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論文

Martensitic transformation-governed Luders deformation enables large ductility and late-stage strain hardening in ultrafine-grained austenitic stainless steel at low temperatures

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.

論文

Polarized and unpolarized neutron scattering for magnetic materials at the triple-axis spectrometer PONTA in JRR-3

中島 多朗*; 齋藤 開*; 小林 尚暉*; 川崎 卓郎; 中村 龍也; 古川 はづき*; 浅井 晋一郎*; 益田 隆嗣*

Journal of the Physical Society of Japan, 93(9), p.091002_1 - 091002_5, 2024/09

 被引用回数:0

Neutron scattering is a powerful tool to study magnetic structures and cross-correlated phenomena originated from symmetry of the magnetic structures in matter. Among a number of neutron scattering techniques, polarized neutron scattering is quite sensitive to the orientations of the magnetic moments, which are essential to understand microscopic mechanisms of the spin-driven emergent phenomena. Here, we present POlarized Neutron Triple-Axis spectrometer PONTA in the Japan Research Reactor 3 (JRR-3), and show the present capabilities of polarized and unpolarized neutron scattering by introducing recent results from the instrument.

論文

Internal strain measurement by neutron diffraction under transverse compressive stress for Nb$$_{3}$$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 Nb$$_{3}$$Sn 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 Nb$$_{3}$$Sn 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 Nb$$_{3}$$Sn 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 Nb$$_{3}$$Sn under transverse compression between the samples with and without Cu-Nb reinforcement, while the Ic measurements showed potential increase in the irreversible stress ($$sigma$$$$_{irr}$$) for Cu-Nb reinforced wires. The reason for this discrepancy was discussed based on the difference in the experimental setups for each measurement.

論文

マルチピークを用いた応力評価

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.

論文

マルチモーダル化したマグネシウム合金の変形中の構成相・組織の挙動

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 Mg$$_{97}$$Zn$$_1$$Y$$_2$$ alloy, initially comprised two phases: the HCP $$alpha$$ matrix ($$alpha$$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 $$alpha$$Mg phase, resulting in a bimodal microstructure. This microstructure consisted of a deformed $$alpha$$Mg component and a recrystallized $$alpha$$Mg component. An analysis employing Electron Backscatter Diffraction (EBSD) data facilitated multimodal characterization, enabling successful determination of stresses within the individual $$alpha$$Mg components, as well as the LPSO phase stress.

論文

Microscopic insights of the extraordinary work-hardening due to phase transformation

Ma, Y.*; Naeem, M.*; Zhu, L.*; He, H.*; Sun, X.*; Yang, Z.*; He, F.*; Harjo, S.; 川崎 卓郎; Wang, X.-L.*

Acta Materialia, 270, p.119822_1 - 119822_13, 2024/05

 被引用回数:2 パーセンタイル:87.51(Materials Science, Multidisciplinary)

We report an in situ neutron diffraction study of 316 L that reveals an extraordinary work-hardening rate (WHR) of $$sim$$7 GPa at 15 K. Detailed analyses show that the major contribution to the excellent strength and ductility comes from the transformation-induced plasticity (TRIP) effect, introduced by the austenite-to-martensite ($$gamma$$-to-$$alpha$$') phase transition. A dramatic increase in the WHR is observed along with the transformation; the WHR declined when the austenite phase is exhausted. During plastic deformation, the volume-fraction weighted phase stress and stress contribution from the $$alpha$$'-martensite increase significantly. The neutron diffraction data further suggest that the $$gamma$$-to-$$alpha$$' phase transformation was mediated by the $$varepsilon$$-martensite, as evidenced by the concurrent decline of the $$varepsilon$$ phase with the $$gamma$$ phase.

論文

In-situ neutron diffraction study of serration-involved ultra-cryogenic deformation behavior at 15 K

Kim, Y. S.*; Chae, H.*; Lee, D.-Y.*; Han, J. H. *; Hong, S.-K.*; Na, Y. S.*; Harjo, S.; 川崎 卓郎; Woo, W.*; Lee, S.-Y.*

Materials Science & Engineering A, 899, p.146453_1 - 146453_7, 2024/05

 被引用回数:1 パーセンタイル:0.00(Nanoscience & Nanotechnology)

This work focused on the mechanical properties and serration-involved deformation behavior of advanced alloys at 15 K. Evolution of stacking faults and $$varepsilon$$-martensite improved the mechanical performance of CoCrNi alloys, and significant strain-induced martensite transformation of DED-SS316L led to superior strength and strain hardening. A magnitude in stress drop was governed by dislocation density, phase type, and lattice defects, irrespective of processing method. FCC {200} notably was influenced recovery behavior after stress drop, and the contribution of strain energy density by serration on tensile toughness was the greatest for HR-CoCrNi.

論文

Mechanical stability of retained austenite and texture evolution in additively manufactured stainless steel

Chae, H.*; Huang, E.-W.*; Jain, J.*; Lee, D.-H.*; Harjo, S.; 川崎 卓郎; Lee, S. Y.*

Metals and Materials International, 30(5), p.1321 - 1330, 2024/05

 被引用回数:4 パーセンタイル:66.62(Materials Science, Multidisciplinary)

In situ neutron diffraction during tensile deformation was performed for the stainless steels prepared by the additive manufacturing (AM) processes with two strategies: vertically built and horizontally built. The AM steels were further aged without solid solution treatment. As the results, the retained austenite was found to be more stable because the chemical composition became homogeneous by aging, and the onset of deformation induced martensitic transformation was delayed.

論文

Recrystallization of bulk nanostructured magnesium alloy AZ31 after severe plastic deformation; An in situ diffraction study

Liss, K.-D.*; Han, J.-K.*; Blankenburg, M.*; Lienert, U.*; Harjo, S.; 川崎 卓郎; 徐 平光; 行武 栄太郎*; Kawasaki, M.*

Journal of Materials Science, 59(14), p.5831 - 5853, 2024/04

 被引用回数:2 パーセンタイル:67.58(Materials Science, Multidisciplinary)

The magnesium alloy AZ31, which has undergone high-pressure torsion processing, was subjected to in situ annealing micro-beam synchrotron high-energy X-ray diffraction and compared to the as-received rolled sheet material that was investigated through in situ neutron diffraction. While the latter only exhibits thermal expansion and minor recovery, the nanostructured specimen displays a complex evolution, including recovery, strong recrystallization, phase transformations, and various regimes of grain growth. Nanometer-scale grain sizes, determined using Williamson-Hall analysis, exhibit seamless growth, aligning with the transition to larger grains, as assessed through the occupancy of single grain reflections on the diffraction rings. The study uncovers strain anomalies resulting from thermal expansion, segregation of Al atoms, and the kinetics of vacancy creation and annihilation. Notably, a substantial number of excess vacancies were generated through high-pressure torsion, and maintained for driving the recrystallization and forming highly activated volumes for diffusion and phase precipitation during heating. The unsystematic scatter observed in the Williamson-Hall plot indicates high dislocation densities following severe plastic deformation, which significantly decreases during recrystallization. Subsequently, dislocations reappear during grain growth, likely in response to torque gradients in larger grains. It is worth noting that the characteristics of unsystematic scatter differ for dislocations created at high and low temperatures, underscoring the strong temperature dependence of slip system activation.

論文

${it In situ}$ neutron diffraction revealing the achievement of excellent combination of strength and ductility in metastable austenitic steel by grain refinement

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35$$mu$$m(粗粒[CG])から0.5$$mu$$m(超微細粒[UFG])に減少すると3.5倍(158$$rightarrow$$551MPa)に増加したが、引張伸びは大きく維持された(0.87$$rightarrow$$0.82)。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。

論文

Cryogenic deformation behavior of a dual-phase Mg-Li alloy investigated by in-situ neutron diffraction

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.

論文

Fe-5Mn-0.1C中Mn鋼におけるリューダース帯伝播中の階層的不均一変形; その場走査型電子顕微鏡観察

小山 元道*; 山下 享介*; 諸岡 聡; Yang, Z.*; Varanasi, R. S.*; 北條 智彦*; 川崎 卓郎; Harjo, S.

鉄と鋼, 110(3), p.205 - 216, 2024/02

 被引用回数:0 パーセンタイル:0.00(Metallurgy & Metallurgical Engineering)

${it In situ}$ deformation experiments with cold-rolled and intercritically annealed Fe-5Mn-0.1C steel were carried out at ambient temperature to characterize the deformation heterogeneity during L$"u$ders band propagation. Deformation band formation, which is a precursor phenomenon of L$"u$ders band propagation, occurred even in the macroscopically elastic deformation stage. The deformation bands in the L$"u$ders front grew from both the side edges to the center of the specimen. After macroscopic yielding, the thin deformation bands grew via band branching, thickening, multiple band initiation, and their coalescence, the behavior of which was heterogeneous. Thick deformation bands formed irregularly in front of the region where the thin deformation bands were densified. The thin deformation bands were not further densified when the spacing of the bands was below $$sim$$ 10 $$mu$$m. Instead, the regions between the deformation bands showed a homogeneous plasticity evolution. The growth of the thin deformation bands was discontinuous, which may be due to the presence of ferrite groups in the propagation path of the deformation bands. Based on these observations, a model for discontinuous L$"u$ders band propagation has been proposed.

論文

Role of retained austenite and deformation induced martensite in 0.15C-5Mn steel monitored by ${it in-situ}$ 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*

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 660$$^{circ}$$C and 685$$^{circ}$$C both exhibited inhomogeneous deformation with Luders deformation and extremely high work hardening rates, but with different Luders strain and work hardening behavior. ${it In-situ}$ 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.

論文

Fe-5Mn-0.1C中Mn鋼におけるリューダース変形中の微視組織および塑性の発達

小山 元道*; 山下 享介*; 諸岡 聡; 澤口 孝宏*; Yang, Z.*; 北條 智彦*; 川崎 卓郎; Harjo, S.

鉄と鋼, 110(3), p.197 - 204, 2024/02

 被引用回数:0 パーセンタイル:0.02

The local plasticity and associated microstructure evolution in Fe-5Mn-0.1C medium-Mn steel (wt.%) were investigated in this study. Specifically, the micro-deformation mechanism during L$"u$ders banding was characterized based on multi-scale electron backscatter diffraction measurements and electron channeling contrast imaging. Similar to other medium-Mn steels, the Fe-5Mn-0.1C steel showed discontinuous macroscopic deformation, preferential plastic deformation in austenite, and deformation-induced martensitic transformation during L$"u$ders deformation. Hexagonal close-packed martensite was also observed as an intermediate phase. Furthermore, an in-situ neutron diffraction experiment revealed that the pre-existing body- centered cubic phase, which was mainly ferrite, was a minor deformation path, although ferrite was the major constituent phase.

論文

Deformation-induced martensitic transformation at tensile and compressive deformations of bainitic steels with different carbon contents

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.

論文

Martensitic transformation behavior of Fe-Ni-C alloys monitored by ${it in-situ}$ neutron diffraction during cryogenic cooling

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)

${it In situ}$ 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.

論文

Probing deformation behavior of a refractory high-entropy alloy using ${it in situ}$ neutron diffraction

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)$$_{98}$$$$N_2$$ refractory high-entropy alloy (HEA) during tensile loading has been investigated using ${it in situ}$ neutron diffraction. The equivalent strain-hardening rate of each of the primary $$<hkl>$$-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.

論文

Stress evaluation method by neutron diffraction for HCP-structured magnesium alloy

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 [${it hk.l}$] grains. The newly proposed procedure of stress evaluation from the lattice strains shows very high accuracy and reliability by weighting the volume fraction of [${it hk.l}$] grains and evaluating them in many [${it hk.l}$] orientations in addition to multiplication by the diffraction elastic constant. When multiple ${it hk.l}$ peaks cannot be obtained simultaneously, we recommend to use the 12.1 peak for stress evaluation.

論文

Effects of dislocation arrangement and character on the work hardening of lath martensitic steels

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 $$alpha$$ 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 $$alpha$$ unchanged. Thus, both the dislocation arrangement and character affected $$alpha$$, thereby affecting the work-hardening behavior.

論文

Measurement of mechanical behavior of $$^{11}$$B-enriched MgB$$_{2}$$ wire using a pulsed neutron source

町屋 修太郎*; 長村 光造*; 菱沼 良光*; 谷口 博康*; Harjo, S.; 川崎 卓郎

Quantum Beam Science (Internet), 7(4), p.34_1 - 34_17, 2023/10

Measuring the actual strain on the MgB$$_2$$ filaments are of paramount importance, since tensile stress and strain diminish the critical current. In this study, the strain measurement using neutron diffraction during tensile loading was established. We fabricated a MgB$$_2$$ wire enriched with boron-11, an isotope having a smaller neutron absorption cross- section than natural boron, and succeeded in obtaining changes in the lattice constant under tensile loading through Rietveld analysis.

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