Low-hysteresis tensile superelasticity in a Ni-Co-Mn-Sn magnetic shape memory microwire

Hysteresis associated with martensitic transformation in shape memory alloys (SMAs), which reflects the energy dissipation during transformation, seriously harms the functional fatigue life and energy conversion efficiency. Exploration of advanced SMAs with both low stress hysteresis and large superelastic strain is of crucial importance for practical applications. Here, we achieved low-hysteresis large tensile superelasticity in a Ni-Co-Mn-Sn magnetic shape memory microwire, the bulk counterpart of which is highly brittle and can hardly be applied. This microwire exhibits oligocrystalline structure with bamboo-like grains and thus good compatibility during deformation and transformation. As a result, excellent tensile superelasticity with a recoverable strain as high as 6% was obtained, which represents the highest value reported heretofore in Ni-(Co)-Mn-Z (Z=In, Sn, Sb) magnetic SMAs. Strikingly, this tensile superelasticity exhibits very low stress hysteresis of 23 MPa (with the overall strain of 6%), which is only one eighth of that in the bulk. The present microwire shows very promising application prospects in cyclic high-frequency actuators and high efficiency energy conversion devices under the coupling of stress and magnetic field.