Superelasticity and elastocaloric effect in a textured Ti-Nb-Zr-Ta alloy with narrow stress hysteresis

Abstract

Recently, elastocaloric cooling has been authoritatively regarded as the most promising alternative for replacing conventional vapor compression technology, yet obstacles like structural/functional fatigue and high processing cost still exist, which boost the investigation of new elastocaloric materials. In this paper, we investigated the superelasticity (SE) as well as the elastocaloric effect (eCE) in a textured Ti-22 Nb-4Zr-2Ta alloy prepared by cold rolling of 97% in thickness and subsequent annealing at 973 K for 30 min. The strong texture is in favor of harmonizing the superelastic critical stress and enhancing transformation homogeneity. As a result, superelasticity with narrow stress hysteresis of ∼47 MPa at ambient temperature and outstanding homogeneous eCE has been confirmed elaborately through observing strain together with temperature distribution during a superelastic cycle. The standard deviations (Sdev) of the strain distribution during superelastic deformation was in the range of 0.17%− 0.37% accompanying with temperature change (ΔTadi) of ∼4.4 K and ∼3.9 K during loading and unloading processes, respectively. Moreover, the narrow superelastic hysteresis and homogenous transformation behavior allowed for a coefficient of performance (COP) value of 13.2 and little degradation after 240 elastocaloric cycles. As eCE homogeneity and SE hysteresis correlate closely with functional fatigue behavior, the present Ti-22 Nb-4Zr-2Ta alloy may act as potential working materials for stable solid-state refrigeration.