Wear-corrosion of nitrided steel: corrosion potential monitoring to evaluate the effect of test parameters

Corrosion and wear are the most destructive processes for a material surface and the combination of these two phenomena causes severe problems in several engineering applications. In order to characterize wear-corrosion resistance in the most appropriate way it is necessary to measure the degradation parameters (weight loss, corrosion rate) during wear testing carried out in an aggressive environment. As a first approach to study the wear-corrosion phenomenon the corrosion potential (E-corr) was used as a diagnostic of the behaviour of the tested material. In this paper the behaviour of a nitrided steel was evaluated. In this study the effects of some working parameters such as rotation speed, applied load and electrolyte type on such electrochemical parameter were analysed. It was shown that E-corr values are noticeably affected by variations in testing conditions because of both fluodynamical changes and wear mechanisms. During wear-corrosion tests, the application of a load allows a remarkable decrease in E-corr which becomes more evident as the load or the rotation speed increase. When the mechanical action is not so severe (low load and low rotation speed) a partial metal "repassivation" can be observed because of the metal interaction with the electrolyte. However potential measurements only allows us to observe qualitative changes in the system. A quantitative evaluation needs to measure the total weight loss and corrosion rate with and without wear.