Self-generated voltages and their relationship to wear under boundary lubricated conditions

A program has been carried out to determine the relationship which exists between Self-Generated Voltages and wear under Boundary Lubricated Conditions. The observation that voltages are generated between wearing members is shown to be unrelated to such factors as fluid conductivity or fluid viscosity. These voltages are shown to be associated with the wear process itself. A relationship has, indeed, been obtained between wear and Self-Generated Voltages and has been found for both a steel-on-steel system and an aluminum-on-steel system under dry air blanketing. Under these conditions, at low wear, the measured voltages are several millivolts in magnitude, and they decrease as wear increases. A preliminary mechanism to explain how the voltages are generated under the Boundary Lubricated Conditions is discussed. It is suggested that there are two fundamental electrochemical processes which occur under conditions of Boundary Lubrication and wear. One is an electron transfer process involving the shifting of a near surface electron from the metal to an adsorbed surface layer. The other is an oxidation process in which the metal surface is chemically oxidized while another species is chemically reduced. The Self-Generated Voltages and the relative changes in their magnitude and polarity are determined by the relative importance of the above noted processes under the test conditions.