Achieving high-temperature superelasticity and stable actuation response by nanocrystalline engineering in NiTiZr shape memory alloy

We report a nanostructured Ni₅₀Ti₄₆Zr₄ (at. %) alloy that, after 90 % cold drawing combined with low-temperature annealing at 380 °C, exhibits up to 7.8 % recoverable strain over a wide temperature range from 20 °C to 200 °C. Furthermore, the nanocrystalline alloy annealed at 550 °C maintains a martensitic phase transformation start temperature (Ms) of -24 °C during load-biased thermal cycles, exhibits a stable thermally actuation response, and achieves an actuation strain of 7 % under an applied stress of 500 MPa. Detailed microstructural observations reveal that the superior functional stability originates from the synergistic effect of Zr doping and nanocrystalline reinforcement, which inhibits the generation of dislocations during the martensitic phase transformation process. Theoretical phase transformation strain calculations further corroborate the experimentally measured maximum actuation strain. The designed precious-metal-free nanocrystalline NiTiZr alloy holds significant potential for applications in aerospace engineering and solid-state actuation systems.