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

摘要

Different concentrations of formic acid were added into a trivalent chromium electroplating solution to produce chromium carbide (Cr-C) coatings. The influence of the formic acid concentration on chemical composition, microstructure, surface morphology, corrosion resistance, conductivity and carbon content of the resulting Cr-C coatings was studied. Formic acid was found to increase the carbon content in the coatings so as to form Cr-C films. These coatings had a nearly amorphous structure containing Cr, Cr_2O_3, and various Cr-C compounds with carbon content uniformly distributed throughout the coatings. The carbon content and the conductivity of the Cr-C layer were correlated with formic acid concentration. For a formic acid concentration of 2 M, the Cr-C 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/cm~2.