Combinatorial study of phase transformation characteristics of a Ti–Ni–Pd shape memory thin film composition spread in view of microactuator applications

Abstract

Phase transformation characteristics of a Ti–Ni–Pd shape memory thin film composition spread have been investigated. The thin film composition spread was fabricated from elemental targets using an ultra-high vacuum combinatorial magnetron sputter-deposition system and subsequent annealing at 500 °C for 1 h in situ. Automated temperature-dependent resistance measurements ( R( T)), energy dispersive X-ray analysis (EDX) and X-ray diffraction measurements (XRD) have been applied for the high-throughput characterization of the composition spread. Reversible phase transformations within the measurement range of −40 to 250 °C within the Ti–Ni–Pd system were observed for compositions with Ti content between 50 and ∼59 at.%. For Ti-richer films, Ti 2Ni and Ti 2Pd precipitates are inhibiting reversible phase transformations. The transformation temperatures and the thermal hysteresis were determined from R( T) measurements. Rising transformation temperatures with increasing Pd content and significantly lower thermal hysteresis for the B2–B19, compared to the B2–R–B19′ transformations were found in good agreement with published data. For low Pd contents (<7–12 at.%, depending on the Ti content) two-stage B2–R–B19′ transformations were observed. Compositions with higher Pd contents showed a single-stage B2–B19 transformation. Increasing Ti content within the B2–B19 transformation region results in a linear increase of the thermal hysteresis and decreasing transformation temperatures.