A Preparation and Characterization of Crack-free Chromium Coating by Direct and Pulse Reverse Electroplating of Hexavalent Chromium

초록

Electroplated chromium coating has been applied in many industrial applications using its functional properties which benefit from the high levels of hardness, wear and corrosion resistance. However, the coating layer exhibits extensive micro-crack on the surface due to the internal stress induced by electroplating which results in poor corrosion resistance. In this study, we introduced pulse reverse electroplating method as an attempt to reduce micro-crack on surface of the coating layer, leading to improved corrosion resistance. All samples were electroplated by pulse reverse current method in a Sargent bath with HY-30. The structure and morphology of the chromium deposits were investigated by X-ray diffraction (XRD) and scanning electron microscope (SEM), respectively. The surface oxidation states of the samples were examined by X-ray photoelectron spectroscopy (XPS). The mechanical properties of the chromium coatings were characterized by pencil hardness tester. The current efficiency was determined by measuring the weight difference between before and after electroplating. The corrosion resistance of electroplated samples was evaluated using potentiodynamic polarization in 5.0 wt.% NaCl solution.