Giant Elastocaloric Effect and Improved Cyclic Stability in a Directionally Solidified (Ni₅₀Mn₃₁Ti₁₉)₉₉B₁ Alloy

Superelastic shape memory alloys with an integration of large elastocaloric response and good cyclability are crucially demanded for the advancement of solid-state elastocaloric cooling technology. In this study, we demonstrate a giant elastocaloric effect with improved cyclic stability in a <001>_A textured polycrystalline (Ni₅₀Mn₃₁Ti₁₉)₉₉B₁ alloy developed through directional solidification. It is shown that large adiabatic temperature variation (|ΔT|) values more than 15 K are obtained across the temperature range from 283 K to 373 K. In particular, a giant ΔT up to -27.2 K is achieved by unloading from a relatively low compressive stress of 412 MPa at 303 K. Moreover, persistent |ΔT| values exceeding 8.5 K are sustained for over 12,000 cycles, exhibiting a very low attenuation behavior with a rate of 7.5 × 10^-5 K per cycle. The enhanced elastocaloric properties observed in the present alloy are ascribed to the microstructure texturing as well as the introduction of a secondary phase due to boron alloying.