A comparative study of state-of-the-art diamond-like carbon films

Diamond-like carbon (DLC) coatings represent a group of very similar but still very different materials. Their characteristics range from graphite-like to diamond-like to polymer-like, depending on the deposition techniques. The sensitivity of DLC coating properties to processing conditions can be considered a problem, but on the other hand it creates opportunities for adaptation to specific applications. In this study the mechanical and tribological properties of various state-of-the art DLC coatings (from six suppliers) were investigated to generate a basis of data for comparison that should facilitate the selection of DLC coatings for particular applications. Hardness and modulus of elasticity were measured by depth-sensing indentation. Scratch testing was used to determine the adhesive strength of the coatings. The friction and wear tests were conducted using a ball-on-flat and flat-on-flat configuration under unidirectional and reciprocating motion, respectively. The results of this work demonstrate that the mechanical and tribological properties of DLC coatings vary strongly. Each coating type has specific advantages and the complete range of properties should be studied carefully to select the appropriate coating in a particular application. A more general guideline for DLC selection is discussed.