Sialon-based composites prepared from the aluminium oxynitride SHS-derived powders

Reference	Presenter	Authors (Institution)	Abstract
14-058	Miroslaw M. Bucko	Bucko, M.M.(AGH University of Science and Technology);	Sialons which are a specific solid solutions in the Si3N4-Al2O3 system are widely applied as structural or refractory materials due to their good mechanical properties, high thermal shock resistance, and corrosion resistance, especially against molten metals. Dense sialon materials are obtained by pressureless sintering or by HP, HIP and SPS techniques. The starting materials for sintering are previously synthesized monophased powders or mixtures of respective oxides and nitrides usually silicon nitride and corundum. Reaction sintering can be performed also using aluminium nitride, silicon oxide and metallic aluminium and silicon powders and the process is performed in nitrogen atmosphere. In the present work powder of aluminium oxynitride with spinel structure, ?-alon, prepared by self-propagating high-temperature synthesis (SHS) was used as a precursor of sialon-based materials. The ?-alon powder was mixed with different amount of silicon nitride powder and 1 mas% of yttrium oxide and then compacted samples were pressureless sintered at 1750°C for 2 h in argon. It was stated that the samples with small amount of silicon nitride in the starting powder mixture were composed of corundum and Si2Al4O4N4 ?-sialon. An increase of silicon nitride content led to materials composed of the same sialon as a major phase with small amount of Si3Al6O12N2 X’-sialon. Another ?-sialon, Si4Al2O2N6, was the main phase in the samples with the highest amount of silicon nitride and the same X-sialon was the complementary phase. Mechanical properties of the sintered materials as well as resistance to liquid aluminum based alloys reveal strong correlations with their phase compositions. The composites containing corundum show highest hardness, strength and fracture toughness while the best performance in the liquid metals show the sialon-sialon composites.
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