In situ phase engineering during additive manufacturing enables high-performance soft-magnetic medium-entropy alloys

Additive manufacturing (AM) shows promise as a method for producing soft-magnetic multicomponent alloys for use in electric motors and sustainable electromobility applications. However, the simultaneous achievement of a high saturation magnetic flux density (B_s) and a low coercivity (H_c) in AM soft-magnetic materials remains challenging. Herein, we present an approach that integrates an elemental powder mixture of Fe₄₅Co₃₀Ni₂₅ with Fe₂O₃ nano-oxides, which is then subjected to laser powder bed fusion (LPBF) followed by high-temperature annealing to achieve an FCC-structured Fe₄₅Co₃₀Ni₂₅ MEA/FeO composite. The FeO nanoparticles, a byproduct of the reaction between Fe powders and Fe₂O₃ nano-oxides, serve as nucleation sites for the formation of a single FCC phase in the MEA matrix. The resulting LPBF MEA/FeO composite has a B_s of 2.05 T and an exceedingly low H_c of 115 A m^-1, compared to those of the BCC/FCC dual phase MEA and other state-of-the-art additively manufactured soft-magnetic alloys. In situ Lorentz transmission electron microscope (TEM) revealed that the low H_c of the FCC-structured MEA/FeO composite originates from the reduced pinning effect of grain boundaries in the FCC phase on domain wall movement compared with those in the FCC/BCC dual phase.