Paper 8: Recent Developments in Engineering Ceramics

Abstract

Ceramics in the context of this paper will be considered to be inorganic non-metallic materials which are shaped when in a finely divided form, followed by a high-temperature sintering treatment. A better understanding of the properties of ceramics (e.g. alumina) can be gained by the study of the properties of the material in single crystal form (e.g. sapphire). The properties of different materials can be related to their crystal structure. This scientific pursuit has led to a number of new materials (silicon nitride, Si3N4, and boron nitride, BN). Compared with metals ceramics compete favourably on account of their high strength at high temperatures, good wear and corrosion resistance. Their main drawbacks are brittleness and failure by thermal stresses. The application of new methods of fabrication has been aimed at producing ceramics of high density and to accurate dimensions. The properties of the following materials will be discussed in some detail: alumina, Al2O3; silicon nitride, Si3N4; silicon carbide, SiC; and boron nitride, BN. It will be demonstrated that different methods of fabrication can result in widely differing properties of the same material. Small grain size and high density are essential for good mechanical strength. Methods of joining ceramics to metal will be discussed. Some important applications will be reported and consideration will be given to problems facing the designers.