Tribological behavior of diamond-like-carbon (DLC) coatings against aluminum alloys at elevated temperatures

Diamond-like-carbon (DLC) coatings have a low friction coefficient and aluminum tends not to stick with it, which makes it a promising candidate tool coating for aluminum dry machining and hot forming applications. In this work, we compared the tribological properties of hydrogenated and non-hydrogenated DLC coatings made by unbalanced magnetron sputtering. Their friction, wear, and tendency of adherence at room and elevated temperatures were studied by sliding against 319 aluminum pins. In ambient air, aluminum did not stick to hydrogenated or non-hydrogenated DLC. At elevated temperature, aluminum adhered to the non-hydrogenated DLC. Hydrogenated DLC maintained its non-sticking nature at elevated temperature but its wear resistance deteriorated. The wear mechanism of hydrogenated-DLC at elevated temperature was investigated using thermo-gravimetric analysis (TGA), elastic recoil detection (ERD), nano-indentation, and Raman analysis. The accelerated wear of hydrogenated DLC at elevated temperature was attributed to the graphitization process.