Phase relations among D03, α-Mg, and long-period stacking orders in Mg85Zn6Y9 alloy under 3 GPa

Abstract

The crystal structures of Mg85Zn6Y9 alloy under 3 GPa were investigated between room temperature and 973K using in situ X-ray diffraction (XRD). In addition, the crystal structures and microstructures of Mg85Zn6Y9 alloys that were recovered after being heated at various temperatures under 3 GPa were also investigated. The in situ XRD analysis results indicated that 10H- and 18R-type long-period stacking orders (LPSOs) were stable below 673K under 3 GPa; however, the D03 and α-Mg structures, which were not observed at ambient pressure, emerged at 873K in the sample under 3 GPa. When the temperature was increased to 973 K, the D03 and α-Mg phases fused. The D03 and α-Mg phases were also confirmed to be present in Mg85Zn6Y9 alloy that was recovered after being heated at 873K under 3 GPa. In contrast, the XRD pattern of the Mg85Zn6Y9 alloy that was recovered after being heated at 973K under 3 GPa indicated the presence of the 18R-type LPSO, D03, and α-Mg structures. These results indicate that three phases-18R-type LPSO, D03, and α-Mg-were formed during cooling from the molten state at 3 GPa. These results further suggest that the D03, α-Mg, and 18R-type LPSO are energetically very similar under 3 GPa.