Thermomechanical treatment enables large recoverable strain at low temperatures in a Ni_49.4Ti_48.6Sn₂ alloy

Shape memory alloys with large recoverable strain at cryogenic temperatures are critical for advanced aerospace and polar applications. However, achieving pronounced superelasticity in NiTi-based alloys at cryogenic temperatures remains challenging. Here, a total recoverable strain of up to 7.9% at a cryogenic temperature of 193 K, together with wide-temperature-range superelastic response from 153 to 293 K, was achieved in a Ni_49.4Ti_48.6Sn₂ (at.%) alloy. This performance was realized through an appropriate thermomechanical treatment (45% cold rolling followed by annealing at 673 K for 10 min), which induced a strain glass state. Microstructural analysis revealed that this alloy exhibited a heterogeneous microstructure with distinct functional roles: B2 nanograins/nanosubgrains, amorphous regions, dislocation networks and Ni₄Ti₃ nanoprecipitates strengthened the matrix and suppressed irreversible slip. In addition, the temperature sensitivity of the SIMT decreases to 4.6 MPa/K, contributing to the wide-temperature-range superelasticity. Therefore, this work proposes a feasible microstructural design strategy via thermomechanical processing for developing cryogenic NiTi-based SMAs with large total recoverable strains and wide-temperature-range superelasticity.