Abstract
The phase transformation properties of Ti–Ni–Cu shape memory thin films prepared in the form of a continuous composition spread were investigated. The thin film materials library was fabricated from elemental targets using an ultra-high vacuum combinatorial magnetron sputter-deposition system. Alternating wedge-type layers of Ti, Ni, and Cu were deposited on a thermally oxidized Si wafer and subsequently annealed at 500 °C for 1 h in situ. Automated temperature-dependent resistance measurements ( R( T)), energy dispersive X-ray analysis and X-ray diffraction measurements revealed the compositional region in the ternary phase diagram where thermoelastic transformations occur. The transformation temperatures and the thermal hysteresis were determined from R( T) measurements. Within the composition spread an extended transformation region was found. For Ni-rich compositions, a two-stage B2 → R → B19′ phase transformation was observed. Among others, compositions of Ti 51Ni 49− x Cu x (at.%) show a single-stage transformation for a Cu-content <6.5 at.% (B2 → B19′) and >14 at.% (B2 → B19). In the intermediate composition range two-stage transformations (B2 → B19 → B19′) were found. The dependency of the thermal hysteresis on the Cu-content as described in the literature was confirmed.
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