Decomposition Behavior of Tungsten Carbide in Cemented Carbide Machined by EDM

Cemented carbides are composed of tungsten carbide and cobalt as a binder. Tungsten carbide (WC) can be decomposed into tungsten and carbon at about 620°C in air, and the carbon that separates from WC reacts with oxygen to form carbon dioxide gas. In this study, these phenomena are applied to the electrical discharge machining (EDM) of cemented carbides in deionized water. First, using deionized water as the dielectric working fluid, it is ensured that dissolved oxygen exists in the liquid. Secondly, as EDM is a removal method based on melting and evaporation, the workpiece temperature around the sparking area exceeds the melting point of the material. Therefore, cemented carbides are machined by EDM in deionized water. As a result, it was found that the debris obtained during EDM is composed of tungsten (W) and tungsten oxide (WO3). Moreover, the carbon that separates from WC reacts with the dissolved oxygen in the gap between the electrode and the workpiece to form carbon dioxide gas. Thus, in the EDM of cemented carbides in deionized water, the removal mechanism based on the decomposition of tungsten carbide is in effect as well as that based on melting and evaporation.