Multi-target sputter deposition of Ni50Ti50 − xHfx shape memory thin films for high temperature microactuator application

High temperature shape memory NiTiHf thin films with varying hafnium contents up to 28.7 at.% were fabricated by DC magnetron sputtering using simultaneous sputter deposition from separate elemental targets. The required film composition was achieved by adjusting the power ratio to the targets. The as-deposited films were amorphous; a post deposition annealing was performed at 550 °C to crystallize the films. Two-micron thick films were characterized by energy dispersive spectroscopy in a scanning electron microscope, temperature controlled X-ray diffraction, differential scanning calorimetry, and atomic force microscopy. The results showed that above 10 at.% Hf additions the transformation temperatures increased considerably over NiTi. The crystallization temperature of the films varied as a function of Hf concentration and was as high as 519.2 °C, at Hf content of 28.7 at.%. The R-phase transformation was observed during cooling at compositions less than 16 at.% Hf. The transformation temperatures confirmed that the films are comparable with bulk NiTiHf alloy of similar composition.