Transmission electron microscopy of antiphase boundary-like structure y induced by displacive transformation in Ti-Pd shape memory alloy

An antiphase boundary (APB)-like structure in the B19 martensite of Ti-Pd alloy has been investigated by transmission electron microscopy. High-resolution and high-angle annular dark-field scanning transmission electron microscopy images demonstrate the presence of an APB-like contrast along the (001) basal plane of the B19 martensite. The contrast is not inherited from the APB with a displacement vector of the type R = (1/2)<111> in the B2 parent phase. In-situ heating observations indicate that the APBlike contrast disappears above A_f temperature. These facts suggest that the boundary is induced by the local heterogeneity of atomic movements during the martensitic transformation. Therefore, we have newly proposed that the APB-like structure in the B19 martensite is defined as the displacive transformation-induced APB.