フェーズフィールド法に基づく Mg-Y-Zn 合金の準安定 hcp 相分離の解析

Abstract

It has been proposed that the long-period stacking ordered (LPSO) structure in Mg-Zn-Re (Re: the rare-earth elements) alloys establishes the excellent mechanical properties among Mg-based light metals. In this study, the phase separation of metastable hcp phase in Mg-Y-Zn system is simulated on the basis of the phase-field method in order to understand the stability and formation mechanism of the LPSO structure. The obtained results are as follows. The metastable spinodal decomposition is observed near the Mg corner in Mg-Y-Zn ternary system before the conventional spinodal decomposition in accordance with the miscibility gap of the hcp phase. That is the supersaturated solid solution of Mg-7 at%Y-7 at%Zn alloy separates into two phases; Mg-12 at%Y and Mg-17 at%Zn. The morphology of the microstructure is lamellae structure elongated along the [0001] direction of hcp phase, and the wavelength of the lamellae structure is about 7nm. These results suggest that the metastable spinodal decomposition might be correlated with the stability of the LPSO structure.