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High-temperature properties of Si3N4/SiC microcomposites
Hochtemperatureigenschaften von Si3N4/SiC Mikrokompositen
The influence of nano- or micro-sized SiC additions on the high-temperature behavior of Si3N4 materials was studied. Comparing a Si3N4-SiC composite with a monolithic Si3N4 material with the same chemical composition of the grain boundary phase, no significant effect of the nano- or micro-sized SiC additions on the mechanical properties at elevated temperatures was observed. The main advantage of the Si3N4-SiC composites was found to be the improved oxidation resistance in comparison to the monolithic Si3N4 material. A significantly less degraded microstructure was observed after long-term oxidation of the Si3N4-SiC composites due to an altered oxidation mechanism which promotes the formation of Si2ON2 below the outer oxidation layer in the bulk of the Si3N4-SiC composites. This is also the reason for the improved behavior in terms of time to failure reported in the literature for these Si3N4-SiC composite materials.