Effect of carbon on helium trapping in tungsten: A first-principles investigation

We investigate the effect of carbon (C) on helium (He) trapping in tungsten (W) using a first-principles method. We show C can effectively reduce the solution energy of He in the bulk W originated from the charge density redistribution. This leads to a strong attraction between He and C in W. We demonstrate the C-vacancy (C-V) complex can serve as a trapping center by reducing charge density in its vicinity to induce He nucleation in comparison with the defect-free W. The maximal number of He atoms that can be trapped by such C-V complex is 5, and He diffusion into the C-V complex is kinetically feasible. Further, it is found the binding energy of He to a C-V complex is weaker than that to a C-free vacancy, suggesting C will decrease the He trapping capability of vacancy. We thus propose that C plays a key role in He trapping behavior. (C) 2013 Elsevier B.V. All rights reserved.