Mitigating the Effects of Stray-Current Attack on Non-Machined Surfaces in Electrochemical Machining Through Gas-Shielding in C6H5K3O7 Solution

Abstract

Electrochemical machining (ECM) is a promising method for processing the leading and trailing edges of the blades that are composed of nickel-based superalloys (Inconel 718), but often leads to unwanted stray corrosion on non-machined surfaces. This study investigates the use of a novel C6H5K3O7 solution to fabricate the leading and trailing edges of the blade that is free of stray corrosion. First, the basic electrochemical dissolution behavior of Inconel 718 in the C6H5K3O7 solution is analyzed in comparison with that in NaNO3 solution by means of a potentiodynamic polarization. The results showed that Inconel 718 in the C6H5K3O7 solution has a lower breakdown potential and the structure of its passive film was looser than that in the NaNO3 solution. Second, the current efficiency of Inconel 718 in the C6H5K3O7 solution exhibited non-linear dissolution behavior, and the material removal rate was much lower than that in the NaNO3 solution. In-situ observations indicated that a stable and continuous insulating gaseous layer was induced surrounding the anode surface through C6H5K3O7 solution to suppress the stray-current attack on the non-machined surfaces. Third, corresponding models and simulations of ECM process in the C6H5K3O7 solution were formulated to examine the effects of gaseous layer on stray corrosion. Fourth, the effects of the parameters of pulse processing on stray corrosion on the non-machined surfaces was analyzed. Experimental results showed that the self-induced gaseous layer could suppress stray machining by insulation effect, and a pulsed current with a short-pulse duration and a high-pulse frequencies was helpful for reducing the zones of stray corrosion. Precise structure of the leading/trailing edges of the twisted blade free of stray corrosion were successfully fabricated in the C6H5K3O7 solution. In comparison with that manufactured in the NaNO3 solution, the zones of stray corrosion was reduced by 8.4 times under the same processing parameters. The results here verify the feasibility of C6H5K3O7 as an electrolyte to reduce the stray-current attack on non-machined surfaces.