Microstructure, mechanical properties and low-temperature tribological behavior of Cr/Cr-W/W-DLC/DLC multilayer coatings on 5A06 Al alloy

In this study, the Cr/Cr-W/W-DLC/DLC multilayer coating was deposited on 5A06 Al alloy using a combination of unbalanced magnetron sputtering system and filter cathode vacuum arc technique. Dry linear reciprocating sliding wear tests were performed to evaluate the tribological properties of the deposited coating at different temperatures from −100 °C to 25 °C. The microstructure, mechanical properties and wear characteristics of the multilayer coating were also characterized by SEM, EDS, nanoindenter and nanoscratch tester, respectively. The results show that, compared with 0 °C and 25 °C, the tribological behavior of the multilayer DLC coating exhibits significant differences at low temperatures. The formation of the transfer layer and the graphitization caused by the flash temperature contribute to explain the excellent tribological performance of the coating at room temperature and 0 °C. The deterioration of the tribological properties of the multilayer coating at subzero temperatures is ascribed to the inhibition of the graphitization process, as well as the oxidation and capillary action of water molecules. Cyclic shear stress and low temperature lead to the formation of microcracks and surface spalling, which also increases the friction coefficient and wear rate of the multilayer DLC coating.