Deposition and characterization of Ti1−x(Ni,Cu)x shape memory alloy thin films

TiNiCu films with different Cu contents (up to 15 at.%) were prepared by co-sputtering of TiNi and Cu targets using a magnetron sputtering system. Film crystalline structure, phase transformation and shape memory behaviors were characterized by X-ray diffraction, differential scanning calorimeters (DSCs) and curvature method. The substitution of Ni by Cu in TiNi based films resulted in a dramatic change in martensite structure, film orientation and phase transformation behavior. With the increase of Cu content in the films, both the transformation temperatures and hysteresis decreased significantly. From DSC and curvature measurement results, the specific heat and the maximum recovery stress (corresponding to actuation force) generated during martensite transformation decreased with Cu contents, indicating the weak performance of phase transformation, especially at high Cu contents above 9 at.%. There was a maximum value for the stress increase rate (corresponding to actuation speed) at a Cu content of 9 at.%.