Ni-Co-Mn-Ti-B high performance multiferroic phase transformation material: simultaneous modulation of mechanical properties and successive caloric effects by B doping

Ni-Mn-based multiferroic phase transformation materials are emerging as one of the most promising candidates in the field of solid-state refrigeration. However, the high intrinsic brittleness and the narrow working temperature region of these alloys limit their practical applications. Here, we demonstrate a composition design strategy for B doping in Ni-Co-Mn-Ti alloys, which simultaneously improves mechanical properties and maintains giant successive caloric effects with a broad working region near room temperature (RT). Our results reveal that the original Ti-rich second phase in the Ni-Co-Mn-Ti alloys has little contribution to the mechanical properties, while the grain refinement and grain boundary strengthening mechanisms formed by the doping of B can ensure the excellent mechanical properties. Through composition optimisation, the low-cost (Ni37Co13Mn34Ti16)98.5B1.5 as-cast alloy prepared by arc-melting can exhibit excellent mechanical properties and functional behaviour. The fracture compressive strength and strain of alloy can reach up to 1553 MPa and 17.7% at 290 K, respectively. Besides, the maximum magnetic entropy change induced by 70000 Oe magnetic field is 40.3 J kg−1 K−1, and a large elastocaloric adiabatic temperature change of 18.0 K can be yielded through applying a stress field. A combination of magnetocaloric and elastocaloric effect can achieve a broad working temperature region of over 90 K.