Combination of laser surface texturing and DLC coating on PEEK for enhanced tribological properties

Poly-ether-ether-ketone (PEEK) is a thermoplastic polymer marked by high mechanical properties and chemical inertia. PEEK is also a well-known biomaterial which has been subjected to intensive research over the last decades. In particular, it has recently been shown that laser surface texturing as well as diamond-like carbon (DLC) film deposition was able to reduce PEEK wear in tribological testing. This study focuses on evaluating the mechanical and tribological performance of PEEK surfaces modified via laser surface texturing (LST) combined with DLC coating. An ultrashort-pulse laser was used in order to pattern a hexagonal array of 33 pm in diameter dimples onto the PEEK surface. The depth of dimples was varying (2, 12 and 21 pm) as well as the dimple density (10, 30 and 48%). Subsequently, a 2-mu m thick DLC film was deposited on the textured PEEK surface. It was shown that LST did not significantly affect the DLC/PEEK adhesion in pull-off testing, however, deep dimples and high dimple densities led to a large deformation of the substrate and caused the film to be more susceptible to cracking in scratch testing. The DLC-coated LST PEEK surfaces were rubbed against an alumina ball in dry conditions, water and bovine calf serum solutions. DLC-coated PEEK with shallow dimples and a low dimple density enabled to significantly, reduce wear and friction in distilled water and reduce wear in bovine calf serum compared with smooth DLC-coated PEEK. Smooth and LST DLC films exhibited a great stability in terms of microstructure and chemistry in all tested media.