Modeling Current Transients in a Reciprocal Motion Tribocorrosion Experiment

Tribocorrosion of passivating metals is a dynamic phenomenon causing degradation of materials by a combination of mechanical wear and electrochemical dissolution. The mechanical action typically produces a local removal of particles, metal as well as oxides, resulting in an exposure of the metal surface and is followed by a repassivation process, of which the time-dependent current response is a direct measure. Kinetics for interface-limited film growth were used to find an analytical expression for the current transients, including the conductivity of the electrolyte as well as the contribution from the confined geometry within the mechanical contact. The solution gave a good experimental fit to a series of experiments with a range of electrolyte conductivities, and also to correlate well with values obtained using electrochemical impedance spectroscopy. Parameters from the rubbing experiment were used to calculate curves that compared well with passivation transients recorded on a bare metal surface for the same electrolyte series. The evaluation procedure made it possible to assess the relative resistance contributions from the growing passive film, the confined mechanical contact geometry, and the electrolyte.