First principles study of helium trapping by solute elements in tungsten

The behavior of helium in metals is particularly important in fusion research due to the He induced degradation of materials. A small amount of impurities introduced by alloying or transmutation reactions will interact with He and lead the microstructure and mechanical properties of materials to change. In this paper, we present the results of first-principles calculations on the interactions of He with impurities in tungsten (W), including the interstitials C, N, O, and substitutional 3d, 4d and 5d transition metals. We find that the trapping radii of interstitial atoms for He are almost twice larger than those of substitutional solutes. A preliminary evaluation of the effective trapping of He is also given when considering the detrapping of He at high temperature. The binding energies between the substitutional impurities and He increase linearly with the relative charge densities at the He occupation site, implying that He atoms easily aggregate at low charge density sites. The present results suggest that Ta might be chosen as a relatively suitable alloying element compared to other possible choices. (C) 2014 Elsevier B.V. All rights reserved.