A DLC/diamond bilayer approach for reducing the initial friction towards a high bearing capacity

Sliding contact mechanics is used to account for the net increase of the bearing capacity of high wear-resistant CVD diamond coatings when an outer layer of a DLC lubricant film is deposited on their top surface. Experimental results, namely the critical failure load, taken from reciprocating ball-on-plate tribological testing of such DLC/diamond bilayers, are on the basis of this statement. DC magnetron sputtering was used to grow thin DLC lubricant coatings (non-hydrogenated and hydrogenated varieties) on the top of CVD diamond films (microcrystalline and nanocrystalline types). The application of the von Mises maximum yield parameter (J2) criterion demonstrates to be an adequate method for designing low-friction and high-bearing capacity systems for high-demanding tribological applications. Calculation of J2supports that the most significant increase observed on the coatings’ bearing capacity (from 20 N to 60 N) takes place when microcrystalline diamond is coated by hydrogenated DLC that decreases the initial friction coefficient peak (from 0.76 to 0.41).

► DLC lubricant coatings deposited on top of CVD diamond coated silicon nitride.
► Ball-on-plate homologous tests assessed critical failure load, friction and wear.
► DLC-H on MCD decreases initial friction coefficient (μmax) peak by 46%.
► Threefold increase in bearing capacity of MCD coatings with DLC-H.
► von Mises maximum yield parameter describes dependence of bearing capacity on μmax.