Effects of annealing treatment on the microstructure of tantalum coatings on TiNi alloys

Multi-arc ion plating technique was employed to coat TiNi shape memory alloy with tantalum about 3 μm. Then the as-deposited samples were annealed at different temperature in vacuum atmosphere. The results of XRD show that the as-deposited film is composed of a metastable tetragonal β-phase which can transform into α-phase tantalum after annealing at 700, 800, 900°C for 1 h respectively. TEM observations show that thin nano-structured Ta layers are obtained in the as-deposited samples. Mixture of microcrystallite (about 40 nm) and large-size crystal (about 150 nm) α-phase tantalum were formed in the film after annealing at 700°C. When annealed at 900°C, the film is mainly composed of dominantly uniform large-size α-phase tantalum.