Quantitative investigation on sink strength of nano-grain boundary for irradiation resistance

Highlights: • Dilute Cu–W alloys exhibit significantly enhanced thermal stability. • Irradiation-induced voids highly depend on grain size and irradiation temperature. • A critical nano-grain size exists for excellent irradiation tolerance. • The nano-GB energy is almost comparable in GBs with different characters. • Nano-GB characters have limited influence on the nano-GB sink strength. - Abstract: It has long been recognized that grain boundary (GB) is an effective sink to trap irradiation-induced defects. Introducing large densities of GBs becomes an effective strategy to enhance irradiation resistance. However, the nano-grained materials have poor stability under the extreme irradiation, and the effect of nano-GB characters on the irradiation sink strength is largely unknown. Here, the sink strength of nano-GB is quantitatively investigated in the nano-grained Cu and dilute Cu–W alloys with the average grain size ranging from ∼20 to ∼50 nm by ∼300 keV He ions irradiation at room temperature and 673 K. The irradiation induced void volume ratio, size and distribution are confirmed to strongly depend on the grain size and irradiation temperature. The nano-GBs with different characters, such as the misorientation and GB plane, have similar relative energy. The nano-GB sink strength is independent on the GB characters, deriving from the highly curved nano-GB plane having excess volume and energy. Combining with molecular dynamics simulations, we can conclude that nano-grain size is the most vital factor for the sink strength with respect to the GB characters. With the increase of temperature and the decrease of grain size, the stable nano-GBs exhibit a behavior of "ideal" defects sink due to their high volume ratio and the increased point defect recombination probability. Our work provides a fundamental understanding of the nano-GB sink efficiency and offer a guidance for designing nano-grained structural materials with optimum anti-irradiation performance for future fusion reactors.