Effects of iron concentration on the microstructure of V–Fe alloys after low-dose neutron irradiation

To examine the mechanism of huge swelling of V–Fe alloys, TEM observation was applied to V–x at.%Fe (x = 0, 0.3, 1, 5, 7), after low-dose neutron irradiation of 0.1–1.17 dpa at 400–600 °C. Concentric Multi-Dislocation Loops (CMDLs) and rafts were observed in V–Fe alloys irradiated to 0.1 dpa. Voids were observed only within dislocation loops in both types of configurations. Ashby-Brown (AB) contrasts were always observed around voids, indicating that shell-like iron segregation with substantial elastic strain exists on the inner surface of the voids. For 1.17 dpa, swelling V–Fe alloys was always greater than those of un-alloyed vanadium, whatever the dislocation microstructures. Implication of a segregation shell in the swelling mechanism is discussed in addition to a model based on the dislocation bias.

► TEM observation was applied to V–Fe alloys after low-dose neutron irradiation.
► Concentric Multi-Dislocation Loops were observed in the 0.1 dpa irradiated specimen.
► Ashby-Brown contrasts indicate iron segregation on the surface of the voids.
► The damage microstructure was markedly affected by the addition of 0.3 at.% iron.