Nonlinear dynamics of self-organized microstructure under irradiation.

Abstract

We analyze the formation and evolution of point and line defect microstructure in irradiated materials. The effects of irradiation on materials are described by dynamical conservation equations for two mobile atomic size species (vacancies and interstitial atoms), and two basic immobile elements of the microstructure (vacancy and interstitial clusters). It is shown that, under specific irradiation and material conditions, uniform vacancy and interstitial cluster populations become unstable, forming large-scale spatially organized distributions. The structure and symmetry of these organized distributions are shown to evolve with time. The selection and stability of the resulting microstructure are studied in the quasistatic approximation and in the weakly nonlinear regime around the bifurcation point. It is shown that point defect recombination does not affect the long time evolution of the microstructure, and that the final pattern should correspond to planar wall structures, in agreement with experimental observations. Time-dependent evolution of self-organized microstructure is demonstrated for various irradiation and temperature conditions, placing special emphasis on the role of dislocation bias and direct cascade clustering on the self-organization of extended defects.