Sputter-deposited Ti–Ni–Cu shaped memory alloy thin films

Ti50NiCu5 thin films were prepared by r.f. magnetron sputtering. The compositions were determined by electron probe microanalysis. The phase transformation characteristics were examined by resistivity measurements. The substrate-curvature measurements were applied to determine the residual stress of the films based on silicon substrates. Tensile residual stress induces a two-stage transformation: B2→orthorhombic→monoclinic; and lowers martensitic transformation temperatures, while compressive residual stress accelerates the one-stage transformation: B2→monoclinic; and results in a transformation without temperature hysteresis. The reason is analyzed.