Influence of alpha and beta SiC seeds on microstructure development and mechanical properties of liquid phase sintered SiC with RE2O3 and AlN additives

Liquid phase sintering of silicon carbide (SiC) with different sintering additives (Y2O3, Yb2O3, Sm2O3 together with AlN) have been performed. Samples were doped with alpha-SiC or beta-SiC seeds to emphasize the effect of sintering additives on microstructural development. Remarkable influence of sintering additives and seeds on the microstructure and mechanical properties was observed. Vickers hardness and fracture toughness have been evaluated in more details. It was found that by decreasing the ionic radius of rare-earth elements the hardness of SiC ceramics increased, while the fracture toughness decreased. This trend of mechanical properties was attributed to the difference in chemistry of the intergranular phases.