Nucleation mechanism of {1012} twin with low schmid factor in hexagonal close-packed metals

{1012} twin is one of the most common twins in the plastic deformation of hexagonal close-packed metals. It has been found that some {1012} twinning behaviors do not comply with the Schmid law, but the mechanism is not well understood. In the present study, high resolution transmission electron microscopy and electron backscattered diffraction technique were used to comprehensively study the nucleation and growth of {1012} twins with low Schmid factor at small angle grain boundaries in pure Titanium. The experimental results revealed that the basal <ɑ> dislocations slipped to the small angle grain boundaries and reacted with the preexisted misfit dislocations, resulting in twinning dislocations. It was identified to be a crucial process for twin nucleation with low Schmid factor. A novel dislocation reaction mechanism for the low SF twin nucleation was proposed.