Low temperature irradiation of crystalline materials is known to result in hardening and loss of ductility, which limits the usefulness of candidate materials in harsh nuclear environments. In bcc metals, this mechanical property degradation is caused by the interaction of in-grown dislocations with irradiation defects, particularly small dislocation loops resulting from the microstructural evolution of displacement cascades. In this work, we present a multi scale model encompassing molecular dynamics (MD), dislocation dynamics (DD), crystal plasticity, and finite element (FE) simulations of bcc Fe containing various concentrations of dislocation loops produced by irradiation at room temperature. The study is motivated and inspired by experimental observation of plastic flow localization and softening in a variety of structure materials for nuclear applications, and the very formulation of the models is guided by observed phenomena. At the macroscopic scale, the simulations reveal a transition from homogenous to highly localized deformation at a critical loop density. Above it, plastic flow proceeds heterogeneously, creating defect-depleted channels as a principal signature of softening. These simulations are then used to calibrate a tensorial crystal plasticity model capable of reaching strains in excess of 10% for linkage with the engineering scale. The calibrated crystal plasticity model is used as the constitutive relation in FE simulations of polycrystalline irradiated Fe systems, and the results compared to experiments.

Plastic localization in irradiated fusion steels: New insights from modeling and simulation

247th National Meeting (2014)

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