Interaction of {11■2} twin variants in hexagonal close-packed titanium

As multiple{11■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}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}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}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}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.