Deformation mechanism of martensite in Ti-rich Ti–Ni shape memory alloy thin films

The microstructural evolution of deformed B19′ martensite in Ti-rich Ti–48.9 at.% Ni shape memory thin films was studied by transmission electron microscopy and the deformation mechanism of the martensite was clarified. The thin film was fabricated by sputter deposition. In this thin film the thermally formed martensite has (0 0 1) twinning as its substructure due to the effect of Guinier–Preston zones. The tensile deformation involves the reorientation of (0 0 1) twinning domains, formation of (1 0 0), (201¯), and (1¯1¯3) deformation twins, and detwinning of the existing (0 0 1) twins. The (1 0 0) twins and the (201¯) twins grow one by one and form a zigzagged configuration. The (1¯1¯3) twin is a newly found deformation twin in the Ti–Ni alloy. The irrecoverable strain is caused by the irreversibility of the deformation-induced (201¯) and (1¯1¯3) twins during heating.