Hydrogen embrittlement of grain boundaries in nickel: an atomistic study

Abstract

The chemomechanical degradation of metals by hydrogen is widely observed, but not clearly understood at the atomic scale. Here we report an atomistic study of hydrogen embrittlement of grain boundaries in nickel. All the possible interstitial hydrogen sites at a given grain boundary are identified by a powerful geometrical approach of division of grain boundary via polyhedral packing units of atoms. Hydrogen segregation energies are calculated at these interstitial sites to feed into the Rice-Wang thermodynamic theory of interfacial embrittlement. The hydrogen embrittlement effects are quantitatively evaluated in terms of the reduction of work of separation for hydrogen-segregated grain boundaries. We study both the fast and slow separation limits corresponding to grain boundary fracture at fixed hydrogen concentration and fixed hydrogen chemical potential, respectively. We further analyze the influences of local electron densities on hydrogen adsorption energies, thereby gaining insights into the physical limits of hydrogen embrittlement of grain boundaries.

Revealing the Atomic Origin of Heterogeneous Li‐Ion Diffusion by Probing Na

“…Such highly strained lattice could act as a high speed pipe for ion diffusion according to the literature report that expanded lattice can significantly increase ion transport kinetics. [24] It is also consistent with the dislocation mediated fast ion migration www.advmat.de www.advancedsciencenews.com observed in other materials. [12,25] For the first time, these speculations were visualized at atomic-scale resolution.…”

Hydrogen embrittlement controlled by reaction of dislocation with grain boundary in alpha-iron

“…On the other hand, our calculation reveals that the introduction of H atoms on the 24 GB can slightly decrease the GB cohesive strength without the activation of the GB (see Fig. 11 and Table 2), which is in good agreement with previous calculations for H segregation on GBs (Geng et al, 1999;Huang et al, 2017;Solanki et al, 2012;Tahir et al, 2014;Wang et al, 2016). While this chemical effect of bond weakening by hydrogen has long been recognized as the root of hydrogen embrittlement as proposed by the HEDE theory (Gerberich, 2012;Oriani, 1987;Troiano, 1960), we suggest that the GB activation by dislocation-GB reaction is at least equally important in realization of the hydrogen embrittling effect in polycrystalline materials.…”

On the suitability of slow strain rate tensile testing for assessing hydrogen embrittlement susceptibility

“…We follow Serebrinsky et al [62] and assume ∆g 0 b = 30 kJ/mol for H trapped at a grain boundary. While it is anticipated that variations in grain boundary character will give rise to a distribution of trap binding energies, the use of 30 kJ/mol in the current study as an average value for H trapped at grain boundaries is justified based on experimental and computational studies [63][64][65]. Assuming that H linearly degrades the fracture energy, the variation in G 0 with grain boundary H coverage can be defined as:…”