Damage structures in fission-neutron irradiated Ni-based alloys at high temperatures

Abstract

The defects formed in Ni based (Ni–Si, Ni–Cu and Ni–Fe) alloys which were irradiated with fission-neutrons were examined by electron microscopy. Irradiations were carried out at 473 K and 573 K. In the 473 K irradiated specimens, a high density of large interstitial loops and small vacancy clusters with stacking fault tetrahedra (SFT) were observed. The number densities of these two types of defects did not strongly depend on the amount of solute atoms in each alloy. The density of the loops in Ni–Si alloys was much higher than those in Ni–Cu and Ni–Fe alloys, while the density of SFT only slightly depended on the kind of solute. Also, the size of the loops depended on the kinds and amounts of solute. In 573 K irradiated Ni-Cu specimens, a high density of dislocation lines developed during the growth of interstitial loops. In Ni–Si alloys, the number density and size of the interstitial loops changed as a function of the amount of solute. Voids were formed in Ni–Cu alloys but scarcely formed in Ni–Si alloys. The number density of voids was one hundredth of that of SFT observed in 473 K irradiated Ni–Cu alloys. Possible formation processes of interstitial loops, SFT dislocation lines and voids are discussed.