Search

Wood modification processes based on citric acid in combination with various copolymers have gained in importance in recent years. These processes also include modification with citric acid (CA) and sorbitol, a sugar alcohol, which is currently in the industrial realisation phase in Germany (SorCA) and Norway (CIOL). The modification of wood with sorbitol and citric acid (SorCA) can significantly improve the dimensional stability and durability of the wood. It is hypothesised that the addition of a copolymer may improve the fixation of the chemicals within as well as the flexibility of the modified wood matrix. In this study, the macroscopic changes, the fixation of the chemicals and the impact bending properties of wood modified with CA and SorCA are compared. Both modifications cause a permanent increase in mass (WPG) and volume (CWB). The fixation of the chemicals was comparable for both modifications; at high chemical concentrations, the SorCA polyester fixed slightly better within the wood matrix. Both modifications led to embrittlement of the wood, measured by a decrease in the impact bending strength (IBS). This embrittlement was clearly concentration-dependent and slightly more pronounced for the modification with CA. [ABSTRACT FROM AUTHOR]

This article reports the coexistence of hardening and softening phenomena when polyurea is submitted to repeated nano‐impacts with various impact forces while controlling the strain rate. The manifestation of these phenomena is further elucidated by interrogating ultraviolet irradiated samples under ambient and nitrogen atmospheres, wherein artificial weathering accelerates hardening by reducing the nano‐impact depths as a function of exposure duration while increasing the impact load, nano‐impact repetitions and strain rate sensitivity favored softening. A 21% and 48% increase in indentation depth are recorded after 100 repetitions at a relatively higher force (10 mN) at a low strain rate and low force (2.5 mN) at a relatively higher rate for pristine and weathered polyurea, respectively. Electron microscopy evidences the induced, progressive damage at the nanoscale based on the agglomeration of hard segments, reduced free volume, and weathering‐induced surface embrittlement. [ABSTRACT FROM AUTHOR]

Deformation twins in the ferrite matrix of an age-hardened duplex stainless steel have been observed using on-axis transmission Kikuchi diffraction (TKD) in a scanning electron microscope. This provided details of the lattice misorientation and dislocation arrangement, including the dislocation-free zone at the twin tip. These observations provide evidence for the link between microcracking of the irregular twin/parent interface and relaxation of the residual strains that arise from twin growth, offering new insights into fracture mechanics in these materials. [ABSTRACT FROM AUTHOR]

Environment effects in plasticity and fracture of metals, well studied for several decades, still pose many unanswered questions. A micro-mechanics explanation of how dislocation activity is influenced by the material surface state, that can answer these questions, has been elusive. We build on a recently discovered effect in metal cutting – organic monolayer embrittlement (OME) – wherein metal surfaces are rendered brittle by long-chain organic adsorbates, to explore how material state variables influence surface plasticity and fracture. In particular, cutting experiments with Al containing Self Assembled Monolayers (SAMs), show that the OME is controlled by surface stress (f) induced by the adsorbates. This is contrary to many instances of environment-assisted fracture which are usually attributed to surface energy changes, and wherein f is largely ignored. Other contributions include (a) a cantilever technique to measure surface stress, (b) demonstration of strong effect of SAM molecule chain length on f, (c) characterization of how dislocation activity at crack-tips is affected by adsorbate-induced f, and (d) large improvements in machining processes enabled by controlled environment-assisted fracture. We make the case that surface stress, due to adsorbates, likely influences all environmentally assisted cracking (EAC) phenomena, warranting a revisit of extant models of EAC. [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]

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]

This review sets out to investigate the detrimental impacts of hydrogen gas (H2) on critical boiler components and provide appropriate state-of-the-art mitigation measures and future research directions to advance its use in industrial boiler operations. Specifically, the study focused on hydrogen embrittlement (HE) and high-temperature hydrogen attack (HTHA) and their effects on boiler components. The study provided a fundamental understanding of the evolution of these damage mechanisms in materials and their potential impact on critical boiler components in different operational contexts. Subsequently, the review highlighted general and specific mitigation measures, hydrogen-compatible materials (such as single-crystal PWA 1480E, Inconel 625, and Hastelloy X), and hydrogen barrier coatings (such as TiAlN) for mitigating potential hydrogen-induced damages in critical boiler components. This study also identified strategic material selection approaches and advanced approaches based on computational modeling (such as phase-field modeling) and data-driven machine learning models that could be leveraged to mitigate potential equipment failures due to HE and HTHA under elevated H2 conditions. Finally, future research directions were outlined to facilitate future implementation of mitigation measures, material selection studies, and advanced approaches to promote the extensive and sustainable use of H2 in industrial boiler operations. [ABSTRACT FROM AUTHOR]

This study investigates the fatigue behavior of cold-finished mild steel subjected to electrochemical hydrogen charging under controlled conditions. Samples were subjected to hydrogen charging at constant time in a fixed electrolyte pH, after which the samples underwent fatigue testing under constant loading condition with fixed frequency. The primary objective was to assess the impact of varying hydrogen permeation levels on the number of cycles to failure. The experimental results revealed a complex relationship between hydrogen concentration and fatigue life. Initially, as hydrogen permeation increased, the number of cycles to failure substantially decreased, demonstrating the detrimental effect of diffused hydrogen on the fatigue resistance of samples. This decline in fatigue life was attributed to hydrogen embrittlement (HE) and hydrogen-enhanced decohesion (HEDE) phenomena, which collectively facilitate crack initiation and propagation. However, at high hydrogen concentrations, an unexpected increase in the number of cycles to failure was observed suggesting the existence of a threshold hydrogen concentration beyond which the fatigue mechanisms may be altered, potentially due to a saturation of hydrogen-related defects and mechanisms such as hydrogen-enhanced localized plasticity (HELP). The discovery from this research has significant implications for the material's application in hydrogen-rich environments, such as those encountered in the energy and transportation industries. [ABSTRACT FROM AUTHOR]

The key objective of this study is to determine the effect of interphase boundaries, the formation of which is caused by the variation of Li2ZrO3/MgLi2ZrO4 phases in lithium-containing ceramics based on lithium metazirconate, on the resistance to near-surface layer destruction processes associated with irradiation with He2+ ions. During the observation of the deformation effects that have an adverse impact on the volumetric swelling of the near-surface layers of ceramics, the thermal expansion factor caused by high-temperature irradiation was considered, simulating conditions as close as possible to the operating conditions of these materials as blankets for tritium propagation. During the studies conducted, it was established that an elevation in the contribution of MgLi2ZrO4 in the composition of ceramics leads to a rise in resistance to deformation swelling caused by structural distortions of the crystal lattice, due to a decrease in the effect of thermal expansion, alongside the presence of interphase boundaries. The established dependencies of the change in the hardness of the near-surface layer of the studied ceramics made it possible to establish the kinetics of softening caused by the deformation distortion of the crystalline structure, as well as to determine the relationship between volumetric swelling and softening (change in hardness) and a decrease in crack resistance (change in the value of resistance to single compression). [ABSTRACT FROM AUTHOR]

Based on theoretical and experimental studies of hydrogen effect on the electron structure of iron, nickel and titanium, an electron concept is proposed for hydrogen embrittlement as well as for hydrogen-improved plasticity of engineering metallic materials. This concept implies a hydrogen-caused redistribution of valence electrons across their energy levels and an increase in the density of electron states at the Fermi level, causing a softening of the crystal lattice and, thereby, leading to a decrease in the specific energy of dislocations with consequent increase in their mobility. Innate phenomena in metallic solid solutions, namely, short-range atomic order in its two versions, short-range ordering and decomposition, are shown to be a precondition for the localization of plastic deformation. Hydrogen enhances merely this effect resulting in pseudo-brittle fracture. The role of hydrogen-induced superabundant vacancies in hydrogen-caused localization of plastic deformation and grain-boundary fracture in pure metals is discussed. Using the temperature- and strain-dependent internal friction, the enthalpies of hydrogen diffusion and hydrogen–dislocation binding are studied, and their controlling effect on the temperature- and strain-rate-dependent hydrogen embrittlement is demonstrated. Finally, a physical rationale is proposed for using hydrogen as a temporary alloying element in the technological processing of titanium alloys, and for a positive hydrogen effect on the fatigue life and plasticity of austenitic steels.

The key objective of this study is to determine the effect of interphase boundaries, the formation of which is caused by the variation of Li2ZrO3/MgLi2ZrO4 phases in lithium-containing ceramics based on lithium metazirconate, on the resistance to near-surface layer destruction processes associated with irradiation with He2+ ions. During the observation of the deformation effects that have an adverse impact on the volumetric swelling of the near-surface layers of ceramics, the thermal expansion factor caused by high-temperature irradiation was considered, simulating conditions as close as possible to the operating conditions of these materials as blankets for tritium propagation. During the studies conducted, it was established that an elevation in the contribution of MgLi2ZrO4 in the composition of ceramics leads to a rise in resistance to deformation swelling caused by structural distortions of the crystal lattice, due to a decrease in the effect of thermal expansion, alongside the presence of interphase boundaries. The established dependencies of the change in the hardness of the near-surface layer of the studied ceramics made it possible to establish the kinetics of softening caused by the deformation distortion of the crystalline structure, as well as to determine the relationship between volumetric swelling and softening (change in hardness) and a decrease in crack resistance (change in the value of resistance to single compression).

This review sets out to investigate the detrimental impacts of hydrogen gas (H2) on critical boiler components and provide appropriate state-of-the-art mitigation measures and future research directions to advance its use in industrial boiler operations. Specifically, the study focused on hydrogen embrittlement (HE) and high-temperature hydrogen attack (HTHA) and their effects on boiler components. The study provided a fundamental understanding of the evolution of these damage mechanisms in materials and their potential impact on critical boiler components in different operational contexts. Subsequently, the review highlighted general and specific mitigation measures, hydrogen-compatible materials (such as single-crystal PWA 1480E, Inconel 625, and Hastelloy X), and hydrogen barrier coatings (such as TiAlN) for mitigating potential hydrogen-induced damages in critical boiler components. This study also identified strategic material selection approaches and advanced approaches based on computational modeling (such as phase-field modeling) and data-driven machine learning models that could be leveraged to mitigate potential equipment failures due to HE and HTHA under elevated H2 conditions. Finally, future research directions were outlined to facilitate future implementation of mitigation measures, material selection studies, and advanced approaches to promote the extensive and sustainable use of H2 in industrial boiler operations.

Neutron irradiation causes embrittlement of reactor pressure vessel (RPV) steels. Post-irradiation annealing is capable of partly or fully restoring the unembrittled condition. While annealing at high temperatures (e.g., 475°C) was successfully applied to extend the lifetime of operating VVER-440 reactors, the benefit of annealing at lower temperatures (e.g., 343°C-the maximum to which the primary cooling water can be heated) is a matter of debate. In this study, neutron-irradiated VVER-440 RPV base metal and weld were exposed to isothermal annealing at 343°C up to 2,000 h. Given the limited amount of material, the degree of recovery was estimated in terms of Vickers hardness, the ductile-brittle transition temperature derived from small punch tests, and the master curve reference temperature derived from fracture mechanics tests of mini samples. For the base metal, small-angle neutron scattering was applied to underpin the findings at the nm-scale. We have found significant partial recovery in both materials after annealing for 300 h or longer. The variations of the degree of recovery are critically discussed and put into the context of wet annealing. [ABSTRACT FROM AUTHOR]

Hydrogen embrittlement in ductile metals, such as steel, is a significant concern, for instance, in the safety assessment of existing pipeline infrastructure intended for hydrogen transport. The ductile damage mechanism in steels is characterized by the nucleation, growth, and coalescence of microvoids, which is further enhanced by the presence of hydrogen. This leads to material damage and premature failure in components. Mechanisms contributing to hydrogen‐induced reduction of strength in steels include hydrogen‐enhanced decohesion (HEDE), hydrogen‐enhanced local plasticity (HELP), and hydrogen‐enhanced strain‐induced vacancies (HESIV). The HEDE mechanism leads to a principal stress‐controlled brittle failure mode. Conversely, the HELP and the HESIV mechanisms, which are dominated by plastic deformation, alter the ductile damage behavior as they lead to accelerated void growth and coalescence. Furthermore, interstitial diffusion of hydrogen leading to lattice expansion, commonly referred to as swelling, also contributes to hydrogen‐induced embrittlement. Hydrogen embrittlement is therefore a stress‐diffusion process that involves chemo‐mechanical coupling, where hydrogen atoms primarily diffuse toward areas with high hydrostatic stress. In this regard, we propose a framework using the finite element method and combining coupled chemo‐mechanics and the well‐known Gurson‐Tvergaard‐Needleman (GTN) damage model. The framework is motivated by mixed rate‐type potentials, that account for the influence of hydrogen concentration on the damage behavior. An additional dependence of the fracture strain and evolution of the void volume fraction on hydrogen is included. A comparison of the fully‐coupled model to simplified versions is conducted to individually assess the role of hydrogen concentration on damage evolution and the stress state on diffusion. [ABSTRACT FROM AUTHOR]

The antioxidant N-isopropyl-N′-phenyl-p-phenylenediamine (4010NA) was dissolved in ethanol and impregnated into silica aerogel (SAG) via vacuum-pressure cycles, yielding composite particles (A-N) with enhanced sustained-release and reinforcing capabilities. The effect of A-N on the mechanical properties and thermal-oxidative aging resistance of styrene-butadiene rubber (SBR) vulcanizates was investigated. TGA and BET assessments indicated that the loading efficiency of 4010NA in SAG reached 14.26% within ethanol's solubility limit. Incorporating A-N into SBR vulcanizates significantly elevated tensile strength by 17.5% and elongation at break by 41.9% over those with fumed silica and free 4010NA. Furthermore, A-N notably enhanced the thermal-oxidative aging resistance of SBR. After aging for 96 h at 100 °C, the tensile strength and elongation at break of SBR with A-N sustained 70.09% and 58.61% of their initial values, respectively, with the retention rate of elongation at break being 62.8% higher than that of SBR with fumed silica and free antioxidant. The study revealed that A-N composite particles significantly inhibited the crosslinking in SBR's molecular chains, reducing hardening and embrittlement during later thermal-oxidative aging stages. [ABSTRACT FROM AUTHOR]

We document the complex interaction between metamorphic reactions and deformation behaviour at high‐pressure conditions by combining (micro‐) structural, petrographical and geochemical data from an eclogite body. The well‐equilibrated eclogite fabric is crosscut by mineral veins. Precipitated veins host the eclogitic high‐pressure assemblage with variation in modal composition, indicating that fracturing occurred at eclogite facies conditions. Deflection of the eclogite fabric adjacent to the veins implies ductile reactivation of the veins as flanking structures and strain localization under continuous aseismic shearing. In consequence, the reactivated veins are characterized by undulatory extinction and subgrain formation in quartz indicating crystal plasticity. We show that prograde post‐eclogitization metamorphism resulted in progressive dehydration and melting of the eclogite. Subsequent increase in pore‐pressure‐induced rock failure. The mesoscopic to microscopic characteristics of eclogite‐facies veins indicate a cyclic behaviour of fracturing, vein formation and crystal‐plasticity which demonstrates the strong interaction of chemical and mechanical processes operating at depth. [ABSTRACT FROM AUTHOR]

The study of fracture mechanics is usually within the paradigm of a failure mode that needs to be avoided. However, both in nature and in modern technology, there exist several situations where an ability to fracture is essential. In this work, we consider the problem of machining highly ductile and strain-hardening metals, such as annealed Cu, Al and Ta. These metals are known by the moniker "gummy metals" due to the large forces and poor surface finish associated with machining them. We investigate a chemo-mechanical technique involving adsorption of organic monolayers on the metal surfaces that causes the metals to become relatively brittle. This transition from ductile to brittle results in > 50% drop in the cutting force and an order of magnitude improvement in the surface finish. Molecular dynamics simulations of the phenomenon show the organic monolayers impose a surface stress on the metal surface which results in arresting of the dislocations close to the surface. The results suggest that a deeper understanding of the underlying mechanism has implications in environment-assisted cracking, stress-corrosion cracking and hydrogen embrittlement. [ABSTRACT FROM AUTHOR]

Irradiation-induced defects such as dislocation loops, cavities or solute clusters and chemical composition segregation of reactor pressure vessel (RPV) steel are the root causes of irradiation embrittlement. Combining two nucleation mechanisms, namely, the uniform nucleation and non-uniform nucleation of solute clusters (such as Cu-rich phase), a cluster kinetic simulation was established based on the reaction rate theory, and the co-evolution of matrix damage and Cu-rich phase in low-copper RPV steel was simulated under irradiation. And the average size and number density of defective clusters and solute clusters were established with irradiation dose. Compared with the average size and number density of dislocation loops observed by transmission electron microscopy (TEM) of proton irradiated RPV steel at 290°C, the verification results show that the cluster dynamics model considering both the nucleation mechanism of interstitial dislocation loops and vacancy clusters can well simulate the irradiation damage behavior of materials. [ABSTRACT FROM AUTHOR]

X80 steel plays a pivotal role in the development of oil and gas pipelines; however, its welded joints, particularly the heat-affected zone (HAZ), are susceptible to stress corrosion cracking (SCC) due to their complex microstructures. This study investigates the SCC initiation mechanisms of X80 steel welded joints under practical pipeline conditions with varying levels of cathodic protection. The SCC behaviors were analyzed through electrochemical measurements, hydrogen permeation tests, and interrupted slow strain rate tensile tests (SSRTs) conducted in a near-neutral pH environment under different potential conditions (OCP, −1.1 VSCE, −1.2 VSCE). These behaviors were influenced by microstructure type, grain size, martensite/austenite (M/A) constituents, and dislocation density. The sub-zones of the weld exhibited differing SCC resistance, with the fine-grain (FG) HAZ, base metal (zone), welded metal (WM) zone, and coarse-grain (CG) HAZ in descending order. In particular, the presence of coarse grains, low dislocation density, and extensive M/A islands collectively increased corrosion susceptibility and SCC sensitivity in the CGHAZ compared to other sub-zones. The SCC initiation mechanisms of the sub-zones within the X80-steel welded joint were primarily anodic dissolution (AD) under open-circuit potential (OCP) condition, shifting to either hydrogen-enhanced local plasticity (HELP) or hydrogen embrittlement (HE) mechanisms at −1.1 VSCE or −1.2 VSCE, respectively. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this paper is to assess the hydrogen embrittlement sensitivity of carbon gradient heterostructure materials and to verify the reliability of the scratch method. Design/methodology/approach: The surface-modified layer of 18CrNiMo7-6 alloy steel was delaminated to study its hydrogen embrittlement characteristics via hydrogen permeation, electrochemical hydrogen charging and scratch experiments. Findings: The results showed that the diffusion coefficients of hydrogen in the surface and matrix layers are 3.28 × 10−7 and 16.67 × 10−7 cm2/s, respectively. The diffusible-hydrogen concentration of the material increases with increasing hydrogen-charging current density. For a given hydrogen-charging current density, the diffusible-hydrogen concentration gradually decreases with increasing depth in the surface-modified layer. Fracture toughness decreases with increasing diffusible-hydrogen concentration, so the susceptibility to hydrogen embrittlement decreases with increasing depth in the surface-modified layer. Originality/value: The reliability of the scratch method in evaluating the fracture toughness of the surface-modified layer material is verified. An empirical formula is given for fracture toughness as a function of diffused-hydrogen concentration. [ABSTRACT FROM AUTHOR]

SiC-based fibers are key constituents for the reinforcement of SiC/SiC thermo-structural composites. Their tensile strength is however known to decrease if oxidized because of stresses associated to the oxide scale growth, which in turns is affected by the fiber type (chemical composition, microstructure). This phenomenon is here reported for several types of fibers (five in total, Nicalon® or Tyranno®) between 450 and 950 °C in ambient air. The highest strength loss rate was noticed on Tyranno® Grade S, also known to be more sensitive to oxidation. The initial strength was nevertheless recovered when the oxide scale was removed. This report uses a simplistic empirical model to fit the embrittlement phenomenon, relating the tensile strength to x −1/2. The strength distribution and the projection to larger scale thicknesses are discussed. Assuming the same conditions (environment, scale crystallization rate), the oxidation kinetic could be used to estimate the embrittlement phenomenon. [Display omitted] • On top of oxide scale growth, the oxidation of SiC filaments reduces their tensile strength. • Strength proportional to x−1/2, where x is the oxide scale thickness. • Analysis of the fracture pattern did not revealed stresses at the scale-fiber interface. • The strength dispersion tends to become broader on oxidized fibers. • Introduction of flaw size-dependent geometrical factor to solve projection inconsistency. [ABSTRACT FROM AUTHOR]

Based on theoretical and experimental studies of hydrogen effect on the electron structure of iron, nickel and titanium, an electron concept is proposed for hydrogen embrittlement as well as for hydrogen-improved plasticity of engineering metallic materials. This concept implies a hydrogen-caused redistribution of valence electrons across their energy levels and an increase in the density of electron states at the Fermi level, causing a softening of the crystal lattice and, thereby, leading to a decrease in the specific energy of dislocations with consequent increase in their mobility. Innate phenomena in metallic solid solutions, namely, short-range atomic order in its two versions, shortrange ordering and decomposition, are shown to be a precondition for the localization of plastic deformation. Hydrogen enhances merely this effect resulting in pseudobrittle fracture. The role of hydrogen-induced superabundant vacancies in hydrogencaused localization of plastic deformation and grain-boundary fracture in pure metals is discussed. Using the temperature- and strain-dependent internal friction, the enthalpies of hydrogen diffusion and hydrogen-dislocation binding are studied, and their controlling effect on the temperature- and strain-rate-dependent hydrogen embrittlement is demonstrated. Finally, a physical rationale is proposed for using hydrogen as a temporary alloying element in the technological processing of titanium alloys, and for a positive hydrogen effect on the fatigue life and plasticity of austenitic steels. [ABSTRACT FROM AUTHOR]

The monitoring of invasion/permeation hydrogen on entry/exit surfaces of cathodically charged SUS316 columnar crystals was conducted with a scanning Kelvin probe force microscope (SKPFM) under atmospheric pressure. Columnar crystal specimens covered with oxide films on their surfaces under room conditions were prepared for cathodic charging tests and subsequent SKPFM measurements. The invaded hydrogen on the entry surface was detected at the δ-ferrite phases for 7 d after charging, and the segregation of invaded hydrogen at the boundaries between the δ-ferrite and austenite matrix was prolonged for >10 d after charging. The permeated hydrogen on the exit surface was detected at the δferrite phases for 3 d after charging, but was not substantial at some of the δ-ferrite phases regardless of the charging. Segregation of permeated hydrogen at the boundaries between the δ-ferrite and some of the intermetallic precipitates was prolonged for 7 d after charging. The behaviors of invaded/permeated hydrogen based on heterogeneous microstructures are discussed to improve understanding of the hydrogen embrittlement mechanism in weld metals. [ABSTRACT FROM AUTHOR]

Cu–Ag in-situ composites, renowned for their amalgamation of high strength and superior electrical conductivity, find extensive applications as conductors in high field magnets. This investigation delves into the microstructural intricacies and mechanical characteristics of Cu–18 pct Ag (wt pct) in-situ composites following the incorporation of alloying elements (Nb, Cr, and Zr) via a comprehensive process involving casting, heat treatment, and cold deformation. The outcomes reveal that the introduction of Nb or Cr elements intricately refines the Cu dendrites and eutectic phase. Simultaneously, the Cu matrix experiences fortification through the inclusion of Nb or Cr particles, imparting notable improvements in mechanical properties. Remarkably, Cr addition exhibits the most pronounced impact on elevating both ultimate tensile strength and hardness. Under a deformation rate (η) of 5.28, the ultimate tensile strength surges by 21.00 pct compared to that of the Cu–18 pct Ag alloy, albeit with a marginal 7.36 pct decrease in conductivity for the Cu–18 pct Ag–1 pct Cr alloy. The introduction of Nb augments ultimate tensile strength by 12.23 pct, with no apparent impact on conductivity under identical deformation conditions. In contrast, Zr addition significantly disrupts the precipitation of the Ag phase, fostering the formation of the intermetallic compound Cu4AgZr. This disruption induces a reduction in both mechanical properties and conductivity, leading to embrittlement at high drawing strains. [ABSTRACT FROM AUTHOR]

Due to its characteristic of low stress brittle fracture, hydrogen embrittlement (HE) is a great challenge for the alloys exposed to hydrogen-containing environments, threatening the safety and integrity of structural components. The physical and chemical status of the interfaces, among which grain boundary (GB), twin boundary (TB), and matrix/nano-precipitate interfaces (coherent, semi-coherent, and incoherent) are the representative ones, play a crucial role in determining the HE susceptibility of materials. Hence, this study mainly reviews recent progress in the interaction between hydrogen and these interfaces, i.e., 1) hydrogen-GB interaction (dominant HE mechanisms, crystallographic features of hydrogen-assisted intergranular cracking, and the strategies for resisting HE through GB segregation and GB engineering); 2) hydrogen-TB interaction (the effect of deformation/pre-existing twins on HE susceptibility, four types of TB-related cracking mechanisms, and the improvement of HE-tolerance by the control of pre-twins, gradient-twins, and twin orientations); and 3) hydrogen-precipitate interaction (hydrogen capacity, hydrogen trapping sites, hydrogen activation energy, and the effect of nano-precipitates on HE of alloys). The correlation between HE susceptibility, active HE mechanisms and their synergy (HELP + HEDE model), and three types of interfaces have been comprehensively summarized and discussed. Also, the strategies for the improvement of HE resistance are proposed in terms of the control of these microstructural interfaces in metallic alloys. [Display omitted] • Effect of the interfaces on hydrogen embrittlement (HE) of alloys is reviewed. • Hydrogen-assisted interface cracking mechanisms of alloys is summarized. • Strategies for resisting HE are proposed through the control of the interfaces. • Semi-coherent precipitates are suggested to balance strength and HE-resistance. [ABSTRACT FROM AUTHOR]

Utilizing a preliminary interatomic potential, this work represents an initial exploration into the thermomechanical behavior of NbCr solid solutions. Specifically, it examines the effect of different amounts of Cr solute, for which information in the literature is limited. The employed interatomic potential was developed according to the embedded atom model (EAM), and was trained on data derived from density functional theory calculations. While the potential demonstrated reasonable accuracy and predictive power when tested, various results highlight deficiencies and encourage further development and training. Mechanical strength, heat capacities, thermal expansion coefficients, and thermal conductivities were found to decrease with Cr content. Elastic coefficients, too, were observed to be strongly dependent on Cr composition. The Pugh embrittlement criterion was not satisfied for any of the compositions and temperatures explored. Gibbs free energy calculations performed on C14, C15, and C36 NbCr 2 allotropes predicted the C36 structure to be the most thermodynamically favorable across all investigated temperatures and it was found that C36 becomes increasingly more stable relative to the other two phases with increased pressure. The inability of this work to accurately capture the stability of the different Laves phases is most likely due to the shortcomings in the developed potential. [ABSTRACT FROM AUTHOR]

This paper discusses the effect of reversed austenite (RA) on hydrogen embrittlement (HE) behavior of a high-strength multi-alloyed steel. Three heat treated samples were fabricated by quenching-lamellarization-tempering (QLT) treatment with varying the features of RA. The experimental results revealed that the existence of reversed austenite could reduce the effective diffusion coefficient and HE susceptibility. QLT specimens exhibited the optimization of the strength and HE resistance with 6.7% filmy and stable reversed austenite, which could hinder the hydrogen diffusion, reduce local hydrogen concentration, delay the crack initiation and further arrest the crack propagation. Moreover, a 23% reduction in hydrogen embrittlement susceptibility of QLT specimens was achieved by comparing with quenching-tempering (QT)specimens. However, the interface of RA and matrix was a preferred site for crack initiation. • The role of "lamellarization" on the hydrogen embrittlement was investigated. • Both fraction and stability of revered austenite affected the HE behavior. • The interface of revered austenite and matrix is a preferred site for crack initiation. • The role of RA on the crack propagation was discussed. [ABSTRACT FROM AUTHOR]

Martensitic steels, engineered to meet automotive weight reduction and crashworthiness requirements, are highly susceptible to hydrogen embrittlement (HE). Despite extensive research to improve HE resistance, these steels remain vulnerable to HE after undergoing resistance spot welding (RSW). HE in spot-welded steels has been largely unexplored, and its underlying mechanism remains unclear. This study investigates the HE mechanism in RSWed steel sheets by examining microstructural alterations and hydrogen trapping sites before and after RSW. Additionally, the study analyzes variations in tensile-shear test (TST) properties relative to increasing hydrogen content. In spot-welded steels, the tensile-shear strength and fracture displacement decline as diffusible hydrogen levels increase. Specifically, fracture displacement sharply declines within the first 3 h of hydrogen charging, but this loss rate significantly decreases thereafter. This slope shift is attributed to a transition in the crack propagation path. Initially, cracks propagate along the fusion zone line, featuring transgranular failure. However, beyond a critical hydrogen content, crack propagation shifts to the prior austenite grain boundary (PAGB) in the upper critical heat-affected zone (UCHAZ), exhibiting intergranular failure. Consequently, when hydrogen content surpasses this critical threshold, the PAGB in the UCHAZ is weakened due to hydrogen-enhanced decohesion (HEDE) and hydrogen-enhanced localized plasticity (HELP). Cracks then propagate along the PAGB in the direction of maximum stress during the tensile-shear test (TST), leading to a change in the crack propagation path. [Display omitted] • The resistance to hydrogen embrittlement for spot-welded advanced high strength steel is evaluated by tensile-shear test. • The difference in the behaviors of hydrogen embrittlement between steel matrix and welded part is compared. • The phenomenon of crack propagation path transition is observed over certain hydrogen content. • The mechanism of crack propagation path transition is discussed. [ABSTRACT FROM AUTHOR]

Hydrogen embrittlement (HE) remains a pressing issue in materials science and engineering, given its significant impact on the structural integrity of metals and alloys. This exhaustive review aims to thoroughly examine HE, covering a range of aspects that collectively enhance our understanding of this intricate phenomenon. It proceeds to investigate the varied effects of hydrogen on metals, illustrating its ability to profoundly alter mechanical properties, thereby increasing vulnerability to fractures and failures. A crucial section of the review delves into how different metals and their alloys exhibit unique responses to hydrogen exposure, shedding light on their distinct behaviors. This knowledge is essential for customizing materials to specific applications and ensuring structural dependability. Additionally, the paper explores a diverse array of models and classifications of HE, offering a structured framework for comprehending its complexities. These models play a crucial role in forecasting, preventing, and mitigating HE across various domains, ranging from industrial settings to critical infrastructure. [ABSTRACT FROM AUTHOR]

This study compares the hydrogen embrittlement susceptibility of a Fe-30Mn-8Al-1.2C austenitic low-density steel aged at 600 °C for 0 (RX), 1 min (A1) and 60 min (A60), each exhibiting varying sizes and distributions of nano-sized κ-carbides. Slow strain rate tests were conducted to assess hydrogen embrittlement susceptibility, while thermal desorption analysis was applied to investigate hydrogen trapping behaviors. Fracture surface analysis was employed to discuss the associated failure mechanisms. The results suggest that nano-sized κ-carbides with sizes ranging from 2–4 nm play a crucial role in mitigating hydrogen embrittlement, contrasting with the exacerbating effect of coarse grain boundary κ-carbides. This highlights the significance of controlling the sizes and morphology of precipitates in designing hydrogen-resistant materials. [ABSTRACT FROM AUTHOR]

This study aims to investigate the influence of zirconium addition on the corrosion behavior of the FeAl40Ti3B intermetallic alloy, which was synthesized in an arc furnace under argon atmosphere at 950 °C for 2 h and subsequently annealed for 168 h at 500 °C in quartz capsules. Electrochemical techniques, specifically potentiodynamic polarization curves and electrochemical impedance spectroscopy measurements (EIS), were employed to assess the corrosion characteristics. The study also delves into the morphological and phase composition changes through scanning electron microscopy (SEM) and X-ray diffraction (XRD) analyses. The addition of zirconium to the FeAlTiB alloy led to the formation of zirconium carbide (ZrC) and other phases, including the Laves phase (Fe,Al)2Zr. The electrochemical behavior in a 0.5 M H2SO4 solution revealed significant improvements in the corrosion potential (Ecorr), current density (icorr), and corrosion rate after the addition of Zr to FeAl40Ti3B. While the corrosion rate for the unalloyed alloy was primarily diffusion-controlled, the alloy with Zr exhibited charge transfer control. Observations via SEM confirmed the occurrence of pitting corrosion in the FeAl40Ti3B alloy, but the addition of zirconium substantially enhanced its corrosion resistance. These findings shed light on the positive impact of zirconium addition on the corrosion resistance of the FeAl40Ti3B alloy, offering valuable insights for potential industrial applications. [ABSTRACT FROM AUTHOR]

In engineering applications, the phenomenon of cracking is often accompanied by a coupled multiphysics effect. Peridynamics (PD) is an effective approach for solving cracking problems, but currently, no general PD model accounts for the coupling of multiple physical fields. In this work, we develop a PD model of coupled deformation, heat conduction, species diffusion, and chemical reactions. First, we establish the equations for mass, linear momentum, and energy. Then we establish fully coupled constitutive laws that interpret the interactions between the various fields and formulate evolution equations that govern the flux of species and heat. These laws and equations are developed based on the inequality of energy dissipation and the principles of chemical kinetics. Species diffusion and chemical reactions are treated as separate processes to study their effects on the Helmholtz free energy density of solids and the subsequent formation and propagation of cracks. In addition, certain coupling coefficients are calibrated by equating the corresponding physical quantities in the PD model with those in continuum mechanics. Four specific cases are simulated to validate the model, including redistribution of vacancies in ceramics, hydrogen traps, and embrittlement in metals. • A thermo-chemo-mechanically coupled peridynamics model is developed. • The expansion factor is defined to reveal its effect. • The chemical kinetics in a nonlocal form is derived. • The different effects of species diffusion and chemical reactions on cracks are investigated. [ABSTRACT FROM AUTHOR]

Certain metals experience a substantial deterioration in mechanical properties when exposed to a hydrogen environment, an effect termed hydrogen embrittlement. To understand, predict, and counteract this hydrogen‐assisted material degradation, sufficiently accurate material models are needed. According to the current hypothesis, hydrogen diffusion is driven by gradients of concentration and hydrostatic stress. To capture this, a phase‐field model is formulated as a multi‐field problem coupling deformation, crack propagation, and diffusion to analyze hydrogen‐promoted fracture. Here, the displacements, a fracture‐related phase‐field, the hydrogen lattice occupancy, and the chemical potential are considered as primary field variables. Approaches proposed in the literature often use an extrapolation of the hydrostatic stress calculated at the material point level onto the nodes and later use the B‐matrix to compute the gradient of hydrostatic stress. In order to circumvent this potentially inaccurate extrapolation, the model is recast into a mixed rate‐type variational setting, where the chemical potential—whose gradient governs the hydrogen flux—is obtained from the numerical solution of a saddle point problem. A representative boundary value problem is presented to demonstrate the applicability of the developed numerical framework. [ABSTRACT FROM AUTHOR]

Embrittlement of steels and alloys in contact with hydrogen gas under pressure is a key problem in metallurgy with important implications for a future energy economy based on hydrogen. Here we report stress–strain measurements recorded under 200 MPa (∼30,000 PSI) hydrogen gas pressure to evaluate the resistance of MP35N to embrittlement. We find that MP35N with a tensile strength of more than 1800 MPa does not suffer any strength loss, retains a significant amount of ductility and hence appears to be highly resistant to hydrogen embrittlement even under elevated stress when exposed over a time-scale of hours. This exceptional resistance to H-embrittlement seems to be unique among all high-performance steels and alloys of comparable strength and bears on the use of this material for high pressure H2 research devices and storage applications. [ABSTRACT FROM AUTHOR]

In this work, a finite element cohesive fatigue model for concrete is proposed. A procedure to simulate monotonic rupture is included. Damage is calculated as a function of accumulated crack openings and the current traction on the cohesive zone. Only mode I fracture is considered. Concretes with different strengths and specimens with different sizes are considered. Size dependency was introduced in the model through the cohesive strength and the corresponding cohesive length. Other monotonic and cyclic properties are considered constant or dependent on the material strength. An excellent fit with experiments is obtained. Methodology is able to capture an embrittlement of the fatigue process with increase in size. In this case, crack (or process zone) becomes unstable for shorter sizes and a more abrupt change to unstable growth is observed. Predictive capabilities of the model are observed considering S‐N curves. A good match was observed in the low‐cycle fatigue range. Highlights: Size dependency is introduced in the model by the cohesive strengthExponent parameter used to estimate damage depends primarily on concrete strengthRelative endurance limit magnitude is related to the process zone sizeModel is able to capture a size embrittlement in the fatigue propagation [ABSTRACT FROM AUTHOR]

This paper presents a hazard identification analysis for Liquid Hydrogen (LH2) in transfer operations, focusing on identifying sources of LH2 release and the associated initiating events. The analysis involves the loading of an LH2 storage tank from a trailer. The Master Logic Diagram (MLD) methodology, developed for chemical installations, is employed to identify initiating events. Two major categories of events leading to Loss of Containment are further investigated: events that lead in the direct structural failure of the containment, such as overpressure, embrittlement, etc., and events that lead to containment bypass. The development of the MLD is also based on a systematic analysis of previous accidents. Following the identification of initiating events, the paper outlines the possible accident sequences and damage states resulting to LH2 release. [ABSTRACT FROM AUTHOR]

The growing importance of hydrogen as an energy carrier in a future decarbonised energy system has led to a surge in its production plans. However, the development of infrastructure for hydrogen delivery, particularly in the hard-to-abate sectors, remains a significant challenge. While constructing new pipelines entails substantial investment, repurposing existing pipelines offers a cost-effective approach to jump-starting hydrogen networks. Many European countries and, more recently, other regions are exploring the possibility of utilising their current pipeline infrastructure for hydrogen transport. Despite the recent efforts to enhance the understanding of pipeline compatibility and integrity for hydrogen transportation, including issues such as embrittlement, blend ratios, safety concerns, compressor optimisation, and corrosion in distribution networks, there has been limited or no focus on pipeline expansion options to address the low-energy density of hydrogen blends and associated costs. This study, therefore, aims to explore expansion options for existing natural gas high-pressure pipelines through additional compression or looping. It seeks to analyse the corresponding cost implications to achieve an affordable and sustainable hydrogen economy by investigating the utilisation of existing natural gas pipeline infrastructure for hydrogen transportation as a cost-saving measure. It explores two expansion strategies, namely pipeline looping (also known as pipeline reinforcement) and compression, for repurposing a segment of a 342 km × 36 inch existing pipeline, from the Escravos–Lagos gas pipeline system (ELPS) in Nigeria, for hydrogen transport. Employing the Promax® process simulator tool, the study assesses compliance with the API RP 14E and ASME B31.12 standards for hydrogen and hydrogen–methane blends. Both expansion strategies demonstrate acceptable velocity and pressure drop characteristics for hydrogen blends of up to 40%. Additionally, the increase in hydrogen content leads to heightened compression power requirements until approximately 80% hydrogen in the blends for compression and a corresponding extension in looping length until around 80% hydrogen in the blend for looping. Moreover, the compression option is more economically viable for all investigated proportions of hydrogen blends for the PS1–PS5 segment of the Escravos–Lagos gas pipeline case study. The percentage price differentials between the two expansion strategies reach as high as 495% for a 20% hydrogen proportion in the blend. This study offers valuable insights into the technical and economic implications of repurposing existing natural gas infrastructure for hydrogen transportation. [ABSTRACT FROM AUTHOR]

The evolution of ideas concerning the nature of hydrogen embrittlement of engineering metallic materials is described based on a number of the proposed hypotheses and corresponding experiments. The main attention is paid to two of them, namely hydrogen-enhanced decohesion (HEDE) and hydrogen-enhanced localized plasticity (HELP). Recent attempts to interconnect the both models as HELP + HEDE and HELP-mediated HEDE ones are also estimated. A conclusion is made that HELP model is preferential for understanding the entire array of experimental data with a caveat that it is necessary to consider the chemical nature of hydrogen atoms and view them not only as point defects. Based on the studies of hydrogen effect on the atomic interactions in iron, nickel, titanium, and its alloys, it is shown that the electron approach to HELP phenomenon adequately describes two competitive features of hydrogen behavior in metals: increased brittleness and enhanced plasticity. Due to the increase in the concentration of free electrons, hydrogen decreases the elasticity moduli, which causes the crystal lattice to soften. For this reason, the formation of hydrogen atmospheres around the dislocations decreases the start stress of dislocation sources, as well as line tension of emitted dislocations, enhancing thereby their mobility, and weakens repulsion between dislocations in their pile-ups. The range of temperatures and strain rates in which hydrogen embrittlement occurs is controlled by the enthalpies of hydrogen atoms' diffusion and their binding to dislocations. The resulting consequences for mechanical properties depend on the short-range atomic order, SRO, which inherently occurs in the metallic solid solutions and localizes plastic deformation both in the cases of short-range atomic ordering and of short-range atomic decomposition. Hydrogen enhances slip localization because of its different solubility in the submicrovolumes of short-range decomposed solid solutions. If SRO is absent or not remarkably formed, the hydrogen-increased concentration of free electrons results in enhanced plasticity. Available positive hydrogen effects on the plasticity of titanium β-alloys and austenitic steels are presented and interpreted. [ABSTRACT FROM AUTHOR]

The transition to a fossil-free energy matrix may require large quantities of hydrogen gas, which could be stored efficiently in underground lined rock caverns (LRCs). Since the consequences of failure can be catastrophic, the LRC design needs to have a small failure probability. However, the current deterministic design practice for LRCs limits the possibility to stringently address geotechnical uncertainties. In this paper, a reliability-based design tool is presented for LRCs. The adaptive directional importance sampling (ADIS) method, which requires a relatively small number of samples, is used with a 3D finite element (FE) model to evaluate small probabilities of failure. An illustrative example based on the LRC in Skallen, southwestern Sweden, demonstrates the implementation and applicability of the developed design tool. The considered uncertainties are related to the geological conditions and the steel lining. The results show that the reliability of this LRC design meets the expected safety requirements. Considering different geological conditions with correlations, at least "good" quality rock mass is needed for the LRC design. An additional sensitivity analysis is performed to study the potential influence of corrosion and hydrogen embrittlement, showing that the LRC design could meet safety requirements for a lower category of the weld quality. [ABSTRACT FROM AUTHOR]

With escalating global regulatory pressure for countries to adhere to emission laws, repurposing existing natural gas pipelines for hydrogen-based commodities stands to be an economical solution. However, the effects of hydrogen embrittlement must be thoroughly considered for this application to avoid the unexpected catastrophic failure of these pipelines. The literature proposes several physicochemical embrittlement models. This paper reports one aspect of hydrogen embrittlement that remains to be quantified: the recovery of ductility (embrittlement) of mild steel specimens subjected to artificially accelerated hydrogen absorption via electrochemical charging as a function of time. The effects of charging duration and particularly the delay period between charging and mechanical tensile testing were investigated. Unsurprisingly, longer charging time shows a greater loss of elongation; however, a more extensive recovery of ductility correlated with longer charging time in the first few days after charging. The data also show that while the uncharged mild steel met all minimum required values for strength and elongation for the specified grade, there was a substantial variability in the elongation to failure. The same trends in variability of elongation translated to the hydrogen-charged specimens. Due to this extensive variability, failure to meet the elongation specification of the grade is reported based on the worst-case scenario obtained for a given set of samples for each exposure condition. These results have practical implications for the monitoring and testing of infrastructure exposed to hydrogen, particularly as this relates to industry planned operational shutdown schedules. [ABSTRACT FROM AUTHOR]

With escalating global regulatory pressure for countries to adhere to emission laws, repurposing existing natural gas pipelines for hydrogen-based commodities stands to be an economical solution. However, the effects of hydrogen embrittlement must be thoroughly considered for this application to avoid the unexpected catastrophic failure of these pipelines. The literature proposes several physicochemical embrittlement models. This paper reports one aspect of hydrogen embrittlement that remains to be quantified: the recovery of ductility (embrittlement) of mild steel specimens subjected to artificially accelerated hydrogen absorption via electrochemical charging as a function of time. The effects of charging duration and particularly the delay period between charging and mechanical tensile testing were investigated. Unsurprisingly, longer charging time shows a greater loss of elongation; however, a more extensive recovery of ductility correlated with longer charging time in the first few days after charging. The data also show that while the uncharged mild steel met all minimum required values for strength and elongation for the specified grade, there was a substantial variability in the elongation to failure. The same trends in variability of elongation translated to the hydrogen-charged specimens. Due to this extensive variability, failure to meet the elongation specification of the grade is reported based on the worst-case scenario obtained for a given set of samples for each exposure condition. These results have practical implications for the monitoring and testing of infrastructure exposed to hydrogen, particularly as this relates to industry planned operational shutdown schedules.

This study uses plane wave density functional theory (DFT) to investigate the effect of certain metal carbides (Niobium carbide, Vanadium carbide, Titanium carbide, and Manganese sulfide) on hydrogen embrittlement in pipeline steels. Our results predict that the interaction of hydrogen molecules with these metal carbides occurs in the long range with binding energy varying in the energy window [0.043 eV to 0.70 eV].In addition, our study shows the desorption of H2 molecules from these metal carbides in the chemisorptions. Since atomic state hydrogen interacts with NbC, VC, TiC, and MnS to cause embrittlement, we classified the strength of the hydrogen trapping as TiC + H > VC + H > NbC + H> MnS + H. In addition, our study reveals that the carbon site is a more favorable hydrogen-trapping site than the metal one.

Intermediate temperature embrittlement (ITE) is very common in Ni and Ni–Co based superalloys, which seriously restricts the application of these alloys. In this work, we developed a new Ni–Co based superalloy by increasing the content of Cr to eliminate ITE. The superalloy has a yield strength of ∼950 MPa in the intermediate temperature range (600–780 °C), while also maintain a tensile elongation of ∼15 %. Microstructural investigations showed that in the temperature range of 600–780 °C, the microstructure of the alloy consists of nano-sized L12 phase (γ′) distributing inside the γ matrix, and the deformation is dominated by anti-phase boundary (APB) shearing γ′ precipitates, which makes the yield strength of the alloy decrease only slightly at 600–780 °C (compared to that tested at room temperature). More importantly, the element Cr is enriched along the grain boundaries (GBs) to form a protective layer without the formation of brittle topologically close-packed (TCP) phases due to the inverse two-stage aging design. In addition, the formation of a discontinuous precipitation (DP) zone at the GBs can act as a stress buffer and introduce GB serrations to withstand intergranular cracking.

The influence of hydrogen charging potentials on the hydrogen embrittlement susceptibility of R6 ultra-high strength mooring chain steel was investigated via constant potential hydrogen charging slow strain rate tensile tests combined with thermal desorption analysis. The results reveal that hydrogen charging leads to a 38.94% decrease in elongation, while the impact on tensile strength is relatively minor. Furthermore, the specimens experienced intergranular cracking at the critical potential of −1150 mV, with the size of the brittle region increasing as the negative charging potential becomes more negative. And, hydrogen atoms can cause local embrittlement of materials and increase KAM value. [ABSTRACT FROM AUTHOR]