Crystallography of deformation twin boundaries in a B2 type Ti-Ni alloy

The deformation structure of B2 parent phase in Ti-Ni shape memory alloy around 573 K has been investigated by transmission electron microscopy. Serrations are seen in stress-strain curve, which corresponds to the formation of various planar defects of twin relation with respect to {1 1 2} {1 1 3}, {1 1 5}, {4 4 7} planes and so on. These defects can be expressed by particular Σ values on the basis of the coincidence site lattice model, since they are <1 1 0> symmetric tilt boundaries in a wide sense. It is also demonstrated that the sigma combination rule of the coincidence site lattice model can be applied to the triple junction of such defects