Microstructure evolution and phase transformation in thermally cycled Ni-Ti-Hf film

摘要

A Ni49.8Ti34.4Hf15.8 film was synthesized through magnetron sputtering followed by crystallization and thermal cycling. Microstructure evolution and phase transformation were investigated through transmission electron microscopy and differential scanning calorimetry. Crystallization can be partially completed when heating temperature was increased to 540 degrees C, which is higher than the usually thought crystallization temperature of 503.6 degrees C. After crystallization occurs, the film consists of large Ni-Ti-Hf grains and small granular particles of (Ti, Hf)(2)Ni precipitates dispersed in an amorphous pattern. As the number of thermal cycles increases, crystallization is completed gradually and martensite transformation temperature decreases gradually.