The dynamics of dislocation interaction with sessile self-interstitial atom (SIA) defect cluster atmospheres

The interaction dynamics between dislocations and radiation induced sessile self-interstitial atom (SIA) dislocation loops in FCC metals are investigated. As a result of dislocation line flexibility, its equilibrium configuration is found to be sensitive to the elastic field of nearby SIA dislocation loops. Dislocation line flexibility also influences the critical stress to free trapped dislocations from pinning atmospheres (i.e. the critical resolved shear stress (CRSS)). Calculated CRSS values differ by up to 100% from the estimates of Trinkaus et al. J. Nucl. Mater. 249 (1997) 91; J. Nucl. Mater. 251 (1997) 172], which are based on cluster forces exerted on static rigid dislocations. The mechanism of dislocation unpinning from random cluster atmospheres is shown to be a consequence of morphological instabilities on the dislocation line. The initial location of the unlocking instability is always associated with regions of minimum line tension in the vicinity of the lowest cluster density. The growth of dislocation shape fluctuations leads to a sequence of unzipping events, freeing the dislocation from the elastic field of cluster atmospheres. The relative critical shear stress to unlock dislocations in FCC metals, (τ_C/μ), is found to be in the range: 0.001–0.002, for random atmosphere cluster densities of 10²⁴–10²⁵ m³, and in the range: 0.0014–0.003, for coherent cluster atmospheres of the same density range. These values are factors of 4–6 smaller than Kroupa's estimates. Implications of these results to the determination of the upper yield point of irradiated FCC metals are discussed.