Carbon nanomaterials in nickel and iron helping to disperse or release He atoms

Experimental and theoretical studies have shown that helium (He) atoms in metal tend to form into nano-sized bubbles which greatly affects mechanical properties of metals. Thus, designing nanostructure to control the growth of He bubbles and increase its radiation resistance is an important task. In this work, we systematically study the atomistic mechanism on how the carbon (C) nanomaterials embedded inside metals with different crystal structures (FCC-Ni and BCC-Fe) disperse or release He atoms using molecular dynamics simulations. The dynamic evolution of He atoms in different Ni/C and Fe/C nanocomposites were observed and compared. It is found that the presence of multiple C72 with vacancy defects and graphene with multiple vacancy defects can suppress the formation of large He bubbles and dislocations by helping to disperse He atoms, while, the C nanotube with vacancy defects can suppress the formation of large He bubbles and dislocations by helping to release He atoms. The formation energies of He in different Ni/C and Fe/C nanocomposites were also calculated to explain why the He atoms tend to diffuse into the region near C structures. The average diffusion coefficients of He in bulk Ni and bulk Fe were calculated to explain the mechanism for the better abilities of C structures in Ni/C nanocomposites than in Fe/C nanocomposites help to disperse or release He atoms.