Radiation-enhanced self-diffusion in α-iron

Radiation-enhanced self-diffusion coefficients of 55Fe in almost dislocation-free single crystals of α-iron were determined after irradiation with 1.85 MeV electrons by means of sputtering. The diffusion coefficients, which were obtained after irradiation in the temperature range between 430 and 730 K, were surprisingly very large and dependent on the irradiation temperature. The analysis of the data revealed that the radiation-induced point defects annihilate during irradiation mainly by pair recombination and that self-interstitials are the rate-determining point defects responsible for the observed large diffusion coefficients. It was found that the activation energy of migration of self-interstitials decreases with increasing high-energy particle flux from EIIM=0.55 eV to about EIIM=0.41 eV for a production rate of point defects of KII,IV=1.85 .10-10 dpa..-1. The value for the activation energy of migration of self-interstitials, which has been obtained in the present experiments, namely EIIM=0.55 eV, is also reported in the literature for recovery stage III after irradiation with high-energy particles. It is concluded that self-interstitials in α-iron migrate and annihilate in the recovery stage III temperature region after an irradiation with high-energy particles. Thus, the basic features of the modified two-interstitial radiation damage model, which has been developed for fcc materials during the last ten years, must also be valid for bcc materials. (orig.)