Micromechanics of dislocation channeling in intergranular stress corrosion crack nucleation

While driven by a combination of stress, a susceptible microstructure and an aggressive environment, the mechanistic origin of stress corrosion cracking remains poorly understood. The emergence of localized deformation as a key process in SCC has resulted in considerable experiment and simulation studies. The effectiveness of irradiation in localizing deformation into dislocation channels has provided a tool for studying the interaction between channels and grain boundaries. Experiment and simulation have shown that normal stress can be in excess of twice the applied stress and that cracking correlates well with the high normal stress. Shear stresses in the channel can add an additional component to the normal stress at the channel-boundary intersection. While the exact role of localized deformation in stress corrosion cracking is not yet full understood, it is known that the degree of localized deformation correlates well with SCC susceptibility. Further, both experiments and simulations indicate that cracks preferentially nucleate in grain boundaries that are perpendicular to the loading direction, are non-special high angle boundaries, are not oriented for easy deformation under the applied load, and are effective barriers to slip transmission. This paper will review recent progress in understanding the behavior of localized deformation and the impact on stress corrosion cracking.

► Grain boundary-dislocation channel intersections are sites of high local stress and strain.
► Normal stress can reach twice the applied stress and lead to cracking.
► Shear stresses in the channel can add an additional component to the normal stress.
► The degree of localized deformation correlates with SCC susceptibility.
► Cracks preferentially nucleate on grain boundaries perpendicular to the loading direction.