Improvement of ion plated Ag and Au film adhesion to Si 3 N 4 and SiC surfaces for increased tribological performance

A modified dc diode plating system, utilising a metallic screen cage as a cathode and designated screen cage ion plating, is used to deposit Ag and Au lubricating films on Si₃ N₄ and SiC surfaces. When deposition is performed in Ar or N₂ glow discharge, the surface displays poor adhesive strength (<5 MPa). A dramatic increase in adhesive strength (>80 MPa) is achieved when plating is performed in a reactive 50O₂–50Ar glow discharge. The excited/ionised oxygen species (O⁺₂ /O⁺) in the glow discharge contribute to the oxidation of the Si₃ N₄ or SiC surfaces as determined by X-ray photoelectron spectroscopy depth profiling. The reactively sputter oxidised Si₃ N₄ or SiC surfaces and the activated oxidised metastable Ag or Au species formed in the plasma, cooperatively contribute to the increased adhesion. As a result, the linear thermal expansion coefficient mismatch at the interface is reduced. These lubricating Ag and Au films under sliding conditions reduce the friction coefficient by a factor of 2·5–4.