Kinetics of reactions in FeAl synthesis studied by the DTA technique and JMA model

Abstract

The phenomena of Fe–Al intermetallic phase formations preceding the SHS reaction were investigated. The XRD analysis and SEM observations have shown that not only the Fe 2Al 5 phase and the solid solution of aluminum in iron, but also the FeAl 3 and FeAl 2 phases are formed before the start of the SHS reaction. The kinetics of the sintering process of elemental Fe and Al powders was investigated by the DTA technique. The kinetics of the phase transformations was determined at different temperatures with heating rates of 0.5–10 °C/min for non-isothermal conditions using the Johnson–Mehl–Avrami model (JMA). The activation energy of specific phase formations was determined by the Kissinger method. Moreover, the Avrami coefficients, describing the rate and the character of specific phase transformations were calculated. The influence of the heating rate of the powder mixture on the rate of phase transformation was shown. It was found that a heating rate lower than 2.5 °C/min yields the full sequence of phase transformations: Fe + Al → FeAl 3 → Fe 2Al 5 → FeAl 2 → FeAl, compatible with the binary phase diagram of Fe–Al.