On the formation of intermetallics in Fe–Al system – An in situ XRD study

Self-propagating high-temperature synthesis (SHS) was previously proposed as alternative preparation route for Fe–Al intermetallics. However, this process was not optimized and the mechanism and kinetics of the phasesʹ formation was not fully clarified up to current days. In this work, in situ high energy X-ray diffraction analysis was carried out during the SHS process and the mechanism of the intermetallicʹ formation in FeAl25 powder mixture was described during rapid heating and isothermal annealing at 800 °C as well as during a slower continuous heating to 900 °C. During slower heating, the formation of Fe2Al5 and FeAl2 intermetallics starts below the melting point of aluminium. When the heating rate is high, intermetallics are created after melting of aluminium. During long-term annealing, all of the phases can be transformed to FeAl phase when fine powders were applied. Detailed mechanism is proposed in this paper and kinetics of the intermetallicsʹ formation is described.