Crack-free chromium coating using direct current and pulse-reverse electroplating method

초록

Abstract Objective: Electroplated chromium coating was widely used in decorative covering and engineering purposes using its high anti-corrosion behavior. However, electroplated chromium coating layer generated a lot of cracks on surface are generated during electroplating due to internal stress, leading to low corrosion resistance. In this study, we proposed a pulse reverse (PR) electroplating method to reduce micro-crack on surface of the coated layer, in order to improve corrosion resistance. Method: All samples were electroplated in a Sargent bath with HY-30 using direct-current and pulse-reverse electroplating method. The structure and hardness of the chromium coating were characterized by X-ray diffraction (XRD) and pencil hardness tester, respectively. The morphology of coating was investigated by scanning electron microscope (SEM). The surface composition of samples was determined by X-ray photoelectron spectroscopy (XPS). The corrosion resistance of electroplated samples was evaluated using potentiodynamic polarization in a 5.0 wt.% NaCl solution. Result: The surface of electroplated Chromium was composed of Cr2O3, CrO3, Cr(OH)3, Cr metal, and Cr3C2. Whereas the hardness of PR method was HB-2H of the pencil hardness, the hardness of DC method was 3H-4H. The difference of hardness was probably related to difference in crystal size, roughness and composition of the film. Conclusion: The Cr electroplating using DC and PR method was successfully conducted in sargent bath. The film deposited by PR method showed rough and particle-like morphologies. In case of DC, flat surface was observed. However, the surface of PR electroplating method exhibited crack free chromium compared with that of the DC method.