The process of severe plastic deformation under high pressure through high-pressure torsion (HPT) was applied to an Al-Mg-Si alloy containing excess Fe and Si, which was designed as a model alloy for aluminum recycling. It was shown that the tensile strength exceeded 500 MPa with a total elongation to failure more than 20% after HPT processing under 2 GPa for 1 revolution. Microstructure observation was carried out using transmission electron microscopy for grain size and dislocations. Three dimensional image analyses were also carried out using high-energy X-rays in SPring 8 of JASRI for pores and intermetallic particles. Strain rate change tests were further performed for the evaluation of strain rate sensitivity (m). It was found that the m value increases with the imposed strain (the number of HPT revolution). This increase in the m value is attributed to a significant decrease in the activation volume through a reduction in mobile dislocation segments and/or their gliding distances along with the reduction in the grain size to the submicrometer range. [doi:10.2320/matertrans.MT-L2025015]

The effects of severe shear strain on the magneto-structure correlations of chromium oxide Cr2O3 were investigated. Shear stress was applied through high-pressure torsion (HPT) processing at a pressure of P-HPT = 6 GPa. Through ac magnetization measurements, a maximum increase in the N & eacute;el temperature T-N of Cr2O3 of approximately 30 K was observed in the HPT-processed sample for a revolution number of N = 1/2. This demonstrates the potential of HPT to expand the temperature stability range of antiferromagnetic order in Cr2O3. Analysis of the x-ray diffraction patterns of HPT-processed Cr2O3 revealed a special state of lattice expansion induced by shear strain within the unit cell. Direct exchange interactions originating from the overlapping of the Cr3+ ion orbitals and superexchange interactions involving the O2- ligands were examined using the variations in atomic distances and bonding angles. The increase in T-N at a small N is attributed to enhanced antiferromagnetic interactions resulting from the decrease in the distance between the closest neighboring Cr3+ ions. By contrast, the reduction in T-N observed at a higher N is explained by the modifications of the interchain interactions.

We successfully synthesized a metastable phase of Y-based cuprate superconductors with an onset Tc of 130 K using a high-pressure torsion (HPT) synthesis method, in which intense shear stress was applied under high-pressure compression. A mixture of copper oxide, yttrium oxide, and barium oxide was subjected to HPT processing and subsequently annealed at low temperatures. The HPT processing generated seed crystals of Y-based cuprates, while the low-temperature annealing enlarged the superconducting grains. In addition, the annealing modified the oxygen concentration, stabilizing the metastable structure and inducing further carrier doping. As a result, magnetic shielding signals with the onset Tc of 130 K were detected through magnetic measurements. The value exceeds the Tc = 93 K of optimally doped YBa2Cu3O7−δ synthesized via a conventional high-temperature solid-state reaction. The expanded unit-cell feature of YBa2Cu3O7−δ was confirmed through structural analyses. It is necessary to examine how variations in the apical-oxygen distance relative to the CuO2 plane influence the superconducting properties.

This study examined the tensile behavior of an AZ61 Mg alloy processed by severe plastic deformation through high-pressure torsion. Tensile testing at room temperature yielded the tensile strength (0.2

Titanium and its alloys exhibit advantageous ductility and strength-to-weight ratios, which makes them suitable for use as structural materials in numerous industrial applications. The ω phase has been observed to precipitate during the aging process of titanium alloys, resulting in a loss of ductility. Here we report tensile behavior of bulk polycrystalline ω-titanium with a chemical composition of commercially pure titanium grade 4 and an average grain size of 3.4 μm. We observed that stress-induced ω → α martensitic phase transformation occurs exclusively in the plastic regime. As plastic deformation proceeds, the volume fraction of α-phase increases. The 0.2% offset yield strength, tensile strength, and elongation to failure were determined to be 1130 ± 30 MPa, 1220 ± 30 MPa, and 16 ± 2%, respectively. The present study revealed transformation-induced plasticity in this material. The mechanical properties of this material with the pure titanium composition are comparable to those of a titanium alloy Ti-6Al-4 V. The bulk polycrystalline ω-titanium can potentially be utilized for biomedical applications, such as dental implants.

This study applied solution treatment under high pressures as 2 and 6 GPa to an Al-11.5 mass%Cu alloy for increasing the solubility limit of Cu atoms. In-situ high-energy X-ray diffraction (XRD) analysis using a facility at SPring-8 in JASRI (Japan Synchrotron Radiation Research Institute) revealed dissolution behavior of & ordf;-Al2Cu phase during the solution treatment. After the solution treatment under 6 GPa, all the Cu atoms in 11.5 mass% were dissolved in the Al matrix, almost twice as much as the solubility limit under ambient pressure, resulting in the increased Vickers microhardness to 148 HV. Further increase in Vickers microhardness to 206 HV was obtained after aging at 190 degrees C, and the aging behavior was also examined by the in-situ high-energy XRD analysis. In this study, the effect of ultrafine-grained structure produced by severe plastic deformation through high-pressure sliding method was also elucidated. [doi:10.2320/matertrans.MT-M2025181]

Vanadium oxide V2O3 is a strongly correlated transition-metal oxide, in which electrons are strongly coupled with the lattice system. It exhibits a first-order type of metal-insulator (MI) transition at 168 K. A series of vanadium oxides VxOy, between V2O3 and VO2 with various valence states of vanadium between +3 and +4, also exhibits similar MI transitions, and the transition temperature depends on the valence. In this study, we expected a change in the valence state of vanadium in V2O3 subjected to shear under compression using the process of the high-pressure torsion (HPT). Disk-like samples were subjected to the HPT processing under pressure (P-HPT = 6 GPa) for a certain number of revolutions (N) at room temperature. Originally, the MI transition occurred within a narrow temperature range of 160 +/- 10 K, whereas after HPT processing with N = 10, it occurred over a wide temperature range of 180 +/- 60 K. Consequently, the effects of shear resulted in the coexistence of high- and low-temperature phases in the temperature range over 120 K. Furthermore, the onset temperature of MI transition was enhanced from approximately 170 to 240 K. Thus, the HPT processing of V2O3 expanded the temperature range of low-temperature insulating phase.

The effects of severe shear stress on the electron-transfer-induced ferromagnetism of lanthanum manganite LaMnO3+δ have been investigated. Shear stress was applied via high-pressure torsion (HPT) processing and controlled by varying the number of rotations N. A decrease of 30 K in the Curie temperature TC was observed under shear strain, in contrast to hydrostatic compression, which increases TC. Examination of the x-ray diffraction patterns revealed an increase in the unit-cell volume, indicating negative pressure. A correlation between the decrease in TC and the increase in lattice parameter a was observed. A decrease in the valence state of Mn after HPT processing was also confirmed via x-ray photoelectron spectroscopy. Thereby, the valence change, as well as defect insertion and lattice strain, weakens the double-exchange interaction. This underscores the potential of shear strain as a platform for tuning electron-transfer-induced ferromagnetism and for strain engineering in LaMnO3+δ.

This study presents the tensile strength of 1010 MPa with the total elongation to fracture of 13% in an A2024 aluminum alloy. The alloy was solution-treated and processed by high-pressure torsion (HPT) under 6 GPa for 10 turns at room temperature to refine the grain size to 3130 nm. A micro tensile specimen with gauge dimensions of 50 & micro;m in length, 20 & micro;m in width and 15 & micro;m in thickness was fabricated by focused ion beam at a position 2 mm away from the center of the HPT-processed disk. The high-strength with ductility was achieved because (i) the micro tensile specimen minimized larger inclusions which may lead to a premature fracture due to stress concentration, (ii) the ultrafine-grained structure produced by HPT processing enhanced the strain rate sensitivity due to lower activation volume, and (iii) the reduction of pore density due to application of high pressure by HPT processing. This study thus demonstrates that the A2024 alloy has a potential to be highly strengthened with the tensile strength more than 1 GPa and with ductility when the alloys are processed by severe plastic deformation under high pressure.

This study presents tensile properties of Al-Mg-Si alloys after processing by severe plastic deformation through high-pressure torsion (HPT). The alloys were fabricated so as to include excess Fe and Si with different additions of Cu as model alloys for recycling purpose. The tensile strength well exceeded 500 MPa with the total elongation more than 15% after HPT-processing under 2 GPa for 1 turn in all the model alloys. The strength further increases to more than 700 MPa with increasing addition of Cu while maintaining reasonable ductility (similar to 8%). Transmission electron microscopy confirmed that the grain size was reduced to 180 nm and further reduced to 160 nm with increasing Cu addition. Micros structural analyses using scanning transmission electron microscopy and atom probe tomography revealed that Cu was segregated at grain boundaries, contributing to the increase in the tensile strength. The high strength with enhanced ductility is discussed in terms of strain rate sensitivities measured from strain rate change tests.

Material synthesis and material manipulation using shear stress under compression have been conducted to enhance electronic functionalities of inorganic magnets and superconductors. Through the shear stress under compression, dislocation-like defects are inserted, which result in grain structure changes. During subsequent pressure release, lattice strains occur at the unit-cell level, such as anisotropic change in lattice parameters and/or lattice expansion, resulting in the creation of novel functionalities in electronic materials. Here, we demonstrate the possibility of stabilizing novel metastable materials using shear stress under high pressure through high-pressure torsion (HPT) processing. Metastable states created via HPT processing, which may be regarded as excited states, can be modified by simultaneous and/or successive heating. Regarding successful properties in the metastable states, high-Tc superconductivity appears in single-element metals such as Re with lattice expansion accompanied by an increase in density-of-states at Fermi energy and Ba with residual high-pressure phases accompanied by strained unit cell, Al-Ti oxides characterized by Magnéli phases with unique valence states, and hyperoxia cuprates of La2CuO4 with carrier control via oxygen defects. These features are different from those in high-quality materials obtained via the high-pressure synthesis using isotropic compression at high temperature.

This paper presents an overview of the recent development of incremental feeding high-pressure sliding (IF-HPS) process for grain refinement of metallic sheets with enlarged areas. The IF-HPS process is a method of severe plastic deformation (SPD) under high pressure without increasing the machine capacity. The IF-HPS process combines an incremental feeding technique with the high-pressure sliding (HPS) process so that a severely deformed area can be extended. Development of the IF-HPS process includes the use of flat-type anvils instead of groove-type anvils, which makes it easier to enlarge the SPD-processed areas. The development is also described in terms of the sliding mode and the feeding pattern, where the former is determined by the sliding distance and the numbers of the reciprocation of the sliding and the latter by the feeding distance and the feeding direction. The application of the IF-HPS process is made to metallic materials such as a Ni-based superalloy (Inconel 718), a Ti-6Al-7Nb alloy (F1295) and commercially available Al alloys (A1050, A3105, A5052 and A5182). It is shown that the grain refinement is successfully achieved so that superplastic elongation more than 400% is attained in the Ni-and Ti-based alloys, and the room-temperature tensile strength is well enhanced in the Al alloys. It is then demonstrated that the IF-HPS process is promising to extend the SPD-processed area without increasing the machine capacity. Furthermore, a new approach is suggested for material design, such as the hybrid materials composed of conventional and fine-grained materials and functionally graded materials.

Ceramics are typically brittle at ambient conditions due to their covalent or ionic bonding and limited dislocation activities. While plasticity, and occasionally superplasticity, can be achieved in ceramics at high temperatures through thermally activated phenomena, creep, and grain boundary sliding, their deformation at ambient temperature and pressure remains challenging. Processing under high pressure via the high-pressure torsion (HPT) method offers new pathways for severe plastic deformation (SPD) of ceramics. This article reviews recent advances in HPT processing of ceramics, focusing primarily on traditional ceramics (e.g., oxides, carbides, nitrides, oxynitrides) and to a lesser extent advanced ceramics (e.g., silicon, carbon, perovskites, clathrates). Key structural and microstructural features of SPD-processed ceramics are discussed, including phase transformations and the generation of nanograins and defects such as vacancies and dislocations. The properties and applications of these deformed ceramics are summarized, including powder consolidation, photoluminescence, bandgap narrowing, photovoltaics, photocatalysis (dye degradation, plastic waste degradation, antibiotic degradation, hydrogen production, CO2 conversion), electrocatalysis, thermoelectric performance, dielectric performance, and ion conductivity for Li-ion batteries. Additionally, the article highlights the role of HPT in synthesizing novel materials, such as high-entropy ceramics (particularly high-entropy oxides), black oxides, and high-pressure polymorphs, which hold promise for energy and environmental applications.

We successfully stabilized the hyperoxia superconducting phase of La2CuO4, the parent insulating compound of La-based cuprate superconductors, by applying compression under high pressure and successive shear strains via the process of high-pressure torsion (HPT). Superconducting phases in the La2CuO4 system are created via the hole doping by replacing the La-sites with alkali-earth metals or by overdoping oxygen. However, the present study demonstrates that the HPT processing induces structural strain, and subsequent annealing stabilizes the hyperoxia phase, i.e., the superoxide phase. The superconducting transition temperature Tc systematically varies as a function of the revolution number N in HPT processing under compression of 6 GPa, and Tc has the maximum value of approximately 40 K for N≤1. Stabilized superconducting states intrinsically have a large critical field at the 20 T level. This approach proposes a high-pressure material synthesis method that is useful for mechanically tuning carriers in insulating La2CuO4.

The ten best papers for young scientists were awarded by The Japan Institute of Light Metals (JILM) and The Japan Institute of Metals and Materials (JIMM) in Materials Transactions. Here, the awarded papers are briefly summarized as current trends in research of Materials Transactions. Among the ten best papers, six were from JILM for young scientists whose ages are 30 or below and four from JIMM for those with ages of 35 or below. A total of six best papers were originally published in Japanese in Journal of the Japan Institute of Light Metals and Journal of The Japan Institute of Metals and Materials as cutting-edge research in JILM and JIMM. In association with all the awarded papers, special issues edited in Materials Transactions are also briefly introduced to show the recent activities of Materials Transactions.

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 in situ 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.

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.

An AZ61 Mg alloy was processed by high-pressure sliding (HPS) at room temperature under a pressure of 2 GPa for ultrafine grain refinement. The hardness measurement resulted in 120 HV on the transverse cross section and slid plane of the processed sample, indicating homogeneous introduction of strain throughout the HPS-processed sample. Tensile tests at elevated temperatures showed a superplastic elongation of 510