Hydrogen embrittlement defactant concept applied to discrete dislocation dynamics

Hydrogen Embrittlement is an over 100-year-old problem; its mechanism is unresolved and often contradicting. The Hydrogen Enhanced Localized Plasticity (HELP) mechanism suggests that hydrogen promotes dislocation activity, either by lowering elastic interactions between dislocations or increasing the mobility of dislocations. The Defactant concept, an alternative theory proposed by Kirchheim[1], suggest that hydrogen can lower the energy of defects in the lattice. The reduced defect energy can be applied to nanoindentation results where a lowered pop-in load is reported under the influence of hydrogen[2]. In light of the Defactant concept it can be argued that due to the reduced defect energy of a dislocation loop, homogeneous dislocation nucleation will occur at lower stresses, explaining the Hydrogen effect of lowered pop-ins. In the interest of taking the Defactant concept further, it has been applied within Discrete Dislocation Dynamics (DDD) to investigate the impact of lowered elastic interactions between dislocations. This is done by representing dislocation energy in a simplified manner with the shear modulus, G, and burgers vector, b, as shown in Eq. 1.

Eq. 1: E_disl ∼ Gb²/2

One can argue that the lowered elastic interaction can be modeled by reducing the burgers vector of dislocations. Simulation results of DDD simulation from 3D Bending models and 2D Crack models will be presented and discussed.

1. R. Kirchheim, Scr. Mater. 62, 67 (2010).
2. A. Barnoush, N. Kheradmand, and T. Hajilou, Scr. Mater. 108, 76 (2015).