SHAPE-MEMORY THIN-FILM OF TI-NI FORMED BY SPUTTERING

Thin films of Ti-Ni alloy were formed by sputtering under various Ar gas pressures and r.f. powers to investigate the optimum sputtering conditions and to demonstrate their shape memory effect. The composition and structure of the films were examined by electron microprobe analysis and scanning electron microscopy. These films were annealed in order to crystallize them. The mechanical property of the annealed films was evaluated by a conventional bending test. The martensitic transformation temperatures were determined by differential scanning calorimetry. The shape memory behaviour was examined quantitatively by changing the sample temperature under various constant loads. It was found that the Ar gas pressure had a critical effect on the mechanical property of the thin films, although the r.f. power also affected it. The films formed at a high Ar gas pressure were too brittle to be bent successfully. However, the films formed at a low Ar gas pressure could be bent and their shape memory behaviour was found to be comparable with that of bulk Ti-Ni.