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.
Li et al. (Thu,) studied this question.