Helium bubble formation in refractory single-phase concentrated solid solution alloys under MeV He ion irradiation

Abstract In order to investigate the compositional effects on helium bubble formation in the refractory concentrated solid-solution alloys with single-phase body-centered cubic structures, TiVNbTa and TiVTa alloys, as well as a conventional V-alloy are irradiated with 1.5 MeV He ions to the fluences of 2 × 1016 and 1 × 1017 ion/cm2 at 700 °C. Under the same irradiation fluence, the average sizes of helium bubbles in TiVNbTa and V-alloy are similar, but the bubbles in TiVTa are much larger. Moreover, while the bubbles in TiVNbTa and V-alloy are uniformly distributed at both fluences, bubble clusters are observed in TiVTa as irradiated to the higher fluence. Both faceted and spherical bubbles are observed in all the three alloys, but the edges of the faceted bubbles have different preferential orientations: mostly in TiVTa, mostly in the V-alloy, and co-appearance in TiVNbTa. Radiation induced segregation becomes more significant with increasing irradiation fluence; Clear V-enrichment as well as Ti-, Nb-, and Ta-depletion around He bubbles is observed in TiVNbTa under the high fluence irradiation, while the segregation in the other two alloys is much less considerable.