Effect of heating rate on the combustion synthesis of Ti-Al intermetallic compounds

Titanium aluminide compounds were synthesized by the thermal explosion mode of self-propagating high-temperature synthesis (SHS). The effects of heating rate on the combustion characteristics and the microstructures of the products were studied. It was found that the low density of the reacted sample was due to the outgassing of water vapour and other gases, which were released by dissociation of hydrated aluminium oxides. Higher heating rates resulted in a product of higher density and single-phase microstructure. At lower heating rates, the reaction product was a mixture of phases for TiAl and Ti3Al reactions. A liquid (Al)-solid (Ti) reaction mechanism is predicted for slow heating while a solid-solid mechanism is expected for high heating rates. The origin of porosity in the product is also discussed.