Hydrogen Embrittlement Mechanism Research Articles

Embrittlement of notched duplex stainless steel: Role of hydrogen-assisted void growth and cleavage

The micro-degradation processes related to the ductile-brittle transition are crucial for revealing hydrogen embrittlement mechanisms. This study investigates the evolution and transition of hydrogen-assisted damages in notched duplex stainless steel using a combination of microstructural characterization, numerical simulations, and mechanistic models. The results show that the brittle area of the fracture surface increases rapidly with decreasing cathodic potential, accompanied by the fractography transition in a sequence of voids, voids mixed with quasi-cleavage, and quasi-cleavage. While hydrogen-assisted dislocation emission from the void surface and stress concentration at the phase boundary promote nanovoid growth, hydrogen-enhanced plasticity facilitates preferential void growth along the ferrite block. At higher hydrogen concentrations, ferrite cleavage cracking may originate from prolate voids and hydrogen-augmented Cottrell dislocation reactions, reducing plastic strain near the crack tip and hence diminishing the formation of vacancies as void nuclei. Previous studies have focused on the statistics of hydrogen's effect on void size. This work demonstrates the dislocation mechanism of hydrogen-assisted void growth and provides new insights into the development of micro-mechanism-based models to predict hydrogen embrittlement.

In-depth understanding in the effect of hydrogen on microstructural evolution, mechanical properties and fracture micro-mechanisms of advanced high-strength steels welded joints

The hydrogen embrittlement (HE) mechanism of QP980 steels laser welded joints with complex microstructures is unclear. The joint with hydrogen pre-charging fractured at the inter-critical heat affected zone (ICHAZ) in slow strain rate tensile test, and the relative loss of elongation amounted to 84.8 %. Hydrogen-induced microcracks mainly initiated inside martensite (∼ 60 %). Hydrogen-induced crack propagation paths of the joint were transgranular propagation of martensite and intergranular propagation of ferrite/martensite interface. The HE mechanism of the joint was the combination of the effects in hydrogen-enhanced localized plasticity (HELP) and hydrogen-enhanced decohesion (HEDE).

Molecular dynamics study on the effect of hydrogen on the plastic behavior of α-Fe crack tip

In this paper, the unilateral tension of α-Fe in the local region of the crack tip are simulated by molecular dynamics method, the plastic deformation behaviors and hydrogen embrittlement mechanism of the crack tip under different hydrogen concentration and hydrogen positions are analyzed. The results show that for the hydrogen-containing models, there exists a critical hydrogen concentration c0 that can make the plasticity of the α-Fe material reduce greatly. For the crack-free model, the main hydrogen embrittlement mechanism is adsorption-induced dislocation emission (AIDE), and the critical hydrogen concentration c0 is 0.3%. When the hydrogen concentration cH<c0, the plastic deformation mechanism is mainly dominated by phase transformation; when cH≥c0, the plastic deformation mechanism is phase transformation at low strains and dislocation motion at high strains. For the cracked model, the main mechanism of hydrogen embrittlement is hydrogen-enhanced local plasticity at the crack tip, with a critical c0 of 1.7%. When cH<c0, the plastic deformation mechanism of the model is a combination of phase transformation and dislocation; when cH≥c0, the plastic deformation mechanism is controlled by phase transformation. When the hydrogen is far away from the crack tip, the local mechanical behavior of the crack tip does not change significantly, while when hydrogen gathered at the crack tip, the addition of a small amount of hydrogen atoms will make the fracture strain decrease rapidly, which shows a mechanism of hydrogen-enhanced strain-induced vacancies (HESIV). A saturation value of hydrogen concentration at the crack tip is confirmed in this paper, when the local hydrogen concentration exceeds this saturation value, the plastic behaviour tends to be stable. The influence of hydrogen atoms distribution on the crack initiation behavior was determined by atomic configuration analysis.

Correlation between pre-strain and hydrogen embrittlement behavior in medium-Mn steel

In this study, we investigated the correlation between the pre-strain and hydrogen embrittlement (HE) mechanisms in medium-Mn steel. Intercritically annealed Fe-7Mn-0.2C-3Al (wt.%) steel, which showed a two-phase microstructure comprising α ferrite and γR retained austenite, was used as a model alloy. As the pre-strain level increased from 0 % to 45 %, the volume fraction of γR gradually decreased owing to the strain-induced α′ martensite transformation accompanied by an increase in dislocation density. The HE resistance decreased with increasing the pre-strain level because the sample with a higher pre-strain level revealed a higher amount of dissolved hydrogen, combined with a more extensive brittle fracture region owing to the enhanced diffusion and permeation of hydrogen from the reduced γR fraction. Additionally, the H-assisted crack in the sample without pre-strain was initiated and propagated from the γR grains when the strain-induced α′ phase was formed, because most of the dissolved hydrogen was concentrated in the γR grains, and these grains were predominantly deformed compared to the other phases. However, the pre-strained sample showed more pronounced multiple H-assisted cracking at the constituent phases, such as α and α′, because it exhibited relatively well-dispersed hydrogen atoms and reduced microstrain localization at the γR grains, due to the reduced γR fraction.

Towards understanding stress corrosion cracking of austenitic stainless steels exposed to realistic sea salt brines

Stress corrosion cracking behavior of stainless steel 304 L was investigated in full immersion, evaporated artificial sea salt brines (ASW) at 55 °C. It was observed that brines representative of thermodynamically stable brines at lower relative humidity (40% RH, MgCl2-dominant) had a faster crack growth rate than high relative humidity brines (76% RH, NaCl-dominant). Observed crack growth rates (da/dt) under constant stress intensity (K) conditions were determined to be independent of transitioning procedure (rising K or decreasing frequency) regardless of solutions investigated for the orientation presented. Further, positive strain rates had little to no impact on the observed da/dt. The observed behavior suggests an anodic dissolution enhanced hydrogen embrittlement mechanism for SS304L in concentrated ASW environments at 55 °C. Additional explorations further examined environmental influences on da/dt. Nitrate additions to 40% ASW at 55 °C solutions were shown to decrease measured da/dt and further additions stopped measurable crack growth. After sufficient nitrate had been added to fully stifle crack growth, a temperature increase to 75 °C induced cracking again, and a subsequent decrease to 55 °C once again stopped da/dt. These tests demonstrate the importance of ascertaining both brine-specific chemical and dynamic environmental influences on da/dt.

Deciphering Hydrogen Embrittlement Mechanisms in Ti6Al4V Alloy: Role of Solute Hydrogen and Hydride Phase.

Ti6Al4V (Ti64) is a versatile material, finding applications in a wide range of industries due to its unique properties. However, hydrogen embrittlement (HE) poses a challenge in hydrogen-rich environments, leading to a notable reduction in strength and ductility. This study investigates the complex interplay of solute hydrogen (SH) and hydride phase (HP) formation in Ti64 by employing two different current densities during the charging process. Nanoindentation measurements reveal distinct micro-mechanical behavior in base metal, SH, and HP, providing crucial insights into HE mechanisms affecting macro-mechanical behavior. The fractography and microstructural analysis elucidate the role of SH and HP in hydrogen-assisted cracking behaviors. The presence of SH heightens intergranular cracking tendencies. In contrast, the increased volume of HP provides sites for crack initiation and propagation, resulting in a two-layer brittle fracture pattern. The current study contributes to a comprehensive understanding of HE in Ti6Al4V, essential for developing hydrogen-resistant materials.

Hydrogen embrittlement behaviors during SSRT tests in gaseous hydrogen for cold-worked type 316 austenitic stainless steel and iron-based superalloy A286 used in hydrogen refueling station

To consider an appropriate evaluation method for hydrogen compatibility, slow strain rate tensile (SSRT) tests were conducted on high strength piping materials, cold-worked type 316 austenitic stainless steel (SUS316CW) and iron-based superalloy A286, used in hydrogen stations for two years.SUS316CW, used at room temperature in 82 MPa gaseous hydrogen, contained 7.8 mass ppm hydrogen. The SSRT test of SUS316CW was conducted in nitrogen at −40 °C. The fracture surface showed dimples, and no hydrogen embrittlement behavior was observed. While, the SSRT test of SUS316CW in 70 MPa gaseous hydrogen at −40 °C showed a slight decrease in reduction area and a brittle fracture morphology in the outer layer. This was considered to be the effect of high-pressure gaseous hydrogen during the SSRT test in addition to the pre-contained hydrogen.A286, used at −40 °C in 82 MPa gaseous hydrogen, contained negligible hydrogen (0.14 mass ppm). SSRT tests were conducted at 150 °C in 70 MPa gaseous hydrogen and in air, and showed a low relative reduction in area (RRA) value. To investigate the decrease in the RRA, we switched the gas from hydrogen to air in the middle of the SSRT test and closely examined the RRA values and fracture morphology including side cracks. The hydrogen embrittlement was found to originate from the elastic deformation region. Stress cycling in the elastic deformation region also accelerated the effect of hydrogen. These were attributed to an increase in the lattice hydrogen content. While in the plastic deformation region, hydrogen trapped in the defects and hydrogen through the generated surface cracks increased the hydrogen content at the crack tips, reducing the RRA value. And there was a good correlation between the crack lengths and RRA values.Then, hydrogen embrittlement mechanism depends on the operating conditions (stress and temperature) of the material, and evaluating the hydrogen compatibility of materials by controlling their hydrogen content and strain according to the service environment is desirable.

Evaluation of hydrogen interactions with defects induced by deformation in the duplex stainless steel microstructure: An internal friction study

Despite their good corrosion resistance and optimal mechanical properties, duplex stainless steels are affected by hydrogen embrittlement. Therefore, understanding the hydrogen-defect interactions in these steels is crucial. This study uses internal friction to evaluate the interactions of hydrogen with microstructural defects. Analysis of the internal friction spectra of the steels subjected to straining and hydrogen charging, together with thorough microstructural characterization, gives new insights in hydrogen interactions with defects present in the different phases, i.e. ferrite (body centered cubic) and austenite (face centered cubic).While no significant effect of tensile deformation can be observed by thermal desorption spectroscopy, the internal friction spectra show a clear influence of the presence of defects. Detailed analysis of these spectra reveals the interactions in the austenite as dominant, while no indications for hydrogen-dislocation interactions in ferrite are observed. This can be related to limited trapping in ferrite due to the austenite sink action or to limited dislocation formation in ferrite. Indications for hydrogen interactions with dislocations in the austenite are found, possibly suggesting enhanced dislocation mobility when surrounded by hydrogen. Moreover, a pronounced influence of hydrogen charging on the vacancy cluster related peaks is observed, indicating strong interactions between hydrogen and vacancy clusters in austenite. This can be put in contrast to behavior of pure ferritic steels, where dislocations provided the strongest hydrogen interactions. As these specific defects are of primary interest in the hydrogen embrittlement mechanisms, internal friction is concluded to provide important unique insights in hydrogen-defect interactions, even for complicated multiphase microstructures.

Multiscale evaluation of hydrogen-assisted mechanical degradation in grade 2 titanium

The mechanism of hydrogen embrittlement in grade 2 titanium was studied by a combined micro and nanoscale approach. Insights into the hydrogen related deformation and degradation mechanisms were acquired via a unique characterisation procedure, correlating the topological observations on the fracture surface after tensile testing to the dislocation arrangement underneath. Focused ion beam lift-out was employed to extract a subsurface slice perpendicular to the fracture surface. High resolution characterisation provided information about the dislocation configuration and active hydrogen-assisted degradation mechanism. A high hydrogen content forms a brittle titanium hydride phase, failing via hydride cleavage. At a moderate hydrogen quantity, hydrogen in solid solution is responsible for a ductility decrease via the hydrogen-enhanced localised plasticity mechanism.

Hydrogen atom occupancy variation induced fragile to strong transition of titanium hydride

Hydrogen embrittlement is a prevalent issue that restricts the use of titanium as a structural material. To comprehend the hydrogen embrittlement mechanism, it is necessary to investigate the intrinsic mechanical properties of hydrides in titanium. In this study, a fragile to strong transition is observed in δ-TiH2 at 423 K. The in situ high temperature nuclear magnetic resonance measurements reveal that the occupancy of hydrogen atoms undergo a transition from octahedral sites to tetrahedral sites at the same temperature. Further first-principles calculations reveal that the decrease in the generalized stacking fault energy, resulting from the modification in the hydrogen atom occupancy, is the primary reason for the enhancement in the mechanical properties of δ-TiH2. This study suggests comprehending hydride fracture toughness through the lens of hydrogen atom occupancy, providing a novel research perspective on the hydrogen-induced embrittlement mechanism in titanium alloys.

Experimental study on slow tensile, fatigue, and impact on X42 steel and #20 carburizing steel

Hydrogen embrittlement is a common phenomenon in high-strength steels and presents a significant challenge in the research and development process. This study aims to analyze the mechanism of hydrogen embrittlement, investigate the causes of crack growth in steel, and conduct experiments at mesoscopic and microscopic scales to gain a deep understanding of the relationship between hydrogen embrittlement and defects in high-strength steels. The research includes a slow tensile test to study the shrinkage and ductility of X42 steel and 20# carburizing steel under air and hydrogen environments. Furthermore, fatigue testing is conducted to comparatively investigate the crack growth of CT specimens in nitrogen and hydrogen environments at different pressures. Additionally, impact testing is performed to examine the fracture of V-notched specimens in air and hydrogen at different pressures. The findings reveal that 20# carburizing steel exhibits better fracture toughness than X42 steel during the slow tensile process, and its hydrogen embrittlement sensitivity is lower. Moreover, the fatigue crack growth process of 20# carburizing steel is less affected by hydrogen embrittlement, resulting in better fatigue rupture resistance compared to X42 steel. Furthermore, the impact toughness value of 20# carburizing steel is higher than that of X42 steel in the impact toughness test. Both steels show varying effects on crack growth under different hydrogenation pressures. Importantly, the impact toughness of both steels is less affected by different hydrogenation pressures.

An atomistic study on the HELP mechanism of hydrogen embrittlement in pure metal Fe

The Hydrogen Enhanced Localized Plasticity (HELP) mechanism is one of the most important theories explaining Hydrogen Embrittlement in metallic materials. While much research has focused on hydrogen's impact on dislocation core structure and dislocation mobility, its effect on local dislocation density and plasticity remains less explored. This study examines both aspects using two distinct atomistic simulations: one for a single edge dislocation under shear and another for a bulk model under cyclic loading, both across varying hydrogen concentrations. We find that hydrogen stabilizes the edge dislocation and exhibits a dual impact on dislocation mobility. Specifically, mobility increases below a shear load of 900 MPa but progressively decreases above this threshold. Furthermore, dislocation accumulation is notably suppressed at around 1 % hydrogen concentration. These findings offer key insights for future research on Hydrogen Embrittlement, particularly in fatigue scenarios.

A review on hazards and risks to pipeline operation under transporting hydrogen energy and hydrogen-mixed natural gas

As an efficient and clean fuel, hydrogen energy plays an important role in relieving the energy crisis and achieving the orientation of zero carbon emissions. Transportation is the key link in the construction of hydrogen energy infrastructure. For large-scale and long-distance transportation of hydrogen, pipeline transportation has the advantages of high efficiency and cost saving. While using the existing natural gas pipeline to transport hydrogen, it would economize the economic cost, time cost and labor cost. However, the transportation of hydrogen may bring more hazards and risks. Based on the investigation of a large number of literatures, the research advance in hydrogen embrittlement, leakage, combustion and explosion risk of hydrogen and hydrogen-mixed natural gas pipelines was reviewed. The mechanism, research means and evaluation methods of hydrogen embrittlement, as well as the experimental and numerical simulation research results of leakage, combustion and explosion were discussed in detail. The definite and important conclusions include: (1) For buried hydrogen-mixed natural gas transportation pipeline, the leakage rate of hydrogen and methane is the same, the formation of the leakage crater is foreign to the nature of leakage gas. (2) When adding less than 25 volume percentage of hydrogen into the natural gas pipelines, the explosion risk would not be increased. Future research should focus on the risk prediction, quantitative risk assessment, intelligent monitoring, and explosion-suppression technical measures of hydrogen and hydrogen-mixed natural gas transportation pipelines, so as to establish comprehensive and multi-level pipeline safety protection barriers.

Impact of Hydrogen Embrittlement on Hydrogen Economy

In order to mitigate the effect of global warming and climate change by reducing CO2 emission, clean energy options are being explored. Hydrogen generation using renewable energy like solar and wind is one of the clean energy options being considered. Four pillars of hydrogen economy are hydrogen generation, storage, transportation and consumption. The overall life cycle cost of these technologies will depend on the endurance of the material of construction used. Hydrogen is known to cause embrittlement in steels and in hydride forming metals, which can lead to early failure of the components used in hydrogen economy. The overall life cycle cost of these technologies can be significantly reduced if the operating parameters are so chosen to avoid susceptibility to hydrogen/hydride embrittlement or use materials, which are resistant to hydrogen/hydride embrittlement. Hence, investigation of the hydrogen/hydride embrittlement of the materials used during the hydrogen production, storage and transportation has to be in sync with technologies related to hydrogen energy. Significant work has been reported on hydrogen/hydride embrittlement of structural materials such as high strength steels, Ti-alloys, Zr-alloys, Nb-alloys used in power and process industries. The knowhow of the hydrogen/hydride embrittlement mechanisms of these materials will be of immense help in understanding the hydrogen/hydride embrittlement of newer materials of construction used in hydrogen systems. The mechanisms of hydrogen and hydride embrittlement will be discussed.

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

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

Discrete distribution dislocation study on fracture behavior of nanocrystalline materials in the hydrogen environment

A lot of experimental and theoretical work has been done on the traditional macroscopic mechanism of hydrogen embrittlement (HE). There are a lot of theoretical studies on the micro-mechanism of HE recently published. In this article, based on the discrete dislocation method, taking into account the interaction between hydrogen atoms fixed in the defects of crystal materials and dislocation, a theoretical calculation method for the fracture of hydrogen-induced nanocrystalline (NC) materials is proposed. Considering the influence of hydrogen in the dislocation emission (DE) model, the theory of hydrogen inhibiting dislocation emission is put forward under the stable equilibrium state, which restrains the passivation of cracks and intensifies brittle fracture. At the same time, the pinning effect of hydrogen on dislocation is studied by theoretical method. In this paper, the relationship between the grain size and dislocation number in hydrogen free environment and hydrogen environment is described. The results show that the critical stress intensity factor (SIF) of crystal materials in hydrogen environment decreases by about 18.6%, indicating that hydrogen promotes the fracture of crystal materials. This paper provides a theoretical study for understanding the fracture behavior of hydrogen-induced materials.

Peridynamic modeling of crack propagation driven by hydrogen embrittlement

Hydrogen embrittlement is an important metal failure mechanism that affects the large-scale application of hydrogen energy. And developing an effective numerical model is vital for understanding and preventing hydrogen-assisted crack propagation. This paper proposes a peridynamic hydrogen embrittlement model based on the two-parameter model of bond-based peridynamics, where the limitation of Poisson’s ratio is relieved. The bond damage criterion that considers the hydrogen embrittlement mechanism is applied. Both the hydrogen diffusion and the hydrogen embrittlement phenomenon are simulated. The efficiency of the proposed peridynamic hydrogen embrittlement model is validated through four numerical examples, including the mode I crack propagations and complex crack paths simulations. The numerical results of the proposed peridynamic hydrogen embrittlement model are compared to the results of other numerical models and experiments. And the influences from hydrogen diffusion time steps and grain boundary diffusion coefficients on hydrogen-assisted crack propagation are investigated. The numerical results show that more diffusion time steps and larger grain boundary diffusion coefficients lead to faster hydrogen diffusion and faster crack propagation.

The hydrogen embrittlement mechanisms and hydrogen induced cracking process of selective laser-melted GH4169

This study investigates the hydrogen embrittlement sensitivity and brittle failure mechanism of selective laser-melted GH4169 alloy under hydrogen precharged conditions. Fractographic analysis reveals that a high concentration of hydrogen facilitates the formation of small quasi-cleavage steps near the fracture edge. Additionally, hydrogen promotes the migration of {111} planar dislocations, resulting in shear failure of the δ phases and the nucleation of microvoids. These microvoids then propagate, leading to the development of hydrogen-assisted transgranular cracks along the dislocation slip bands. The deformation behaviors of the δ and γ" phases were characterized using high-resolution transmission electron microscopy.

Effect of Chloride Concentration on the Environment-Assisted Cracking Behavior of an Al-Mg Alloy in Atmospheric Environments

The effect of chloride concentration on the environment-assisted cracking (EAC) behavior of AA5083-H131 in atmospheric environments was investigated using high-fidelity fracture mechanics-based testing and concurrent electrochemical potential measurements. EAC susceptibility was found to increase across all environments as chloride concentration increased, denoted by a decrease in the threshold stress intensity and faster stage II crack growth rates. However, EAC susceptibility for a given chloride concentration decreased across all chloride concentrations as cathodic limitation due to solution geometry effects increased. These results are analyzed in the context of the proposed anodic dissolution-enabled hydrogen embrittlement mechanism for EAC in Al-Mg alloys. Specifically, the increase in EAC susceptibility noted at higher chloride concentrations is postulated to arise from an increased overpotential for hydrogen production at the crack tip. Conversely, the decrease in EAC susceptibility observed as the solution geometry becomes more restrictive is attributed to cathodic limitation at the bulk surface decreasing dissolution at the crack tip, resulting in a concomitant less aggressive crack chemistry, and thus lower levels of hydrogen production and uptake at the crack tip. A close correlation between the open-circuit potential on the bulk specimen surface and the crack growth kinetics was also observed across all environments and chloride concentrations, with higher chloride concentrations and cathodic limitations resulting in larger changes in electrochemical potential. This correlates well with known electrochemical potential-dependent EAC observations for these alloys.

Design of high-strength martensitic steels by novel mixed-metal nanoprecipitates for high toughness and suppressed hydrogen embrittlement

To obtain a fundamental understanding of mechanisms of hydrogen embrittlement (HE) and its prevention in advanced high-strength steels containing novel nanoscale mixed-metal precipitates, it is necessary to study local microstructure, H trapping, and crack path with new multiscale experimental and simulation approach. Spatially resolved hydrogen mapping via SKPFM is used together with investigation of the crack path using high-resolution EBSD and HMPT, and global trapping behavior of the alloys by TDS. These results are combined with newly introduced method to elucidate real-time distribution of hydrogen in the alloy using high-energy synchrotron X-ray diffraction (HES-XRD). Mixed-metal precipitates improves HE resistance of the alloy, due to nature of the trapping sites, e.g. irreversible H-trapping by carbon vacancies inside novel nanoprecipitates and high total length of PAGBs. This is because of lower possibility of build-up of critical local hydrogen content at PAGBs for intergranular hydrogen-assisted cracking due to hydrogen-enhanced decohesion mechanism. Less weakly trapped hydrogen also reduces frequency of dislocation activation and enhanced dislocation slip in {011} slip plane due to hydrogen-enhanced localized plasticity in regions with affinity for transgranular hydrogen-assisted cracking at lower local hydrogen content. Direct evidence of carbon vacancies in novel nanoprecipitates is observed for the first time via HAADF-STEM.