Electrochemical machining of the steel 100Cr6 in aqueous NaCl and NaNO3 solutions:: microstructure of surface films formed by carbides

Application of electrochemical machining in microsystem technologies has to take into account the role of microscopic heterogeneities of steel, e.g. of carbides. Therefore, the anodic metal dissolution of the alloyed carbon steel 100Cr6 was investigated in NaCl and NaNO3 electrolytes. In flow channel experiments, high current densities up to 70 A/cm(2) and turbulent electrolyte flow velocities were applied. Insoluble carbide particles cause an apparent current efficiency > 100% in NaCl and > 67% in NaNO3. These particles are enriched at the surface in NaCl solution and detected by ex situ scanning electron microscopy and energy dispersive X-ray experiments. Auger electron spectroscopy, in combination with sputter depth profiling, was used to determine the film composition resulting from the NaNO3 process. This proves the enrichment of carbide particles not vet separated from the surrounding steel. Qualitative metal dissolution models on the basis of the experimental results were proposed for the metal dissolution processes in the NaCl and NaNO3 electrolytes. (C) 2001 Elsevier Science Ltd. All rights reserved.