Composite DLC-metal/metal-carbide coatings produced by electron enhanced unbalanced magnetron sputtering

Composite coatings consisting of metal containing DLC were produced by unbalanced magnetron sputtering in a closed field magnetic configuration. Targets of Ti and W were poisoned with acetylene during the deposition process, enabling the formation of a carbon enriched surface layer, which was then sputtered to produce DLC-metal/metal-carbide composites. Target poisoning was controlled by plasma emission monitoring, and a hot filament was used to regulate the ion current to the substrates independently of the magnetron power and substrate bias. Coating morphology and composition were investigated using scanning electron microscopy techniques and glow discharge optical emission spectroscopy. Additionally the films were characterised by means of Raman spectroscopy. Microhardness, pin on disc, abrasive wheel, impact, and scratch tests were performed to evaluate the mechanical and tribological properties of the coatings. In pin on disc tests, dry sliding friction coefficients of less than 0 .15 were recorded against an SAE 521 00 steel ball, even after 1 km sliding distance. The implications of these extremely favourable tribological properties are discussed.