Sintering and mechanical behaviour of silicon nitride-silicon carbide nano-composites : I. Amato et al. (Turin Polytechnic, Turin, Italy.)

Abstract

The microstructures of liquid phase sintered α-SiC ceramics have been characterised by analytical electron microscopy including electron energy filtered imaging. The materials were fabricated with different additions of Al2O3 and/or Y2O3 and densified by pressureless sintering or hot isostatic pressing (HIP). Y, Al-garnet and α-Al2O3 partitioned from the liquid phase sintering medium during pressure-less sintering leaving only thin intergranular films of residual glass. The formation of α-Al2O3 was promoted by the incorporation of Al2O3 from the surrounding SiCAl2O3 powder bed. The thickness of analysed Al- and O-rich glassy films at SiCSiC grain boundaries was estimated to be 1.4–1.5 nm by Fresnel out-of-focus imaging. The crystallisation of Y-, Al-, Si- and O-rich liquids was suppressed during HIP, however, Y2Si2O7 partitioned from the liquid phase sintering medium in the absence of Al. The applied high pressure during HIP resulted in a limited decomposition of the α-SiC whereby graphite and SiO2 formed.