ECM of tungsten carbide in ammoniacal solution - investigation of anodic dissolution

The present work is focused on the electrochemical behaviour of tungsten carbide in alkaline ammoniacal electrolytes under near-ECM conditions. Potentiodynamic measurements were carried out in sodium nitrate electrolytes with various concentration of NH3. It could be shown that the concentration of NH3 is of fundamental importance on the machining process of WC in alkaline solutions. Additionally, galvanostatic pulse experiments coupled with uv/vis analysis of the waste electrolyte demonstrates the high current efficiency of the machining under the chosen condition. The authors have been shown that WC can be electrochemically machined in alkaline electrolyte mixtures of ammonia and sodium nitrate. The dissolution starts in the active range. However, a high overvoltage is necessary to initi alize the process of the anodic dissolution. The dissolution kinetic changes from the active dissolution to a limited dissolution controlled by an oxide formation dependent on the ammonia concentration. Nevertheless, the current efficiency is between 96 and 100%. The authors assume the existence of a metastable oxide film. The removal rate is determined by the chemical dissolution of this oxide film. Summarizing, the authors are confident to have a suitable electrolyte for homogenous dissolution of cemented carbide as well.