The formation of excess free volume in triple junctions of &lt;111&gt; and &lt;100&gt; tilt boundaries in Ni at crystallization

Полетаев, Г. М.; Novoselova, D. V.; Kaygorodova, Valentina M.; Старостенков, М. Д.

doi:10.1063/1.4937841

Cited by 4 publications

(7 citation statements)

References 9 publications

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“…However it should be taken into account that, firstly, the equilibrium distance between the metal and hydrogen atoms is much less than that between metal atoms (about one and a half times [15]). Secondly, as a result of the thermal oscillations of atoms, the barrier ratio can vary, due to which the probability of realization of the mechanism 1 is nonzero.…”

Section: Resultsmentioning

confidence: 99%

“…When testing these potentials, it was found that they do not satisfactorily describe certain characteristics of hydrogen in the considered metals (for example, the binding energy with defects). Therefore, in addition to them, we have previously developed our own interatomic potentials for Pd-H and Ni-H systems [15]. The choice of Pd and Ni is due to increased attention to these fcc metals and a relatively large amount of experimental data available for them.…”

Section: Description Of the Modelmentioning

confidence: 99%

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Molecular dynamics simulation of hydrogen atom diffusion in crystal lattice of fcc metals

Полетаев

Zorya

Novoselova

et al. 2017

International Journal of Materials Research

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Molecular dynamics simulation of hydrogen atom diffusion in crystal lattice of fcc metalsThe study of diffusion of hydrogen atoms in the crystal lattice of fcc metals Pd, Ni, Al, Ag was performed by the method of molecular dynamics. The diffusion characteristics of hydrogen impurity (activation energy of hydrogen atom migration and pre-exponential factor in the Arrhenius equation) in the considered metals were calculated. It is shown that the prevailing mechanism of the over-barrier hydrogen diffusion in fcc metals consists of successive migration through octahedral and tetrahedral pores. During migration, as a rule, the hydrogen atom is not delayed in tetrahedral pores.Keywords: Molecular dynamics; Metal; Hydrogen; Diffusion; Diffusion mechanism IntroductionThe interaction of hydrogen with metals has been the subject of intensive study over the last century. On the one hand, this is due to the practical interest in using the metal-hydrogen system: creation of radiation-resistant materials, filters for obtaining of pure hydrogen, including for isotope separation, accumulation and storage of light gases in metals and alloys and the problem of hydrogen transportation. On the other hand, this is due to the undesirable effects of hydrogen on the properties of materials (embrittlement, corrosion, cracks spreading) [1,2].Hydrogen atoms have a unique small mass and size in comparison with other interstitial atoms in metals, and for this reason have extremely high diffusion mobility [3,4]. The diffusion coefficients of hydrogen in solid metals are almost the same as in liquids. This feature, in addition to the small size and mass of the hydrogen atom, is also associated with the dissociation of a hydrogen molecule into individual atoms upon ingress into the metal [5,6]. In metal crystals, hydrogen atoms are in interstitials and in the diffusion process they pass from one interstitial site to another. In fcc lattice, hydrogen can occupy two types of interstitial sites: octahedral and tetrahedral. At the present time, the question of the mechanism of hydrogen diffusion in the crystal lattice of metals remains. Even in a pure crystal, transitions between interstitials of different types are possible, which entails, in particular, the ambiguity of the activation energy of hydrogen diffusion. In addition, as noted in [7], the redistribution of hydrogen atoms in interstitial sites of various types due to changes in external conditions, for example, deformation, can lead to a change in the diffusion parameters. It should be noted that other factors may also lead to deviations from the Arrhenius law, in particular, the possibility of diffusion jumps of different lengths and the effect of crystal lattice defects [1,5].The aim of the present work is to study the mechanism of hydrogen atom diffusion in the crystal lattice of fcc metals using the molecular dynamics method and to calculate the diffusion parameters: the activation energy and the pre-exponential factor in the corresponding Arrhenius equation. Typical fcc metals with d...

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Section: Resultsmentioning

confidence: 99%

Section: Description Of the Modelmentioning

confidence: 99%

Molecular dynamics simulation of hydrogen atom diffusion in crystal lattice of fcc metals

Полетаев

Zorya

Novoselova

et al. 2017

International Journal of Materials Research

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“…Indeed, the evolutionary formation of grain boundary networks can be described by crystallization or defect-mediated grain boundary migration [29] with more complex crystallographic constraints at the TJ leading to well-established TJ drag [30]. And it is reasonable that both crystallization and migration can trap complex metastable defects and excess free volume in the TJ, such as illustrated in the work by Poletaev et al [31,32]. This dynamics becomes even more complex during radiation events that are can alter the shape, location, and character of grain boundaries and triple junctions [33][34][35].…”

Section: Comparison To Experimental Observations and Relevance Of Thementioning

confidence: 99%

Statistical analysis of the interaction between irradiation-induced defects and triple junctions

Zarnas

Dingreville

Muntifering

et al. 2020

Adv. Model. and Simul. in Eng. Sci.

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By using a generalized, spatially resolved rate theory, we systematically studied the irradiation-induced diffusion and segregation of point defects near triple junctions. Our model captured not only the formation, growth, and recombination of point defects but also the interaction of these defects with pre-existing defects. We coupled the stress field of the triple junction with defect diffusion via a modified chemical potential. The residual stress fields of grain boundaries and triple junctions are modeled via disclination mechanics theory. By assessing the behavior of 144 triple junctions with vacancy and interstitial defects, we correlated defect-sink efficiencies with key characteristics of triple junctions. For vacancies, the geometric configuration of triple junctions dominated sink efficiency, suggesting that equiaxed grains would resist the accumulation of vacancies more than elongated grains. For interstitials, the sink density of the grain boundaries composing the triple junctions dominated sink efficiency. Hence, the interstitial concentration may be managed by adjusting the structure of the grain boundaries. Overall, we illustrated the complex coupling between pre-existing defects and radiation-induced defects through interaction of their stress fields. This theoretical framework provides an efficient tool to rapidly assess defect management in microstructures.

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“…Несмотря на экспериментальное подтверждение существования " структурно правильных" равновесных тройных стыков, оставался нерешенным вопрос относительно их невысокой доли в поликристаллах, так как, согласно экспериментальным данным, неравновесных стыков, содержащих избыточный свободный объем, значительно больше, чем равновесных [1,2]. В работах [9,10] с помощью компьютерного моделирования нами было показано, что наиболее вероятной причиной формирования избыточного свободного объема в стыках при кристаллизации является фиксация объема жидкой фазы при встрече трех фронтов кристаллизации, в результате затвердевания которой в условиях фиксированного объема (вследствие более низкой плотности жидкой фазы по сравнению с твердой) происходит концентрирование избыточного свободного объема в тройном стыке после затвердевания. Образование в стыке дислокационного или дисклинационного комплексов вследствие зернограничного проскальзывания нами представляется второстепенной причиной.…”

Section: Introductionunclassified

“…Этот недостаток атомов для формирования " идеального" тройного стыка приводит к появлению избыточного свободного объема, который рассматривается в процессе кристаллизации преимущественно в тройном стыке. В [10] было показано, что в этом случае концентрация условных вакансий (т. е. доля недостающих атомов по сравнению с равновесными тройными стыками) может достигать в области стыка 2%.…”

Section: Introductionunclassified

Исследование Формирования Избыточного Свободного Объема В Тройных Стыках Границ Зерен При Кристаллизации На Примере Никеля

Полетаев¹,

Новоселова²,

Зоря³

et al. 2018

Физика Твердого Тела

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The formation of an excess free volume in triple junctions during crystallization has been studied by the molecular dynamics model using nickel as an example. It is shown that an excess free volume that forms during nickel crystallization in triple junctions predominantly forms as a result of the fixation of the liquid phase volume when contacting three crystallization fronts that contains, after crystallization, a high fraction of the free volume. In some cases, as the free volume is concentrated in triple junctions, a comparatively small crystalline subgrain (from one to several nanometers in diameter) forms, and the subgrain has the orientation different from those of contacting grains and exists in the extended state.

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The formation of excess free volume in triple junctions of <111> and <100> tilt boundaries in Ni at crystallization

Cited by 4 publications

References 9 publications

Molecular dynamics simulation of hydrogen atom diffusion in crystal lattice of fcc metals

Molecular dynamics simulation of hydrogen atom diffusion in crystal lattice of fcc metals

Statistical analysis of the interaction between irradiation-induced defects and triple junctions

Исследование Формирования Избыточного Свободного Объема В Тройных Стыках Границ Зерен При Кристаллизации На Примере Никеля

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