The Fabrication of Composite O’-ß’ Sialon Ceramics
Dense sialon ceramics with the structure of silicon oxynitride (O’) are readily prepared by pressureless sintering powder mixtures of Si3N4, SiO2, A12O3 and Y2O3. By suitable heat-treatment, the glassy phase in the product can be devitrified to give yttrium disilicate (Y2Si2O7), and the resulting O’-Y2Si2O7 material has excellent oxidation resistance at high temperatures. Since both these phases occur in equilibrium with ß’-sialon - already established as a good high-temperature engineering ceramic - compositions within the O’-ß’-Y2Si2O7 compatibility region offer good prospects for development as ceramic materials, combining the mechanical properties of Bf with the good oxidation resistance of the O’ and Y2Si2O7 phases. The degradation of the high-temperature properties observed when a grain-boundary glass is present is thereby avoided and, by varying the proportions of the two completely compatible phases in the composite, its microstructure can be more readily tailored than in a single-phase matrix material.
KeywordsSilicon Nitride Oxidation Resistance Good Oxidation Resistance Silicon Monoxide Aluminium Nitride
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