Micromechanics of tensile twinning in magnesium gleaned from molecular dynamics simulations

This work discusses coarse-grained micromechanics of tensile twinning in magnesium (Mg) extracted from molecular dynamics (MD) simulations. We perform MD simulations on Mg single crystal orientations with initial idealized defect structures at temperatures $T=5K$ and $300K$. A detailed atomistic analysis reveals that tensile loading along the c-axis of a defective crystal causes an initial incomplete slip ahead of the defect on the first-order pyramidal $〈c+a〉$ planes, followed by the formation of a $\left\{11\overline{2}1\right\}$ twin embryo and basal dislocation. These mechanisms aid the formation of $\left\{10\overline{1}2\right\}$ twins, which evolve rapidly while $\left\{11\overline{2}1\right\}$ twins disappear. We present a micromechanics picture of the deformation-induced twin structure evolution that is tracked by incorporating a twin orientation analysis (TOA) scheme within Open Visualization Tool. The functional dependencies of the volume fraction (v.f.) and number of twins on the overall plastic strain extracted from this analysis provide a basis to construct kinetic laws for twin evolution in terms of nucleation, growth and coalescence. Preliminary results indicate that $\left\{10\overline{1}2\right\}$ v.f. evolution is dominated by twin growth in the presence of defects at room temperature, and it may not be strongly rate dependent.