Abstract
Electrochemical machining (ECM) is a proven processing technique for fabricating difficult-to-cut nickel-based superalloys with complex shapes using the principle of anodic dissolution. However, the metallic surface is susceptible to stray corrosion under conditions of low current density, which increases the difficulty of using ECM on nickel-based superalloy such as Hastelloy X (HX). In this study the electrochemical dissolution behavior of wrought HX at low current density was systematically analyzed. The results revealed that M23C6 carbides were irregularly distributed on the grain boundaries. The polarization curves and open-circuit potential measurements showed that an appropriate temperature (35°C) and concentration (10 wt.%) aided in the formation of efficient and stable dissolution in NaNO3 solution. The findings also revealed that selective corrosion occurred preferentially on the grain boundary or near the M23C6 precipitations after passivation film polarization. After careful investigation of the different-stage dissolution microstructures and the solid black block-shape products, M23C6 precipitation was found to play a key role in the dissolution of HX alloy at low current density. A qualitative model was established to demonstrate the electrochemical dissolution behavior of wrought HX alloy in NaNO3 solution. This model offers a new insight into the suppression of stray corrosion of Ni-based superalloys in aerospace applications.
Highlights
Electrochemical machining (ECM) is an advanced technology for shaping difficult-to-machine materials
This is consistent with the results reported in previous studies by Kinzel et al, which were obtained by scanning electron microscopy (SEM) and atom probe tomography (APT) [31]–[33]
The microstructure characteristics were systematically examined in the present study
Summary
Electrochemical machining (ECM) is an advanced technology for shaping difficult-to-machine materials It employs the dissolution of anodic metals and thereby bypasses the limitations of the alloy’s mechanical properties [1], [2]. Y. Yin et al.: Electrochemical Dissolution Behavior of Nickel-Based HX Superalloy at Low Current Densities flow rate on the machining accuracy of Inconel 718 can contribute to the formation of uniform contour of the hole [19]. Anodic dissolution behavior is a part of the guiding theories in ECM, whereas stray corrosion at low current densities affects the machining accuracy during the ECM process. It is necessary to systematically investigate the correlation between microstructure and dissolution behavior at low current density, which may offer theoretical guidance to avoid stray corrosion in ECM process. The electrochemical tests were conducted 3 times for each sample to ensure consistency
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