Penta-Twin Destruction by Coordinated Twin Boundary Deformation.

Penta-twinned nanomaterials often exhibit unique mechanical properties. However, the intrinsic deformation behavior of penta-twins remains largely unclear, especially under the condition of high shear stress. In this study, we show that the deformation of penta-twins often subject to a structural destruction via dislocation-mediated coordinated twin boundary (TB) deformation, resulting in a reconstructed pentagon-shaped core. This reconstructed core region is mainly induced by the coordinated TB migration along different directions (for the nucleation and growth) and accelerated by the TB sliding (for the growth). The destructed penta-twin core can effectively accommodate the intrinsic disclination of the penta-twin, which further collapses beyond a critical size, as predicted by an energy-based criterion. These intrinsic deformation behaviors of penta-twins would enable the possibility of controlling the morphology of penta-twinned nanomaterials with unique properties.

Atomistic Simulation on the Twin Boundary Migration in Mg under Shear Deformation.

In this paper, the { 10 1 ¯ 2 } twinning and detwinning was studied by molecular dynamics simulation under different shear directions and strain rates. The results showed that the twin was thickened under [ 1 ¯ 011 ] shear direction and shrunken with shearing in the opposite direction. The critical resolved shear stress of { 10 1 ¯ 2 } twin boundary migration increased with the increase of the strain rate. By analyzing the atom's displacement, it was concluded that the { 10 1 ¯ 2 } twin migration was achieved by both the shear and the atomic shuffling. Every atom would be affected by the shear, and different shear directions would cause opposite move directions, which led to twinning or detwinning. The atom shuffling was only used for adjusting the glide twin boundary and mirror-symmetric twin boundary structure evolution.