Unveiling heterogeneous microstructure and good combinations of high yield strength and low coercivity of in-situ formed NbC/FeNiCo medium-entropy composites

Abstract

It is very challenging to achieve exceptional combinations of soft-magnetic and mechanical properties in conventional soft-magnetic alloys. To tailor combinations of soft-magnetic and mechanical properties, different volume fractions of in-situ formed NbC were designedly introduced into the recently emerged equi-atomic FeNiCo medium-entropy alloy displaying appealing soft-magnetic properties but disappointing strength. The bulk NbC/FeNiCo medium-entropy composite (MEC) with ∼7.8 vol% NbC (MEC7.5) consisted of ultra-fine and fine FCC grains with nano-sized NbC, realized the best combinations of mechanical and soft-magnetic properties. In detail, it showed an ultra-high tensile yield strength of ∼1158 MPa and an improved elongation of ∼4.6%, resulting from dislocation strengthening, dispersion strengthening and hetero-deformation induced strengthening. Simultaneously, the saturation magnetization and coercivity of the MEC7.5 were ∼ 143 emu/g and ∼ 382 A/m, suggesting that it has good soft-magnetic properties. Therefore, our findings provide a new paradigm for realizing outstanding combinations of high yield strength and low coercivity in alloys.