Economical realization of the SiC/Si3N4-nanocomposite concept

The activities presented here, were initiated by the publications of Niihara and Ishizaki. There, the strengthening and toughening of silicon nitride by nanoscaled silicon carbide particles are described. Both authors have used difficult powder production routes to achieve the optimum mechanical properties. However for a commercial purpose these routes are not applicable because of the high cost and low reproducibility. The production route chosen by H.C. Starck together with CFI and Fraunhofer IWM is a powder synthesis based on the carbothermal reaction to silicon nitride as a low cost synthesis method. The investigations performed for the materials made from the synthesis powders and other reference materials, which are densified with relatively high amounts of conventional sintering additives by gas pressure sintering, have shown, that the postulated maxima of strength and fracture toughness at room temperature can not be achieved. However, the high temperature material behaviour is as good as the behaviour of highly developed silicon nitride materials, which are produced by HIP or by consequent minimization of the additive content with the well known difficulties for densification of these materials. An overview will be given here on the powder production route and their specific problems, the mechanical properties, the microstructure and the possible effects of the microstructure which result in an improvement of the creep resistance.