Atomic-resolution investigations on dislocation-assisted evolution of {10[formula omitted]3} twin boundaries in a magnesium alloy

Abstract

{101¯3}〈303‾2‾〉 twinning is usually activated at the later stage of plastic deformation of Mg alloys, which is closely relevant to their fracture behavior. Reactions between slip dislocations and twin boundaries (TBs) are suggested to facilitate TB migration, retarding the premature TB cracking. Here, dislocation-assisted evolution of {101¯3} TBs in a Mg alloy subjected to cyclic deformation were studied and modeled, according to transmission electron microscopy observations, theoretical analyses of interfacial defects, and molecular dynamics simulations. Atomic-resolution experimental observations showed that symmetric tilt grain boundaries (STGBs) near the {101¯3} twin orientation with steps were generated in the deformed Mg alloy. Theoretical analyses and atomistic simulations indicated that transformation of {101¯3} TBs into the STGBs could occur by reactions with incident basal 〈a60〉 dislocations in pairs from the twin and matrix respectively under the normal stress. STGB steps would be produced by reactions of individual basal 〈a60〉 dislocations with GB dislocations at the STGB. Importantly, resultant steps could further emit {101¯3} twinning dislocations to facilitate the STGB migration. Moreover, STGBs near the {101¯3} twin orientation could evolve back into {101¯3} TBs either by reactions with an array of basal 〈a60〉 dislocations, or by a GB sliding of b = 〈303‾2‾〉 theoretically. Our results may provide insights into the mechanisms of {101¯3} TB evolution in Mg alloys, which plays important roles in their plastic deformation and plasticity.