〈a〉 screw dislocation triggered {101¯1} twinning in magnesium

Abstract

Twin nucleation in hexagonal metals is generally described by successive nucleation and gliding of twinning dislocations/disconnections (TDs). Unusual nucleation mechanisms, such as pure-shuffle mechanism for $\left\{10\bar{1}2\right\}$ twins and kinking mechanism for $\left\{11\overline{2}1\right\}$ twins, had been proposed based on experimental observations and atomistic simulations. Here, we reported screw dislocation enabled $\left\{10\overline{1}1\right\}$ twinning mechanisms in magnesium based on atomistic simulations. A $〈a〉$ screw dislocation can have a planar spread core on basal plane or develop into a $\left\{10\overline{1}1\right\}$ twin embryo via a cross-slip mechanism. The cross-slip enabled $\left\{10\overline{1}1\right\}$ twinning mechanism is favored when the basal slip is constrained or suppressed at a high strain condition. This mechanism addresses the experimental puzzle of the $\left\{10\overline{1}1\right\}$ twin absence under c-axis compression.