Ｔｉ‐５０ａｔ．％および５２ａｔ．％Ｎｉ合金薄膜の形状記憶特性に及ぼす熱サイクルの影響

Abstract

The stability of shape memory characteristics in thermal cycling was investigated for Ti-50at.%Ni and Ti-52at.%Ni thin films prepared by r. f. sputtering and annealed for 1h at 773K. The transformation temperatures measured by differential scanning calorimetry indicated less sensitivity to thermal cycling in the Ti-52at.%Ni film than in the Ti-50at.%Ni film. The stability of the shape memory effect was evaluated using a small tensile tester. Under a stress of 120MPa, 100 thermal cycles caused the martensitic and reverse martensitic transformation temperatures of the Ti-50at.%Ni film to decrease by 10 and 20K, respectively. However, the reverse martensitic transformation temperature of the Ti-52at.%Ni film remaind constant, and its martensitic transformation temperature decreased by 5K after the first 20 cycles but then remained constant owing to a training effect. The transformation strains of the films remained constant throughout the thermal cycling. Plastic strain was not observed in the Ti-52at.%Ni film, while in the Ti-50at.%Ni film it varied from 0.4% to 0.03% with thermal cycling. These results, showed that the Ti-52at.%Ni film had highly stable shape memory characteristics against thermal cycling.