First-principles calculations of energies of impurities and doping effects at grain boundaries in nickel

The atomic structure of the ∑ 11(11—)/[110] grain boundaries (GB) in Ni is set up by molecular dynamics (MD) simulation using a first-principles potential. The binding energies and the site-competition ability (environment-sensitive embedding energies) of impurities on the GB environment are calculated using the first-principles discrete variational method (DVM). It turns out that B and C have the highest binding energies to the Ni GB and can successfully drive out the harmful impurities from the GB. Our calculations show that P and S embrittle the Ni GB and B, C and N enhance it. We conclude that the influence of impurities on the GB strength is closely associated with their effects on: (i) The decrease of the cohesion between host atoms due to the presence of impurities; (ii) the cohesion between impurity atoms and host atoms; and (iii) the site-competition ability of impurities.