Influence of Ag doping on the microstructure, mechanical properties, and adhesion stability of diamond-like carbon films

Abstract

Silver (Ag)-doped diamond-like carbon (Ag-DLC) films were deposited on Si wafer and Co-Cr-Mo alloy substrates using a hybrid deposition technique that combined high-power pulsed magnetron sputtering (HPPMS) and high-power pulsed plasma-enhanced chemical vapor deposition (HPP-PECVD). The Ag concentration (0.0–10.0 at.%) in Ag-DLC films was controlled by adjusting the number of Ag rods in the mosaic silver-graphite target. The effects of Ag doping on the microstructure, chemical bonding, mechanical properties, and adhesion stability of DLC films were systematically investigated. The results demonstrated that Ag doping could refine the columnar structure in DLC films and change the shape and size of DLC surface hillocks. The residual stress in the DLC films decreased as the Ag concentration increased, which effectively improved the adhesion between the films and substrates. The fraction of sp3 bonds in the carbon structure decreased with increasing Ag concentration, which resulted in a reduction in the film hardness when the Ag concentration was higher than 3.2 at.%. Ag doping could improve the wear performance of DLC films, and the Ag-DLC film with 3.2 at.% Ag had excellent wear resistance. Compared with pure DLC films, the Ag-DLC films had better adhesion stability in physiological solutions, which is beneficial for the long-term service of DLC films in vivo applications.