Coupling crystal plasticity and stochastic cluster dynamics models of irradiation damage in tungsten

Abstract

Irradiation damage is known to alter a material’s microstructure due to the accumulation of high densities of defect clusters. Such irradiated microstructures change the mechanical response of the material due to dislocation-defect interactions, which leads to a host of issues such as hardening, swelling, irradiation creep, embrittlement, etc. Traditionally, the effect of irradiation on the mechanical response of materials is evaluated via tensile tests of pre-irradiated specimens at different doses and temperatures. From a modeling perspective, methods exist that simulate irradiation and deformation as separate processes, with the former based on kinetic transport theory and the latter on crystal plasticity (CP). Generally, these are connected by a state variable, usually in the form of a characteristic length scale, that represents the defect concentration and strength and its effect on dislocation-mediated slip. However, cases where deformation takes place during irradiation are also important despite being less common. In this paper, we develop a coupled CP and stochastic cluster dynamics (SCD) approach capable of treating all instances of irradiation/deformation in irradiated materials. We apply the methodology to tungsten crystals due to its importance as a high-temperature candidate structural material and to its extensive defect and mechanical data base. SCD evolves the defect microstructure stochastically, providing a statistically-averaged defect cluster spacing parameter that informs CP calculations of the material’s mechanical deformation. The coupling is bi-directional in the sense that the SCD method updates the obstacle density and furnishes a resistance stress to the CP model, while CP feeds updated dislocation densities that act as defect sinks in the SCD calculation cycles. The coupling can be done sequentially, as in standard tensile tests of pre-irradiated materials, or concurrently, as in in situ straining tests during irradiation. We carry out simulations of realistic irradiation/deformation scenarios and highlight the differences between the present method and past works considering similar situations.