Corrosion and wear behavior of ultra-hard Ni-Cr electrodeposits on CK45 steel substrate obtained from Cr(III) based baths

In recent years, attempts have been made to put aside the hard chromium coating due to environmental damage to its plating baths. Due to their low toxicity, the Cr, Ni-Cr, and Cr-Ni coatings produced in the baths containing Cr 3+ ions are perfect substitutes for the hard chromium coatings. In this study, Ni-Cr coatings were created using electroplating, and the effect of formic acid concentration as complexing agents was investigated. Cyclic voltammetry tests studied the electrodeposition mechanism of coatings. The SEM and XRD methods were used to investigate the coatings' microstructure. The pinch-on-disk and potentiodynamic polarization tests were used to study coatings' wear and corrosion behavior. The results of the cyclic voltammetry test showed that increasing the concentration of formic acid resulted in increasing deposition of chromium ions during electrodeposition. Increasing the formic acid concentration in the bath to 30 g/L increased the micro-hardness of coatings to values similar to that obtained for the conventional hard chromium coating. It was due to the formation of chromium carbides during the electrodeposition process, as revealed in XRD patterns of coatings. In this case, the chromium content of the coating increases to 86 weight percent, and the grain size of the coatings is reduced to 40 nm. The coatings' best corrosion and wear resistance was obtained at 30 g/L formic acid in the bath due to the coatings' high hardness and crack-free microstructure.