Elastocaloric effect with a broad temperature window and low energy loss in a nanograin Ti-44Ni-5Cu-1Al (at·%) shape memory alloy

Superelastic Ti-Ni-based shape memory alloys are promising elastocaloric materials for solid-state refrigeration. In this paper, we studied the mechanical properties and elastocaloric effect of a severely cold rolled Ti-44Ni-5Cu-1Al (at.%) alloy composed of nanograins $(\ensuremath{\sim}5\text{--}16\phantom{\rule{0.16em}{0ex}}\mathrm{nm})$. The alloy exhibits partial stress-induced martensitic transformation with a large quasilinear reversible strain of $\ensuremath{\sim}3.4\phantom{\rule{0.16em}{0ex}}%$ and a small energy dissipation of $\ensuremath{\sim}1.6\phantom{\rule{0.16em}{0ex}}\mathrm{MJ}/{\mathrm{m}}³$ when a maximum stress of 1 GPa is applied. The temperature decrease induced by adiabatic removal of a stress of 1 GPa is of about \ensuremath{-}5 K, which is mainly due to the reverse transition occurring during unloading. The effective working temperature window of elastocaloric effect larger than 200 K. The coefficient of performance of this alloy reaches \ensuremath{\sim}13, which is higher than values reported so far for Ti-Ni alloys.