Bi2O3 in-situ oxidizing effect upon the core-shell structure design for the Fe-Si directional alloyed soft magnetic material (DASMM)

Abstract

High performance soft magnetic composites (SMCs) materials require the particles surface coating shell have a high electric resistivity and strong adhesion to the substrate ferromagnetic core. However, it’s very challenging to meet those property demands at the same time. In this research work we proposed a new type of Fe-Si directional alloyed soft magnetic material (DASMM), this core-shell structured Fe-Si DASMM powder particle surface insulating SiO2 shell both have high resistivity and strong metallurgical bonding to the substrate Fe core. The influence of 0–2 wt% doped Bi2O3 upon the microstructure and magnetic properties of sintered Fe-Si DASMM were systematically studied. The melted Bi2O3 in-situ reacted with the surface Si shell in Fe-Si directional alloyed soft magnetic powder (DASMP) and formed high resistive SiO2 shell and Bi metal through a reduction reaction. Consequently, the doped Bi2O3 promoted the Fe-SiO2 core-shell structure formation for the Fe-Si DASMM. As the doped Bi2O3 content increased, the insulating SiO2 shell network structure intensity, continuity and uniformity progressively improved; the resistivity increased first and then decreased. While due to the effective inter-particle eddy current insulating effect by the in-situ reduction formed SiO2 shell, both the core loss (Pcv) and coercivity (Hc) of Fe-Si DASMM decreased gradually.

Keywords

• In-situ oxidation
• Core-shell
• Directional alloyed
• SMCs
• Bi2O3