CuMnNiSi precipitate evolution in irradiated reactor pressure vessel steels: Integrated Cluster Dynamics and experiments

An improved Cluster Dynamics (CD) model of Cu rich and Mn–Ni–Si phase co-precipitation was developed to provide insights on the combined effects of the flux, fluence, temperature and alloy composition on irradiation enhanced precipitation leading to the embrittlement of reactor pressure vessel steels. The CD model was calibrated using a large microstructural database, and key parameters (e.g., interfacial energies) were fitted to minimize the predicted versus measured errors. The CD model was further validated against data not used in the fitting. The CD model predicts that: a) even 0.05% Cu reduces the Mn, Ni, Si precipitation threshold fluence; b) precipitate number densities increase, while their sizes and volume fractions, decrease with increasing flux; c) precipitate number densities and volume fractions increase with decreasing temperature; and, d) most of the matrix Cu precipitates in the early years of vessel service, while MnNiSi precipitates continue to grow up to very high extended life fluence.