Anodic electrochemical behaviors of Inconel 718 and Rene 65 alloys in NaNO3 solution

Studying the behavior of anode materials during their electrochemical dissolution is the premise for and key to their electrochemical machining (ECM). In this study, electrochemical tests and ECM experiments on the Inconel 718 (IN718) and Rene 65 (R65) alloys in a 20 wt% NaNO3 solution were conducted to investigate their behaviors during anodic electrochemical dissolution. The passivation-related behaviors and structures of the interface of the two materials were measured based on the curves of potentiodynamic polarization and EIS. Information on the growth and composition of the passive film was obtained by potentiostatic polarization and XPS. The results showed that compared with IN718, the structure of the passive film on the surface of R65 was loose and unstable such that it had a weak resistance to corrosion. ECM tests were performed under different current densities, and the morphology of dissolution was identified. The grain boundaries of IN718 were completely exposed in the dissolved surface, and it had a lower surface roughness than R65. For R65, a high current density was conducive to the removal of blocky protrusions and lath structures. Finally, a model of dissolution is proposed to characterize the behaviors of IN718 and R65 during electrochemical dissolution.