Microstructure evolution and microstructure-strength correlation predictions in nuclear materials based on grain boundary structure-fractal dimension correlations

Material components for the nuclear fusion and the advanced nuclear fi ssion reactors are exposed to high levels of radiation energy, high temperature, and high thermo-mechanical stresses. Radiation damage is inherently a multiscale phenomenon, with interactions encompassing time scales from femto-seconds to years and length scales from subnanometer to meters. In this study, multiscale modeling is used to investigate radiation effects phenomena using a series of specialized models (each tailored for examining a discrete range of length and time scales). Fractal dimension-based approach is used to link relevant length scale for multiscale simulation. Fractal dimension is a physical quantity to describe atomic arrangement of solid material. Physical mechanism obtained from lower length scale can be passed to higher length scale using fractal dimension. In this study, an ab initio study with a fractal dimension-based approach shows that the changes in atomic confi guration nanostructures are correlated with the corresponding fractal dimensions. The relationship between fractal dimension and irradiation energy proposed in this study is used to derive free energy density for phase-fi eld modeling formulation to investigate void nucleation and growth during W microstructure evolution under irradiation. By incorporating fractal dimension-based relation and the phase-fi eld formulation, the model captures the infl uence of irradiation on the lattice mismatch between grains. Analyses on temporal evolution of porosity show that void structure development is found to follow three distinct stages: (i) incubation, (ii) nucleation, and (iii) growth. During the second stage, the void nucleation rate was found to be constant. In the latter stages, the nucleation rate drops to zero. Porosity is also calculated as a function of GB distance and irradiation energy. It was found that there exists the void denuded zone for all examined irradiation energies. It was shown that the void denuded zone decrease with increasing irradiation energy and decreasing temperature.