Synthesis of Ag-DLC coatings for biomedical implants

Abstract

The diamond-like carbon (DLC) coating has the potential to increase the lifetime of metal on polymer (MoP) type hip joints due to its good tribological and mechanical properties as well as excellent biocompatibility. However, the high internal compressive stress of DLC films limits their adhesion with CoCrMo alloy. The high internal stress can be minimized by doping the DLC coating with metals like Ti, Cu, W, Nb and many more. In the present thesis work, silver (Ag) doped diamond-like carbon (DLC) coatings were prepared on the CoCrMo alloy using direct current (DC) magnetron sputtering for biomedical implants. The silver concentration was varied in the DLC matrix by varying the DC power to the silver target from 12 W to 18 W. Raman spectroscopy was carried out to evaluate the structural changes in the carbon matrix. X-ray photoelectron spectroscopy (XPS) was used to measure the concentration of Ag and sp3 carbon hybridization in the coatings. The hardness, tribological behavior, and adhesion properties were characterized using nano-indentation, wear testing, and Rockwell C indentation, respectively. The hardness values show that initially, with a low percentage of silver, the residual stresses decrease drastically, whereas the hardness values decrease slightly. The lowest wear rate was observed for the coating doped with 7.4 at% of silver among all coatings, and improved adhesion was observed for all the Ag-DLC coating on CoCrMo alloy. The results showed that silver doped DLC coating is promising for a total hip joint replacement application.