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

In the present study, the reversible adiabatic temperature change (Delta T-ad) of shape memory alloys was shown to be proportional to the mechanical work released by the reverse martensitic transformation during unloading (Delta W-u). As there exists a considerable amount of data (Delta W-u) on superelastic stress-strain measurements in shape memory alloys, the proposed relationship allows us to predict Delta T-ad without caloric measurements. The estimated Delta T-ad from the Delta 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 Delta T-ad larger than 35 K under tension were achieved. The large Delta T-ad and Delta 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. (C) 2021 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Automated summary

In this study, it was found that the reversible adiabatic temperature change of shape memory alloys is proportional to the mechanical work released during unloading, allowing for the prediction of temperature change without caloric measurements. By tuning composition and thermo-mechanical treatment, Ti-Ni binary shape memory alloys with large temperature changes were achieved, attributed to grain refinement and internal stress fields.