The boundary of domains which is formed by order-disorder transformation is the so-called antiphase boundary (APB). There are many investigations on the APB in the ordered structure such as B2 or L1₂. Since near equiatomic Ti-Pd alloys of the B2 type intermetallic compound undergo thermoelastic martensitic transformation from the B2 to B19 structures upon cooling around 800 K, the alloys are an attractive high temperature shape memory alloy. In the present study, we have found the APB-like structure in the B19 martensitic phase of Ti-Pd alloy by transmission electron microscopy. High resolution images demonstrate that there is the APB-like contrast along the {001} basal plane of the B19 martensitic phase. The contrast is not inherited from the APB with the R = (1/2)a₀<111> type displacement vector found out in the B2 parent phase [1]. These facts suggest that the boundary is induced by locally heterogeneous shear mode during the martensitic transformation. Therefore, we propose that the APB-like structure in the B19 martensite is defined as the displacive transformation induced APB. 

[1] M. Matsuda, T. Hara, E. Okunishi and M. Nishida: Philos. Mag. Lett. 87 (2007) 59-64.