The effects of filler type on the friction and wear performance of PEEK and PTFE composites under hybrid wear conditions

An effort is made to circumvent the negative effects on the outstanding processability and mechanical properties of poly-ether-ether-ketone (PEEK) when it is blended with solid lubricant (e.g., polytetrafluoroethylene (PTFE)) to improve its tribological performance. A hybrid wear method by composing different type of polymers is proposed and the role of various fillers (i.e., nano-sized, micron-sized particles and short cut carbon fibers) in the PEEK-PTFE-steel hybrid wear system is investigated. Imitating the working condition of a sliding bearing, experiments are conducted under dry conditions on a newly-developed dual-pins-on-disk tribometer in which unfilled PEEK and PTFE composite pins filled with various fillers slide against steel rings in the same wear track. The results reveal a synergistic effect between the two polymer components happened and then improved the tribological performance of the hybrid system. The PTFE composite wear debris generates a fluorine-based tribofilm on the sliding surfaces (i.e., the transfer film on the steel surface, the running film on the PTFE surface, and the secondary transfer film on the PEEK surface), transforming the wear process into one of sliding between the slippery tribofilms. In turn, the hard PEEK component crushes the PTFE wear debris to improve the quality of the formed tribofilms and compacts the transfer film to be thin and uniform.