Anelastic and magnetic relaxations in neutron irradiated α-iron originating from the trapping of mobile carbon atoms

On high purity iron doped with 150 at. ppm carbon internal friction (1.4 Hz) and anelastic aftereffect are studied after irradiation with 3 x 1017 neutrons/cm2 at approximately 20 K (FR2 Karlsruhe). Annealing above Tsub(A) = 320 K decreases the carbon Snoek peak drastically and causes new relaxation peaks to appear at 21.3, 115, and 368 K. These peaks anneal out between Tsub(A) = 450 and 600 K, combined with a re-increase of the Snoek peak. All the peaks are assigned to complexes formed by the trapping of mobile carbon atoms at vacancies. By correlation with magnetic aftereffect measurements it is shown that the peak at 21.3 K which originates from a simple Debye-type relaxation, corresponds to a maximum of the magnetic aftereffect at 18 K. The peak at 368 K was interpreted earlier as a monovacancy-monocarbon complex. Based on this assignment defect configurations for the other peaks are proposed. By these interpretations also some complications in the annealing behaviour of the peaks, which is shown to depend rather sensitively on the annealing program, can be accounted for. (author)