Fabrication of TiNi-based shape memory alloy thin films by simultaneous multi-target sputtering method

Abstract
TiNi-based binary shape memory alloy thin films have been fabricated by means of simultaneous multi-target sputtering method. The films were deposited onto Cu foils by a D.C. magnetron sputtering system with two separate Ti and Ni targets. Deposition of the films was carried out by sputtering both targets simultaneously. Composition of the films was controlled by adjusting sputtering power for each cathode. The thin films were heat-treated at various temperatures for 1 h and then quenched into water. Microstructures of the films were characterized by scanning electron microscopy and transmission electron microscopy. Ti-50.5Ni thin films heat-treated above 700 °C for 1 h were perfectly crystallized, however, those heat-treated at 500 °C for 1 h were not crystallized completely. Fracture stress of the films heat-treated at 700 °C was higher than that of heat-treated at 500 °C. These results are quite different from the case of thin films deposited by sputtering a Ti-Ni alloy target. The brittleness of the films fabricated by simultaneous multitarget sputter-deposition originates in its deposition process.