Method of Applying DLC Coating on Aluminum Alloys

Abstract

A method was developed for applying a diamond-like carbon (DLC) coating on aluminum alloys to obtain sufficient adhesion strength and wear resistance. The key points of this technology consist of two main processes. First, the surface of the aluminum substrate is modified by forming a top layer of dispersed fine tungsten particles on a mechanically hardened layer obtained in a fine tungsten particle shot-peening process. Second, the sharp top edges formed by the shot-peening process are polished lightly to remove them. A DLC film is then coated on the aluminum substrate by plasma chemical vapor deposition (PE-CVD). The adhesion strength and wear resistance of the DLC film were evaluated in sliding tests under a continuously increasing load. The critical load, which was defined as the load where the friction coefficient increased markedly, was compared for three types of DLC-coated samples. One sample had the DLC film coated directly on the smooth surface of aluminum substrate after polishing; another had the DLC film coated on the rough surface following tungsten shot-peening; the third had the DLC film coated on the substrate surface with plateau roughness obtained by polishing the top edges lightly after the shot-peening process. The critical load of the DLC coating on the substrate with light polishing after the tungsten shot-peening process was 40-70% higher than that of the coating on the polished substrate, while that of the coating on the substrate subjected only to tungsten shot-peening was markedly lower.