Formation mechanism of transfer films between PEEK-based materials and silicon nitride ceramic balls under varying loads

Purpose This study aims to further investigate the tribological behavior of polyether ether ketone (PEEK) and its composites against silicon nitride (Si3N4), with a focus on analyzing the transfer film formation mechanism and the lubricating roles of various fillers in the PEEK composites during the film-forming process. Design/methodology/approach The friction coefficients of three PEEK composite discs sliding against Si3N4 balls under dry friction at various loads were investigated using a tribometer. The wear profiles of the three discs were measured using a Taylor surface profilometer, and the specific wear rates were calculated. The surface morphology, infrared spectra and Raman spectra of the transfer films on the Si3N4 balls were characterized using scanning electron microscopy (SEM), Fourier transform infrared (FTIR) microscopy and confocal Raman microscopy, respectively. Finally, the wear resistance of the transfer films was evaluated through additional durability tests. Findings Among the tested composites, PEEK matrix filled with 10 Vol.% graphite, 10 Vol.% carbon fiber (CF) and 10 Vol.% polytetrafluoroethylene (PTFE) (PVX) exhibited the lowest friction coefficient against Si3N4, whereas graphite-filled PEEK (CF30) showed the lowest specific wear rate. The formation of locally graphitized carbon (sp2) films within the polymer transfer layer plays a crucial role in solid lubrication during sliding. The transfer film of neat PEEK mainly consists of organic debris or degradation products of the matrix. In contrast, for CF30 and PVX, the incorporated CFs can generate sp2 carbon films, while in PVX, the presence of PTFE further provides synergistic lubrication with the PEEK matrix. Originality/value The findings provide a theoretical foundation for the improved application of PEEK composites in full ceramic ball bearing cages.