Effects of axial pressure on the evolution of core-shell heterogeneous structures and magnetic properties of Fe-Si soft magnetic powder cores during hot-press sintering

作者：Qiu, Yue; Wang, Rui; He, Yihai; Kong, Hui; Li, Shaogang; Wu, Zhaoyang^*

来源：2022, 12(31): 19875-19884.

DOI：10.1039/d2ra02497g

Silicon dioxide (SiO2) has attracted much attention as an ideal coating material for iron (Fe)-based soft magnetic powder cores (SMPCs). However, maintaining the integrity and uniformity of Fe-based/SiO2 core-shell heterostructures is still a challenge. The evolution mechanism of core-shell heterostructures determines the performance of Fe-based SMPCs. Herein, the evolution of the core-shell structures and heterogeneous interfaces of Fe-Si@SiO2 SMPCs with axial pressure and the influence of the evolution on the SMPCs performance were investigated. The results show that in the axial pressure range of 10-15 kN, the core-shell heterostructures were gradually integrated, whereas the SiO2 insulation coatings underwent an amorphous-to-crystalline transformation. At axial pressure above 16 kN, the Fe-Si powder melted partially, and the core-shell heterostructure collapsed due to overheating, caused by the gradient temperature field during the hot-press sintering. When the core-shell heterostructure was intact, the Fe-Si@SiO2 SMPCs showed a permeability of over 38 with a wide and stable frequency range of 100-300 kHz, a saturation magnetisation of 231.7 emu g(-1), resistivity of 0.8 m omega cm and total loss of 704.7 kW m(-3) at 10 mT and 100 kHz. When the core-shell heterostructure was destroyed, the resistivity dropped dramatically and the loss increased to 765.0 and 897.4 kW m(-3). These results show the relationship between the core-shell heterostructure of Fe-Si@SiO2 SMPCs, axial pressure and magnetic properties, which would be vital in achieving high power density, high efficiency and miniaturisation in SMPCs.