Fatigue resistant elastocaloric effect in TiNi via texture-precipitate synergy

Shape memory alloys with both a large elastocaloric effect and exceptional fatigue resistance are key candidates for next-generation solid-state cooling technologies. Here, we report a textured TiNi alloy containing engineered Ti₄Ni₂O precipitates, fabricated via controlled directional solidification, that achieves a large adiabatic temperature change of −15.9 K after 10 million compressive cycles. Microstructural analyses reveal columnar B2 grains aligned with the solidification direction and a uniform dispersion of high-density Ti₄Ni₂O precipitates. A strong crystallographic texture is observed, enabling a large transformation strain of over 6% under compressive loading, as mapped by digital image correlation. In-situ loading X-ray diffraction confirms a continuous increase in intensity of B19′ martensite under stress, while in-situ cooling transmission electron microscopy captures numerous nucleation and progressive growth of the B19′ martensite from B2/Ti₄Ni₂O interfaces. High-resolution TEM further reveals localized lattice distortions at these interfaces, promoting directional and confined growth of B19′ martensite. This progressive transformation, which preserves functional reversibility, combined with the mutual texture–precipitate architecture that enhances mechanical stability, gives rise to ultrahigh fatigue life. These findings highlight the promise of textured TiNi with tailored precipitate architecture for long-term elastocaloric applications and provide a design strategy for developing fatigue-resistant SMAs through microstructural and textural engineering. There is a need for shape memory alloys that exhibit both a large elastocaloric effect and fatigue resistance for practical, long-term solid-state cooling applications. Here authors fabricate a textured Ti49Ni51 alloy with high-density, epitaxially aligned Ti₄Ni₂O precipitates via controlled directional solidification, and characterize its microstructure and properties.