Effect of substitutional and interstitial elements on void formation in neutron-irradiated vanadium alloys

V-1 at% C and V-3 at% Mo, Nb and Fe alloys were irradiated in the JMTR with fast neutrons (E > 1 MeV) to doses of 5 x 1024 n/m2 at 773 K and 1 x 1025 n/m2 at 740 K, respectively. Microstructural observations and tensile tests were carried out after irradiation and post-irradiation annealing. In the V-C alloy voids were observed to be homogeneously distributed with radiation-induced quasi-carbides. In the V-Mo alloy very small voids were distributed uniformly. On the other hand in V-Nb and V-Fe alloys, voids were formed heterogeneously. The V-Nb alloy shows colonial void zones, and the V-Fe alloy shows large difference in void size. Using the energy-dispersive X-ray microanalysis technique for the detection of substitutional atoms, it was shown that the undersize solute Fe in V was enriched and the oversize solutes Mo and Nb were depleted at the grain boundaries and voids in the irradiated materials. All of the specimens showed the radiation hardening and radiation anneal hardening due to void formation. On post-irradiation annealing of the irradiated alloys, the void number density increased to a maximum value at 870 K. These results suggest that point defects interact with solute atoms giving rise to solute segregation at the defect sinks. These segregation effects influence the void formation. (orig.)