LATTICE DEFECT GRAIN BOUNDARY INTERACTIONS RELATED TO IASCC/

Radiation-induced segregation (RIS) of major alloying elements to grai n boundaries in austenitic stainless steels has emerged as a critical aspect of irradiation-assisted stress corrosion cracking (IASCC). Disc riminating interactions between individual solute species and vacancy and interstitial defects as they migrate to grain boundaries result in redistribution of solute. Measurements of grain boundary Ni enrichmen t and Cr depletion indicate that RIS of major alloying elements is in reasonable agreement with the inverse-Kirkendall mechanism. The discri minating interactions for inverse-Kirkendall segregation are the relat ive rates of solute diffusion by vacancy exchange. Mechanistically, th e ternary composition path, defined by change in Cr relative to Ni, de pends on relative diffusivities. The absolute change in the compositio n, that is, extent along the composition path, depends on the kinetics of vacancy formation and migration. The composition path approach is used to quantify diffusional characteristics at low temperatures. Last ly, model predictions suggest a significant influence of grain boundar y defect characteristics in addition to matrix defect characteristics. These grain-boundary sensitive characteristics may influence IASCC.