Influence of initial grain boundary composition on the evolution of radiation-induced segregation profiles

Radiation-induced segregation (RIS) has been identified as a potential contributor to irradiation-assisted stress corrosion cracking (IASCC) of austenitic stainless steels in reactor core components. The occurrence of grain boundary segregation prior to irradiation influences both the shape and magnitude of RIS profile development during subsequent irradiation. In an effort to better understand the impact of this pre-irradiation enrichment on RIS profile development, the evolution of grain boundary Cr segregation profiles with irradiation dose has been characterized. Commercial purity and high-purity austenitic stainless steels with different initial levels of grain boundary Cr have been irradiated with neutrons (at 275 C) or protons (at 360--400 C) to doses up to ∼5 dpa. Grain boundary composition profiles were measured before and after irradiation using scanning transmission electron microscopy with energy dispersive x-ray spectroscopy (STEM-EDS). The initial enrichment of Cr is shown to delay radiation-induced Cr depletion and produce a ''W-shaped'' profile at low irradiation doses. Further irradiation causes the central peak of the W to decrease, eventually resulting in the classical ''V-shaped'' depletion profile. Possible mechanisms for the pre-irradiation enrichment and its evolution into a W-shaped profile will be discussed