Influence of oxidation temperature on microstructure and electromagnetic performance of Fe-Si/Fe2SiO4 soft magnetic composites

Highlights: • Fe-Si/Fe₃O₄ powders and Fe-Si/Fe₂SiO₄ SMCs were obtained successfully via water oxidation and SPS process. • The influence of oxidation temperature on performance of Fe-Si SMCs was studied. • Higher oxidation temperature would lead to poor uniformity of Fe₂SiO₄ coating layer. • All the Fe-Si SMCs exhibit very high saturation magnetization above 188.5 emu/g. -- Abstract: In this paper, Fe-6.5 wt%Si powders were oxidized with different temperatures, and Fe-Si soft magnetic composites with Fe₂SiO₄ coating layer were transformed successfully by high temperature solid state reaction sintering between the surface oxides and Si element in Fe-6.5 wt%Si powders. The influence of the oxidation temperature on the microstructure and electromagnetic performance of the Fe-Si soft magnetic composites has been studied systematically. The analysis results show that when the oxidation temperature increases from 40 °C to 70 °C, the formed surface oxides are mainly γ-Fe₂O₃ and become more, but are more likely to fall off the surface of the Fe-6.5 wt%Si powders owing to the accelerated oxidation educed by higher oxidation temperature. Hence, the uniformity of the transformed Fe₂SiO₄ coating layer is getting worse, resulting in a downward trend of the resistivity and the deteriorating dynamic loss. And the saturation magnetization decreases slowly, while the coercivity exhibits an opposite trend. In addition, it is worth noting that, due to the generation of ferromagnetic Fe by the reaction between Si and γ-Fe₂O₃, all the Fe-Si soft magnetic composites exhibit very high saturation magnetization above 188.5 emu/g, which is benefit for the miniaturization of electromagnetic devices.