Quantitative characterization of frank loops and their effects on the plastic degradation in heavy ion irradiated alloy 800H

Alloy 800H has recently received significant attention owing to its potential applications in molten salt reactors. However, its irradiation tolerance and plastic degradation after irradiation are not well understood. In this study, Alloy 800H was irradiated by 3 MeV Cu+ ions with irradiation damage up to 10 dpa. The microstructure changes were characterized using two Rel-rods cases and weak beam dark field technology by performing transmission electron microscopy. The plastic mechanical properties before and after the irradiation were extracted from P-h curves derived by performing nanoindentation at loading rates of 0.05, 0.1, and 0.5 nm/s. The microscopy studies demonstrate that the characterization and evolution of the two variations of Frank loops are distinct and the 13⟨1‾11⟩ Frank loops firstly nucleate and coarsening. The nanoindentation results demonstrate that the measured yield stress increases with the increasing irradiation damage and decreasing loading rate. The good agreement on yield stress between the calculated and measured values suggests that using the characteristics of two variations of Frank loops to calculate the contribution of yield stress is appropriate. In addition, the decreasing measured values with increasing loading rate are attributed to the increased geometrically necessary dislocations, which are correlated with the indent size effect.