Diamond-like carbon film deposition on plasma nitrided steel substrates

Abstract

Diamond-like carbon (DLC) films are very hard and wear resistant, and are generally characterized by low friction coefficients. Nevertheless, their adhesion to steel substrates is limited due to the large difference in physical properties ( i.e. hardness) of the materials. In contrast, plasma nitriding of steel gives hardened layers which are fatigue- and wear- resistant, but which often display rather poor friction properties. We describe in this paper a combined plasma nitriding treatment/d.c.-PACVD process giving multicomponent coatings with gradually varying mechanical properties and improved wear resistance and friction characteristics. The influence of the nitrided layers on the mechanical behaviour of deposited DLC films is studied by means of scratch test methods and hardness measurements. Ball-on-disc and ring-on-block experiments are used to evaluate the usefulness of such a duplex process with regard to tribological properties of the treated steel surfaces.