Japan Institute of Metals Acta Medica Okayama 0021-4876 89 11 2025 Ti-18Nb-xAl合金の構成相と材料特性に及ぼすAl添加量の影響 337 343 EN Yoshikazu Mantani Department of Materials Science and Engineering, National Institute of Technology (KOSEN), Suzuka College Yoshito Takemoto Faculty of Environmental, Life, Natural Science and Technology, Okayama University The Ti-18mass%Nb alloy with a quenched α” martensitic structure exhibited a high damping capacity. However, there are issues such as lower strength than annealed α+β structure and decreasing damping capacity due to heating until 400 K. Therefore, in this study, to address these issues, we investigated the effect of Al addition on the constituent phases and material properties of Ti-18Nb-xAl alloys. The crystal structure was determined by examining the lattice constant and unit volume using X-ray diffraction, and optical microscopy was also performed. The material properties were investigated by Vickers hardness, Young’s modulus, internal friction, tensile tests, and DSC measurements. Vickers hardness and tensile strength increased with increasing Al content. This is thought to be due to the combined effects of the refinement of the microstructure and solid-solution strengthening due to Al addition. The Young’s modulus increased slightly from 0Al to 1Al, but increased significantly to 4Al. Internal friction was highest for 0Al and decreased for 4Al, whereas 7Al showed a higher value than 1Al. In the DSC heating curves, there was a decrease in the exothermic peak starting temperature and an increase in the phase-transformation heat with the addition of Al, except for 1Al. It was suggested that these changes in Ti-18Nb-xAl alloys were influenced by the structure of the quenched α” phase, texture, and pseudoelasticity or phase transformation by deformation. No potential conflict of interest relevant to this article was reported.

The Japan Institute of Metals and Materials Acta Medica Okayama 0021-4876 88 10 2024 Ti-10V-2Fe-3Al合金の逆形状記憶効果と靭性回復 239 244 EN Yoshito Takemoto Faculty of Environmental, Life, Natural Science and Technology, Okayama University Daiki Shinomiya Graduate School of Natural Science and Technology, Okayama University Taiki Ishihara Graduate School of Environmental, Life, Natural Science and Technology, Okayama University Hiroto Yokota Graduate School of Environmental, Life, Natural Science and Technology, Okayama University Jinta Arakawa Faculty of Environmental, Life, Natural Science and Technology, Okayama University Ti-10V-2Fe-3Al alloys exhibit shape memory (SM) and reverse shape memory (RSM) effects. When an alloy sample that has been strained by external force at room temperature is heated, the strain recovers and SM effect develops at around 300℃, but as the temperature increases further, the shape changes in the opposite direction due to RSM effect at around 450℃. This RSM effect has potential applications in forming processes such as thin-walled pipes, but has the disadvantage that the RSM treatment makes the material very brittle. Therefore, in this study, a heat treatment to restore toughness while maintaining the shape after forming was investigated. The alloy quenched from 1050℃ had a microstructure consisting of a β matrix phase and α′′-martensite (α′′Mq). Differential scanning calorimetry (DSC) results showed that the continuous heating process occurred in the following order: α′′Mq → β reverse transformation, ω formation, ω disappearance, thermally induced α′′iso phase formation, α precipitation and α → β transformation. Ageing at 300℃, where the SM effect appears, caused significant embrittlement due to the formation of the ageing ω phase. Ageing treatment at 450℃, where the RSM effect is obtained, resulted in the formation of a fine α phase, which also caused significant embrittlement. On the other hand, additional aging at 600℃ for 1.8 ks after RSM treatment significantly improved the toughness and produced material properties comparable to aerospace material specifications. It was found that the embrittlement in the RSM treatment was due to the precipitation of fine α phase, and that the growth of α phase with a width of about 0.2 µm or more was required for toughness recovery. It was also found that the specimen shape formed by the RSM treatment hardly changed after the additional heat treatment of 1.8 ks at 600℃. No potential conflict of interest relevant to this article was reported.

Springer Science and Business Media LLC Acta Medica Okayama 0043-2288 67 8 2023 Study on joint characteristics in laser butt welding of AMed and wrought Ti6Al4V plates 1997 2005 EN Yasuhiro Okamoto Okayama University Togo Shinonaga Okayama University Yoshito Takemoto Okayama University Akira Okada Okayama University Akihiro Ochi Okayama University Ryuya Kishimoto Okayama University Sisa Pityana National Laser Centre, CSIR Nana Arthur National Laser Centre, CSIR Peter Omoniyi University of Johannesburg Rasheedat Mahamood University of Johannesburg Martin Maina Jomo Kenyatta University of Agriculture and Technology Esther Akinlabi University of Johannesburg Titanium alloy Ti6Al4V has been widely applied to medical, automotive, and aerospace industries due to its excellent properties such as high strength and excellent corrosion resistance. On the other hand, additive manufacturing (AM) technology can give the freedom of design of the products. In order to spread the AMed products, the joining of AMed and wrought products are required, and it is important to understand the joint characteristics. In this study, butt welding of Ti6Al4V plate was conducted by fiber laser in argon shielding, and the joint characteristics of laser weld wrought/wrought, AMed/AMed, and AMed/wrought Ti6Al4V plates were experimentally investigated. The AMed plate has higher tensile strength than wrought plate but the elongation of AMed plate is smaller, since AMed plate has α’ martensite due to rapid cooling during laser irradiation in AM process. Then, the laser weld joint of AMed/AMed plates has higher tensile strength, but smaller elongation than that of wrought/wrought plates. The weld joint of AMed/wrought plates shows good welding state, since small heat input leads to formation of small weld bead with higher hardness between wrought and AMed plates. No potential conflict of interest relevant to this article was reported.

Japan Institute of Metals Acta Medica Okayama 0021-4876 85 11 2021 Ti–10Mo–7Al合金の焼戻し誘起マルテンサイトの形成機構 405 412 EN Yoshito Takemoto Graduate School of Natural Science and Technology, Okayama University Mikiko Yasuno Graduate School of Natural Science and Technology, Okayama University Masaki Ikemoto Graduate School of Natural Science and Technology, Okayama University Hiroyuki Ando Faculty of Engineering, Okayama University Ichiro Shimizu Faculty of Engineering, Okayama University of Science The formation mechanism of αAA–martensite (αAAMt) induced by tempering at 450–550℃ for a short time was investigated using Ti–10Mo–7Al alloy. The solution treated and quenched (STQ) sample was composed of β phase and a small amount of αAAMq, and a large amount of αAAMt was generated by rapid tempering at 550℃–3 s using a salt bath. However, αAAMt was completely transformed into a single β phase by aging at 200℃ for 3 min. Reversibility was observed between the αAAMt transformation and the β reverse transformation. In–situ high–temperature X–ray diffraction measurements revealed that αAAMq → β reverse transformation occurred at 200℃ and that a thermally activated αAAiso was generated at 450℃ due to the slow heating rate. In–situ optical microscopic observation of STQ sample with rapid lamp heating revealed that αAAMt was formed during heating process. However, αAAMt did not generate under following conditions; that is, a slow heating rate, thin sample plate, and a small temperature difference until tempering by preheating. On the other hand, rapid tempering using thick plate from liquid nitrogen (−196℃) to 250℃ was performed to ensure a sufficient temperature difference, but αAAMt was not generated at all. From the cross–sectional observation of the STQ plate, it was found that αAAMq was hardly formed on the surface of the sample, but was formed abundantly inside the sample. On the other hand, in the rapidly tempered plate, a large amount of αAAMt was distributed in the surface layer than inside sample. These results suggest that the thermal compressive stress induced by rapid heat treatment contributes to the formation of α''M. No potential conflict of interest relevant to this article was reported.

Elsevier Acta Medica Okayama 0040-6090 698 2020 Strain effects on spinodal decomposition in TiO2-VO(2)films on TiO2(100) substrates 137854 EN Yuji Muraoka Research Institute for Interdisciplinary Science (RIIS), Okayama University Fumiya Yoshii Graduate School of Natural Science and Technology, Okayama University Takahiro Fukuda Graduate School of Natural Science and Technology, Okayama University Yuji Manabe Graduate School of Natural Science and Technology, Okayama University Mikiko Yasuno Graduate School of Natural Science and Technology, Okayama University Yoshito Takemoto Graduate School of Natural Science and Technology, Okayama University Kensei Terashima Research Institute for Interdisciplinary Science, Okayama University Takanori Wakita Research Institute for Interdisciplinary Science (RIIS), Okayama University Takayoshi Yokoya We investigate the influence of lattice strain in the c-axis direction on spinodal decomposition in rutile TiO2-VO2 films on TiO2(100) substrates. The [100]-oriented Ti0.4V0.6O2 (TVO) solid-solution films are fabricated on rutile TiO2(100) substrates using a pulsed laser deposition with a KrF excimer laser, and are annealed inside the spinodal region. X-ray diffraction and scanning transmission electron microscopy are employed for characterization. Consequently, the in-plane tensile strain in the c-axis direction promotes the Ti-V interdiffusion in TVO/TiO2(100) under thermal annealing. In contrast, relaxation of the tensile strain results in the occurrence of spinodal decomposition along the c-axis direction in the film. These results indicate that the relaxation of the tensile strain in the c-axis direction is critically important for enabling spinodal decomposition in TVO/TiO2(100). Our work helps deepen the understanding of spinodal decomposition in the TVO film and provides information on achieving novel nanostructures via spinodal decomposition in TVO/TiO2(100). No potential conflict of interest relevant to this article was reported.

Faculty of Engineering, Okayama University Acta Medica Okayama 0475-0071 33 2 1999 Simulation of Deformation of Ni Twinned Nanocrystal Model by Molecular Dynamics 1 8 EN Yasuhiro Omura Moritaka Hida Akira Sakakibara Yoshito Takemoto 10.18926/19648 Molecular dynamics simulation of nickel crystal under uniaxial tensile and compressive deformation was performed for single nenocrystal model and twinned nanocrystal model composed of 1550 atoms using EAM (embedded atom method) potential with the object of investigating deformation induced phase tranformation (especially twin deformation). In the case of single nanocrystal model, the evolution and development of twin deformation, (111)[11(2)], is observed under compressive loading in [001] direction, whereas either slip or twin deformation is not recognized under tensile loading. In the case of twinned nanocrystal model, twin, (111)[11(2)], decreases and disappears under tensile loading, and develops under compressive loading, It is suggested from the difference of results between single nanocrystal model and twinned nanocrystal model that it is easy for twin to induce local deformation. No potential conflict of interest relevant to this article was reported.

Faculty of Engineering, Okayama University Acta Medica Okayama 0475-0071 31 2 1997 Internal Structure and Phase Transformation of Ti-V Alloy Fine Particles 11 20 EN Yoshito Takemoto Moritaka Hida 10.18926/19589 Fine particles of Ti-V alloy were prepared by means of arc method and were investigated on internal structure and phase transformation using HR-TEM and EDS. Martensite phase was observed in a particle containing comparatively low concentration of V, and ω phase was also found to exist in a nearly 15% V particle. The structure of the ω phase in the fine particle is remarkably expanded in comparison with the bulk sample, and the ω phase is unstable, so that it has disappeared in a few seconds during TEM observation. No potential conflict of interest relevant to this article was reported.

Faculty of Engineering, Okayama University Acta Medica Okayama 0475-0071 31 2 1997 Microstructure of Oxide Layers Formed on Magnesium Surface at Elevated Temperature 1 10 EN Yoshito Takemoto Moritaka Hida 10.18926/19588 The microstructure of oxidizing magnesium at elevated temperatures has been studied using HR-TEM, SEM and EDS. Two kinds of thin magnesium specimen for TEM observation were prepared. One was oxidized after preparing TEM foil of magnesium, the other was prepared from an oxidized bulk magnesium for observing the cross-section of oxide/Mg interfacial region. In the former, several oxides(MgO) morphologies were observed depending on the temperature and time of the oxidization. The growth of needle-like oxides formed at 573K and mottled oxides formed at 773K were recognized as a remarkable phenomenon belonging to the local oxidization. These oxides were composed of poly-crystal. The thin uniform oxidization layer was also observed in all conditions. In the cross-sectional observation, the local oxide layer, nearly 300nm in thickness, on the matrix(Mg) were observed. The thin uniform oxidized layer of bulk samples was identified as a kind of modified layer (~40nm in thickness) in which the formation of HR-TEM lattice fringes were prevented by the strain due to the slight oxidization. No potential conflict of interest relevant to this article was reported.

岡山大学工学部 Acta Medica Okayama 0475-0071 21 2 1987 Depth Dependency of Hardness Change of Ti-Mo Alloys 1 7 EN 10.18926/15837 We investigated the effects of resolved interstitial oxygen or nitrogen atoms and of quenched-in strain on the hardening of the single crystals grown from molten Ti-14 and 20wt pct Mo alloys. The aging treatment at 623K in atmosphere much more increased in the hardness of specimen surface than that in argon atmosphere. The quenched-in compressive stress enhanced age hardening due to omega formation. We surveyed in detail the hardness changes toward the center of plate-shaped single crystal. No potential conflict of interest relevant to this article was reported.

Faculty of Engineering, Okayama University Acta Medica Okayama 0475-0071 25 2 1991 Mechanical Characteristics of Cast Ti Fiber-Reinforced Mg Composite 1 8 EN Hiroyuki Okada Moritaka Hida Akira Sakakibara Yoshito Takemoto 10.18926/15500 Tensile strength and elongation of cast magnesium reinforced with titanium fiber were measured by tensile test. The pull-out test of a titanium rod partially embedded in a magnesium matrix was performed to evaluate interfacial bonding strength between magnesium and titanium. It was found that when the fiber volume fraction was changed from 1% to 14%, the tensile strength was improved with increase of volume fraction, while the improvement of elongation tended to be restrained beyond the volume fraction of 10%. The interfacial strength was revealed to be strong, and this was substantiated by the scanning electron microscopy showing an excellent wettability between the titanium fiber and the magnesium matrix. No potential conflict of interest relevant to this article was reported.

Faculty of Engineering, Okayama University Acta Medica Okayama 0475-0071 24 2 1990 Fine Particles of Ti and Ti-Mo Alloy Prepared by Gas Evaporation 1 9 EN Masayuki Umemoto Yoshito Takemoto Akira Sakakibara Moritaka Hida 10.18926/15489 Fine particles of Ti-Mo alloy were prepared by evaporation. When Ti-40at % Mo alloy was evaporated on tungsten filament, fine particles of Ti contaminated with W were obtained. These particles were polyhedron in shape and 10～250nm in diameter. Average diameter and size distribution increased with pressure of argon gas (100～600 Torr). When pure Ti was placed on the Mo filament and evaporated from melt down of heated Mo filament in helium gas, fine particles of pure Ti and of Ti-Mo alloy were obtained. In this case, Ti particles were of indeterminate form and of several tens nm in diameter, and their diffraction pattern was of common α-Ti. On the other hand, composition of the Ti-Mo particles was determined to be 18at % Mo by an analysis of EDX. Structure of Ti-Mo particles could not be determined because their diameters were more than 600nm. The temperature of Mo filament, for the most part, was about 1800℃, and there pure Ti particles were produced. The temperature of the fused part of the filament was locally higher than 2600℃, and there Ti-Mo particles were produced. Fine structures of contact region among some Ti particles were observed with HRTEM. No potential conflict of interest relevant to this article was reported.

Faculty of Engineering, Okayama University Acta Medica Okayama 0475-0071 28 2 1994 X-Ray Topographic Observation of Strain Generated by Thin Film (TiN) on Silicon Surface 13 20 EN Hisao Kusumoto Moritaka Hida Akira Sakakibara Norihide Nishida Yoshito Takemoto Masuo Yamada 10.18926/15453 The strain in Si substrate induced by locally ion-plated thin film of TiN was observed by X-ray topograph (Lang technique). Circular TiN film was deposited on one side of the Si surface. In all topographs the highest blackness attributed to kinematical diffraction effect occurred at the film edge. Rosette pattern with four-lobes was observed around the film. Blackness as a whole increased with the film thickness. Strain was observed in the depth direction of substrate by limited projection method. When the slit width was narrowed, the kinematical images disappeared, and white images appeared at the film edge. All the contrast disappeared when the TiN film was completely removed in boiling HNO(3). The strain induced by the film deposition was proved to be elastic. No potential conflict of interest relevant to this article was reported.

Faculty of Engineering, Okayama University Acta Medica Okayama 0475-0071 28 2 1994 Internal Structure and Phase Transformation of Ti-Mo Alloy Fine Particles 1 7 EN Yoshito Takemoto Akira Sakakibara Moritaka Hida 10.18926/15448 Fine particles of Ti-Mo alloy have been prepared by means of arc method, and investigated on internal structure and phase transformation using HR-TEM and EDS. Martensite phase was observed in a particle containing comparatively low concentration of Mo, and ω phase was also found to exist in a nearly 14 % M0 particle. The structure of the ω phase in the fine particle is expanded and remarkably unstable in comparison with the bulk sample, so that it has disappeared in a few seconds during TEM observation. Moreover, the β structure of Ti-Mo particles has changed to the unusual fcc phase with irradiation of a strong electron beam. No potential conflict of interest relevant to this article was reported.

Faculty of Engineering, Okayama University Acta Medica Okayama 0475-0071 30 2 1996 Nature of Brittle Fracture in Aged Ti-Mo Alloy 1 7 EN Yoshito Takemoto Moritaka Hida Akira Sakakibara 10.18926/15397 The mechanism of brittle fracture in Ti-14mass % Mo alloy aged for 1x10(6)s at 623K was studied using transmission electron microscopy (TEM) and dynamic hardness test (DHT) on the structure deformed by means of tensile elongation at elevated temperature or cold rolling. Many band products were observed by TEM in either deformed specimens. These band products were identified to neither slips nor twinning bands, moreover, they were different from α , α ' and α " phases. The band product consisted of β phase and granular unknown phase which was transformed by deformation from ω phase. The newly discovered phase, named β" phase, in the band products had a body-centered triclinic structure. The β" was similar to the ω zone with respect to the morphology and the concentration of Mo, but it resembled β in structure. The result of DHT on the band products and the matrix showed that the band products were softer than the matrix. It is suggested that the band products are easily deformed because of the disappearance of obstacles such as ω phase, and consequently behave like paths to lead cracks preferentially. No potential conflict of interest relevant to this article was reported.

Acta Medica Okayama 1997 β型Ti-Mo合金の中間遷移ω相と変態型変形挙動に関する研究 EN No potential conflict of interest relevant to this article was reported.