Influence of sintering temperature on heterogeneous-interface structural evolution and magnetic properties of Fe–Si soft magnetic powder cores

Abstract

Ceramic oxides have attracted considerable research attention as ideal coating layers for novel Fe-based soft magnetic powder cores (SMPCs). However, maintenance of the integrity and uniformity of Fe-based/MOx core–shell heterostructures is challenging. The mechanism underlying the evolution of the core–shell heterostructure is a key determinant of the performance of Fe-based SMPCs. Herein, the laws governing the evolution of the core–shell structure of and heterogeneous interface in Fe–Si/SiO2 SMPCs with temperature and the influence of this evolution on SMPCs performance were investigated. The results revealed that at the sintering temperature of 1093–1183 K, the core–shell heterostructure gradually integrated, while SiO2 insulating coatings underwent amorphous-to-crystalline state transformation. When the sintering temperature was >1243 K, Fe–Si particles melted partially, and the core–shell heterostructure collapsed owing to the overheating induced by the gradient temperature field during the hot-pressing sintering process. When the sintering temperature was 1153 K, the core–shell heterostructure was intact, and the Fe–Si/SiO2 SMPCs had a saturation magnetisation of 245.5 emu/g, resistivity of 0.42 mΩ cm, and total loss of 923.2 kW/m3 at 10 mT and 100 kHz. When the core–shell heterostructure was destroyed, the resistivity dropped drastically, and the total loss increased by approximately 36.7% and 41.8%. Based on these results, the relationship among the core–shell heterostructure of Fe–Si/SiO2 SMPCs, sintering temperature, and magnetic properties was established, which is instrumental in achieving high power density, high efficiency, and miniaturisation in SMPCs.