Modeling the segregation of hydrogen to lattice defects in nickel

In order to better understand the effect of hydrogen on the fracture behavior of nickel, this study uses the embedded atom method (EAM) to model the segregation of hydrogen to lattice defects in nickel. The dislocations modeled include an edge, a screw, and a Lomer dislocation in the locked configuration, i.e. the Lomer-Cottrell Lock (LCL). Several coincident site lattice boundaries are also investigated, these being the Σ3(112) and Σ11(113) tilt boundaries. It will be shown that the trap site energies in the vicinity of both the edge and screw dislocations is only about 0.1 eV while for the LCL and all of the grain boundaries the maximum trap site energy in the vicinity of the defect is on the order of 0.3 eV. Using a Monte-Carlo method to a impose a hydrogen environment produces much stronger segregation of hydrogen to the deeper traps. When compared to recent experimental studies showing that a binding energy between 0.3-0.4 eV is required for trap site controlled fracture in IN903, it can be concluded that the embrittlement process is most probably associated with trapping of hydrogen to the Lomer-Cottrell Locks.