Wear and adhesion resistance of duplex coatings deposited on Ti6Al4V alloy using MAO and CFUBMS

DLC (Diamond-Like Carbon) coatings feature high hardness, good wear resistance and low friction. Applying DLC coatings to titanium alloys using different coating techniques can improve the surface properties. However, in many cases, this hard coating fails under mechanical loading due to the mechanical incompatibility of the coating and substrate. Therefore, an intermediate layer providing improved load support is necessary to prevent the failure of the DLC film. For this purpose, the Micro Arc Oxidation (MAO) and Closed Field Unbalance Magnetron Sputtering (CFUBMS) coating techniques were used to deposit duplex MAO/DLC coating on Ti6Al4V (Grade 5) alloy. The surface topography, morphology, crystallographic structure and thickness of the duplex coatings were determined using Scanning Electron Microscopy (SEM), XRD and RAMAN. The hardness was measured using a nano-hardness tester. The hardness, adhesion to the substrate and load-bearing capacity of DLC increased due to the intermediate layer of TiO2 deposited by MAO because it decreased the mechanical incompatibility between the soft substrate and hard coating. The duplex coating using the MAO/CFUBMS process was effective in maintaining a convenient, low, stable coefficient of friction and improving the tribological behaviour of the Ti6Al4V substrate. It was observed that the duplex coatings deposited on the Ti6Al4V substrate indicate a better tribological performance than the DLC or MAO coatings on the Ti6Al4V alloy substrate.