INTERFACIAL SHEAR-STRENGTH OF DIAMOND-LIKE CARBON COATINGS DEPOSITED ON METALS

The material properties of diamond-like carbon (DLC), which make this material particularly applicable for tribological applications, can only be used if the adhesion of the DLC coating to the substrate is very strong. Ideally the adhesion should be as strong as the substrate and/or the coating itself. DLC coatings often exhibit very high internal compressive stress, increasing the demands for strong adhesion to the substrate. In this work, DLC was deposited on a steel substrate using a plasma-enhanced chemical vapor deposition (PECVD) process. In order to develop processes for the improvement of adhesion, experimental methods measuring the interfacial shear strength of a coating to a substrate are essential. Unfortunately, these methods are limited, both in number and applicability. In this work, the interfacial shear strength was measured using the substrate plastic straining technique (D.C. Agrawal and R. Raj, Acta Metall., 37 (1989) 1265). This method offers an absolute measurement of the interfacial shear strength. It is concluded that the method is easy and fast to perform and is therefore well suited for the optimization of process parameters controlling the adhesion strength.