Effects of heat treatment and compaction pressure on the microstructure and magnetic properties of core-shell structured FeSiBNbCu/SiO2 soft magnetic composites

Here, the FeSiBNbCu/SiO2 soft magnetic composites (SMCs) with core-shell structure were successfully designed and fabricated using nanocrystalline powders as seeds and SiO2 were grown by sol-gel technique onto the surface of the seed particles. We systematically investigated the influences of annealing temperature and compaction pressure on the micromorphology, chemical structure and soft magnetic properties of the SMCs. The results demonstrate that a large number of submicron-sized SiO2 particles are uniformly deposited on the surface of the powders, which significantly improves the insulating characteristics between the magnetic powders. Also, the effective permeability μe increases and the core loss Pcv decreases with increasing annealing temperature from 480 °C to 550 °C, which is attributed to the relaxation of internal stress and the increase of volume fraction of α-Fe(Si) grains. Furthermore, an increase in compaction pressure effectively increases the densification and reduces the porosity, which facilitates a denser microstructure. Under the combined effect of optimal annealing temperature and compaction pressure, the SMCs exhibit high μe of 84 and low Pcv of 174 kW/m3 at 50 kHz for Bm = 0.1 T. This work provides a new strategy for the construction of core-shell structure and a comprehensive understanding of the relationship between process parameters and microstructure, which is of great guiding significance for industrial production.