Effect of surface reactions on steel, Al₂O₃ and Si₃N₄ counterparts on their tribological performance with polytetrafluoroethylene filled composites

Highlights: • The influence of surface reactions with PTFE on the tribo-performance of different counterparts is revealed. • Experiments confirm that friction can be greatly reduced by two F-terminated surfaces sliding over each other. • Al−F and Fe−F chemical bonding form on the surface of alumina and steel counterpart balls during sliding against PTFE-containing composite. • No Si−F bonding formed on Si₃N₄ ball under the same condition, leading to higher friction and wear. - Abstract: The influence of surface reactions on the tribo-performance of steel, Al₂O₃ and Si₃N₄ balls sliding against polytetrafluoroethylene/SiO₂/epoxy composites was investigated. Al₂O₃ ball were found to exhibit the best tribo-performance, namely a low coefficient of friction and the lowest wear rates of both the composites and the counterpart ball, when sliding against the PTFE filled composites. The difference in the tribo-performance of the Al₂O₃ ball and the Si₃N₄ ball can neither be attributed to the different morphology of the worn composite surfaces nor to the amount of PTFE transferred onto the wear surfaces. Instead we found that the friction is greatly reduced in the case of the Al₂O₃ ball because two fluoro-terminated surfaces are sliding over each other; in fact, the formation of Al−F bonding was confirmed by X-ray photoelectron spectroscopy