Thermal analysis of FeAl intermetallic compound sintered at heating rate of 300 °C/min

Only differential thermal analysis at low heating rates or mathematical modelling have been used to determine Fe–Al phase formation reactions up to this day. In this work, Self-propagating High-temperature Synthesis high-speed reaction was analysed during extremely high heating rates using scanning electron microscope with energy dispersive spectroscopy and X-ray diffraction in this work. Samples, whose chemical composition corresponded to FeAl phase, were sintered at heating rate of 300 °C/min, the highest heating rate applied so far. The course of heating was observed by optical pyrometer with sampling rate of 0.02 s. Pre-combustion peak (diffusion stage) was identified in the alloy prior steep combustion peak corresponding to SHS reaction itself. Accordingly to the temperature development, a FeAl phase formed initially allowing to react with aluminium and forming Fe2Al5 phase. Furthermore, the later mentioned phase partially reacted with aluminium resulting in a presence of metastable FeAl3 phase. Resulted microstructure was composed of only FeAl phase. This is completely reverse order of phase formation as was presented in previous studies focusing on lower heating rates where Fe2Al5 formed first during diffusion stage followed by the formation of FeAl at SHS reaction.