Transmission electron microscopy of antiphase boundary-like structure of B19′ martensite in Ti–Ni shape memory alloy

An antiphase boundary (APB)-like structure of the B19′ martensite in Ti–Ni alloy was investigated by transmission electron microscopy. The APB-like structure shows atomic shifts on both the (0 1 0)B19′ plane along the c-axis and the (0 0 1)B19′ plane along the b-axis; a kind of ledge-and-step structure on the b–c plane, in addition to a displacement along the a-axis. The displacement vector can be expressed as R = 〈−0.1648 1/2 0.4328〉 in terms of the conventional atomic coordinates of Ti and Ni in the B19′ martensite. The APB-like structure is not inherited from APB in the B2 parent phase. We conclude that the APB-like structure is developed by accidental impingement of differently nucleated martensitic domains during the transformation. This structure is defined as a kind of stacking fault with an APB-like contrast.