Wear resistant electrically conductive Au-ZnO nanocomposite coatings synthesized by e-beam evaporation

The tribological and electrical behavior of e-beam codeposited Au-ZnO nanocomposite films were investigated for compositions in the range 0.1-28.0 vol% of ZnO. A 2.0 vol% ZnO film did not exhibit measurable wear sliding against a commercial gold alloy rider. Electron backscatter diffraction (EBSD) analysis on film surfaces of varying composition revealed a significant reduction in grain size for a 0.1 vol% ZnO film contrasting with a pure Au film. Electrical resistivity measurements of films in the range 0.0-28.0 vol% ZnO exhibited a linear increase in resistivity from 2.73 μΩ cm to 39.88 μΩ cm. The friction, wear, and electrical contact resistance of 2.0 and 28.0 vol% ZnO films sliding against commercially available hardened Au riders (72Au-14Cu-8Pt-5Ag by weight) were investigated. Friction coefficient and electrical contact resistance data were in the range μ=0.3-0.5 and ECR=40 mΩ and 500-2000 mΩ, respectively, for 2 μm thick films deposited on conductive substrates in unidirectional sliding at 1 mm/s under a 185 MPa maximum Hertzian contact pressure (100 mN contact force). The presence of ZnO transfer to the rider was observed via energy-dispersive X-ray spectroscopy (EDS). Significant improvements in wear resistance and friction behavior were observed for Au-ZnO composite films with volume fractions of ZnO commensurate with the metal species codeposited in traditional hardened gold coatings.