Developing novel high-temperature soft-magnetic B2-based multi-principal-element alloys with coherent body-centered-cubic nanoprecipitates

Multi-principal-element alloys (MPEAs) have attracted considerable attention due to their enhanced possibilities of obtaining superior properties by tailoring chemical compositions in an enormous space. This work developed a series of novel soft-magnetic MPEAs via the cluster formula approach of Al₃(Co,Fe,Cr)₁₄. Through deliberately manipulating their microstructures, ultrafine ferromagnetic body-centered-cubic (BCC) nanoparticles (3 ∼ 8 nm in diameter) are coherently precipitated in a B2 matrix. These alloys exhibit a high saturation magnetization of 107.4 ∼ 167.5 Am²/kg and a low coercivity of 143 ∼ 303 A/m in the as-homogenized and aged states. Even after aging for 480 h at 873 ∼ 1073 K, the prominent soft-magnetic properties can still be retained, which can be ascribed to the excellent stability of the coherent BCC/B2 microstructure. Importantly, these materials also show excellent soft-magnetic properties at high temperatures. The Al₃Co₇Fe₇ alloy exhibits a saturation magnetization of 134.7 Am²/kg and a coercivity of 167.2 A/m at 973 K. Moreover, they have high Curie temperatures (1254 K for Al₃Co₇Fe₇ and 1052 K for Al₃Co₆Fe₆Cr₂) and electrical resistivity (262 ∼ 285 μΩ·cm). The outstanding high-temperature magnetic properties of the presently developed alloys is discussed in light of the microstructural stability and evolution with chemical composition and temperature and the coercivity is found to be closely related to the particle size of BCC nanoprecipitates. With the advantages of the currently developed BCC/B2 MPEAs over conventional soft-magnetic alloys, the coherent precipitation approach opens a new way to design novel high-temperature soft-magnetic materials.