Particle bonding during heat treatment of green compacts intended for AC soft magnetic applications

Previous studies have shown that heating at 175°C for 1h in air increases significantly the mechanical strength of green iron powder compacts. This study examines the effect of temperature, duration and atmosphere on the transverse rupture strength and electrical resistivity of iron powder compacts. Scanning electron microscopy observations, x-ray photoelectron spectroscopy and ultrasonic speed measurements were performed to elucidate the mechanisms responsible for the interpartide bonding enhancement. The results obtained suggest that oxygen plays an important role in interparticulate bonding; the oxide layer growing between the iron particles can form cohesive bonds which are responsible for the mechanical strength increase while maintaining a level of electrical resistivity significantly higher than that in sintered compacts.