Effects of processing parameters on the surface quality of wrought Ni-based superalloy by ultrasonic-assisted electrochemical grinding

Ni-based GH625 superalloy has been widely employed in the aerospace industry due to its high strength, outstanding corrosion resistance, and high-temperature resistance. A novel hybrid processing method of ultrasonic-assisted electrochemical grinding (UAECG) can achieve a high effective removal rate for difficult-to-process materials and thereby avoid stray corrosion during the process. This study systematically investigated the electrochemical dissolution behaviors of GH625 alloy at low current density and the effects of processing parameters on its surface roughness. A qualitative model was proposed to further reveal its removal mechanism for GH625 alloy during the UAECG process. Polarization curves depicted that an efficient and stable electrochemical dissolution was achieved at an appropriate temperature (20 °C) and concentration (10 wt.%) of NaNO3 electrolyte. The findings also revealed that selective corrosion preferentially occurred on the grain boundary or near the NbC carbides under different current density corrosion circumstances. Compared with the ECG process, the excellent surface quality (Ra = 0.37 μm) and taper of the small holes (taper = 0.04 ± 0.005°) are obtained at the optimized condition of a pulse voltage of 5.8 V, feed rate of 0.6 mm/min, cathode speed of 12 kr/min and drive amplitude of 60% by UAECG technology.