Learning from superelasticity data to search for Ti-Ni alloys with large elastocaloric effect

In the present study, the reversible adiabatic temperature change (ΔT_ad) of shape memory alloys was shown to be proportional to the mechanical work released by the reverse martensitic transformation during unloading (ΔW_u). As there exists a considerable amount of data (ΔW_u) on superelastic stress-strain measurements in shape memory alloys, the proposed relationship allows us to predict ΔT_ad without caloric measurements. The estimated ΔT_ad from the ΔW_u of different Ti-Ni alloys shows good linear relationship with the directly measured values. Moreover, following such a design criterion and by tuning of composition and thermo-mechanical treatment, a group of Ti-Ni binary shape memory alloys with directly measured ΔT_ad larger than 35 K under tension were achieved. The large ΔT_ad and ΔW_u can be ascribed to the grain refinement and the heterogeneous internal stress fields after the thermo-mechanical treatment, which have enhanced the critical stress of superelasticity and recoverability of martensitic transformation during unloading.