Grain boundary Cr concentration influences resistance to intergranular stress corrosion cracking of stainless steel reactor core components. Therefore it is important to understand (1) how initial thermal processing affects thermal nonequilibrium segregation (TNES), (2) how service exposure affects radiation-induced segregation (RIS), and (3) how temperature affects post-irradiation annealing (PIA). In this study, each process is shown to be controlled by Cr-vacancy interactions. Mechanistic predictions are in accord with measured kinetics of changes in grain boundary Cr concentration for RIS and PIA but not for TNES.
Inconsistencies between TNES model predictions and TNES measured segregation suggest that multiple solute-defect interactions must be considered and not just the simple interaction between Cr and vacancies. Furthermore, analysis of RIS of enriched TNES profiles suggests that Cr is chemically bound to the grain boundary such that the boundary concentration is influenced both by RIS in the matrix outside of the boundary plane and by chemistry within the TNES enriched boundary. Mechanistic understanding of changes in Cr concentration at grain boundaries may suggest mitigating measures for reduced in-core cracking by control of heat treatments, alloy chemistry and PIA.
Keywords: Grain boundary chemistry, models, irradiation assisted stress corrosion cracking, heat treatment.