Ni-Co-B nanocrystalline alloy electrodeposition for substituting hard chromium

To solve the problem of serious environmental pollution from electroplating chromium process, electroplating Ni-Co-B alloy coatings, which are environment-friendly and with good appearance, were prepared to substitute the hard chromium coating. The effects of electrolyte solution composition and process conditions on the microhardness, appearance, deposition rate of the coatings and current efficiency of the cathode were discussed by single factor experiments. Relatively better compositions of the electrolyte and process conditions were gained. The effects of different heat treatment temperatures on the microhardness of the coatings prepared under the optimized condition were measured. The polarization of electrolyte was analyzed. The surface morphology, microstructure and corrosion resistance of the coatings before and after heat treatment at 200°C for 1 h were characterized. The results show that alloy coatings prepared under the optimized condition are nanocrystalline structure, bright and uniform in macrography, smooth and seamless in micrography. After heat treatment, the grain sizes of coatings slightly increase because of recrystallization, the surfaces become more compact, and the microhardness can be up to 10.875 GPa, which is higher than that of hard chromium coating. Also, the corrosion resistance of alloy coatings after heat treatment is roughly equivalent to that of hard chromium coating. So, this electroplating process is expected to replace the hard chromium plating technology and be widely applied.