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This paper is a review of ceramic tribological characteristics and application of silicon-based ceramics as engine valves and seat inserts. This review has shown that wear of ceramics is not an intrinsic material property or a constant, rather it depends on the operating conditions as well as on microstructure, environment, measurement techniques and material properties. The review also found that the dominant ceramic wear mechanism is a fracture/crack controlled process. There have been many models developed to describe the wear of ceramics, however, the complexity of the wear and the existence of wear transitions suggest that satisfactory results can be obtained for each wear model/equation only for the operating conditions for which it was derived. The application of silicon-based ceramics for engine valves and seat inserts is also reviewed and field engine test results are presented. The advantages and disadvantages of ceramics for engine valves and seat inserts are discussed.

A powder fed, microprocessor controlled plasma transferred arc (PTA) hard facing technique is described for facing valve seats. A comparison of this technique is made with the conventional oxy-acetylene flame welding process to show the differences in the metallurgical characteristics of the respective products. The merits of the PTA process are associated with a) its precision controllable heat source and lower energy consumption b) finer microstructure and narrower heat affected zone, c) its versatility for powders of different raw materials, d) higher volume production capability, and e) minimum raw material waste; however, it does not replace the flame welding process completely. The relative choice between the two processes will depend on investment costs, volume of production and metallurgical quality requirements of the final product.