Combinatorial Development of Ti-Ni-X Shape Memory Thin Film Actuators

A combinatorial approach towards the development of shape memory thin film actuators with respect to high transformation temperatures, low thermal hysteresis and good actuator response is presented. Thin film deposition and high-throughput characterization tools were applied for the fabrication and characterization of ternary Ti-Ni-X (X = e.g. Cu, Pd, Hf, Zr) materials libraries. Continuous compositions spreads were used for identification of the composition regions showing reversible phase transformation using auto. mated energy dispersive X-ray spectroscopy (composition), X-ray diffraction (microstructure), as well as temperature-dependent resistivity measurements (R(T)) revealing the phase transformation properties of the thin films. Temperature dependent stress measurements (sigma(T)) on micro-structured cantilever Si-wafers with linearly varying compositions e.g. Ti(64-x)Ni(27+x)Cu(9) in a temperature range from -100 degrees C up to 600 degrees C were applied to characterize the actuator behavior. In addition to extending the knowledge about transforming compositions in ternary systems, special compositions or compositional regions with optimized properties were found. An emphasis will be on compositions showing a B2 R-phase transformation at elevated temperatures, due to their inherently small thermal hysteresis and potential applicability for high-speed actuators.