Kinetic Monte Carlo modeling of homogeneous precipitation of Y-O and Y-Ti-O Oxides in bulk alpha iron

摘要

Nanostructured Ferritic Alloys (NFAs) are candidate materials for use as cladding inside future nuclear reactors. The high number density of nano-sized (< 2 nm diameter) oxide particles are critical to the NFA's advantageous material properties against irradiation. A Kinetic Monte Carlo (KMC) model was developed to simulate the precipitation of yttrium-oxygen (Y-O) and yttrium-titanium-oxygen (Y-Ti-O) nano-oxides, and was parameterized to the solubility data of each element and compound in iron (Fe). The precipitation simulations were found to be closely aligned with the experimental findings of size, number density, and composition of nano-oxides. The equilibrium shape of the oxide precipitates from this parametrization was investigated and followed expectations from the literature. Raising the heat treatment temperature produced larger oxides in all cases. The presence of Ti in the Fe-Y-Ti-O system was found to produce finer oxides than the Fe-Y-O system. All systems exhibited strong resistance to coarsening. The time dependence of coarsening was found to be much lower than that proposed in the Lifshitz-Slyozov-Wagner (LSW) theory. The source of the coarsening resistance in the KMC is from vacancy binding with the interfaces and the low thermodynamic push for coarsening.