Sintering behaviour of self-propagating high temperature synthesised ZrB2–Al2O3 composite powder

A detailed investigation on sintering behaviour of SHS produced ZrB2–Al2O3 composite was carried out, which showed a maximum densification of 94% of the theoretical density after sintering at 1800 °C for 30 min. Further enhancement on sintering temperatures increased the porosity and decreased the densification due to evaporation of alumina from the surface of pellets during sintering. Severe reaction of the ZrB2–Al2O3 composite with C was observed during high temperature sintering in a graphite furnace. The C was found to react at the surface forming ZrC and further increase in temperature led to formation of AlO vapour and aluminium carbide. The C reaction could be lowered by covering the pellets with alumina powder. The inter-diffusion between ZrB2 and Al2O3 and the formation of a complex boride or oxyboride of Zr and Al was established near the grain-boundary region.