Soft magnetic composites based on hybrid coated Fe-Si nanocrystalline powders

The preparation and characterisation of soft magnetic composite compacts based on hybrid coated nanocrystalline Fe-Si powder are presented. The Fe-Si powder was prepared by mechanical milling of Fe-Si electrical steels sheets up to 20 h. The hybrid coating consists in an electrically insulating phosphate and a polymer layer that covers the Fe-Si particles. The influence of phosphating duration on the particles surface was investigated by SEM, EDX, XRD, and FTIR investigations. The saturation magnetisation of the powders phosphated for 60 s decreases with 17% as compared to the uncoated powder. The influence of the compaction pressure, as well as the phosphating duration, on initial relative permeability and power losses of the compacts was investigated. It was found that increasing the compaction pressure leads to the increase of the compact's permeability and a decrease of the hysteresis losses. A shorter phosphating duration leads to a partial coating with phosphate of the Fe-Si particles and to compacts with higher density characterised by high magnetic permeability.