| Thin films of 55Ti-(45-x)Ni-xCu(x = 0, 5, 10, 20 at.%) 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(=15 ㎚) Ti₂Ni phase. Crystallization temperature(Tc) decreases from 774 K to 747 K with increasing Cu-content from 0 at.% to 20 at.%. Two-stage transformation behavior, i.e., the B2→R→B19`, was observed in a 55Ti-45Ni(at.%) alloy thin film. The B2→B19` transformation occurred in a 55Ti-40Ni-5Cu(at.%) alloy film, while the B2→B19 transformation occurred in 55Ti-35Ni-l0Cu(at.%) and 55Ti-30Ni-20Cu(at.%) alloy films. The stress dependence of transformation temperature(dT/dσ) of 55Ti-40Ni-5Cu(at.%) and 55Ti-35Ni-10Cu(at.%) thin films were 0.015 K/㎫ and 0.016 K/㎫, respectively. They were very small as compared to those of 50Ti-45Ni-5Cu(at.%) and 50Ti-40Ni-10Cu(at.%) alloys. |
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