Influence of methane flow ratios on the structural and mechanical properties of Ti-doped diamond-like carbon films

Diamond-like carbon films with Ti dopant (Ti-DLC) are synthesized by reactive magnetron sputtering using a pure Ti metal target. This study determines the effect of methane flow ratios (Rm=CH4/(Ar + CH4), ranging from 4 to 12%) on the surface morphology, microstructure, mechanical properties, and cermet cutting tool insert features of Ti-DLC films. The GIXRD diffraction spectrum for Ti-DLC film depicts an amorphous structure. There are peaks for nano-crystalline TiC at 2 theta values of 35.88 degrees, 41.52 degrees, and 60.14 degrees, which respectively correspond to the (111), (200), and (220) planes of the face-centered cubic structure. The characteristic binding energy of C 1s, Ti 2p, and O 1s for Ti-DLC film is determined using a high-resolution XPS spectrum. Increasing Rm flow ratio (reducing Ti metal doping) increases the intensity of the Raman spectrum because there is an increased sp2-C (sp2/sp3 ratio) site fraction for DLC components. The experimental results show that the hardness of the DLC film increases from 11.07 to 14.76 GPa as the Rm flow ratio is increased from 4 to 12%. The adhesive strength of the Ti-DLC film coating is measured using a scratch test and shows that the film adheres well to the substrate. The Ti-DLC films are coated onto cutter inserts for the dry milling of an Inconel 718 workpiece, and the results show that all coated tools have a significantly longer tool life than uncoated tools.