Improvement of ion plated Ag and Au film adhesion to Si3 N4 and SiC surfaces for increased tribological performance

Abstract

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.