Optimizing and understanding dry-electropolishing process on WC-Co cemented carbide material

Abstract

Dry-electropolishing (DEP) combines an electrochemical process with soft-mechanical abrasion by using porous ion-exchange particles (also known as dry-electrolyte). In recent years, it has been satisfactorily implemented for reducing surfaces defects, decreasing roughness, and obtaining smooth surface finish in several metallic and ceramic-metal composites. However, it requires a preliminary adjustment of DEP parameters in order to increase the polishing efficiency and avoid pitting or general corrosion issues. Moreover, there is a lack of information concerning the precise material removal mechanisms, this being particularly true for multiphase materials. In that sense, the main objectives of this study are to optimize the electrical parameters as well as to understand the main microstructural and chemical changes behind the DEP process on WC-Co. It is done by implementing several advanced characterization techniques: scanning electron microscopy, X-ray photoelectron spectroscopy and energy-dispersive X-ray spectroscopy. The results demonstrate that optimal electrical parameters in terms of planarity between constitutive phases, average roughness reduction and leaching-free microstructure can be achieved when utilizing a pulse/pulse reverse waveform in comparison to direct current or pulsed current. Optimization using a matrix of electrical parameters is proven to be a useful tool to focus on the results, these being when voltage and time of negative pulse applied higher values than the positive ones. Additionally, it is shown that the chemical compounds generated on the WC-Co surface are meanly Co₃O₄, Co(OH)₂ and WO₃. Material removal combines electrochemical process and also soft-mechanical actions, where particles contact oxides generated on the treated surface. The removed material mainly consists of W oxide, as Co passivates and has a low oxidation rate combined with its low content. To sum up, the corresponding analysis allows to get a deeper understanding of DEP along the roughness removal process as well as to give guidelines for optimizing its operative parameters for its application in multiphase ceramic/metal materials.