Effect of crystal structure on the corrosion resistance of electrodeposited Cr-Mo alloys.

An investigation of electrodeposited chromium-molybdenum alloy films was undertaken to determine the effect of crystal structure on corrosion behavior. X-ray (Cu-Kα) analysis was employed to investigate the crystal structure. Anodic polarization curves and immersion tests in 5% sulfuric acid solution at 30 and 60°C were performed, and pitting potentials in 3% sodium chloride solution at 30°C were observed.It was found that films with excellent corrosion resistant were formed by electrolysis at bath temperatures at 30 and 70°C and cathode current densities of 20-100A/dm2 in solutions containing molybdate. Films deposited at a bath temperature at 50°C and sutable cathode current density were bright, but had poor corrosion resistance and dissolved out in a few minutes in 5% sulfuric acid solution at 60°C. It was shown that in this type of crystal structure the well-oriented Cr {222} face was parallel to the substrate. However, corrosion of this type of film can be improved by passivation treatment in water containing oxygen or in nitric acid solution.