Atomistic simulations of the interactions of hydrogen with dislocations in fcc metals

YZ Tang and JA El-Awady, PHYSICAL REVIEW B, 86, 174102 (2012).

DOI: 10.1103/PhysRevB.86.174102

The interactions of hydrogen with both edge and screw dislocations in face-centered-cubic (fcc) metals are investigated using molecular statics simulations of nickel-hydrogen as a model system. It is shown that the most energetically favorable sites for H occupation are octahedral sites in the perfect fcc lattice, tetrahedral sites in the stacking fault, and both octahedral and tetrahedral sites in the Shockley partial cores of dislocations. Moreover, the diffusion barrier for H is relatively high except for pipe diffusion near the Shockley partial cores. It is also shown that partial dislocation cores have the strongest interactions with hydrogen. The hydrogen-dislocation interactions (attractive or repulsive) and the change in stacking width (increase or decrease) depend on the hydrogen-occupying sites (octahedral or tetrahedral) and the positions of the hydrogen atoms relative to the strongest binding energy sites. In particular, on the dislocation glide plane, only hydrogen atoms in both of the Shockley partial core regions can result in increasing the stacking fault width, while those in the stacking fault region or in the perfect fcc lattice region have no observable effects. On the other hand, uniformly distributed hydrogen in the tension region near the center of a dislocation can result in decreasing the stacking fault width. The stable stacking fault energy also decreases with increasing hydrogen concentration due to the resulting negative binding energy of hydrogen to the stacking fault, while the unstable stacking fault energy increases with increasing hydrogen concentration. This may result in pinning the dislocation due to the nature of short-range interaction between interstitial hydrogen atoms and their neighboring Ni atoms.

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