DLC-based solid-liquid synergetic lubricating coatings for improving tribological behavior of boundary lubricated surfaces under high vacuum condition

► Five DLC-based solid-liquid lubricating dual-layer coatings were successfully fabricated. ► Solid-liquid lubricating coatings of MACs, IL, Zdol exhibited excellent tribological properties. ► Solid-liquid lubricating coatings of PAO and silicon oil showed the poor tribological behaviors. ► Such difference depends on nature of liquid lubricant, and synergy lubricating mechanism with DLC.