The microstructural evolution of a non-equilibrium system of primary defects was considered in which mobile point defects, vacancy loops and sessile interstitial clusters were continuously produced by cascade-damage irradiation. It was shown that, in a fully annealed metal, a spatially homogeneous microstructure could become unstable if the yield of vacancy clusters in collision cascades was sufficiently low. Unlike previous cases studied, in which sessile interstitial clusters were not produced, it was found that the instability condition could be satisfied only for a finite period of time. The duration depended only upon the density of the network dislocation. Spatial heterogeneity began to appear from an homogeneous vacancy loop population, leading to the eventual accumulation of almost all vacancy clusters within very sharp walls. The spatial distribution of interstitial clusters was relatively homogeneous, simply following the spatial variations of the net interstitial flux. Spatial heterogeneity developed with the growth of some concentration peaks and the disappearance of others. As a result, the surviving peaks formed an increasingly well-defined periodic structure. Nevertheless, as the total sink density of interstitial clusters and loops became sufficiently large, the periodic structure disappeared, and spatial homogeneity of the damage microstructure eventually returned.

Spatial Ordering of Primary Defects at Elevated Temperatures. A.A.Semenov, C.H.Woo: Physical Review B, 2005, 71[5], 054109 (14pp)