Crystallography of stress-induced martensitic transformation and giant elastocaloric effect in a <001>A textured Ni27Cu21Mn46Sn6 shape memory alloy

Shape memory alloys exploit the latent heat yielded by stress-induced martensitic transformation to achieve elastocaloric effect, being suited for solid-state cooling technology as an alternative to conventional vapor-compression refrigeration. In this work, the crystallography of stress-induced martensitic transformation and elastocaloric effect in a polycrystalline Ni27Cu21Mn46Sn6 shape memory alloy with <001>(A) preferential orientation produced by means of directional solidification were studied. By performing ex-situ electron backscatter diffraction (EBSD) measurements, the transition from austenite to a single variant of 6 M martensite induced by compressive loading was evidenced, following a specific transformation orientation relationship of {1 0 1}(A)//{1 -2 -6}(M) and <1 0 - 1>(A)//<-6 -6 1>(M) between two phases. Moreover, owing to the synergistic effect of large transformation entropy change tailored through manipulating the lattice volume change across the phase transformation and microstructure texturing promoted by temperature gradient effect during solidification process, the present alloy can demonstrate very remarkable elastocaloric effect, with an extremely high value of adiabatic temperature variation up to -31.8 K upon releasing a moderate compressive loading of 460 MPa. This work is expected to give insight into stress-induced martensitic transformation crystallography and offer some inspirations for designing high-performance elastocaloric materials.