Influence of fundamental mechanical properties on the tribological behavior of a nanocomposite material

Composite materials (e. g. metallic fibers in a polymeric matrix) show improved stiffness, strength and wear behaviour compared to the pure matrix. In the field of wear protective thin films a-C:H films ("diamond-like carbon") have proven to possess outstanding mechanical properties, but often problems are caused by bad adhesion on metallic substrates. Metal containing amorphous carbon films exhibit an improved adhesion while retaining the excellent tribological properties. From investigations on the microstructure the existence of metallic or carbidic nanocrystalline particles, depending on the kind of metal, in an a-C:H matrix can be concluded. By varying the kind of metal and the metal content in the films physical properties like optical absorption, electrical conductivity and mechanical properties can be changed. Using the example of niobium containing amorphous hydrogenated carbon films (Nb-C:H), deposited in a combined RF-plasma CVD / sputtering process, the influence of deposition parameters (kind of hydrocarbon, hydrocarbon flow, total pressure during deposition) on the mechanical properties of the nanocomposite were studied. Hardnesses and Young's moduli of the films were determined by nanometer indentation, residual stresses by substrate bending, fracture strain in a four point bending tester. Tribological properties were studied with a three body abrasive wear test and a ball-on-disc friction test. The mechanical properties are correlated with the microstructure of the films. The elemental composition was obtained from EPMA (electron probe micro-analysis), the precipitations were characterized previously with small and wide angle X-ray scattering and X-ray photon spectroscopy.