Large elastocaloric effect covering a broad temperature window in a composition-graded Ni50Mn31.5Ti18.5 alloy prepared by magnetic field-assisted directional solidification

Elastocaloric effect in shape memory alloys relies on the latent heat associated with stress-induced martensitic transformation, which can be exploited for solid-state cooling applications. However, large stress hysteresis inherent to the first-order transformation greatly restricts the energy conversion efficiency and working temperature window. Here, by utilizing compositional gradient engineering to tailor mechanical hysteresis and microstructure texturing to promote elastocaloric response, a composition-graded Ni50Mn31.5Ti18.5 alloy with <001>A preferred orientation has been fabricated through magnetic field-assisted directional solidification. Owing to the composition segregation induced by a transverse magnetic field applied during solidification, considerable amounts of preexisting martensite domains are embedded in the austenite matrix, which contributes to the reduced critical driving stress and stress hysteresis of martensitic transformation. In combination with large cooling capacity favored by highly preferred orientation, the material's coefficient of performance has been greatly improved. Moreover, a broad refrigeration temperature span of 200 K covering 263 K to 463 K is also realized, with a maximum adiabatic temperature variation of –18.4 K. We attribute the enhanced elastocaloric properties to the synergy of preferred orientation and compositional gradient, which can be developed as an effective route towards performance improvement of elastocaloric materials.