Grain size effect on radiation tolerance of nanocrystalline Mo

We report a significant grain size effect on radiation tolerance of nanocrystalline Mo under He ion irradiation. Irradiation -induced dislocation loops mainly contribute to the irradiation-induced hardening of Mo films with grain size of >90 nm, while few such loops in those with grain size of <90 nm. The hardness increment after irradiation decreases with decreasing the grain size, and approaches zero at the grain size of 25 nm. Also, the size and the density of irradiation-induced He bubbles decrease as the grain size decreases. This observation provides direct evidence that nanocrystalline body-centered-cubic metals have greater radiation tolerance than their ultra-fine-grained or coarse-grained counterparts. Published by Elsevier Ltd.