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.