Electrochemical dissolution behavior of phosphorus and boron doped Inconel 718 alloy in NaNO3 solution

Abstract

As a promising material for the blisk of high-pressure compressors in aeroengines, modified Inconel 718 (IN718) alloy with phosphorus and boron additions is a new derivative of IN718 with higher temperature capabilities. Herein, electrochemical tests and electrochemical machining (ECM) experiments of the modified IN718 alloy in NaNO3 solution were conducted to investigate the electrochemical dissolution behavior. Microstructure and microtexture analysis revealed that modified IN718 fabricated by forging mainly comprises γ phase, carbide, and δ phase, and its grain size distribution is uneven. Furthermore, the anodic behavior of the modified IN718 alloy in NaNO3 solution was investigated by the polarization curve and electrochemical impedance spectroscopy. The results show that an uneven passivation film forms on the surface of modified IN718 due to the inhomogeneous grain size, which reduces the corrosion resistance. Then, ECM experiments at different corrosion times (1 s, 3 s,5 s, 7 s) and current densities (50 A/cm2, 100 A/cm2, 130 A/cm2, 160 A/cm2) were conducted. The results show that the δ phase existed like a needle-plate and the machined surface quality was poor. The corrosion resistance of the fine grains and δ phase was better than that of the coarse grains, which is the main factor influencing the surface quality. Finally, dissolution models were proposed to characterize the dissolution behavior of modified IN718 in NaNO3 solution.