Structure of martensite in sputter-deposited (Ni,Cu)-rich Ti–Ni–Cu thin films containing Ti(Ni,Cu)2 precipitates

Abstract The martensite structure in sputter-deposited thin films of Ti 48.6 Ni 35.9 Cu 15.5 was studied. The Ti(Ni,Cu) 2 phase precipitates during the annealing process. Fine Ti(Ni,Cu) 2 precipitates can be deformed by the shear deformation of martensitic transformation, but they obstruct the movement of the twin boundaries to some extent. Coarse Ti(Ni,Cu) 2 precipitates seriously impede the growth of martensite plates and lead to a rectangular-cell-like structure of martensite in the film annealed at 873 K. The resistance of Ti(Ni,Cu) 2 precipitates to the growth of the martensite plates enhances with the coarsening of Ti(Ni,Cu) 2 precipitates, which is one of the reasons for the decrease in the maximum recoverable strain with increasing annealing temperature. B19′ martensite with (0 0 1) compound twinning is frequently observed near coarse Ti(Ni,Cu) 2 precipitates and grain boundaries in films annealed at 873 and 973 K. The local stress concentration should be responsible for the presence of B19′ martensite.