Vacuum tribological performance of DLC-based solid–liquid lubricating coatings: Influence of sliding mating materials

The friction and wear behaviors of DLC-based solid–liquid lubricating coatings for three liquid lubricants sliding against different counterface materials were examined under high vacuum conditions. Seven kinds of balls with the diameter of 3 mm were chosen as counterparts, which were GCr15, bronze, ZrO2, Al2O3, SiC, WC, and Si3N4. Under high vacuum condition, the friction coefficient (COF) and wear rate of carbon-based solid–liquid lubricating coatings sliding against different counterparts were diverse, due to different liquid lubrications and counterface materials. In analyzing the friction and wear mechanism, the contact radius and the contact pressure were introduced. The COF showed the inverse varied trend with Hertzian contact radius for the three liquid lubricants. COF decreased with the increase of contact radius, which was different from the dry sliding of DLC film. The possible reason was that the synergetic lubrication between the DLC films and the liquid lubricants formed a new solid–liquid synergistic system (DLC-oil-DLC), which improved the ability of plasticity-resistant deformation, reduced the real contact area and friction coefficient. The contact pressure was consistent with the wear rate varied trend for the three liquid lubricants, and this varied trend was in good agreement with each other for MACs lubricant.