Phase Transformation Behaviors and Shape Memory Characteristics of Ti-rich Ti-Ni-Cu Alloy Thin Films

摘要

Thin films of 55Ti-(45-x)Ni-xCu(x =0, 5, 10, 20 at. percent) compositions were fabricated by d.c. magnetron sputtering method. Deposited films were annealed at 973 K for 3.6 ks to induce crystallization. The phase transformation behaviors of these thin films were investigated by differential scanning calorimetry and X-ray diffraction. Shape memory characteristics were studied by thermal cycling test under a constant load. As-sputtered films contained a mixture of amorphous and very fine(approx =15 nm) Ti_2Ni phase. Crystallization temperature (Tc) decreases from 774 K to 747 K with increasing Cu-content from 0 at. percent to 20 at. percent. Two-stage transformation behavior, i.e., the B2->R->B19', was observed in a 55Ti-45Ni(at. percent) alloy thin film. The B2->B19' transformation occurred in a 55Ti-40Ni-5Cu(at. percent) alloy film, while the B2->B19 transformation occurred in 55Ti-35Ni-10Cu(at. percent) and 55Ti-30Ni-20Cu(at. percent) alloy films. The stress dependence of transformation temperature(dT/d#sigma#) of 55Ti-40Ni-5Cu(at. percent) and 55Ti-35Ni-10Cu(at. percent) thin films were 0.015 K/MPa and 0.016 K/MPa, respectively. They were very small as compared to those of 50Ti-45Ni-5Cu(at. percent) and 50Ti-40Ni-10Cu(at. percent) alloys.