Coupled cluster-dislocation dynamics of irradiation-induced defects

We present a new formulation for modeling concurrent radiation damage and plasticity of irradiated materials during service . We consider the case of irradiated zirconium as an example, where the dominant microstructure features are vacancy and interstitial type dislocation loops. We first develop Cluster Dynamics (CD) equations that describe the temporal evolution of both types of loops, taking into account their nucleation and growth. The size distribution is described, where interstitial loops agglomerate mainly by single-step absorption of a few mobile defect species. Vacancy loops are nucleated heterogeneously at collision cascades sites by collapse of loose vacancy clusters into Stacking Fault Tetrahedra (SFT) that transform into sessile vacancy loops on the basal planes within a dose of a few displacements per atom (dpa). A quasi steady-state for fast mobile point defects is quickly reached, while the nucleation and further growth of dislocation loops continues in a slow transient to high radiation dose. The results are consistent with experimental observations of dislocation loop density, mean size and size distribution. CD equations are then used to establish a discrete representation of the dislocation microstructure and point defect radiation-induced super-saturation conditions in finite grains of Zr as function of irradiation dose through statistical sampling of the size distribution. Discrete Dislocation Dynamics (DDD) simulations involving glide motion of dislocations are performed to determine the mechanical state of deformation and the collective behavior of dislocation loops in post-irradiated materials. Results of DDD simulations show that spatial correlation of loops, their reorientation, and their dose-dependent evolution are in qualitative agreement with experimental observations.