Radiation damage accumulation mechanisms at iron grain boundaries revealed by coupled atomic and coarse-grained simulations via the parameter-passing and structural feedback

Nano-crystalline metals (NCs) exhibit radiation-tolerance due to the sink of grain boundaries (GBs) for radiation-induced defects such as self-interstitial atoms (SIAs) and vacancies (Vs). However, the relevant mechanisms for the radiation damage accumulation and GB structural relaxation under high radiation field in NCs are still not well understood. By combining coarse-grained and atomistic simulations, we proposed an iterative method to investigate the evolution of the microstructure and SIA/V-GB interaction under cumulative irradiation in NC iron. The SIA overloaded effect was revealed in iron GBs when subjected to irradiation at a high radiation dose rate and/or low temperature. With the SIAs accumulated at the GB, the new GB phase was formed and then a critical concentration of the SIAs at the GB transited to a small quantity of the Vs during the GB structural recovery, accompanied by the local GB motion. Consequently, the GB`s role for Vs nearby alternated between the trapping and annihilation center with radiation dose. Alternatively, the GB with relatively low defect formation energy developed to a disordered structure after trapping abundant SIAs. The GB response pattern to cumulative irradiation is related to the SIA formation energy at the GB or the GB thermal stability, which is well manifested in the cumulative distribution function of the defects formation energy and its energy level density. At a high temperature, the SIA was found to be clustered at the GB in the form of planar configurations with unique energetics that cannot be described by the capillary law. The present work reveals a dynamic healing picture for radiation damage near the GB under cumulative irradiation.