Correlation of microstructural and multicaloric properties of suction ‐ cast Ni ‐ Mn ‐ In

Novel multicaloric cooling utilizing the giant caloric response of Ni‐Mn‐based metamagnetic shape‐ memory alloys to different external stimuli such as magnetic field, uniaxial load and hydrostatic pressure is a promising candidate for energy‐efficient and environmentally‐friendly refrigeration. However, the role of microstructure when several external fields are applied simultaneously or sequentially has been scarcely discussed in literature. Here, we synthesized ternary Ni‐Mn‐In alloys by suction casting and analyzed the microstructural influence on the response to magnetic fields and uniaxial load. SEM‐EBSD reveals a distinct core‐shell microstructure with a radially symmetric <001> solidification texture resulting in a two‐step martensitic transformation. In correlation with temperature‐dependent XRD a significant effect of grain orientation on the stress‐induced martensitic transformation is demonstrated. The influence of microstructure on the magnetic‐field‐induced transformation dynamics is studied by strain measurements in static and pulsed fields. Temperature‐ stress and temperature‐magnetic field phase diagrams are established and single caloric performances are characterized in terms of ΔsT and ΔTad. The cyclic ΔTad values are compared to the ones achieved in the multicaloric exploiting‐hysteresis cycle. It turns out that a tailored microstructure and the combination of both stimuli enable outstanding caloric effects in moderate external fields which can significantly exceed the single caloric performances. In particular for Ni‐Mn‐In, the maximum cyclic effect in magnetic fields of 1.9 T is increased by more than 200 % to ‐4.1 K when a moderate sequential stress of 59 MPa is applied. Our results illustrate the crucial role of microstructure for multicaloric cooling using Ni‐Mn‐based metamagnetic shape‐memory alloys.