Self-lubrication by formation of graphite films in the sliding of silicon nitride against cast iron

Self-fabrication by the formation of a graphite film was studied for the sliding pair of silicon nitride/cast iron using a ball-on-disk tribometer. In these experiments, the normal load and initial cast iron surface finish were changed to investigate the necessary conditions for the formation of a self-lubricating graphite film. The experimental results show that there are optimum values of load and initial cast iron surface condition in which a state of low friction can be prolonged. Low friction coefficient (mu congruent to 0.1) is obtained when the graphite performed on the sliding surface cart act most effectively as a solid lubricant. Furthermore, transitions of friction are discussed from the standpoint of the the formation and depletion of the graphite film.