Super‐Stable Triphase Nanostructured NiTi for Elastocaloric Heat Pump

ABSTRACT Shape memory alloys (SMAs) hold significant promise for elastocaloric heat pumps but are hindered by thermal and mechanical instabilities that lead to temperature‐dependent responses and functional fatigue. Herein, we report a triphase nanostructured NiTi sheet, consisting of nanocrystalline martensite and austenite embedded within an amorphous matrix, fabricated via a simple cold‐rolling process. This material not only demonstrates a temperature‐independent stress–strain response and adiabatic temperature change ( ∆T ad of 7.0°C) across a 20°C–120°C range but also maintains stable superelasticity over 2 × 10 8 cycles under a stress of 2 GPa, underscoring its exceptional thermal and mechanical stability. Microstructural analysis indicates that stabilized B19' nanocrystals counteract the modulus hardening of the B2 phase, ensuring a temperature‐independent mechanical response. Furthermore, the synergy of nanocrystallization and the high strength of the amorphous phase preserves the structural integrity of the triphase nanostructure, leading to the remarkable temperature‐independent ∆T ad and the high fatigue resistance. This work offers a robust pathway toward the development of high‐performance, super‐stabilized SMAs for advanced elastocaloric heat pump applications.