Journal of the european ceramic society vol:13 issue:6 pages:529-544
Five Si3N4-Al2O3 ceramic grades were prepared by hot pressing at 1650-degrees-C. Backscattered electron micrographs revealed four different phases. Quantitative electron probe microanalysis allowed the identification of these phases as X-sialon, alpha-Al2O3, O'-sialon and beta-sialon. The maximum solubility of Al2O3 in Si3N4 and in Si2N2O at 1650-degrees-C was determined as well as the chemical composition of X-sialon. Based on these results, a slightly revised phase diagram is proposed. The general features describing the microstructure of the various phases have been investigated by transmission electron microscopy. The influence of the various phases on the mechanical properties was investigated; hardness, fracture toughness and elastic modulus were measured. The oxidation behaviour has been studied in air at 1300-degrees-C and 1450-degrees-C The metastable phase diagram of Al2O3-SiO2 in the absence of mullite can be used to predict the oxidation products and relative amounts formed in the oxide layers.