A lattice Monte Carlo simulation of nanophase compositions and structures in irradiated pressure vessel Fe-Cu-Ni-Mn-Si steels

A self-consistent analysis, combining thermodynamic calculations, recent small angle neutron scattering and atom probe field ion microscopy measurements and lattice Monte Carlo (LMC) simulations, is used to characterize the ultra fine coherent precipitates that form in irradiated reactor pressure vessel steels. These nanofeatures are typically rich in impurity copper precipitated from highly supersaturated solution at vessel operating temperatures around 300 °C at rates greatly accelerated by radiation enhanced diffusion. Although some copper appears to be needed to catalyze their formation, manganese nickel-rich precipitates may replace copper-rich precipitates at high concentrations of these alloying elements and/or lower temperatures. Thermodynamic and kinetic models are generally consistent with observations on the number densities, sizes, compositions and nucleation, growth and coarsening behavior of the nanofeatures. However, the LMC atomic scale simulations of complex nanofeature structures are needed to fully unify experiment and theory.