Functionally gradient NiTi films fabricated by sputtering

The processing of homogeneous NiTi film has already been reported, but not that of heterogeneous NiTi film. The deposition and processing of functionally gradient films (FGF) of NiTi are discussed and demonstrated. NiTi-FGF were fabricated by RF magnetron sputtering with control of the input power to a titanium target. Films were heat-treated to induce crystallization and memorization. The characteristics have been investigated using a differential scanning calorimeter (DSC) and an electric resistance meter, respectively. The films that were solution-treated at 700° C had a gradient composition, and they showed two types of crystal structure, namely, a nickel-rich layer and a titanium-rich layer in the film. The entire NiTi-FGF transformed gradually and the temperature range between the start and finish of transformation was twice that of homogeneous film. It was verified that motion of FGF could be controlled easily by current intensity.