Mechanical and chemical mechanisms in the tribocorrosion of a Stellite type alloy

The tribocorrosion of a Stellite 21 type alloy sliding against alumina in sulfuric acid was investigated in order to identify relevant degradation mechanisms. Tribocorrosion tests were performed using a reciprocating motion pin-on-plate system operating under potentiostatic conditions as well as open circuit potential under different loadings. Scanning electron microscopy, optical microscopy, laser profilometry and focus ion beam (FIB) were used for characterizing wear pattern and subsurface deformation. Results show that the prevailing electrochemical conditions, and in particular the presence or not of a passive film, crucially affect the tribocorrosion behavior of this alloy. The passive film was found to significantly enhance tribocorrosion damage and this for two reasons: (i) abrasion of the passive film induces wear accelerated corrosion, (ii) the presence of the passive film significantly increases subsurface deformation in the metal and thus mechanical wear. The effect of electrode potential and normal load on the overall degradation by tribocorrosion could be accurately described by the Archard's wear law (taking into consideration the effect of the passive film) and existing models for wear accelerated corrosion.