How irradiation promotes intergranular stress corrosion crack initiation.

• High temperature water combined with irradiation induces in oxidation of grain boundaries that weaken the boundaries. • Applied tensile stress enhances the rate of grain boundary oxidation. • Deformation induced dislocation channels create local stresses sufficient to crack a grain boundaryweakened by oxidation. • Fracture of the oxidized grain boundary allows for oxidation of the boundary beneath the crack tip. • Oxidation of silicon at the grain boundary forms highly soluble amorphous silica that aids crack extension via dissolution. Irradiation assisted stress corrosion cracking (IASCC) is a form of intergranular stress corrosion cracking that occurs in irradiated austenitic alloys. It requires an irradiated microstructure along with high temperature water and stress. The process is ubiquitous in that it occurs in a wide range of austenitic alloys and water chemistries, but only when the alloy is irradiated. Despite evidence of this degradation mode that dates back to the 1960s, the mechanism by which it occurs has remained elusive. Here, using high resolution electron backscattering detection to analyze local stress-strain states, high resolution transmission electron microscopy to identify grain boundary phases at crack tips, and decoupling the roles of stress and grain boundary oxidation, we are able to unfold the complexities of the phenomenon to reveal the mechanism by which IASCC occurs. The significance of the findings impacts the mechanical integrity of core components of both current and advanced nuclear reactor designs worldwide. [ABSTRACT FROM AUTHOR]