Hydrogen diffusion and trapping in nanocrystalline tungsten
PM Piaggi and EM Bringa and RC Pasianot and N Gordillo and M Panizo-Laiz and J del Rio and CG de Castro and R Gonzalez-Arrabal, JOURNAL OF NUCLEAR MATERIALS, 458, 233-239 (2015).
The hydrogen behavior in nanocrystalline W (ncW) samples with grain size of 5 and 10 nm is studied using Molecular Dynamics (MD) with a bond order potential (BOP) for the W-H system. The dependence of the hydrogen diffusion coefficient on grain size (5 and 10 nm) and hydrogen concentration (0.1 at.% < H < 10.0 at.%) is calculated. These data show that in all cases the hydrogen diffusion coefficient is lower for ncW than for coarse-grained samples. Trapping energies of grain boundaries are estimated and a broad distribution roughly centered at the vacancy trapping energy is found. Hydrogen diffusion results are interpreted within the trapping model by Kirchheim for nanocrystalline materials. The H-H interaction is evaluated and the possible formation of H-2 is disregarded for the conditions in these simulations. Hydrogen segregation and trapping in grain boundaries for ncW is discussed, including extrapolations for micron-sized polycrystals. (C) 2014 Elsevier B.V. All rights reserved.
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