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An Atomistic Study of Hydrogen Effects on the Fracture of Tilt Boundaries in Nickel.

  • N. R. Moody (a1) and S. M. Foiles (a1)


In this study, molecular dynamics simulations were used to fracture Σ9 tilt boundaries in nickel lattices containing a range of trap site hydrogen concentrations. These lattices were created in a previous study using Monte Carlo simulations and the Embedded Atom Method to duplicate room temperature exposure to a hydrogen environment. The molecular dynamics simulations were run at absolute zero to immobilize the hydrogen distributions for determination of trap site occupancy effects on grain boundary fracture. In all lattices, fracture began by the breaking of bonds next to polyhedral defect sites that characterize the boundary structure followed by rapid failure of the remaining bonds. The effect of hydrogen was to lower the stress for fracture from 18 GPa to a lower limiting value of 8 GPa as the trap sites along the boundary plane filled. The simulations showed that the atoms at these sites were the only atoms involved in the fracture process. Within the constraints imposed on these calculations, the results of this study showed that the ‘inherent’ effect of hydrogen in the absence of plastic deformation is to reduce the cohesive force between atoms across the boundary.



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