Significant efficiency improvements have been predicted resulting from the practical application of low-heat-rejection engines (1,2). With associated predictions of top-ring-reversal temperatures exceeding 300 C and possibly reaching 650 C (3,4), these engines require solutions to wear problems for such sliding components as rings, cylinders, pistons, and valve mechanisms. Liquid lubricants, the traditional proven approach for controlling wear of metals used in conventional internal combustion engines, are not available for continuous service at the predicted temperatures to be encountered in low-heat-rejection engines. Therefore, ceramics as a class of materials are of interest to address the wear problems. High hardnesses, corrosion resistance, strength at elevated temperatures, and high elastic moduli are attractive properties not generally available in metals, which could be expected to compensate at least partially for the lack of availability of liquid lubricants. All-ceramic and part-ceramic engines have been assembled and evaluated on a limited basis (5,6). Basic studies of the friction and wear of ceramics in sliding contact have also been made, mostly using pin-on-disk apparatuses (7-9). However, few studies have been made to study the wear mechanisms of ceramics using a controlled laboratory apparatus to reproduce the important sliding parameters of actual engines without the problems associated with operating fired engines. The study described in this paper addresses the wear mechanisms of ceramics applied to the reciprocating sliding contact of the ring/cylinder interface in low-heat-rejection engines. The approach has been to use simple ceramic specimens in a laboratory apparatus that reproduces the important parameters of actual engines. Models of the wear process are being developed based on experimental data.

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