Updated on 2024/10/28

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写真a

 
TANG YONGPENG
 
Organization
Faculty of Engineering Sciences Department of Advanced Materials Science and Engineering Assistant Professor
Title
Assistant Professor
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Papers

  • Superconductivity of barium with highest transition temperatures in metallic materials at ambient pressure

    Mito M., Tsuji H., Tajiri T., Nakamura K., Tang Y., Horita Z.

    Scientific Reports   14 ( 1 )   2024.12

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    Publisher:Scientific Reports  

    Pressure-induced superconductivity often occurs following structural transition under hydrostatic pressure (P HP) but disappears after the pressure is released. In the alkali-earth metal barium, superconductivity appears after structural transformation from body-centered cubic structure to hexagonal-close-packed (hcp) structure at P HP = 5 GPa, and the superconducting transition temperature (T c) reaches a maximum of 5 K at P HP = 18 GPa. Furthermore, by stabilizing the low-temperature phase at P HP ~ 30 GPa, Tc reached a higher level of 8 K. Herein, we demonstrate a significantly higher T c superconductivity in Ba even at ambient pressure. This was made possible through severe plastic deformation of high-pressure torsion (HPT). In this HPT-processed Ba, we observed superconductivity at T c = 3 K and T c = 24 K in the quasi-stabilized hcp and orthorhombic structures, respectively. In particular, the latter T c represents the highest value achieved at ambient pressure among single-element superconducting metals, including intermetallics. The phenomenon is attributed to a strained high-pressure phase, stabilized by residual strains generated from lattice defects such as dislocations and grain boundaries. Significantly, the observed T c far exceeds predictions from DFT calculations under normal hydrostatic compressions. The study demonstrates the importance of utilizing high-pressure strained phases as quasi-stable superconducting states at ambient pressure.

    DOI: 10.1038/s41598-023-50940-5

    Scopus

  • Severe plastic deformation for producing superfunctional ultrafine-grained and heterostructured materials: An interdisciplinary review

    Edalati, K; Ahmed, AQ; Akrami, S; Ameyama, K; Aptukov, V; Asfandiyarov, RN; Ashida, M; Astanin, V; Bachmaier, A; Beloshenko, V; Bobruk, E; Bryla, K; Cabrera, JM; Carvalho, AP; Chinh, NQ; Choi, IC; Chulist, R; Cubero-Sesin, JM; Davdian, G; Demirtas, M; Divinski, S; Durst, K; Dvorak, J; Edalati, P; Emura, S; Enikeev, NA; Faraji, G; Figueiredo, RB; Floriano, R; Fouladvind, M; Fruchart, D; Fuji, M; Fujiwara, H; Gajdics, M; Gheorghe, D; Gondek, L; Gonzalez-Hernandez, JE; Gornakova, A; Grosdidier, T; Gubicza, J; Gunderov, D; He, LQ; Higuera, OF; Hirosawa, S; Hohenwarter, A; Horita, Z; Horky, J; Huang, Y; Huot, J; Ikoma, Y; Ishihara, T; Ivanisenko, Y; Jang, JI; Jorge, AM Jr; Kawabata-Ota, M; Kawasaki, M; Khelfa, T; Kobayashi, J; Kommel, L; Korneva, A; Kral, P; Kudriashova, N; Kuramoto, S; Langdon, TG; Lee, DH; Levitas, VI; Li, C; Li, HW; Li, YT; Li, Z; Lin, HJ; Liss, KD; Liu, Y; Cardona, DMM; Matsuda, K; Mazilkin, A; Mine, Y; Miyamoto, H; Moon, SC; Müller, T; Muñoz, JA; Murashkin, MY; Naeem, M; Novelli, M; Olasz, D; Pippan, R; Popov, VV; Popova, EN; Purcek, G; de Rango, P; Renk, O; Retraint, D; Révész, A; Roche, V; Rodriguez-Calvillo, P; Romero-Resendiz, L; Sauvage, X; Sawaguchi, T; Sena, H; Shahmir, H; Shi, XB; Sklenicka, V; Skrotzki, W; Skryabina, N; Staab, F; Straumal, B; Sun, ZD; Szczerba, M; Takizawa, Y; Tang, YP; Valiev, RZ; Vozniak, A; Voznyak, A; Wang, B; Wang, JT; Wilde, G; Zhang, F; Zhang, M; Zhang, P; Zhou, JQ; Zhu, XK; Zhu, YT

    JOURNAL OF ALLOYS AND COMPOUNDS   1002   2024.10   ISSN:0925-8388 eISSN:1873-4669

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    Publisher:Journal of Alloys and Compounds  

    Ultrafine-grained and heterostructured materials are currently of high interest due to their superior mechanical and functional properties. Severe plastic deformation (SPD) is one of the most effective methods to produce such materials with unique microstructure-property relationships. In this review paper, after summarizing the recent progress in developing various SPD methods for processing bulk, surface and powder of materials, the main structural and microstructural features of SPD-processed materials are explained including lattice defects, grain boundaries and phase transformations. The properties and potential applications of SPD-processed materials are then reviewed in detail including tensile properties, creep, superplasticity, hydrogen embrittlement resistance, electrical conductivity, magnetic properties, optical properties, solar energy harvesting, photocatalysis, electrocatalysis, hydrolysis, hydrogen storage, hydrogen production, CO2 conversion, corrosion resistance and biocompatibility. It is shown that achieving such properties is not limited to pure metals and conventional metallic alloys, and a wide range of materials are currently processed by SPD, including high-entropy alloys, glasses, semiconductors, ceramics and polymers. It is particularly emphasized that SPD has moved from a simple metal processing tool to a powerful means for the discovery and synthesis of new superfunctional metallic and nonmetallic materials. The article ends by declaring that the borders of SPD have been extended from materials science and it has become an interdisciplinary tool to address scientific questions such as the mechanisms of geological and astronomical phenomena and the origin of life.

    DOI: 10.1016/j.jallcom.2024.174667

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  • Improving thermoelectric properties of Bi2Te3 by straining under high pressure: Experiment and DFT calculation

    Wang, Q; Tang, YP; Miura, A; Miyazaki, K; Horita, Z; Iikubo, S

    SCRIPTA MATERIALIA   243   2024.4   ISSN:1359-6462 eISSN:1872-8456

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    Publisher:Scripta Materialia  

    Bi2Te3 intermetallic compounds show high thermoelectric performance near room temperature and are widely used for cooling and power generation applications. It is still necessary to improve its dimensionless figure of merit zT for large-scale industrial use. In this study, high-pressure torsion processing is applied to Bi2Te3 powder samples to investigate the crystal structure and enhance their thermoelectric properties. The processed Bi2Te3 samples show reduced cell volume, higher electrical conductivity, enhanced Seebeck coefficient and higher zT value compared with the original powder sample, even if the grain refinement is not remarkable. First-principles calculations are also used to investigate the electronic structure and thermoelectric properties to clarify the influence of high-pressure torsion processing.

    DOI: 10.1016/j.scriptamat.2024.115991

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  • Achieving high-T<inf>c</inf> superconductivity in Magnéli phase based on Ti oxides: prediction by machine learning and material synthesis by high-pressure torsion processing

    Mito M., Mokutani N., Tang Y., Matsumoto K., Tajiri T., Horita Z.

    Journal of Materials Science   59 ( 14 )   5981 - 5994   2024.4   ISSN:00222461

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    Publisher:Journal of Materials Science  

    We explored superconductors with high superconducting transition temperatures (Tc) tuning the stability of Magnéli phase through high-pressure torsion (HPT). This study has started from exploring superconducting states in the Al–Mg–O ternary system along with the prediction using machine learning. We successfully found superconducting states with Tc = 4.0 and 7.3 K for a composition of Al:Ti = 1:2 in the mixture of Al and surface-oxidized Ti powders. Another magnetic anomaly was also observed at ~ 93 K, being supported by the Tc prediction using the machine learning for the Al–Ti–O system. In this study, the HPT processing was also performed on a Magnéli material Ti4O7 and such mixtures of stable materials as Al + TiO2, Al2O3 + Ti, Al2O3 + TiO2, and Al + Ti4O7. In HPT-processed Ti4O7, the metal–insulator transition was maintained even after the HPT processing. HPT experiments using stable oxides indicate the difficulty of newly stabilizing the Magnéli phase starting from thermodynamically stable materials under severe plastic deformation. A series of attempts reveals that the superconducting state in the mixture with ratio Al:Ti = 1:2 is attributed to both strained Ti-oxide created on the surface of the Ti powder and its reaction with Al under HPT processing, resulting in the stabilization of a Magnéli phase. Graphical Abstract: (Figure presented.).

    DOI: 10.1007/s10853-024-09406-w

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  • Microstructural modification and mechanical improvement of ultrafine-grained Ti alloy through electron wind force: An innovative approach

    Tang, YP; Ju, Y; Gu, SJ; Wang, Q; Kimura, Y; Toku, Y; Iikubo, S

    MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING   891   2024.1   ISSN:0921-5093 eISSN:1873-4936

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    Publisher:Materials Science and Engineering: A  

    This study focuses on the effect of high-density pulsed electric current (HDPEC) on the microstructure and mechanical properties of ultrafine-grained (UFG) Ti–6Al–7Nb (mass%) alloy. After the UFG Ti alloy prepared by high-pressure torsion (HPT), the samples exhibit high tensile yield strengths of 1200 MPa with total elongation of ∼20 %. Interestingly, an unusual improved elongation of ∼33 % with a yield strength of 1100 MPa was obtained in samples processed by HPT plus HDPEC. Quantitative evaluation shows that the improved ductility is attributed to the decreasing of dislocation density. The electron wind force played an important role to promote the movement of dislocation easier with the assistance of local Joule heating during HDPEC processing. It is shown that the bimodal structure with a low dislocation density leads to the high strength and high ductility. It indicated that HDPEC give an effective method to improve the ductility in UFG alloys.

    DOI: 10.1016/j.msea.2023.145845

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  • <i>In Situ</i> Synchrotron High-Pressure X-ray Analysis for ZnO with Rocksalt Structure

    Horita Zenji, Tang Yongpeng, Masuda Takahiro, Edalati Kaveh, Higo Yuji

    Journal of the Japan Institute of Metals and Materials   advpub ( 0 )   2024   ISSN:00214876 eISSN:18806880

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    Language:Japanese   Publisher:The Japan Institute of Metals and Materials  

    <p>Zinc oxide (ZnO) with a rocksalt crystal structure is attractive because of the bandgap which lies in the range of visible light absorption (1.2-2.6 eV). However, the rocksalt structure is not stable at ambient pressure and temperature according to an equilibrium phase diagram. Nevertheless, this study demonstrates, for the first time, that it is possible to realize a 100% fraction of the rocksalt structure at ambient pressure and temperature. ZnO powder is initially processed by severe plastic deformation under high pressure through a technique of high-pressure torsion (HPT). The HPT-processed ZnO is then examined using a high-pressure application system available at BL04B1 of SPring-8 and <i>in situ </i>X-ray diffraction (XRD) analysis is conducted under high pressures at elevated temperatures. It is shown that the initial presence of the rocksalt structure produced by the HPT process is effective to attain a 100% fraction of the rocksalt structure.</p>

    DOI: 10.2320/jinstmet.jd202402

    CiNii Research

  • Comparison of Mechanical Properties in Ultrafine Grained Commercial-Purity Aluminum (A1050) Processed by Accumulative Roll Bonding (ARB) and High-Pressure Sliding (HPS)

    Tang Yongpeng, Fujii Toshiki, Hirosawa Shoichi, Matsuda Kenji, Terada Daisuke, Horita Zenji

    Journal of the Japan Institute of Metals and Materials   advpub ( 0 )   2024   ISSN:00214876 eISSN:18806880

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    Language:Japanese   Publisher:The Japan Institute of Metals and Materials  

    <p>This study presents that A1050 commercial-purity aluminum increases the tensile strength and ductility using the processes of accumulative roll bonding (ARB) and high-pressure sliding (HPS). Both processes yield a similar tensile strength exceeding 240 MPa after processing by ARB for 10 cycles and by HPS for the sliding distance of 15 mm, respectively. The stress-strain behavior is evaluated through microstructure observations and measurements of strain hardening rates. Significant grain refinement with well-defined grain boundaries is responsible for the strength increase. The grain refinement also leads to an increase in strain hardening rate and thus an increase in the ductility.</p>

    DOI: 10.2320/jinstmet.jd202411

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  • Simultaneous enhancement of strength and ductility in nonflammable Mg alloys through dynamic precipitation using severe plastic deformation under high pressure

    Tang, YP; Inoue, S; Mito, M; Masuda, T; Higo, Y; Tange, Y; Ohishi, Y; Kawamura, Y; Horita, Z

    MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING   881   2023.8   ISSN:0921-5093 eISSN:1873-4936

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    Publisher:Materials Science and Engineering: A  

    This study focuses on the effect of high-pressure torsion (HPT) on the microstructure, mechanical properties, electrical conductivity and ignition temperature of a Mg–6Al–3Ca-0.02Mn-0.008Be (at%) alloy. The HPT-processed samples exhibit high tensile yield strengths of 400 MPa with total elongations of ∼5%. Quantitative evaluation shows that the high tensile strength is attributed to the ultrafine grain refinement, the generation of high dislocation density and the fragmentation of intermetallic particles to nanoscales. Dynamic precipitation of nanosized particles during the HPT processing at elevated temperature might have also contributed to the high strengthening. It is shown that homogeneous grain refinement throughout the sample leads to the simultaneous enhancement of strength and ductility. The electrical conductivity is restored due to concomitant precipitation during the HPT processing at 573 K. There is no appreciable difference in the ignition temperature between before and after the HPT processing.

    DOI: 10.1016/j.msea.2023.145395

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  • Comparison of Mechanical Properties in Ultrafine Grained Commercial-Purity Aluminum (A1050) Processed by Accumulative Roll Bonding (ARB) and High-Pressure Sliding (HPS)

    Tang Yongpeng, Fujii Toshiki, Hirosawa Shoichi, Matsuda Kenji, Terada Daisuke, Horita Zenji

    MATERIALS TRANSACTIONS   64 ( 8 )   1902 - 1911   2023.8   ISSN:13459678 eISSN:13475320

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    Language:English   Publisher:The Japan Institute of Metals and Materials  

    <p>This study presents that A1050 commercial-purity aluminum increases the tensile strength and ductility using the processes of accumulative roll bonding (ARB) and high-pressure sliding (HPS). Both processes yield a similar tensile strength exceeding 240 MPa after processing by ARB for 10 cycles and by HPS for the sliding distance of 15 mm, respectively. The stress-strain behavior is evaluated through microstructure observations and measurements of strain hardening rates. Significant grain refinement with well-defined grain boundaries is responsible for the strength increase. The grain refinement also leads to an increase in strain hardening rate and thus an increase in the ductility.</p>

    DOI: 10.2320/matertrans.mt-mf2022047

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  • Enhancement of Activation and Hydrogen Storage Kinetics of TiFe(Mn) Using High-Pressure Sliding (HPS) Process

    Horita Zenji, Tang Yongpeng, Matsuo Motoaki, Edalati Kaveh, Yumoto Manabu, Takizawa Yoichi

    MATERIALS TRANSACTIONS   64 ( 8 )   1920 - 1923   2023.8   ISSN:13459678 eISSN:13475320

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    Language:English   Publisher:The Japan Institute of Metals and Materials  

    <p>A titanium–iron intermetallic with minor addition of manganese (TiFe<sub>0.7</sub>Mn<sub>0.3</sub>) was processed by severe plastic deformation through high-pressure sliding (HPS). A rectangular strip sample was embedded in stainless steel and strained under a pressure of 4 GPa at room temperature. The hydrogen storage kinetics and activation of the HPS-processed sample were significantly enhanced in comparison with the as-received ingot without the HPS processing.</p>

    DOI: 10.2320/matertrans.mt-mf2022059

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  • Ultrafine-grained AZ61 alloy produced by high-pressure torsion: Advent of superplasticity and effect of anisotropy

    Masuda, T; Tang, YP; Mohamed, IF; Horita, Z

    MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING   879   2023.7   ISSN:0921-5093 eISSN:1873-4936

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    Publisher:Materials Science and Engineering: A  

    In this study, an AZ61 Mg alloy was processed by high-pressure torsion (HPT) for grain refinement. The HPT process was carried out using the facility with an upscaled capacity of 500 ton so that 30 mm diameter disks were processed under 6 GPa. Tensile tests were carried out at elevated temperatures and microstructures were observed by transmission electron microscopy (TEM). The grain size was well reduced to ∼320 nm after HPT processing at 423 K for 10 turns. This reduction in the grain size led to superplastic elongation more than 400% at 473 K with an initial strain rate of 1.0 × 10−3 s−1. The results were then compared with those obtained using conventional 10 mm diameter disks. The total elongation is invariably higher for the 30 mm disks than the 10 mm disks. This difference is discussed based on the anisotropy due to material flow.

    DOI: 10.1016/j.msea.2023.145240

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  • <i>In Situ</i> Synchrotron High-Pressure X-ray Analysis for ZnO with Rocksalt Structure

    Horita Zenji, Tang Yongpeng, Masuda Takahiro, Edalati Kaveh, Higo Yuji

    MATERIALS TRANSACTIONS   64 ( 7 )   1585 - 1590   2023.7   ISSN:13459678 eISSN:13475320

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    Language:English   Publisher:The Japan Institute of Metals and Materials  

    <p>Zinc oxide (ZnO) with a rocksalt crystal structure is attractive because of the bandgap which lies in the range of visible light absorption (1.2–2.6 eV). However, the rocksalt structure is not stable at ambient pressure and temperature according to an equilibrium phase diagram. Nevertheless, this study demonstrates, for the first time, that it is possible to realize a 100% fraction of the rocksalt structure at ambient pressure and temperature. ZnO powder is initially processed by severe plastic deformation under high pressure through a technique of high-pressure torsion (HPT). The HPT-processed ZnO is then examined using a high-pressure application system available at BL04B1 of SPring-8 and <i>in situ</i> X-ray diffraction (XRD) analysis is conducted under high pressures at elevated temperatures. It is shown that the initial presence of the rocksalt structure produced by the HPT process is effective to attain a 100% fraction of the rocksalt structure.</p>

    DOI: 10.2320/matertrans.mt-mf2022036

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  • <i>In Situ</i> Synchrotron X-ray Analysis: Application of High-Pressure Sliding Process to Ti Allotropic Transformation

    Horita Zenji, Maruno Daisuke, Ikeda Yukimasa, Masuda Takahiro, Tang Yongpeng, Arita Makoto, Higo Yuji, Tange Yoshinori, Ohishi Yasuo

    Journal of the Japan Institute of Metals and Materials   87 ( 2 )   56 - 65   2023.2   ISSN:00214876 eISSN:18806880

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    Language:Japanese   Publisher:The Japan Institute of Metals and Materials  

    <p>In this study, severe plastic deformation through high-pressure sliding (HPS) was applied for <i>in situ</i> high-energy X-ray diffraction analysis at SPring-8 in JASRI (Japan Synchrotron Radiation Research Institute). Allotropic transformation of pure Ti was examined in terms of temperatures, pressures and imposed strain using a miniaturized HPS facility. The true pressure applied on the sample was estimated from the peak shift. Peak broadening due to local variation of pressure was reduced using white X-ray. The phase transformation from α phase to ω phase occurred at a pressure of ∼4.5 GPa. Straining by the HPS processing was effective to promote the transformation to the ω phase and to maintain the ω phase even at ambient pressure. The reverse transformation from ω phase to α phase occurred at a temperature of ∼110℃ under ambient pressure, while under higher pressure as ∼4 GPa, the ω phase remained stable even at ∼170℃ covered in this study. It was suggested that the reverse transformation from the ω phase to the α phase is controlled by thermal energy.</p><p> </p><p>Mater. Trans. <b>62</b> (2021) 167-176に掲載</p>

    DOI: 10.2320/jinstmet.j2022040

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  • Mechanical Properties and Microstructures of Highly Fe-Containing Al–Mg–Si Alloys Processed by Severe Plastic Deformation under High Pressure

    Tang Yongpeng, Tomita Yuto, Horita Zenji

    MATERIALS TRANSACTIONS   64 ( 2 )   448 - 457   2023.2   ISSN:13459678 eISSN:13475320

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    Language:English   Publisher:The Japan Institute of Metals and Materials  

    <p>In this study, A6022-based Al–Mg–Si alloys with three additional Fe contents are processed by high-pressure torsion (HPT) and high-pressure sliding (HPS). Both processes yield a similar tensile strength exceeding 400 MPa. Fe intermetallics were finely and homogeneously fragmented to an average size of ∼2 µm by the HPT process. The high tensile strength is attributed to such a fine and homogeneous fragmentation of Fe intermetallics. It is also demonstrated that the finely fragmented Fe intermetallics play an important role to maintain finer grain size even after solution treatment.</p>

    DOI: 10.2320/matertrans.mt-la2022054

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  • Production of Ultrafine-Grained Aluminum Alloys in Upsized Sheets Using Process of Incremental Feeding High-Pressure Sliding (IF-HPS)

    Komatsu Takuya, Masuda Takahiro, Tang Yongpeng, Mohamed Intan Fadhlina, Yumoto Manabu, Takizawa Yoichi, Horita Zenji

    MATERIALS TRANSACTIONS   64 ( 2 )   436 - 442   2023.2   ISSN:13459678 eISSN:13475320

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    Language:English   Publisher:The Japan Institute of Metals and Materials  

    <p>This study introduces a process of severe plastic deformation (SPD) called incremental feeding high-pressure sliding (IF-HPS) where significant grain refinement is possible in an enlarged sheet area. The IF-HPS process is applied to Al alloys such as A1050, A3105, A5052 and A5182. The grain sizes were refined to the submicrometer ranges and the tensile strength increased to almost twice as much as the annealed states. The conditions for the IF-HPS process are optimized so that the tensile strength remains high without initiation of cracks. The process conditions are also investigated to achieve homogeneous development of the tensile properties throughout the processed sheets. It is demonstrated that the IF-HPS process is useful to extend the SPD-processed area without increasing the machine capacity while maintaining enhanced mechanical properties.</p>

    DOI: 10.2320/matertrans.mt-la2022032

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  • Exploration of Superconductivity in Three-elements Light Metal System~Proposing Exploration Strategy and Assuming Superconducting Components by Machine Learning~

    Mokutani Narimichi, Tang Yongpeng, Mito Masaki, Matsumoto Kaname, Murayama Mitsuhiro, Horita Zenji

    Materia Japan   61 ( 12 )   870 - 877   2022.12   ISSN:13402625 eISSN:18845843

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    Language:Japanese   Publisher:The Japan Institute of Metals and Materials  

    DOI: 10.2320/materia.61.870

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  • Structural and thermoelectric properties of CH<sub>3</sub>NH<sub>3</sub>SnI<sub>3</sub> perovskites processed by applying high pressure with shear strain

    Wang, Q; Tang, YP; Horita, ZJ; Iikubo, S

    MATERIALS RESEARCH LETTERS   10 ( 8 )   521 - 529   2022.8   ISSN:2166-3831

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    Publisher:Materials Research Letters  

    CH3NH3SnI3 perovskites, which can be created using printing technology, are environmentally friendly thermoelectric materials, but their applications are limited by unsatisfactory thermoelectric efficiency and structural stability. In this work, CH3NH3SnI3 perovskites are processed by applying high pressure with shear strain for the first time, resulting in better structural stability, enhanced electrical conductivity and the Seebeck coefficient with CH3NH3SnI3 tube structures after processing. First-principles calculations verified the reasonable changes in lattice constants, electronic band structures, electrical conductivity and the Seebeck coefficient. The present study demonstrates a potential strategy to improve the structural and thermoelectric properties of CH3NH3SnI3 and uncovers the possible mechanism.

    DOI: 10.1080/21663831.2022.2057821

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  • Severe Plastic Deformation under High Pressure: Upsizing Sample Dimensions

    Horita Zenji, Tang Yongpeng, Masuda Takahiro, Takizawa Yoichi

    Journal of the Japan Institute of Metals and Materials   86 ( 7 )   107 - 120   2022.7   ISSN:00214876 eISSN:18806880

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    Language:Japanese   Publisher:The Japan Institute of Metals and Materials  

    <p>It is well known that severe plastic deformation (SPD) produces ultrafine-grained structures in bulk metallic materials. The SPD process becomes more versatile when it is performed under high pressure as high-pressure torsion (HPT) and high-pressure sliding (HPS). Not only the grain size is more refined but also the process is applicable to hard-to-deform materials such as intermetallics, semiconductors and ceramics, leading to enhancement of functional properties as well as structural properties. The major drawback is that the sample size is small so that the applicability is limited to a laboratory scale and it is an important subject to increase the sample dimensions. This paper presents an overview describing efforts devoted thus far to deal with this upscaling issue.</p><p> </p><p>Mater. Trans. <b>61</b> (2020) 1177-1190に掲載</p>

    DOI: 10.2320/jinstmet.j2022009

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  • Achieving superconductivity with higher <i>T</i><sub>c</sub> in lightweight Al-Ti-Mg alloys: Prediction using machine learning and synthesis via high-pressure torsion process

    Mito, M; Mokutani, N; Tsuji, H; Tang, YP; Matsumoto, K; Murayama, M; Horita, Z

    JOURNAL OF APPLIED PHYSICS   131 ( 10 )   2022.3   ISSN:0021-8979 eISSN:1089-7550

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    Publisher:Journal of Applied Physics  

    Aluminum (Al) and titanium (Ti) are superconducting materials but their superconducting transition temperatures (T c) are quite low as 1.20 and 0.39 K, respectively, while magnesium (Mg) never exhibits superconductivity. In this study, we explored new superconductors with higher T c in the Al-Mg-Ti ternary system, along with the prediction using machine learning. High-pressure torsion (HPT) is utilized to produce the superconducting states. While performing AC magnetization measurements, we found, for the first time, superconducting states with T c = 4.0 and 7.3 K for a composition of Al:Ti = 1:2. The magnetic anomalies appeared more sharply when the sample was processed by HPT at 573 K than at room temperature, and the anomalies exhibited DC magnetic field dependence characteristic of superconductivity. Magnetic anomalies also appeared at ∼55 and ∼93 K, being supported by the prediction using the machine learning for the Al-Ti-O system, and this suggests that Al-Ti oxides play an important role in the advent of such anomalies but that the addition of Mg could be less effective.

    DOI: 10.1063/5.0086694

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  • Phase transformations in Al-Ti-Mg powders consolidated by high-pressure torsion: Experiments and first-principles calculations

    Tang Y., Murayama M., Edalati K., Wang Q., Iikubo S., Masuda T., Higo Y., Tange Y., Ohishi Y., Mito M., Horita Z.

    Journal of Alloys and Compounds   889   2022.1   ISSN:09258388

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    Publisher:Journal of Alloys and Compounds  

    A powder mixture of Al-Ti-Mg with an equal atomic fraction was subjected to severe plastic deformation using high-pressure torsion (HPT) under 6 GPa at room temperature for full consolidation. Microstructural evolution with respect to straining and annealing was examined by X-ray diffraction (XRD) analysis and high-resolution transmission electron microscopy. The XRD analysis revealed that Ti prevails in the consolidated sample and a phase transformation occurs from α phase to ω phase during HPT processing while the total fraction of the ω phase increases with straining. Grain refinement to ~100 nm was achieved through the HPT processing for 100 revolutions as well as the formation of nanograined intermetallics such as Al3Ti, AlTi3 and TiAl. The hardness gradually increases with straining, and further increases by annealing at 573 K for 1.5 h due to the formation of an Al12Mg17 phase despite the fact that the harder ω phase was reversely-transformed to the softer α phase and grains were coarsened to ~450 nm. First-principles calculations show that Al and Mg elements are dissolved into the ω − Ti during HPT processing.

    DOI: 10.1016/j.jallcom.2021.161815

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  • Creep Resistance of S304H Austenitic Steel Processed by High-Pressure Sliding

    Kral P., Dvorak J., Sklenicka V., Horita Z., Takizawa Y., Tang Y., Kral L., Kvapilova M., Roupcová P., Horvath J.

    Materials   15 ( 1 )   2022.1

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    Publisher:Materials  

    Sheets of coarse-grained S304H austenitic steel were processed by high-pressure sliding (HPS) at room temperature and a ultrafine-grained microstructure with a mean grain size of about 0.14 µm was prepared. The microstructure changes and creep behavior of coarse-grained and HPS-processed steel were investigated at 500–700◦C under the application of different loads. It was found that the processing of S304H steel led to a significant improvement in creep strength at 500◦C. However, a further increase in creep temperature to 600◦C and 700◦C led to the deterioration of creep behavior of HPS-processed steel. The microstructure results suggest that the creep behavior of HPS-processed steel is associated with the thermal stability of the SPD-processed microstructure. The recrystallization, grain growth, the coarsening of precipitates led to a reduction in creep strength of the HPS-processed state. It was also observed that in the HPS-processed microstructure the fast formation of σ-phase occurs. The σ-phase was already formed during slight grain coarsening at 600◦C and its formation was enhanced after recrystallization at 700◦C.

    DOI: 10.3390/ma15010331

    Scopus

  • Severe Plastic Deformation under High Pressure: Upsizing Sample Dimensions

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