Prediction of stacking fault energies and critical resolved shear stresses for hexagonal close-packed Mg solid solutions from first principle alloy theory

Stacking fault energies and critical resolved shear stresses (CRSSs) of different slip systems are predicted as a function of chemical composition for Mg solid solutions by accounting for chemical disorder, using the exact muffin-tin orbitals method involving coherent potential approximation and the semi-discrete variational Peierls–Nabarro model. A correlation between the stability of local atomic structure and stacking fault energies is established to understand the mechanisms behind the varied influences of alloying species. While addition of Ni, Co, Ti, and Ag (Sn, Ca, and Y) are demonstrated to significantly increase (decrease) the unstable stacking fault energy (γ_us) of prismatic and pyramidal 〈a〉 slip, Al, Li, and Zn yield relatively small influence. In addition, Sn, Ca, and Li decrease significantly both the intrinsic stacking fault energy (γ_isf) and γ_us of pyramidal 〈c+a〉 slip. The varied influences of alloying species on stacking fault energies of prismatic/pyramidal 〈a〉 and pyramidal 〈c+a〉 slip are demonstrated to strongly correlate with the local structural stability of the body-centered orthorhombic and triclinic structure, respectively. The counterbalance between the influence of volume change and chemical composition on the local structural stability dominates the alloying effect on γ_isf and γ_us. Furthermore, the predicted dislocation core structure and CRSSs of both basal and non-basal slips based on the calculated stacking fault energies and elastic parameters are in line with the available experimental findings. Among the studied alloying species, addition of Ca, Li, Sn, and Y are found to significantly reduce the difference of CRSS between basal and non-basal slips of Mg alloys. The present advances provide a solid basis for understanding the atomic mechanisms of plastic deformation and intelligent design of high-performance Mg alloys.