NONLINEAR DYNAMICS OF SELF-ORGANIZED MICROSTRUCTURE UNDER IRRADIATION

We analyze the formation and evolution of point and line defect micros tructure in irradiated materials. The effects of irradiation on materi als are described by dynamical conservation equations for two mobile a tomic size species (vacancies and interstitial atoms), and two basic i mmobile elements of the microstructure (vacancy and interstitial clust ers). It is shown that, under specific irradiation and material condit ions, uniform vacancy and interstitial cluster populations become unst able, forming large-scale spatially organized distributions. The struc ture and symmetry of these organized distributions are shown to evolve with time. The selection and stability of the resulting microstructur e are studied in the quasistatic approximation and in the weakly nonli near regime around the bifurcation point. It is shown that point defec t recombination does not affect the long time evolution of the microst ructure, and that the final pattern should correspond to planar wall s tructures, in agreement with experimental observations. Time-dependent evolution of self-organized microstructure is demonstrated for variou s irradiation and temperature conditions, placing special emphasis on the role of dislocation bias and direct cascade clustering on the self -organization of extended defects.