Evolution of the Irradiation Induced Defect Landscape through Dislocation Vacancy Loop Interactions in Tungsten

Abstract

Structural materials for fusion reactors undergo neutron irradiation, generating defect populations that govern their mechanical response through irradiation hardening. Physically based mesoscale constitutive models require accurate descriptions of dislocation defect interactions and, critically, how both defect morphology and obstacle strength evolve during plastic deformation as the irradiation-induced defect landscape changes. Vacancy loops provide an ideal prototype for addressing this problem because they are among the most prevalent irradiation-induced defects in tungsten, yet their interaction mechanisms with dislocations and subsequent evolution remain poorly understood. Molecular dynamics simulations are used to systematically investigate interactions between edge dislocations and vacancy loops in tungsten by varying loop size, crystallographic orientation, and dislocation loop intersection geometry. Parallel loops exhibit strong geometry dependent behaviour, undergoing complete annihilation, transformation into weaker remnant defects, or defect transport depending on the interaction geometry. In contrast, inclined loops interact through Burgers vector reactions that form sessile <100> dislocation segments, producing substantially higher pinning strengths with little sensitivity to the intersection position. Finally, a framework is demonstrated for translating atomistically determined obstacle strengths into constitutive parameters, such as irradiation hardening, for mesoscale models. The mechanistic understanding developed here provides the physical basis for future mesoscale constitutive laws that explicitly account for the evolution of irradiation-induced defect populations and the resulting changes in dislocation-defect interaction mechanisms and obstacle strength, thereby improving predictive capability beyond calibrated conditions.