The influence of microstructural variations on mechanical and tribological properties of low-friction TiC/diamond-like carbon nanocomposite films

TiC/diamond-like carbon (DLC) nanocomposite films were deposited via steered cathodic arc deposition with various C2H2 flow rates (fC2H2) to study the relationship among the molar fraction of DLC ([DLC]) and the structural, mechanical, and tribological properties of the films. The X-ray diffraction results indicate that the crystallite size of TiC decreased from 14.1 to 3.2 nm when fC2H2 was increased from 60 to 151 sccm. Transmission electron microscopy images show that an elongated TiC grain shape appeared at low fC2H2 values (<100 sccm), the long axis of most grains aligned along the growth direction of the film, and the aspect ratio of elongated TiC grains decreased from 3 to 1.6 when fC2H2 was increased from 80 to 100 sccm. Furthermore, the structure of film became a nano-dot TiC/DLC superlattice when fC2H2 was increased to 151 sccm. Rockwell-C indentation tester results indicate that the Ti-TiN-TiC/DLC nanocomposite layer structure had good adhesion between the substrate and films. The hardness increased from 32.5 to 39.3 GPa when fC2H2 was increased from 60 to 80 sccm, and then decreased to 25.1 GPa when fC2H2 was further increased to 151 sccm. The initial increase in hardness was due to grain refinement leading to suppressed multiplication and mobility of dislocations and the subsequent decrease in hardness was due to grain boundary sliding. The toughness was enhanced by the formation of the nanodot TiC/DLC superlattice, as indicated by plasticity calculated from nanoindentation measurements. The friction coefficient decreased from 0.13 to 0.05 with increasing [DLC].