Stability and formation of long period stacking order structure in Mg-based ternary alloys

Abstract

Long period stacking ordered (LPSO) structure plays an important role in determining the strength and ductility of Mg-based ternary alloys. In this work, we investigated the thermodynamic stability of 10H LPSO structures in comparison with those of 14H and 18R LPSO structures. A trimer model was proposed to predict the possibility of forming LPSO structure in Mg–XL–XS (XL=Rare earth, Ca, Sr and XS=Al, Zn, Cu, Ni) with first-principles calculations. The formation of LPSO structure was determined based on the intrinsic stacking fault energy, mix energy and segregation energy. An element which decreases the intrinsic stacking fault energy is essential for the formation of LPSO structure. Decreasing the stacking fault energy favors the formation of local FCC layers, which would attract solid solutes segregating from HCP to local FCC Mg and forming L12 cluster and finally the LPSO structure.