Electrochemical Dissolution Behavior of Haynes 214 Honeycomb Structure in NaNO3 Solutions for Low Current Density Electrochemical Machining

High current density electrochemical machining (ECM) and high temperature corrosion behavior of nickel-based alloys have been well researched, but these works cannot provide reference for precision removal and refurbishment of Haynes 214 honeycomb structure carried out at ambient temperature. Thus, we propose micron-scale removal of the Haynes 214 structure by using the low current density ECM technique at ambient temperature and have systematically investigated the electrochemical dissolution behavior of Haynes 214 alloy under such process conditions. Compared with the NaCl solution, the NaNO3 solution is a preferred electrolyte for electrochemical machining of Haynes 214 due to its good electro-dissolution stability. For Haynes 214 machined in NaNO3 solutions, a low dissolution resistance can be obtained at the concentration of 7 wt.% and temperature of 40 degrees C, and in a current density range of 0.1 similar to 0.5 A.cm(-2), a material removal rate at the micron scale (1.5 similar to 7.5 mu m.min(-1)) is maintained. The breakdown of passive films on the Haynes 214 surface occurs preferentially at grain boundaries. Continuous Al enrichment is found throughout the polarization process. In the transpassive region, a large number of gamma' particles are exposed on the Haynes 214 surface due to the preferential dissolution of gamma matrix. The corrosion products identified by x-ray photoelectron spectroscopy are composed of Ni(OH)(2), Cr2O3, Cr(OH)(3), Al2O3 , Fe2O3, and Fe3O4. This study provides an experimental and theoretical basis for the electrochemical machining of Haynes 214 alloy. The results demonstrate the viability of the proposed method for micron-scale removal of Haynes 214 honeycomb structure at ambient temperature.