Electrochemical dissolution behavior of Inconel 718 alloy in NaNO3 solution: A comparison between wrought and cast

Abstract

Cast IN718 and wrought IN718 are highly capable materials for blisks in aeroengines, owing to their high-temperature capabilities. Understanding their anodic electrochemical behavior is crucial for electrochemical machining (ECM) applications. In this study, electrochemical tests and ECM experiments were conducted on both cast IN718 and wrought IN718 alloys in a 10 wt% NaNO3 solution to explore their passivation-related behaviors and interface structures. The investigation included analysis via open circuit potential, polarization curve, and electrochemical impedance spectroscopy (EIS). Results indicate that compared to wrought IN718, the passive layer formed on cast IN718 surfaces contains numerous pores, rendering the corrosion resistance of cast IN718 less challenging in the 10 wt% NaNO3 environment. Additionally, X-ray photoelectron spectroscopy (XPS) was used to characterize the chemical composition of the passive layer. The analysis revealed that the passive layer on both cast and wrought IN718 surfaces primarily consisted of NiO, Ni(OH)2, Cr2O3, CrO3, Fe3O4, α-FeOOH, γ-Fe2O3, Fe2O3, NbO, Nb2O5, MoO2, and MoO3. Notably, the passive layer on cast IN718 was richer in NiO and lacked Cr2O3 and MoO3, which supports its porous and loose structures. Furthermore, ECM experiments were conducted at various current densities (1, 4, 8, and 15 A·cm−2) to identify the dissolution morphology. The results revealed several pitting pits on the machined surface of cast IN718 at low current densities, with lower surface roughness compared to wrought IN718. Conversely, for wrought IN718, the presence of needle-like structures dispersed on the machined surface improved substantially as the current density increased, significantly influencing surface quality.