Structural characteristics of {10 1 ¯ 1} contraction twin-twin interaction in magnesium

Twin interface characteristics play a crucial role in elucidating twin propagation, twin-twin and twin-dislocation interactions, and then affect their mechanical properties. Herein, focusing on magnesium as a model of a hexagonal close-packed structure, we investigate the structural characteristics of {10 1 ¯ 1} contraction twin, depending on crystallographic analysis, molecular dynamics simulations and transmission electron microscopy observations. The geometrical features reveal that it is preferential to form acute twin boundaries during the processes of twin-twin interactions. Subsequently, the dynamics simulations results demonstrate that the propagation process of {10 1 ¯ 1} contraction twin is mainly related to the migration of {10 1 ¯ 3} twin boundaries in twin tip, and its thickening process is dominantly associated with the movement of multiple-layered steps. Additionally, two twin-twin interaction modes- tip-twin boundaries crossing transmission and tip-tip collision-have been successfully constructed, dependent on the preferential acute growth mode of contraction twins. Finally, typically structural characteristics on both free-growth of single contraction twin and twin-twin interactions have been confirmed in the ultrahigh pressure pure magnesium by transmission electron microscopy observations. This work clarifies fundamental physics of {10 1 ¯ 1} contraction twins in hexagonal close-packed metals, which can also be applied to other systems to explain twin strengthening mechanisms.