Tribocorrosion testing of stainless steel (SS) and PVD coated SS using a modified scanning reference electrode technique

A conventional scanning reference electrode technique (SRET) has been modified to provide a novel method for characterising the real-time localised tribocorrosion behaviour of uncoated and physical vapour deposition (PVD) coated samples. The modification was carried out based upon the principle of a ball-on-cylinder contact. Here a sliding probe, in this case a changeable alumina ball, is positioned diametrically opposite a pseudo (Pt) reference electrode probe which is positioned 100 μm away from the surface of a cylindrical specimen which rotates at a set speed. The contact probe, specimen and reference probe are immersed within a chosen electrolyte, which for this study, is aqueous 0.01% NaCl. The dynamic corrosion activity is monitored via the Pt probe by recording variations in ionic flux emanating at the surface of the corroding sample. The SRET can operate in two modes, namely line scan, in which corrosion activity along the circumference of the specimen is measured, or map scan in which a 2D corrosion activity area map of the surface of the specimen is obtained. This paper presents the design, calibration procedures, and real-time tribocorrosion behaviour of uncoated and PVD (C/Cr) coated 316 stainless steel as a function of the contact load, and test conditions. Evidence of the effects of wear damage due to contact by the alumina ball was obtained by monitoring the SRET activity during loading (contact) and unloading conditions. The real-time local tribocorrosion activity can be detected immediately a load was applied. Such activity was found to stop, due to surface repassivation, upon removal of the load (alumina ball). The results show that the applied loads affect the free corrosion potential, local current density, active anodic areas and the sample recovery time of the tested samples. The wear tracks were investigated using optical and scanning electron microscopy and laser profilometer. Correlation of tribocorrosion damage and contact load has been investigated.