Improved wear resistance at high contact stresses of hydrogen-free diamond-like carbon coatings by carbon/carbon multilayer architecture

Diamond-like carbon (DLC) coatings are widely used in tribological applications because it can provide high hardness and low friction coefficient. However, hydrogen-free DLC coatings tend to fracture and delaminate where high contact stresses (> 1 GPa) are required. We proposed that the carbon/carbon (C/C) multilayer may have the potential for tribological applications under high contact stresses. In this study, C/C multilayer coatings consisting of alternate soft-layer and hard-layer were deposited using unbalanced magnetron sputtering technique. The effect of multilayer architecture (the ratio of hard-layer to softlayer and bilayer thickness) on tribological behavior was investigated. The tribological performance at different high contact stresses (1.82 GPa, 2.30 GPa, 2.89 GPa and 3.65 GPa) was evaluated by a ball-on-disc tribometer. The C/C multilayer coatings can withstand the maximum contact stress of similar to 3.65 GPa with low wear rate. In contrast, the single layer hard DLC failed when the stress is higher than 2.30 GPa. The 50% hard multilayer with 61 nm bilayer thickness shows the best overall wear resistance, especially at a stress of 3.65 GPa. The wear rate of our C/C multilayer (similar to 10(-8) mm(3)/Nm) is 10 times lower than that of DLC coatings (similar to 10(-7) mm(3)/Nm) from the current literature. The excellent wear resistance of the multilayer DLC can be explained by the combination of good toughness and the lubrication effect of the transfer layer. Such C/C multilayer structure offers an alternative to deposit DLC coatings for high stress applications without introducing other elements. (c) 2017 Elsevier B.V. All rights reserved.