An Atomistic Study of the Equilibrium Segregation of Hydrogen to Tilt Boundaries in Nickel

Abstract

AbstractIn this study, Monte Carlo simulations have been combined with Embedded Atom Method (EAM) calculations to study hydrogen segregation at the atomic level in an ideal nickel lattice with a Σ9 tilt boundary. The calculations indicate that trap binding energies exceed 0.5 eV on the tilt boundary, but decrease rapidly with distance. Furthermore, the calculations show that trap site occupancy increases with trap site binding energy and hydrogen activity, and reach saturation at high hydrogen concentrations. Most importantly, significant rearrangements in tilt boundary structure are predicted to occur as hydrogen concentration increases. The results are consistent with observations that show significant hydrogen concentration enhancement at grain boundaries in nickel and palladium. They also parallel the effect of hydrogen concentration on crack growth susceptibility in nickel and iron-rich alloys. However, the change in boundary structure as hydrogen concentration increases challenges our understanding of hydrogen-induced fracture.