An experimental study on Ti5Si3 formation by combustion synthesis in self-propagating mode

The production of titanium silicide, Ti5Si3, from elemental powder compacts was conducted by self-propagating high-temperature synthesis (SHS) in this study. Effects of sample green density and initial sample temperature on the combustion characteristics, as well as on the composition of final products were studied. The combustion process was preceded by the fast propagation of a self-sustained combustion front, followed by vigorous bulk combustion. The phase transformation was found to continue during the cooling of the burned sample, leading to an afterburning stage featuring the emergence of a luminous glow on the luster-lacking compact. The propagation velocity of combustion front was increased by increasing the sample green density or by preheating the sample prior to ignition. For the samples preheated at 200 °C, a significant increase by about twofold in the flame-front velocity was observed in comparison to those without any preheating. This is due to the fact that the combustion temperature not only is higher than the lowest eutectic temperature of the Ti-Si mixture at 1330 °C, but also exceeds the melting point of Si (1410 °C). The dissolution of solid reactants into the molten liquid and the precipitation of products from the oversaturated solution were adopted to describe the formation of titanium silicides. According to the XRD analysis, the dominant composition in combustion products was identified as the Ti5Si3 phase. The presence of an intermediate phase of Ti5Si4 in the final products was the consequence of the insufficient reaction time caused by the rapid propagation of combustion wave and the fast cooling rate on the burned sample. Based upon the measured data of this study, the activation energy with a value of 205.2 kJ/mol was deduced for the synthesis of Ti5Si3 by SHS.