The microstructure and magnetic properties of a permanent magnet alloy in the FeAlC system

Specimens of the alloy FeAl7.74C1.77have been quenched from 1200°C at different rates and annealed at 350°C for various times to optimise their magnetic properties. The remanent magnetisation and saturation magnetisation were found to increase at the expense of coercivity as the quench rate was reduced. A similar effect was observed during heat treatment at 350°C. X-ray diffractometry suggests that the transformation of austenite into ferrite and K-carbide is responsible for the increase in saturation magnetisation observed during heat treatment. Transmission electron microscopy revealed a finely divided micro-structure consisting of Widmanstatten type ferrite regions in a matrix of austenite and K-carbide. Preliminary studies of the domain structure indicate that domain wall impedance at the boundaries of the ferrite and K-carbide phases is a contributing factor to the coercivity of this material.