Effect of irradiation-induced microstructure on dislocation channeling and strain localization in Zircaloy-4

At the microscale, nucleation and movement of dislocations directly contribute to plastic deformation in a material. The movement of dislocations is significantly affected by the presence of prior defects in the material and can result in phenomena like slip localization and dislocation channeling. Highly localized slip bands are thus often observed in irradiated materials. In the present work, we investigate the effects of irradiation-induced defect structures on strain localization during subsequent deformation of proton-irradiated Zircaloy-4. Strain localization behaviour is compared amongst four different irradiation-induced microstructures with two different damage levels (0.1 dpa and 1 dpa) delivered at two irradiation temperatures (280°C and 450°C). In-situ SEM high-resolution digital image correlation is used to characterize the strain localization behaviour. The role of irradiation-induced defect structures on strain localization and dislocation channeling behaviour is estimated by TEM characterization. Prominent dislocation channeling is observed in both 280°C irradiated regions (0.1 dpa and 1 dpa) and the 1 dpa region in the 450°C irradiated specimen. In contrast, the strain localization behaviour in the 0.1 dpa region in the 450°C irradiated specimen is more comparable to responses seen in non-irradiated Zircaloy-4. This can be correlated to the irradiation-induced dislocation loop size and density. It is observed that the dislocation channeling effect is inversely related to the dislocation loop size and directly related to the density of the dislocation loops. Moreover, the smaller dislocation loops exhibit greater stability than the larger dislocation loops; the latter easily break away during interaction with slip dislocations.