Improving the friction and wear of poly-ether-etherketone (PEEK) by using thin nano-composite coatings

Polyether ether ketone (PEEK), an engineering polymer with many advantages such as lightweight, high thermal stability, high-strength coupled with toughness, has often been used as a substitute for metals in applications such as bearings, piston rings, pumps and even biomaterials. However, in pristine form, PEEK exhibits poor wear resistance and higher coefficient of friction (~0.25 to 0.3) leading to frictional losses because of which the usage of PEEK is widely restricted in applications where energy efficiency is of utmost importance. Hence, in this study a thin nanocomposite coating of ultra-high molecular weight polyethylene (UHMWPE) reinforced with carbon nanotubes (CNTs) is deposited using a simple dip coating process on the surface of PEEK to reduce its wear and the coefficient of friction. Different loadings of CNTs (0.1 and 0.2 wt%) with different concentrations of UHMWPE (3 and 5 wt%) are used to deposit nanocomposite coatings on PEEK. Ball-on-disc wear tests with an AISI 440 C stainless steel standard ball as a counterface are performed to evaluate the tribological properties under dry conditions. FESEM, 3D-optical profilometry and raman spectroscopy are used to characterize the coatings in terms of thicknesses, wear morphology and dispersion, respectively. The nanocomposite coating is found to be very effective in improving the tribological properties of PEEK with 3 wt% UHMWPE coating reinforced with 0.2 wt% of CNTs showed a very low-coefficient of friction of ~0.09 and a wear life of more than 25,000 cycles at a normal load of 9 N and a sliding speed of 0.5 m/s.