Temperature dependence of elastocaloric effect in a microstructurally graded NiTi alloy

Abstract

The temperature dependence of elastocaloric cooling properties of a NiTi alloy with a grain size gradient, which was obtained by cold rolling and subsequent laser surface annealing, was evaluated and compared with those of coarse-grained and as-rolled NiTi. Results show that the adiabatic temperature change (|ΔTad|) and cooling efficiency of the gradient-structured NiTi are significantly enhanced over a wider temperature span (Tspan), making it a superior elastocaloric refrigerant candidate. Detailed analyses show that while the fine grains present in the core of NiTi sheets reduce the global martensitic autocatalytic nucleation potency and increase strength to broaden Tspan, the coarser grains near the surfaces accommodate interlayer deformation to improve |ΔTad|. The work provides a method for overcoming the trade-off between cooling capacity and service temperature span of elastocaloric materials.