INFLUENCE OF POTENTIAL ON THE FRICTION AND WEAR OF MILD-STEEL IN A MODEL AQUEOUS LUBRICANT

An electrochemical cell has been designed, based on a Cameron-Plint fr iction machine, which enables measurement of friction and wear under c onditions of controlled potential. For mild steel in a pH 9 aqueous so lution of sodium octanoate, varying the potential of the steel over th e range - 1 to + 1 V vs SHE produced three distinct friction-wear regi mes: high friction/low wear, low friction/high wear, and low friction/ low wear. These regimes were ascribed to potential dependent changes i n the coverage and stability of a lubricating octanoate film on the su rface of the steel. Increasing the contact stress amplified the effect of potential on wear, and confirmed that the surface film retained it s lubricity at contact stresses capable of causing plastic deformation of the steel.