First-principles calculations of the temperature dependence of stacking fault energies in Mg

Abstract

Here, we calculate the Gibbs Free Energy of stacking faults relevant to 〈c+a〉 slip as well as the cross-slip energy barrier of the 〈c+a〉 screw dislocations in Mg, Mg-Al, and Mg-Ca alloys using density functional theory and the quasiharmonic approximation. While pyramidal II stacking fault energy is lower than pyramidal I in pure Mg for a large temperature range, the opposite is true at all temperatures in alloys. The addition of Al and Ca significantly reduce the pyramidal I stacking fault energy at room temperature working to assist in the stabilization of pyramidal I dislocations.