Hydrogen-enhanced vacancy embrittlement of grain boundaries in iron

Momida, Hiroyoshi; Asari, Yusuke; Nakamura, Yoshimichi; Tateyama, Yoshitaka; Ohno, Takahisa

doi:10.1103/physrevb.88.144107

Cited by 61 publications

(30 citation statements)

References 59 publications

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“…All the atomic positions were relaxed based on Hellmann-Feynman forces until all of the forces were less than 0.03 eV/Å. The lattice dimensions in the GB plane were fixed during the calculations, ignoring the Poisson's ratio to simplify the calculations [6,27,28]. This step was iterated until the GB fractured.…”

Section: Methodsmentioning

confidence: 99%

Atomic bond-breaking behaviour during grain boundary fracture in a C-segregated Fe grain boundary

Miyazawa

Hakamada

Mabuchi

2017

Philosophical Magazine Letters

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First-principles fully relaxed tensile tests were performed on a C-segregated Fe Σ3 (111)/[ 0 1 1 ] symmetrical tilt grain boundary (GB) to investigate the breaking behavior of C-Fe bonds during tensile straining. Fe atoms around a C atom moved obliquely to the tensile direction, and C-Fe bonds stretched in the tensile direction without premature bond breaking. Analyses of the electronic states during deformation showed that a variation in the charge density at the bond critical point was much larger for the C-Fe bond than for the P-Fe bond and that the C atom exhibited larger variations of s and p states involved in the covalentlike characteristics than the P atom. It is suggested that these lead to a high mobility of the C-Fe bonds. On the other hand, first-principles shear tests on the Fe GB imply that C-segregated Fe GB toughening is not associated with increased crack blunting by dislocation emission.

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Section: Methodsmentioning

confidence: 99%

Atomic bond-breaking behaviour during grain boundary fracture in a C-segregated Fe grain boundary

Miyazawa

Hakamada

Mabuchi

2017

Philosophical Magazine Letters

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“…In such conditions, it is difficult to interpret the impact of H on diffusivity. Vacancies, produced by intense plasticity [10,11] and stabilized by H, have been proposed as a possible source of H related degradation of metallic materials [12,13] at room temperature. Furthermore, simultaneous H and vacancy uptake can be obtained by oxidation in aqueous media.…”

Section: Introductionmentioning

confidence: 99%

Hydrogen influence on diffusion in nickel from first-principles calculations

2015

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We propose a method to evaluate the diffusion coefficient of vacancy-hydrogen clusters (VH n ) in metals. The key is a good separation of time scales between H diffusion and the metal-vacancy exchange. The Ni-H system is investigated in details, using ab initio calculations, but the arguments can be transposed to other systems. It is shown that cluster diffusion can be treated as an uncorrelated random walk and that H is always in equilibrium before the vacancy-metal exchange. Then, the diffusion coefficient is a sum over jump paths of the equilibrium probability of being in a specific VH n configuration times the corresponding activation terms. The influence of H on the energy barrier is well reproduced by effective pair interactions between the jumping Ni and the H atoms inside the vacancy. This model is motivated by an analysis of the electronic charge redistribution in key saddle configurations. The interaction is repulsive and decreases with distance. The model is used to find easy jump path, reduce the number of saddle searches, and provide an estimate of the error expected from this reduction. The application to the Ni-H system shows that vacancies are drastically slowed down by H. The effects of temperature and bulk H concentration are explored and the origin of the non-Arrhenius behavior is explained. At equilibrium, VH n clusters always induce a speedup of metal diffusion. The implications concerning H induced damage, in particular in regards to Ni-Cr oxidation, are discussed.

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“…Many theories have been proposed to explain this phenomenon including hydrogen-enhanced localized plasticity mechanism, [1][2][3][4] hydrogen-enhanced decohesion mechanism [5][6][7] and hydrogen-enhanced vacancies and nanovoids coalescence mechanism. [8][9][10][11] Among these explanations, there is consensus in that mobile hydrogen causes degradation in steels. 12) Therefore, it is appropriate for reducing the HE susceptibility by preventing the ingress of hydrogen or immobilizing free hydrogen by trapping them in certain sites.…”

Section: Introductionmentioning

confidence: 99%

Hydrogen Traps and Hydrogen Induced Cracking in 20CrMo Steel

Zhu

Yao

et al. 2017

ISIJ Int.

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The hydrogen trapping sites of commercial 20CrMo steel samples with electrochemically charged hydrogen were characterized by thermoelectric power (TEP) and scanning Kelvin probe force microscope (SKPFM). A surface potential drop of about 190 mV was found for the globular MnS inclusion and 150 mV for the elongated one due to the hydrogen absorption of MnS inclusions. Similar to thermal desorption measurement, TEP is a potential method in analyzing hydrogen traps of solid solution, dislocations and irreversible traps. The fracture morphology and hydrogen induced cracking can be explained by combined hydrogen embrittlement mechanisms. Although hydrogen induced cracks are found to initiate at the elongated inclusions, only longitudinal cracks were observed in this study which is not detrimental to the embrittlement.

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Hydrogen-enhanced vacancy embrittlement of grain boundaries in iron

Cited by 61 publications

References 59 publications

Atomic bond-breaking behaviour during grain boundary fracture in a C-segregated Fe grain boundary

Atomic bond-breaking behaviour during grain boundary fracture in a C-segregated Fe grain boundary

Hydrogen influence on diffusion in nickel from first-principles calculations

Hydrogen Traps and Hydrogen Induced Cracking in 20CrMo Steel

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