20 - Silicon nitride and silicon carbide-based ceramics

Abstract

Despite the excellent combination of thermal mechanical properties of Si 3 N 4 and SiC ceramics, the wide application of these materials is still hampered by their relatively low fracture toughness. Improvements in fracture toughness of Si 3 N 4 and SiC ceramics are mainly achieved by crack deflection and bridging mechanisms. To enhance crack deflection toughening, high aspect ratio acicular grains and a weak interface between the grains and grain boundary phases are desirable; to enhance crack bridging toughening, high aspect ratio grains with large diameters are required. However, weak interfaces and subsequently the debonding of large elongated grains result in the development of fracture origins and loss of strength of the material. Therefore, to develop a superior material with both high toughness and strength, optimization of the microstructure is essential. Sialon ceramics are genetically associated with Si 3 N 4 , but have greater phase complexity and more degrees of freedom for tailoring of microstructures. It offers an ideal system for studying the role of microstructure on erosion of advanced ceramics.