Structure and magnetic properties of FeSiAl-based soft magnetic composite with AlN and Al2O3 insulating layer prepared by selective nitridation and oxidation

FeSiAl is widely used in switching power supply, filter inductors and pulse transformers. But when used under higher frequencies in some particular condition, it is required to reduce its high-frequency loss. Preparing a homogeneous insulating coating with good heat resistance and high resistivity, such as AlN and Al2O3, is supposed to be an effective way to reduce eddy current loss, which is less focused on. In this project, mixed AlN and Al2O3 insulating layers were prepared on the surface of FeSiAl powders after 30 min exposure at 1100 °C in high purity nitrogen atmosphere, by means of surface nitridation and oxidation. The results revealed that the insulating layers increase the electrical resistivity, and hence decrease the loss factor, improve the frequency stability and increase the quality factor, especially in the high-frequency range. The morphologies, microstructure and compositions of the oxidized and nitrided products on the surface were characterized by Scanning Electron Microscopy/Energy Disperse Spectroscopy, X-Ray Diffraction, Transmission Electron Microscopy, Selected Area Electron Diffraction and X-ray Photoelectron Spectroscopy.

► AlN and Al2O3 layers were produced on the surface of FeSiAl powder.
► Thermodynamics involved in nitridation and oxidation process was studied.
► Morphologies of the nitrided and oxidized products were characterized.
► Insulating layers decrease the loss factor and increase the quality factor.
► Insulating layers improve the frequency stability in the high-frequency range.