Evolution of insulating layers during Heat–Treatment and their effects on magnetic behavior of Fe–Si–Al based soft magnetic composites

Abstract

As a symbolic ceramic oxide, the reaction of SiO2 as an insulating layer with the Fe–Si–Al/SiO2 soft magnetic composites (SMCs), substrate during heat treatment, as well as the resulting microscopic phase transition of the core–shell structure and its influence on the magnetic properties, are worth investigating. In this study, based on the successful synthesis of Fe–Si–Al based SMCs using fluidised chemical vapour deposition combined with an electric hot–press sintering method, the evolution of the insulating layers was investigated under different heat–treatment temperatures and closely linked to the magnetic performance of the composites. During heat treatment at high temperatures, the formation of high–resistivity oxides (Al2O3) after heat treatment results in a low inter–particle eddy current loss, while excessive temperature causes disintegration of the core–shell heterostructure. This leads to a discernible increase in eddy current and hysteresis losses and a decrease in permeability and resistivity. The SMCs had an Ms of 115.8 emu/g, a resistivity of 6.86 mΩ cm, and a hysteresis loss of 56.3 kW/m3 at 10 mT and 100 kHz when heat-treated at 1373 K for 120 min, which was the best among all samples. This research provides a novel approach to building SMCs with inorganic ceramic insulating layers and a comprehensive understanding of the relationship between the heat–treatment process parameters, microstructure, and magnetic properties which is highly significant for industrial production.