Large elastocaloric effect with high refrigeration efficiency in a polycrystalline Co50V35Ga15 Heusler alloy

Abstract

Superelastic martensitic transformation (MT) confers a considerable elastocaloric response to shape memory alloys, but the significant hysteretic loss cripples the energy conversion efficiency. In the present work, large elastocaloric effect with high refrigeration efficiency is realized in a polycrystalline Co₅₀V₃₅Ga₁₅ Heusler alloy. Experimental results show that the studied alloy undergoes a paramagnetic type MT from L2₁ cubic austenite to D0₂₂ tetragonal martensite with a small thermal hysteresis \((\Delta T_{{{\text{hys}}}} )\) of ~ 3 K. By carefully examining the strain rate dependence of superelastic response, it is also found that the stress hysteresis \((\Delta \sigma_{{{\text{hys}}}} )\) consists of two components including intrinsic stress hysteresis \((\Delta \sigma_{{{\text{hys}}}}^{{{\text{int}}{.}}} )\) caused by inherent attribute of MT and extrinsic stress hysteresis \((\Delta \sigma_{{{\text{hys}}}}^{{{\text{ext}}{.}}} )\) aroused by applied strain rate. Accordingly, we put forward a strain relaxation equation to separate the relative contributions between \(\Delta \sigma_{{{\text{hys}}}}^{{{\text{int}}{.}}}\) and \(\Delta \sigma_{{{\text{hys}}}}^{{{\text{ext}}{.}}}\) quantitatively, which demonstrates that a small \(\Delta T_{{{\text{hys}}}}\) is conducive to substantial decrease in \(\Delta \sigma_{{{\text{hys}}}}^{{{\text{int}}{.}}}\). Moreover, associated with stress-induced superelastic MT, large reversible adiabatic temperature changes \((\Delta T_{{{\text{ad}}}} )\) higher than 11 K are achieved under an applied strain of 6.5% over a temperature range of at least 60 K. With the combination of a large elastocaloric cooling capacity and a low energy dissipation, significant improvements in refrigeration efficiency can be obtained in a wide strain range, being superior to those reported in most of typical elastocaloric materials near room temperature.

Graphical abstract