Interaction of {112¯2} twin variants in hexagonal close-packed titanium

Abstract As multiple {11 2 ¯ 2} twin variants are often formed during deformation in hexagonal close-packed (hcp) titanium, the twin-twin interaction structure has a profound influence on mechanical properties. In this paper, the twin-twin interaction structures of the {11 2 ¯ 2} contraction twin in cold-rolled commercial purity titanium were studied by using electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). Formation of the {11 2 ¯ 2} twin variants was found to deviate the rank of Schmid factor, and the non-Schmid behavior was explained by the high-angle grain boundary nucleation mechanism. All the observed twin-twin pairs manifested a quilted-looking structure, which consists of the incoming twins being arrested by the obstacle twins. Furthermore, the quilted-looking {11 2 ¯ 2} twin-twin boundary was revealed by TEM and high resolution TEM observations. De-twinning, lattice rotation and curved twin boundary were observed in the obstacle twin due to the twin-twin reaction with the impinging twin. A twin-twin interaction mechanism for the {11 2 ¯ 2} twin variants was proposed in terms of the dislocation dissociation, which will enrich the understanding for the propagation of twins and twinning-induced hardening in hcp metals and alloys.