Obtaining High Surface Quality in Electrochemical Machining of TC17 Titanium Alloy and Inconel 718 with High Current Densities in NaNO3 Solution

Electrochemical machining (ECM) is a very promising technology for the processing of titanium alloys (such as TC17) due to its many inherent advantages. Halogen electrolytes are commonly used in ECM of such alloys, but this often results in unwanted stray corrosion and poor surface quality. In this study, a processing mode of titanium alloy in NaNO3 solution with high current density is proposed. Inconel 718 is used for comparison with TC17. The passive characteristics of the sample are analyzed by polarization curves and electrochemical impedance spectroscopy. The results show that TC17 has a high breakdown potential and the structure of its passive film is more compact than Inconel 718. The corresponding schematic model is established to characterize the interface structure between the sample's surface and passive film. The effects of current density on surface microstructure and surface quality are investigated. It is found that the α phase has a faster electrochemical dissolution rate than the β phase for TC17, and it can obtain a good surface quality (about Ra 0.69 μm) when the current density reaches 160 A cm−2. Finally, the corresponding dissolution model is established to characterize the electrochemical dissolution mechanism of the sample in NaNO3 solution at high current density.