Structure Formation in the Combustion Synthesis of Al2O3–TiC Composites

Structure formation in the combustion synthesis of Al2O3–TiC composites from TiO2, Al, and graphite powders was investigated using cylindrical samples and cone-shaped “quenching samples.” It is shown that the phases Ti and Ti3Al exist as intermediates in the combustion synthesis process. Titanium carbide forms in a secondary step through reactions between graphite and liquid Ti or Ti3Al, then nucleates from a liquid mixture of the three phases Ti, Ti3Al, and alumina. The nucleated particles grow in the postcombustion stage. Liquid alumina, containing TiC as a dissolved phase, solidifies into corundum grains in the postcombustion stage. Moreover, it is shown that the temperature gradient in the postcombustion stage markedly affects the microstructures of the products. Higher-temperature gradients, typical at the surface of the samples, give rise to the formation of corundum whiskers and TiC agglomerates. In contrast, lower gradients, typical in the center of the samples, lead to the formation of relatively large TiC particles and corundum grains.