A new experimental technique for quantifying the galvanic coupling effects on stainless steel during tribocorrosion under equilibrium conditions

Abstract

Galvanic coupling during tribocorrosion of passive metals at open circuit potential (OCP) generates a wear-accelerated corrosion process within the depassivated area (worn surface) that is electrically in contact with the still passive one. The galvanic coupling effect at OCP was recently modeled using an electrochemical approach allowing for the theoretical quantification of the wear-accelerated corrosion under equilibrium conditions. Despite the usefulness of this model that mathematically determines the electrochemical conditions inside the wear track in terms of anode potential via the approximation of the net anodic current density, an experimental technique allowing for their experimental determination is essential in the effort to verify the galvanic coupling models and further understand the tribocorrosion mechanisms at OCP. In the present work, a new experimental technique based on galvanic current and potential measurements through a Zero-Resistance Ammeter (ZRA) for quantifying the electrode potential and anodic current inside the wear track during rubbing at OCP has been assessed. This experimental set-up has allowed for the first time to determine the prevailing electrochemical conditions (electrode potential and anodic current) inside the wear track by solely exposing the wear track to the electrolyte and physically separating the cathode from the anode (wear track). The effects of sliding wear at open circuit potential have been investigated for a super duplex stainless steel (UNS S32750) in 3.4 wt% NaCl. The new experimental set-up proposed in this work separates the cathode from the anode and exposes solely the wear track to the electrolyte. Using well-established electrochemical theories, the effect of the extent of the galvanic coupling on wear at the open circuit potential conditions has been quantified.