Grain boundary metastability controls irradiation resistance in nanocrystalline metals

• In-situ TEM-irradiation experiments are performed in nanocrystalline iron. • Defect denuded zones were shown to collapse as a function of dose. • A radiation damage evolution model is demonstrated based on Molecular Dynamics and kinetic Monte Carlo simulations. • Microstate changes in grain boundaries after their ability to absorb irradiation induced defects. • Microstate changes give rise to the formation of a defect network that manifests itself as a net Nye-tensor signal detectable via lattice curvature experiments. Grain boundaries (GBs) in polycrystalline materials are powerful sinks for irradiation defects. While standard theories assume that a GB’s efficiency as a sink is defined solely by its character before irradiation, recent evidence conclusively shows that the irradiation sink efficiency is a highly dynamic property controlled by the intrinsic metastability of GBs under far-from-equilibrium irradiation conditions. In this paper, we reveal that the denuded (i.e., defect-free) zone, typically the signature of a strong sink, can collapse as irradiation damage accumulates. We propose a radiation damage evolution model that captures this behavior based on the emergence of a series of irradiation defect-enabled metastable GB microstate changes that dynamically alter the ability of the GB to absorb further damage. We show that these microstate changes control further defect absorption and give rise to the formation of a defect network that manifests itself as a net Nye-tensor signal detectable via lattice curvature experiments.