocations and vacancies are identified as critical areas for further research.
Wang, S.*; Wang, J.*; Zhang, S.*; Wei, D.*; Chen, Y.*; Rong, X.*; Gong, W.; Harjo, S.; Liu, X.*; Jiao, Z.*; et al.
Journal of Materials Science & Technology, 185, p.245 - 258, 2024/06
被引用回数：27 パーセンタイル：97.07(Materials Science, Multidisciplinary)Nanoprecipitates and nanoscale retained austenite (RA) with suitable stability play crucial roles in determining the yield strength (YS) and ductility of ultrahigh strength steels (UHSSs). However, owing to the kinetics incompatibility between nanoprecipitation and austenite reversion, it is highly challenging to simultaneously introduce high-density nanoprecipitates and optimized RA in UHSSs. In this work, through the combination of austenite reversion treatment (ART) and subsequent flash austenitizing (FA), nanoscale chemical heterogeneity was successfully introduced into a low-cost UHSS prior to the aging process. This chemical heterogeneity involved the enrichment of Mn and Ni in the austenite phase. The resulting UHSS exhibited dual-nanoprecipitation of Ni(Al,Mn) and (Mo,Cr)
C and nanoscale austenite stabilized via Mn and Ni enrichment. The hard martensitic matrix strengthened by high-density dual-nanoprecipitates constrains the plastic deformation of soft RA with a relatively low fraction, and the presence of relatively stable nanoscale RA with adequate Mn and Ni enrichment leads to a marginal loss in YS but keeps a persistent transformation-induced plasticity (TRIP) effect. As a result, the newly-developed UHSS exhibits an ultrahigh YS of 1.7 GPa, an ultimate tensile strength (UTS) of 1.8 GPa, a large uniform elongation (UE) of 8.5 percent, and a total elongation (TE) of 13 percent. The strategy of presetting chemical heterogeneity to introduce proper metastable phases before aging can be extended to other UHSSs and precipitation-hardened alloys.
Wei, D.*; Gong, W.; 都留 智仁; Lobzenko, I.; Li, X.*; Harjo, S.; 川崎 卓郎; Do, H.-S.*; Bae, J. W.*; Wagner, C.*; et al.
International Journal of Plasticity, 159, p.103443_1 - 103443_18, 2022/12
被引用回数：147 パーセンタイル：99.83(Engineering, Mechanical)Face-centered cubic single-phase high-entropy alloys (HEAs) containing multi-principal transition metals have attracted significant attention, exhibiting an unprecedented combination of strength and ductility owing to their low stacking fault energy (SFE) and large misfit parameter that creates severe local lattice distortion. Increasing both strength and ductility further is challenging. In the present study, we demonstrate via meticulous experiments that the CoCrFeNi HEA with the addition of the substitutional metalloid Si can retain a single-phase FCC structure while its yield strength (up to 65%), ultimate strength (up to 34%), and ductility (up to 15%) are simultaneously increased, owing to a synthetical effect of the enhanced solid solution strengthening and a reduced SFE. The dislocation behaviors and plastic deformation mechanisms were tuned by the addition of Si, which improves the strain hardening and tensile ductility. The present study provides new strategies for enhancing HEA performance by targeted metalloid additions.
吉田 周平*; Fu, R.*; Gong, W.; 池内 琢人*; Bai, Y.*; Feng, Z.*; Wu, G.*; 柴田 曉伸*; Hansen, N.*; Huang, X.*; et al.
IOP Conference Series; Materials Science and Engineering, 1249, p.012027_1 - 012027_6, 2022/08
被引用回数：5 パーセンタイル：94.12(Metallurgy & Metallurgical Engineering)This study revealed characteristics of the deformation behavior in high/medium entropy alloys (HEAs/MEAs) with face-centered cubic (FCC) structure. A Co
Ni
alloy and a Co
CrNi MEA having low and high friction stresses (fundamental resistance to dislocation glide in solid solutions), respectively, but similar in other properties, including their stacking fault energy and grain sizes, were compared. The MEA exhibited a higher yield strength and work-hardening ability than those in the CoNi alloy at room temperature. Deformation microstructures of the CoNi alloy were composed of coarse dislocation cells (DCs) in most grains, and a few deformation twins (DTs) formed in grains with tensile axis (TA) nearly parallel to 
111
. In the MEA, three microstructure types were found depending on the grain orientations: (1) fine DCs developed in TA//100-oriented grains; (2) planar dislocation structures (PDSs) formed in grains with other orientations; and (3) dense DTs adding to the PDSs developed in TA//111-oriented grains. The results imply difficulty in cross-slip of screw dislocations and dynamic recovery in the MEA, leading to an increase in the dislocation density and work-hardening rate. Our results suggest that FCC high-alloy systems with high friction stress inherently develop characteristic deformation microstructures advantageous for achieving high strength and large ductility.
Co
Ni
Al
TiMo medium-entropy alloy; In situ neutron diffraction analysisKwon, H.*; Harjo, S.; 川崎 卓郎; Gong, W.; Jeong, S. G.*; Kim, E. S.*; Sathiyamoorthi, P.*; 加藤 秀実*; Kim, H. S.*
Science and Technology of Advanced Materials, 23(1), p.579 - 586, 2022/00
被引用回数：18 パーセンタイル：67.20(Materials Science, Multidisciplinary)Metastability engineering is a strategy to enhance the strength and ductility of alloys via deliberately lowering phase stability and prompting deformation-induced martensitic transformation. In this work, the martensitic transformation and its effect on the mechanical response of a FeCoNiAlTiMo medium-entropy alloy (MEA) were studied by in situ neutron diffraction under tensile loading. This work shows how great a role FCC to BCC martensitic transformation can play in enhancing the mechanical properties of ferrous MEAs.
Kong, L.*; Gong, J.*; Hu, Q.*; Capitani, F.*; Celeste, A.*; 服部 高典; 佐野 亜沙美; Li, N.*; Yang, W.*; Liu, G.*; et al.
Advanced Functional Materials, 31(9), p.2009131_1 - 2009131_12, 2021/02
被引用回数：37 パーセンタイル：82.53(Chemistry, Multidisciplinary)有機-無機ハロゲン化物ペロブスカイトは非常に柔らかいために、圧力などの外部刺激により格子定数を容易に変化させることができ、有用な光電特性を引き出すのに有効である。一方でこの特性は、多少の加圧でも、格子を歪ませてしまい、光と物質の相互作用を弱め、それによる性能の低下を引き起こす。そこで本研究では、代表的な物質であるヨウ化メチルアンモニウム鉛に対して圧力効果および同位体効果を調べ、それらが格子歪を抑制することが分かった。このことは、それらが、これまで得られなかったような光学的,機械的特性を持つ物質を得る手段として有効であることを示している。
investigation of the microstructure evolution in Long-Period-Stacking-Ordered (LPSO) magnesium alloys as a function of the temperatureM
this, K.*; Drozdenko, D.*; N
meth, G.*; Harjo, S.; Gong, W.*; 相澤 一也; 山崎 倫昭*; 河村 能人*
Frontiers in Materials (Internet), 6, p.270_1 - 270_9, 2019/11
被引用回数：8 パーセンタイル：26.21(Materials Science, Multidisciplinary)Deformation behavior of two Mg-Zn-Y magnesium alloys, having a different fraction of the long-period-stacking-ordered (LPSO) phase, has been investigated at room temperature and 200
C by a combination of 
neutron diffraction (ND) and acoustic emission (AE) measurements. The results indicate that the twinning in the magnesium matrix and the kinking in the LPSO phase strongly depend on the composition of the material and the testing temperature. Further, active deformation mechanisms and particularly the load transfer from the magnesium matrix to the LPSO phase define the mechanical properties of the investigated alloys.
徐 平光; Harjo, S.; 小島 真由美*; 鈴木 裕士; 伊藤 崇芳*; Gong, W.; Vogel, S. C.*; 井上 純哉*; 友田 陽*; 相澤 一也; et al.
Journal of Applied Crystallography, 51(3), p.746 - 760, 2018/06
被引用回数：30 パーセンタイル：88.67(Chemistry, Multidisciplinary)Neutron diffraction texture measurements provide bulk textures with excellent grain statistics even for large grained materials, together with the crystallographic parameters and microstructure information such as phase fractions, coherent crystallite size, root mean square microstrain, macroscopic/intergranular stress/strain. The procedure for high stereographic resolution texture and residual stress evaluation was established at the TAKUMI engineering materials diffractometer. The pole figure evaluation of a limestone standard sample with a trigonal crystal structure suggested that the obtained precision for texture measurement is comparable with the oversea well-established neutron beam lines utilized for texture measurements. A high strength martensite-austenite multilayered steel was employed for further verification of the reliability of simultaneous Rietveld analysis of multiphase textures and macro stress tensors. By using a geometric mean micro-mechanical model, the macro stress tensor analysis with a plane stress assumption showed a RD-TD in-plane compressive stress (about -330 MPa) in martensite layers and a RD-TD in-plane tensile stress (about 320 MPa) in austenite layers. The phase stress partitioning was ascribed to the additive effect of volume expansion during martensite transformation and the linear contraction misfit during water quenching.
neutron diffraction line profile analysisHarjo, S.; 川崎 卓郎; 友田 陽*; Gong, W.*; 相澤 一也; Tichy, G.*; Shi, Z.*; Ungr, T.*
Metallurgical and Materials Transactions A, 48(9), p.4080 - 4092, 2017/09
被引用回数：78 パーセンタイル：93.95(Materials Science, Multidisciplinary) neutron diffraction during tensile deformation of lath martensite steel containing 0.22 mass% of carbon, is performed using TAKUMI of J-PARC. The diffraction peaks at plastically deformed states exhibit asymmetries as the reflection of redistributions of the stress and dislocation densities/arrangements in lath-packets where the dislocation glides are favorable (soft packet) and unfavorable (hard packet). The dislocation density is as high as 10
m
at the as-quenched state, and then during tensile straining, the load and the dislocation density become different between the two lath-packets. The dislocation character and arrangement vary also in the hard packet, but hardly change in the soft packet. The hard packet plays an important role in the high work hardening in martensite, which could be understood by taking into account not only the increase of the dislocation density but also the change in dislocation arrangement.
徐 平光; Harjo, S.; 伊藤 崇芳*; 森井 幸生*; Gong, W.; 鈴木 裕士; 秋田 貢一; 鈴木 徹也*; 友田 陽; Lutterotti, L.*
JPS Conference Proceedings (Internet), 8, p.031022_1 - 031022_6, 2015/09
The current status of bulk texture measurements both using angle dispersive neutron diffraction and time-of-flight neutron diffraction at JAEA was briefly reviewed, then the effect of sample orientation coverage in the time-of-flight neutron diffraction on the reliability of reconstructed pole figure on the reliability of reconstructed pole figure was simply compared after the simultaneous Rietveld texture analysis. The similar texture results obtained at different orientation coverage levels suggests that it is possible to reduce the sample rotation times reasonably during the bulk texture measurement.
MillerOjiewo, C. O.*; Agong, S. G.*; 村上 賢治*; 田中 淳; 長谷 純宏; 桝田 正治*
Journal of Horticultural Science & Biotechnology, 81(4), p.559 - 564, 2006/07
は栄養価が高く薬用的価値もあるためアフリカで消費量が上昇している葉物野菜であるが、比較的早くに多数の種子をつけるため葉の収量が低いことが問題となっている。本研究では、この問題を克服するため、炭素イオンビーム照射による雄性不稔性誘発についての効果を調査した。生育抑制や種子稔性への影響を考慮すると20-30Gyの炭素イオン照射が適切と考えられた。炭素イオンビーム照射により、新規の雄性不稔変異体が得られた。この変異体は、春は不稔性を示すが、夏は中間型でやや稔性が回復し、秋には種子を形成した。季節に応じて稔性が回復する形質は、収量の増加と同時に種子の増殖に利用できる可能性がある有用な形質である。
-ray irradiation of African nightshade (
L. ssp. 
) seedOjiewo, C. O.*; Agong, S. G.*; 村上 賢治*; 田中 淳; 長谷 純宏; 桝田 正治*
Journal of Horticultural Science & Biotechnology, 80(6), p.699 - 704, 2005/11
アフリカンナイトシェード( L. spp. )はアフリカでよく消費される葉野菜であるが、発芽から開花・結実までの期間が短いことから葉の収量が比較的少ない。つまり、生殖生長の開始後、花粉や種子,果実の発達に養分が送られるため、葉に対する養分の転流が少なくなることが原因である。本研究では、雄性不稔性を利用することによって、養分の転流を葉に向けることにより収量を増加させることを考え、線の種子照射により得られたさまざまな変異体を調査した。照射種子の発芽率,生存率,種子稔性並びに雄性不稔変異体誘発率から、100Gyの線が変異誘発に最適であると考えられた。M2世代で選抜された雄性不稔変異体には4つのタイプ、すなわち、(1)稔性は無いが酢酸カーミンで花粉が染色される個体、(2)酢酸カーミンで花粉が染色されない個体、(3)花粉が形成されない個体、及び(4)花粉量が著しく少ない個体、が見られた。本研究で得られた雄性不稔変異体は、生殖や果実形成を制限することによって、葉の収量の増加につながると期待される。
内馬場 優太; 伊藤 由太; 佐藤 哲也; 青木 涼太; 浅井 雅人; Gong, G.; 宮地 優太*; 永目 諭一郎*; 名取 日菜*; 塚田 和明
no journal, ,
原子番号が104以上である超重核の精密質量測定を見据え、崩壊分光による測定対象イオンの事前同定や崩壊情報との相関による質量決定の確度向上を目的としたイオントラップの開発を進めている。トラップされた不安定核イオンからの放射線を大立体角で捉えるために、一般的な円形電極とは異なり薄い板状のベーン電極を用いたベーン電極型イオントラップを開発した。性能の指標として、トラップ寿命や蓄積電荷量について円形電極型イオントラップと比較し評価を行った。
青木 涼太; 佐藤 哲也; 内馬場 優太; 宮地 優太*; Gong, G.; 名取 日菜*; 伊藤 由太; 浅井 雅人; 塚田 和明; 永目 諭一郎*
no journal, ,
原子番号が100を超える超重元素のイオンビームを物理・化学研究に応用するため、短寿命単一原子に適用可能な新しいイオン源としてEBGP(Electron Beam Generated Plasma)イオン源を構築した。本EBGPイオン源を、オンライン同位体分離器(Isotope Separator On-Line: ISOL)用に装着し、各種貴ガスを用いて、イオンビーム生成条件の探索を行った結果、イオン源が安定して動作することを確認するとともに、イオンビームが生成できることを確かめた。
徐 平光; 石島 暖大; Qiu, H.*; 諸岡 聡; Gong, W.*; 川崎 卓郎; Harjo, S.
no journal, ,
High strength steels for pipelines and high-pressure vessels are susceptible to hydrogen embrittlement (HE), which is typically characterized by a loss of tensile ductility. In addition to the conventional factors including microstructure, hydrogen content, strain rate, temperature, and residual stress, the crystallographic texture has recently been reported to affect the HE susceptibility of steel plates. Here, the anisotropic tensile deformation behaviors and the texture evolution were comparably evaluated by using hydrogen-charged and non-charged tensile samples to investigate the mutual effect of texture and hydrogen charging. The changes in normalized diffraction intensities show that 110//RD (RD: rolling direction) preferred orientation becomes stronger during the RD tensile deformation of hydrogen-charged and non-charged samples; the multiaxial stress field during necking deformation induces more evident weakening of final 110//RD preferred orientation in the non-hydrogen steel. It suggests that the in situ neutron diffraction is suitable to monitor the plastic deformation behavior of hydrogen-charged high strength steel. Moreover, during the RD extension, 110//RD texture component becomes strong and the 200//TD200//ND components (TD: transverse direction; ND: normal direction) have a uniform pole density distribution, and the hydrogen charging accelerates the formation of this distribution. During the TD extension, 110//TD component becomes strong, 200//ND component disperses towards the circular direction 60-tilted from ND, and the hydrogen charging accelerates such grain rotations. The appearance of higher maximum pole density of (200) pole figure shows good correspondence to lower uniform ductility of hydrogen-charged TD sample.
佐藤 哲也; 青木 涼太; 宮地 優太*; 浅井 雅人; 伊藤 由太; 内馬場 優太; Gong, G.; 名取 日菜*; 塚田 和明; 永目 諭一郎*
no journal, ,
極限重元素核科学研究グループでは、迅速化学実験への超重元素イオンビームの応用を目的に、ガスジェット結合型EBGP(Electron Beam Generated Plasma)イオン源の開発を進めている。EBGPイオン源では、電子衝撃によって対象原子・分子のイオン化をおこなうため、多様な元素のイオンビーム生成が期待できる。種々の希ガス安定同位体を用いてイオンビーム強度を調べたところ、原子番号の増加に伴ってビーム強度が増大することを確認した。得られたイオン源安定動作条件下で、
Cf自発核分裂生成核種を用いて様々な短寿命核種のイオン化を試みたので報告する。
