A comparative study in the tribological behaviour of different DLC coatings sliding against titanium alloys

In this study, the tribological behaviour of different Diamond-like-Carbon (DLC) coatings sliding against titanium alloy (Ti6Al4V) was analysed in a pin-on-disc tribometer at different applied loads to study effectiveness of tool coatings in titanium alloys machining. Three different DLC coatings were deposited on cemented carbide substrate using HiPIMS (DLC-Ar, DLC-Ne) and arc (DLC-Bn) deposition techniques. A detailed analysis of the wear track and titanium countersurfaces were performed following the tribotest to develop understanding about the wear mechanism and associated variation in the friction response. The results indicated that DLC-Ar presents low friction and reduced wear of coating and respective titanium countersurface at lowest load, seemingly due to its inherent tendency to spontaneously form graphitic transfer-layer at the interface. With an increase in the applied load, the tendency to retain tribofilm decreases as shearing ensue quickly exposing the underneath substrate material. The wear performance of DLC-Ne coatings is better than DLC-Ar under highest load and friction behaviour relatively close to DLC-Ar coatings. In comparison, under increased applied loads, DLC-Bn coatings offered better wear resistance and low friction compared with DLC-Ne and DLC-Ar coatings, which would offer improved performance in machining of titanium alloys.