Hydrogen embrittlement of grain boundaries in nickel: an atomistic study

Shan Huang,David L Mcdowell,Ting Zhu,Dengke Chen,Jun Song

doi:10.1038/s41524-017-0031-1

Shan Huang, David L Mcdowell + Show 3 more

Open Access

https://doi.org/10.1038/s41524-017-0031-1

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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.

Highlights

Challenges associated with a hydrogen economy are substantial, ranging from hydrogen generation and storage to transportation.[1]
We have performed an atomistic study of H embrittlement of grain boundaries (GBs) in Ni by combining the geometrical analysis of polyhedral packing units for H interstitial adsorption, atomistic calculation of H segregation energies, and thermodynamic theory of interfacial embrittlement
The H embrittlement effects are quantitatively evaluated for symmetric tilt GBs of ∑5(310)[001], ∑17(140)[001], ∑11(113)[011] and ∑27(115)[011]

Summary

INTRODUCTION

Challenges associated with a hydrogen economy are substantial, ranging from hydrogen generation and storage to transportation.[1]. The former is much larger than the latter, consistent with the previous quantum mechanical analysis of chemo–mechanical coupling of impurities at GBs.[12] These results indicate that the positivity of ΔEgad À ΔEsad can be mainly attributed to the chemical (electronic) effect of H binding to Ni. That is, the electron density at the Ni surface is lower than that of the GB, enabling the lower embedding energy of H to the surface.[34] In contrast, the elastic relaxation due to size mismatch between the small H atom and the interstice of polyhedral holes plays a minor role. Segregated GBs, we analyze the H adsorption energies at both GBs and separated surfaces based on the electronic theory of H alloying in metals.[36] Figure 4 shows a collection of calculated ΔEgad;i and ΔEsad;i at various sites of [001] and [011] GBs studied. This value gives a reasonable order-of-magnitude estimate to the reduction of W0 at

Evaluation of H lattice concentration

Findings

DISCUSSION