Influence of PTFE content in PEEK–PTFE blends on mechanical properties and tribo-performance in various wear modes

Abstract

Few papers are available on the optimum composition of PEEK–PTFE blends for the best possible combination of mechanical and tribological properties in the adhesive wear mode. Nothing is reported in this context on low amplitude oscillating/fretting wear mode. Moreover, the influence of increasing amounts of PTFE in the blend on abrasive wear behaviour along with a correlation with strength properties is not reported. Hence, in this work, five injection-moulded blends of PEEK with PTFE (in the range of 0–30 wt.%) were evaluated on a pin-on-disc configuration on an SRV Optimol Tester for their tribo-behaviour in the low amplitude oscillating wear mode. The data in the abrasive wear mode were generated by abrading a pin loaded against an abrasive paper fitted on the rotating disc. Data on neat PTFE were also included for comparison. It was observed that inclusion of PTFE affected the adhesive wear and low amplitude oscillating wear (LAOW) in a beneficial way. With an increase in PTFE contents, coefficient of friction in both the wear modes (adhesive and low amplitude oscillating) decreased but the trends in wear performance differed. In the adhesive wear mode, the specific wear rate showed minima for 7.5% PTFE inclusion followed by a slow increase for further PTFE addition. In the case of LAOW mode, on the other hand, the wear rate continuously decreased for the selected compositions. The 30% PTFE blend showed excellent combination of μ, wear rate and limiting pressure–velocity (PV) values. Unfilled PEEK proved to be fairly good wear-resistant material but exhibited high μ, a stick-slip tendency and a low PV limit value. Abrasive wear performance of the blends on the other hand, deteriorated with increasing amount of PTFE. Fairly good correlation was observed between the wear rate and product of H and S ( H-hardness and S-ultimate tensile strength) rather than Ratner–Lancaster plot (product of S and e, where e is elongation to break). Thus, with increase in PTFE contents, though adhesive and LAOW performance increased substantially, it was at the cost of deterioration in all mechanical properties (except impact strength) and abrasive wear performance.