Solid solutions under irradiation. II. Radiation-induced precipitation in AlZn undersaturated solid solutions

A systematic study of radiation-induced Zn precipitation in undersaturated Al-Zn solid solutions is presented. Zn solubility in Al may be drastically decreased by high-flux 1-MeV electron irradiation (e.g., by a factor greater than 10 at 235°C under 2.5 × ${10}^{20}$ $e$ ${\mathrm{cm}}^{-2\mathrm{}}$ ${\mathrm{s}}^{-1\mathrm{}}$). The shape and location of the Zn solvus in the AlZn phase diagram is flux dependent. The precipitate volume fraction does not obey the lever rule when applied to the solvus under irradiation. The above features are well accounted for by the model for radiation-induced solid-solution metastability presented in I. According to this model, the irreversible vacancy-interstitial mutual recombination is at the root of the destabilization of the solid solution by irradiation. We therefore suggest that radiation-induced precipitation in this system is an example of a nonequilibrium phase transition.