Investigation of the stray corrosion of Inconel 718 at low current density in NaNO3 solution

Abstract

Abstract Surface integrity and machining accuracy have important effects on the fatigue life of blisk. During the electrochemical machining (ECM) of blisk, the blade is processed piece by piece. The machined blade profile is exposed to the electric field under low current density and is corroded when the next blade is processed. To investigate stray corrosion during the ECM of blisk, we analyzed the ηω–icurve of Inconel 718 and found that Inconel 718 continues to dissolve at very low current density. We then established a mathematical model of the stray corrosion of blisk in consideration of the electric field factor. Numerical simulations demonstrated that stray corrosion occurs during the ECM of blisk when the machining gap is large (> 1 mm). In a basic experimental investigation of the stray corrosion of Inconel 718, when the machining gap reached 40 mm, the machining time was 220 s, and the amount of corrosion was 0.033 mm. We also carried out ECM experiments with and without protecting the blade from attack by stray current using electrical insulation tape. The maximum corrosion amount of the machined blade was 0.035 mm without protection. In contrast, the protected machined blade was not corroded, and protection enhanced the accuracy and quality of the blisk blade ECM profile.