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板倉 充洋; 山口 正剛; 江草 大佑*; 阿部 英司*
no journal, ,
Kink boundaries formed in Mg-based long period stacking order (LPSO) alloys play a key role in strengthening of these materials. As the kink structure grows, many high-angle kink boundaries are eventually formed which has inclination angle close to 34 degrees. We show that this peculiar structure is a result of irreversible structural transformation and is energetically stable. We also calculate segregation energies of alloying elements Y and Zn to this boundary. Segregation energy is greater for Zn case and the maximum value is about 0.7 eV. Finally, the critical resolved shear stress for the migration of kink boundary is estimated for a pure-Mg kink and that with saturated with segregation. We show that segregated kink boundary requires very high shear stress about 700 MPa for migration. Kink structure shows apparent asymmetry with respect to the boundary. This asymmetry is induced by irreversible relaxation of the boundary structure. Stress-strain relation for the applied shear stress acting on the kink boundary indicates that without solute atoms, the critical resolved shear stress (CRSS) for boundary migration is about 400 MPa, whereas saturation of solute atoms increases the CRSS to about 700 MPa. In the actual LPSO structure where hard solute clusters prevent local shuffling of atoms, the CRSS for boundary migration should be much higher and expected to be irrelevant to plastic deformation.
Mg/LPSO dual phase alloy by hot-extrusion using in situ neutron diffraction during deformationHarjo, S.; 相澤 一也; Gong, W.; 川崎 卓郎; 山崎 倫昭*
no journal, ,
In this study, in situ neutron diffraction during deformation was performed using three kinds of samples of Mg
Zn
Y
alloy: an as-casted sample (As-Cast), hot extruded samples with the extrusion ratio (R) values of 5.0 (R=5.0) and 12.5 (R=12.5). Crystallographic evolutions of Mg and LPSO phases by hot-extrusion and deformation behavior of the individual phases were investigated, and the unique deformation mechanism by hot-extrusion in this alloy will be discussed based on the obtained results.
Gong, W.; 相澤 一也; Harjo, S.; 川崎 卓郎
no journal, ,
Recently, a new class of dispersion strengthened magnesium alloys has attracted high attention due to their excellent mechanical properties. A long period stacking ordered (LPSO) phase in these alloys contributing to the enhanced strength and ductility has been clarified. The LPSO phase includes polytypic structures such as 14H, 18R, 24R, and 10H. These polytypic LPSO structures can coexist with other precipitations in the Mg-RE-TM system depending on chemical composition and temperature. In order to clarify the stability and the structure evolution of LPSO phase at high temperature, an as-cast Mg
Zn
Y
alloy with duplex LPSO structure of 18R and 10H was investigated by in-situ neutron diffraction during annealing. A 10H-LPSO to 18R-LPSO structure transformation was observed during heating. The evolutions of phase fraction and lattice parameters were estimated quantitatively from the diffraction profiles, and these results will be discussed to reveal the phase transformation behavior in the as-cast MgZnY.