Silicon carbide ceramics with sintering additives from the system AlN-Y2O3 can be gas-pressure sintered to theoretical density. While commonly a combination of sesquioxides is used such as Al2O3-Y2O3, the oxynitride additives offer the advantage that only a nitrogen atmosphere is required instead of a powder bed for thermochemical stabilisation at the sintering temperature. When a moderate nitrogen overpressure is applied, mass loss during densification becomes small and depends only on the oxygen content of the SiC starting powder. By starting from a mixture of β-SiC and α-SiC, and by performing dedicated heat treatments after densification, anisotropic grain growth is obtained which leads to a platelet microstructure showing enhanced fracture toughness. In the present work, recent improvement of the mechanical behaviour of these materials at ambient and high temperatures is reported. By means of a surface oxidation treatment in air it is possible to obtain four-point bending strengths in excess of 1 GPa, and the strength retention at high temperatures is significantly improved.

Keywords: Ceramics, Silicon Carbide, Sintering, Microstructure, Mechnical Properties