Particulate PTFE as a super-efficient secondary solid lubricant in PAEK composites for exceptional performance in adhesive wear mode

In this paper tribo-comparison of two SLs viz. graphite and PTFE as a secondary lubricant in composites with identical composition (20 wt%) is presented. The mechanical, thermal and tribological properties as well as mechanism of PAEK composites were investigated in detail. It was found that although incorporation of PTFE reduced most of the mechanical properties and thermal conductivity, it was responsible for increasing the tribo- potential of composites to a significant level. Compared to a composite with graphite as a secondary SL, a reduction in wear rate (18–30 %) and friction (2–18%) was exhibited due to PTFE and nano-PTFE. The composites showed very high PVsafe (pressure x velocity) value of 182 MPa m/s with low (0.04) and wear rate (1.33×10−16 MPa m/s). It was shown that the formation of a polymeric transfer film on a metal countersurface is crucial in achieving ultralow wear and friction in dry condition. The investigations on worn surfaces and the transfer films with scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) analysis and Raman spectroscopy proved useful to understand wear mechanisms.