Dislocation spreading and ductile-to-brittle transition in post-irradiated ferritic grains: Investigation of grain size and grain orientation effect by means of 3D dislocation dynamics simulations

Abstract : Post-irradiation plastic strain spreading in ferritic grains is investigated by means of three-dimensional dislocation dynamics simulations, whereby dislocation-mediated plasticity mechanisms are analyzed in the presence of various disperse defect populations, for different grain size and orientation cases. Each simulated irradiation condition is then characterized by a specific "defect-induced apparent straining temperature shift" (DDIAT) magnitude, reflecting the statistical evolutions of dislocation mobility. It is found that the calculated DDIAT level closely matches the ductile-to-brittle transition temperature shift (DDBTT) associated with a given defect dispersion, characterized by the (average) defect size D and defect number density N. The noted DDIAT/ DDBTT correlation can be explained based on plastic strain spreading arguments and applicable to many different ferritic alloy compositions, at least within the range of simulation conditions examined herein. This systematic study represents one essential step toward the development of a fully predictive, dose-dependent fracture model, adapted to polycrystalline ferritic materials.