First-Principles Study of Generalized Stacking Fault Energy in Mg–Zn–Y Alloy with Long-Period Stacking-Ordered Structures

Abstract

This study investigated the basal and prismatic slip systems in the 10H, 14H, and 18H long-period stacking-ordered (LPSO) structures using first-principles calculations based on density functional theory to understand the plastic deformation behavior of Mg–Zn–Y alloy with an LPSO structure from the atomistic scale. The generalized stacking fault energies (GSFEs) of the basal plane at positions not crossing the solute clusters, along the 〈a〉 direction of LPSO structures are 14%–27% higher than that of hexagonal close-packed (hcp)-Mg, thus causing the basal slip in LPSO structures slightly more difficult than hcp-Mg. The GSFEs of the prismatic plane along the 〈a〉 direction were over 50% higher than that of hcp-Mg due to the influence of solute clusters. These results suggest that the LPSO structures in Mg–Zn–Y alloys have a higher resistance to dislocation motion than hcp-Mg in terms of the basal and prismatic slips, and the anisotropy is more emphasized in LPSO structures. A linear relationship was found between the GSFE and the solute cluster density on the prismatic plane of the hexagonal-type LPSO structures, i.e., GSFE increases as Mg layers sandwiched between solute cluster layers in the unit cell decrease. We proposed an equation to estimate the stacking fault energy of the solute cluster regions on the prismatic planes with LPSO structures. The estimated stacking fault energy in the part of solute cluster layers on the prismatic plane was almost the same regardless of the hexagonal-type LPSO structure.