Investigations were made of diffusion rates after plastic deformation, after quenching from 700C or 1030C, and after irradiation with 18MeV protons and 1.85MeV electrons. The diffusion rate was deduced from the electrical resistivity, which increased with increasing short-range order. It was found that the characteristic temperature, below which short-range order developed, was 550C. At below about 400C, the atomic mobilities of the component atoms of the alloy were so small that no further increase in the degree of short-range order was found. The activation energy for self-diffusion was determined, after quenching from 700C, to be equal to 2.88eV. A value of 1.18eV was obtained for the migration activation energy of vacancies after quenching from 1030C. From measurements of radiation-enhanced diffusion, values of 1.04eV and 1.16eV were derived for the migration activation energies of interstitials and vacancies, respectively. These values decreased with increasing high-energy particle flux. It was also found that a vacancy diffusion mechanism was rate-determining for an increase in the degree of short-range order during irradiation. It was noted that the interstitials had to jump some 150 times more often, than did vacancies, for the degree of short-range order to increase by a given amount. The characteristic temperature for interstitial cluster formation was 300C. Above this temperature, radiation-induced interstitials and vacancies annihilated mainly via pair recombination. Below this temperature, interstitials also annihilated at sinks which were formed during irradiation. Thus, the concentration of vacancies increased with irradiation time. Their migration activation energy was estimated from the experimental data. At temperatures above about 380C, the radiation-enhanced diffusion rate was surprisingly smaller than the thermal diffusion rate. The quasi-dynamic vacancy concentration which built up during irradiation was much lower than the thermal vacancy concentration.

M.Gieb, J.Heieck, W.Schüle: Journal of Nuclear Materials, 1995, 225, 85-96