Studies On Tribological Properties Of Modified DLC Coatings Under Water And Oil Lubricated Conditions

Diamond like carbon(DLC) coating is one of the excellent ductile coatings with favorable properties. While the friction behavior of DLC coating was sensitive to changing of environments. Especially high temperature, strong corrosion and other severe environments can make coating failed. In order to enhance the practicality of DLC coating, various coatings need be deposited with various environmental suitable abilities. The DLC coating and WC/DLC coating in the paper were made to adapt to water and oil lubricated conditions. The coatings were deposited on 304 L stainless steel and silicon wafers by unbalanced sputtering technology. Microstructures were analyzed by SEM, Raman,XRD and TEM. Mechanical properties were analyzed by nanoidentation. Hydrophilic properties were analyzed by optical contact angle measuring device. Corrosion resistances were analyzed by polarization tests. Tribological properties and tribocorrosive behaviors of coatings were all investigated by multifunctional tribological tester. The hydrophilic properties, corrosive resistance, tribological properties and tribocorrosive property of hydrogenated DLC coating and 304 L stainless steel were investigated. The tribological properties of WC/DLC coating and 304 L stainless steel in PAO-40 base oil, engine lubricating oil, and corrosive engine oil conditions were tested. The tribological properties of DLC coating and WC/DLC coating under PAO-40 base oil at 23 ??100 ??200 ? were investigated. The results were shown as follows:(1) When compared with 304 L stainless steel, DLC coating exhibited better corrosion resistance and friction properties in seawater. There was a high content of sp3 bonds in the coating. So the coating exhibited high hardness and elastic modulus. For dense cross section and surface structure, DLC coating exhibited good corrosion resistance in seawater. For the hydrophilic property of DLC coating in seawater, there were lubricated films should be deposited on surface of DLC coating. The coating had good friction adaption under seawater condition.(2) There were no declines of corrosion resistances of DLC coating during friction process. So does no declines of friction coefficients at different electrode potentials. The mainly volume loss of DLC coating was mechanical wear. So DLC coating exhibited excellent comprehensive performance in corrosive liquids.(3) When compared with WC/DLC coated 304 L stainless steel, the mechanical properties of base material were increased. For the excellent lubricated effect of amorphous carbon, WC/DLC coating exhibited lower friction coefficients and wear rates under different oil lubricated conditions.(4) For incorporation of WC in DLC coating, the bonding force of DLC coating was enhanced. During the friction process in seawater, WC was benefit to increase surface activity of DLC coating, which had promotion effect on interaction of DLC coating and oil film. The heighten interaction between coating and oil offered a lower wear rate of WC/DLC coating under oil lubricated condition under boundary lubricated condition.