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Gong, W.; Gholizadeh, R.*; 川崎 卓郎; 相澤 一也; Harjo, S.
Magnesium Technology 2024, p.89 - 90, 2024/03
Mg and its alloys generally exist as a single hcp crystal structure at room temperature. It is widely recognized that the application of Mg alloys is hindered by their limited formability at room temperature, primarily attributable to the scarcity of readily activated deformation modes within the hcp phase. The addition of Li in Mg alloy can stable the bcc phase at room temperature, and these dual-phase (hcp+bcc) Mg-Li alloys exhibit excellent formability. The Li-enriched bcc phase has been frequently considered as the origin for improving formability. However, these Mg-Li alloys show poor work-hardening ability and the resultant low strength at room temperature. Considering that the dislocation recovery can be suppressed by decreasing the deformation temperature and the activity of deformation mode may be changed with temperature, we investigated the deformation behavior of a commercial LZ91 magnesium alloy at cryogenic temperatures using in-situ neutron diffraction.
諸岡 聡; 井川 直樹; 佐々木 未来; 生田目 望; 樹神 克明
no journal, ,
Medium Mn steels have been actively investigated due to their excellent balance between material cost and mechanical properties. In particular, medium Mn steel with a nominal chemical composition of Fe-5.0Mn-0.1C (mass%) fabricated by intercritical annealing 923 K for 1.8 ks after cold-rolling, was the high-strength mechanical properties at low temperature. This strengthening mechanism evaluated by means of in-situ neutron diffraction under low temperature (High Resolution Powder Diffractometer (HRPD) at Japan Research Reactor-3(JRR-3)), electron back scatter diffraction (EBSD), low temperature differential scanning calorimetry (DSC) and low temperature magnetic susceptibility measurement. We found that as the sample temperature decreases, face- centered cubic (FCC) structure transferred face-centered tetragonal (FCT) structure. Namely, it suggests that austenite transformed martensite like Fe-Pd or Fe-Pt alloy. Therefore, the origin of the high-strength mechanical properties at low temperature was in the presence of FCT martensite.
Gong, W.; 川崎 卓郎; Zheng, R.*; 眞山 剛*; 相澤 一也; Harjo, S.; 辻 伸泰*
no journal, ,
Mg and its alloys possess great potential for a wide range of applications, particularly in cryogenic applications. However, the deformation mechanisms of Mg alloys at cryogenic temperatures are not fully understood due to the absence of appropriate methods. In this study, we investigated the deformation behavior of a commercial AZ31 alloy at cryogenic temperatures using in-situ neutron diffraction. The yield stress of AZ31 alloy significantly increased with decreasing temperature in tensile deformation, but slightly increased in compressive deformation. Interestingly, both the fracture strain and stress at 20 K exhibited a substantial increase compared to 298 K in compressive deformation. In-situ neutron diffraction experiments were conducted using the engineering diffractometer TAKUMI at J-PARC to reveal the deformation mechanisms in the AZ31 alloy at cryogenic temperatures. The stress-strain response of the AZ31 alloy with temperature will be discussed in relation to the temperature-dependent activity of deformation mechanisms.
