Wear-accelerated corrosion of passive metals in tribocorrosion systems

A model is presented which describes the effect of mechanical and materials parameters on the wear-assisted corrosion rate of passive metals under sliding wear conditions. The model is based on a consideration of contact between the sliding surfaces at multiple asperities and it takes into account the passivation behavior of the metal. Wear experiments were carried out in a reciprocating pin-on-plate tribometer permitting the control of mechanical and electrochemical conditions. An alumina pin was rubbed on nickel, chromium, stainless steel, and titanium alloy plates, in sulfuric acid or sodium sulfate solution. The relative importance of mechanical and electrochemical metal removal was evaluated while applying an anodic potential. Additional experiments were performed under cathodic polarization. The results show that the proposed model can describe correctly the effect on dissolution rate of different mechanical parameters such as applied normal force, stroke length, frequency, and sliding speed. Qualitative agreement was observed with the predicted effect of the materials parameters hardness and passivation charge, but uncertainties concerning the real value of passivation charge and, in some cases, wear of the alumina pin limit the predictive capability of the model when comparing different materials. The experimental results obtained in this study demonstrate that to understand the mutual interactions between mechanical and electrochemical parameters affecting wear-accelerated corrosion it is necessary to look: at the tribocorrosion system as a whole.