DISLOCATION LOOPS AND THEIR DEPTH PROFILES IN HE+ AND D+ ION-IRRADIATED NICKEL

Effects of implanted deuterium and helium on the formation of dislocation loops in Ni have been systematically investigated in terms of the irradiation temperature and dose by means of transmission electron microscopy. Significant enhancement of loop formation is observed only for He+ irradiation. The number density of loops at 200-degrees-C for He+ irradiation is about one order of magnitude higher than that of D+ irradiation and the difference increases at higher temperatures. Significant decrease in the density occurs at about 300-degrees-C for D+ irradiation, but it appears at about 600-degrees-C for He+ irradiation. Below 200-degrees-C, continuous nucleation of loops is observed only for He+ irradiation. The change in the loop depth distribution suggests that the nucleation of loops for He+ irradiation is enhanced by some defects with a low mobility such as small He-vacancy complexes. The significant decrease in the loop density above 600-degrees-C is explained by the decrease in the concentration of the small He-vacancy complexes due to their absorption by large cavities or their escape to the specimen surface.