Hydrogen Diffusion Coefficient Research Articles

Hydrogen Permeation Property and Hydrogen Embrittlement Susceptibility of Pipeline Steel with Oxide Film

In this study, the oxide film on X80 steel was fabricated to decrease hydrogen embrittlement of pipeline steel. The microstructures and mechanical properties in 10MPa hydrogen gas and hydrogen permeation properties were investigated. The phase structure of oxide film was mainly composed of Fe2O3. With the increasing of oxidation temperature, surface oxygen content improves gradually. Oxide film plays an important role in resisting hydrogen penetrating. Hydrogen diffusion coefficient decreases from 38.81☓10-7cm2s-1 to 1.26☓10-7 cm2s-1 for oxidation at 450 ℃. The plastic deformation increases obviously after oxidation. HEI decreases from 40.96% to 11.61% for oxidation at 450 ℃.

Determining the effective hydrogen diffusion coefficient in 100Cr6

AbstractIn the present study, the diffusion constant for hydrogen in hardened 100Cr6 was measured in permeation tests. The tests were conducted on samples of different thicknesses. The diffusivity of hydrogen was also measured in prestrained samples to study the influence of plastic strain on the diffusion rate. A finite element‐based diffusion model was applied to confirm the experimental results by computing the concentrations of diffusible hydrogen and trapped hydrogen due to deformation‐induced defects. The results showed that the concentration of trapped hydrogen remained very low throughout the plastic strain regime under consideration. The average effective diffusion coefficient of hydrogen in 100Cr6 at 30°C was found to be Deff = 4.9 × 10−12 m2/s.

Effective hydrogen diffusion coefficient for CoCrFeMnNi high-entropy alloy and microstructural behaviors after hydrogen permeation

Herein, the first observation of the effective hydrogen diffusion coefficient of CoCrFeMnNi high-entropy alloy (HEA) was performed using electrochemical hydrogen permeation; further, it was compared with those of stainless steels (SS) 304 and 316L. HEA and SS 316L showed similar effective hydrogen diffusion coefficient of 1.75 × 10−11 m2/s and 1.91 × 10−11 m2/s, respectively. SS 304 showed the smallest that of 0.58 × 10−11 m2/s in the study. Hydrogen diffusion through the grain boundary was dominant in face-centered cubic metals. Hydrogen permeation resulted in no change in the microstructure of HEA and SS 316L; however, it caused a martensitic transformation in SS 304.

Evaluation of hydrogen-induced cracking in high-strength steel welded joints by acoustic emission technique

Hydrogen-induced cracking behavior in high-strength steel mainly composed of martensite was analyzed by acoustic emission (AE) technique and finite element method (FEM) in slow strain-rate tensile (SSRT) tests and welding tests. The crack initiation was detected by the AE signals, and the time evolution of stress concentration and hydrogen diffusion were calculated by FEM. The effect of hardness and plastic strain on the hydrogen diffusion coefficient was explicitly introduced into the governing equation in FEM. The criterion and indicator parameter for the crack initiation were derived as a function of maximum principal stress and locally accumulated hydrogen concentration. The results showed that the cracking criterion derived by AE and FEM is useful for predicting the cold cracking behavior and determining the critical preheat temperature to prevent hydrogen-induced cracking.

Hydrides of Laves type Ti–Zr alloys with enhanced H storage capacity as advanced metal hydride battery anodes

The present work was focused on the studies of the effect of variation of stoichiometric composition of Ti–Zr based AB2±x Laves phase alloys by changing the ratio between A (Ti + Zr) and B (Mn + V + Fe + Ni) components belonging to both hypo-stoichiometric (AB1.90, AB1.95) and over-stoichiometric (AB2.08) alloys further to the stoichiometric AB2.0 composition to optimize their hydrogen storage behaviours and performances as the alloy anodes of nickel metal hydride batteries.AB2-xLa0.03 Laves type alloys (A = Ti0.15Zr0.85; B = Mn0.64–0.69V0.11–0.119Fe0.11–0.119Ni1.097–1.184; x = 0, 0.05 and 0.1) were arc melted and then homogenized by annealing.The studies involved probing of the phase-structural composition by X-Ray diffraction (XRD), together with studies of the microstructural state, hydrogen absorption–desorption and thermodynamic characteristics of gas–solid reactions and electrochemical charge-discharge performance, further to the impedance spectroscopy characterization. The alloys were probed using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and XRD.These studies concluded that the alloys contained the main C15 FCC Laves type AB2 intermetallic co-existing with a secondary C14 hexagonal Laves phase and a small amount of LaNi intermetallic. The gaseous H storage capacity and electrochemical performances were found to be closely dependent on the stoichiometric compositions of the alloys. High discharge capacities approaching 500 mAh/g were achieved for the AB1.95 alloy. At 500 mA/g current density, the discharge capacity was maintained as high as 80%, with very low capacity retention after 500 cycles. The alloy which had the highest capacity retention after 500 cycles was found to be AB2.0 alloy. Furthermore, AB2.0 alloy showed an excellent cyclic stability together with a high hydrogen diffusion coefficient. Studies of hydrogen diffusion coefficients showed that annealing enhanced the H diffusion rates allowing advanced performance at high discharge current densities. This has been related to a higher content of C15 Laves compound which allows to reach a higher H mobility in contrast with higher storage capacity observed for the C14 Laves type polymorph.

Communication—The Mechanism of Hydrogen Permeation Resistance of Ni Coating Enhanced by the Incorporation of Graphene

As suggested in our previous study, graphene containing Ni-based coating possessed a lower diffusion coefficient of hydrogen that pure Ni did. In this study, Pure Ni and Ni-graphene coatings were prepared in the Watts’ bath by electrodeposition, moreover, the enhancing mechanism of graphene on hydrogen permeation resistance of Ni coating was discussed for the first time. By means of various characterization techniques such as EBSD, SEM and TEM, it was revealed that both the refinement of grain size and the increase of special grain boundaries (GBs) fraction played the main roles due to the introduction of graphene into Ni deposits.

Critical assessment of the evaluation of thermal desorption spectroscopy data for duplex stainless steels: A combined experimental and numerical approach

The present study evaluates thermal desorption spectroscopy (TDS) data measured for UNS S32205 duplex stainless steel. Variations in the TDS spectra are obtained by electrochemical hydrogen charging for different times and by applying different heating rates for desorption to evaluate the desorption activation energy. Good agreement is found when comparing the experimental TDS curves with the desorption flux based on a numerical diffusion model using a homogeneous average hydrogen diffusion coefficient for the two-phase (ferrite-austenite) duplex microstructure. Trapping cannot be distinguished from the experimental TDS data since hydrogen diffusion in austenite is the rate-determining process during desorption. An average diffusion activation energy of 43.4 kJ/mol is determined from the experiments. Moreover, similar findings are obtained with a finite-element model that includes the heterogeneous hydrogen-related properties of the two phases of this duplex stainless steel.

Effects of doping with a third element (Pd, Ru, Ta) on the structure and hydrogen permeation properties of V–10Mo solid solutions

Alloying is an effective method for improving the resistance of V metals to hydrogen embrittlement. The effects of the doping with a third element (Pd, Ru, Ta) on the structure and hydrogen permeation properties of V–10Mo solid solutions have been investigated in this study. As-prepared V–5Mo-5TM (TM = Mo, Pd, Ru, Ta) alloy samples composed of V-based solid solution with a bcc structure are hydrogenated into their corresponding solid solutions (α-phase). Structural changes caused by TM-doping have notable effects on the hydrogen permeation properties (particularly the hydrogen solubility) of V–10Mo alloy, and the ability of the doping element in decreasing the hydrogen solubility of the V–10Mo alloy follows the sequence: Pd > Ru > Ta. Their doping causes a slight decrease in the hydrogen diffusion coefficient as well as an increase in the Vickers hardness of the resulting alloys. This work demonstrates that the mechanical property of V–10Mo alloy can be improved via suitable structure control caused by alloying it with an appropriate element. In addition, this approach might be suitable for improving properties of other relevant binary alloys.

Effect of microstructural inhomogeneity on hydrogen diffusion in welded joints

Hydrogen is a main factor in cold cracking or hydrogen-induced cracking. The most crack susceptible region of a steel welded joint is the heat affected zone (HAZ). Formulation and functional-analytical solution of the one-dimensional problem of hydrogen diffusion in an inhomogeneous butt-welded joint taking into account weld and joint dimensions as well as hydrogen diffusion coefficients and solubilities are presented. It is shown that the peak hydrogen concentration in the HAZ of inhomogeneous joints varies in direct proportion to the initial hydrogen concentration in the weld metal. Peak hydrogen concentration is inversely proportional to the ratio of hydrogen solubilities in the weld and HAZ and the square root of diffusion coefficient ratio of the HAZ and weld. The peak hydrogen concentration in the HAZ can exceed 80% of the initial concentration in the weld if martensitic steel is welded using low-carbon low-alloy welding consumables. Utilization of austenitic consumables leads to reduction in hydrogen concentration in the HAZ by 75–85% in comparison with non-austenitic consumables.

On the Estimation of the Diffusion Coefficient and Distribution of Hydrogen in Stainless Steel

In this work, the localisation of hydrogen in an electrochemically charged stainless steel was investigated by Scanning Kelvin Probe Force Microscopy and Glow Discharge Optical Emission Spectroscopy analysis. Both techniques indicated a high hydrogen content at less than 90 micrometres under the charged surface. Thermal Desorption Spectroscopy was used to calibrate the data from both techniques and thus to calculate the hydrogen concentration. Finally, after assuming certain hypotheses, Fick's laws were used to calculate the coefficient of diffusion and subsurface concentration of hydrogen in cathodic charging conditions.

The Role of Hydrogen on the Separation of Interfaces of  Supermartensitic Stainless Steel S13Cr

This paper outlines experimental procedures and numerical analyses to research Hydrogen embrittlement (HE) of the supermatensitic stainless steel (SMSS) S13Cr submitted to different cathodic potentials. Hydrogen diffusion behavior was investigated by means of two electrochemical permeation techniques, namely the double potentiostatic method (DPM) and the step method (SM), and it was also performed thermal desorption spectroscopy (TDS) tests. Apparent Hydrogen diffusion coefficients vary from 1.4 x 10-13 m²/s to 4.7 x 10-12 m²/s and TDS reveals the existence of deep traps, such as interfaces of precipitates and between retained austenite and ferritic matrix. HE effects in terms of reduction of ductility were analyzed through tensile tests and fractographic analysis, where a maximum reduction of elongation of around 14% was measured and a majority of brittle fracture along entire net section was observed in test samples pre charged under -1.5 V/SCE and -1.7 V/SCE. A calculation procedure based on computational simulation via finite element method has been performed, in order to predict mentioned loss of ductility using the experimental data mentioned before. The computational model used a fracture-controlled method under static structural condition, which links reduction of elongation of tensile specimens to the decreasing of critical fracture energies, which, in turn, were achieved through a new mean field approach regarding thermodynamic excess variables. Herein presented observations make it possible to suggest, that S13Cr has good resistance to HE and that the mentioned calculation procedure is reliable, since slight deviations in the magnitude of 5% were observed.

Generation of Microstructural Gradients for Improved Mechanical Properties via Thermo-Hydrogen Treatment of the Metastable Beta Titanium Alloys Beta CTM and Ti 10V-2Fe-3Al

Structural components must be lightweight and produced resource-saving while still fulfil the increasing durability and reliability requirements. One approach to fulfil these requests is a temporary hydrogen charging of Ti-alloys, which generates lattice distortion and hydrides. The volume difference between hydride precipitates and the alloy matrix results in localized plastic deformation. This triggers recrystallization and enables a finer microstructure as attainable by a conventional heat treatment. The study aims at an elaboration of a thermo-hydrogen treatment that establishes a change in grain size and/or an alteration in distribution and morphology of strengthening secondary α precipitates as a function of the distance to surface (microstructural gradient). The gradient is based on a gradient of the hydride volume fraction. Generally, THT design requires kinetic (temperature dependency of the hydrogen diffusion coefficient DH) in addition to thermodynamic (H/β-Ti-alloy interaction) data, which has been obtained for Ti 3Al-8V-6Cr-4Mo-4Zr and Ti 10V-2Fe-3Al. Subsequent to a solution treatment the variation of hydrogenation time and temperature is operated to establish comparably slight microstructural gradients on these materials. For further investigations it is concluded that materials with less alloying elements ((α+β)-Ti-alloys (e.g.,Ti 6Al-4V)) than these β-Ti-alloys can satisfy the requirements to generate steeper microstructural gradients even better.

The effect of a constant tensile load on the hydrogen diffusivity in dual phase steel by electrochemical permeation experiments

This work considers the effect of a constant load on the hydrogen diffusion characteristics studied by electrochemical permeation experiments. Dual phase steel and Armco iron are used for this purpose. Different degrees of load, both in the elastic and plastic regime, are applied on the sample during the permeation experiment when hydrogen is migrating through the material. The resulting transients show that applied elastic tensile stresses increase the hydrogen diffusion coefficient of both materials. Due to the elastic stress, the crystallographic lattice expands which increases hydrogen diffusivity. From an applied constant load of 100% of the yield strength and higher, the diffusivity decreases again. This is associated to the formation of lattice defects such as vacancies, vacancy clusters and dislocations. The strain state of the specimen in the constant loading device at different loading conditions is obtained by digital image correlation. This revealed that the in-situ instrumentation is key and confirmed that a homogeneous strain distribution is present in the zone of interest for the permeation experiments.

The effect of microstructure on hydrogen permeability of high strength steels

AbstractHydrogen diffusivity and trapping have been studied in two advanced high strength steel grades and model samples using electrochemical permeation test. Microstructures of CP1000 and DP1000 steels consist of ferrite, martensite and a small fraction of retained austenite. In addition, bainite is present in CP1000. Model phases with predominance of a particular phase have been prepared by specific heat treatment. DP1000 has shown the lowest diffusivity among all materials, while ferritic model sample has shown the highest. Differences in hydrogen diffusion coefficient values are linked to trapping microstructural characteristics and grain size.

Clusters of flower-shaped CuO nanosheets: microstructure and enhanced high-rate dischargeability properties of LaNi3.81Mn0.30Co0.78Al0.11 alloy electrodes

Nickel metal hydride (Ni-MH) batteries play an important role in new-energy vehicles; however, the poor high rate dischargeability (HRD) of the negative electrode materials (hydrogen storage alloy) limits its further application in high-power fields. In this work, a facile strategy was applied to improve the HRD performance of AB5-type alloy (LaNi3.81Mn0.30Co0.78Al0.11) by introducing flower-shaped CuO nanosheets to the electrode. Compared with the bare alloy, the modificatory electrode (3 wt.% CuO) shows enhanced HRD performance of increasing from 8.4 to 31.4% at a discharge current density of 1800 mA g−1. Besides, the corresponding capacity retention rate at the 100th cycle (S100) increases from 83.3 to 93.6%. For kinetic property, the exchange current density increases from 144.6 to 267.9 mA g−1 and the hydrogen diffusion coefficient increases from 1.96 × 10−15 to 6.52 × 10−15 cm2 s−1 (3 wt.% CuO), which mean the faster hydrogen diffusion rate. These are contributed to the 3-dimensional clusters of flower-shaped CuO nanosheets seamlessly integrated with hydrogen storage alloy and the formation of Cu particles deposited at the surface of alloy particles during charge/discharge process, decreasing the internal resistance and polarization of the hybrid electrode.

Effect of Nb–Ti multi-microalloying on the hydrogen trapping efficiency and hydrogen embrittlement susceptibility of hot-stamped boron steel

Multi-microalloying technique has been widely used to improve strength and ductility in steels, however, the effect of multi-microalloying on the hydrogen diffusion and hydrogen embrittlement (HE) behavior of steels is still not completely understood. This study evaluates the effect of Nb–Ti multi-microalloying on the hydrogen trapping efficiency and HE of hot-stamped steel by a combination of hydrogen permeation test, slow strain rate tensile (SSRT) test and quantitative analysis. The microstructural examination and hydrogen permeation tests showed that with increasing Nb + Ti content, more nano-sized (Nb, Ti) C precipitates were formed, and the martensite grain boundaries areas increased, thus increasing the irreversible and reversible hydrogen trap sites and decreasing the hydrogen diffusion coefficient in the hot-stamped steel. A quantitative analysis of the hydrogen traps demonstrated that the number of hydrogen traps induced by the (Nb, Ti) C precipitates was larger than that of the grain boundaries and dislocations in the Nb–Ti bearing steels. In addition, the SSRT tests showed that the HE susceptibility of the test steel decreased with increasing Nb + Ti content. This was because the additional hydrogen traps generated by the Nb–Ti addition hindered localized hydrogen accumulation at prior austenite grain boundaries, the cracking resistance was improved by a lower Σ3 boundary fraction, and the pinning role of the (Nb, Ti) C precipitates on the movable dislocation could inhibit H-dislocation interaction.

Hydrogen diffusion in creep-resistant 9% Cr P91 multi-layer weld metal

Welded components of P91 9% Cr steel demand for careful welding fabrication with necessary post weld heat treatment (PWHT). Before the PWHT, a hydrogen removal heat treatment is necessary for avoidance of hydrogen assisted cracking (HAC). In this context, the microstructure and temperature-dependent hydrogen diffusion is important, and reliable diffusion coefficients of P91 weld metal are rare. For that reason, the diffusion behavior of P91 multi-layer weld metal was investigated for as-welded (AW) and PWHT condition by electrochemical permeation experiments at room temperature and carrier gas hot extraction (CGHE) from 100 to 400 °C. Hydrogen diffusion coefficients were calculated, and the corresponding hydrogen concentration was measured. It was ascertained that both heat treatment conditions show significant differences. At room temperature the AW condition showed significant hydrogen trapping expressed by to seven times lower diffusion coefficients. A preferred diffusion direction was found in perpendicular direction expressed by high permeability. The CGHE experiments revealed lower diffusion coefficients for the AW condition up to 400 °C. In this context, a hydrogen concentration of approximately 21 ml/100 g was still trapped at 100 °C. For that reason, a certain HAC susceptibility of as-welded P91 weld metal cannot be excluded, and hydrogen removal should be done before PWHT.

Study of hydrogen redistribution in Ti49.1Ni50.9 alloy (at %) with nanocrystalline structure by resistometric and durometer methods

The electrolytical hydrogenation of TiNi-based alloys with shape memory and super elasticity results in a significant (by 1,5 times) increase in the microhardness of the surface layer. It is shown that the change of microhardness at long-term aging at room temperature in wire samples of Ti50,1Ni50,9 (at %) alloy with nanocrystalline structure can be used for estimation of diffusion mobility of hydrogen. On wire samples with different diameters it is shown that the increase in the relative electrical resistance at 83K at long-term aging at room temperature for this alloy is also associated with the diffusion mobility of hydrogen. Estimates of the hydrogen diffusion coefficient DH show that in nanocrystalline samples Ti50,1Ni50,9 (at %) the diffusion mobility of hydrogen is higher than in coarse-grained samples. This is connected with the increased contribution of grain boundary hydrogen diffusion in samples with nanocrystalline structure.

The Effect of Hydrogen on Martensite Transformations and the State of Hydrogen Atoms in Binary TiNi-Based Alloy with Different Grain Sizes.

The analysis presented here shows that in B2-phase of Ti49.1Ni50.9 (at%) alloy, hydrogenation with further aging at room temperature decreases the temperatures of martensite transformations and then causes their suppression, due to hydrogen diffusion from the surface layer of specimens deep into its bulk. When hydrogen is charged, it first suppresses the transformations B2↔B19′ and R↔B19′ in the surface layer, and when its distribution over the volume becomes uniform, such transformations are suppressed throughout the material. The kinetics of hydrogen redistribution is determined by the hydrogen diffusion coefficient DH, which depends on the grain size. In nanocrystalline Ti49.1Ni50.9 (at%) specimens, DH is three times greater than its value in coarse-grained ones, which is likely due to the larger free volume and larger contribution of hydrogen diffusion along grain boundaries in the nanocrystalline material. According to thermal desorption spectroscopy, two states of hydrogen atoms with low and high activation energies of desorption exist in freshly hydrogenated Ti49.1Ni50.9 (at%) alloy irrespective of the grain size. On aging at room temperature, the low-energy states disappear entirely. Estimates by the Kissinger method are presented for the binding energy of hydrogen in the two states, and the nature of these states in binary hydrogenated TiNi-based alloys is discussed.

Effective Hydrogen Diffusion Coefficient and Microstructural Behaviors Measured by Electrochemical Hydrogen Permeation for CoCrFeMnNi High-Entropy Alloy

Herein, the first observation of the effective hydrogen diffusion coefficient of CoCrFeMnNi high-entropy alloy (HEA) was performed using electrochemical hydrogen permeation; further, it was compared with those of Fe-17Cr-10Ni and Fe-18Cr-8Ni stainless steels (SS). HEA and Fe-17Cr-10Ni SS showed similar effective hydrogen diffusion coefficient of 1.75×10-11m2/s and 1.91×10-11 m2/s, respectively. Fe-18Cr-8Ni SS showed the smallest that of 0.58×10-11 m2/s in the study. Hydrogen diffusion through the grain boundary was dominant in face-centered cubic metals. Hydrogen permeation resulted in no change in the microstructure of HEA and Fe-17Cr-10Ni SS; however, it caused a martensitic transformation in Fe-18Cr-8Ni SS.