Electrochemical noise analysis of tribocorrosion processes under steady-state friction regime

Tribocorrosion processes of austenitic stainless steel in a medium close to that used in pressurized water reactor nuclear plants have been investigated using electrochemical impedance and noise measurements. The experiments were carried out under a steady-state friction regime yielded by the continuous circular displacement of a fretting probe against a large disk electrode. Finite-element-method simulations of the current distribution in a conventional three-electrode cell showed that a significant part of the anodic current generated by the film removal and surface repassivation at the wear track does not flow to the counter electrode and, therefore, is not measured by the potentiostat. A specific arrangement with two working electrodes, a small disk electrode inserted at the center of the large one and electrically isolated from it, was devised to monitor the anodic current induced by the tribocorrosion process. Results have shown that only a small part of the current lines flows to the central region connected through the zero-resistance ammeter. In spite of this, the power spectral density of the current fuctuations generated at the wear track could be estimated, provided that the impedances of the two working electrodes have been previously measured.