Helium desorption studies on vanadium and V5Ti and V3Ti1Si alloys and their relevance to helium embrittlement

Abstract

This paper investigates the trapping of helium in pure vanadium and V5Ti, V3Ti1Si alloys using thermal helium desorption spectroscopy (THDS). The implantation of helium has been carried out with energies varying from 50 eV subthreshold implantation up to 3 keV with irradiation temperatures between 300 and 1000 K. On a separate set of samples of the same alloys, tensile measurements were performed at 773, 873, and 973 K. The samples used for the tensile measurements were pre-irradiated with neutrons up to 6.4 dpa. Helium was injected by cyclotron irradiation. The differences observed in the desorption spectra for pure vanadium and the alloys after different irradiation conditions are discussed with respect to their mechanical properties. The role of interstitially dissolved impurities in helium-vacancy clustering and helium trapping was investigated both experimentally and by Monte-Carlo simulations of clustering processes. By matching the calculation results to the THDS results the interstitially dissolved fraction of impurities is estimated.