Dependency of the pulsed electrochemical machining characteristics of Inconel 718 in NaNO3 solution on the pulse current

Pulsed electrochemical machining (PECM) has attracted increasing interest as a technique to improve material dissolution localization and surface quality. This work systematically investigates the effects of pulse current on the surface morphology, profile accuracy, and corrosion behavior of Inconel 718 (IN718) in NaNO3 solution. Polarization behavior reveals that IN718 in NaNO3 solution during pulse current machining exhibited significant passive, transpassive, and re-passive characteristics. The passive film generated at the re-passive state contained some oxides and had a loose porous structure. The critical value for the quantity of electric charge to rupture the passive film was determined to be 26.88 C cm−2. The current efficiency indicates that the material removal rate of IN718 in NaNO3 solution during pulse current machining was nonlinear. The PECM experiments indicate that the loading process of the electrical double layer was prolonged with an increased workpiece scale, i.e., the loading process of the electrical double layer lasted for the entire pulse-on time when the workpiece scale was 100 mm2 at a frequency of more than 10 kHz regardless of the duty cycle. A pulse current with a short pulse length and short pulse period improved the profile accuracy, as did the low applied voltage and small workpiece scale. The dissolution mechanism of IN718 in NaNO3 solution was also investigated based on the effective pulse current time. Finally, the leading-edge structure of a ruled blade with good dimensional accuracy and surface quality was successfully fabricated. The maximum deviations of the machined profile were effectively restricted within 0.057 mm, and the surface roughness was Ra = 0.358 µm.