Coupled effect of filler and countersurface roughness on the tribological performance of the PEEK-PTFE-steel hybrid wear system

The hybrid wear system consisting of independent polyether-ether-ketone (PEEK) and polytetrafluoroethylene (PTFE) components sliding together against steel has been proven to improve the tribological performance of PEEK without compromising its excellent mechanical properties. In the present work, the effect of the countersurface roughness upon the tribological performance of the hybrid wear system is investigated. In a dual-pin-on-disk tribometer, steel rings with various roughness (Ra = 0.04–0.5) are introduced to PEEK-PTFE/Al2O3-steel (PPAS) hybrid wear systems containing hard nano particles and to PEEK-PTFE/brass-steel (PPBS) hybrid wear systems containing soft micron-scale particles. The morphologies of the worn surfaces demonstrate that the outstanding tribological performance of the hybrid wear system is closely related to the tribo-chemistry and the formation of tribofilms, which jointly depend on the properties of the fillers and on the roughness. The PPAS hybrid wear system is more suitable for low roughness conditions, as the wear debris containing nano-alumina particles will be pressed into the deep processing grooves of the steel surface, thereby hindering the occurrence of the tribo-chemical reaction. By contrast, the PPBS hybrid wear system exhibits good performance under high roughness conditions. With a smooth countersurface, the micron-sized brass particles will deposit onto the worn PTFE surface, and lead to severe abrasive wear on the countersurface, thereby hindering the formation of a transfer film. However, both the PPAS and the PPBS system provide exceptional tribological performance under moderate roughness conditions, due to the formation of high-quality fluorine-based tribofilms on each worn surface with the assistance of tribo-chemistry.