Atomic-resolution studies on reactions of slip dislocations with { 10 1 ¯ 1 } twin boundaries and local plastic relaxation in a Mg alloy

Reactions of $\left\{10\overline{1}1\right\}$ 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 $\left\{10\overline{1}1\right\}$ TBs and low-angle grain boundaries composed of basal mixed $1/3〈11\overline{2}0〉$ dislocations (referred to as $〈a_{60}〉$) could produce asymmetric tilt grain boundaries. Each $〈a_{60}〉$-TB reaction created a step with a $b_{\pm 3/\pm 2}$-type residual dislocation and a two-layer twinning dislocation (TD) gliding away. A one-layer step with a $b_{\pm 1/\pm 1}$-type residual dislocation could be generated either by the reaction of an $〈a_{60}〉$ or a $〈c+a_s〉$ dislocation from one side of a $\left\{10\overline{1}1\right\}$ TB with another $〈a_{60}〉$ dislocation from the other side, or through direct reaction with the $\left\{10\overline{1}1\right\}$ TB, emitting another $〈a_{60}〉$ dislocation into the other side. Local atomic structures of steps at $\left\{10\overline{1}1\right\}$ TBs could be modified by either emission of or reaction with TDs, $〈a_{60}〉$, $〈c+a_{60}〉$ or $1/6〈20\overline{2}3〉$ Frank partial dislocations, reducing local lattice strains at steps. Our experimental results may provide insights for understanding the plastic relaxation mechanisms at $\left\{10\overline{1}1\right\}$ TBs.