Highly stable nanocrystalline oxide dispersion strengthened alloys with outstanding helium bubble suppression

Abstract

Oxide dispersion strengthened (ODS) alloys containing high-density nano-oxides show excellent mechanical properties and irradiation tolerance. However, ODS alloys are often ultrafine-grained materials since the grain size of matrix is located between 100 and 1000 nm. Here, nanocrystalline and ultrafine-grained ODS alloys with different grain sizes (50 nm and 300 nm) were prepared by mechanical alloying and high-pressure consolidation techniques, which show exceptional thermal stability. To understand their irradiation response, the two alloys were irradiated with 400 keV helium ions to a fluence of 1 × 1017He+ /cm2 at 350 ℃, 400 ℃ and 450 ℃. The results show that the size and volume fraction of helium bubbles in nanocrystalline ODS alloys increase when the irradiation temperature increases from 350 ℃ to 450 ℃. Grain boundaries (GBs) play a key role in bubble formation and evolution. We identified the bubble denuded zone (BDZ) near the GBs, but the width of the denuded zone narrowed and finally vanished with increasing helium concentration. Nanocrystalline ODS alloy with 50 nm grains (Y50) can disperse helium into much finer bubbles than ultrafine-grained ODS alloy with 300 nm grains (Y300) because of the extremely high density of GBs and oxide-matrix boundaries. To our best knowledge, Y50 alloy presents the best helium bubble suppression ability among all studied ODS and nanostructured ferritic alloys (NFA), which makes it a promising candidate material for using in fission and fusion nuclear reactors.