Electrodeposition of High-bright and Hard Cr-C Layers with High-current Efficiency from Chromium(III) Sulfate/Organic Additives Aqueous Baths

This study was conducted to improve four characteristics as objectives:（1） high current efficiency, （2） high surface brightness, and （3） high hardness of chromium-carbon （Cr-C） alloy layers during electrochemical deposition from Cr（III） ions, and （4） reproducibility of the Cr-C layer formation during repeated plating with a Cr-C electroplating bath. A malonic-acid-containing sulfuric acid bath （sulfuric acid bath II） was prepared by adding an arrangement to a conventional sulfuric acid bath （sulfuric acid bath I）. The malonic-acid-containing sulfuric acid bath II achieves the four objectives. Optimizing the bath composition and the electrochemical deposition conditions of the sulfuric acid bath II containing malonic acid was accomplished with a 0.2 M added malonic acid concentration, a 1.5 pH bath, and 33.4 A dm－2 plating current density. The current efficiency under these optimized conditions was 55.9%. Also, the C co-deposition percentage was 39.7%. Using a plating bath with a sulfuric acid bath II containing 0.2 M malonic acid, testing for the Cr-C layer reproducibility was performed repeatedly when plating: both the current efficiency and the C co-deposition percentage continued to be greater than 55% and 39%, respectively. However, the surface uniformity of the Cr-C layer tended to decrease after the fifth plating. Comparison of the surface brightness with that achieved using conventional baths demonstrated that the 0.2 M malonic-acid-containing sulfuric acid bath II was able to maintain high brightness.