Crystallization of Amorphous Sputtered NiTi Shape-Memory Alloy Films

Abstract

ABSTRACTThe crystallization of amorphous sputtered NiTi films was investigated for selected heat treatments. From x-ray diffraction patterns, when the films were annealed below the crystallization temperature, the intensity of the broad maximum centered at 2θ = 43.5° increased with increasing the annealing temperature and time. When the films were annealed at 550°C for 0.5hr, parent B2 phase and Ni4Ti3 precipitates appeared. For annealing temperature above 700°C, the films showed embrittlement and volatilization. Therefore the optimum heat treatment for the optimum shape memory effect is found. The average grain size increased slowly in the initial stage of annealing but remained almost unchanged when the films were annealed for more than 1hr. This is because the grain boundary grooving caused by the titanium at a certain temperature volatilization seriously hinder the grain growth.