Tailoring of microstructure and martensitic transformation of nanocrystalline Ti–Ni-Hf shape memory thin film

Abstract

The amorphous Ti–Ni-Hf thin films with the specific compositions were prepared from single Ti–Ni-Hf alloy target by adjusting processing parameters of direct current magnetron sputtering deposition. Prior to the crystallization, a glass transition occurred in the present Ti–Ni-Hf thin films. The annealed Ti–Ni-Hf thin films were characterized by the nano-crystalline. With the annealing temperature increasing, the grain size firstly increased and then decreased owing to the presence of (Ti,Hf)2Ni precipitate. Two endothermic and exothermic peaks corresponding to B19’⇌B2 martensitic transformation in heating and cooling curves were observed for the Ti–Ni-Hf thin films with the lower annealing temperature and shorter annealing time, which was closely related to the inhomogeneous composition. However, the Ti–Ni-Hf thin films annealed at higher annealing temperature and longer annealing time showed the single stage B19’⇌B2 martensitic transformation. In addition, the martensitic transformation temperatures firstly increased and then decreased with the annealing temperatures rising.