PNNL

Abstract

Stainless steels are used in a myriad of engineering applications, including construction, automotives, and nuclear reactors. Developing accurate, predictive mechanistic models for corrosion and electrochemical corrosion kinetics of stainless steels, specifically in chloride environments, has been a topic of research studies over many decades. Herein, we quantified the aqueous corrosion kinetics of a model austenitic Fe–18Cr–14Ni (wt.%) alloy in the presence and absence of applied potential using systematic in situ electrochemical atomic force microscopy (EC-AFM) studies and transmission electron microscopy (TEM). Without an applied bias, dissolution along the vertical direction of corrosion pits is controlled by surface kinetics/diffusion hybrid mechanism, whereas the dissolution along the lateral direction of pits is diffusion controlled. In the absence of an applied bias, both the “nucleation” and “lateral growth” of the pits contribute to total corrosion. When an electrical bias is applied, the increase in corrosion rate is dominated by nucleation of new pits rather than lateral growth of existing ones. This shift in the corrosion mechanism is attributed to the bias-induced redistribution of species with different charges. These insights gained by the in situ EC-AFM will allow applications of this method for quantitative understanding of corrosion of wider class of materials.