Optimizing the tribological performance of DLC-coated NBR rubber: The role of hydrogen in films

Diamond-like carbon (DLC) films directly deposited on rubber substrate is undoubtedly one optimal option to improve the tribological properties due to its ultralow friction, high-hardness as well as good chemical compatibility with rubber. Investigating the relationship between film structure and tribological performance is vital for protecting rubber. In this study it was demonstrated that the etching effect induced by hydrogen incorporation played positive roles in reducing surface roughness of DLC films. In addition, the water contact angle (CA) of DLC-coated nitrile butadiene rubber (NBR) was sensitive to the surface energy and sp2 carbon clustering of DLC films. Most importantly, the optimum tribological performance was obtained at the 29 at% H-containing DLC film coated on NBR, which mainly depended on the following key factors: (1) the DLC film with appropriate roughness matched the counterpart surface; (2) the contact area and surface energy controlled interface adhesive force; (3) the microstructure of DLC films impacted load-bearing capacity; and (4) the generation of graphitic phase acted as a solid lubricant. This understanding may draw inspiration for the fabrication of DLC films on rubber to achieve low friction coefficient.