Comparative Tribology Studies of Hard Ceramic and Composite Metal-DLC Coatings in Sliding Friction Conditions

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Abstract
The design of anti-friction coatings able to perform well in different wear conditions without lubricants requires a combination of adequate hardness and toughness, good adhesion, a low friction coefficient and a low wear rate. Recently introduced metal-diamond-like carbon (DLC) coatings can be a major step towards the achievement of such combination. These coatings consist of an amorphous a.CH matrix with the possible incorporation of metal, metal carbide and/or graphite grains. Previous studies of Tix%-DLC coatings deposited on Ti-TiN-TiCN-TiC supporting interlayers showed their good protective properties against abrasive, impact and single scratch wear. Here, ball-on-disk experiments are carried out to investigate these coatings in conditions of sliding wear against steel and WC balls. A comparison of the results for Tix%-DLC and ceramic. TiN, TiCN and CrN coatings shows particularly low friction coefficients (below 0.2) and low normalized wear rates for the Tix%-DLC coatings. The results reveal a correlation between the tribological properties of these coatings and the amount of the metal component in their matrix; the Ti35%-DLC and Ti20%-DLC are recommended for sliding wear applications.