High current density copper-on-copper sliding electrical contacts at low sliding velocities

Metal fiber brushes are of interest in many high current density applications due to their high conductivity and low wear rates in humid environments. The frictional properties and wear behavior of a copper fiber brush sliding against a copper counterface in humid environments under high current densities (180 A/cm2) were investigated at low sliding velocities (10 mm/s). A linear reciprocating tribometer integrated with a scanning white light interferometer was used to acquire volume loss measurements of the copper counterface. Counterface wear was found to be independent of both the direction of current flow and the presence of current. X-ray photoelectron spectroscopy (XPS) showed carbonate species in all wear tracks after testing in humidified carbon dioxide. Only slight differences in the relative amounts of oxide on the counterface wear tracks were observed. Effects of water adsorption on friction coefficient and contact resistance were studied by varying the temperature of the counterface while maintaining a constant ambient temperature and humidity in carbon dioxide and argon environments. As sample temperature increased above the ambient temperature, both friction coefficient and contact resistance increased. Friction coefficient was lower for the carbon dioxide environment, which may be related to the presence of the carbonate species in the wear track region.