Instabilities in concentrated alloys under irradiation

Spatial fluctuations in composition have been observed in a number of concentrated Fe-Cr-Ni alloys after irradiation. It has been suggested that these fluctuations are the result of a spinodal-like decomposition of the material during irradiation. In this paper the development of such oscillations during irradiation is investigated using Manning's random-alloy model. The results of numerical calculations for an Fe-35 at.% Ni alloy are presented, and it is found that fluctuations arise only when interstitials show a strong preference for exchanging with atoms of one of the species of the alloy, and when the thermodynamic factor for diffusion is small, so it is concluded that the observed fluctuations in composition are probably not caused by a spinodal-like decomposition. It is more likely that they are associated with the trapping of vacancies or interstitials at impurity atoms. (author)