Design for Passivity in Engineering Alloys

The solute‐vacancy interaction model (SVIM), which is an extension of the point‐defect model, has been utilized to investigate the effect of minor alloying on passivity breakdown. Experimental data of nickel binary alloys, aluminum binary alloys and Fe-Cr steels were used to calculate various SVIM parameters, and compare SVIM predictions to experimental observations. We found that the SVIM is capable to predict the effect of minor alloying on passivity breakdown potential for different alloying systems. Some systems showed an increase in pitting potential beyond the SVIM prediction, especially at high concentrations. This observation points to a different mechanism at higher concentrations, e.g., the formation of stable molybdates is a possible mechanism when the alloying concentration exceeds minor alloying, i.e., 3% wt. However, for lower concentrations, we postulate that the effect of the solute-vacancy interaction to be the most dominant.