Microstructure and properties of heat treated iron powder compacts intended for ac soft magnetic applications

Abstract

This paper describes the effect of heat treatments on the microstructure and properties of iron powder specimens intended for ac soft magnetic applications at 60 Hz. The specimens were fabricated by compacting iron powder–lubricant (zinc stearate) mixes and heat treating the compacted specimens at 450–550°C in nitrogen. The microstructure and chemical characteristics of particle interfaces (X-ray photoelectron spectrometry) and the presence of microstrains (neutron diffraction) were correlated with the electrical and magnetic properties of the material. During the heat treatments (450–550°C), lubricant burns out and iron oxide contacts are created at particle interfaces (thermal oxidation bonding). Iron powder oxidation, which depends on the heat treatment temperature, reduces the electrical resistivity of the material and affects eddy current loss. The heat treatments modify the microstrains in the specimens and allow reduction of the hysteresis portion of the magnetic loss.