A 2-D Reaction-Transport Model for Investigating Pit Morphology Under the Influence of a Salt Film

Abstract

A 2-D reaction transport model with the phase field method was employed here to simulate the propagation stage of corrosion pitting in stainless steels in a chloride environment. The influence of the salt film on pitting dissolution kinetics was incorporated into the model to study its effect on the pit morphology under various settings. In potentiostatic conditions, the pit morphology tends toward a dish-like shape due to the presence of the salt film inside a corrosion pit. This leads to diffusion-controlled dissolution at the pit bottom and active dissolution near the pit mouth. On the contrary, in galvanostatic conditions and at a high applied current, although the salt film was initially present, its effect diminished as the chemistry inside the pit became diluted and the pit growth transitioned into active dissolution near the repassivation current. This effect is attributed to the limited resources to support the enlargement of a corrosion pit under constant applied current. As a result, the pit morphology in galvanostatic conditions is likely to be hemispherical and can transition into complex morphology, as discussed in a previous paper.