Elastocaloric effects in ultra-fine grained NiTi microwires processed by cold-drawing

Efficient elastocaloric cooling in shape memory alloys requires a stable superelastic behavior in which high yield strength is needed. Here Ni_50.4Ti_49.6 microwires with diameter 130 μm and ultra-fine grains ∼30 nm were prepared by multi-step cold-drawing and low-temperature annealing. Enhanced cyclic stability of the elastocaloric effects induced by the superelastic training was demonstrated. The pre-trained microwire showed a stable ΔS_e 43 J/(kg K) with a broad working temperature range ΔT ∼ 70 K. The superelastic trained microwire, with giant and stable ΔS_e over a wide working temperature window, may act as a promising elastocaloric cooling material for minor-sized devices.