Turkin A. Theory of phase transformations in disordered substitutional alloys under irradiation

The kinetics of phase transformations and phase stability in substitution random alloys under irradiation are considered theoretically. The method is developed to construct radiation-modified phase diagrams taking into account the major mechanisms of phase stability loss (radiation-induced segregation and cascade disorder-dissolution of precipitates). It is shown that there exist four types of diagrams with different topology, depending on the irradiation type and the direction of segregation of solute atoms (to defect sinks or away from them). Radiation-modified phase diagrams of model alloys Ni-Si, Ni-Al, Al-Zn and Zr-Nb are calculated. A new numerical method is developed for simulation of precipitate ensemble evolution, i.e. the nucleation, the transient stage and the coarsening stage (Ostwald ripening). Evolution of a mixed population of coherent, semicoherent and incoherent precipitates in irradiated alloys is studied. It is shown that under certain conditions in irradiated alloys a quasistationary size distribution of semicoherent precipitates forms. The effect of heterophase fluctuations on kinetics of diffusion-limited decomposition of supersaturated solid solutions under thermal conditions and under irradiation is studied. Simulations of precipitation kinetics in alloys with strong heterophase fluctuations are carried out, which show that heterophase fluctuations slow down the homogeneous nucleation even in highly supersaturated solid solutions. The effect of second phase precipitates on the growth of vacancy voids in irradiated materials is studied.