Temperature dependence of generalized stacking fault free energy profiles and dissociation mechanisms of slip systems in Mg

Abstract

A machine learning-derived interatomic potential coupled with the Projected Average Force Integrator (PAFI) method was utilized to examine the temperature-dependent Generalized Stacking Fault Free Energies (GSFFE) profiles across all slip systems in Mg, fully accounting for anharmonic thermal vibrations. Intrinsic Stacking Fault Free Energies (ISFFE) and Unstable Stacking Fault Free Energies (USFFE) were assessed for temperatures ranging from 0 K to 800 K, marginally below the anticipated Mg melting temperature of approximately 900 K. The findings revealed that anharmonic vibrational effects are comparable to harmonic effects for Basal slip above 200 K, approximately half the Debye temperature. Anharmonic contributions were minimal for non-basal slip systems. The USFFEs of Pyramidal-I and II slip systems are predicted to crossover around 385 K due to vibrational effects. Marginally higher ISFFEs in Pyramidal-I across all temperatures also indicate possible cross-slip or SF transformation between the systems. A comprehensive examination of slip trajectories and atomic displacements unveiled intricate atomic displacements across all Mg slip systems and complex shuffle mechanisms for non-basal slips. In addition to corroborating previously documented dislocation dissociation mechanisms for Basal, Pyramidal-〈a〉, and Pyramidal-I slips, a new dissociation mechanism was discerned for dislocation slip in Pyramidal-II. This study offers crucial insights into the temperature-dependent behavior of SFFEs in Mg, the significance of intrinsic anharmonic thermal contributions to Basal slip, and the intricate atomic displacements and dissociation mechanisms of hexagonal close packed slip systems.