The electrochemical and wear behaviour of amorphous diamond-like carbon coatings and multilayered coatings in aqueous environments

R.f. plasma CVD deposited diamond-like carbon coatings (DLC) possess interesting wear properties in dry testing conditions or in vacuum applications. Extremely low friction coefficients are displayed in dry test conditions, the friction coefficient being dependent on relative humidity and presence of oxygen. The question arises whether these coatings are equally effective in an aqueous medium. Parameters controlling the through-coating porosity are discussed and their relative importance indicated. A coulometric quantitative porosity measurement has been used. Characterisation by light optical microscopy, profilometric measurements and EPMA suggest the importance of the microstructure of the substrate material. Further, pin-on-disk wear tests in water show a detrimental 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 the initial contact stress and the development of this stress by initial wear.