Tribological properties of diamond-like carbon and boron carbide coatings against aluminum: Adhesion & friction at different temperatures and environments

This thesis investigates the adhesion, friction and wear behaviour of diamond-like carbon (DLC) coatings and boron carbide (B4C) coatings. Both temperature and environmental stability of these coatings were investigated. Pin-on-disc tests against a 319 Al alloy revealed that tungsten carbide (WC) doped hydrogenated DLC coatings displayed lower coefficient of friction (COF) and wear rates than monolithic nonhydrogenated DLC coatings. WC-DLC coatings with a top layer of DLC (DLC/WC-DLC) withstood higher temperatures than WC-DLC coatings. Aluminum adhesion with the WC-DLC and DLC/WC-DLC coatings was observed at 300 and 350°C, respectively. B4C coatings exhibited higher COF and more aluminum adhesion under all test conditions. While testing under the N2 atmosphere reduced COF values for all the coatings, the humidity level of the test environment exerted various influence on each coating. The mechanisms of adhesion, friction and wear of the tribosystems were discussed based on the Al alloy-coating interactions under specific test conditions.