Fe-Si/ZrO2 composites with core-shell structure and excellent magnetic properties prepared by mechanical milling and spark plasma sintering

Fe-Si alloy powders were coated with ZrO2 nanopowders via mechanical milling to fabricate Fe-Si (core)/ZrO2 (shell) composite powders. The resultant composite powders were consolidated to magnetic powder cores by spark plasma sintering (SPS). The effects of sintering temperature on microstructure, resistivity and magnetic properties were investigated along with the densification process of the composite compacts. X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS) revealed that the surfaces of the composite powders were coated with a layer of ZrO2 powders after mechanical milling. Moreover, the polished surface of the sintered composite compacts displayed a micro-morphology of core-shell structure with core of Fe-Si alloy particles and shell of ZrO2 layers indicating that the electric Fe-Si alloy particles were well insulated by the intergranular ZrO2 layers. The Fe-Si/ZrO2 magnetic powder cores with 7.5 wt.% ZrO2 sintered at 825 °C exhibited excellent magnetic properties: 1.43 T for saturation magnetic induction, 220 for maximum permeability and 25.48 Oe for coercivity. The core-shell structured powder cores possessed much higher resistivity and lower core loss (688 μΩ cm and 147 W/kg) than those of the raw Fe-Si powder cores (94 μΩ cm and 471 W/kg). Overall, the preparation process of magnetic powder cores by SPS provides a promising method to reduce core loss and improve magnetic properties of soft magnetic composite materials.