Potential of fibers and solid lubricants to enhance the tribo-utility of PEEK in adverse operating conditions

Purpose - Poly-ether-ether-ketone (PEEK), a specialty polymer, does not have any tribo-utility as a bearing material in a virgin form since it exhibits quite a high coefficient of friction (mu) and stick-slip behavior. The present paper seeks to deal with the adhesive wear behavior of series of PEEK composites based on inclusion of short fibers of glass (GF) and carbon (CF) and solid lubricants such as Polytetrafluoroethylene and graphite. The studies are focused to examine the role of these ingredients on enhancing PV limit, which is an indication of utility of a tribo-polymer in severe operating conditions. Design/methodology/approach - The Adhesive wear studies were performed on a pin on disc machine fabricated for high speed, load and temperature conditions. A composite pin slid over a disc of mild steel under two selected sliding speeds (2 and 3 m/s) for an hour. The load was varied in each experiment till the pin showed failure. The performance assessment was done based on multiple parameters such as magnitude of mu and its fluctuations with time, specific wear rate, PV limit, compatibility with the counterface, etc. PV limit was judged by observing either sudden increase in mu or wear rate (or both), deformation of the pin or change in the color of the disc. Findings - It was observed that the neat PEEK exhibited very high and fluctuating mu with very low P-V limit value (150 Nm/s) and high wear rate (2 x 10(-14) m(3) /Nm). Inclusion of 30 percent CF benefited the strength properties but not the tribo-performance appreciably. Composite D with a combination of GF (25 percent) and solid lubricants (30 percent) excelled in performance with a wide margin. The highest PV limit along with the lowest mu and lowest wear rate and counterface friendliness proved it to be most promising bearing material for the selected harsh operating conditions. Practical implications - The composite D-1 which worked better than the commercial composite in almost all the selected operating conditions, indicates its commercial potential as a bearing grade material for high PV conditions. Originality/value - Synergism between reinforcement and solid lubricants in right amount led to excellent friction and wear performance which was very well analysed based on worn surface topography.