THE ELECTROCHEMICAL AND WEAR BEHAVIOR OF AMORPHOUS DIAMOND-LIKE CARBON COATINGS AND MULTILAYERED COATINGS IN AQUEOUS ENVIRONMENTS

R.f. plasma CVD deposited diamond-like carbon coatings (DLC) possess i nteresting wear properties in dry testing conditions or in vacuum appl ications. Extremely low friction coefficients are displayed in dry tes t conditions, the friction coefficient being dependent on relative hum idity and presence of oxygen. The question arises whether these coatin gs are equally effective in an aqueous medium. Parameters controlling the through-coating porosity are discussed and their relative importan ce indicated. A coulometric quantitative porosity measurement has been used. Characterisation by light optical microscopy, profilometric mea surements and EPMA suggest the importance of the microstructure of the substrate material. Further, pin-on-disk wear tests in water show a d etrimental damage when compared to dry wear tests. De-adhesion of the coating occurs in an early stage with subsequently a rapid destruction of the coating. Important parameters in this failure mechanism are th e initial contact stress and the development of this stress by initial wear.