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Comparison of helium ion irradiation resistance between nanocrystalline and coarse grained 304 austenitic stainless steel

Improving the radiation resistance of structural materials in the presence of helium is significant for the development of advanced nuclear power systems. Nanostructured materials reduce the grain size and significantly increase the grain boundary density. Hence, it is considered to be an effective method to improve the radiation resistance of materials. In this work, we studied the radiation resistance of nanocrystalline (NC) and coarse grained (CG) 304 austenitic stainless steel (304-SS) by helium ion irradiations. The mean grain sizes of NC and CG 304-SS are ∼45 nm and ∼30 μm, respectively. The results of positron annihilation Doppler broadening spectroscopy and transmission electron microscopy indicate that NC 304-SS not only has better swelling resistance than CG 304-SS, but also has better helium effect resistance. And the swelling of NC 304-SS is reduced by a factor of ∼5.7 compared with CG 304-SS under the irradiation of 170 keV He+ to 2 × 1020 ions m−2 at 723 K. The mechanisms for the excellent swelling resistance of NC 304-SS are discussed.