Kinetic Monte Carlo Modeling of Helium Bubble Nucleation onto Oxides in the Fe-Ti-Y-O System.

A kinetic Monte Carlo model is developed to simulate the introduction of transmutation helium (He) atoms into nanostructured ferritic alloys (NFAs) during neutron irradiation. In this simulation, interstitial He atoms diffuse through the NFA until they become trapped within clusters consisting of other He atoms and vacancies that result from the irradiation process. The Y-Ti-O nano-oxides present in the NFAs are found to be highly effective in capturing these He atoms. As a result, they prevent the formation of He bubbles at grain boundaries. Helium bubbles form on the nano-oxides, exhibiting characteristics such as size and number density that closely resemble those observed in experimental studies. Moreover, the simulations reveal that the bubbles tend to prefer nucleation at the <111> oxide interface, and stable bubbles maintain a He-to-vacancy (He/Vac) ratio ranging from 1.3 to 1.8. Importantly, the presence of He bubbles is found to have a negligible impact on the segregation of solutes to the grain boundaries or on the stability of the nano-oxides in the NFAs.