Electrochemical Hydrogen Permeation Tests Research Articles

The significance of inclusion morphology and composition in governing hydrogen transportation and trapping in steels

In this paper, two steels with different morphology of inclusions are studied. Scanning electron microscopy, finite element calculations, and electrochemical hydrogen permeation tests were conducted. Furthermore, in-situ observations of hydrogen de-trapping from the surface of steels were achieved using a hydrogen charging device and optical microscope. Results show that stripe-shaped complex inclusions exhibit a higher level of residual stress, especially at the boundary of oxide components. The hydrogen molecule is also prone to emerge at the oxide composition and intensifies the risks of cracking. In contrast, the residual stress levels around spherical inclusions are comparatively lower due to discrete sites of stress concentration. Thus, the effect of dispersed tiny dioxide sphere inclusions can help relieve the local hydrogen pressure and promote the resistance against hydrogen-induced cracking.

An integrated experimental and modeling approach to determine hydrogen diffusion and trapping in a high-strength steel

The hydrogen diffusion and trapping in AISI 4330 V high-strength steel is investigated by repetitive electrochemical hydrogen permeation tests, thermal desorption analysis, and hot and melt extraction. The analysis is coupled with a numerical model based on McNabb and Foster's kinetics with varying degrees of trap occupancy. The trapping parameters are obtained by fitting the numerical model to the experimental data, which permits to describe the diffusion and trapping processes for all tested conditions. In addition, the predictions calculated by the model are critically discussed and compared with those derived from usual approaches based on analytical solutions from Fick's laws and from Choo and Lee's method. An important difference is observed, indicating that the use of general analytical methods may not be adequate in the case of the studied steel. The use of more rigorous analysis provides a better understanding of trapping phenomenon and improved predictions of charging times and contents.

Deuterium permeability of a novel AlCrTaTiZr high entropy alloy coating

AlCrTaTiZr, AlCrTaTiZr nitride, and AlCrTaTiZr oxide coatings as tritium permeation barriers (TPBs) were prepared by magnetron co-sputtering technology on a CLF-1 (RAFM) substrate, to evaluate their hydrogen/deuterium permeation resistance. X-ray diffraction (XRD) analysis showed that the as-deposited coatings were amorphous. Scanning electron microscopy (SEM) results revealed that the deposition rates of the AlCrTaTiZr coating, AlCrTaTiZr nitride coating and AlCrTaTiZr oxide coating were approximately 2 μm h−1, 0.75 μm h−1 and 0.15 μm h−1, respectively. The properties of these high-entropy alloy (HEA) coatings were studied with electrochemical hydrogen (ECH) permeation test equipment and a high-temperature gas-driven deuterium permeation (GDP) device. The AlCrTaTiZr HEA coating had the best hydrogen permeation resistance during the electrochemical hydrogen permeation test. However, the AlCrTaTiZr nitride coating had the best deuterium permeation resistance during the gas-deuterium permeation test. Annealing experiments of these coatings showed that changes in their microstructures during the gas-driven deuterium permeation test were the main reasons for the different permeabilities of these coatings during the heating and cooling processes. The oxidization of the HEA coating during the deuterium permeation experiment may have been the main reason that the HEA coating showed better deuterium permeation resistance than the HEA oxide coating.

Quantitative calibration of the relationship between Volta potential measured by scanning Kelvin probe force microscope (SKPFM) and hydrogen concentration

The quantitative relationship between the Volta potential measured by scanning Kelvin probe force microscope (SKPFM) and hydrogen concentration values on the pure nickel surface has been calibrated. With continuous SKPFM scanning on the back of hydrogen charged side of a foil specimen, the changing Volta potential was achieved. On the other hand, the evolution of hydrogen concentration values on the SKPFM measured surface was obtained by combining the diffusion equation and electrochemical hydrogen permeation tests, which could estimate the constant hydrogen concentration on charging surface C0 and the hydrogen diffusion coefficient inside the nickel foil D simultaneously. The results suggest that the Volta potential involving SKPFM sharply decreases with the increase of hydrogen concentration in the low hydrogen concentration range. However, the change of the Volta potential is less considerable with the increase of hydrogen concentration at a high hydrogen amount level. The relationship between the SKPFM derived Volta potential and hydrogen concentration is quantitatively described by a modified Nernst equation model. The study shows that SKPFM is a powerful tool to quantify the hydrogen distribution, but may only prevail in low hydrogen concentration range. In addition, it is reasonable to consider the Volta potential to be linearly proportional to hydrogen concentration over a wide range of potential change.

Experimental and numerical analysis of hydrogen diffusion behaviors in an ultra-fine bainitic steel

The microstructure and hydrogen diffusion behavior of a typical high carbon bainitic steel experienced two different heat treatment history were firstly examined by optical microscope, scanning electron microscope and electrochemical hydrogen permeation test. Hydrogen diffusivity in this investigated steel lies in between those of the pure iron or mild steels and austenitic steels. The underlying mechanism is that although hydrogen diffusion in bainitic ferrite dominated hydrogen transport, percolation effect of the retained austenite as well as its tortuosity effect can significantly decrease hydrogen effective diffusivity and permeability, which was further verified by simplified formulas and models solved by numerical simulation.

Effect of internal hydrogen on the tensile properties of different CrMo(V) steel grades: Influence of vanadium addition on hydrogen trapping and diffusion

The influence of hydrogen on the mechanical behaviour of different quenched and tempered CrMo steels with or without vanadium were investigated by means of tensile tests. Smooth and circunferentially-notched round-bar specimens pre-charged with gaseous hydrogen in a high pressure hydrogen reactor were tested. The degradation of the tensile properties was correlated with the interaction between hydrogen atoms and microstructure, which was analysed by means of thermal desorption analysis (TDA) and permeation tests. A LECO DH603 hydrogen analyzer was used to study the activation energies of the different microstructural traps and also to study the hydrogen eggresion kinetics at room temperature. Moreover, electrochemical hydrogen permeation tests were also used to determine the apparent hydrogen diffusion coefficients and the density of traps present in the different steel grades.Hydrogen embrittlement measured in notched specimens was much greater than that observed in the smooth samples, being this effect more notable in the steel grades with higher yield strengths, tempered at the lowest temperatures, where a change in the fracture micromechanism from ductile in the absence of hydrogen to intermediate and brittle in the presence of internal hydrogen was clearly observed, especially in tests performed at the lowest displacement rates. Results were discussed through FEM simulations of local stresses acting on the process zone. On the other hand, the V-added steel grades were less sensitive to hydrogen embrittlement due to the effect of the submicrometric VC precipitated during the tempering treatment, which might be considered non-diffusible hydrogen-trapping sites, in view of their strong hydrogen-trapping capability (35–41 kJ/mol). In these steels (V-added grades), diffusible hydrogen and hydrogen accumulation in the process zone decrease, improving hydrogen embrittlement resistance.

Effect of interaction between corrosion film and H2S/CO2 partial pressure ratio on the hydrogen permeation in X80 pipeline steel

ABSTRACT The hydrogen permeation behaviour of X80 pipeline steel exposed to corrosion environments with different H2S/CO2 partial pressure ratios at room temperature was investigated through the high-pressure electrochemical hydrogen permeation test. Both CO2 and H2S have a hydrogen permeation promoting effect; however, CO2 hydrogen permeation promoting effect is much weaker than H2S. The hydrogen permeation curves have the rising, falling then stable stage. When at a total pressure of 1 MPa, as the H2S partial pressure decreases, the hydrogen permeation promoting effect weakens, but the peak current of hydrogen permeation gradually increases. The main reason is that the role of corrosion products has changed from promoting hydrogen permeation to hindering hydrogen permeation during the reaction.

Hydrogen Absorption Behavior of Pre-Rusted Steels under an NaCl Droplet

In this study, we investigated the hydrogen absorption behavior of pre-rusted steel in an NaCl droplet by measuring the hydrogen permeation current and corrosion potential. To prepare the pre-rusted steel, a 30-μL droplet of a 0.1-mol/dm3 NaCl solution was placed on the surface of steel and exposed to wet-dry cyclic conditions by changing the relative humidity (RH) repeatedly from 40% to 95% at a constant rate of 27.5%/h and 298 K. The hydrogen permeation current and corrosion potential of the pre-rusted steel were measured during the drying of an electrolyte droplet using an electrochemical hydrogen permeation test and the Kelvin probe (KP) technique, respectively. The corrosion potential of the pre-rusted steel shifted in the negative direction simultaneous with the evolution of the hydrogen permeation current during the drying of the droplet. The hydrogen permeation current increased with the number of wet-dry cycles in the early stages of the rusting process, which related to the negative shift in corrosion potential. As the whole surface of the steel was covered with iron rust in the later stages of the rusting process, the corrosion potential shifted in the positive direction and the hydrogen absorption current decreased gradually.

Novel Methodology for the Selection, Dosing and On-Line Control of Corrosion Inhibitors for Industrial Acid Pickling

A novel methodology based on electrochemical hydrogen permeation tests is proposed to study the efficiency of commercial inhibitors for industrial acid pickling of iron and mild steels. Weight loss measurements and hydrogen permeation tests have been carried out in order to compare the sensitivity of different techniques to variations of low inhibitor dosages. It has been found a close dependence between low amounts of filming inhibitors and hydrogen uptake in the metallic surface with related permeation currents. The high sensitivity of permeation currents may be very useful to establish and also control the optimum amount of active substances in industrial pickling baths, with related cost savings. The implementation of the proposed methodology to improve the control of industrial pickling plants is also envisaged, since it would be possible to improve both sensitivity and time response of experimental permeation curves.

What's in a name? Neural response to hearing one's own and other names in children with and without autism spectrum disorder

Electrochemical hydrogen permeation tests were utilized to investigate the diffusion and trapping of hydrogen in API X70 pipeline steel. Thermomechanical processing was used in order to produce 4 samples with different microstructural features. Detailed characterization was performed to measure the size and fraction of microstructural constituents of the samples and their effects on hydrogen diffusion were studied. After thermomechanical treatment the samples contained pearlite, polygonal ferrite, acicular ferrite, and martensite/austenite islands, the size and amount of which depends on the processing parameters. Hydrogen trapping density and hydrogen diffusion coefficient were measured for each sample and it is showed that depending on the properties of the microstructural constituents the diffusion coefficient can vary in the range of 0.33 × 10−6 cm2/s to 1.61 × 10−6 cm2/s.

Effect of thermomechanical processing on hydrogen permeation in API X70 pipeline steel

Electrochemical hydrogen permeation tests were utilized to investigate the diffusion and trapping of hydrogen in API X70 pipeline steel. Thermomechanical processing was used in order to produce 4 samples with different microstructural features. Detailed characterization was performed to measure the size and fraction of microstructural constituents of the samples and their effects on hydrogen diffusion were studied. After thermomechanical treatment the samples contained pearlite, polygonal ferrite, acicular ferrite, and martensite/austenite islands, the size and amount of which depends on the processing parameters. Hydrogen trapping density and hydrogen diffusion coefficient were measured for each sample and it is showed that depending on the properties of the microstructural constituents the diffusion coefficient can vary in the range of 0.33 × 10−6 cm2/s to 1.61 × 10−6 cm2/s.

Effect of Carbon Contents on Corrosion and Hydrogen Diffusion Behaviors of Ultra-Strong Steels for Automotive Applications

Recently developed ultra-strong GIGA STEEL exhibites superior mechanical properties, with a high tensile strength of more than 1.5 GPa and good impact toughness. Nevertheless, its application to auto parts has been severely restricted, mainly due to a substantial reduction in the resistance to hydrogen embrittlement (HE) induced by aqueous corrosion. The susceptibility to this HE is closely associated with the carbon content, which leads essentially to the precipitation of iron carbides (Fe2.4C/Fe3C) with a low hydrogen overvoltage. This study focuses mainly on the effect of carbon content on the aqueous corrosion and hydrogen diffusion characteristics of ultra-strong steels. The hydrogen reduction reaction on the steel surface, and its diffusion kinetics in the steel matrix were evaluated using electrochemical polarization and hydrogen permeation tests, respectively. Furthermore, the HE indices of steels with different carbon contents were determined in a weakly acidic solution using the slow strain rate test (SSRT). This study demonstrates clearly that the hydrogen reduction rates were increased and its diffusion kinetics were decreased significantly, with increasing carbon content. Based on the present results, it is concluded that the critical technical issue for the development of ultra-strong automotive steels is the effective control of the carbide fractions in the microstructure. Key words: ultra-strong steel, carbide, corrosion, hydrogen diffusion, hydrogen embrittlement

Effect of quenching temperature on sulfide stress cracking behavior of martensitic steel

A medium-carbon Cr-Mo-V martensitic steel was quenched at a decreased temperature from 1200° to 900°C and tempered at an identical temperature of 700 °C, thus provided with an enhanced KISSC value. The effect of quenching temperature, Tq, on the sulfide stress cracking (SSC) behaviors was estimated via the double cantilever beam (DCB) and the electrochemical hydrogen permeation (EHP) tests, and the microstructure characterizations. The results indicate that, as the Tq decreased, the overall and local hydrogen concentration around the inclusions decreased, owing to the decreased solute atoms and dislocation density, therefore preventing the SSC initiation. Moreover, the martensitic microstructure were refined and the fraction of the high angle grain boundaries (HAGBs) increased with the decreased Tq, thus decreasing the SSC propagation rate by diverting more frequently the propagating direction and further hindering the SSC propagation. The overall SSC resistance of this martensitic steel was therefore significantly enhanced.

Sulfide Stress Cracking Behavior of a Martensitic Steel Controlled by Tempering Temperature.

A medium-carbon Cr–Mo–V martensitic steel was thermally processed by quenching (Q) at 890 °C and tempering (T) at increasing temperatures from 650 °C to 720 °C and the effect of tempering temperature, Tt, on sulfide stress cracking (SSC) behaviors was estimated mainly via double cantilever beam (DCB) and electrochemical hydrogen permeation (EHP) tests and microstructure characterization. The results indicate that the threshold stress intensity factor for SSC, KISSC, increased with increasing Tt. The overall and local H concentration around the inclusions decreased with increasing Tt, due to reductions in the amounts of solute atoms, grain boundaries and dislocations, which effectively prevented SSC initiation. Also, increasing Tt caused an increased fraction of high-angle boundaries, which evidently lowered the SSC propagation rate by more frequently diverting the propagating direction and accordingly restricted SSC propagation. The overall SSC resistance of this Q&T–treated steel was therefore significantly enhanced.

Evaluation of hydrogen permeation through standalone thermally sprayed coatings of AISI 316L stainless steel

This research evaluates hydrogen permeation and its diffusion characteristics through standalone thermally sprayed coatings of AISI 316L stainless steel. The effects of various charging currents and other parameters on hydrogen diffusion coefficient were scrutinized using electrochemical hydrogen permeation tests. Hydrogen permeation through the thermally sprayed coatings displayed anomalous behavior such that a maximum pinnacle was observed in the permeation curves, attributed to heavily trapped hydrogen atoms in the delayed surface cracks. Therefore, new diffusion parameters were defined for modeling of the anomalous permeation curves. The fitted diffusion parameters were consistently identified, and hence, the model perfectly explained experimental data. The results showed that the increase in charging current caused fast activation and development of surface cracks. The measured diffusion coefficient of hydrogen in the stainless steel thermally sprayed coating was relatively high because the microstructure of the coating contained some ferritic phases and dense dendritic structure, which configure fast diffusion paths.

Electrochemical Hydrogen Permeation Tests under Conventional Potentiostatic Hydrogen Charging Conditions Conventionally Used for Hydrogen Embrittlement Study

Electrochemical hydrogen permeation tests were carried out under potentiostatic hydrogen charging conditions in various solutions, and the hydrogen entry behavior was compared with that of galvanostatic method. The relationship between hydrogen permeation current density and potential was similar in potentiostatic and galvanostatic methods and wide range of hydrogen concentration could be covered as well as galvanostatic method by varying NH4SCN content and potential. However, slight differences in hydrogen permeation current density and efficiency of hydrogen entry were seen between the methods, and the stability of hydrogen entry of potentiostatic method was slightly higher than that of galvanostatic method. In both methods, hydrogen permeation current density tended to increase with time in a NH4SCN containing solution suggesting that it is recommended to measure resulted hydrogen content by means of thermal desorption analysis for accuracy, though the relationship between hydrogen permeation current density and potential can be used as a rough standard.

北京，重慶および沖縄に室外暴露した試験片を用いた温湿度制御下の電気化学的水素透過試験

北京，重慶および沖縄に室外暴露した試験片を用いた温湿度制御下の電気化学的水素透過試験

Electrochemical Hydrogen Permeation Tests Under Potentiostatic Hydrogen Charging Conditions Conventionally Used for Hydrogen Embrittlement Study

Electrochemical hydrogen charging is a commonly used method for hydrogen embrittlement study of high strength steels as well as immersion in ammonium thiocyanate solutions. Hydrogen concentration in specimens in wide range, from low hydrogen concentration simulating that caused by atmospheric corrosion to relatively high hydrogen concentration to emphasize the effect of hydrogen on hydrogen embrittlement fracture, can be obtained either by changing hydrogen charging solutions with/without catalyst poisons and by controlling current density and potential applied to specimens. However, in many cases, hydrogen concentration is controlled in a trial-and-error manner. To understand the behavior of hydrogen entry in various hydrogen charging conditions and to obtain guidelines for efficient electrochemical hydrogen charging, electrochemical hydrogen permeation tests were performed in galvanostatic hydrogen charging conditions and the effects of current density and solution were reported in our previous study. In the present study, aiming at the same purpose, potentiostatic hydrogen charging was carried out using varied conditions and the hydrogen entry was monitored by means of electrochemical hydrogen permeation test and the results were compared with that obtained by using galvanostatic hydrogen charging. In the same way of the previous study, 0.5 mm-thick pure Fe sheet specimens set in a Devanathan-Stachurski cell were used in this study. The hydrogen input side of the specimen was potentiostatically polarized in 3 wt% NaCl solutions containing varied concentration of ammonium thiocyanate and a 0.1 M NaOH solution, open to air at room temperature. The Ni-plated hydrogen output side was polarized at 20 mV vs. Hg/HgO in a 0.1 M NaOH solution and the electrochemical hydrogen permeation current density was monitored in various potentiostatic hydrogen charging conditions. Hydrogen permeation current density was increased almost linearly with decrease in hydrogen charging potential. Exceptionally, at relatively high potential region the hydrogen permeation current density was lower than the extrapolation of the line probably because oxygen reduction decreases the efficiency of hydrogen entry. The efficiency of hydrogen entry expressed by the ratio of hydrogen permeation current density to hydrogen charging current density at the applied potential was decreased with decrease in potential accompanied with increase in cathodic current density. The increase in ammonium thiocyanate concentration led to enhancement of hydrogen entry drastically. These results were almost the same as that obtained for galvanostatic hydrogen charging in the previous study, and the relationship between hydrogen charging potential and hydrogen permeation current density of the potentiostatic hydrogen charging was similar to the relationship between potential of hydrogen input side resulted by galvanostatic hydrogen charging and hydrogen permeation current density. The relationship obtained in the present study can be used as guidelines for potentiostatic hydrogen charging. Though it is assumed that potentiostatic and galvanostatic hydrogen charging are similar to each other in principle, stability of hydrogen permeation current density showed some differences. In the presentation, stability of hydrogen permeation current density under the potentiostatic and galvanostatic hydrogen charging will be also discussed.

Electrochemical Hydrogen Permeation Test under Controlled Temperature and Humidity after Outdoor Exposure at Beijing, Chongqing and Okinawa

Electrochemical Hydrogen Permeation Test under Controlled Temperature and Humidity after Outdoor Exposure at Beijing, Chongqing and Okinawa

Graphene Containing Composite Coatings as a Protective Coatings against Hydrogen Embrittlement in Quenching & Partitioning High Strength Steel

Pure Ni and Ni-graphene coatings fabricated by reverse pulse electrodeposition were applied to protect quenching & partitioning (QP) steel as the substrate from hydrogen embrittlement (HE). The inhibitory effects of coatings on HE in steel were assessed by slow strain rate test (SSRT) after electrochemical hydrogen charging and hydrogen permeation test using the Devanathan-Stachurski (D-S) cells. According to the results of the total elongation loss Elloss and steady state permeation current I∞ as well as the diffusion coefficient D, it is suggested that the effect of pure Ni coatings on HE in QP steel was slight, whereas Ni-graphene coatings could act as a more effective protecting coatings against HE. Finally, the mechanisms affecting the performance of coatings on HE in QP steel were also discussed.