The Elastocaloric Effect in TiNi-based Foils

The elastocaloric effect in cold-rolled Ti49.1Ni50.5Fe0.4 foils of 30 μm thickness is studied by means of uniaxial tensile tests, digital image correlation and infrared thermography. During pseudoelastic cycling the evolution and orientation of Lüders-like strain bands and the associated local release and absorption of latent heat depend on the rolling direction. The resulting pseudoelastic plateau stress is smaller, whereas the transformation strain is larger in rolling direction compared to the transverse direction. The high surface-to-volume ratio of the foil samples results in a short heat transfer time of about 1.5 s in air. The adiabatic limit is reached at strain rates larger than dɛ/dt = 0.2 s-1. In this case, unloading gives rise to a maximum temperature drop of -17 K. The corresponding coefficient of performance of the material is 10.5.