Varied shearing mechanisms of β'_s-Mg₇Sm by basal 〈a〉 dislocations under thermo-kinetic correlation: a phase-field simulation

Previously, only superficial experimental observations have indicated that β'-series precipitates with significant strengthening effect can be sheared by basal 〈a〉 dislocations in Mg-rare earth (RE) alloys, while the corresponding mechanisms remain unclear. To address this issue, a phase-field (PF) simulation is conducted for a representative case: the interaction of β'_s-Mg₇Sm and basal 〈a〉 dislocations in Mg-Sm alloys. As a critical input for PF model, γ-surface (i.e., generalized stacking fault energy surface) of β'_s is computed using a novel ab-initio based method, where a carefully constructed multi-term Fourier series as a bridge, allowing molecular dynamics (MD) simulations to provide rough topography information to significantly reduce cost of first-principles (FP) calculations. The obtained γ-surface reveals multiple stable and unstable stacking faults (SFs) that may form during β'_s shearing. PF results further demonstrate that these SFs emerge along diverse deformation pathways of β'_s, governed by thermo-kinetic correlation, and reflect varied shearing mechanisms, including spontaneous SF transitions from an unstable one to a stable one, spontaneous formations of dislocation loops, complex stacking fault (CSF) ribbons and 2/3<11‾00>-type compact super-dislocations, and SF accelerated dislocation cutting. These findings provide a reference for future experimental comparisons. The proposed γ-surface computation method is applicable to other β'-series precipitates, encouraging similar PF simulations in other Mg-RE alloys, while the dominant role of thermo-kinetic correlation in activating specific shearing mechanisms offers deeper insight into the design of precipitation strengthening.