Assessing the Tribocorrosion Performance of Three Different Nickel-Based Superalloys

Tribocorrosion, which is a material deterioration caused by the synergistic effect of corrosion and wear acting together, is encountered in many engineering applications. Ni-based superalloys, which are widely used in chemical, petrochemical and nuclear power industries as well as in hot sections of turbine engines, owing to their excellent corrosion resistance, high strength and capability to retain hardness at elevated temperatures, are subjected to corrosive wear in service conditions. Therefore, an understanding of the tribocorrosion behavior of these superalloys allows choosing the right material for specified applications and predicting the material damage. In this study, the tribocorrosion behavior of Hastelloy C2000, Hastelloy G35 and Haynes 625 was studied using different electrochemical test techniques including open circuit potential (OCP) measurement, potentiodynamic and potentiostatic polarization tests under sliding contact in 3.5 wt% NaCl solution. Scanning electron microscopy (SEM) was employed in order to characterize corrosive-wear damage, and the surface profiles of wear tracks were obtained using a high-resolution surface profilometer for calculating wear loss. Also the metal dissolution caused by corrosive wear was detected using an inductively coupled plasma optical emission spectrometer (ICP-OES). Test results indicated that the tribocorrosion performance of superalloys is affected by their elemental composition and microstructural characteristics, which induce changes in mechanical properties. Haynes 625, which has the highest hardness value owing to decreasing grain size, showed less material volume loss than other superalloys in all tests. However, the protective oxide film on Haynes 625 especially thickened in potentiodynamic tests provided inhibition of excessive metal dissolution. Cathodic protection resulted in decreasing material loss, but on the other hand hydrogen intake was observed on cathodically polarized specimens.