The Effects of Graphite Filler on the Tribological Properties of Polydopamine/PTFE Coatings

This investigation examines the effects of incorporating graphite as a filler in the polytetrafluoroethylene (PTFE) topcoat of a polydopamine/PTFE dual-layer coating. Polydopamine (PDA) is used to enhance the adhesion of PTFE coatings to the substrate, and graphite is used to improve the formation of a transfer film on the counterface and to take advantage of the low-friction properties of graphite. The results show that incorporating only 1.0 wt% graphite in PDA/PTFE coatings can increase their durability fivefold and reduce friction by 17 %. Examination of the wear morphology indicates that these improvements in tribological properties are in fact the result of the formation of a transfer film on the counterface that allows the coating to essentially slide against itself, creating a low shear strength interface that exhibits exceptionally low friction and low wear. Linearly increasing load scratch tests show that the improvement in durability is also the result of improved adhesion between the PTFE topcoat and the PDA basecoat, preventing large-scale delamination of the coating.