Synergetic Role of Carbon Fibers and Calcium Fluoride Particles on Enhancing Tribological Performance of PTFE

By reason of the self-lubrication characteristic and high chemical resistance of polymer composites, they are more and more utilized for designing motion systems in the fields of automotive and equipment. In this work, calcium fluoride (CaF₂) particles were compounded into polytetrafluoroethylene (PTFE) and conventional PTFE composite reinforced with carbon fibers (CF). It was demonstrated that the addition of CaF₂ improves wear resistance of PTFE. More interestingly, a synergetic role of CF and CaF₂ on enhancing wear resistance of PTFE was identified. The composites filled with combined CF and CaF₂ exhibits a very low specific wear rate, i.e. 8.9×10⁻⁷ mm³/(N·m). In comparison to the PTFE composites filled with CaF₂ ceramic particles or CF, the wear resistance of the composite filled with multiple CF and CaF₂ was improved by 11.1 and 2.47 times, respectively. Multiple characterization methods were used to comprehensively analyze microstructures and the transfer film and to shed light on complex tribo- physicochemical reactions and products occurring at the friction interface. Our results demonstrated that carboxylic acid groups were generated due to tribo-chemical reactions of PTFE molecules. Afterwards, tribological products of PTFE, graphitic carbon ceramic deriving most probably from pulverized CF, CaF₂ particles, and tribological products of CaF₂ (CaCO₃ and CaO) were mixed at the interface and finally tribo-sintered into a compact transfer film. It was surmised that the high tribological performance of the CF/CaF₂-filled PTFE was associated with growth of the hybrid transfer film probably having an easy-shearing characteristic and high load-bearing capability. Outcome of the present work pave a route for formulating novel extremely wear-resistant polymer composites.