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. o f carbides. Therefore, the anodic metal dissolution of the alloyed carbon s teel 100Cr6 was investigated in NaCl and NaNO3 electrolytes. In flow channe l experiments, high current densities up to 70 A/cm(2) and turbulent electr olyte flow velocities were applied. Insoluble carbide particles cause an ap parent current efficiency > 100% in NaCl and > 67% in NaNO3. These particle s are enriched at the surface in NaCl solution and detected by ex situ scan ning electron microscopy and energy dispersive X-ray experiments. Auger ele ctron spectroscopy, in combination with sputter depth profiling, was used t o determine the film composition resulting from the NaNO3 process. This pro ves the enrichment of carbide particles not vet separated from the surround ing steel. Qualitative metal dissolution models on the basis of the experim ental results were proposed for the metal dissolution processes in the NaCl and NaNO3 electrolytes. (C) 2001 Elsevier Science Ltd. All rights reserved .