Hydrogen embrittlement in nickel, visited by first principles modeling, cohesive zone simulation and nanomechanical testing

Alvaro, Antonio; Jensen, Ingvild Thue; Kheradmand, Nousha; Løvvik, Ole Martin; Olden, Vigdis

doi:10.1016/j.ijhydene.2015.06.069

Cited by 107 publications

(59 citation statements)

References 27 publications

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“…Significant plasticity was associated with intergranular crack advance; this result is consistent with experimental observations [66] as well as simulations [26,67]. The snapshots presented in Figure 14 show crack nucleation and growth in the sample with hydrogen coverage of 4.8 H/nm 2 .…”

Section: Crack Initiation and Propagationsupporting

confidence: 88%

Atomistic studies of hydrogen effects on grain boundary structure and deformation response in FCC Ni

Kuhr

Farkas

Robertson

2016

Computational Materials Science

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The effect of hydrogen in the grain boundary on the mechanical response of random microstructures was studied by using atomistic simulation techniques and model interatomic potentials. The model interatomic potentials mimic properties of interstitial H in fcc materials within the limitations of empirical force laws. We report fully three-dimensional atomistic molecular dynamics studies of the mechanical response of identical samples with and without H in the grain boundaries. H content changes the structure of the grain boundaries and plays a critical role in the emission of dislocations from the grain boundaries under an applied stress. For lower deformation levels, the presence of H increased the yield strength of the samples, whereas for higher deformation levels, it increased dislocation emission from grain boundary sources, resulting in an increase in the number of dislocations in pileups at the grain boundaries. Increasing the H content resulted in increasingly larger cracks being formed on the grain boundaries, consistent with decreased grain boundary cohesion. Our results support a picture of hydrogen embrittlement resulting from the combined effects of hydrogen on plasticity as well as grain boundary decohesion.

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Section: Crack Initiation and Propagationsupporting

confidence: 88%

Atomistic studies of hydrogen effects on grain boundary structure and deformation response in FCC Ni

Kuhr

Farkas

Robertson

2016

Computational Materials Science

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“…For example, in the case of H-enhanced grain boundary decohesion, it can be inferred from atomistic calculations. The assumption of a linear degradation is supported by recent density function theory (DFT) analyses of H-induced decohesion in nickel, which observed a linear decrease in the surface energy with increasing H coverage [66].…”

Section: Phase Field Fracture Of Embrittled Elastic-plastic Solidsmentioning

confidence: 91%

“…), our objective is to provide a hydrogenassisted fracture mechanics assessment of cracking in SSRT. Thus, χ does not have the same physical meaning as the hydrogen damage coefficients that can be determined from the atomistic simulations of Jiang and Carter [105] or Alvaro et al [66]. In these prior studies, a brittle fracture paradigm was invoked, where χ would generally be interpreted as the potency of hydrogen in reducing the ideal work of fracture.…”

Section: 4mentioning

confidence: 99%

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

et al. 2020

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The onset of sub-critical crack growth during slow strain rate tensile testing (SSRT) is assessed through a combined experimental and modeling approach. A systematic comparison of the extent of intergranular fracture and expected hydrogen ingress suggests that hydrogen diffusion alone is insufficient to explain the intergranular fracture depths observed after SSRT experiments in a Ni-Cu superalloy. Simulations of these experiments using a new phase field formulation indicate that crack initiation occurs as low as 40% of the time to failure. The implications of such sub-critical crack growth on the validity and interpretation of SSRT metrics are then explored.

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“…Alvaro et al [29] show that H binds to octahedral-like sites at the boundary, with site #5 in a very 100 open region of the GB being unstable. This result is slightly counter-intuitive because H atoms have large misfit volume and so generally prefer to occupy sites with more open structure, and surfaces are also quite favorable relative to the bulk.…”

Section: Validated Ni-h Interatomic Potentialmentioning

confidence: 99%

Atomistic study of hydrogen embrittlement of grain boundaries in nickel: I. Fracture

Tehranchi

Curtin

2017

Journal of the Mechanics and Physics of Solids

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Hydrogen ingress into a metal is a persistent source of embrittlement. Fracture surfaces are often intergranular, suggesting favorable cleave crack growth along grain boundaries (GBs) as one driver for embrittlement. Here, atomistic simulations are used to investigate the effects of segregated hydrogen on the behavior of cracks along various symmetric tilt grain boundaries in fcc Nickel. An atomistic potential for Ni-H is first recalibrated against new quantum level computations of the energy of H in specific sites within the NiΣ5(120)⟨100⟩ GB. The binding energy of H atoms to various atomic sites in the NiΣ3(111) (twin), NiΣ5(120)⟨100⟩, NiΣ99(557)⟨110⟩, and NiΣ9(221)⟨110⟩ GBs, and to various surfaces created by separating these GBs into two possible fracture surfaces, are computed and used to determine equilibrium H concentrations at bulk H concentrations typical of embrittlement in Ni. Mode I fracture behavior is then studied, examining the influence of H in altering the competition between dislocation emission (crack blunting; "ductile" behavior) and cleavage fracture ("brittle" behavior) for intergranular cracks. Simulation results are compared with theoretical predictions (Griffith theory for cleavage; Rice theory for emission) using the computed surface energies. The deformation behavior at the GBs is, however, generally complex and not as simple as cleavage or emission at a sharp crack tip, which is not unexpected due to the complexity of the GB structures. In cases predicted to emit dislocations from the crack tip, the presence of H atoms reduces the critical load for emission of the dislocations and no cleavage is found. In the cases predicted to cleave, the presence of H atoms reduces the cleavage stress intensity and makes cleavage easier, including NiΣ9(221)⟨110⟩ which emits dislocations in the absence of H. Aside from the one unusual NiΣ9(221)⟨110⟩ case, no tendency is found for H to cause a ductile-to-brittle transformation for cracks along GBs in Ni, either according to theory or simulation for initial equilibrium H segregation and with no, or limited, H diffusion near the newly-created fracture surfaces. The NiΣ3(111) twin boundary does not absorb H at all, suggesting that embrittlement is more difficult in materials with higher fraction of such twin boundaries, as found experimentally. Experimental observations of cleavage-like failure are thus presumably caused by mechanisms involving H diffusion or dynamic crack growth.

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Hydrogen embrittlement in nickel, visited by first principles modeling, cohesive zone simulation and nanomechanical testing

Cited by 107 publications

References 27 publications

Atomistic studies of hydrogen effects on grain boundary structure and deformation response in FCC Ni

Atomistic studies of hydrogen effects on grain boundary structure and deformation response in FCC Ni

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

Atomistic study of hydrogen embrittlement of grain boundaries in nickel: I. Fracture

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