MICROSTRUCTURAL EVOLUTION IN VANADIUM ALLOYS BY FAST-NEUTRON IRRADIATION

Some of the vanadium alloys have been found recently to exhibit enormous amount of swelling. The factor common to most of these high-swelling alloys is that they have undersized solutes as alloying elements. Several possible mechanisms for the large swelling have been discussed in previous papers, while the interpretation is still not conclusive. In order to clarify the mechanism of the observed large swelling, the evolution of microstructure in several vanadium-based binary alloys has been examined by electron microscopy after irradiation at 400, 500 and 600-degrees-C in JOYO to displacement levels between 4.6 and 14 dpa. Among the alloys studied, the maximum swelling at the damage level of approximately 14 dpa was observed in the V-5 at% Fe alloy and was as high as 30% at 600-degrees-C. Alloys with oversized solutes show only limited amounts of swelling. Detailed microstructural examination has been conducted and it has been found that there is a systematic difference in the dislocation Burgers vectors with solute atomic size factor, with the exception of V-1% Si. The mechanism of the large swelling is discussed in terms of the observed microstructural differences in the two groups of alloys.