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Mao, W.; Gao, S.*; Gong, W.; Bai, Y.*; Harjo, S.; Park, M.-H.*; 柴田 曉伸*; 辻 伸泰*
Acta Materialia, 256, p.119139_1 - 119139_16, 2023/09
被引用回数：5 パーセンタイル：90.35(Materials Science, Multidisciplinary)変形誘起塑性(TRIP)鋼は、変形誘起マルテンサイト変態(DIMT)に伴う加工硬化率の向上により、強度と延性の優れた組み合わせを示す。TRIP鋼や合金の加工硬化挙動におけるDIMTの役割を定量的に評価することは、強度と延性の両立を可能にする先進材料を設計するための指針を与えるが、変形中に相組成が変化し続け、応力と塑性ひずみの両方が構成相間で動的に分配されるため、その評価は困難である。本研究では、Fe-24Ni-0.3C(wt.%)TRIPオーステナイト鋼の引張変形とその場中性子回折測定を行った。中性子回折測定による応力分割と相分割に基づく解析手法を提案し、試験片の引張流動応力と加工硬化率を、オーステナイト母相,変形誘起マルテンサイト、DIMT変態速度に関連する因子に分解し、試料の加工硬化挙動における各因子の役割を考察した。さらに、回折プロファイル解析により測定した転位密度を用いてオーステナイトとマルテンサイト間の塑性ひずみ分配を間接的に推定し、材料中のオーステナイトとマルテンサイト間の応力・ひずみ分配の全体像を構築した。その結果、変形誘起マルテンサイト変態速度とマルテンサイトが負担する相応力の両方が、材料の全体的な引張特性に重要な役割を果たしていることが示唆された。提案した分解解析法は、TRIP現象を示す多相合金の機械的挙動を調べるために広く適用できる可能性がある。
neutron diffractionGong, W.; Harjo, S.; 友田 陽*; 諸岡 聡; 川崎 卓郎; 柴田 曉伸*; 辻 伸泰*
Acta Materialia, 250, p.118860_1 - 118860_16, 2023/05
被引用回数：2 パーセンタイル：74.65(Materials Science, Multidisciplinary)Martensitic transformation is accompanied by the generation of microscale and macroscale internal stresses during cooling below the martensitic transformation start temperature. These internal stresses have been determined through X-ray or neutron diffraction, but the reported results are not consistent, probably because the measured lattice parameter is influenced not only by the internal stress but also by several factors, including solute elements and crystal defects. Therefore, neutron diffraction combined with dilatometry measurements during martensitic transformation and subsequent cyclic tempering were performed for an Fe-18Ni alloy. The phase strains calculated by lattice parameter variations show that a hydrostatic compressive strain in austenite and a tensile strain in martensite arose as the martensitic transformation progressed during continuous cooling or isothermal holding. However, the phase stresses of austenite and martensite estimated from these strains failed to hold stress balance law when dense crystal defects involved in the processes. After these crystal defects were removed by appropriate tempering, the stress balance law held well. Meanwhile, the phase stresses of austenite and martensite were changed to opposite, revealing their true identity. Various crystal defects in austenite and martensite, introduced by plastic accommodation, were suggested to affect their lattice parameters and then their phase stresses.
phase to 
phase in zirconium alloy revealed by in-situ neutron diffraction during high temperature deformationGuo, B.*; Mao, W.; Chong, Y.*; 柴田 曉伸*; Harjo, S.; Gong, W.; Chen, H.*; Jonas, J. J.*; 辻 伸泰*
Acta Materialia, 242, p.118427_1 - 118427_11, 2023/01
被引用回数：5 パーセンタイル：64.46(Materials Science, Multidisciplinary)Dynamic transformation from alpha (HCP) to beta (BCC) phase in a zirconium alloy was revealed by the use of in-situ neutron diffraction during hot compression. The dynamic transformation was unexpectedly detected during isothermal compression at temperatures of 900
C and 950C (alpha + beta two-phase region) and strain rates of 0.01 s
and 0.001 s, even though equilibrium two-phase states were achieved prior to the hot compression. Dynamic transformation was accompanied by diffusion of Sn from beta to alpha phase, which resulted in changes of lattice parameters and a characteristic microstructure of alpha grains. The details of dynamic transformation are discussed using the evolution of lattice constants.
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：0 パーセンタイル：0.83(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.
Mao, W.; Gao, S.*; Bai, Y.*; Park, M.-H.*; 柴田 曉伸*; 辻 伸泰*
Journal of Materials Research and Technology, 17, p.2690 - 2700, 2022/03
被引用回数：9 パーセンタイル：83.6(Materials Science, Multidisciplinary)超微細結晶粒(UFG)組織を有する準安定オーステナイト鋼は、冷間圧延中の変形誘起マルテンサイト変態と焼鈍時のオーステナイトへの逆変態を利用することにより、従来の冷間圧延および焼鈍プロセスで製造することができる。しかし、変形誘起マルテンサイト変態に対するオーステナイトの機械的安定性が高い場合には、冷間圧延中に十分な量のマルテンサイトが生成しないため、このようなプロセスは適用できない。本研究では、高い機械的安定性を有するFe-24Ni-0.3C準安定オーステナイト鋼に対して、冷間圧延と焼鈍の2段階プロセスを適用した。冷間圧延に先立ち、繰り返しサブゼロ処理と逆焼鈍処理を施した。このような処理により、オーステナイトの機械的安定性が劇的に低下し、その後の冷間圧延工程で変形誘起マルテンサイトの生成が大幅に促進された。その結果、結晶粒の微細化が著しく促進され、平均オーステナイト粒径0.5mmの完全再結晶試験片の作製に成功し、高強度と高延性を両立させた。
岡田 和歩*; 柴田 曉伸*; Gong, W.; 辻 伸泰*
Acta Materialia, 225, p.117549_1 - 117549_13, 2022/02
被引用回数：15 パーセンタイル：93.62(Materials Science, Multidisciplinary)In this study, the deformation microstructure of hydrogen-charged ferritic-pearlitic 2Mn-0.1C steel was characterized using SEM-BSE, SEM-EBSD, TEM, and neutron diffraction. The microscopic mechanism of hydrogen-related quasi-cleavage fracture along the 
planes was also discussed. It was found that hydrogen increased the relative velocity of screw dislocations to edge dislocations, leading to a tangled dislocation morphology, even at the initial stage of deformation (strain = 0.03). In addition, the density of screw dislocations at the later stage of deformation (strain = 0.20) increased in the presence of hydrogen. Based on the experimental results, it is proposed that a high density of vacancies accumulated along slip planes by jog-dragging of screw dislocations, and coalescence of the accumulated vacancies led to the hydrogen-related quasi-cleavage fracture along the {011} slip planes.
neutron diffraction study on the deformation of a TRIP-assisted multi-phase steel composed of ferrite, austenite and martensiteLavakumar, A.*; Park, M. H.*; Gao, S.*; 柴田 曉伸*; 興津 貴隆*; Gong, W.; Harjo, S.; 辻 伸泰*
IOP Conference Series; Materials Science and Engineering, 580, p.012036_1 - 012036_6, 2019/09
被引用回数：3 パーセンタイル：83.68(Engineering, Mechanical)Multi-phase steels showing transformation induced plasticity (TRIP), can exhibit an excellent combination of high strength and good ductility by the aid of martensitic transformation during deformation. Even though TRIP-assisted multi-phase steels have been widely used in industry, the role of each phase in the enhancement of mechanical properties is still unclear given their complicated microstructures. In order to understand better the nature of the TRIP effect, the mechanical interaction between different phases at the micro-scale should be clarified. In the present study, the mechanical behavior of a transformation induced plasticity (TRIP) assisted multi-phase steel, has been characterized by neutron diffraction during tensile testing. The result of strain partitioning between the different phases obtained from the neutron analysis revealed that the martensite phase took much more elastic strain than the ferrite and retained austenite phases, which suggests that the work hardening behavior in the present steel is affected by the higher load borne by deformation-induced martensite.
neutron diffraction analysis during thermomechanical processing柴田 曉伸*; 竹田 泰成*; Park, N.*; Zhao, L.*; Harjo, S.; 川崎 卓郎; Gong, W.*; 辻 伸泰*
Scripta Materialia, 165, p.44 - 49, 2019/05
被引用回数：29 パーセンタイル：85.46(Nanoscience & Nanotechnology)Nowadays, a new concept of process utilizing dynamic ferrite transformation, which can achieve ultrafine-grained structure with a mean grain size of approximately 1
m, has been proposed. This paper reports transformation mode of dynamic ferrite transformation and formation mechanism of ultrafine-grained structure revealed by our novel technique of neutron diffraction analysis during thermomechanical processing. Dynamic ferrite transformation occurs in a diffusional manner, whose partitioning behavior changes from para- to ortho-equilibrium with the progress of transformation. Moreover, we propose that dynamic recrystallization of dynamically-transformed ferrite is the main mechanism for the formation of ultrafine-grained structure.
中村 良彦*; 柴田 曉伸*; Gong, W.*; Harjo, S.; 川崎 卓郎; 伊東 篤志*; 辻 伸泰*
Proceedings of International Conference on Martensitic Transformations: Chicago, p.155 - 158, 2018/04
The microstructure evolution of medium manganese steel (Fe-5Mn-2Si-0.1C (wt%)) during thermo-mechanical processing in ferrite + austenite two-phase region was investigated by in situ neutron diffraction analysis and microstructure observations. When the specimens were isothermally held at a temperature of 700
C, the fraction of reversely transformed austenite increased gradually with an increase in the isothermal holding time. However, it did not reach the equilibrium fraction of austenite even after isothermal holding for 10 ks. On the other hand, the fraction of reversely transformed austenite increased rapidly after the compressive deformation at a strain rate of 1 s at 700C and reached the equilibrium state during subsequent isothermal holding for around 3 ks.
奴賀 秀男; 松山 顕之; 柴田 欣秀; 矢木 雅敏; 河野 康則; 福山 淳*
no journal, ,
ITERを含む将来の大型トカマクでは、ディスラプション時に発生する大量の逃走電子が第一壁との衝突することで装置寿命に悪影響を及ぼすと考えられている。したがって、逃走電子発生のメカニズムを明らかにすることは、ディスラプション制御手法を開発する上で重要な役割を果たす。本研究では、運動論的輸送コードであるTASK/FPを用いて熱クエンチ時に発生する速度分布のテイルの影響を考慮した逃走電子の生成と誘導電場の時間発展との自己無撞着な解析を行い、JT-60Uにおける実験データとの比較によりモデルの妥当性を評価する。
Harjo, S.; 柴田 曉伸*; Park, N.*; 川崎 卓郎; 大石 毅一郎*; 相澤 一也; 辻 伸泰*
no journal, ,
A new sample environmental device for simulating thermo-mechanical processes of materials (thermec-mastor) has been installed in a collaboration between a research group in Kyoto University and BL19 in MLF of J-PARC, within a scheme of Elements Strategy Initiative for Structural Materials supported by Ministry of Education, Culture, Sports, Science and Technology, Japan. This new device is designed to heat the specimens by induction heating and cool them by gas injection. The highest rates for heating and cooling are about 30 K/s. It can also apply compressive deformation with the highest rate of 100 mm/s. The basic design and the commissioning progress of the thermec-mastor will be briefly introduced together with the first neutron diffraction data on steels. At 300 kW accelerator operation, diffraction patterns sliced with the interval time of about 1 s could be used to determine the occurrence of phase transformation during thermo-mechanical processes.
Harjo, S.; 川崎 卓郎; 友田 陽*; 柴田 曉伸*; 辻 伸泰*; 相澤 一也
no journal, ,
Two topics done at TAKUMI of MLF, J-PARC are introduced. Evolutions of dislocation characteristics during tensile deformation in a lath martensitic steel have been possible to be monitored by applying the convolutional multiple whole profile (CMWP) fitting method, to understand the strengthening behavior of metallic material with extremely high dislocation density induced during the material preparation. This method is possible to be applied to understand the deformation behaviour of bulk nano materials. A new sample environmental device for simulating Thermo-Mechanical Controlling Process of materials (thermec-mastor) has been installed in a collaboration between a research group in Kyoto University and TAKUMI. This new device is designed to heat and cool a specimen rapidly, and to apply compression with a high strain rate. The basic design and the commissioning progress of the thermec-mastor will be briefly introduced together with the first neutron diffraction data on steels.
Harjo, S.; 川崎 卓郎; 相澤 一也; 柴田 曉伸*; 辻 伸泰*
no journal, ,
金属材料の加工熱処理制御プロセスをシミュレートするための新しいサンプル環境装置(thermec-mastor)は、文部科学省の構造材料元素戦略プロジェクト内で、京都大学とMLFのBL19(匠)研究グループ間の共同で開発し匠にインストールされた。本装置は、試験片を誘導加熱により加熱し、ガス注入によって冷却できるように設計されている。加熱と冷却の最高速度は約30K/sで、最高速度が100mm/sの圧縮変形を適用することが可能である。本装置の基本設計及び本装置を用いた鉄鋼材料の加工熱処理制御プロセス中のその場中性子回折実験について紹介する。
Gong, W.*; Harjo, S.; 柴田 曉伸*; 友田 陽*; 篠崎 智也*; 辻 伸泰*
no journal, ,
Quenching and partitioning (Q&P) process is an effective approach to control the amount and stability of retained austenite. Our previous study confirmed that carbon partitioning and isothermal transformation simultaneously occurred below martensitic transformation starting (Ms) temperature. In order to deepen the understanding on controlling microstructures through Q&P processes, the effect of ausforming on phase transformation and carbon partitioning during the Q&P process were investigated by the use of in-situ neutron diffraction in the present study.
Mao, W.; Gao, S.*; Gong, W.; Bai, Y.*; Park, M.-H.*; 柴田 曉伸*; 辻 伸泰*
no journal, ,
In this study, strain hardening behavior of Fe-24Ni-0.3C metastable austenitic steel having deformation induced martensitic transformation (DIMT) during deformation was investigated by tensile test with in-situ neutron diffraction, aiming to clarify the mechanism of the enhanced strain hardening caused by the DIMT. The results suggested that the evolution of phase stress of martensite during the deformation plays an important role in the strain hardening. It was found that during deformation the phase stress of martensite firstly increased rapidly from a low value, and then the rate of increase decreased as it approached 1.8 GPa. A dramatic increase in the stress partitioning between austenite and martensite was generated due to the rapid increase of martensite phase stress, which contributed significantly to the increase in the overall strain hardening rate of the material. The analysis of plastic deformation of austenite and martensite reveals that the rapid increase in stress partitioning occurred during the elasto-plastic deformation stage and arose from the occurrence of the plastic strain misfits.
Mao, W.; Gao, S.*; Gong, W.; Park, M. H.*; Bai, Y.*; 柴田 曉伸*; 辻 伸泰*
no journal, ,
Deformation induced martensitic transformation (DIMT) during plastic deformation of metastable austenitic steels plays an important role in enhancing their strain hardening, leading to an outstanding combination of strength and tensile ductility. In this study, Fe-24Ni-0.3C metastable austenitic steel specimens having mean grain sizes ranging from 1.3 micrometer to 35 micrometers were fabricated by cold rolling and subsequent annealing processes. The effect of the grain size on the strain hardening behavior and DIMT in the material was investigated by tensile test at room temperature with in-situ neutron diffraction. Results obtained by the in-situ neutron diffraction showed that the enhanced strain-hardening rate was caused not only by the increase of the volume fraction of martensite but also by the rapid increase of the internal stress within martensite. When the grain size changed within the coarse grained region (35 micrometers to 4 micrometers) the influence of the grain size on the stress partitioning between austenite and martensite was relatively small, thus the work-hardening behavior was mainly determined by the increasing rate of the volume fraction of martensite. However, when the grain size decreased down to ultrafine grain regime (smaller than 2 micrometers), the internal stress in martensite significantly increased, which resulted in the increasing work-hardening rate. The increasing stress in martensite in the ultrafine grained specimens is explained by the enhanced elastic stress associated with the incompatibility between martensite and austenite phases.
Gong, W.; Harjo, S.; 友田 陽*; 諸岡 聡; 川崎 卓郎; 柴田 曉伸*; 辻 伸泰*
no journal, ,
Austenite to martensite transformation in steels is a volume expansion phase transformation. However, the puzzling results have still been reported that a hydrostatic compressive stress was observed in austenite as opposite to the Eshelby's inclusion theory. In present study, we carried out neutron diffraction experiments having higher penetration ability than above methods to investigate the lattice parameter changes in real time during martensitic transformation. A high-purity Fe-18Ni binary alloy was selected to avoid the chemical contribution from the interstitial element. Several measuring processes were carefully designed and performed by in-situ neutron diffraction. Thermal phase stresses in martensite and austenite phases were separated from those stemmed from the face-centered cubic to body-centered cubic transformation strains and lattice defects. As results, the plastic accommodation is suggested to affect the lattice parameter of austenite and then its phase stress.
伊東 達矢; 小川 祐平*; Gong, W.; 川崎 卓郎; 岡田 和歩*; 柴田 曉伸*; Harjo, S.
no journal, ,
近年、水素添加によりSUS310Sの強度と延性が共に向上することが報告された。本研究では、「匠」を利用した引張試験中その場中性子回折実験を行い、転位密度や積層欠陥密度など、個々の因子に対する水素の影響を定量的に解明することを試みた。
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.
no journal, ,
カーボンニュートラルの実現のため、水素は化石燃料を代替するエネルギーキャリアとして注目を集めている。歴史的に水素は鉄鋼材料の脆化を引き起こすとされてきたが、小川らはSUS310Sに水素を添加することで強度と延性が共に向上することを報告した。これらは水素による固溶強化と双晶変形の促進によると定性的に説明されているが、変形中の転位や積層欠陥の発達に対して、水素がどのような影響を与えるかその詳細は明らかとなっていない。本研究は、その場中性子回折により、これらの欠陥に対する水素の影響を明らかにすることを目的とする。
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.
no journal, ,
近年、高圧ガス環境中で均一に水素を固溶させたオーステナイト系ステンレス鋼SUS310Sにおいて、強度・延性が共に向上することが報告された。これは水素による固溶強化と双晶変形の促進によると説明されているが、転位密度や積層欠陥など、個々の因子に対する水素の影響の詳細は明らかとなっていない。本研究では、J-PARCの工学材料回折装置「匠」での引張試験中その場中性子回折により、変形メカニズムを明らかにすることを試みた。得られた中性子回折パターンから、水素による体積変化や固溶強化の存在を確認した。更に、転位密度、積層欠陥密度、双晶変形開始ひずみ・応力を評価した。これらの解析により、水素が変形メカニズムに与える影響を明らかにした。
