Caloric effects in shape memory alloys – optimizing alloy compositions for solid state refrigeration

Alternative cooling technologies have received significant attention during the last decade. It was found that pseudoelastic Ni-Ti shape memory alloys (SMAs) are very attractive as a functional material for solid state refrigeration due to their large elastocaloric effect. Within a single unloading step from stress-induced martensite to austenite, adiabatic temperatures drops between 15 and 30K can be obtained. In order to optimize Ni-Ti for elastocaloric cooling, the effects of alloy composition as well as loading/unloading conditions need to be understood. For a high cooling efficiency, large latent heats, low mechanical hysteresis widths and stable performance during pseudoelastic cycling are required. In the present work, we perform a systematic alloy screening focussing on binary Ni–Ti, ternary Ni–Ti–X (X = Cr, Co, Fe, V, Y) and quaternary Ni–Ti–Cu–Z (Z = Co, Fe, V) SMAs.

The alloys were prepared through arc melting and thermomechanical processing. Mechanical induced heat effects were characterized through a special designed test setup. We used a modified tensile test system where adiabatic temperature changes can be monitored through thermography imaging. We provide preliminary results on the performance of our alloys in a first air cooling prototype which is being developed by our partners at Saarland University.