Cr-C alloy coatings were electrodeposited from a trivalent chromium bath containing formic acid on copper substrate. The coating had amorphous structure with a homogeneous granular morphology containing cracks. The effects of plating parameters such as pH and current density on composition, structure, morphology and corrosion behavior of as-deposited coatings were investigated. Results showed that the suitable current density for Cr-C alloy deposition is increased as the pH is decreased. Furthermore, by decreasing the pH, higher amount of carbon was introduced into the coatings. The Cr-C alloy coatings deposited at lower pH showed higher passive current density. By annealing the amorphous Cr-C alloy coatings at 300 o C, a nanocrystalline structure, having higher hardness was obtained. However, the corrosion resistance was seen to be impaired. Annealing at 600 o C led to the precipitation of Cr 23 C 6 which resulted in a higher hardness. The formation of Cr 23 C 6 enhanced the corrosion resistance of coatings due to an increase of corrosion potential. However, formation of micro-cells between the Cr 23 C 6 precipitates and bulk chromium prevented the formation of passive film. In addition, wear behaviour of the coating showed that the wear mechanism includes the adhesion and abrasion wear. The coatings after heat treatment at 300 o C for 1 h exhibited better wear resistance than the amorphous coatings.The coatings were electrodeposited on steel substrate too. Active anodic behaviour was observed for Cr-C coatings deposited onto steel substrate. Evaluation of coatings produced on steel substrate with different surface preparations, showed a crack-free surface morphology coating on the anodically etched surface. This coating also showed the lowest porosity which provided the most barrier effect and thus led to the lowest dissolution of steel substrate. Keywords Cr-C alloy; coating; amorphous; nanocrystalline; annealing; corrosion resistance
