ABSTRACT
Friction and wear tests were conducted on three types of ceramic: alumina-titanium carbide composite, partially stabilized zirconia, and silicon nitride in lubricated rolling contact against nodular cast iron. In the case of silicon nitride, three variations in processing techniques were evaluated: pressureless sintered, reacted, and hot-pressed. The friction coefficients of the different ceramic materials were approximately the same, but they had different wear rates. The wear rate differences were found to be related to their wear modes. The wear of the ceramic rollers in a 100-hour test was very small (of the order of 0.1 mg) except for the partially stabilized zirconia rollers, whose wear was of the order of 1 mg. Full-scale motorized valve train tests were conducted on these ceramics as cam roller followers in contact with a nodular cast iron camshaft and compared to steel roller followers. The reduction in the largest diameter of the nodular cast iron cam lobes increased in the first 400 hours as a result of initial run-in, but
no further reduction in diameter was observed after that period. The ceramic rollers exhibited negligible wear. The wear modes of the ceramic rollers and the cam lobes were analyzed by scanning electron microscopy. The results indicate that ceramic materials can replace steel roller followers.
