LAUSR

Abstract The tribological and conductive properties of current-carrying rolling pairs were investigated in humid air and water drops. As the environment changes from a very low RH atmosphere (10% relative humidity) to liquid water, current-carrying friction coefficient increased from 0.14 to 1.03. It is speculated that current-induced adhesion, meniscus force and current-induced meniscus force can provide additional friction force. With the increasing of the friction coefficient, the wear mechanism current-carrying pairs transforms from adhesive and abrasive wear to severe fatigue wear. When water changes from a gaseous state to a liquid state, the form of fatigue changes from scale to spalling because of pressurization effect. X-ray photoelectron spectroscopy (XPS) analysis shows that water is advantageous to tribo-oxidation and electrochemical oxidation, resulting in the formation of CuO. The weakening effect of oxidation on the electrical conductivity can be illustrated by contact resistance and conductive atomic force microscopy (CAFM) map. The paper reported the mechanical and chemical effects on the current-carrying contact pairs in wet conditions, which could be very helpful in understanding on water-involved surface damage and oxidation.