Transfer Film Formation in PTFE/Oxyfluorinated Graphene Nanocomposites During Dry Sliding

Oxyfluorinated graphene (OFGR) was incorporated in 0, 0.75, 1, 2, 4 and 7 vol%, respectively, in polytetrafluoroethylene (PTFE) via solvent-assisted dispersion prior to sintering. PTFE/OFGR nanocomposites were subjected to dry sliding tests using a ring (metal)-on-plate (PTFE) configuration. The steady dynamic coefficient of friction and specific wear rate data were determined. The coefficient of friction of PTFE (≈0.3) was reduced by almost 30% already at 0.75 vol% OFGR content and scattered in this range as a function of OFGR loading. The specific wear rate of PTFE (≈2 × 10 −4 mm 3 (N m) −1 first peaked at 0.75 vol% OFGR before dropping to values as low as ≈1 × 10 −6 mm 3 (N m) −1 at 2 vol% OFGR and above. This change was attributed to the formation of a robust transfer film on the metal ring countersurface according to the scanning electron microscopy inspection. Infrared analysis of the transfer film indicated that in its development tribochemical reactions (viz. complexation via carboxylic groups formed) were involved.