Preparations and tribological properties of soft-metal/DLC composite coatings by RF magnetron sputter using composite targets

This work reports the characteristics and tribological properties of both Ag/DLC nanocomposite coatings (RF-Ag-DLC) and Cu/DLC nanocomposite coatings (RF-Cu-DLC) with hydrogen-free DLC matrix deposited by RF magnetron sputtering using a concentric composite target (CCT). The CCT consisted of a C base target and metal tablet, and the tablet was located on the center of the base target concentrically where the etching rate by Ar ions is extremely low. By changing the diameter of Ag or Cu tablets in CCT, RF-Ag-DLC with an Ag concentration ranging from 6 to 65 at.% and RF-Cu-DLC with Cu concentration ranging from 7 to 75 at.% can be prepared. These coatings show a granular structure having Ag or Cu nano-crystals with a diameter ranging from 5 to 10 nm dispersed homogeneously in the hydrogen-free DLC matrix. The friction coefficient of DLC varied depending on the species and content of metal. The transition of the friction coefficient became stable when metal-rich tribofilms formed on the counterfaces.