Phase boundary mediated twinning in stress-induced martensitic bands in metastable Ti-6Mo-3.5Cr-1Zr alloy

The obstruction of boundaries on propagation of deformation twinning requires accommodation mechanisms with the largest compatibility ability. In this work, two types of localized shear mechanisms acting as incident banding, i.e., β→αʹ martensitic transformation and β→{332} twinning, interact with residual αʹ phase boundary (PB) in Ti-6Mo-3.5Cr-1Zr alloy. Both types of interactions trigger secondary {101¯2} twins inside the residual αʹ phase as accommodation. Surprisingly, the potential {101¯2} twinning variant with the maximum accommodation capacity is not activated, but the one that intersects the PB along a <112¯0> direction is frequently preferred. Our analysis indicates that the determination of the preferred mechanism correlates with minimization of the misalignment between the intersection lines of the accommodative twinning plane and the transformation plane of the incident banding with the residual PB. The geometrical feature is important because small misalignment of intersection lines at PB facilitates resultant dislocations dissociation for the nucleation of secondary twins.