"Understanding the Chemical and Mechanical Factors of the Pit to Crack Transition in Stress Corrosion Cracking via the Slip Dissolution Mechanism " 

Nathan Gehmlich, MSE PhD Candidate 

Advisor: Professor Maria Okuniewski

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ABSTRACT

One of the most prevalent mechanisms for stress corrosion cracking in face-centered cubic metals is the slip dissolution mechanism. Slip planes cause unpassivated metal to be exposed to corrosive media; dissolution of the matrix then causes a crack to propagate until the exposed surface repassivates. This mechanism is well understood when a crack is already propagating, however the driving force behind the initiation phase or the “pit to crack transition” is less understood. This review aims to highlight the important chemical and mechanical factors that influence how and when the pit to crack transition occurs. Principal chemical mechanisms that are discussed within this study include: the effect of the material repassivation rate on the pit to crack transition, the charge transfer between material and environment, the corrosion potential within a system, and the effect of localized strain rate on repassivation rates. Other mechanical effects are also discussed, such as the stress concentration around a pit, the effect of pit size and shape on initiation, and whether a crack initiates at the pit base or along a pit wall. It can be determined that there is a lack of data in literature on both chemical and mechanical critical parameters and thresholds for materials in common corrosive environments. Additionally, the coupling of 2D and 3D characterization techniques should be used when evaluating the pit to crack transition in a material. Finally, the advantages and limitations of recent models (phase field and peridynamic models) coupling chemical and mechanical effects are discussed.