High-performance FeSiAl/(Al2O3-Ni) soft magnetic composites prepared by in situ synthesis method

FeSiAl/(Al₂O₃-Ni) soft magnetic composites (SMCs) were prepared by sintering FeSiAl/NiO composite powders, and the formation mechanism of the Al₂O₃-Ni composite coating and performance of the FeSiAl SMCs with different NiO coating content were studied. During sintering, high temperature promoted a reaction between Al and NiO at the FeSiAl/NiO interface, resulting in the in-situ formation of a composite coating comprising Al₂O₃ coating with high integrity and ferromagnetic Ni coating. The interdiffusion of Al and O^2– toward the interface ensured the continuation of the reaction and growth of the composite coating. The composite coating thickened with the increasing NiO coating content, thus showing reduced real part of permeability. Saturation magnetization considerably increased until the NiO coating content exceeded 12.5 wt% owing to residual NiO. Excessive NiO coating content led to the generation of a large amount of Ni, which was not conducive to the integrity of the Al₂O₃ coating and increased magnetic loss. The FeSiAl SMCs with 5.0 wt% NiO coating content exhibited exceptional performance with high saturation magnetization (135.3 emu/g), good frequency stability of permeability, and low magnetic loss (63.7 W/kg at 0.05 T/20 kHz).