SiC-Si3N4 particle composites for high temperature applications

By using different methods and processing techniques composites on the basis of Si3N4 were obtained. The microstructures are similar to those observed for the nanocomposite materials made by Niihara and co-workers. The nano-composite concept which predicts an increase of strength and toughness at room temperature for a given SiC content in the range of 5-25% SiC could not been verified. However, the values for strength and toughness are good in comparison to other Si3N4 materials. The properties of Si3N4 at high temperature are determined by the amount and composition of the secondary phase. Furthermore, the investigated materials with SiC as an additional component have shown that a further possibility for a control of microstructure exists which can lead to an improvement of creep resistance. Additionally, the material degradation by the formation of pores due to oxidation is suppressed, so that the long term high temperature stability at 1400øC is improved. The materials can be produced by the conventional route of mixing and milling, followed by gas pressure sintering. Thus, components with complex shapes can be produced in an economic way.