Annealing Behavior of Defect Structures in Ni lrradiated by High Energy

Isochronal annealing experiments for H and He ion irradiated Ni were carried out to study the interactions between gas atoms and vacancy clusters. The accelerating energy of H and He ions was 1.0 MeV and 3.3 MeV, respectively. The total dose was 1.0 x 1017 H ions/cm2 (0.2 dpa) and 9.6 x 101s He ions/cmz (0.3 dpa), and the irradiation temperature was 300"C. In order to study the recovery behavior of the defect structures, positron annihilation lifetime and coincidence doppler broadening (CDB) measurements were carried out after irradiation and annealing for I hour up to 950"C. The microvoids were detected after the H and He ion irradiation. The characteristic difference mainly appeared in the annealing behavior of the defect structures. The results of the positron lifetime and CDB measurements after annealing indicated that the recovery of the defect structures in Ni irradiated by H ions finished completely at 600'C, while that in Ni irradiated by He ions finished at 950"C. In addition, the microvoids formed by the He ion irradiation grew after annealing at 750'C. The stability of the vacancy clusters, H-vacanc) ' complexes, and He-vacancy complexes is discussed from these results. Keywords: nickel, hydrogen, helium, ion irradiation, positron spectroscopy, microvoid, gas-vacancy comple