Effective Hydrogen Diffusion Coefficient Research Articles

A comprehensive study on the kinetics and isotherms of D2/H2 adsorptive separation using pure and composite Cu-BDC-NH2 MOFs at 77 K

Pure and composite Cu-Amino-terephthalate MOF has been produced by ultrasound wave to evaluate the adsorption capacity and adsorptive separation of D2 and H2 at 77 K up to 1000 mbar. The frameworks are characterized by XRD, SEM, FTIR, ICP, BET, and EDX analysis. Separation studies were performed using idealized adsorption solution theory (IAST) and direct measurements. Isotherm studies showed the data had good agreement with the Langmuir model and the adsorption capacity of deuterium was greater than hydrogen in all samples. Linear Driving Force (LDF) model was applied to investigate the effective diffusion coefficients of deuterium and hydrogen in the frameworks. The LDF model showed hydrogen molecules diffused faster than deuterium molecules in all frameworks. In the adsorption enthalpy studies, there was a slight difference between deuterium and hydrogen adsorption energy. In this regard, Cu-BDC-NH2@rGO showed a higher adsorption enthalpy difference compared to Cu-BDC-NH2. Finally, the D2/H2 selectivity of the composite framework was greater than the pure one. Regarding this matter, the Cu-BDC-NH2@rGO MOF showed a maximum selectivity factor of about 2.2 at 77 K and 1000 mbar based on the IAST model.

Electrochemical hydrogen permeation in wrought and electron beam melted Ti-6Al-4V alloys

Ti-6Al-4V is one of the most widely used titanium alloys. However, it is susceptible to hydrogen embrittlement, e.g. due to hydride formation. Hydrogen permeability through Ti-based alloys is affected by the rapid formation of hydride or oxide surface layers as well as by trapping in the bulk alloy. Here, we analyze and compare the electrochemical hydrogen permeation (EHP) through wrought and electron beam melted (EBM) Ti-6Al-4V alloys. Hydrogen diffusion coefficients are calculated from the permeation current transients. The effective diffusion coefficient of hydrogen in the wrought alloy is found to be an order of magnitude higher than in the AM’ed alloy. The different microstructures of the wrought and EBM alloys are found to play an important role in hydrogen distribution and phase transformation in the alloy. In the EBM alloy, hydrogen is distributed more uniformly and, consequently, more pronounce phase transformations occur, eventually leading to brittle cracking. In the wrought alloy, on the other hand, hydrogen is distributed unevenly in the bulk of the membrane, forming hydride clusters, most probably at α/β interphase boundaries. These findings suggest that the EBM Ti-6Al-4V alloy is more susceptible to HE than its wrought counterpart.

Hydrogen and Oxygen Permeability through PEFC Membrane and Membrane Electrode Assembly

A proton exchange membrane (PEM) is an important component of a polymer electrolyte fuel cell (PEFC) from the viewpoint of proton transport. Only protons are desired to be transported through a membrane, but the feed gases also permeate. The permeation of the feed gas through a membrane affects the PEFC performance. Temperature and relative humidity dependencies of the hydrogen and oxygen permeability through a perfluorosulfonic acid (PFSA) membrane were measured. By considering that a membrane consists of three layers, i.e. a bulk layer sandwiched between skin layers, the transport properties of each layer were separated. The bulk layer effective diffusion coefficients of hydrogen and oxygen through both a PEM and an MEA were formulated as a function of temperature and RH. The oxygen transfer coefficient in the skin layer increased with RH, whereas the hydrogen transfer coefficient was almost constant regardless of RH.

On the Change in Hydrogen Diffusion and Trapping Behaviour of Pearlitic Rail Steel at Different Stages of Production.

To avoid hydrogen flaking in rail production, it is of crucial importance to understand the differences in hydrogen diffusion and trapping between different production steps. Therefore, as-cast unfinished material was compared with two finished rails, hot-rolled and head-hardened, using electron backscattered diffraction (EBSD), electrochemical permeation, and thermal desorption spectroscopy (TDS). A significant increase in dislocation density was in the head-hardened rail compared with the other material states. This leads to an effective hydrogen diffusion coefficient of 5.8 × 10-7 cm2/s which is lower by a factor of four than the diffusion coefficients examined in the other states. Thermal desorption spectroscopy analyses show a clear difference between unfinished and finished rail materials. While a peak in activation energy between 32 and 38 kJ/mol is present at all states, only as-cast unfinished material shows a second peak with an activation energy of 47 kJ/mol, which is related to microvoids. The results show that in the investigated material, the effect of increasing dislocation density has a stronger influence on the effective diffusion coefficient than the presence of a second active trapping site.

Hydrogen accumulation and diffusion in cylindrical-shaped pipeline steels with coating defects

The effective diffusion of hydrogen in a cylindrical geometry, mimicking a pipe with a coating defect, was investigated by modelling and verified experimentally. Analytical solutions for the extreme cases of no hydrogen uptake and constant hydrogen uptake were developed. Simulations showed less than 5% error, when compared to two well-documented reference cases for diffusion. The intermediate case of modelling kinetic controlled hydrogen uptake was investigated and the effects of time, position, effective diffusion coefficient, corrosion protection current density and their binary interactions, were reported. Modelling results show, that certain parameter combinations such as effective hydrogen diffusion coefficients between 10−11 - 10−9.5 m2 s−1, particularly in combination with a hydrogen uptake jH of more than 0.1 A m−2, may lead to locally increased hydrogen concentrations in the material.

Effect of Cold Deformation on the Hydrogen Permeation Behavior of X65 Pipeline Steel

In this study, an electrochemical hydrogen permeation experiment was used to determine the diffusion parameters, and a hydrogen microprint test was used to visualize the distribution of hydrogen in X65 pipeline steel with different levels of cold deformation. The hydrogen permeation curves show that both hydrogen permeation current density and effective hydrogen diffusion coefficient decrease with increasing cold deformation. The density of reversible and irreversible hydrogen traps is calculated from the permeation parameters, and it is found that the amount of both traps increases with increasing deformation, especially a significant increase in reversible hydrogen traps, which is in agreement with the results measured by thermal desorption spectroscopy. Hydrogen microprint test results indicate that the degree of hydrogen aggregation on the specimen surface increases with increasing cold deformation, especially at phase and grain boundaries. In addition, the dislocation configuration after cold deformation was further investigated by transmission electron microscopy.

Hydrogen Embrittlement Susceptibility of Corrosion-Resistant Spring Rod Used in High-Speed Railway

The corrosion of spring steel is very important for vehicle safety. In this work, we conducted an experiment on multi-element micro-alloy composition design; the corrosion resistance of a 60Si2Mn spring was improved by adding Cr, Ni, Cu and other corrosion-resistant elements, and the corrosion resistance index (I) was increased from 3.21 to 8.62. Hydrogen embrittlement resistance was studied using a hydrogen permeation experiment and a slow strain rate tensile experiment. For this study, the following steps were performed: Firstly, the material composition was designed, and the experimental materials that met the experimental design were prepared according to the corresponding deformation and heat treatment process; secondly, the experimental materials were charged with hydrogen; and finally, conventional tensile testing, slow tensile testing and fracture morphology testing were carried out. A hydrogen permeation experiment was carried out for the materials. The result showed that, with the increase of hydrogen charging time, the hydrogen content of two steel samples increased, and the plasticity indexes such as elongation and reduction of the area appeared in three different stages which rapidly decreased, slowly declined, and then tended to balance. The uniform NbC nano precipitated phase can double the number of irreversible hydrogen traps (Nir) per unit volume, and decreased the effective hydrogen diffusion coefficient (Deff) from 1.135 × 10−10 to 6.036 × 10−11. It limited the free diffusion of hydrogen and made the immersed hydrogen harmless, thus improving the hydrogen embrittlement resistance of corrosion-resistant spring steel 60Si2Mn.

Response of hydrogen diffusion and hydrogen embrittlement to Cu addition in low carbon low alloy steel

Hydrogen embrittlement (HE) has arisen as a critical issue for the development of high strength steel. The austenite and Cu-rich precipitates can provide stable trapping sites for diffusible hydrogen, and thus improved the resistance to HE. But the research on the synergistic effect of Cu and austenite on HE in low carbon low alloy steel has not been actively reported. In this study, four steels with varying Cu addition (0-3 wt%) were fabricated, and their resistance to HE was evaluated. The role of Cu addition was investigated by the ductile-brittle transition temperature (DBTT) value obtained from Charpy impact test and the loss of elongation measured from slow-strain-rate tensile (SSRT) test after hydrogen charging. Also, the hydrogen diffusivity and concentration were evaluated by electrochemical hydrogen permeation test. Cu addition resulted in a first decrease and subsequent increase of effective diffusion coefficient (D eff ), elongation loss and DBTT, and the minimum value was achieved in steel with 1.5 wt% Cu addition, indicating a higher resistance to HE. The unraveled mechanism was that Cu addition increased the content of retained austenite, which impeded the diffusion of hydrogen during deformation. But the stability of retained austenite decreased when the content of retained austenite reached a high value, which led to martensitic transformation and accordingly increased HE susceptibility. Moreover, Cu addition promoted the formation of Cu-rich precipitates in which Cu cluster/bcc Cu-rich precipitate coherent/semi-coherent with matrix can be strong trapping sites for hydrogen, and fcc Cu-rich precipitate acted as weak trapping sites for hydrogen. In addition, a higher density of dislocations was found in the steel with 1.5 wt% Cu addition, which may contribute to lower D eff and higher density of hydrogen traps (N T ). The present work suggested that Cu addition can enhance the resistance to HE during tensile and impact processes for the design of high strength steel. • Cu addition resulted in a first decrease and subsequent increase in the effective diffusion coefficient (D eff ) of hydrogen. • Cu addition increased the elongation rate and decreased the ductile-brittle transition temperature (DBTT) of the steels after hydrogen embrittlement. • The resistance to hydrogen embrittlement during tensile and impact process was determined by retained austenite, Cu-rich precipitates and dislocations in the microstructure. • The resistance to hydrogen embrittlement varied with the content and stability of austenite and the structure of Cu-rich precipitates.

Hydrogen embrittlement behavior in the nugget zone of friction stir welded X100 pipeline steel

Hydrogen-induced damage is an inevitable challenge in pipeline safety applications, especially, the fusion welded joints owing to microstructure heterogeneity caused by welding process. In this work, X100 pipeline steel was subjected to friction stir welding (FSW) at rotation rates of 300–600 rpm under water cooling, and the relationship among the microstructure, hydrogen diffusivity, and hydrogen embrittlement (HE) behavior of the nugget zone (NZ) were studied. The NZ at 600 rpm had the highest effective hydrogen diffusion coefficient (Deff) of 2.1 × 10−10 m2/s because of the highest dislocation density and lowest ratio of effective grain boundary. The Deff decreased with decreasing rotation rate due to the decrease of dislocation density and the increase of ratio of effective grain boundary, and the lowest Deff of 1.32 × 10−10 m2/s was obtained at 300 rpm. After hydrogen charging, the tensile strength of all specimens decreased slightly, while the elongation decreased significantly. As the rotation rate decreased, the elongation loss was obviously inhibited, and ultimately a lowest elongation loss of 31.8% was obtained at 300 rpm. The abovementioned excellent mechanical properties were attributed to the fine ferrite/martensite structure, low Deff, and strong {111}//ND texture dramatically inhibiting hydrogen-induced cracking initiation and propagation.

Effect of cold deformation on the hydrogen permeation in a dual-phase advanced high-strength steel

The diffusion behaviour of hydrogen in a 1180 MPa ferrite/martensite dual-phase (DP) advanced high-strength steel was investigated using electrochemical permeation tests in the following conditions: as manufactured, cold deformed and annealed. The effective hydrogen diffusion coefficient (0.46 × 10−6 cm2 s−1) for the cold-deformed DP1180 was considerably lower than for the steel as-received (0.74 × 10−6 cm2 s−1) and annealed (2.2 × 10−6 cm2 s−1). The increased diffusible hydrogen concentration by cold deformation was attributed to increased reversibly trapped hydrogen. This work provides an experimental underpinning for the increased hydrogen embrittlement sensitivity caused by plastic deformation of the steel.

Hydrogen diffusion and trapping in nickel-based alloy 625: An electrochemical permeation study

This work studied the effect of cathodic charging conditions on hydrogen diffusion and trapping behavior in a nickel-based Alloy 625 using the electrochemical permeation approach. Results showed that the effective diffusion coefficient of hydrogen can be expressed as Deff=1.82×10−7exp(−44.46kJmolRT)m2/s. A sinusoidal trend in Deff with charging current density was observed showing a deflection point at -40 mA/cm2, which contributes to the most efficient hydrogen permeation. In addition, the thermodynamic relationship between hydrogen activity and electrochemical potential was investigated. Furthermore, the energy associated with the solubility energy of interstitial hydrogen and reversible trapping site was determined as 9.90 kJ/mol and 26.04 kJ/mol, respectively.

A microstructure informed and mixed-mode cohesive zone approach to simulating hydrogen embrittlement

Hydrogen induced failure under uniaxial tension is simulated in a duplex stainless steel considering microstructural feature of the material. There are three key ingredients in the modelling approach: image processing and finite element representation of the experimentally observed microstructure, stress driven hydrogen diffusion and diffusion coupled cohesive zone modelling of fracture considering mixed failure mode. The microstructure used as basis for the modelling work is obtained from specimens cut in the transverse and longitudinal directions. It is found that the microstructure significantly influences hydrogen diffusion and fracture. The austenite phase is polygonal and randomly distributed in the transverse direction, where a larger effective hydrogen diffusion coefficient and a lower hydrogen fracture resistance is found, compared to the specimen in the longitudinal direction, where the austenite phase is slender and laminated. This indicates that the proper design and control of the austenite phase help improve hydrogen resistance of duplex stainless steel. The strength of the interface in the shear direction is found to dominate the fracture mode and initiation site, which reveals the importance of considering mixed failure mode and calibrating the hydrogen induced strength reduction in shear.

Hydrogen Trapping States and Apparent Hydrogen Diffusion in Laser Additively Manufactured Ultra-High Strength AerMet100 Steel as a Function of Secondary Hardening

Microstructures, reversible hydrogen trapping states, and effective hydrogen diffusion coefficients (DH,eff) of laser additively manufactured (LAM) ultra-high-strength AerMet100 steel in tempered conditions were studied by several material characterization methods, to determine diffusible, trapped, and total hydrogen content. With secondary hardening temperatures in the range of 454°C to 566°C, increasing temperature mainly promotes M2C carbide coarsening and film-like reverted austenite thickening in the steel. Reversible hydrogen traps of tempered LAM AerMet100 steel are closely related to the precipitation behavior of highly coherent M2C carbides. The desorption activation energy of the reversible hydrogen traps in the steel is seen to increase from 17.9±0.3 kJ/mol to 21.8±1.3 kJ/mol with temperature increasing from 454°C to 566°C. This correlates with the composition and size change of M2C carbides at a higher tempering temperature. Hydrogen trapping capability of the steel has a peak value at a tempering temperature of 482°C corresponding to the combination of both high amount and medium trapping intensity of these reversible hydrogen traps. This results in the lowest diffusible and highest total hydrogen concentration for precharged H specimens of the steel. In addition, the DH,eff of LAM AerMet100 steel in the overaged condition is not only influenced by the increased thickness of film-like reverted austenite but also simultaneously affected by the altered density of M2C carbides. In comparison with the lowest DH,eff (approximately 2.4 × 10−9 cm2/s) of LAM AerMet100 steel tempered at 482°C, a slightly higher DH,eff of the steel tempered at a higher temperature is achieved by the apparent decrease of reversible hydrogen traps due to a decrease in density of the highly coherent M2C carbides. These findings are important when considering achieving improved hydrogen embrittlement resistance for LAM high Co-Ni secondary hardening ultra-high-strength steel in an over-aged condition at the strength level of interest.

The potential significance of microalloying with Nb in enhancing the resistance to hydrogen-induced delayed fracture of 1300-MPa-grade high-strength bolt steel

The present work aims to explore the potential significance of microalloying with Nb in enhancing the resistance to hydrogen-induced delayed fracture (HIDF) of a novel 1300-MPa-grade V-microalloyed high-strength bolt steel 42CrNiMoV using constant load tensile test. The results show that ∼ 82% of the added 0.03 wt% Nb is consumed to form NbC carbides which causes significant grain refinement and thus an overall strengthening of ∼ 60 MPa. The effective hydrogen diffusion coefficient is reduced by ∼ 39% and the corrosion resistance is significantly improved through the Nb addition. The Nb-added steel has enhanced tolerance of diffusible hydrogen content and its resistance to HIDF is enhanced by ∼ 13%. The mechanism of Nb in enhancing the resistance to HIDF was discussed. It is suggested that microalloying with Nb is an effective approach to further improve the HIDF resistance for high-strength bolt steels.

Hydrogen diffusivity and tensile properties degradation in SLMed Inconel 718

Besides elevated temperature applications, Inconel 718 is widely chosen for components subjected to heavy loads operating in aggressive environments, which can promote the production of hydrogen on the metal surface. Selective Laser Melting (SLM) is an emerging technology for the production of structural components in Inconel 718 or Inconel 625 alloys, allowing to create functionally optimized shapes and overcome the traditional manufacturing limitations. However, the SLM process introduces a peculiar microstructure and severe residual stresses that can affect hydrogen migration and accumulation. While the mechanical properties were deeply investigated in recent years, the resistance of SLMed Inconel 718 to the Hydrogen Embrittlement (HE) is still an open issue. The present work deals with a preliminary assessment of the hydrogen embrittlement susceptibility of the SLMed In718 in the as-built condition. Slow strain rate tests were carried out on unnotched specimens that were pre-charged by electrochemical cathodic charging. Fractographic analyses, carried out with a Scanning Electron Microscope (SEM), were used to identify the effects produced by the hydrogen intake on the material microstructure. The material resulted to be susceptible to hydrogen embrittlement, featuring a significant ductility reduction in presence of extremely elevated hydrogen concentrations. The hydrogen content was measured by employing the Hot Extraction Method (HEM), for each mechanical test. Due to a low diffusivity value, hydrogen penetrates only within a thin external layer of the specimen. Therefore, to identify the concentration profile, the effective hydrogen diffusion coefficient was identified and the hydrogen diffusion was simulated using Fick’s equation. The loss in mechanical resistance was then correlated to the hydrogen concentration near the fracture onset.

Thickness and microstructure effect on hydrogen diffusion in creep-resistant 9% Cr P92 steel and P91 weld metal

Martensitic 9% Cr steels like P91 and P92 show susceptibility to delayed hydrogen assisted cracking depending on their microstructure. In that connection, effective hydrogen diffusion coefficients are used to assess the possible time-delay. Limited data on room temperature diffusion coefficients reported in literature vary widely by several orders of magnitude (mostly attributed to variation in microstructure). Especially P91 weld metal diffusion coefficients are rare so far. For that reason, electrochemical permeation experiments had been conducted using P92 base metal and P91 weld metal (in as-welded and heat-treated condition) with different thicknesses. From the results obtained, diffusion coefficients were calculated using to different methods, time-lag, and inflection point. Results show that, despite microstructural effects, the sample thickness must be considered as it influences the calculated diffusion coefficients. Finally, the comparison of calculated and measured hydrogen concentrations (determined by carrier gas hot extraction) enables the identification of realistic diffusion coefficients.

Dislocation cell walls with high dislocation density as effective hydrogen traps in Armco iron

AbstractThe effect of cold rolling (CR) deformation on the hydrogen permeation and trapping behavior of pure iron was systematically investigated. Increased deformation resulted in a decreased effective hydrogen diffusion coefficient, an extended effective lattice interstitial hydrogen diffusion path length, and increased hydrogen trap densities. However, the proportion of irreversible hydrogen traps to all traps was constant irrespective of the deformation level in the range of 30%–70% CR and increased when the deformation reached 80%. This is because the dislocation cell wall is composed of a central layer with high trap‐binding capacity and an outer layer with low trap‐binding capacity. More importantly, once the dislocation density in the center layer of the dislocation cell walls reached a relatively high value due to the severe plastic deformation, these regions become effective irreversible hydrogen traps.

Hydrogen Diffusion and Trapping in Laser Additively Manufactured Ultra-High Strength AerMet100 Steel

Hydrogen trapping and the permeation behavior of laser additively manufactured (LAM) AerMet100 (UNS K92580) steel with an as-deposited specimen (AD) and after three types of heat-treated specimens (bainite microstructure [BM], tempered bainite and martensite microstructure [TBMM], and tempered martensite [TM]) was investigated. At least three types of different hydrogen traps were identified in each microstructure of the LAM steel, including both reversible and irreversible H traps. For as-deposited microstructure, the main reversible H trap states are related to the precipitation of M3C carbides associated with a detrapping activation energy (Ed) of 17.3±0.2 kJ/mol. After heat treatment, the dominant reversible hydrogen trap states in the tempered martensite microstructure have a different Ed value of 19.3±0.5 kJ/mol, which is attributed to the precipitation of highly coherent M2C carbides. In comparison with the reported Ed value of approximately 21.4 kJ/mol for main reversible hydrogen traps in wrought UNS K92580 steel, the lower Ed value in the LAM steel is closely related to the composition change of M2C carbides. In all of the H precharged samples, the diffusible and total H concentration of the TM specimen and the TBMM specimen are about three to four times higher than that of the AD specimen and the BM specimen. The TM specimen with tempered martensite microstructure has the highest diffusible and total H concentration due to its high density of dominantly reversible H traps. The effective hydrogen diffusion coefficient (Deff) of the LAM steel is on the order of 10−9 cm2/s, and decreases with increasing density of the dominant reversible H traps brought about by heat treatment. The LAM steel has a comparable Deff of about 2.8 × 10−9 cm2/s compared to the wrought steel of a similar yield strength (∼1,750 MPa),

Hydrogen diffusivity in different microstructural components in martensite matrix with retained austenite

We elucidate the hydrogen diffusivity in martensite matrix with retained austenite (RA). Two aspects are focused: effect of microstructure on hydrogen diffusion behavior; hydrogen diffusivity calculation for different microstructural components. Quenched martensite (QM) had the highest effective hydrogen diffusion coefficient because of high dislocation density. Effective hydrogen diffusion coefficient decreased with the increase of intercritical annealing temperature because of decrease in dislocation density and increase of RA. According to the principle of Maxwell-Garnett equation, the hydrogen diffusion coefficient for grain boundary (GB) was 7.99 × 10−8 m2/s and hydrogen diffusion coefficient of tempered martensite (TM) was 7.84 × 10−11 m2/s.

Hydrogen Diffusion and Its Effect on Hydrogen Embrittlement in DP Steels With Different Martensite Content

The hydrogen diffusion behavior and hydrogen embrittlement susceptibility of dual phase (DP) steels with different martensite content were investigated using the slow strain-rate tensile test and hydrogen permeation measurement. Results showed that a logarithmic relationship was established between the hydrogen embrittlement index (IHE) and the effective hydrogen diffusion coefficient (Deff). When the martensite content is low, ferrite/martensite interface behaves as the main trap that captures the hydrogen atoms. Also, when the Deff decreases, IHE increases with increasing martensite content. However, when the martensite content reaches approximately 68.3%, the martensite grains start to form a continuous network, Deff reaches a plateau and IHE continues to increase. This is mainly related to the reduction of carbon content in martensite and the length of ferrite/martensite interface, which promotes the diffusion of hydrogen atoms in martensite and the aggregation of hydrogen atoms at the ferrite/martensite interface. Finally, a model describing the mechanism of microstructure-driven hydrogen diffusion with different martensite distribution was established.