Nucleation and growth of helium-vacancy clusters in vanadium and vanadium alloys: V-5Ti, V-3Ti-1Si, V-5Ti-5Cr

Thermal helium desorption spectrometry (THDS) is applied to the study of helium trapping and clustering in vanadium and a number of selected vanadium alloys. A comparative analysis of the desorption spectra reveals the presence of at least two different trap sites responsible for the helium desorption observed in the investigated materials. These are (1) helium-vacancy clusters nucleated at interstitial impurities (C, N, O) and developed during the irradiation, and (2) pre-existing traps, e.g. precipitates and undersized alloying elements. The contribution of these two types of traps in pure vanadium and the alloys appeared to vary in magnitude depending on the material. In addition to the experiments, a Monte Carlo computer program has been developed for the simulation of both the irradiation and the annealing of the materials. The results obtained for nucleation, growth and dissociation of helium-vacancy clusters are compared to the experimental results. The model takes into account interstitially dissolved impurities, i.e. C, N and O interacting with helium-vacancy clusters.