NUCLEATION AND GROWTH OF ANODIC FILMS ON STAINLESS-STEEL ALLOYS .1. INFLUENCE OF MINOR ALLOYING ELEMENTS AND APPLIED POTENTIAL ON PASSIVE FILM GROWTH

The influence of minor alloying elements (Mo, V, W) when added to a Fe18Cr alloy on the ability of a passive film to nucleate and grow on a freshly generated metal surface, and on the subsequent stability of the film was investigated as a function of electrolyte composition and applied potential using a scratch chronoamperometric technique. Mo and V decreased the rate of active dissolution prior to passivation, allowing the onset of passivation to occur more rapidly, and also improved the stability of the passive film, especially to attack by Cl- in acidic (H2SO4, HClO4) solutions. W additions had a detrimental effect on the repassivation behaviour of Fe18Cr. Repassivation of the scratch scars was evaluated, from the current transients, in terms of the number of layers of surface film formed. © 1990 Chapman and Hall Ltd.