Superelasticity and elastocaloric effect of NiTiNb shape memory alloys over a wide working temperature window

Solid-state refrigeration based on the elastocaloric effect is a promising alternative to conventional vapor-compression refrigeration technology due to its environmental friendliness and high energy efficiency. NiTi-based shape memory alloys with a great elastocaloric effect in a wide working temperature window are particularly needed for solid-state refrigeration applications. In this study, a series of Ni_50.8-xTi_49.2Nb_x (x = 0, 1, 2, and 3) shape memory alloys were fabricated via arc melting, followed by thermal treatment. The experimental results showed that the martensite transformation temperature decreases with increasing Nb content due to the stabilization of the parent phase by doped Nb atoms. Combining solution strengthening and precipitation strengthening of the Nb addition, the Ni_48.8Ti_46.2Nb₂ alloy demonstrated a significant improvement in the critical stress for martensite transformation and transition strain over a large temperature range of 216–316 K. Meanwhile, it exhibited a large adiabatic temperature change of −10.07 K during rapid stress loading-unloading cycles and a large refrigeration capacity of 3.26 kJ/kg. These findings highlight the high potential of Nb-doping NiTi shape memory alloys for solid-state refrigerants.