2021 W.R. Whitney Award: The Importance of Local Chemistry and Potential in Localized Corrosion and Stress Corrosion Cracking

Abstract

The nature and rates of the chemical and electrochemical reactions that occur within the occluded regions of a given alloy are controlled by the local electrochemical potential and the local solution composition. The very small physical dimensions of these regions lead to challenges in both measurement and modeling. When performed in a coordinated and complementary way, measurements and modeling provide insights into the controlling processes of a range of localized corrosion phenomena, including crevice corrosion, pitting, intergranular corrosion, and stress corrosion cracking. Examples of attempts to overcome the measurement challenges are described for a range of corrosion scenarios, including identification of the critical ionic species in stainless steel crevice corrosion and in the corrosion of aircraft lap joints, operando measurement of chemistry and potential simultaneously within stress corrosion cracks, and monitoring of water layer thickness in salt spray testing. Examples of work addressing the challenges in modeling localized corrosion including intergranular corrosion of AA5XXX alloys, scaling laws in crevice corrosion, the extent to which the Laplace Equation can be used and applied to geometrically complex galvanic structures, and an approach to modeling localized corrosion for extraordinarily long service times. Finally, suggestions regarding future avenues of research are provided.