On the migration of {101¯1} and {101¯3} coherent twin boundaries in magnesium

In this work, migrations of (101¯1) and (101¯3) coherent twin boundaries (CTB) in pure magnesium are studied by first-principles methods. The migration process is divided into nucleation and gliding of twinning disconnection (TD), with the TD nucleation being approximated by a rigid-shifting of the CTB. Full energetic maps obtained from this analysis reveal the necessity of applying shear strains simultaneously along the twinning direction η1 and along k1, which is normal to η1, to activate the 2-layer CTB migration in these two different twinning modes. The energetic map identifies the most efficient external shear strain direction for activating CTB migration. This direction lies between the Burgers vectors bTD-2 of the 2-layer-height TD and η1. The shear strain required to initiate TD gliding is smaller than that needed for TD nucleation, implying that the migrations of (101¯1) and (101¯3) CTBs are primarily governed by the TD nucleation.