Processing and Characterization of Shape Memory Films for Microactuators

Titanium-rich NiTi thin films were deposited by DC magnetron sputtering from a single alloy target (Ni/Ti: 50:50 at. %). X-ray diffraction investigations indicated that the deposited films were amorphous. When annealed to 500 °C, diffraction peaks corresponding to (110) and (200) planes of Austenite phase started emerging. Annealing at 600 °C resulted in the appearance of two sharp Austenite peaks (110) and (200), along with four additional peaks (110), (020), (111), and (021) of the Martensite phase of NiTi, respectively. Scanning electron microscope studies indicated that annealing at 600 °C resulted in densification of the coating. The thermal response using differential scanning calorimeter recorded for the second thermal cycle, for films deposited at 300 and 500 °C, showed single endothermic and exothermic peaks during heating and cooling cycles. For the films deposited at 400 °C and annealed at 450 °C, the elastic modulus was found to be around 110 ± 5.5 GPa and the hardness around 7.8 ± 0.5 GPa.