Binary potential loop electrodeposition and corrosion resistance of cr coatings

Abstract

This work aims to electrodeposit Cr from a solution containing only Cr3+ ions but not any other complexing, buffering and pH agents, and study its corrosion behavior. The solution was investigated by cyclic voltammetry and ultraviolet-visible spectroscopy. It was obtained that it is rich in native Cr complexes including Cl. Cr was successfully coated from this solution by binary potential loop electrodeposition. First, - 0.7 V potential was applied for a time interval ranging from 5 to 30 s. Then, a - 1.8 V potential was applied to deposit the Cr layer with the thickness changed from 50 to 1000 nm. X-ray diffraction patterns showed that all films are in a bcc crystal structure. The Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy and optical profilometry measurements inferred that the coatings include hydrated-Cl complexes mostly edges of the coating and cracks. The scanning electron microscopy images indicated that the cracks on the surface are tiny for the layers thinner than 500 nm but prominent for the layers thicker than 500 nm. The corrosion behavior was examined by electrochemical impedance spectroscopy and Tafel measurements. The coatings electrodeposited by the binary potential loop had a corrosion rate lower and resistance higher than those of the coatings electrodeposited at - 1.8 V potential. The corrosion parameters became superior for the coatings with layers thinner than 500 nm and the aged ones.