Influence of non-glide stresses on {101¯2} twin boundary migration in magnesium

Twin thickening occurs via the migration of a twin boundary during deformation and serves as an important mechanism for accommodating plastic strain. While the local stress state significantly influences twin boundary migration, the precise relationship remains unclear and difficult to determine experimentally. Here, we investigate $\left\{10\overline{1}2\right\}$ coherent twin boundary migration in Mg under various stress fields by using the nudged elastic band method to calculate its minimum energy path and hence migration barrier. The results reveal an appreciable influence of non-glide stresses on coherent twin boundary migration. Specifically, the presence of a compressive normal stress reduces the energy barrier. We formulate a phenomenological model to describe the energy barrier as a function of the ratio between the shear stress and the critical resolved shear stress for coherent twin boundary migration. Our results reveal that non-glide stresses can change the critical resolved shear stress and, consequently, the probability of coherent twin boundary migration. In addition, by examining the atomic mechanisms underlying coherent twin boundary migration, we find that the relative atomic displacement at the twinning disconnection observed during coherent twin boundary migration is smaller than the one widely reported in the literature. The energetically favorable configuration of this twinning disconnection varies for different non-glide stresses, causing a non-glide stress-dependent energy barrier. This study advances the understanding of fundamental deformation mechanisms and can contribute to improving models of twinning-induced plasticity.