Effects of external D. C. electric fields on friction and wear behavior of alumina/brass sliding pairs

Abstract

A plate/plate type test rig, in which one end face of the alumina cylinder test piece rubs reciprocally against a static brass plate at a low speed, was developed for measuring friction coefficient and weight loss under different electric field conditions. Emulsion of 1wt% zinc stearate dispersed in deionized water was used as lubricant in the experiments. Experiment results show that the friction coefficient can be obviously affected by the presence of positive voltages (the voltages in which the lower specimen was used as cathode were called positive voltages or “+” voltages, while the voltages with a reverse polarity were called negative voltages or “−” voltages). A+20D. C. V. voltage can lead to a dramatic increase of friction coefficient by up to 200%. When the external voltage is turned on and off periodically, the friction coefficient goes up and down almost synchronously. The average response time is 1 min. The preliminary analytic results imply that the equilibrium between the generation and destruction of the boundary films composed of stearate on the sliding surface was changed by the applied external electric fields. By consideration of the dramatic increase of friction coefficient and the rapid response to the external voltage, it is expected that active controlling of friction coefficient by external electric fields is feasible.