Structure of martensite in deformed Ti-Ni-Cu thin films

Microstructural evolution in a high-Cu-content Ti_50.2Ni ₃₀Cu_19.8 shape-memory thin film deformed in the B19 martensite state was studied by transmission electron microscopy, and the deformation mechanisms were clarified. The thin film was prepared by magnetron sputtering deposition. In the undeformed film, the B19 martensite has mainly {0 1 1}_B19 twins with a small number of {1 1 1}_B19 twins. The tensile deformation involves a reorientation of the {0 1 1}_B19 twin domains, de-twinning of the {0 1 1}_B19 and {1 1 1}_B19 twins, and a stress-induced B19-B19′ transformation with the production of (0 0 1)_B19′ compound twins. The film shows a large recoverable strain of 5.5%, which is far beyond the stress plateau.