COMPARATIVE TRIBOLOGY STUDIES OF HARD CERAMIC AND COMPOSITE METAL-DLC COATINGS IN SLIDING FRICTION CONDITIONS

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 ear rate. Recently introduced metal-diamond-like carbon (DLC) coating scan 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 Ti-x%-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 Ti-x%-DLC and ceramic TiN, TiCN and CrN coatings shows particularly low friction coefficients (below 0.2) and low normalized wear rates for the Ti-x%-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 Ti-35%-DLC and Ti-20%-DLC are recommended for sliding wear applications.