Twin nucleation at prismatic/basal boundary in hexagonal close-packed metals

Abstract

ABSTRACTThis paper examines {10} twin nucleation and growth under uniaxial tension at the prismatic/basal boundary through both molecular dynamics simulations and continuum mechanics modelling. Our results show that two disconnection dipoles exist on every intrinsic prismatic plane of the crystal which constructs the prismatic/basal boundary. Only one of the two disconnection dipoles is at the nucleus of {10} twins. The disconnection is activated and glides plane-by-plane along the direction throughout twin growth. The prismatic plane of the matrix is converted to the basal plane of the twin during the sliding of the disconnection. It is also predicted that a twin nucleates when the local gradient of elastic-energy or the average elastic-energy difference along the prismatic/basal boundary exhibit a sharp increase. Furthermore, the critical strain for twin nucleation can be obtained with the aid of local energy-based descriptors, when viewing twin nucleation as an instability phenomenon. Simulations suggest that both the local gradient and spatial average of elastic-energy difference are fundamental quantities behind the onset of twin nucleation at the prismatic/basal grain boundary in hexagonal close-packed metals under uniaxial loadings. Furthermore, results from our simulations and mechanics model, provide the position and the critical strain of the {10} twin nucleation at the prismatic/basal boundary.