Effect of hydrogen incorporation on the mechanical properties of DLC films deposited by HiPIMS in DOMS mode

Abstract

The automobile industry has increased its efforts in reducing the emissions of internal combustion engines by improving their efficiency. Decreasing the energy losses by friction in the engines parts is at the core of this attempt. One of the technologies that have been applied in achieving this is the application of carbon coating in engine parts surfaces because of their low friction coefficient characteristics. In this study, DLC films, a specific type of carbon coatings, were deposited using the Deep oscillation magnetron sputtering (DOMS) method, which is a variation of the high-power impulse magnetron sputtering (HiPIMS) method. Those films were deposited with an increasingly higher hydrogen content, and then their mechanical, morphological, and tribological properties were studied. All of this was carried out to verify if the higher hydrogen content is beneficial to use as piston ring coatings in order to decrease friction losses. The variation in the hydrogen content was achieved by increasing the partial pressure of methane inside the deposition chamber during the deposition, which allowed the deposition of films with up to 30 at. % of hydrogen. The variation allowed the depositions of films with a hardness above 10 GPa, a friction coefficient lower than 0.16 (30 % lower when compared to hydrogen-free DLCs), and with specific wear rates in the order of 10−16 mm3/Nm. The hydrogen content also changed the morphology of the films' surface, as well as increasing its deposition rates by 27 %.