Atomistically-informed cluster dynamics modeling of concurrent interstitial and vacancy a-loop evolution in irradiated alpha-zirconium

Abstract

A cluster dynamics framework is described that incorporates an extensive database of atomistic simulation results to minimize assumptions in microstructure evolution modeling in irradiated alpha-zirconium. This database informs mechanisms of: 1) defect production behavior in displacement cascades, 2) thermal dissociation rates for all defect clusters, 3) point defect and defect cluster mobility (including anisotropy), 4) spontaneous and thermal drift defect capture at dislocation loops, and 5) cascade overlap effects on defect generation rates. The proposed model mechanistically predicts the concurrent nucleation and growth of interstitial and vacancy a-loops; vacancy loop nucleation is assisted by in-cascade vacancy clustering while vacancy loop growth is stabilized by the incorporation of thermal drift capture radii. Cascade overlap effects on defect generation rates are found to be a necessary component for model predictions of a-loop densities and sizes consistent with the experimental literature. Key characteristics such as average loop diameters, number densities, and the relative ratio of loops with interstitial and vacancy character are in good agreement with experimental observations for neutron-irradiated pure, single-crystalline α-zirconium. As such, the scale-bridging approach between atomistic simulations and cluster dynamics modeling provides several improvements over the assumptions that are commonly implemented in cluster dynamics models and set the stage for future experimental validation.