The nucleation and migration of \(\{10\bar{1}1\}\) twins in hcp materials

Abstract

\(\{10\bar{1}1\}\) twins are known to play a pivotal role in the deformation and fracture of hcp materials under c-axis compression. In this paper, the nucleation and migration of \(\{10\bar{1}1\}\) twins are investigated through the integration of atomistic simulations and theoretical calculations. The atomistic simulations reveal extensive nucleation of \(\{10\bar{1}1\}\) twins, occurring either directly at the free surface or via a bcc intermediate state in bulk. The theoretical calculations identify the surface-nucleation as the low-shear mode with conjugate twinning plane \(K_2=\{10\bar{1}3\}\). In contrast, the bulk-nucleation is determined as the high-shear mode with irrational twinning shear and \(K_2\) plane. Our analyses pinpoint that their fundamental distinction lies in whether the twinning shear encompasses an \(\langle a \rangle\) component along the common zone axis. During subsequent twin growth, the high-shear mode activates sequential \(b_2\) dislocations, while the low-shear mode involves concurrent activation of two stacked \(b_2\) dislocations, collectively forming a \(b_4\) dislocation. This paper provides valuable insights into the critical distinctions and the complex interplay between the two \(\{10\bar{1}1\}\) modes in hcp materials.

Graphical abstract