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Hydrogen embrittlement (HE) extant a substantial concern to press-hardened steel (PHS) owing to superior strength. The high strength to light-weight automobile structures necessitates the advancement of superior HE resistance PHS. This study investigated the HE susceptibility of Nb-microalloyed PHS by slow strain rate tensile testing, u-shaped constant bending load test, and thermal desorption spectroscopy. Nb enhances microstructure and HE resistance by introducing retained austenite, refining prior austenite grains (21.14–13.73 μm), forming low-angle grain boundaries, and nano-scale precipitates. Nb-alloyed steel exhibits no-cracking over 300 h under high pre-bending stress and decreases elongation loss up to 48% in hydrogen environment as compared to Nb-free steel. Diffusible H-content in 0.12 wt% Nb-steel reduces to 14.9% of that in Nb-free steel owing to enhanced hydrogen traps, the Fcc/Bcc matrix, and carbide precipitation. The multi-phase microstructure with nano-scale NbC precipitation impeded the localized H-dispersion, enhancing the HE resistance in PHS despite its high strength. [Display omitted] • Grain boundary strengthening achieved by refined microstructure in Nb-steel. • Retained austenite with NbC enhances hydrogen embrittlement resistance. • 0.12 wt% Nb steel mitigate diffusible hydrogen content to 14.9% of that Nb-free steel. • Nb-alloying decreases elongation loss by up to 48% in presence of hydrogen. [ABSTRACT FROM AUTHOR]

The effect of co-existence of Mo and B on hydrogen embrittlement (HE) of equiatomic CoCrFeNi and (CoCrFeNi) 96.96 Mo 3 B 0.04 (MoB-doped) alloys are investigated through electrochemical hydrogen charging, tensile tests and advanced microstructural characterization. The MoB-doped alloy exhibits higher HE resistance than CoCrFeNi alloy, which is attributed to MoB-promoted twinning deformation process instead of conventionally strengthening grain boundary (GB) effect resulting from Mo and B segregation. As hydrogen charging time increases, the ductility of both alloys first increases and then decreases, which correlates with the competition relation between H-promoted formation of gradient twins/stacking faults and hydrogen-enhanced decohesion mechanism. For the samples charged 3 h, the beneficial effect of gradient nanostructure caused by chemical composition gradients of hydrogen overcompensates its HE effect, leading to the defeating HE of the alloys by hydrogen itself. This result indicates that the introduction of gradient nanostructures through hydrogen-concentration gradients could be a way forward for designing hydrogen-tolerant alloys. [Display omitted] • Hydrogen can enhance the ductility of CoCrFeNi and MoB-doped alloys. • Hydrogen promotes the formation of twins and stacking faults. • Segregation of Mo and B along grain boundaries are not observed. • MoB-promoted twin deformation process favors high HE-resistance of the alloy. [ABSTRACT FROM AUTHOR]

The hydrogen embrittlement behavior of Ni–Cr–Mo-based superalloy fabricated by wire arc additive manufacturing (WAAM) with or without solution treatment was investigated by electrochemical hydrogen charging. The results show that the dissolution of the Laves phase promotes the precipitation of the δ phase in the matrix of WAAM superalloy after solution treatment at 980 °C. When the solution temperature goes up to 1080 °C, the large Laves phase disappears and only MC exists in the matrix. The interfaces between the Laves phase/δ phase and matrix generally could act as hydrogen traps, which would reduce the motion of hydrogen and lead to high hydrogen embrittlement resistance of the WAAM and ST-980 °C samples. However, hydrogen mainly accumulates on grain boundaries in the ST-1080 °C due to the disappearance of the Laves phase and δ phase. Hydrogen-induced intergranular brittle fracture occurs during the slow strain rate tensile test and the ST-1080 °C samples exhibit higher hydrogen embrittlement susceptibility than that of the WAAM and ST-980 °C samples. • The solid solution changes the element distribution and precipitates in the WAAM superalloy. • The effect of hydrogen on the mechanical properties of the WAAM superalloy was investigated. • The hydrogen diffusion in the WAAM superalloy is affected by dendrite, Laves phase and δ phase. • The fracture mode of the hydrogen-containing WAAM superalloy is different under different solid solution temperatures. [ABSTRACT FROM AUTHOR]

The location of the H atoms in Ti, Zr, and Hf is crucial to the formation of the hydrides in these metals as it influences the crystal lattice transformation and the hydrogen diffusion involved in the hydride formation process. Although Ti, Zr, and Hf are all of hexagonal close-packed structure with similar lattice parameters, the solute H atom occupies the octahedral interstice in Ti but the tetragonal interstice in Zr and Hf, of which the origin is still mysterious. In the present work, the origin of the distinct site occupation behavior of H atom in Ti and Zr/Hf is investigated through first principles calculations. The calculated solution energies confirm that H prefers the octahedral interstice in Ti but the tetrahedral interstice in Zr and Hf. We ascribe the distinct site occupations of H in Ti and Zr/Hf to the varying Coulomb repulsion between the H (as a screened proton in the metals) and the matrix atoms against the interstitial size. The competition between the H-induced electron accumulation effect and the matrix atom debonding effect might matter as well. We propose that, as a general rule, a H atom prefers the site with a trade-off between a large space and a high electron density in metals. • Hydrogen occupies octahedral interstice in Ti but tetrahedral interstice in Zr/Hf. • H-metal atom Coulomb repulsion is responsible for the distinct site occupation of H. • H-induced electron redistribution might matter to the distinct site occupation of H. • H prefers the site with a trade-off between large space and high electron density. [ABSTRACT FROM AUTHOR]

Hydrogen energy is becoming increasingly important worldwide. Due to cost-effectiveness, ferritic and martensitic steels have been commonly used for hydrogen services such as pipelines and storage tanks. However, these steels are prone to hydrogen embrittlement (HE), which causes ductility loss without affecting yield and ultimate tensile strength. Assessing hydrogen compatibility in terms of strength, especially under localized stress, which might correlate with the relative notch tensile strength (RNTS) is necessary. This study aims to establish a procedure to determine the RNTS through the small punch test (SPT) using U-shaped notch specimens in high-pressure environments at room temperature. The notch tensile strength (NTS) was calculated through simulation from the maximum equivalent stress (σ max) at corresponding fracture displacement (δ f) using the load-displacement curve obtained by SPT under each test condition. The combined experiment and numerical approach effectively determined the RNTS, confirming the SPT of notched specimens in screening the HE susceptibility of the steels. • A novel RNTS determination for hydrogen compatibility screening of ferritic steels. • A 0.2 mm depth U-shaped notch specimen as suitable geometry for NTS determination. • δ f was an effective parameter to represent the HE effect for NTS calculation. • A combined approach of SPT and simulation effectively determined the RNTS. • A strength-based HE susceptibility evaluation using notched SP specimens. [ABSTRACT FROM AUTHOR]

This study investigated the pressure-dependent CO 2 effect on the hydrogen embrittlement of X80 and GB20# pipeline steels by combining experiments and first-principles calculations. Results revealed that the CO 2 effect enhanced the fatigue crack growth for GB20# steel in 10 MPa CO₂-enriched hydrogen mixtures. However, the improved degree by the CO₂ effect at 10 MPa was less pronounced than at 0.4 MPa, which was found for the first time. This was attributed to the decreased adsorption rate of CO₂ on iron as hydrogen pressure increased. Therefore, in high-pressure CO₂-enriched hydrogen mixtures, CO 2 could not significantly accelerate the inherent rapid hydrogen uptake at high pressure. [Display omitted] • Enhanced hydrogen embrittlement by CO 2 effect was pressure-dependent. • CO 2 effect at low pressure was more pronounced than that at high pressure. • CO 2 adsorption rate on iron decreased with increasing surface hydrogen coverage. [ABSTRACT FROM AUTHOR]

Understanding hydrogen–grain boundary (GB) interactions is critical to the analysis of hydrogen embrittlement in metals. This work presents a mesoscale fully kinetic model to investigate the effect of GB misorientation on hydrogen diffusion and trapping using phase‐field‐based representative volume elements (RVEs). The flux equation consists of three terms: a diffusive term and two terms for high and low angle grain boundary (H/LAGB) trapping. Uptake simulations show that decreasing the grain size results in higher hydrogen content due to increasing the GB density. Permeation simulations show that GBs are high‐flux paths due to their higher enrichment with hydrogen. Since HAGBs have higher enrichment than LAGBs, due to their higher trap‐binding energy, they generally have the highest hydrogen flux. Nevertheless, the flux shows a convoluted behavior as it depends on the local concentration, alignment of GB with external concentration gradient as well as the GB network connectivity. Finally, decreasing the grain size resulted in a larger break‐through time and a larger steady‐state exit flux. [ABSTRACT FROM AUTHOR]

First-principles study is used to comparatively study the hydrogen embrittlement resistance, elastic properties, and electronic structures of VWH and VMoH phases with various W and Mo concentration. Calculations reveal that the VMo phases have lower hydrogen solubility compared to VW phases, leading to higher hydrogen embrittlement resistance in VMo. In addition, the concentrations of W and Mo above 0.1875 would enhance the hydrogen embrittlement resistance of V membrane. Conversely, the W or Mo concentrations below 0.1875 would reduce the hydrogen embrittlement resistance. It is also demonstrated that adding W and Mo at concentrations below 0.25 would reduce the solid-solution strengthening of VH phase, thereby reducing its brittleness. This study will enhance comprehension of the underlying physics of VWH and VMoH phases and align with existing experimental literature. • Adding Mo is more effective than adding W in improving the hydrogen embrittlement resistance of V membrane. • The concentrations of W or Mo above 0.1875 would enhance the hydrogen embrittlement resistance of V membrane. • The W or Mo concentrations below 0.1875 would reduce the hydrogen embrittlement resistance. • Adding W and Mo at concentrations below 0.25 would reduce its brittleness. [ABSTRACT FROM AUTHOR]

In this research, wear resistance of chromium nitride (CrN) coated aluminum alloy with hydrogen charging was investigated. Delamination rates of the CrN coating layer after 6 and 12 h of hydrogen charging were measured to be 42.37% and 86.96%, respectively. In particular, damage by hydrogen attack was observed in the exposed area of aluminum alloy. Increasing in applied load and hydrogen charging time decreased the friction coefficient, and when the two factors interacted, a significantly higher increasing rate of wear damage was observed. The increasing rate in wear depth due to hydrogen charging was greater at the applied of 1 N than at 5 N. This is because hydrogen permeation affects the wear resistance of the CrN coating layer and aluminum alloy in the depth direction. In addition, re-transfer and re-adhesion of the CrN coating, whose adhesion strength had decreased due to hydrogen charging, actively occurred. • The high durability of hydrogen valve is a very important factor for the commercialization of fuel cells. • The surface damage and delamination of the CrN coating layer by hydrogen charging were obviously observed. • The delamination of the CrN coating layer occurred in a bulk, and the wear resistance decreased accordingly. • In particular, hydrogen charging affected the adhesive wear of CrN-coated specimens. • Nevertheless the CrN coating technology is significantly excellent performance for resistance of hydrogen embrittlement. [ABSTRACT FROM AUTHOR]

The influence of hydrogen on the fracture of X65 was studied. The fracture toughness in air was 369 MPa√m. The ASTM-valid fracture toughness with cathodic hydrogen charging was lower but was similar for these charging conditions 189 MPa√m and 181 MPa√m at 9 mA/cm2; 192 MPa√m and 179 MPa√m at 16 mA/cm2; and 177 MPa√m at 25 mA/cm2; even though the fractography changed from (i) ductile fracture by microvoid coalescence in air and at 9 mA/cm2 to (ii) more brittle fracture for hydrogen charging at 16 mA/cm2 and 25 mA/cm2, with flat facets and secondary cracks, which increased with increasing current density. • The influence of hydrogen on the fracture of X65 was studied. • The fracture toughness in air was 369 MPa√m. • The ASTM-valid fracture toughness with cathodic hydrogen charging was lower. • The fracture toughness with hydrogen was 152–186 MPa√m. • The fractography changed from ductile fracture to more brittle fracture with increasing hydrogen. [ABSTRACT FROM AUTHOR]

A theoretical model was established to investigate the interaction between hydrogen clusters and edge dislocations emitted from a semi-elliptical surface crack tip in deformed nanometallic materials. The model's solution was obtained by using the complex method, and the influence of the concentration and location of hydrogen clusters, temperature, crack shape, material constants, and the dislocation emission angle on the critical stress intensity factor (SIFs) corresponding to the first dislocation emission from crack tips was investigated through numerical analysis. The results show that dislocations are easily emitted from the crack tip at high hydrogen concentration, and hydrogen clusters close to the crack tip will hinder the emission of dislocations from its crack tip. When considering the influence of hydrogen cluster, an increase in temperature, an extension of crack length or an increase in crack tip curvature radius can all make the emission of dislocations at the crack tip difficult, thereby reducing the toughness of the material caused by dislocation emission. [ABSTRACT FROM AUTHOR]

The effect of plastic deformation on the hydrogen embrittlement behavior of high-strength martensitic steels was investigated using a U-bend test. The hydrogen embrittlement susceptibility appeared to be enhanced with increasing plastic strain. Based on fractographic and stress-strain analyses, the maximum principal stress dominated the hydrogen embrittlement fracture. Although an apparent enhancement with increasing plastic deformation was observed, the origin of this enhancement was increased residual stress arising from the evolution of graded plastic strain during U-bending. We conclude that residual stress, rather than plastic strain induced by plastic deformation strongly affects hydrogen embrittlement susceptibility in deformed high-strength steel components. • Hydrogen embrittlement susceptibility of U-bend specimens was independent of plastic strain. • Maximum principal stress was the primary criterion for the hydrogen embrittlement susceptibility. • The apparent decrease in hydrogen embrittlement resistance with reduced bending radii was due to increased residual stress. [ABSTRACT FROM AUTHOR]

The influence of simulated reheated coarse-grained heat-affected zones (CGHAZ) on the microstructural evolution and hydrogen embrittlement in high-strength naval steel was investigated by scanning electron microscopy, microhardness testing, electron backscatter diffraction, slow strain rate tensile test and fracture morphology analysis. Twinned martensites were observed in both the intercritical and super-critically reheated CGHAZ, with a widely spaced region in the former. Intercritical reheated coarse-grained HAZ (ICCGHAZ) was the weakest zone of reheated CGHAZ when the peak temperature was 660 °C, exhibiting the intergranular cracking feature. Twinned martensite and coarsening grain size were therefore concluded to be the main reasons for high hydrogen embrittlement susceptibility in the reheated CGHAZ. • The microstructural evolution in different regions of reheated HAZ was investigated. • Twinned martensite was the susceptible microstructure to hydrogen embrittlement. • Second peak temperature affected the formation of twins. • Inter-critical reheated CGHAZ was the weakest zone of reheated HAZ. [ABSTRACT FROM AUTHOR]

In this study, the effect of dislocation and grain boundary (GB) on hydrogen embrittlement of aluminum alloys was investigated using pre-strain and molecular dynamics (MD). Hydrogen increased the yield strength (YS) and ultimate tensile strength (UTS) of pre-strain alloys. MD simulations revealed that hydrogen enhance the critical resolved shear stress (CRSS) for dislocation, and hydrogen segregation GB reduce material strength. The YS and UTS of Al alloys are affected by both mechanisms during deformation, and the two mechanisms exhibit a competitive relationship. Hydrogen enhanced CRSS dominates in higher dislocation density deformations. [Display omitted] • H increase the YS and UTS of pre-strain 7075 Al alloys. • H has a pinning effect on dislocation and enhanced the CRSS. • Hydrogen segregation GB reducing the tensile strength of Al. • The YS and UTS of Al are influenced by a combination of two distinct mechanisms. • H enhanced dislocation slip CRSS dominates in higher dislocation density deformation. [ABSTRACT FROM AUTHOR]

The hydrogen embrittlement behavior of a prerolled Fe–15Mn–0.65C–2Al–2Si high‐Mn steel with various cut‐edge properties is studied via hydrogen precharging and slow strain rate test. In the presence of hydrogen, samples prepared by laser cutting under atmosphere of N2 exhibit the best total elongation at about 39%. Press blanking produces severe shear deformation, tensile residual stresses, and strain‐induced martensite, resulting in a high risk to hydrogen‐induced cracking. With compressive residual stresses produced from waterjet, corresponding samples exhibit the lowest elongation loss against hydrogen. Despite hydrogen charging, the fracture surfaces show transgranular quasi‐cleavage features, for which mechanical twinning from prerolling plays a critical role. The hydrogen‐enhanced decohesion mechanism accounts for cleavage fracture since hydrogen segregation reduces cohesive stress at twin boundaries. [ABSTRACT FROM AUTHOR]

Investigating the interaction between hydrogen and dislocations is essential for understanding the origin of hydrogen-related fractures, specifically hydrogen embrittlement (HE). This study investigates the effect of hydrogen on the mobility of ½<111>{110} and ½<111>{112} edge dislocations in body-centered cubic (BCC) iron (Fe). Specifically, molecular dynamics (MD) simulations are conducted at various stress levels and temperatures for hydrogen-free and hydrogen-containing lattices. The results show that hydrogen significantly reduces dislocation velocities due to the pinning effect. Based on the results of MD simulations, phenomenological mobility laws for both types of dislocations as a function of stress, temperature and hydrogen concentration are proposed. Current findings provide a comprehensive model for predicting dislocation behavior in hydrogen-containing BCC lattices, thus enhancing the understanding of HE. Additionally, the mobility laws can be utilized in dislocation dynamics simulations to investigate hydrogen-dislocation interactions on a larger scale, aiding in the design of HE-resilient materials for industrial applications. [Display omitted] • Effect of hydrogen and temperature on the mobility of edge dislocations is studied. • The effect of hydrogen on kink-pair formation and propagation is discussed. • Thermally activated mechanisms and viscous damping dynamics are discussed. • Hydrogen decreases the mobility of both dislocations via pinning effect. • Hydrogen-induced phenomenological mobility laws are proposed. [ABSTRACT FROM AUTHOR]

Small-hole components of Inconel 718 are widely used in aerospace engineering, medical devices, and other fields. Limited by material properties, its machining efficiency seriously restricts its wide application. The objective of this study is to investigate a novel machining technique for Inconel 718 that integrates ultrasonic machining (UM) and hydrogen embrittlement (HE) treatment. Accordingly, the technique is designated as hydrogen embrittlement-enhanced ultrasonic machining (HEUM). Prior to machining, a stress layer is formed on the surface of the workpiece. To ascertain the fundamental characteristics of Inconel 718, the influences of ultrasonic amplitude, HE time, and HE voltage on the specific material removal rate and surface roughness in the presence of HE were empirically examined. To investigate the material removal process for HEUM, the nanoscratch test and nanoindenter were also conducted with HE samples. Further, the subsurface for HEUAG samples were obtained with SEM. The specific material removal rate under experimental conditions of 10 min and 5 V HE increased by 27.4%. Finally, HEUM is proposed to be used for a 1 mm through-hole with Ra 0.318 μm. A precision hole with a diameter as small as 0.5 mm has been manufactured. [ABSTRACT FROM AUTHOR]

The susceptibility of subzones of the coarse-grained heat-affected zone (CGHAZ) in X65 pipeline steel to hydrogen embrittlement was studied through an in situ crack-tip opening displacement test in an H 2 S-containing environment. The intercritically reheated CGHAZ (IC-CGHAZ) exhibited the highest embrittlement factor of 89.4%, compared to 64.0% for the sub-critically reheated CGHAZ (SC-CGHAZ). Hydrogen transportation by dislocations to massive-slender martensite/austenite (M/A) constituents initiated cracks in IC-CGHAZ. Deterioration of lath bainite (LB) boundaries, with separation of M/A-ferrite interface, accelerated crack propagation across prior austenite grains and promoted hydrogen-assisted degradation of fracture toughness. Reheated CGHAZ at a peak temperature of 620 °C led to an increased intensity of the {110} LB boundary texture by up to 52% in SC-CGHAZ. This enhanced texture facilitated dislocation slipping along {110} LB boundary planes, thereby promoting deformation compatibility and preventing the deterioration of LB boundaries in the presence of hydrogen. • SC-CGHAZ exhibits the lowest embrittlement factor of 64.0% in H 2 S. • Reheated CGHAZ at 620 °C leads to increased {110} LB boundary texture by up to 52%. • {110} LB boundary significantly influences cracking associated with hydrogen. [ABSTRACT FROM AUTHOR]

This work is aimed at a comprehensive solution to the problem of reliable and safe operation of a transport energy system with a high energy concentration based on a universal energy carrier - cryogenic liquid hydrogen. The article discusses the possibility of using various methods and techniques to assess the reliability of machines and equipment operated in emergency situations and extreme conditions. The obtained results are analyzed. Currently, the oil and gas complex pays great attention to the development of hydrogen technologies, as well as hydrogen energy in connection with the relevance of the Climate Agenda. In this regard, hydrogen energy facilities are of the greatest interest: cryogenic hydrogen reservoirs, cryogenic hydrogen pipelines, cryogenic oxygen reservoirs and cryogenic oxygen pipelines, as well as cryogenic reservoirs and pipelines for storing process nitrogen gas. An important role for global energy exchange is played by LH 2 tankers for transporting cryogenic hydrogen. For example, Australia and Japan built the first LH 2 tanker to transport hydrogen from Australia to Japan. In addition, another 85 LH 2 tankers are expected to be built. After transportation, cryogenic hydrogen is stored in cryogenic hydrogen storages, usually also representing cryogenic hydrogen tanks with piping in the form of cryogenic pipelines, as well as cryogenic nitrogen tanks for storing process nitrogen gas. Further, hydrogen is used in road transport, aviation, ship fleet, industry, and energy. The main elements of mobile, stationary and airborne hydrogen storage systems are under critical loads and are in the area of increased study and attention. In this regard, we considered the functions of changing the main operational characteristics, made proposals on the possibility of predicting the development of accumulated faults and proposals for ensuring safety and extending the life of objects, taking into account the determination of local and integral damage to cryogenic tanks and pipelines. Project for the creation of a main cryogenic hydrogen pipeline from Azerbaijan to Europe across the Adriatic Sea. [Display omitted] [ABSTRACT FROM AUTHOR]

Understanding the interactions between hydrogen and material integrity in polycrystalline α-Fe is essential for advancing the reliability of critical infrastructure and energy systems. In this study, molecular dynamics simulations were implemented to pinpoint the crack propagation behaviour and mechanism in polycrystalline α-Fe under various hydrogen concentrations and temperatures. The results show that a phase transition from body-centred cubic to face-centred cubic structure first occurs at the crack tip, followed by grain boundary-mediated plasticity activities at room temperature devoid of hydrogen. A limited amount of hydrogen atoms (H/Fe atomic ratio<1%) induces twinning emission from the tip, and increasing temperature further enhances dislocation plasticity as a consequence of decreased unstable stacking fault energy, thereby leading to the blunting of the crack tip. At high hydrogen concentrations (H/Fe atomic ratio>1%), the formed hydrides ahead of the crack tip suppress the phase transition, and concurrently temperature-enhanced dislocation plasticity disappears. As a consequence, the crack propagation proceeds via grain boundary cavity nucleation and growth, and ultimately evolves into intergranular fracture. These findings provide an atomistic-level explanation for temperature-dependent hydrogen-crack interaction mechanisms, and reveal a transition in the fracture mode from ductile transgranular to intergranular failure associated with locally high hydrogen concentrations found in the experiments. • Illumination of temperature-dependent hydrogen-induced cracking in polycrystalline α-iron. • Low hydrogen concentrations induce twin emission after phase transition at the crack tip. • Increasing temperature enhances dislocation plasticity, thus blunting the crack tip. • High hydrogen concentrations encourage the formation of hydrides, and facilitate the crack propagation. • The initial crack coalesces with GB cavities, ultimately leading to an intergranular fracture. [ABSTRACT FROM AUTHOR]

A hydrogen economy will require the use of steel pipelines to transport and store hydrogen. Methods and materials are urgently needed to prevent the embrittlement of steel pipelines in hydrogen service. In this work, we show that hydrogen permeation into pipeline steel can be mitigated by organic inhibitors, as demonstrated by a typical organic inhibitor benzotriazole (BTA) under simulated X65 steel pipeline cathodic protection conditions. Electrochemical and surface analytical techniques were used to probe the efficiency and mechanism of hydrogen permeation inhibition. In particular, a novel multi-electrode array method was designed to probe the inhibitor film by measuring local impedance and hydrogen charging currents. The ability and efficiency of BTA to inhibit hydrogen permeation were found to be closely associated with the formation and coverage of inhibitor films on steel surfaces. A model is proposed to illustrate the mechanism of hydrogen permeation inhibition by organic inhibitors. • The efficiency and mechanism of an organic hydrogen permeation inhibitor is investigated. • A multi-electrode array was used to probe the inhibitor film formation and coverage. • The capability of hydrogen permeation inhibition is related to inhibitor film formation. • The efficiency of hydrogen permeation inhibition is affected by inhibitor film coverage. • A model is proposed to explain the mechanism of hydrogen permeation inhibition. [ABSTRACT FROM AUTHOR]

This study explores the impact of microstructural features on fatigue crack initiation in poly‐crystalline materials, emphasizing hydrogen‐induced complexities. Grain anisotropy, misorientations, grain size variations, and elastic–plastic inhomogeneities concentrate stress at grain boundaries, making them susceptible to crack initiation during fatigue loading. The presence of hydrogen compounds this process, due to complications of characterization of local hydrogen content and activating embrittling mechanisms. Building upon a model for nickel, this research investigates 316L austenitic stainless steel specimens with varying grain sizes, both uncharged and hydrogen‐charged. In situ low‐cycle fatigue loading experiments establish correlations between fatigue crack initiation and microstructural features. The study reveals specific combinations of features crucial in the initiation process, undergoing alterations in the presence of hydrogen. A proposed qualitative model links microstructural features with accumulated plastic shear strain during fatigue and prevalent hydrogen embrittlement mechanisms like hydrogen‐enhanced local plasticity and hydrogen‐enhanced decohesion. Highlights: The effects of hydrogen on fatigue crack initiation (FCI) sites in stainless steel 316L are studied.Two different grain sizes were analyzed by in‐situ scanning electron microscopy (SEM) and electron back‐scattered diffraction (EBSD) and high‐resolution digital image correlation (HR‐DIC).Hydrogen‐assisted FCI is correlated with initial features of the microstructure.A model is proposed linking FCI with microstructure and accumulated plastic shear strain. [ABSTRACT FROM AUTHOR]

With the increasing focus on reducing carbon emissions, hydrogen has emerged as a promising alternative energy source. However, the safe transportation of hydrogen poses challenges due to its potential impact on the integrity of pipeline materials. This study aims to investigate the effect of hydrogen charging time on the plastic behavior and ductile fracture characteristics of API 5L X42 pipelines, which are commonly used for transporting hydrocarbons. Tensile tests were conducted on various types of hydrogen-charged specimens at room temperature to assess different fracture modes. Hydrogen was introduced into the specimens using a cathodic electrolytic method, and 24-h charging time durations were considered. Finite element analyses were performed on standard dog-bone and notched tension specimens to evaluate the plastic behavior, employing the Swift hardening law to model the flow stress. Numerical analyses were conducted to determine the loading path leading to fracture initiation. A damage framework based on the Hosford–Coulomb model was utilized to predict ductile fracture under non-proportional loading conditions. The findings of this study provide insights into the fracture behavior of pipelines under hydrogen exposure, aiding in the design and assessment of safe and reliable hydrogen transport systems. [ABSTRACT FROM AUTHOR]

This study investigates the hydrogen embrittlement behavior of API X70 linepipe steel. The microstructure was primarily composed of a dislocation-rich bainitic microstructure and polygonal ferrite. Slow strain-rate tests (SSRTs) were performed under both ex situ and in situ electrochemical hydrogen charging conditions to examine the difference between hydrogen diffusion and trapping behaviors. The ex situ SSRTs showed almost the same tensile properties as air and a limited brittle fracture confined to near the surface. In contrast, the in situ SSRTs showed an abrupt failure after the maximum tensile load, leading to a brittle fracture across the entire fracture surface with stress-oriented hydrogen-induced cracking (SOHIC). The crack trace analysis results indicated that SOHIC propagation paths were influenced by localized hydrogen accumulation due to high-stress fields. As a result, the dominant hydrogen embrittlement mechanisms, such as hydrogen-enhanced localized plasticity (HELP) and hydrogen-enhanced decohesion (HEDE), changed. These findings provide critical insights into the microstructural factors affecting hydrogen embrittlement, which are essential for the design of hydrogen-resistant steels in hydrogen infrastructure applications. [ABSTRACT FROM AUTHOR]

This study investigates the role of coalesced bainite in enhancing the hydrogen embrittlement resistance of tempered martensitic steels. By analyzing the microstructural characteristics and mechanical properties under varying cooling rates, it was found that the presence of coalesced bainite significantly impedes hydrogen accumulation at prior austenite grain boundaries. This leads to a transition in the fracture mode from intergranular to transgranular, thereby improving the overall resistance to hydrogen embrittlement in steels. Slow strain rate tests (SSRTs) on both smooth and notched specimens further confirmed that steels cooled at lower rates, which form a higher fraction of coalesced bainite, exhibiting superior hydrogen embrittlement resistance. These findings suggest that optimizing the cooling process to promote coalesced bainite formation could be a valuable strategy for enhancing the performance of tempered martensitic steels in hydrogen-rich environments. [ABSTRACT FROM AUTHOR]

The influence of the centerline segregation region (CSR) on the hydrogen embrittlement (HE) of two different API 5L X80 pipeline steel plates was investigated. The novelty of this work was to establish relationships between the CSR, microstructure, and distribution of localized fragile particles on HE susceptibility and on fracture morphology. This work intended to establish a relationship between centerline segregation and HE susceptibility in high-strength low-alloy steels submitted to inhomogeneous transformations. Microscopy, hydrogen permeation, and slow strain rate (SSR) tests were used to investigate hydrogen-related degradation. The solution used on the charging cell of the permeation tests—and on the SSR test cell—was 0.5 mol L−1 H2SO4 + 10 mg L−1 As2O3, and in the oxidation cell, 0.1 M NaOH was used as a solution. The CSR led the thicker plate to present the highest HE index (0.612) in analyses carried out in the mid-thickness; however, the same plate showed the lowest HE index in near-surface tests. The presence of hydrogen changed the fracture morphology from ductile to a brittle and ductile feature; this occurred due to the interaction with localized fragile particles and the significant reduction of the shear stress necessary for the dislocation movement. [ABSTRACT FROM AUTHOR]

This study employs a custom hollow specimen setup to investigate the HE in API 5L X60 pipeline base and welded materials exposed to pure hydrogen and a 20% hydrogen–natural gas blend at 2.07 MPa. Results indicate embrittlement with increasing hydrogen concentration. The base material showed a hydrogen embrittlement index (HEI) of 11.6% at 20% hydrogen and 12.4% at 100% hydrogen. For the welded material, the HEI was 14.6% at 20% hydrogen and 18.0% at 100% hydrogen. Fractography analysis revealed that the base and welded materials exhibited typical ductile fracture features in the absence of hydrogen, transitioning to a mixture of quasi-cleavage and micro-void coalescence (MVC) features in hydrogen environments. Additionally, with hydrogen, increased formation of secondary cracks was observed. Notably, the study identified the Hydrogen-Enhanced Localized Plasticity (HELP) mechanism as a probable contributor to hydrogen-assisted fracture. [ABSTRACT FROM AUTHOR]

The utilization of micro-sample testing has demonstrated its effectiveness in conducting quantitative research on mechanical properties, damage evolutions and fracture features. For in-service equipment, millimicron sampling allows for non-destructive testing and analysis of mechanical performance evolution during operation. This paper presents a comparative study of the miniature uniaxial tensile test (MUTT) and small punch test (SPT) by experimental and finite element methods. As a comparison, the standard conventional-size tensile tests were also carried out. Detailed analyses of the elastoplastic behaviors and damage evolutions of MUTT and SPT were presented, followed by an application case illustrating the characterization of hydrogen embrittlement sensitivity based on MUTT and SPT. An inverse finite element modeling method of load–displacement curve reproduction was used to calibrate the variations of damage parameters of hydrogen-charged MUTT and SPT specimens. Hydrogen embrittlement (HE) indexes were determined by using different calculation methods. The results reveal that the HE sensitivity estimated by MUTT is higher than that measured by SPT, which is related to the different deformation processes and strain rates of the two testing methods. [ABSTRACT FROM AUTHOR]

Environmentally assisted cracking can significantly affect the performance of high strength alloys and limit material selection to minimize the risk of subcritical crack growth in service. UNS N07718 is widely used in marine service applications and under a variety of conditions, such as: alternate immersion, different levels of cathodic protection, and freely corroding galvanic couples, because of its demonstrated corrosion and fracture resistance in these environments. In this work we developed a representative model of the material microstructure including the metal grains, the material texture, and the precipitates along the grain boundaries and within the grains. The microstructural model was subjected to the boundary conditions identified at the notch root of a fracture mechanics sample and the results are used as input for a simulation of hydrogen diffusion from the surface of the notch, assuming the material has been introduced to a hydrogen producing environment. The diffusion of hydrogen was modeled by Fick's law and included both hydrostatic stress and mobile dislocation velocity as driving forces. The influence of immobile dislocations was also modeled to account for the irreversible trapping. The results show that hydrostatic stress and immobile dislocation trapping can significantly alter the highest concentration of hydrogen and its location within the microstructure towards the fracture process zone. Mobile dislocation velocity has a small influence in determining the hydrogen distribution near the fracture process zone. [ABSTRACT FROM AUTHOR]

This study investigates the impact of friction stir processing (FSP) on the hydrogen embrittlement (HE) in AA6082-T6 heat-treatable aluminum alloy. The effects of different number of FSP passes and different hydrogen cathodic charging (HCC) conditions on the material's response to HE are examined through comprehensive mechanical testing, microhardness analysis, and microstructural characterization. The results revealed that FSP leads to a decrease in yield strength, ultimate tensile strength, and microhardness, accompanied by an increase in energy absorption. The introduction of hydrogen through HCC significantly reduces mechanical properties, particularly in non-FSPed specimens. Notably, specimens with 8 FSP passes exhibit an interesting behavior with a slight increase in energy absorption and microhardness values after HCC. Microstructural analysis shows that FSP refines the microstructure, resulting in enhanced resistance to hydrogen-induced blistering effects. These findings contribute to the understanding of hydrogen embrittlement in FSPed aluminum alloys, providing insights for developing surface-modified materials suited for hydrogen-rich applications. [ABSTRACT FROM AUTHOR]

The microstructure and hydrogen embrittlement sensitivity of two X65 pipeline steels at different t 8/5 (the time required to cool from 800 °C to 500 °C) were investigated employing thermal simulation. With the increase of t 8/5 for both steels, the martensite transferred to acicular ferrite (AF) and bainite, and further converts to bainite and martensite/austenite (M/A) constituents. Elongated polygonal Mn–Nb–S inclusions appear in steel A, which are easy to fall off and the hydrogen embrittlement sensitivity is thus increased. However, spherical Al–Ca–Nb–N–O–S inclusions appear in steel B, which can promote nucleation of AF, thus obtaining lower hydrogen embrittlement sensitivity under lower t 8/5. • The HE sensitivity of two X65 pipeline steels at different t 8/5 were investigated. • The elimination of M and the nucleation of AF can reduce HE sensitivity. • Elongated polygonal Mn–Nb–S inclusions easily shed and increase HE sensitivity. • Spherical Al–Ca–Nb–O–S inclusions promote AF nucleation and reduce HE sensitivity. [ABSTRACT FROM AUTHOR]

Hydrogen segregation behaviors at BCC-Fe Σ3 (111) grain boundary (GB) as well as the effects of alloying solutes were studied by the first-principles method. The segregation energy of alloying solutes at different periods presents a concave-down parabolic-like relationship with the atomic number, and the 4 d transition alloying solutes show a higher averaged segregation tendency. At the favorable trapping site, hydrogen segregation energy decreased by increasing the number of hydrogen atoms up to 0.85/Å2 in the plane vertical to the GB. Mo, Tc, Ru, Ta, W, Re, Os, and Ir strengthen GB and inhibit hydrogen segregation. Significantly, the interaction between alloying solutes and hydrogen segregation was elucidated by emphasizing the separation of the chemical and the mechanical contributions, and appropriate descriptors on hydrogen segregation energy influenced by alloying solutes were screened. This work offers theoretical backing to comprehend hydrogen segregation behaviors and the effects of alloying solutes to design advanced high-strength steels resistant to hydrogen embrittlement. • Hydrogen segregation behaviors at pure BCC Σ3 (111) grain boundary were studied. • Alloy solute segregation behaviors at pure BCC Σ3 (111) grain boundary were studied. • Interaction between alloying solutes and hydrogen at grain boundary was elucidated. • Descriptors on hydrogen segregation energy at grain boundary were screened. • Relationship between hydrogen segregation at grain boundary and HE was discussed. [ABSTRACT FROM AUTHOR]

Hydrogen embrittlement (HE) is a significant challenge to the safe operation of hydrogen-blended natural gas pipelines. The mechanical properties of X80 steel were studied after H 2 pre-charging followed by mechanical properties tests and fracture morphologies observation. Results indicated that the hydrogen saturation time of X80 steel was roughly 48 h. H 2 pre-charging induced a decline in strength, plasticity, and fatigue properties, while hydrogen-assisted fatigue crack growth occurred during the early stage of fatigue crack growth rate tests. Additionally, the fracture morphologies transited from primary microvoid coalescence to a mixed mode characterized by ductile dimples and quasi-cleavage planes with increasing hydrogen. The HE susceptibility increased with increasing hydrogen partial pressure and decreasing loading frequency, but there existed a critical value (6 × 10−7 s−1) for the strain rate effect on the HE susceptibility. Under H 2 pre-charging conditions, the predominant HE mechanism was the hydrogen-enhanced local plasticity (HELP) mediated hydrogen-enhanced decohesion (HEDE) mechanism. • Permeation parameters of X80 steel were obtained through H 2 permeation tests. • The mechanical properties of hydrogen pre-charged X80 steel were obtained. • 6 × 10−7 s−1 was determined as the critical strain rate to HE susceptibility. • The predominant HE mechanism under hydrogen pre-charging conditions was analyzed. [ABSTRACT FROM AUTHOR]

Hydrogen, the lightest and most abundant element in the universe, plays essential roles in a variety of clean energy technologies and industrial processes. For over a century, it has been known that hydrogen can significantly degrade the mechanical properties of materials, leading to issues like hydrogen embrittlement. A major challenge that has significantly limited scientific advances in this field is that light atoms like hydrogen are difficult to image, even with state-of-the-art microscopic techniques. To address this challenge, here, we introduce Atom-H, a versatile and generalizable machine learning-based framework for imaging hydrogen atoms at the atomic scale. Using a high-resolution electron microscope image as input, Atom-H accurately captures the distribution of hydrogen atoms and local stresses at lattice defects, including dislocations, grain boundaries, cracks, and phase boundaries. This provides atomic-scale insights into hydrogen-governed mechanical behaviors in metallic materials, including pure metals like Ni, Fe, Ti and alloys like FeCr. The proposed framework has an immediate impact on current research into hydrogen embrittlement and is expected to have far-reaching implications for mapping "invisible" atoms in other scientific disciplines. [ABSTRACT FROM AUTHOR]

The hydrogen embrittlement (HE) susceptibility of the X52 pipeline steels in simulated hydrogen-blended natural gas (HBNG) environments were investigated with a combination of in situ high-pressure gaseous hydrogen permeation tests, slow strain rate tensile (SSRT) tests and molecular dynamics simulation, the results were compared with the X80 steel. The HE susceptibility of the X52 steel was found higher than that of the X80 steel. The mechanism of the two steels showing different HE susceptibility was analyzed from a point of permeation parameters and molecular dynamics simulation. The results showed that the X52 steel contained more impurity elements and a larger grain size, leading to a higher hydrogen solubility and a microstructure with lower HE resistance. This study suggests that the steel microstructure and the hydrogen permeation property are crucial for the understanding and prediction of the HE susceptibility of the steels. • N 2 partial pressure would not influence the hydrogen permeation behaviour. • HE susceptibility is not necessarily positively correlated with steel grade. • Phase transition/dislocation emission is main deformation mechanism of boundaries. • Hydrogen atom inhibit local energy release and promote crack initiation. • Finer grain weakens the inhibition of local energy release caused by H. [ABSTRACT FROM AUTHOR]

Alloy 625 plays a crucial role in high-pressure hydrogen environments typical of hydrogen refuelling stations, where cyclic temperature and loading conditions prevail. In this study, we reveal that hydrogen-induced ductility loss of nickel-based alloy 625 significant difference which change from 11.9% at slow strain rate to 20.1% at conventional strain rate. The difference can be attributed to a change in deformation mode: from dislocation slipping under slow strain rate to twinning under conventional strain rate. Specifically, hydrogen-refined deformation twins and the promotion of twin bundles under conventional strain rates diminish the twin-induced plasticity effect of the alloy. This shift in deformation mode also alters the hydrogen embrittlement mechanism across the two strain rates. These findings provide valuable insights for hydrogen embrittlement-resistant designing and evaluating hydrogen compatibility for alloy 625. [Display omitted] • The nickel-based alloy 625 has more significant hydrogen-induced ductility loss at 5 × 10−3 s−1 than that at 5 × 10−6 s−1. • The deformation mode change from dislocation slipping at 5 × 10−6 s−1 to twinning at 5 × 10−3 s−1. • Hydrogen weakens the TWIP effect of the alloy because of hydrogen refining DTs. • Hydrogen will promote the formation of deformation twin bundles, resulting in cracking along DTs. • A new mechanism of hydrogen-induced cracking along DTs in nickel-based alloys was proposed. [ABSTRACT FROM AUTHOR]

Common alloying elements such as Mn and Al can significantly influence the local dynamics of Hydrogen in steel, promoting or attenuating the mechanisms associated with Hydrogen induced Embrittlement (HIE). Here, we propose a first principles-based framework to systematically unlock the physical underpinnings of such influence in Mn/Al-alloyed γ-Fe. Our framework can be readily adapted to analyse H behaviour in the bulk phase of any face-centred cubic (FCC) Fe-X-Y alloy, provided that solutes X and Y substitute the Fe sites. In our scheme, all thermodynamically stable substitutional solute sites were identified (≤5.4 wt% Mn; ≤4 wt% Al) up to the third nearest neighbour (NN) shell of a single H atom. The impact of Mn/Al on H-binding was quantitatively evaluated, indicating a surprisingly strong correlation with the local Al distribution regardless Mn content, and indirect stabilization by Al when present in the 2nd NN shell. Nonetheless, Al strongly repels H bonding. The contradictory role of Al was explained in terms of bonding/anti-bonding orbitals occupancy in H-M interactions (M = Al, Mn, Fe). The barriers to H hopping between adjacent local environments and the corresponding jump frequencies were subsequently calculated, providing insights into the limits imposed by the presence of Al and Mn on H mobility in Mn/Al-alloyed γ-Fe. Most notably, presence of Al in the 2nd NN shell of H severely reduces the H jump frequency, leading to potential irreversible trapping at high Al contents. Such behaviour may critically contribute to mitigate H-induced delayed fracture in Al-rich austenite steel. [Display omitted] • H-binding strength is strongly correlated with local distribution of Al, regardless Mn content. • Al repels H but indirectly strengthen the H-binding when present in the 2nd NN shell. • The unique dual role of Al on H-binding is explained via COHP analysis. • Reversible and irreversible trapping sites are isolated for Fe-Mn-Al alloys. • Irreversible H-trapping may contribute to mitigate H-induced delayed fracture. [ABSTRACT FROM AUTHOR]

Herein, the interaction between hydrogen, microstructure, and mechanical properties in low-alloy high-strength marine steel was elucidated via microstructural characterization, internal friction analysis, hydrogen diffusion, and hydrogen-embrittlement sensitivity evaluation. Results indicated that the bainite structure of hot-rolled steel transformed into a coarse ferrite–pearlite structure after normalizing, and the hydrogen trap density decreased with decreasing grain boundary and dislocation densities. Therefore, the effective diffusion coefficient of hydrogen in the normalized steel plates increased with decreasing hydrogen permeation time. Owing to the coarsening of the microstructure, the normalized steel plates exhibited higher sensitivity to hydrogen embrittlement. The diffusion of a large amount of hydrogen into the steel considerably deteriorated its plasticity, resulting in a transition of its fracture mode from microvoid coalescence fracture to cleavage fracture. The internal friction behavior indicated that hydrogen in the microstructure generated a hydrogen-induced Snoek peak, as well as reduced the activation energy of Snoek–Kê–Köster and Kê peaks. Finally, the internal friction spectra revealed that the interaction between hydrogen and point defects, dislocations, grain boundaries, and precipitates was sequentially enhanced due to the increase in activation energy. [ABSTRACT FROM AUTHOR]

The effect of interstitial hydrogen on the elastic properties of bcc Fe, bcc Fe–Cr, and bcc Fe–Ni was investigated using density functional theory calculations. Our results indicate that the elastic moduli decrease linearly with increasing hydrogen concentration. The consequences of hydrogen for the mechanical properties of bcc Fe, bcc Fe–Cr, and bcc Fe–Ni were analyzed, considering various factors such as the ideal shear stress, Peierls stress, number of dislocation pile-ups, and critical crack growth lengths. At the same hydrogen concentration, compared to the bcc Fe and bcc Fe–Ni systems, fewer dislocation pile-ups and shorter critical crack growth lengths can facilitate the nucleation and propagation of cracks in the bcc Fe–Cr system. Finally, we propose a mechanism to explain the influence of Cr and Ni on hydrogen embrittlement. [ABSTRACT FROM AUTHOR]

Underwater laser direct metal deposition (UDMD) shows great application potential in underwater high-performance repair. The susceptibility of underwater repaired components to hydrogen embrittlement (HE) is not extensively researched yet. In this study, HE in 316L stainless steel repaired by UDMD is systematically investigated and compared with in-air direct metal deposited (DMD) 316L and conventionally manufactured (CM) 316L. The experimental results show that the high cooling rates involved in UDMD contribute to a "austenite-ferrite" solidification mode. The cellular structure with a high-density of dislocations increases the tensile strength of as-built UDMD 316L. Thermal desorption spectroscopy analysis reveals that the hydrogen concentrations are similar for 316L manufactured by three processing methods, suggesting that the complex microstructural features by UDMD and DMD do not provide additional H-trapping sites. SSRT results show that the HE susceptibility is in the sequence: CM 316L (30.7%) > UDMD 316L (15.1%) > DMD 316L (9.6%). Compared with CM 316L, the stable cellular structure and higher stability towards martensitic transformation of as-built 316L are beneficial for the HE resistance. In the hydrogen-charged UDMD 316L, the hydrogen-assisted dislocation movement and mechanical twinning formation enhance the localized plasticity and induce cracking. The micron-sized oxide particles and micro-pores further contribute to the fast decohesion of interfaces in the presence of hydrogen. Those combined effects lead to the reductions in tensile strength and elongation of the hydrogen-charged UDMD 316L. • High cooling rates in UDMD lead to cellular structures with high dislocation density. • Complex microstructures in UDMD 316L do not provide additional H-trapping sites. • HE susceptibility of UDMD 316L is larger than that of in-air DMD 316L. • H-assisted dislocation movement and twinning formation induce cracking of UDMD 316L. • Micron-sized oxide particles and micro-pores with H contribute to premature failure. [ABSTRACT FROM AUTHOR]

In the present study, twinning-induced plasticity (TWIP) steels with varying grain size and distribution were obtained by adjusting the thermomechanical methods such as pre-torsion, pre-strain and heat treatment. The advantage of gradient structure design over traditional grain refinement lies in its ability to optimize material strength while reducing ductility loss. Furthermore, the hydrogen embrittlement (HE) behavior of TWIP steels with various grain sizes and distributions was investigated under in-situ hydrogen charging conditions. The results revealed that the gradient structural specimen with finer equiaxed grains in the edge region exhibited lower lattice distortion, fewer stress concentration points and delayed plastic deformation. This decelerated the initiation and propagation of cracks, thus optimizing HE resistance and demonstrating comprehensive mechanical properties superior to all the other investigated specimens in the hydrogen environment. [Display omitted] • Quasi in-situ observation of deformation characteristics. • Gradient design can make steels have superior comprehensive mechanical properties. • Gradient structural materials exhibit the good HE resistance. • In-situ hydrogen charging is more likely to cause HE vs hydrogen pre-charging. • Grain refinement can improve HE resistance. [ABSTRACT FROM AUTHOR]

The effect of hydrogen atoms on the generalized stacking fault energy (GSFE) of 1/6[11-2]{111} stacking fault slip system in γ-Fe is investigated using first-principles. Hydrogen atoms at two different interstitial sites on the slip plane exert opposite effects on stacking fault formation. Occupying the tetrahedral site decreases unstable GSFE from 591.61 to 519.25 mJ/m2 in pure γ-Fe, while occupancy of the octahedral site increases unstable GSFE to 733.99 mJ/m2. Hydrogen atoms not on the slip plane have minimal impact on the GSFE. As hydrogen concentration increases along [11-2] direction at the slip plane octahedral site, the GSFE curve increases significantly. Electron structure analysis reveals that the influence of hydrogen atoms on stacking faults is short-ranged, the quantity and strength of H–Fe bonds and weakened Fe–Fe bonds, govern the unstable GSFE, which provides a novel perspective to evaluate the influence of hydrogen atoms on dislocation nucleation in metals. [Display omitted] • H atom increases the stable generalized stacking fault energy of 1/6[11-2]{111} stacking fault slip system. • The H atoms occupying two different interstitial sites on the slip plane exert opposite effects of stacking fault formation. • H atom is located away from the slip plane, and the changes in generalized stacking fault energy curves are minimal. • Studied the impact of H atom concentration in different directions on generalized stacking fault energy curves. • Elucidated the mechanism of the H atom's impact on generalized stacking fault energy via H–Fe Interaction. [ABSTRACT FROM AUTHOR]

Influence of hydrogen at pressures up to 35 MPa (and absorbed hydrogen with concentration up to 32,7 ppm) on the nanopore nucleation, crack initiation and propagation in Ni–Co superalloys for disk application with different chemical composition and tempering modes has been investigated. It was established that under the influence of gaseous hydrogen, the tensile strength, true fracture stress, relative elongation, and reduction of area of disk alloys samples decrease both at room and close to operating temperatures (1073 K). The cyclic durability of the samples under the influence of prolonged exposure to high pressures and temperatures in the hydrogen gas environment decreases by about 3 times.We have discussed the mechanisms of hydrogen-assisted nickel-cobalt superalloys fracture on mesa-, macro-, micro-, and nano-levels. [Display omitted] • Experimental results of cyclic crack resistance of Ni–Co superalloys in gaseous hydrogen with extreme parameters. • Hydrogen (with concentration up to 32,7 ppm) influence on the nanopore nucleation in Ni–Co superalloys. • SIF diagrams and Paris equation parameters for lifetime predict the Ni–Co superalloys for disks applications. [ABSTRACT FROM AUTHOR]

In this study, fracture behaviors of base metal and weld metal of ferritic steel welded joint in the thick wall pipeline for hydrogen transportation were investigated and the effects of hydrogen and specimen thickness (B) on fracture toughness were comprehensively considered in detail. A series of single edge notched tensile (SENT) tests for base metal and weld metal with B/W (width) ratio of 0.5, 1 and 2 were conducted with and without pre-electrochemical hydrogen charging, and crack tip opening displacement (CTOD) of δ m value was obtained by the double clip gauges method. It was found that fracture toughness (δ m) of base metal and weld metal decreased with increasing specimen thickness or hydrogenating, and δ m of hydrogenating specimen with B/W ratio of 2 was smallest. It was believed that large specimen thickness decreased fracture toughness by constraining plastic deformation at crack tip and restricting dislocations movement, while hydrogen promoted embrittlement by reducing cohesive energy of fracture. In the hydrogenating specimen with larger thickness, there was lower dislocation density near crack tip, leading to a decrease in trapped hydrogen and intensifying the cohesive energy reduction effect, which resulted in reduced δ m and the worse fracture toughness, and it means that hydrogen and specimen thickness synergistically affected fracture toughness. In addition, effect of thickness and hydrogen on decreasing fracture toughness was more pronounced for weld metal than base metal, which could be attributed to poorer plastic deformation ability of weld metal and lower dislocation density at crack tip. It is concluded that the hydrogen and thickness effects should be taken into account for the structural integrity evaluation of welded joint in hydrogen transportation pipeline. • Hydrogen coupled with specimen thickness severely deteriorated fracture toughness of base metal and weld metal. • Significant hydrogen embrittlement in thicker specimen was due to hydrogen, plastic deformation and dislocation interaction. • The hydrogen embrittlement effect was more pronounced for weld metal than base metal. • Structural integrity evaluation for welded pipelinemust take hydrogen and thickness into account. [ABSTRACT FROM AUTHOR]

Hydrogen (H), emerging as a sustainable and promising clean energy source, holds significant potential for transitioning towards a H-based economy, offering a cleaner alternative to traditional fossil fuels. However, hydrogen embrittlement (HE) poses a substantial obstacle to this transition, impacting critical sectors such as transportation, defense, energy production, and construction. Computational modeling, driven by the continuous development of new algorithms and high-performance computing platforms, emerges as an attractive avenue to unravel and address the complexities associated with HE. In particular, a multidisciplinary modeling approach shows potential in investigating the intricate interactions between H and materials across different temporal and spatial scales. Over the last few decades, there have already been many developments in computational modeling investigations based on a coupled study of H diffusion, deformation, and fracture processes to address multifaceted aspects of the HE problem. This comprehensive review sheds light on these advancements, providing insights into the modeling methodologies adopted in these investigations and their results. The review begins with a concise overview of commonly adopted mechanisms to explain HE. Thereafter, the discussion shifts to various advancements in H diffusion modeling, from early works to most recent developments, encompassing diverse aspects, such as H uptake and diffusion through the lattice structure and the role of microstructural traps and material microstructure. The last section of the review focuses on several theoretical and numerical studies that simulate how H affects the fracture characteristics and mechanical properties of various metals and alloys. This discussion includes applications of various state-of-the-art fracture models to predict H-assisted crack growth, as well as a range of theoretical models, continuum-based finite element simulations, and micro-meso scale modeling studies. • Advances in hydrogen diffusion modeling using coupled deformation-diffusion models. • Comprehensive review of coupled deformation-diffusion-fracture models. • Insights into micro-meso scale investigations to study hydrogen embrittlement mechanisms. [ABSTRACT FROM AUTHOR]

This study describes a novel approach for determining the electrochemical charging conditions corresponding to the hydrogen gas pressures associated with transportation of hydrogen in X65 pipeline steel, using a custom-made setup. Electrochemical charging conditions representing cathodic protection at −1050 mV vs. Ag/AgCl are found to be equivalent to a hydrogen pressure of ∼15–20 bar. Additions of recombination poisons increase the equivalent pressure up to ∼200 bar, which is the desired pressure for transportation of hydrogen gas in existing pipelines. The results are compared with data from fracture mechanical testing of a X65 steel under equivalent charging conditions, thereby verifying the reliability of the new custom-made setup. The electrochemical production of hydrogen on the outer wall and its diffusion into the sample is simulated with a transient, 1-D diffusion model. The model predicts the evolution of hydrogen pressure, elucidating the impact of varying operational and material parameters, such as increased pressure with more negative potentials and increased time to reach steady state with larger internal volume. The model is validated with experimental pressure measurements. [Display omitted] • Equivalent hydrogen pressure determined from equivalent electrochemical charging. • Equivalent hydrogen pressure was dependent on charging conditions. • Modelling reveals pressure evolution and the influence of operational parameters. • Initial fracture mechanical testing validates the equivalent charging conditions. [ABSTRACT FROM AUTHOR]

The effect of different tempering temperatures on the hydrogen embrittlement (HE) resistance of a V + Nb-microalloyed medium-carbon bolt steel was studied by slow strain rate tensile testing and hydrogen thermal analysis. The HE resistance represented by notch tensile strength σ bN of hydrogen-charged specimens increases with increasing tempering temperature T tem , and the σ bN of the in situ hydrogen-charged sample is considerably lower than that of the pre-hydrogen-charged sample. Both the diffusible hydrogen content C diff and hydrogen-trapping capability of the precipitates show a significant increase-decrease change trend with T temp. The ratio of C diff primarily trapped by nanoscale V-rich MC precipitates increases linearly with increasing T temp. The control of V-rich MC through suitable increasing T temp is vital for obtaining the best HE resistance although at the cost of decreased strength. It is thus suggested that a compromise between strength and HE resistance should be considered for the practical application of this type of steel. [Display omitted] • Effect of tempering temperature T tem on HE of V + Nb-added bolt steel was studied. • T tem has significant effect on both HE resistance and diffusible hydrogen content. • Control of V-rich MC carbide by T temp is vital for obtaining the best HE resistance. • Mechanisms for the variation of HE resistance with T tem were explored. • A compromise between strength and HE resistance should be considered. [ABSTRACT FROM AUTHOR]

Governments worldwide are actively committed to achieving their carbon emission reduction targets, and one avenue under exploration is harnessing the potential of hydrogen. Blending hydrogen with natural gas is emerging as a promising strategy to reduce carbon emissions, as it burns cleanly without emitting carbon dioxide. This blending could significantly contribute to emissions reduction in both residential and commercial settings. However, a critical challenge associated with this approach is the potential for Hydrogen Embrittlement (HE), a phenomenon wherein the mechanical properties of pipe steels degrade due to the infiltration of hydrogen atoms into the metal lattice structure. This can result in sudden and sever failures when the steel is subjected to mechanical stress. To effectively implement hydrogen-natural gas blending, it is imperative to gain a comprehensive understanding of how hydrogen affects the integrity of pipe steel. This necessitates the development of robust experimental methodologies capable of monitoring the presence and impact of hydrogen within the microstructures of steel. Key techniques employed for this assessment include microscopic observation, hydrogen permeation tests, and tensile and fatigue testing. In this study, samples from two distinct types of pipeline steels used in the natural gas distribution network underwent rigorous examination. The findings from this research indicate that charged samples exhibit a discernible decline in fatigue and tensile properties. This deterioration is attributed to embrittlement and reduced ductility stemming from the infiltration of hydrogen into the steel matrix. The extent of degradation in fatigue properties is correlated not only to the hydrogen content but also to the hydrogen permeability and diffusion rate influenced by steel's microstructural features, with higher charging current densities indicating a more significant presence of hydrogen in the natural gas pipeline blend. [ABSTRACT FROM AUTHOR]