Solute‐Vacancy Interaction Model and the Effect of Minor Alloying Elements on the Initiation of Pitting Corrosion

Abstract

A solute‐vacancy interaction model (SVIM) is proposed to account for the effects of minor alloying elements (e.g., Mo) on the breakdown of passive films. This model, which is an extension of the point‐defect model (15–17) that was previously developed to account for the growth and breakdown of passive films, assumes that highly charged solutes (e.g., Mo⁶⁺) form complexes with negatively charged cation vacancies . This interaction has the effect of reducing the flux of cation vacancies from the film/solution interface to the metal/film interface, and hence of increasing the breakdown voltage and the induction time for pitting attack. By using experimental data for 18%Cr‐1%Mo to calculate values for various parameters, we found that the SVIM accurately predicts the changes in and for higher molybdenum concentrations in these ferritic stainless steels.