PNNL

Abstract

Collision cascades in metals produce small interstitial clusters and perfect dislocation loops that glide in thermally activated, one-dimensional (1D) random walks. These gliding defects can change their Burgers vectors by thermal activation or by interactions with other defects. Their migration is therefore ?mixed 1D/3D migration? along a 3D path consisting of 1D segments. The defect reaction kinetics under mixed 1D/3D diffusion are different from both pure 1D diffusion and pure 3D diffusion, both of which can be formulated within analytical rate theory models of microstructure evolution under irradiation. Atomic-scale Kinetic Monte Carlo defect migration simulations are used to investigate the effects of mixed 1D/3D migration on defect reaction kinetics as a guide for implementing mixed 1D/3D migration into the theory. The dependence of sink strength on the size and concentration of sinks under mixed 1D/3D migration lies between those for pure 1D and pure 3D migration and varies with the average distance between direction changes, L. The sink strength for sinks of size R under mixed 1D/3D migration can be approximated by an expression that varies directly as R2 for values of L greater than the sink size. The transition from mixed 1D/3D to pure 3D diffusion as L decreases is demonstrated in the simulations.