Atomic-resolution studies on reactions of slip dislocations with [formula omitted] twin boundaries and local plastic relaxation in a Mg alloy

Abstract

Reactions of {101¯1} twin boundaries (TBs) with slip dislocations and evolution of associated steps at TBs in a Mg alloy were investigated and modeled, based on atomic-resolution observations and theory of interfacial defects. It was found that reactions between {101¯1} TBs and low-angle grain boundaries composed of basal mixed 1/3〈112¯0〉 dislocations (referred to as 〈a60〉) could produce asymmetric tilt grain boundaries. Each 〈a60〉-TB reaction created a step with a b±3/±2-type residual dislocation and a two-layer twinning dislocation (TD) gliding away. A one-layer step with a b±1/±1-type residual dislocation could be generated either by the reaction of an 〈a60〉 or a 〈c+as〉 dislocation from one side of a {101¯1} TB with another 〈a60〉 dislocation from the other side, or through direct reaction with the {101¯1} TB, emitting another 〈a60〉 dislocation into the other side. Local atomic structures of steps at {101¯1} TBs could be modified by either emission of or reaction with TDs, 〈a60〉, 〈c+a60〉 or 1/6〈202¯3〉 Frank partial dislocations, reducing local lattice strains at steps. Our experimental results may provide insights for understanding the plastic relaxation mechanisms at {101¯1} TBs.