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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:1 パーセンタイル:71.29(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.
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.
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.
Harjo, S.; Gong, W.; 相澤 一也; 山崎 倫昭*; 川崎 卓郎
日本材料学会第58回X線材料強度に関するシンポジウム講演論文集, p.58 - 60, 2024/07
The experiment and analysis procedures for a sample exhibiting multimodal structures were outlined. The sample, a MgZnY alloy, initially comprised two phases: the HCP matrix (Mg) and the long-period stacking ordered phase (LPSO), constituting approximately 25% of the volume. Through hot extrusion at 623 K with an extrusion ratio (R) of 5.0, the alloy was rendered multimodal. Specifically, at an R value of 5.0, dynamic recrystallization occurred partially within the Mg phase, resulting in a bimodal microstructure. This microstructure consisted of a deformed Mg component and a recrystallized Mg component. An analysis employing Electron Backscatter Diffraction (EBSD) data facilitated multimodal characterization, enabling successful determination of stresses within the individual Mg components, as well as the LPSO phase stress.
Harjo, S.; Gong, W.; 川崎 卓郎
日本材料学会第58回X線材料強度に関するシンポジウム講演論文集, p.51 - 54, 2024/07
In-situ neutron diffraction was used to study tensile deformation in an extruded AZ31 alloy. The aim was to validate existing methods and develop new ones for stress evaluation in magnesium alloys. Results showed varied increases in lattice strains among grains, posing challenges for conventional procedures. A new method, considering grain volume fraction and multiple orientations, proved highly accurate. When simultaneous hk.l peaks weren't available, the 12.1 peak was recommended for stress evaluation, showing a linear relationship with applied stress throughout deformation.
Mao, W.; Gong, W.; Harjo, S.; 諸岡 聡; Gao, S.*; 川崎 卓郎; 辻 伸泰*
Journal of Materials Science & Technology, 176, p.69 - 82, 2024/03
被引用回数:0 パーセンタイル:0.00(Materials Science, Multidisciplinary)Fe-24Ni-0.3C(wt.%)準安定オーステナイト鋼の降伏応力は、平均結晶粒径が35m(粗粒[CG])から0.5m(超微細粒[UFG])に減少すると3.5倍(158551MPa)に増加したが、引張伸びは大きく維持された(0.870.82)。結晶粒径が力学特性と変形機構に及ぼす影響を定量的に明らかにするため、室温での引張変形中にCGとUFG Fe-24Ni-0.3C鋼のその場中性子回折測定を行った。CGとUFG試料における塑性変形の初期段階は転位すべりによって支配され、変形後期には変形誘起マルテンサイト変態(DIMT)も生じた。結晶粒の微細化により、DIMTの開始応力が大きく増加し、ひずみに関するDIMTの速度が抑制されることがわかった。結果として、(i)結晶粒微細化によりオー ステナイトが安定化し、DIMTに対して最も安定な結晶粒である111//LD(LD:負荷方向)オーステナイト粒でのDIMTの開始が大幅に遅れた。その結果、UFG試験片の111//LDオーステナイト粒のほとんどはマルテンサイトに変態しなかった。(ii)結晶粒の微細化は、マルテンサイト変態の自己促進効果も抑制した。それにもかかわらず、UFG試験片の変態速度が低いDIMTは、CG試験片のより応力を増加させるのに効率がよく、変形中に均一な変形を維持するのに適していた。以上の現象は、UFG準安定オーステナイト鋼の優れた強度と延性の両立に相互に寄与している。
Gong, W.; Gholizadeh, R.*; 川崎 卓郎; 相澤 一也; Harjo, S.
Magnesium Technology 2024, p.89 - 90, 2024/03
Mg and its alloys generally exist as a single hcp crystal structure at room temperature. It is widely recognized that the application of Mg alloys is hindered by their limited formability at room temperature, primarily attributable to the scarcity of readily activated deformation modes within the hcp phase. The addition of Li in Mg alloy can stable the bcc phase at room temperature, and these dual-phase (hcp+bcc) Mg-Li alloys exhibit excellent formability. The Li-enriched bcc phase has been frequently considered as the origin for improving formability. However, these Mg-Li alloys show poor work-hardening ability and the resultant low strength at room temperature. Considering that the dislocation recovery can be suppressed by decreasing the deformation temperature and the activity of deformation mode may be changed with temperature, we investigated the deformation behavior of a commercial LZ91 magnesium alloy at cryogenic temperatures using in-situ neutron diffraction.
萩原 幸司*; 眞山 剛*; 山崎 倫昭*; Harjo, S.; 徳永 透子*; 山本 和輝*; 杉田 三佳*; 青山 海琳*; Gong, W.; 西本 宗矢*
International Journal of Plasticity, 173, p.103865_1 - 103865_21, 2024/02
被引用回数:5 パーセンタイル:98.05(Engineering, Mechanical)The unique control mechanisms of the plastic deformation of two-phase extruded alloy composed of Mg and long-period stacking ordered (LPSO) phase were clarified by comparison with those of other Mg solid-solution alloys, focusing on the question of why do the Mg/LPSO two-phase alloys exhibit both large elongation and high strength? The stress-strain curves for each grain in the alloys could be imaginary estimated using neutron diffraction analysis during the tensile test. The results demonstrate that the deformation behaviors of the worked and recrystallized grains are significantly different in all the Mg-extruded alloys owing to the strong plastic anisotropy in Mg with hexagonal close-packed (hcp) structure. Therefore, the deformation behavior is controlled by a composite-like deformation mechanism, even in single-phase Mg solid-solution alloys.
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*
鉄と鋼, 110(3), p.241 - 251, 2024/02
被引用回数:0 パーセンタイル:0.00(Metallurgy & Metallurgical Engineering)A Fe-0.15C-5Mn-0.5Si-0.05Nb medium Mn steel annealed at 660C and 685C both exhibited inhomogeneous deformation with Luders deformation and extremely high work hardening rates, but with different Luders strain and work hardening behavior. neutron diffraction measurements during tensile test were performed to investigate changes in the phase stresses and in the contributed stresses to the strength of the constituent phases, and crystal orientation of austenite. The role of each constituent phase in the deformation and the effect of crystallographic orientation on austenite stability were discussed. Deformation induced martensite showed excellent phase stress and contributed to the strength approximately 1000 MPa, which is close to macroscopic tensile strength.
上路 林太郎*; Gong, W.; Harjo, S.; 川崎 卓郎; 柴田 曉伸*; 木村 勇次*; 井上 忠信*; 土田 紀之*
ISIJ International, 64(2), p.459 - 465, 2024/01
被引用回数:0 パーセンタイル:0.00(Metallurgy & Metallurgical Engineering)Deformation-induced martensitic transformation (DIMT) during tensile or compressive deformations of the bainitic steels with various carbon content (0.15%C, 0.25%C, 0.62%C) was studied. In all of the bainitic steels, the tensile deformation exhibited larger work hardening than the compression. This difference indicates the suppression of the DIMT at the compression, and actually the measurements of electron back scattering diffraction (EBSD) confirmed the less reduction of retained austenite at the compression of all the bainitic steels. Additionally, the steel with the highest carbon content was examined by in situ neutron diffraction and clarified the difference similar to that obtained by the EBSD measurement. The regression of the relation between the fraction of austenite and applied strain with the conventional empirical equation revealed that the kinetic of DIMT is strongly dependent with the stress polarity, but not significantly changed by the carbon content.
山下 享介*; Harjo, S.; 川崎 卓郎; 諸岡 聡; Gong, W.; 藤井 英俊*; 友田 陽*
ISIJ International, 64(2), p.192 - 201, 2024/01
被引用回数:0 パーセンタイル:0.00(Metallurgy & Metallurgical Engineering)neutron diffraction measurements were performed on Fe-33Ni-0.004C alloy (33Ni alloy) and Fe-27Ni-0.5C alloy (27Ni-0.5C alloy) during cooling from room temperature to the cryogenic temperature (4 K) to evaluate changes in the lattice constants of austenite and martensite, and changes in the tetragonality of martensite due to thermally induced martensitic transformation. As the martensitic transformation progressed, the lattice constants of austenite in both alloys deviated to smaller values than those predicted considering the thermal shrinkage, accompanied by an increase in the full width at half maximum of austenite. The fresh martensite formed in both alloys had a body-centered tetragonal (BCT) structure, regardless of the carbon content. The tetragonality of martensite decreased with progressive martensitic transformation during cooling in the 33Ni alloy, but was almost constant in the 27Ni-0.5C alloy. This suggests that carbon is necessary to maintain the tetragonality of martensite during cooling. The tetragonality of martensite in the 27Ni-0.5C alloy decreased during room temperature aging because of carbon mobility.
Zhou, Y.*; Song, W.*; Zhang, F.*; Wu, Y.*; Lei, Z.*; Jiao, M.*; Zhang, X.*; Dong, J.*; Zhang, Y.*; Yang, M.*; et al.
Journal of Alloys and Compounds, 971, p.172635_1 - 172635_7, 2024/01
被引用回数:1 パーセンタイル:22.95(Chemistry, Physical)The grain orientation-dependent lattice strain evolution of a (TiZrHfNb) refractory high-entropy alloy (HEA) during tensile loading has been investigated using neutron diffraction. The equivalent strain-hardening rate of each of the primary -oriented grain families was found to be relatively low, manifesting the macroscopically weak work-hardening ability of such a body-centered cubic (BCC)-structured HEA. This finding is indicative of a dislocation planar slip mode that is confined in a few single-slip planes and leads to in-plane softening by high pile-up stresses.
Harjo, S.; Gong, W.; 川崎 卓郎
Quantum Beam Science (Internet), 7(4), p.32_1 - 32_13, 2023/12
Tensile deformation in situ neutron diffraction of an extruded AZ31 alloy was performed to validate conventional procedures and to develop new procedures for stress evaluation from lattice strains by diffraction measurements of HCP-structured magnesium alloys. Increases in the lattice strains with respect to the applied true stress after yielding largely vary among [] grains. The newly proposed procedure of stress evaluation from the lattice strains shows very high accuracy and reliability by weighting the volume fraction of [] grains and evaluating them in many [] orientations in addition to multiplication by the diffraction elastic constant. When multiple peaks cannot be obtained simultaneously, we recommend to use the 12.1 peak for stress evaluation.
段野下 宙志*; 長谷川 寛*; 樋口 翔*; 松田 広志*; Gong, W.; 川崎 卓郎; Harjo, S.; 梅澤 修*
Scripta Materialia, 236, p.115648_1 - 115648_5, 2023/11
被引用回数:0 パーセンタイル:0.00(Nanoscience & Nanotechnology)Work-hardening behavior of a lath martensitic Fe-18Ni alloy during tensile deformation is discussed based on the Taylor's equation. The dislocation characteristics are monitored using in situ neutron diffraction. In the specimens of as-quenched (AQ) and tempered at 573 K (T573), the dislocations are extremely dense and randomly arranged. The dislocations in AQ and T573 form dislocation cells as deformation progresses. Consequently, a composite condition comprising cell walls and cell interiors is formed, and the coefficient in the Taylor's equation increases. Cells are already present in the specimen tempered at 773 K (T773), which has a low dislocation density and a large fraction of edge-type dislocations. As deformation continues, the dislocation density of T773 increases, its cell size decreases, and its composite condition become stronger. Simultaneously, the edge-type dislocation fraction decreases, keeping unchanged. Thus, both the dislocation arrangement and character affected , thereby affecting the work-hardening behavior.
Mao, W.; Gao, S.*; Gong, W.; Harjo, S.; 川崎 卓郎; 辻 伸泰*
Scripta Materialia, 235, p.115642_1 - 115642_6, 2023/10
被引用回数:8 パーセンタイル:87.13(Nanoscience & Nanotechnology)本研究では、巨大なリューダースバンド変形を示す超微細粒(UFG)ステンレス鋼の引張その場中性子回折とデジタル画像相関測定を行い、バンド伝播中の歪硬化に対するオーステナイト母相と変形誘起マルテンサイトの個々の寄与を評価した。定量的解析の結果、UFG構造によって流動応力が大幅に増加した場合、オーステナイト母相のひずみ硬化は均一な変形を維持するには不十分であることがわかった。リューダースバンドの伝播に必要なひずみ硬化は、マルテンサイトの形成とその内部の高い内部応力によってもたらされた。
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:18 パーセンタイル:97.30(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。
Harjo, S.; Gong, W.; 相澤 一也; 川崎 卓郎; 山崎 倫昭*
Acta Materialia, 255, p.119029_1 - 119029_12, 2023/08
被引用回数:18 パーセンタイル:97.94(Materials Science, Multidisciplinary)An as-cast sample and two hot-extruded samples with different extrusion ratios (R) of MgZnY alloy containing the HCP matrix (Mg) and the long-period stacking ordered phase (LPSO) of about 25-vol%, were used in tensile deformation in situ neutron diffraction experiments, to elucidate the effects of uniquely different microstructural evolutions in Mg and LPSO with varying the R value to the mechanical properties. Mg behaved as the soft phase and LPSO as the hard phase, and hot-extrusion improved the strength of both. At the R value of 5.0, a bimodal microstructure was created in Mg, increasing largely the yield strength of Mg. With increasing the R value to 12.5, the bimodal microstructure of Mg collapsed and the yield strength of Mg decreased. However, the strength of LPSO increased monotonously with increasing the R value due to the developments of kink bands and texture.
Wang, Y.*; Gong, W.; 川崎 卓郎; Harjo, S.; Zhang, K.*; Zhang, Z. D.*; Li, B.*
Applied Physics Letters, 123(1), p.011903_1 - 011903_6, 2023/07
被引用回数:4 パーセンタイル:68.65(Physics, Applied)Bulk AgS is a plastic inorganic semiconductor at room temperature. It exhibits a compressive strain greater than 50%, which is highly different from brittle conventional counterparts, such as silicon. Here, we present the experimental investigation of the deformation behavior in a plastic inorganic semiconductor AgS using neutron diffraction during compressive deformation at room and elevated temperatures. At room temperature, the lattice strain partitioning among -orientated grain families could be responsible for the significant work-hardening behavior in the bulk AgS with a monoclinic structure. The rapid accumulation of lattice defects and remarkable development of the deformation texture suggest that dislocation slip promotes plasticity. At 453 K, a monoclinic phase transforms into a body-centered cubic phase. A stress plateau appears at -4.8 MPa, followed by a rehardening state. The deformation mode of bulk AgS at the initial stage is likely attributable to the migration of silver ions, and as strain increases, it is closer to that of room temperature, leading to rehardening.
Gong, 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:12 パーセンタイル:92.97(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.
Kwon, H.*; Sathiyamoorthi, P.*; Gangaraju, M. K.*; Zargaran, A.*; Wang, J.*; Heo, Y.-U.*; Harjo, S.; Gong, W.; Lee, B.-J.*; Kim, H. S.*
Acta Materialia, 248, p.118810_1 - 118810_12, 2023/04
被引用回数:31 パーセンタイル:99.38(Materials Science, Multidisciplinary)Maraging steels, known for ultrahigh strength and good fracture toughness, derive their superior properties from lath martensite structure with high-density nanoprecipitates. In this work, we designed a novel Fe-based medium-entropy alloy with a chemical composition of FeCoNiMo in atomic% by utilizing the characteristics of the maraging steels. By a single-step aging of only 10 min at 650 C, the alloy showed microstructures consisting of a very high number density of (Fe, Co, Ni)Mo-type nanoprecipitates in lath martensite structure and reverted FCC phase, which led to ultrahigh yield strength higher than 2 GPa. This work demonstrates a novel direction to produce strong and ductile materials by expanding the horizons of material design with the aid of high-entropy concept and overcoming the limits of conventional materials.