Construction of radiation-modified phase diagrams under cascade-producing irradiation: application to Zr–Nb alloy

A general theoretical formalism developed for the description of phase stability alteration in substitutional binary alloys under irradiation is applied to Zr–Nb alloys. We examine the stability of β-Nb precipitates in Zr–Nb alloy subjected to the cascade-producing irradiation. The results of phase stability studies are presented in the form of radiation-modified phase diagram. Evolution of large precipitates (as compared to the size of cascade region) differs from that of small precipitates. In the radiation-modified phase diagram there exists a low temperature boundary for stability of large precipitates, the location of which depends on interface type and displacement rate. Above this boundary large precipitates coarsen with radiation-enhanced rate. Below it the alloy is maintained in a quasi-steady-state of supersaturated solid solution with a population of fine-grained precipitates. The competition between processes of cascade destruction; nucleation and growth of coherent precipitates; and coherency loss can lead to the formation of the distribution of fine-grained precipitates with slowly varying parameters. In particular, such a distribution may form in Zr–Nb alloys under thermal reactor conditions.