Manipulation of NiTi-based shape memory alloy nanostructures via a hybrid approach of phase separation and selective leaching

• A novel damage-free approach for fabricating shape memory alloy nanostructures. • Thermodynamic phase separation enables the fabrication of NiTi shape memory alloys. • Selective dealloying yields freestanding nanoparticles and nanoporous shape memory foams. • Dealloyed structures exhibit reversible martensitic transformation and superelasticity. • Nb, Zr, Al, and Si additions tune the characteristics of shape memory alloy nanostructure. This study proposes a novel strategy for fabricating polycrystalline NiTi-based shape memory alloy (SMA) nanostructures via a hybrid approach combining liquid–liquid phase separation and selective chemical leaching in the Ti-Ni-X-Gd system (X = Nb, Zr, Al, Si). This strategy addresses the limitations of conventional nanoscale SMA fabrication techniques, which often cause processing damage. As the base system, nanoparticles derived from the Ti-Ni-Gd ternary system exhibited thermally induced reversible martensitic transformation near room temperature with a small thermal hysteresis of 5.9 ℃, and demonstrated superelasticity with a fully recoverable strain of 8.6 % during in-situ scanning electron microscopy compression tests. Additionally, freestanding nanoparticles and nanoporous structures with tunable morphology, including particle size, ligament length, and porosity, were synthesized by tailoring the thermodynamic properties of multicomponent precursor alloys. Notably, Nb, Zr, Al, and Si enabled precise control over phase transformation temperatures and thermal hysteresis, expanding the applicability of SMA nanostructures. This work establishes a scalable and versatile fabrication strategy for fabricating SMA nanostructures without processing damage, offering potential applications in self-healing coatings and providing a new framework for investigating the unique behavior of nanoscale SMAs.