Papers by Author: Yoko Yamabe-Mitarai

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Authors: Taichi Abe, Machiko Ode, Hideyuki Murakami, Chang Seok Oh, Cenk Kocer, Yoko Yamabe-Mitarai, Hidehiro Onodera
Abstract: The thermodynamic assessment of the Al-Ir binary system, one of the key sub-systems of the Ir-based alloys, was performed using the CALPHAD technique. The AlIr(B2) phase was described using the two sublattice model with the formula (Al,Ir)0.5(Ir,Va)0.5, while other intermetallic phases were treated as stoichiometric compounds. The calculated data of the phases in the Al-Ir system can be used to accurately reproduce experimental data, such as phase equilibria, invariant reactions, and formation enthalpies of the intermetallic phases.
Authors: Chen Huang, Yoko Yamabe-Mitarai, Shizuo Nakazawa, Hiroshi Harada
Authors: Yoko Yamabe-Mitarai, Hiroshi Harada
Authors: Yoko Yamabe-Mitarai, Y. Ro, Shizuo Nakazawa, Tomohiro Maruko, Hiroshi Harada
Authors: M. Danylenko, Victor F. Gorban, Yu.N. Podrezov, Sergiy A. Firstov, O. Rosenberg, S. Shejkin, F. Morito, Yoko Yamabe-Mitarai
Abstract: Severe plastic deformation (SPD) techniques are the best for producing of massive nanostructured materials. The methods of equal channel angular pressure (ECAP) and twist extrusion (TE) are realized by simple shear uniform deformation without change of cross-section sizes of sample. In the case of roll forming (RF) the shear strain is localized in the near-surface layer of metal. Intensity of shear strain in the near-surface layer depends on variation of parameters of deformation and conditions of friction in a contact. Steel 65G (0.65C, 0.3Si, 0.6Mn, 0.3Cr, and 0.3Ni) was deformed by roll forming. Transmission electron microscopy (TEM) of “cross-section” samples was used for studying of gradient structure of deformed material. TEM investigation shown that cell substructure in a near-surface layer have been formed. The depth of deformed layer is approximately 40 micrometers. Average cell size in cross-section direction is about 100 - 200 nm. Thin nanostructure layer with cell size about 20-30 nm was detected. In our opinion such substructure formed due to effect of “good” impurities.
Authors: Nobuaki Sekido, Yoko Yamabe-Mitarai
Abstract: Possibilities of heat resistant alloys based on a C15 Laves phase and an FCC phase have been examined in the Ir-Pt-Y ternary system. Although the Ir solid solution phase (A1) and the Ir2Y phase (C15) are not in equilibrium in the Ir-Y binary system, this equilibrium is attained by small Pt additions to the binary system. High temperature compressive strength of an A1/C15 monovariant eutectic alloy was found to be much lower than that of Ir-15Nb, an Ir based γ/γ' alloy. Low strength of the present alloys is attributed to the absence of effective strengthening mechanisms that operate in the A1 phase; for Y is hardly dissolved within the A1 phase, by which solution hardening and precipitation hardening are not available.
Authors: Yoko Yamabe-Mitarai, X. Yu, Y. Gu, Y. Ro, Shizuo Nakazawa, Tomohiro Maruko, Hiroshi Harada
Authors: Yoko Yamabe-Mitarai, Toru Hara, Seiji Miura, Hideki Hosoda
Abstract: Shape recovery and superelasticity of Ti-50at%Pt and Ti-50at%(Pt, Ir), whose martensitic transformation temperature are above 1273 K, were investigated by thermal expansion measurement in dilatometer and loading-unloading compression test. The shape recovery was found in all compounds in at least one of the testing methods. The highest shape recovery, about 4% was found in Ti-25Pt-25Ir using loading-unloading compression test. On the other hand, superelasticity was found in only ternary compounds. Larger superelasticity was observed in ternary compounds with higher Ir contents. Potential of Ti-50Pt and Ti-50(Pt, Ir) as high-temperature shape memory alloys is discussed.
Authors: X.H. Yu, Yoko Yamabe-Mitarai, Y. Ro, Hiroshi Harada
Authors: Taku Aoki, Masaki Tahara, Kenji Goto, Yoko Yamabe-Mitarai, Hiroyasu Kanetaka, Tomonari Inamura, Hideki Hosoda
Abstract: The effects of Fe addition on martensitic transformation and mechanical properties of AuTi were investigated in this study. It was found that B2 parent phase is stabilized by the Fe addition and that AuTi can contain at least 20mol%Fe. The lattice deformation strain evaluated from θ-2θ X-ray diffraction analysis (XRD) is not significantly changed by the Fe addition. The decrease in Ms evaluated by differential scanning calorimetry (DSC) is-40K/mol%Fe. Tensile tests revealed that, with increasing Fe content, the yield stress decreases up to about 13mol%Fe, largely increases up to 15mol%Fe and then decreases gradually. By taking into account XRD and DSC results, these behaviors are judged to correspond to reorientation of martensite variants, stress induced martensitic transformation and slip deformation of parent phase, respectively. The values of dσSIMT/dCFe and dσSIMT/dT are evaluated to be-170MPa/mol%Fe and-4.3MPa/K, respectively. The elongation is degraded with increasing Fe content from 8% in AuTi (0mol%Fe, martensite phase) to 2% in AuTi-20mol%Fe (parent phase) depending on the apparent phase.
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