Abstract
Electrochemical machining (ECM) is a cost-effective method for the machining of difficult-to-cut Inconel 718 superalloy. However, the machining accuracy of ECM is still limited by the poor localization effect due to the existence of stray corrosion. In this paper, a mixed solution of neutral NaNO3 and alkaline NaOH is used to improve the localization effect during ECM of Inconel 718. The potentiodynamic polarization curves and current efficiencies for metal dissolution are measured, and the micro morphologies are examined. The results show that the use of an alkaline solution can promote the formation of a compact passive film on the surface of Inconel 718. ECM tests with cylindrical electrodes are specially designed to verify the effect of alkaline solution on the localization of anodic dissolution. The experimental results indicated that the stray corrosion of the non-machined surface of Inconel 718 alloy can be effectively eliminated by using a mixed solution of NaNO3 and NaOH. The surface roughness of the non-machined area can be noticeably improved.
Highlights
Inconel 718 is a type of nickel-based super alloy that has been widely employed in the aerospace industry because of its high-temperature strength
The potentiodynamic polarization curves and current efficiencies for metal dissolution were measured and showed that the use of an alkaline solution can help promote the formation of a compact passive film, and the anodic metal dissolution can be completely eliminated by adding a certain proportion of
Inconel 718 specimens in the form of cuboids of dimensions 5 mm × 5 mm × 8 mm were used for electrochemical analysis and current efficiency measurements, and cylinders of dimensions Φ200 mm × 30 mm were specially prepared for the Electrochemical machining (ECM) tests
Summary
Inconel 718 is a type of nickel-based super alloy that has been widely employed in the aerospace industry because of its high-temperature strength. The nickel-based super alloy Inconel 718 has been found to suffer serious stray corrosion in NaNO3 solution due to the formation of a porous oxide film on the specimen surface, as reported in our previous studies [24,25]. As reported in some studies [26,27], the use of an alkaline solution can help promote the formation of a passive film on the surface during the ECM process. The potentiodynamic polarization curves and current efficiencies for metal dissolution were measured and showed that the use of an alkaline solution can help promote the formation of a compact passive film, and the anodic metal dissolution can be completely eliminated by adding a certain proportion of. The experimental results showed that the non-machined surface of Inconel 718 alloy can be effectively protected by a compact passive film formed in alkaline solution. The anodic dissolution can be effectively localized, and the stray corrosion was eliminated
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