Abstract
The time-resolved strain and temperature profiles of magnetron-sputtered pseudoelastic TiNi films of 20μm thickness are investigated during tensile stress cycling for different strain rates. Based on simultaneous infrared thermography and digital image correlation, a good correlation between the evolution of temperature profiles and the local formation and propagation of Lüders-like strain bands is observed. The evolution of temperature profiles can be quantitatively described by a phenomenological Tanaka-type model of the martensitic transformation combined with a heat transfer model taking into account the local interaction between transformed and untransformed regions in the transformation kinetics. The investigated film samples exhibit an undercooling of −16K upon mechanical unloading under adiabatic conditions at a strain rate of 0.2s−1. A coefficient of performance of 7.7 is determined. Due to the high surface-to-volume ratio, the films show fast heat exchange in air of the order of 1.5s. Based on these results, the prospects of SMA film-based elastocaloric cooling are discussed.
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