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

Abstract In the present study, the reversible adiabatic temperature change ( Δ T a d ) of shape memory alloys was shown to be proportional to the mechanical work released by the reverse martensitic transformation during unloading ( Δ W u ). As there exists a considerable amount of data ( Δ W u ) on superelastic stress-strain measurements in shape memory alloys, the proposed relationship allows us to predict Δ T a d without caloric measurements. The estimated Δ T a d from the Δ W 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 Δ T a d larger than 35 K under tension were achieved. The large Δ T a d and Δ W 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.
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