Self-Lubrication by Formation of Graphite Films in the Sliding of Silicon Nitride Against Cast Iron

Self-lubrication by the formation of a graphite film was studied for the sliding pair of silicon nitride/cast iron using a ball-on-disk tribomeier. 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 tow friction can be prolonged. Low friction coefficient (μ ≅ 0.1) is obtained when the graphite film formed on the sliding surface can act most effectively as it solid lubricant. Furthermore, transitions of friction are discussed from the standpoint of the formation and depletion of the graphite film.