Effects of AC-Modulated Passivation and Post-Treatment on Composition and Stability of Passive Films

An investigation of the effects of alternating voltage modulated passivation (AC-modulated passivation) and post-treatment on the composition and stability of passive films on 302 and 316 stainless steels by ellipsometry, electrochemistry, and surface Auger electron spectroscopy analysis was carried out. AC-modulated passivation increases the concentration of elements O, and the ratio Cr/(Cr + Fe) in the passive film, changes the depth composition profile of the film, roughens the surface of the passive film and makes it more favorable to the adsorption of molybdenum-containing ions during post-treatment. Hence, the resistance against the chemical dissolution of the passive film increased and the stability of the passive film improved.