Tribological response of multilayered gold nickel coating deposited on fine turned surfaces

Gold coating are widely used in industry due to their corrosion resistance, electrical conductivity and low contact resistance. However, friction and wear can limit their functionality and lifetime. This study addresses the degradation of a commercial finely turned brass surface coated with an adhesion chromium layer, a NiP hard coating and finally at the surface by a self-lubricating gold layer. The degradation mechanisms and the consequences on friction were investigated using a laboratory tribometer combined with surface analysis by confocal microscopy, AES (Auger Electron Spectroscopy), SEM (Scanning Electron Microscopy) and FIB (Focussed Ion Beam). During rubbing the gold was extruded away from asperities and this resulted in an increase in friction. Moreover, gold wear by ratcheting was also observed. The progressive replacement of gold by the underlying NiP coating resulted in higher friction and wear of the latter. Possible improvement measures for this kind of surfaces could be formulated.