Effect of the type, size and concentration of solid lubricants on the tribological properties of the polymer PEEK

Poly-ether-ether-ketone (PEEK) is a high-performance, temperature-resistance polymer that is finding an increasing range of applications. In order to even enhance PEEK's mechanical and tribological properties particles of different compositions, shapes and sizes are added into its matrix. PEEK has already been combined with many different particles; however, very rarely MoS2 and WS2 - two state-of-the-art solid lubricants - were added into the PEEK matrix. Furthermore, a comprehensive tribological study combining MoS2 and WS2 particles of different sizes and concentrations has not yet been reported. In this investigation we looked at the effect of micro- and nanosized MoS2 and WS2 particles in PEEK on the dry sliding tribological behaviour against stainless steel (100Cr6). A non-conventional technique, i.e., the sintering of dry-pressed compacts, was used to prepare the PEEK composites. The results show that all the particles, irrespective of their composition and size, reduce the friction (up to 30%); however, the nanoscale particles require a higher concentration to form an effective low-friction tribofilm. The formation of a tribofilm is necessary to reduce the wear of all the composites (up to 51%); this is strongly promoted by the addition of nano- or microparticles of both the MoS2 and WS2 materials. In addition, the hardness, which is greatly increased by the addition of all the particles, significantly improves the wear behaviour. The results of XPS analyses showed that the oxidation occurs during tribological sliding, which reduces particles beneficial wear behaviour effects. (C) 2016 Elsevier B.V. All rights reserved.