Enhanced elastocaloric effect in Sc-doped TiNi shape memory alloys

We report a giant elastocaloric effect in Sc-doped TiNi shape memory alloys, demonstrating their potential for solid-state cooling applications. The solution-treated (Ti_49.2Ni_50.8)_99.8Sc_0.2 alloy achieves a high entropy change of ∼74 J/kg·K and a adiabatic temperature change (∆T_ad) of 37.41 K, though it suffers from poor thermal cycling stability. However, after ageing at 623 K for 10 hours, the alloy retains a high ∆T_ad of −31.56 K with coefficient of performance (COP_materials) of 21. Furthermore, it demonstrates a stable ∆T_ad of −15.05 K and a high COP_materials of 32 under reduced stress after 100 loading cycles. Microstructural analysis reveals that the two-step B2-R-B19′ martensitic transformation, combined with the formation of Ni₄Ti₃ precipitates and Sc₂O₃/ScO particles, strengthens the matrix and enhances the cycling stability of the elastocaloric effect. This study demonstrates a pathway to achieve a giant elastocaloric effect in Sc-doped TiNi alloys, underscoring their promise for practical solid-state cooling technologies.