Nucleation and growth of {1011} compression twin in Mg single crystals

The {1011} compression twin is more commonly observed under a-axis tension rather than c-axis compression in hexagonal close-packed (hcp) Mg single crystals both in experiments and atom-istic simulations. In this work, molecular dynamics simulations are applied to investigate the nucleation and growth of {1011} twin in Mg single crystal, which is crucial for a comprehensive understanding of the plasticity of hcp metals. A {1011} twin embryo with 4-layer height is found to be naturally nucleated at the free surface via (a) dislocation slip in Mg single crystal. The nucleation of the {1011} twin embryo involves the cross-slip of the nucleated prismatic (a) dislocation onto pyramidal {1011} plane, which is achieved by slip of (a) dislocation and shear along the (1012) direction. Basal stacking faults (SFs) forms in twin embryo and grows with the migration of {1011} twin boundary. The formation of basal SFs in {1011} twin embryo can greatly reduce the required atomic shuffling in (1210) direction, thus facilitate the development of a {1011} twin embryo. The basal SFs inside {1011} twin are anomalous SFs without dislo-cation activities involved, thus the {1011} twinning shear is not influenced by the existence of basal SFs, which is consistent with the irrational shear of 2-layer twinning dislocation.

Automated summary

The nucleation and growth of {1011} twin in Mg single crystal are investigated through molecular dynamics simulations. The twin embryo is found to be naturally nucleated at the free surface via dislocation slip, and its growth involves the formation of basal stacking faults.