The effect of formic acid concentration on the conductivity and corrosion resistance of chromium carbide coatings electroplated with trivalent chromium

Different concentrations of formic acid were added into a trivalent chromium electroplating solution to produce chromium carbide (Crsingle bondC) coatings. The influence of the formic acid concentration on chemical composition, microstructure, surface morphology, corrosion resistance, conductivity and carbon content of the resulting Crsingle bondC coatings was studied. Formic acid was found to increase the carbon content in the coatings so as to form Crsingle bondC films. These coatings had a nearly amorphous structure containing Cr, Cr2O3, and various Crsingle bondC compounds with carbon content uniformly distributed throughout the coatings. The carbon content and the conductivity of the Crsingle bondC layer were correlated with formic acid concentration. For a formic acid concentration of 2 M, the Crsingle bondC layer had the highest carbon content (∼28%), the lowest contact resistance, and the best corrosion resistance along with a corrosion current density of ∼6.4 × 10−7 A/cm2.