Hydrogen Diffusion Coefficient Research Articles

Predictive evaluation of hydrogen diffusion coefficient on Pd(111) surface by path integral simulations using neural network potential

Quantum diffusion of hydrogen (H) on palladium (Pd) (111) was studied using two types of path integral simulations: quantum transition state theory (QTST) and ring polymer molecular dynamics (RPMD). The use of an artificial neural network potential trained by density functional theory calculations has made it feasible to perform path integral simulations considering nuclear quantum effects (NQEs) of a many-body Pd-H system with accuracy. The QTST result has shown a clear non-Arrhenius behavior in the diffusion coefficient (D) of H below the temperature of 150–200 K due to the NQEs. Comparing the D on Pd surface and bulk Pd, it was found that surface and bulk diffusion are competitive at high temperature. Consistent with this, it was observed in the RPMD simulation at 800 K that a part of the quantum trajectories of H on the surface bifurcates to the Pd subsurface. As the temperature decreases, the surface diffusion becomes much faster than the bulk diffusion. Furthermore, distinct quantum behaviors of H were identified at the surface and within the bulk. The D values obtained from this study using a “flexible” Pd surface model differed considerably from those previously reported using “frozen” Pd surface models, indicating an important contribution from Pd vibrations coupled with H diffusion. Published by the American Physical Society 2024

Prediction of Hydrogen Diffusion Behavior under the Influence of Defect Structures in Stainless Steel Passivation Film Based on Molecular Dynamics.

The excellent corrosion resistance of stainless steel primarily relies on the formation of a dense passivation film on its surface. Stress corrosion and hydrogen embrittlement are the primary forms of damage to the stainless steel passivation film, leading to film rupture and subsequent corrosion of the stainless steel substrate. The passivation film exhibits semiconducting properties and typically consists of a bilayer structure with a chromium-rich inner layer and an iron-rich outer layer. This study employs molecular dynamics simulations to investigate the interaction energy between hydrogen atoms and pristine stainless steel passivation films (Fe2O3/Cr2O3) as well as those containing three different types of defects and predicts the diffusion processes of hydrogen atoms in passivation films. The results indicate that the strongest interaction energy of -1.4402 eV is observed between hydrogen atoms and the pristine passivation film. However, as defects emerge within the passivation film, the interaction energy decreases, with a minimum energy of -0.1931 eV observed for the film containing chromium vacancies (VCr), representing a nearly one-order-of-magnitude reduction compared to the defect-free case. Furthermore, the diffusion coefficients of hydrogen atoms in the three defective passivation films are calculated as 6.437 × 10-10, 8.249 × 10-10, and 50.892 × 10-10 m2/s, respectively. Notably, the presence of a VCr defect enhances the hydrogen diffusion coefficient by an order of magnitude compared to the pristine film. Anisotropic diffusion paths and properties are elucidated through an analysis of the self-diffusion behavior of hydrogen in different detective passivation films, providing a theoretical basis for the prediction of hydrogen-induced cracking and the development of early warning technologies for passivation film surface failure.

Hydrogen diffusion mechanisms in the 4130X steel: An integrated study with electrochemical experiments and molecular dynamics simulations

In this work, hydrogen diffusion behavior and mechanisms in the 4130X steel influenced by temperature, locally high concentration, and grain boundary were studied by leveraging both electrochemical hydrogen permeation experiments and molecular dynamics simulations. It was revealed that the hydrogen diffusion coefficient of the 4130X steel was increased with increasing temperature and decreasing locally high hydrogen concentration. The grain boundaries with misorientation below 15° characterized by an electron backscatter diffraction map were identified as hydrogen trapping sites, thus rendering a lower mean square displacement of hydrogen atoms and localized hydrogen diffusion trajectories. Furthermore, at a high hydrogen concentration of 4 at. %, these grain boundaries were saturated by hydrogen atoms, and platelet-like hydrogen clusters were formed within the lattice, which further inhibited the diffusive motion of hydrogen atoms. These findings would deepen our understanding of hydrogen embrittlement mechanisms by establishing the connections between macroscopic permeation behavior and atomic-scale hydrogen diffusion in structural materials.

Simulated hydrogen diffusion in diamond grain boundaries

To evaluate hydrogen diffusion within diamond, a series of molecular dynamics simulations have been carried out in which diffusion coefficients and activation energies were determined. Diamond grown via chemical vapour deposition (CVD) contains a high hydrogen concentration within grain boundaries, because of this, common tilt grain boundaries were recreated from transmission electron microscopy images taken from literature. Diffusion coefficients of hydrogen placed within the grain boundary were estimated and compared to the bulk diffusion. Unlike many crystalline structures, some grain boundaries presented limited diffusion when compared to the bulk. Diffusion characteristics of grain boundaries are thought to be a result of channelling effects combined with the formation of sp3C-H bonds with sp2 carbon present within some grain boundaries - increasing and decreasing diffusion rates respectively. Potential wells were observed across some but not all the grain boundaries resulting in hydrogen trapping and anisotropic diffusion.

Understanding the correlation of aging treatments and stress corrosion crack growth of a secondary hardening ultra-high strength steel

The correlation of aging treatments and stress corrosion crack growth of a secondary hardening ultra-high strength steel was investigated using microstructural characterization, electrochemical hydrogen penetration experiment, thermal desorption spectroscopy analysis, and stress corrosion crack growth test. The results showed that increase of aging duration led to slight increase in the fraction of reversed austenite but decrease in dislocation density while no notable variation in grain boundary misorientation distribution and the corrosion behavior was observed. The shrinkage and fracture toughness continued to increase with aging duration while the yield strength reaching a maximum value after 5 hours of aging. Longer aging durations led to the decrease in effective hydrogen diffusion coefficient but improvement of stress corrosion cracking resistance, mainly due to the coarsening and nucleation of M2C carbides, as well as the higher fraction of reversed austenite. This work provided the theoretical and technical basis for improving the stress corrosion cracking resistance of this steel.

ВІДНОВЛЕННЯ ПАЛАДІЄВИХ МЕМБРАН ПІСЛЯ КОНТАКТУ З ВОД-НЕМ ДЛЯ ВОДНЕВО-КИСНЕВИХ ПАЛИВНИХ ЕЛЕМЕНТІВ

Annotation. Studying the deformations of palladium membranes under the influence of hydrogen, which is a relevant issue for hydrogen energy and the nuclear industry. The mechanisms of palladium membrane shape change due to hydrogen penetration and the formation of temporary gradient alloys such as α-PdHn are consid-ered. Experiments were conducted using a hydrogen-vacuum installation, where the processes of membrane satu-ration and degassing were studied at temperatures from 100°C to 360°C and hydrogen pressures from 0.01 MPa to 2.5 MPa. It was established that the change in the shape of the membrane occurs in two stages: first, a rapid bending of the membrane is observed, and then a gradual return to the initial state. It was established that the maximum change in the shape of the membrane, which occurs at a constant temperature, depends on the diffu-sion coefficient and the equilibrium solubility of hydrogen in palladium. However, when the temperature chang-es, the diffusion coefficient of hydrogen in palladium and the equilibrium concentration of hydrogen in palladi-um also change, which affects the temperature dependence of the final shape change of the membrane. This fact makes it possible to effectively determine the time of hydrogen penetration into the membrane, control the change in shape and adjust the operating modes of the fuel cell. Special attention is paid to the use of palladium alloys with copper and silver to increase the resistance of membranes to the influence of hydrogen. It is shown that such alloys have better mechanical characteristics and a longer service life at high temperatures. The effect of degassing on the restoration of membranes after contact with hydrogen was studied, the main factors affecting the efficiency of this process were determined. The results of the work confirm the need for further research on increasing the resistance of palladium membranes to deformations, as well as the development of new materials and technologies to improve their operational characteristics

Study of Hydrogen Migration in Titanium Using a Vortex Electromagnetic Field and Accelerated Electrons in Subthreshold Values

The migration of hydrogen in an in homogeneously hydrogen-saturated commercial titanium VT1-0 has been studied using a high-frequency electromagnetic field and an accelerated electron beam. The use of a high-frequency 50–1000 kHz electromagnetic field, which generates eddy currents in the material, made it possible to observe the process of hydrogen migration near the surface and in the depth of the sample. To accelerate the migration of hydrogen in the volume of the sample, electron irradiation with an energy of 30–45 keV was used. The migration process was studied in an inhomogeneously hydrogen-saturated commercial titanium sample with a titanium nitride film deposited on its surface by magnetron sputtering. Flat samples VT1-0 were saturated with hydrogen using the Sieverts method. The diffusion coefficient of hydrogen in titanium was determined from the change in the magnitude of the signal from the eddy current sensor along the depth of the sample and along the sample, as hydrogen migrated in the sample. The values of the diffusion coefficients of hydrogen along the surface and in the depth of the sample under equilibrium conditions and under stimulation by an accelerated electron beam are obtained.

Very high cycle fatigue properties of ultrahigh strength steels in the presence of hydrogen

The very high cycle fatigue (VHCF) properties of 2000 MPa ultrahigh strength martensitic steels after hydrogen pre-charging were investigated by means of ultrasonic fatigue tests. Results showed that the VHCF lives of the experimental steels were drastically decreased by about two orders after pre-charged with a hydrogen concentration of CH = 1.23 wppm. The experimental steel tempered at a higher temperature of 300 °C with some epsilon-carbides and a lower density of dislocations showed higher VHCF lives in the presence of hydrogen. It could be attributed to the lower hydrogen diffusion coefficient since hydrogen might accelerate fatigue crack propagation in the granular bright facet (GBF) area.

Study on the continuous cooling transformation behavior of X65 hydrogen transportation pipeline steel

Abstract In this work, the continuous cooling transformation (CCT) behavior of X65 hydrogen transportation pipeline steel was studied by Gleeble-3800 machine. The CCT curve was constructed by temperature-dilation curves and microstructures of samples at different cooling speeds. The Ac1 and Ac3 temperatures of the tested steel are 715 °C and 901 °C. Polygonal ferrite and pearlite can be recognized when the cooling speed is between 0.2 °C/s ~ 5 °C/s, bainite and polygonal ferrite can be recognized when the cooling speed is higher than 10 °C/s. The hot-rolling process was designed according to CCT. After finishing rolling, the air cooling steel plates possesses higher hydrogen diffusion coefficient, and the steel plates coiled at 650 °C possesses lower hydrogen diffusion coefficient.

Crystal structure and hydrogen sorption properties of Nd0.5Y0.5MgNi4-xCox alloys (x = 0–3)

The gas-phase and electrochemical hydrogenation properties of Nd0.5Y0.5MgNi4-xCox (where x varies from 0 to 3) were studied. Samples were prepared using sintering and annealing procedures. X-ray diffraction analysis indicated that all the alloys were single-phase. The alloys readily absorbed hydrogen, and the crystal structures of the resulting saturated hydrides were refined. Nd0.5Y0.5MgNi4H4.2 and Nd0.5Y0.5MgNi3CoH4.4 belong to the NdMgNi4H3.6 structural type, while Nd0.5Y0.5MgNi2Co2H5.5 and Nd0.5Y0.5MgNiCo3H6.0 belong to the LaMgNi4H4.85 structural type. Electrochemical studies revealed that the maximum discharge capacity of Nd0.5Y0.5MgNi4-xCox electrodes increased from 236 mAh/g to 328 mAh/g as the cobalt content increased. The high-rate dischargeability (HRD1000) initially decreased from 48 % to 7 % with increasing cobalt content, but then increased to 32 % at the highest cobalt concentration. Additionally, the electrochemical kinetic properties were determined and compared for these electrodes, including the charge-transfer resistance (Rct), polarization resistance (Rp), exchange current density (I0), limiting current density (IL), and hydrogen diffusion coefficient (DH).

Hydrogen permeation behavior and mechanisms in nitrile butadiene rubber composites for hydrogen sealing

As the most widely used sealing component in hydrogen systems, rubber seals are affected by hydrogen over long-term service. Hydrogen molecules can dissolve into rubber materials and diffuse through the material. Studies have shown that adding fillers can enhance rubber's performance, improve its compatibility with hydrogen, and reduce the damage caused by hydrogen diffusion. Therefore, this study integrates experimental hydrogen permeation research with finite element modeling for nitrile butadiene rubber (NBR). The aim is to investigate the influence of filler properties on the microstructure, hydrogen permeation behavior, and hydrogen concentration distribution within NBR. Ultimately, the study elucidates the mechanisms governing hydrogen distribution evolution and permeation in NBR under hydrogen environments. The results indicate that the crosslink density of NBR filled with carbon black (NBR-CB) and silica (NBR-SC) is directly proportional to the filler content. NBR with higher filler content exhibits a lower hydrogen permeation coefficient and superior hydrogen barrier properties. In contrast to silica fillers, carbon black fillers demonstrate strong adsorption and a more pronounced barrier effect against hydrogen molecules, thereby enhancing the hydrogen barrier efficiency. The increase in carbon black's hydrogen solubility (from 2.2 × 10-4 to 16.9 × 10-4 cc(STP)·cm-3(polymer)·cmHg-1) effectively reduces the hydrogen permeation coefficient. In contrast, the rise in carbon black's hydrogen diffusion coefficient (from 0.1 × 10-6 to 4.1 × 10-6 cm2·s-1) exacerbates the overall hydrogen permeation coefficient of NBR-CB, thereby intensifying the hydrogen permeation process.

Hydrogen embrittlement in Nickel oligocrystals: Experimentation and crystal plasticity-phase field fracture modeling

This work investigates the hydrogen embrittlement (HE) behavior of Nickel-201 alloy using experimental and numerical approaches. In experimentation, the effect of electrochemical hydrogen charging on the deformation behavior of tensile oligocrystals is investigated at different strain rates. Irrespective of the strain rate levels, all the hydrogen-charged tensile oligocrystals exhibited intergranular (IG) fracture exclusively along the random high-angle grain boundaries (RHAGBs). At the same time, no crack was observed along the coincident site lattice (CSL) Σ3 type grain boundaries. The absence of an interconnected grain boundary network, lower stress levels, and insensitivity of H-induced IG fracture to the strain rate levels of investigated FCC oligocrystals (with low lattice hydrogen diffusion coefficient) established the insignificance of dynamic H-redistribution toward HE. In numerical simulations, a crystal plasticity-phase field fracture finite element model simulates the macroscopic tensile response and corresponding microscopic fracture evolution behavior for hydrogen-free and hydrogen-charged tensile oligocrystals. The experimental results corroborated by numerical simulations, validate that the reduction in fracture energy of RHAGBs, induced by hydrogen segregation through thermodynamic equilibrium during hydrogen charging prior to deformation, is the dominating factor governing HE.

Hydrogen diffusion and hydrogen embrittlement in iron (steel)

This article examines the diffusion of hydrogen (H-diffusion) and the temperature dependences of the diffusion coefficient of hydrogen (DH) in the metal (M)-hydrogen system. The metal used was iron and low-alloy steel. Taking into account experimental data on hydrogen diffusion in the Fe-H and steel-H systems, the main diffusion parameters were calculated and compared. It is shown that the temperature dependences of the hydrogen diffusion coefficient in metal samples in a one-stage reaction under isothermal conditions are described by the Arrhenius equation. For some M-H systems, experimental data show a deviation of the diffusion coefficient from the ideal one calculated using the Arrhenius equation. This discrepancy can be eliminated using the statistical theory of absolute reaction rates. For the temperature range 25–1250 oС, the pre-exponential coefficient and activation energy of hydrogen diffusion in a body-centered cubic (bcc) lattice of iron (α–Fe) were calculated using the Arrhenius equation. These parameters make it possible to describe the dependence of the rate of hydrogen diffusion in a metal on temperature and to predict the behavior of hydrogen diffusion when changing the conditions of the kinetic process (concentration of substances, pressure, structure, composition, etc.). Tabular values of the calculated pre-exponential factor and activation energy of hydrogen diffusion in previously studied iron-based samples are presented. The temperature dependences of the hydrogen diffusion coefficient in a lattice of iron α–Fe can be divided into low-temperature and high-temperature regions. The calculated diffusion parameters of hydrogen in the metal lattice for the low-temperature 25– 800 oC and high-temperature 800–1250 oC regions differ markedly from each other. In addition, these calculated values are significantly influenced by the structure and composition of the metal. We also studied the diffusion of hydrogen in α-iron using ab initio density functional calculations. Molecular dynamics calculations using transition state theory were used. The calculated diffusion coefficient of hydrogen in α-Fe is consistent with previously obtained experimental data. Hydrogen embrittlement (HE) is considered using internal pressure, hydrogen enhanced localized plasticity (HELP) and hydrogen enhanced decohesion embrittlement (HEDE) theories.

Mobilities of volatiles (H, F and C) in apatite at high temperatures

Apatite serves as a notable host for diverse volatiles, but experimental data concerning the mobilities of volatiles out of its lattice remains scarce. Despite several investigations elucidating the diffusivities of F, Cl, and OH, their interplay mechanism remains poorly understood. Herein, to unveil the mobilities of hydrogen, fluorine, and carbon out of the apatite lattice and their intricate interaction mechanisms during high temperature processes, we carry out annealing experiments at 900, 1000, and 1100 °C on two apatite samples with distinct fluorine contents. Our findings indicate that along the c-axis, hydrogen diffusion coefficients surpass those of fluorine by 2–3 orders of magnitude, with lower activation energies observed. Hydrogen diffusion shows strong anisotropy, with lager diffusivities and lower activation energies along the c-axis than the a-axis. For both hydrogen and fluorine, the Durango apatite shows smaller diffusivities along the c-axis than the Imilchil apatite. Contrarily, carbon diffusion is absent in both samples at these temperatures. These differences in diffusivity may suggest that hydrogen diffuses as OH− along the a-axis and as H+ along the c-axis, while fluorine diffusion relies on hydrogen diffusion along the c-axis. Based on these new data, the capacity of apatite to record volatiles can be evaluated. All volatiles, including hydrogen, is likely preserved within the core of apatite during thermal events from several days to years, such as rapid volcanic eruptions. However, for prolonged thermal events lasting hundreds of millions of years, apatite preserves volatiles for F, Cl and C, but not hydrogen.

Highly reversible Mg-containing multicomponent high-entropy alloys for electrochemical hydrogen storage applications

Magnesium containing high entropy alloys have gained attention recently as a potential material for hydrogen storage applications. In this work, five non-equiatomic compositions of MgTiZrNiAl HEAs were synthesized using a high-energy ball milling technique and electrochemically characterized for hydrogen storage performance. The concentrations of Mg and other constituent alloying elements are critical to achieving good storage capacity and other hydrogen storage properties. Interestingly, higher Mg atomic percent (40–50 at%) in the HEA matrix showed high gravimetric capacity, and increasing the constituent element like Ni has significantly enhanced the overall storage capacity, kinetics, and thermodynamic properties. Overall, 1 wt% of hydrogen was electrochemically stored with high reversibility, improved hydrogen diffusion coefficient, and anticorrosion ability.

Microelectrode-Based Diffusivity Measurements of Hydrogen in Molten 2LiF-BeF2

Detailed knowledge of the mass transport behavior of hydrogen isotopes in molten 2LiF-BeF2 salt (FLiBe) is essential to the design of new nuclear fusion technologies that make use of this molten salt to breed tritium to fuel the fusion reaction. However, typical studies of hydrogen transport using macroelectrodes are limited to solely measuring the permeability of an analyte—a property defined as the product of concentration squared and diffusivity. This challenge necessitates the development of microelectrodes capable of dynamically measuring diffusion coefficients when concentrations are variable. Unlike macroelectrodes, microelectrodes can measure diffusivity and concentration independently due to a steady-state current proportional to the product of diffusivity and concentration captured in addition to the Cottrellian current response.This steady-state current is established due to a continuously expanding diffusion layer from the electrode that cannot expand indefinitely within finite experimental setups. Therefore, COMSOL Multiphysics simulations mirroring experimental conditions were performed to validate the analytical mass transport model based on the solution of Fick’s Second Law in radial coordinates. These simulations employed a 2D axisymmetric model to examine the conditions under which the infinite bulk solution approximation is valid, confirming that our electrode design would yield true steady-state current responses indicative of radial diffusion.Platinum microelectrodes developed in this study served a dual purpose: they not only addressed previous limitations in high-temperature molten salt experimentation but also enabled dynamic measurements of both the diffusion coefficient and concentration of hydrogen in molten FLiBe introduced by lithium hydride. Square wave voltammetry and chronoamperometry were performed on a three-electrode cell using a platinum working microelectrode, a tungsten counter electrode, and a Ni/Ni2+ thermodynamic reference electrode. The successful measurement of hydrogen diffusivity in these experiments not only offers essential insights into molten FLiBe behavior but also sets the stage for future investigations into the effects of redox conditions, impurities, and equilibration time on tritium within nuclear fusion reactors.

Examine stability polyvinyl alcohol-stabilized nanosuspensions to overcome the challenge of poor drug solubility utilizing molecular dynamic simulation

The pharmaceutical industry faces a significant challenge from the low water solubility of nearly 90% of newly developed Active Pharmaceutical Ingredients (APIs). Despite extensive efforts to improve solubility, approximately 40% of these APIs encounter commercialization hurdles, impacting drug efficacy. In this context, a promising strategy will be introduced in which nanosuspensions, particularly polyvinyl alcohol (PVA) as a stabilizer, are applied to increase drug solubility. In this work using molecular dynamics simulations, the nanosuspension of four poorly water-soluble drugs (flurbiprofen, bezafibrate, miconazole, and phenytoin) stabilized with PVA is investigated. The simulation data showed van der Waals energies between polyvinyl alcohol with flurbiprofen and bezafibrate are − 101.12 and − 58.42 kJ/mol, respectively. The results indicate that PVA is an effective stabilizer for these drugs, and superior interactions are obtained with flurbiprofen and bezafibrate. The study also explores the impact of PVA on water molecule diffusion, providing insights into the stability of nanosuspensions. Obtained results also provide valuable insights into hydrogen bond formation, diffusion coefficients, and nanosuspension stability, contributing to the rational design and optimization of pharmaceutical formulations.

Impact of SOFC anode carbon deposition and hydrogen adsorption on the cell performance by molecular simulation.

This study primarily investigates the changes in carbon adsorption capacity and hydrogen adsorption capacity on the anode catalyst surface when using methane fuel and mixed gas fuel as the anode fuel for SOFC systems. To reduce the carbon adsorption capacity of the commonly used anode catalyst-nickel-based catalysts-towards hydrocarbon fuels, copper and gold are doped into the nickel-based catalysts to compare the effects on carbon and hydrogen adsorption capacities. Moreover, aside from calculating the carbon and hydrogen adsorption capacities, this project also evaluates the impact of mixed gas effects and doping effects on SOFC performance through the analysis of hydrogen diffusion coefficients and performance polarization curves. The findings reveal a noteworthy enhancement in the diffusion coefficient of syngas within the Au-doped Ni catalyst, showing an improvement of up to 45.46% at 973K. Furthermore, the electrical power generated by syngas in the Au-doped Ni catalyst at 973K demonstrates an increase of up to 12.06%. This study primarily employs DFT to calculate the carbon and hydrogen adsorption energies on methane, utilizing CASTEP for the calculations. During these calculations, the adsorption energy is determined through a three-layer surface approach, in conjunction with the Kohn-Sham equations, combining the Generalized Gradient Approximation and ultrasoft pseudopotentials for TS-search calculations. On the other hand, this project will analyze the diffusion coefficient of hydrogen on the anode catalyst using MD methods combined with the ReaxFF potential field, with GULP being utilized to complete all dynamics calculation theories. Finally, the project will analyze the performance of SOFC cells, incorporating relevant numerical equations with Matlab for numerical analysis.

Effects of nanocrystals on hydrogen permeation and diffusion in amorphous electroless Ni-P coatings

Amorphous electroless-plated Ni-P coatings readily form nanocrystalline at relatively low temperatures. The current efforts to investigate the impact of proportion of nanocrystals on hydrogen permeation remain relatively limited, particularly when seeking to determine the impact of surface and internal nanocrystals on hydrogen permeation. The present work addresses this issue by conducting detailed analyses for amorphous electroless-plated Ni-P coatings and heat-treated coatings with a greater nanocrystalline concentration. The results show that the plated state samples exhibit excellent hydrogen permeation barrier properties.In addition, the heat-treated coatings exhibit a greater surface free energy and lower corrosion resistance due primarily to the higher density of phase boundaries arising from the increased crystallinity. The hydrogen diffusion coefficient of the heat-treated coating remains relatively stable (between 1.148×10−11 to 1.517×10−11 cm2/s) with increasing hydrogen charging current from 1 to 10 mA/cm², while the hydrogen diffusion coefficient of the as-plated amorphous coating increases from 3.406×10−12 to 7.996×10−12 cm2/s with increasing hydrogen charging current. The diffusion of hydrogen in the amorphous coating is primarily governed by low activation energy positions (i.e., 23.16 kJ/mol) associated with gaps between short-range-ordered atomic clusters in the material. A few high-energy positions (i.e., 45.58 kJ/mol) may be related to reversible hydrogen traps. The increasing crystalline content arising under heat treatment drastically reduces the prominence of low activation energy positions.

Theoretical study on hydrogen permeation and fault slip of γ-Ni/γ'-Ni3Al interface with alloying elements (Zr, Nb, Ru, Re, and Hf)

In order to elucidate the role of hydrogen behavior at γ-Ni/γ'-Ni3Al interface with alloying elements, we performed comprehensive research of the permeation and slip properties by using DFT calculations. The result figures out that the alloying elements (Zr, Nb, Ru, Re, and Hf) tends to occupy corner-point sites in γ-Ni phase, while Re has the lowest substitution formation energy. The octahedron interstitial site is the favorable position for hydrogen adsorption due to its lower solution energy compared to the tetrahedron site. The diffusion energy barrier of hydrogen follows the influence order of Zr < Ru< Hf < Re < Nb. Meanwhile, Nb-doped interface has the highest hydrogen diffusion coefficient and permeability compared to other doped interfaces. By analyzing the partial density of states, the hybridization between Re-d orbital and neighbor Ni-d orbital is conducive to affect the permeability behavior of hydrogen. The generalized stacking fault energy reveals that all the alloying elements can improve the creep strength of γ-Ni/γ'-Ni3Al interface. As a barrier, Hf element is more effective to improve the dislocation slip resistance. These results can help people deepen the understanding of hydrogen behavior with alloying elements at the γ-Ni/γ'-Ni3Al interface and provide fundamental theories data for the further design of Ni-based superalloy.