Electrochemical machining (ECM) is characterized amongst other things, by extremely high current densities and a high dissolution rate of material. Due to the extreme current densities under ECM conditions, tungsten carbide forms adherent, supersaturated, viscous films of polytungstates close to the interface. This film is permanently dissolved by electrolyte flow and is reproduced at the electrode surface. The dissolution proceeds in an active state up to 30 A cm−2. An additional layer is formed at higher current densities which means that there is a passive state and the presence of high-field oxide films with thicknesses around 10 nm. The complex interaction between current, field strength, and oxide thickness yields a constant resistance to the oxide film. The formation of an oxide film is also indicated by the onset of oxygen evolution which consumes about 20% of anodic charge. The interaction of ionic currents (oxide formation and dissolution) and electronic currents (oxygen evolution) is small due to completely different conduction mechanisms
Cover: The cover shows an illustration of the experimental set up for in‐situ investigations of the anodic metal dissolution under ECM conditionsA specially designed channel flow cell is placed under an optical microscope with long distance lens. A gold disc with a small conical glass lens in the centre is embedded in the glass lid of the channel flow cell and works as cathode. The sample is placed beneath the cathode and works as anode. The gap width of the channel amounts 0.35mm. A maximum electrolyte flow rate of 12.3m/s was realized. The anodic dissolution was carried out by current controlled pulses. The test assembly allows the observation of the surface topography development of the anode as well as possible interface reactions (e.g. gas evolution). More detailed information can be found in: M. Schneider, S. Schroth, N. Schubert, A. Michaelis, In‐situ investigation of the surface‐topography during anodic dissolution of copper under near‐ECM conditions, Materials and Corrosion 2012, 63, 96.
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