Effect of solidification rate on martensitic transformation behavior and adiabatic magnetocaloric effect of Ni50Mn35In15 ribbons

Ni50Mn35In15 compound has become an archetype for investigating the functional properties of metamagnetic shape memory alloys. We have fabricated Ni50Mn35In15 melt spun ribbons to study the crystal structure, microstructure, martensitic transformation, magnetic properties and magnetocaloric effect as a function of the ribbon solidification rate controlled by the wheel speed. We have found that an increase of the cooling rate refines the alloy grain size, which, in turn, influences the chemical order of austenite phase and functional properties: ribbons produced at low wheel speed (10, 20 and 30 m/s) present majorly L21 structure associated with higher magnetic entropy change, ΔSM (up to 18.6 J/kgK for a magnetic field change of μ0ΔH = 5 T) and Curie temperatures of austenite, TCA, and martensite, TCM (TCA = 309 K and TCM = 199 K) compared with the B2-ordered single phase ribbons (ΔSM = 11.3 J/kgK for μ0ΔH = 5 T; TCA = 293 K; TCM = 178 K) obtained at higher cooling rates (40 and 50 m/s). Besides, we have also observed a correlation between the grain size reduction and a shift of the martensitic transformation to lower temperatures. Direct measurements of the adiabatic temperature change have been performed during both the first- and second-order phase transitions. The results disclose the correlation between structural and magnetic properties of the ribbon and the wheel speed, which opens an innovative tool to adjust the transformation characteristics and magnetocaloric properties through the solidification rate control.