Simultaneous enhancement of high-temperature magnetocaloric and mechanical properties via microstructural engineering in zone-melted Ni-Co-Mn-Ti alloys

Ni-Co-Mn-Ti Heusler alloys are promising magnetocaloric materials due to their tunable magnetostructural phase transformations across a broad temperature range. However, emerging applications in advanced manufacturing, high-temperature thermal management of power electronics, and waste heat recovery urgently demand further exploitation of their high-temperature magnetic refrigeration potential. This work demonstrates that microstructural design via zone melting rate control effectively tunes the phase transition temperature while maintaining a large magnetocaloric response. As the zone melting rate decreases, alloy grains evolve from equiaxed to columnar morphologies, accompanied by grain coarsening, enhanced axial texture, and a continuous shift of the phase transition temperature toward higher temperatures. Remarkably, the phase transition temperature is successfully extended to approximately 350 K, and the sample processed at 3 mm·min -1 achieves a maximum magnetic entropy change of 40.82 J·kg -1 ·K -1 under a 5 T field change, ranking among the highest values reported. More importantly, benefiting from the fracture mechanism dominated by transgranular fracture, the 0.5 mm·min -1 sample reaching a maximum compressive strength of 1027.7 MPa. These results indicate that zone melting rate control enables synergistic optimization of magnetocaloric performance, phase transition temperature, and structural reliability, providing novel insights and a technical pathway for designing high-performance magnetocaloric materials for high-temperature magnetic refrigeration.