The clustering of defects in pure Ni, under bombardment with 0.5 to 20keV He+ ions, was studied by means of in situ electron microscopy. The density of interstitial-type dislocation loops increased sharply with the fluence, but was only slightly dependent upon the ion flux. It was demonstrated that the formation of interstitial-type loops at room temperature was enhanced by 3 to 4 orders of magnitude with respect to the behavior in the absence of He atoms. The results suggested a possible nucleation mechanism in which He-vacancy complexes trapped the self-interstitial atoms and acted as nucleation sites for interstitial-type loops. Bombardment with 20keV He+ ions led to the formation of stacking-fault tetrahedra, coexisting with interstitial loops, even at room temperature. Bubbles formed preferentially within interstitial loops. Under heavier bombardment, they coalesced or became interconnected, thus leading to a characteristic channel structure.

Dynamic Process of Defect Clustering in Ni under Irradiation with Low-Energy Helium Ions. K.Ono, K.Arakawa, N.Yoshida: Journal of Nuclear Materials, 1999, 271-272, 214-9