Liquid phase sintering of SiC with additions of Y2O3, Al2O3 and SiO2

Liquid phase sintering of SiC has been studied using different sintering aids with and without the application of pressure during sintering. After Pressureless Sintering the densification behaviour of the SiC-based powder mixtures was observed to be markedly dependent not only on the type and amount of sintering aids used, but also on the crystal structure of the SiC powder. In contrast, hipping leads to high densities in all cases, independently of the chemical composition of the mixture and the type of SiC powder used. When carbon was added to these compositions, fully dense materials were still obtained. However, a pronounced grain growth was observed. Compositions containing additions of SiO2 and Y2O3 did not show any densification after pressureless sintering, due to the high viscosity and extensive volatilisation of the liquids formed at the sintering temperature. On the other hand, fully dense specimens obtained after hiping contained crystalline intergranular phases, which turned to a vitreous structure, as Al2O3 was included as a third component.