Nano-crystallize materials have been known for decades to potentially owe the novel self-healing ability for radiation damage, which has been demonstrated to be especially linked to preferential occupation of interstitials at grain boundary (GB) and promoted vacancy-interstitial annihilation. A major obstacle to better understanding the healing property is the lack of an atomistic picture of the interstitial states near GBs, due to severely separation of the timescale of interstitial segregation from other events and abundance of interstitials at the GB. Here, we report a generic self-blocking effect of the interstitial cluster (SIAn) near the metallic GB in W, Mo and Fe. Upon creating a SIAn near the GB, it is immediately trapped by the GB during the GB structural relaxation and blocks there, impeding GBs further spontaneous trapping of the SIAn in the vicinity and making these SIAns stuck nearby the GB. The SIAn in the stuck state surprisingly owes an exceptionally larger number of annihilation sites with vacancies near the GB than the SIAn trapped at the GB due to maintaining its bulk configuration basically. Besides, it also has an unexpectedly long-ranged repelling interaction with the SIA in the bulk region, which may further affect the GBs trap of the SIAn. The self-blocking effect might shed light on more critical and extended role of the GB in healing radiation-damage in NCs than previously recognized the GBs limited role based on GBs trap for the SIA and resulted vacancy-SIA recombination.
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