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 the high-effective removal rate for difficult-to-process materials and thereby avoids the stray corrosion during the process. This study systematically investigated the electrochemical dissolution behaviors of GH625 alloy at low current density and effects of processing parameters on its surface roughness. A qualitative model was proposed to further reveal its removal mechanism for GH625 alloy during 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 NaNO 3 electrolyte. The findings also revealed that selective corrosion preferentially occurred on the grain boundary or near the NbC carbides under different current density corrosion circumstance. Compared with ECG process, the excellent surface quality ( R a = 0.37 μm) and taper of the small holes (taper = 0.04 ±0.005°) are obtained at the optimized condition of pulse voltage of 5.8V, feed rate of 0.6mm /min, cathode speed of 12kr /min and ultrasonic drive amplitude of 60 % by UAECG technology.

Effect of the Al2O3 powder addition on the metal removal rate and the surface roughness of the electrochemical grinding machining

The integrated electrochemical grinding machining has received wide acceptance in the aircraft turbine industry for the machining of blades, vanes, and honeycomb seal rings. Also, medical devices, instruments and forceps, shells, precision nozzles, instrument coupling, and air rotor motors that produced from stainless steel and new materials have all successfully been accomplished with electrochemical grinding. To improve the metal removal rate and to reduce the surface roughness ( Ra) of the electrochemical grinding at high voltages, an integration between the alumina abrasive jet and the electrochemical grinding machining has been performed. The effect of the Al2O3 abrasive content on the metal removal rate and the Ra of the K110 alloy steel using Everite electrochemical grinding 618 at different voltages, different feed rates, different electrolyte NaCl concentrations, and different depths of the cut were successfully investigated. The results revealed that the abrasive electrochemical grinding was better than the electrochemical grinding results. The maximum effect of the Al2O3 on the metal removal rate was achieved at 5 wt.%. The current density in the machining gap was affected by the addition of the Al2O3, where it was decreased at percentages over 5-wt.% Al2O3. The abrasive electrochemical grinding resulted in lower surface roughness than the electrochemical grinding process.