Hydrogen Diffusion In Metals Research Articles

Investigating Hydrogen in Zirconium Alloys by Means of Neutron Imaging.

Neutrons interact with the magnetic moment of the atomic shell of an atom, as is common for X-rays, but mainly they interact directly with the nucleus. Therefore, the atomic number and the related number of electrons does not play a role in the strength of an interaction. Instead, hydrogen that is nearly invisible for X-rays has a higher attenuation for neutrons than most of the metals, e.g., zirconium, and thus would be visible through dark contrast in neutron images. Consequently, neutron imaging is a precise, non-destructive method to quantify the amount of hydrogen in materials with low attenuation. Because nuclear fuel cladding tubes of light water reactors are made of zirconium (98%), the hydrogen amount and distribution in metallic claddings can be investigated. Even hydrogen concentrations smaller than 10 wt.ppm can be determined locally with a spatial resolution of less than 10 μm (with a high-resolution neutron microscope). All in all, neutron imaging is a very fast and precise method for several applications. This article explains the basics of neutron imaging and provides samples of investigation possibilities, e.g., for hydrogen in zirconium alloy cladding tubes or in situ investigations of hydrogen diffusion in metals.

Atomic insight into the hydrogen diffusion in Al-doped iron structures

Hydrogen diffusion plays an important role in hydrogen embrittlement, which leads to the degradation of metal's mechanical properties. Understanding the hydrogen diffusion in metal at atomic level is helpful to clarify the mechanism of hydrogen embrittlement. In the present work, hydrogen diffusions in Al-doped iron structures were performed by first-principles calculations. The results show that the doped Al atoms can suppress the hydrogen diffusion, and the diffusion energy barrier initially increased with the doping concentration. With a doping concentration of 11.1 %, the hydrogen remained immobile even the temperature increased up to 600 K.

Explainable machine learning for hydrogen diffusion in metals and random binary alloys

Explainable machine learning for hydrogen diffusion in metals and random binary alloys

The INCHAMEL facility – a new device for in-situ neutron investigations under defined temperatures with applicable mechanical load

In order to in-situ quantify the hydrogen diffusion in metals or more precisely in zircaloy cladding tubes with the influence of an applied stress field, a new device was constructed in cooperation with the company ZwickRoell - the transportable INCHAMEL facility. It is a modification of ZwickRoell’s Kappa Mini 1 kN tensile testing machine. The facility is equipped with all features of a tensile testing machine, additionally a defined temperature can be applied. The machine’s design was dedicated in detail to fulfil the requirements for the usage in facilities with neutron radiation. In this manner, neutron radiography investigations can be performed in-situ with the neutron beam passing through the sample without any disturbances by installations like beam windows, thermo-couples, furnace tubes, heater wires, clamps for strain measurements, etc.

Classification of EBSD Kikuchi Patterns for Stainless Steel by Unsupervised Learning Methods to Investigate Grain Boundaries

Electron backscatter diffraction (EBSD) indexing based on Kikuchi diffraction patterns, which indicate the types and orientation of the crystal lattice, is effective for characterizing crystals. Most regions in a sample can be indexed due to simulation of diffraction patterns of possible crystal types, orientations, and angles. However, indexing some of the complex regions related to the grain boundaries, dislocations, and strain areas is difficult. Moreover, minor crystal structures are possibly omitted from the index results. To characterize all the regions, including such complicated boundaries, the analysis of raw data, including all Kikuchi patterns, is necessary. By analyzing all the Kikuchi patterns, significant information can be extracted from mixed crystal conditions. Stainless steel was used as the model sample in this study. As hydrogen diffusion in metals strongly depends on the crystal structure and grain boundaries, structural analysis is required to study hydrogen behavior in steel. In this study, all Kikuchi patterns at all pixels in a measurement area of stainless steel were analyzed simultaneously using unsupervised learning methods, such as principal component analysis and multivariate curve resolution, and the pixels of the measurement area were classified based on the Kikuchi patterns to investigate the grain boundaries and dislocations in detail.

A Modeling Framework for Coupling Plasticity with Species Diffusion

This paper presents a modeling framework---mathematical model and computational framework---to study the response of a plastic material due to the presence and transport of a chemical species in the host material. Such a modeling framework is important to a wide variety of problems ranging from Li-ion batteries, moisture diffusion in cementitious materials, hydrogen diffusion in metals, to consolidation of soils under severe loading-unloading regimes. The mathematical model incorporates experimental observations reported in the literature on how (elastic and plastic) material properties change because of the presence and transport of a chemical species. Also, the model accounts for one-way (transport affects the deformation but not vice versa) and two-way couplings between deformation and transport subproblems. The resulting coupled equations are not amenable to analytical solutions; so, we present a robust computational framework for obtaining numerical solutions. Given that popular numerical formulations do not produce nonnegative solutions, the computational framework uses an optimized-based nonnegative formulation that respects physical constraints (e.g., nonnegative concentrations). For completeness, we will also show the effect and propagation of the negative concentrations, often produced by contemporary transport solvers, into the overall predictions of deformation and concentration fields. Notably, anisotropy of the diffusion process exacerbates these unphysical violations. Using representative numerical examples, we will discuss how the concentration field affects plastic deformations of a degrading solid. Based on these numerical examples, we also discuss how plastic zones spread because of material degradation. To illustrate how the proposed computational framework performs, we report various performance metrics such as optimization iterations and time-to-solution.

Debye Temperature and Quantum Diffusion of Hydrogen in Body-Centered Cubic Metals.

Diffusion of deuterium in potassium is studied herein. Mass transfer is controlled predominantly by the mechanism of overbarrier atomic jumps at temperatures 120–260 K and by the tunneling mechanism at 90–120 K. These results together with literature data allowed us to determine conditions under which the quantum diffusion of hydrogen in metals can be observed, which is a fundamental problem. It is established that in metals with a body-centered cubic lattice tunneling can be observed only at temperatures below the Debye temperature θD solely for metals with θD < 350 K. Predictions are made for metals in which quantum diffusion of hydrogen can be experimentally registered. Metals for which such results cannot be obtained are specified as well. Among them are important engineering materials such as α-Fe, W, Mo, V, and Cr.

Modeling Dislocation-Mediated Hydrogen Transport and Trapping in Face-Centered Cubic Metals

Abstract The diffusion of hydrogen in metals is of interest due to the deleterious influence of hydrogen on material ductility and fracture resistance. It is becoming increasingly clear that hydrogen transport couples significantly with dislocation activity. In this work, we use a coupled diffusion-crystal plasticity model to incorporate hydrogen transport associated with dislocation sweeping and pipe diffusion in addition to standard lattice diffusion. Moreover, we consider generation of vacancies via plastic deformation and stabilization of vacancies via trapping of hydrogen. The proposed hydrogen transport model is implemented in a physically based crystal viscoplasticity framework to model the interaction of dislocation substructure and hydrogen migration. In this study, focus is placed on hydrogen transport and trapping within the intense deformation field of a crack tip plastic zone. We discuss the implications of the model results in terms of constitutive relations that incorporate hydrogen effects on crack tip field behavior and enable exploration of hydrogen embrittlement mechanisms.

Mathematical Model for Process of the Hydrogen Permeability Management of Metals with Internal Stresses Taking into Account the Formation and Decay of Motionless Complexes

A model is proposed for mathematical description of hydrogen diffusion in metals taking into account formation and decay of motionless complexes, taking into account internal elastic stresses. Simple ratios are obtained for calculations of hydrogen permeability and internal stresses in cylindrical metal structures.

A modelling framework for coupled hydrogen diffusion and mechanical behaviour of engineering components

In this paper, we propose a finite element formulation for solving coupled mechanical/diffusion problems. In particular, we study hydrogen diffusion in metals and its impact on their mechanical behaviour (i.e. hydrogen embrittlement). The formulation can be used to model hydrogen diffusion through a material and its accumulation within different microstructural features of the material (dislocations, precipitates, interfaces, etc.). Further, the effect of hydrogen on the plastic response and cohesive strength of different interfaces can be incorporated. The formulation adopts a standard Galerkin method in the discretisation of both the diffusion and mechanical equilibrium equations. Thus, a displacement-based finite element formulation with chemical potential as an additional degree of freedom, rather than the concentration, is employed. Consequently, the diffusion equation can be expressed fundamentally in terms of the gradient in chemical potential, which reduces the continuity requirements on the shape functions to zero degree, {mathcal {C}}_{0}, i.e. linear functions, compared to the {mathcal {C}}_{1} continuity condition required when concentration is adopted. Additionally, a consistent interface element formulation can be achieved due to the continuity of the chemical potential across the interface—concentration can be discontinuous at an interface which can lead to numerical problems. As a result, the coding of the FE equations is more straightforward. The details of the physical problem, the finite element formulation and constitutive models are initially discussed. Numerical results for various example problems are then presented, in which the efficiency and accuracy of the proposed formulation are explored and a comparison with the concentration-based formulations is presented.

Analysis of hydrogen permeation tests considering two different modelling approaches for grain boundary trapping in iron

The electrochemical permeation test is one of the most used methods for characterising hydrogen diffusion in metals. The flux of hydrogen atoms registered in the oxidation cell might be fitted to obtain apparent diffusivities. The magnitude of this coefficient has a decisive influence on the kinetics of fracture or fatigue phenomena assisted by hydrogen and depends largely on hydrogen retention in microstructural traps. In order to improve the numerical fitting of diffusion coefficients, a permeation test has been reproduced using FEM simulations considering two approaches: a continuum 1D model in which the trap density, binding energy and the input lattice concentrations are critical variables and a polycrystalline model where trapping at grain boundaries is simulated explicitly including a segregation factor and a diffusion coefficient different from that of the interior of the grain. Results show that the continuum model captures trapping delay, but it should be modified to model the trapping influence on the steady state flux. Permeation behaviour might be classified according to different regimes depending on deviation from Fickian diffusion. Polycrystalline synthetic permeation shows a strong influence of segregation on output flux magnitude. This approach is able to simulate also the short-circuit diffusion phenomenon. The comparison between different grain sizes and grain boundary thicknesses by means of the fitted apparent diffusivity shows the relationships between the registered flux and the characteristic parameters of traps.

Advanced modeling and numerical simulations for the thermo-chemico-mechanical behaviour of materials with damage and hydrogen, based on the thermodynamics of irreversible processes

In the present article, we propose a fully coupled thermo-elasto-plastic-damage theory, which includes both kinematic and isotropic hardening, and also accounts for hydrogen diffusion in metals. This theory is based on the thermodynamics of irreversible processes under small deformation hypothesis and suppose that hydrogen diffuses in both normal interstitial lattice sites and trapping sites. This model is implemented into Abaqus/Standard by developing a UEL user subroutine and using an “assumed strain” method. A numerical application is performed to simulate hydrogen diffusion in a metallic welded joint submitted to a long-time severe environment at constant temperature.

Magnesium for Dynamic Nanoplasmonics.

ConspectusThe key component of nanoplasmonics is metals. For a long time, gold and silver have been the metals of choice for constructing plasmonic nanodevices because of their excellent optical properties. However, these metals possess a common characteristic, i.e., their optical responses are static. The past decade has been witnessed tremendous interest in dynamic control of the optical properties of plasmonic nanostructures. To enable dynamic functionality, several approaches have been proposed and implemented. For instance, plasmonic nanostructures can be fabricated on stretchable substrates or on programmable templates so that the interactions between the constituent metal nanoparticles and therefore the optical responses of the plasmonic systems can be dynamically changed. Also, plasmonic nanostructures can be embedded in tunable dielectric materials, taking advantage of the sensitive dependence of the localized surface plasmon resonances on the neighboring environment. Another approach, which is probably the most intriguing one, is to directly regulate the carrier densities and dielectric functions of the metals themselves.In this Account, we discuss a relatively new metal in nanoplasmonics, magnesium, and its important role in the development of dynamic plasmonic nanodevices at visible frequencies. We first elucidate the basic optical properties of Mg and compare it with conventional plasmonic materials such as Au, Ag, and others. Then we describe a unique characteristic of Mg, i.e., its reversible phase transitions between the metallic state and a dielectric state, magnesium hydride, through hydrogenation and dehydrogenation. This sets the basis for Mg in dynamic nanoplasmonics. In particular, the structural properties and dielectric functions of the two distinct states are discussed in detail. Subsequently, we highlight the experimental investigations of the physical mechanisms and nanoscale understanding of Mg nanoparticles during hydrogenation and dehydrogenation. We then introduce a plethora of newly developed Mg-based dynamic optical nanodevices for applications in plasmonic chirality switching, dynamic color displays with Mg nanoparticles and films, and dynamic metasurfaces for ultrathin and flat optical elements. We also outline strategies to enhance the stability, reversibility, and durability of Mg-based nanodevices. Finally, we end this Account by outlining the remaining challenges, possible solutions, and promising applications in the field of Mg-based dynamic nanoplasmonics. We envision that Mg-based dynamic nanoplasmonics will not only provide insights into understanding the catalytic processes of hydrogen diffusion in metals by optical means but also will open an avenue toward functional plasmonic nanodevices with tailored optical properties for real-world applications.

Evolution of Dislocation Loops Induced by Different Hydrogen Irradiation Conditions in Reduced-Activation Martensitic Steel.

Hydrogen can be induced in various ways into reduced-activation ferritic/martensitic (RAFM) steels when they are used as structural materials for advanced nuclear systems. However, because of the fast diffusion of hydrogen in metals, the effect of hydrogen on the evolution of irradiation-induced defects was almost neglected. In the present work, the effect of hydrogen on the evolution of dislocation loops was investigated using a transmission electron microscope. Specimens of reduced-activation ferritic/martensitic (RAFM) steels were irradiated with hydrogen ions to 5 × 1020 H+ • m−2 at 523–823 K, and to 1 × 1020 H+ • m−2 − 5 × 1020 H+ • m−2 at 723 K. The experimental results reveal that there is an optimum temperature for dislocation loop growth, which is ~723 K, and it is greater than the reported values for neutron irradiations. Surprisingly, the sizes of the loops produced by hydrogen ions, namely, 93 nm and 286 nm for the mean and maximum value, respectively, at the peak dose of 0.16 dpa under 723 K, are much larger than that produced by neutrons and heavy ions at the same damage level and temperature. The results indicate that hydrogen could enhance the growth of loops. Moreover, 47.3% a0 <111> and 52.7% a0 <100> loops were observed at 523 K, but a0 <111> loops disappeared and only a0 <100> loops existed above 623 K. Compared with the neutron and ion irradiations, the presence of hydrogen promoted the formation of a0 <100> loops.

Electron-Stimulated Hydrogen Desorption from Nickel and Palladium

New experimental data are presented on the radiation-stimulated diffusion of hydrogen in metals, in particular, nickel and palladium, under the action of a 30-keV accelerated electron beam. Hydrogen desorption rates from nickel and palladium are determined for thermal and electron beam heating; a substantial shift of the thermal gas-desorption peaks to the low-temperature range is detected upon radiationinduced heating. The presence of an internal hydrogen atmosphere is shown to create favorable conditions for the vibrational-translational exchange (V–T exchange), non-equilibrium redistribution, and desorption of hydrogen from a solid upon irradiation. Accelerated hydrogen migration stimulated by electrons with an energy below the defect-formation threshold is explained at a qualitative level. First-principles calculations of the electronic structure of the metal–hydrogen system reveal that plasmons are also an efficient mechanism for radiation-energy dissipation over the whole crystal.

Corrosion News

Corrosion News

A generalised model of hydrogen diffusion in metals with multiple trap types

Continuum modelling of hydrogen diffusion in metals, which accounts for both trapping and an imposed force field, is revisited. A generalised model of hydrogen diffusion and trapping is developed as a continuous interpretation of the discrete random-walk theory. A system of nonlinear equations describing the phenomenon of diffusion with multiple types of traps is derived without the assumption of a local equilibrium among hydrogen populations in dissimilar positions. Lattice-trap interchange kinetics can degenerate into local equilibrium as a limit case. Moreover, certain terms in general equations may be negligible in specific situations. By removing these terms, known particularised models of hydrogen diffusion and trapping are recovered. Determining the terms, which are disregarded in reduced models, enables a straightforward assessment of the applicability of these models. The advantages and limitations of particularised models applied to hydrogen embrittlement analyses are discussed.

Modeling Trapping of Hydrogen Absorbed into Aluminum during Corrosion

Hydrogen absorption is a leading cause of degradation of metal structures, during gas-phase exposures and aqueous corrosion processes. Hydrogen absorption and transport in the metal influence kinetics of degradation, and thus incubation periods before fracture and crack propagation rate. Quantitative models of hydrogen embrittlement include descriptions of hydrogen absorption and diffusion coupled to H-induced failure mechanisms.1 Hydrogen diffusion in metals depends critically on reversible and irreversible trapping of H atoms at defects such as dislocations, precipitates, and vacancies. In the case of the high purity aluminum-hydrogen system of interest here, hydrogen diffusion and thermal desorption measurements both suggest the importance of trapping by vacancies and dislocations.2 Evidence for strong hydrogen interactions with vacancies in many metals has been obtained both experimentally,3,4 and through first-principles density function theory (DFT) calculations.5,6 The equilibrium distribution of hydrogen among traps is governed by the hydrogen chemical potential (μH ) or fugacity in the metal, and the formation energies of the various hydrogen traps. A model for hydrogen capture in aluminum during aqueous corrosion is presented, incorporating near-surface trapping of H atoms at vacancies produced by metal dissolution.7 Vacancy-hydrogen interactions are described by a simple non-interacting thermodynamic model incorporating binding of multiple H atoms at vacancies, with energetics derived from first-principles calculations.5 At large absorption rates, submicron-thickness near-surface layers containing elevated vacancy-hydrogen defects concentrations are predicted, consistent with prior experimental observations. The defect layers arise because of the high sensitivity of the vacancy-hydrogen defect concentration to hydrogen chemical potential, resulting from inclusion of interactions of multiple H atoms with vacancies. Vacancy-hydrogen interactions therefore lead to self-concentration of hydrogen near corroding surfaces, at levels orders of magnitude higher than the H interstitial concentration. Similarly elevated hydrogen concentrations near crack surfaces on Al alloys after testing in humid environments.8 Further, the elevated hydrogen concentration explains observations of hydride formation during corrosion, and may be relevant to hydrogen-based microscopic degradation mechanisms.9 The model predictions are quantitatively consistent with results of hydrogen permeation experiments (Figure 1).10 REFERENCES 1. A. Turnbull, in Gaseous Hydrogen Embrittlement of Materials in Energy Technologies,R. P. Gangloff and B. P. Somerday, Eds., Woodhead, Oxford p. 89 (2012). 2. G. A. Young and J. R. Scully, Acta Mater., 46,6337 (1998). 3. Y. Fukai, J. Alloys Compd., 356-357, 263 (2003). 4. H. K. Birnbaum et al., J. Alloys Compd, 253,260 (1997). 5. L. Ismer, M. S. Park, A. Janotti, C. G. Van de Walle, Phys. Rev. B, 80,184110 (2009). 6. R. Nazarov, T. Hickel, J. Neugebauer, Phys. Rev. B, 89, 144108(2014). 7. K. R. Hebert, Electrochim. Acta, 168,199 (2015). 8. G. A. Young, J. R. Scully, Metall. Mater. Trans. A., 33,101 (2002). 9. S. Adhikari, K. R. Hebert, J. Electrochem. Soc., 155, C16 (2008). 10. S. Adhikari, J. H. Ai, K. R. Hebert, K. M. Ho, C. Z. Wang, Electrochim. Acta,, 55,5326 (2010). Figure 1. Evolution of hydrogen chemical potential on the exit side of an Al membrane, during open-circuit corrosion at an equivalent current density of 1 mA/cm2.7 Calculated results (solid lines) at two H absorption current densities, and experimental results (dashed lines) for corrosion in NaOH solutions at the indicated pH values.10 Figure 1

Numerical modeling of hydrogen diffusion in metals accounting for large deformations

While the deleterious effects of hydrogen on metals and alloys are well known, the precise role of hydrogen in the underlying microscopic mechanisms is still not well understood and as of yet, the modeling attempts on hydrogen embrittlement and hydrogen induced cracking have not led to a proper method for life-time prediction. This work aims at the development of a robust numerical strategy in order to solve the non-linear coupled problem presented in the work of Anand [1]. The numerical implementation is performed for finite element method and the analysis are done to address the issue of hydrogen transport and hydrogen-embrittlement-related failures in metals. Specifically, problems related to the mechanism of hydrogen enhanced localized plasticity (HELP) is studied and macroscale shear localization phenomenon resulting from hydrogen induced material softening is considered at the phenomenological level.

A Critical Review of Existing Hydrogen Diffusion Models Accounting for Different Physical Variables

The present paper offers a continuum modelling of trap-affected hydrogen diffusion in metals and alloys, accounting for different physical variables of both macroscopic nature (i.e., related to continuum mechanics, e.g., stress and strain) and microscopic characteristics (material microstructure, traps, etc.). To this end, the model of hydrogen diffusion assisted by the gradients of both hydrostatic stress and cumulative plastic strain,stress-and-strain assisted hydrogen diffusion, proposed and frequently used by the authors of the present paper (Toribio &amp; Kharin) is analysed in addition to other well-known models such as those proposed by (i) McNabb &amp; Foster, (ii) Oriani, (iii) Leblond &amp; Dubois, (iv) Sofronis &amp; McMeeking, (v) Krom and Bakker, showing their physical and mathematical differences and similarities to account for different physical variables.