Study on martensitic transformation, superelasticity, and elastocaloric effect of Ti50.5–xNi37.5Cu12Nbx alloys

Abstract

Shape memory alloys based on Ti-Ni-Cu, known for their excellent Elastocaloric phenomenon, are promising candidates for solid-state refrigeration. Nb doping is a key strategy for tailoring their phase transformation and mechanical properties. Ti50.5–xNi37.5Cu12Nbx (at.%, x = 0, 1, 2, 3, 4, 5, 6) alloys were fabricated by vacuum arc furnace melting, and the role of Nb content in phase transition, microstructure, superelasticity, as well as elastocaloric effect, was systematically studied. The results show that the martensitic transformation temperature drops linearly by approximately 50 K for each 1 at.% increase in Nb concentration. For x ≥ 2, the material consists of B2 austenite with the formation of precipitates, a Nb-enriched β-Nb phase. Among the compositions, Ti48.5Ni37.5Cu12Nb2 exhibits the best overall behavior, with a peak adiabatic 7.4 K temperature decrease at 4% strain.