CERAMICS TECHNOLOGY: application to engine components

In the development of engine components a number of special techniques are used to combat the hostile operating environment which usually includes high and cyclic forces, high and cyclic temperatures, sliding and often corrosion and/or erosion. Examples of the use of these techniques, namely the development of special materials for substrate and surface, of mathematical modelling verified by telemetry, and of special machining, to solve the problems of the operating environment, are given in respect of piston rings, cylinder liners, bearings, camshafts and valve seat inserts. It is noted that of these techniques the development of special surface and substrate materials provides the most assistance. The application of materials technology to surface and substrate is illustrated with respect to ceramics, including silicon nitride, silicon carbide, zirconia and alumina. Applications under development include insulation, improvement of wear resistance, reduction of mass, increase of operating temperature and the reinforcement of metals, for example reinforcement of aluminium alloys using alumina fibres incorporated by squeeze casting. The several means open to improve the properties of gravity cast aluminium silicon alloys are reviewed and the improvement of properties obtained by squeeze casting without reinforcement are illustrated. The further enhancement of these properties by the design of an appropriate fibre reinforcement system, incorporated by squeeze casting, is then described. Its application to the reinforcement of a combustion bowl subject to high thermal stress is discussed and the performance of the resulting piston in relation to unreinforced pistons is described. In conclusion the market, product and process aspects of the development are correlated to demonstrate its overall value and to identify further applications.