Giant elastocaloric effect with wide temperature window in an Al-doped nanocrystalline Ti-Ni-Cu shape memory alloy

Ti-Ni based shape memory alloys are promising elastocaloric materials for solid-state refrigeration. In this paper, we made a comprehensive study on elastocaloric effect of a nanocrystalline Ti-44Ni-5Cu-1Al (at%) alloy exhibiting successive B2-B19-B19' transformation. The maximum adiabatic temperature decrease by stress removal from 600 MPa is Delta T-adi similar to 25 K with a small temperature distribution of similar to 0.5 K. The value of Delta T-adi is consistent with that calculated from strain-temperature relation. The effective working temperature window is similar to 55 K, resulting in a high refrigeration capacity of RC = 4.2 kJ/kg. Material coefficient of performance reaches COP similar to 9.6 when an Otto cycle is considered. The middle eigenvalue of the transformation matrix is lambda(2) similar to 0.99, implying high lattice compatibility between the parent and martensite phases. These properties are related to the diffuse nature of successive B2-B19 -B19' martensitic transformation of this alloy. (C) 2019 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.