Self-interstitial atoms, vacancies and their agglomerates in electron-irradiated nickel investigated by diffuse scattering of X-rays

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Abstract
Frenkel defects of concentrations varying between 200 and 600 PPM were produced in single crystals of Ni by irradiation with 3 MeV electrons at 4.5K. These radiation-induced defects and their reactions during thermal annealing were investigated by measuring the Huang diffuse scattering of X-rays, the change of the lattice parameter and the electrical resistivity. At 6K the authors observed statistically distributed Frenkel pairs. The configuration of the self-interstitial atoms (SIA) agrees with the (100) split configurations. The relaxation volume of the SIA was determined to be 1.8 (+or-0.2) atomic volumes and the Frenkel defect resistivity was rho F=7.1(+or-0.8) mu Omega cm at.%-1. This set of values implies a relaxation volume for the vacancy of -0.22 atomic volumes. The annealing behaviour of Ni is characterised by interstitial motion during stage I and growth of interstitial type clusters during stage II that eventually form dislocation loops on (111) planes. Impurities of Si (undersized) and Al (oversized) in concentrations comparable to the concentration of the Frenkel defects cannot effectively suppress the cluster growth. Vacancy agglomeration has been observed directly after annealing in stage III. The additional diffuse scattering from the vacancy agglomerates can be distinguished from the scattering from interstitial type loops by its different asymmetry relative to the Bragg reflections. There is a simultaneous decrease of rho F with the formation of the vacancy agglomerates. All of these reactions are similar to those in Cu although the growth of the interstitial clusters is retarded for Ni.