An electron microscope study of neutron irradiation damage in alpha-iron

Abstract The technique of transmission electron microscopy has been used to study neutron irradiation damage in α -iron. Foils were irradiated to a fission neutron dose of ∼ 2 × 1020 cm−2 at 60°c and the effects of annealing up to 500°c on the micro-hardness and structure were studied. The irradiated foils contained visible point defect clusters which remained unchanged on annealing up to 300°c. Above 300°c the size of clusters remained fairly constant but the number decreased steadily until they had all disappeared after annealing at 500°c. The micro-hardness also remained unchanged up to 300°c and then recovered steadily until it returned to the unirradiated value at 500°c. The results of a diffraction analysis carried out on loops in annealed foils indicated that their Burgers vector was in a ⟨111⟩ direction and that both interstitial and vacancy loops were present. It is suggested that the visible clusters in the irradiated iron are interstitial in nature, the vacancies being trapped by interstitial impurity atoms. The annealing behaviour above 300°c is consistent with the vacancies breaking free from their traps to recombine with the clustered interstitial point defects.