Wear resistant composite coatings deposited by electron enhanced closed field unbalanced magnetron sputtering

There is presently considerable interest in wear resistant coatings produced using closed field unbalanced magnetron sputtering technology. For example, layered films of diamond-like carbon (DLC) with tungsten or titanium additions have been widely reported. The benefit is that the mechanical properties are enhanced (e.g. giving greater toughness); also it is possible to control the stress state and enhance adhesion. Here we report the further development of this concept by the addition of TiN, TiCN and TiC layers in DLC-based composites, utilizing an additional source of electrons in the vicinity of substrate to enhance ionisation of the plasma and increase coating density. Composite coatings of ceramics TiN, TiC_xN_y, TiC, CrN, TiCrN, TiCrCN, TiCrC, metal doped Ti_x%-DLC and their combinations were deposited on 316 stainless steel substrates. The mass flow of reactive gases into the chamber was controlled using plasma optical emission monitoring to achieve the desired coating composition. The morphology of the coatings was investigated and correlated with Knoop microhardness, scratch adhesion, pin-on-disc and wet abrasive wheel tests. Dense T-type structures were found for most of the coatings and a high toughness of Ti_30%-DLC coating with a TiC interlayer was observed. Low friction coefficients of 0.15-0.18 for coatings with Ti_x%-DLC layers confirmed their benefit in sliding wear applications, while TiCN coatings were found to be the best in abrasive wear conditions.