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This work aims to describe the formation of intermetallics in the Ni-Ti-Al system in dependence on the heating rate, which has been determined previously as the crucial factor of thermal explosion self-propagating synthesis (TE-SHS). The tested alloys contained 1–7 wt % aluminum. Thermal analysis has been realized by the optical pyrometer under the conditions of high heating rates up to 110 °C·min−1. TE-SHS process in Ni-Ti-Al system is initiated by exothermic reaction of nickel aluminides Ni2Al3 and NiAl3 at the temperature of 535–610 °C. The next reactions occur in dependence on the heating rate. Samples containing 1–3 wt % of aluminum exhibit the similar initiation temperature as Ni-Ti binary mixture. The samples containing 5 wt % and more of aluminum were fully reacted after sintering at 800 °C with the heating rate of 300 °C·min−1 and the initiation temperature of the TE-SHS was observed close to Al-Al3Ni eutectic temperature (between 630–640 °C). [ABSTRACT FROM AUTHOR]

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 Fe 2 Al 5 phase. Furthermore, the later mentioned phase partially reacted with aluminium resulting in a presence of metastable FeAl 3 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 Fe 2 Al 5 formed first during diffusion stage followed by the formation of FeAl at SHS reaction. [ABSTRACT FROM AUTHOR]