Embrittlement Behavior Research Articles

Experimental Study on Hydrogen Embrittlement Behavior of X80 and X70 Pipeline Steels Evaluated by Hydrogen Permeation and Slow Strain Rate Tensile Tests

Experimental Study on Hydrogen Embrittlement Behavior of X80 and X70 Pipeline Steels Evaluated by Hydrogen Permeation and Slow Strain Rate Tensile Tests

Effect of Steel Subsurface Structure on the Liquid Metal Embrittlement Behavior of Third-Generation Advanced High-Strength Steels

Effect of Steel Subsurface Structure on the Liquid Metal Embrittlement Behavior of Third-Generation Advanced High-Strength Steels

Hydrogen-induced cracking behaviors of Ni–Cr–Mo-based superalloy fabricated by wire arc additive manufacturing under different solution temperature

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.

Corrosion and Te embrittlement behaviors of Ni-Mo-Cr-Nb alloy in Te-containing molten salts

The corrosion and Te embrittlement behaviors of Ni-Mo-Cr-Nb based alloy in the Te-containing molten salts have been investigated as compared with the standard GH3535 alloy. Nb is more resistant to molten salt dissolution than Cr due to the less negative Gibbs formation energy of fluoride and the more sluggish lattice diffusion. Furthermore, it was verified the Ni-Mo-Cr-Nb alloy possesses the obvious better Te embrittlement resistance than GH3535 alloy. Our results confirmed that Ni-Mo-Cr-Nb alloy is one of the most promising candidate materials in molten salt reactors.

Hydrogen Embrittlement Behavior of API X70 Linepipe Steel under Ex Situ and In Situ Hydrogen Charging.

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.

Hydrogen and vacancy concentrations in [formula omitted]-iron under high hydrogen gas pressure and external stress: A first-principles neural network simulation study

The metal-hydrogen-vacancy interaction in α-iron is crucial for understanding hydrogen embrittlement behavior and developing reliable materials for green gaseous hydrogen applications; however, it remains underexplored, particularly in contexts involving external stress and high hydrogen gas pressure. In this study, we performed quantitative analyses of metal-vacancy–hydrogen interactions in α-iron, measured by hydrogen solubility and the thermodynamics of vacancy–hydrogen complexes, under such challenging conditions using a reliable first-principles neural network potential. High hydrogen gas pressures reaching up to 2 GPa were investigated. As the atomic concentration surpasses approximately 0.01, hydrogen solubility is dominated by hydrogen-induced lattice distortion (primarily volumetric expansion) and the interactions between hydrogen atoms within the metal matrix, resulting in significant deviations from Sieverts’ law. Our results reveal a significant effect of shear stress on hydrogen solubility, deviating from previously used equations. Moreover, the influence of external stress on the thermodynamics of the vacancy–hydrogen complex, particularly vacancy formation free energy, is uniquely characterized by hydrogen solubility, regardless of the external stress magnitude. It thereby offers a rapid method to estimate the vacancy properties under external stress based on readily accessible external-stress-free data.

The regulation of dislocation and precipitated phase improving hydrogen embrittlement resistance of pipeline steel in high pressure hydrogen environment

In this study, the hydrogen embrittlement behavior of quenched pipeline steel tempered at 550 °C to 650 °C in a high-pressure hydrogen environment was analyzed. Hydrogen permeation tests and microstructural analyses indicated that the dislocation density of the steel decreases with increasing tempering temperature, while precipitates gradually nucleate and grow. These hydrogen traps interact with hydrogen atoms, resulting in significantly higher diffusible hydrogen content in steel tempered at 550 °C compared to that tempered at 600 °C and 650 °C. Fatigue crack growth (FCG) test results show that steel tempered at 600 °C and 650 °C exhibits significantly better hydrogen embrittlement resistance than steel tempered at 550 °C. This is primarily due to the combined effect of the high hydrogen concentration, high dislocation density and low nano carbide content in the steel tempered at 550 °C, which inhibits dislocation slip and emission, leading to high crack tip stress and rapid crack propagation. In contrast, the low dislocation density and and dispersed nano carbides in steel tempered at 600 °C and 650 °C facilitate some dislocation slip and emission, result in crack tip stress relaxation and reduced crack propagation rate. Properly controlling the initial dislocation density and increasing the density of irreversible hydrogen traps can enhance the strength of materials while improving their resistance to hydrogen embrittlement.

Effect of I-phase formation on hydrogen embrittlement behaviour of as-cast Mg-8 wt%Li based alloys

By performing microstructural characterization, tensile testing and failure analysis, the effects of electrochemical H-charging on microstructure and mechanical behaviour of two as-cast Mg-8Li (in wt%) based alloys were investigated and compared. Due to the in-situ formation of I-phase, the failure elongation ratio for Mg-8Li-6Zn-1Y alloy was 31.2 % and its hydrogen embrittlement (HE) susceptibility was about 1/4 that of Mg-8Li alloy after H-charging for 24 h. Moreover, the preferential location of H-induced pores transferred from two matrix phases to I-phase/matrix eutectic pockets due to the preferential H absorption of I-phase, resulting in the higher HE resistance of Mg-8Li-6Zn-1Y alloy.

Hydrogen embrittlement in Nickel oligocrystals: Experimentation and crystal plasticity-phase field fracture modeling

This work investigates the hydrogen embrittlement (HE) behavior of Nickel-201 alloy using experimental and numerical approaches. In experimentation, the effect of electrochemical hydrogen charging on the deformation behavior of tensile oligocrystals is investigated at different strain rates. Irrespective of the strain rate levels, all the hydrogen-charged tensile oligocrystals exhibited intergranular (IG) fracture exclusively along the random high-angle grain boundaries (RHAGBs). At the same time, no crack was observed along the coincident site lattice (CSL) Σ3 type grain boundaries. The absence of an interconnected grain boundary network, lower stress levels, and insensitivity of H-induced IG fracture to the strain rate levels of investigated FCC oligocrystals (with low lattice hydrogen diffusion coefficient) established the insignificance of dynamic H-redistribution toward HE. In numerical simulations, a crystal plasticity-phase field fracture finite element model simulates the macroscopic tensile response and corresponding microscopic fracture evolution behavior for hydrogen-free and hydrogen-charged tensile oligocrystals. The experimental results corroborated by numerical simulations, validate that the reduction in fracture energy of RHAGBs, induced by hydrogen segregation through thermodynamic equilibrium during hydrogen charging prior to deformation, is the dominating factor governing HE.

Transformational faulting in Mn2GeO4 from olivine to wadsleyite structure: Implications for physical mechanism of deep-focus earthquakes

High-pressure and temperature deformation experiments interfaced with acoustic emission (AE) monitoring have been conducted to study transformational faulting in Mn2GeO4 olivine, which transforms to the β phase, isostructural to wadsleyite. Metastable Mn2GeO4 olivine exhibits a marked embrittlement behavior at temperatures between 800 and 1100 K, emitting numerous AEs. At each temperature, brittle deformation is characterized by a two-stage process: (1) a “preparation” stage with numerous diffusedly located low-magnitude AEs and large b values (>2), and (2) a failure stage where larger-magnitude AEs form a planar distribution with b values about 1. Microstructure analysis reveals extensive kink band development in olivine grains in the recovered samples. Kink band boundaries (KBBs), with a typical thickness of ∼100 nm, are filled with a nanometric β-Mn2GeO4 “gouge”. A dense array of secondary shear localizations is often present within the kink bands, suggesting significant shear deformation therein. The combined observations suggest that faulting in metastable Mn2GeO4 olivine is a self-similar process, from grain-scale to the sample-scale. Both observed embrittlement behavior and the microstructure of metastable Mn2GeO4 olivine are essentially identical to those in Mg2GeO4 olivine we have reported previously, indicating that the physical mechanism of faulting in metastable olivine is insensitive to the specific crystallographic structure of the high-pressure phase. The low b values (about 1) observed in the faulting process in our experiments are similar to those of deep focus earthquakes in cold subduction zones. Our observed mechanism explains deep focus seismicity in cold metastable mantle wedges, provided that the self-similarity assumption holds to geological scales.

Enhanced hydrogen embrittlement resistance of additive manufacturing Ti-6Al-4V alloy with basket weave structure

The hydrogen embrittlement (HE) behavior of tungsten inert gas arc additive manufacturing (AM) Ti-6Al-4V alloy was studied through tensile tests with/without hydrogen charging. The influence of hydrogen on the microstructure and crack propagation of AM Ti-6Al-4V alloy was investigated. The results indicated that the AM Ti-6Al-4V alloy with a basket weave structure alleviated local stress at grain boundaries during deformation, thus avoiding intergranular cracking and brittle fracture. The AM alloy displayed less HE susceptibility than that of the wrought alloy, which was due to the basket weave structure hindering the propagation of hydrogen-induced cracks, thereby improving the HE resistance.

A Review on hydrogen embrittlement behavior of steel structures and measurement methods

Hydrogen can be found within metals under a variety of industrial and environmental conditions. Hydrogen-metal interactions can take place through hydrogen embrittlement, hydrogen sulfide corrosion, or hydrogen absorption. Steel and other metals that are exposed to hydrogen may experience a difficulty known as hydrogen embrittlement that affects their mechanical properties. The material's ductility and toughness may be reduced as a result of this phenomena, it also increasing the risk of brittle fracture. In steel, atomic hydrogen mainly diffuses into the microstructure of the steel, causing hydrogen embrittlement. Localized weakening of the bonds between the metal atoms might result from hydrogen atoms occupying interstitial positions in the metal lattice. Especially when under stress, this may lead to a more susceptible to fracture and cracking. Concerns with hydrogen embrittlement arise in sectors like aerospace and oil and gas that use high-strength steels. If not appropriately handled, it may result in catastrophic failures. Use of hydrogen-resistant alloys, appropriate heat treatments, and protection from conditions that promote hydrogen uptake are examples of preventive measures. This literature review paper covers the definition of hydrogen embrittlement (HE), mechanisms causing HE, measurement of hydrogen concentration and preventive measures that restrict hydrogen diffusion to the steel.

Crack propagation determined by energy release rate in cortical bone ultrasonic vibration assisted cutting

In orthopaedic surgery, bone cutting may occur serious mechanical damage due to large crack propagation, which impedes patient postoperative recovery. Ultrasonic vibration assisted cutting (UVAC) has emerged as a leading technique in bone cutting owing to its remarkable advantages, including minimal damage and cutting force. However, how to diminish its damage during bone UVAC remains challenging. Hence, this study established a sophisticated model to calculate the energy release rate for cortical bone UVAC and predicted the critical cutting depths of shear and fracture crack propagation. This superiority stems from the synergistic effects of periodic tool separation and the acoustic softening effect inherent in UVAC, which contribute to a lower average energy release rate and a subsequently reduced cutting force. Nevertheless, the high instantaneous energy release rate during UVAC can exceed the material's critical threshold for crack propagation, leading to the initiation of microcracks and thereby inducing material embrittlement behaviour. These insights shed light on the material removal mechanism of bone UVAC in medical orthopaedic surgery, thus enriching our understanding and potentially guiding further advancements in this field.

Influence of Nb on the hydrogen-assisted cracking behaviour in multiphase stainless steel: Phase fractions, stacking fault energies, and nanosized NbC precipitation

Nb alloying has been reported to deteriorate the hydrogen embrittlement resistance of multiphase steels, which contrasts to the case of single-phase metallic materials. This study clarifies the impact of Nb alloying on the hydrogen embrittlement behaviour of a novel multiphase stainless steel. The findings revealed a 17 % reduction in the hydrogen embrittlement sensitivity upon Nb incorporation. It was found that higher austenite fractions in the Nb-bearing steels impeded hydrogen ingress. The austenite phase in such Nb-bearing steels possesses a higher stacking fault energy, thereby delaying martensitic transformation and crack initiation. The precipitation of nanometre-sized NbC in the matrix obstructed hydrogen diffusion, which indirectly inhibited crack initiation and propagation.

Effect of heat treatment on hydrogen embrittlement susceptibility of Al0.25CoCrFeNi high entropy alloy

In this study, the influences of annealing and aging treatments on the hydrogen embrittlement (HE) behavior of the cryo-rolled Al0.25CoCrFeNi high entropy alloy (HEA) were investigated through tensile tests and electrochemical hydrogen charging experiments. The results found that the aged sample showed high strength but was more susceptible to HE. A trade-off between the strength and HE resistance was achieved in the annealed + aged sample. Electron backscatter diffraction analysis and fracture characteristics were performed to clarify the HE mechanism. The high dislocation density and aggregated second phase along the grain boundaries in the aged sample were the important factors to help the initiation of HE crack, and then increasing the HE susceptibility. The annealed + aged sample with low dislocation density and aging precipitation reduced the risk of hydrogen-induced cracking and resulting in the excellent HE resistance. This work offered the method to obtain a comprehensive improvement in the strength and HE resistance of this alloy.

The Impact of Impurity Gases on the Hydrogen Embrittlement Behavior of Pipeline Steel in High-Pressure H2 Environments.

The use of hydrogen-blended natural gas presents an efficacious pathway toward the rapid, large-scale implementation of hydrogen energy, with pipeline transportation being the principal method of conveyance. However, pipeline materials are susceptible to hydrogen embrittlement in high-pressure hydrogen environments. Natural gas contains various impurity gases that can either exacerbate or mitigate sensitivity to hydrogen embrittlement. In this study, we analyzed the mechanisms through which multiple impurity gases could affect the hydrogen embrittlement behavior of pipeline steel. We examined the effects of O2 and CO2 on the hydrogen embrittlement behavior of L360 pipeline steel through a series of fatigue crack growth tests conducted in various environments. We analyzed the fracture surfaces and assessed the fracture mechanisms involved. We discovered that CO2 promoted the hydrogen embrittlement of the material, whereas O2 inhibited it. O2 mitigated the enhancing effect of CO2 when both gases were mixed with hydrogen. As the fatigue crack growth rate increased, the influence of impurity gases on the hydrogen embrittlement of the material diminished.

Correlation between hydrogen absorption capacity and microstructure of Fe-rich Sm-Co-Fe-Cu-Zr permanent magnetic alloys

The correlation between hydrogen absorption capacity (HAC) and the microstructure of Sm26.2CobalFexCu4.0Zr2.3 (x = 23 wt%, 25 wt%, 27 wt%, 30 wt%) ingots and cast strips was systematically investigated. As the temperature rises from 373 to 423 K, the activation time, hydrogen absorption time and HAC of the Sm26.2CobalFe23Cu4.0Zr2.3 ingot decrease by 14.4%, 14.1%, and 19.3%, respectively. Dispersed 1:5 phase provides more channels for hydrogen diffusion, which is the main reason that HAC increases with the x increasing. The HAC of the same compound strips increases as the particles size of the pre-crushed decreases. However, no further embrittlement behavior appears in pre-crushed strips, which reaches an equal HAC as ingots. Micro-computerized tomography reveals that ingots contain small spherical-like holes and large flake micro-cracks, whereas strips mainly contain elliptical pores. The effects of grain size and inner defects size on structure stability were invested by Abaqus. Simulation results reveal that the superior embrittlement behavior of the ingots is predominantly influenced by the presence of large flake-like micro-cracks.

Effects of lattice misfit of γ/γ′ phases on hydrogen embrittlement behavior in Ni-based single crystal superalloy

The effect of γ/γ′ phase lattice misfit on hydrogen embrittlement (HE) behavior was fundamentally investigated by utilizing a Ni-based single crystal CMSX-4 superalloy with a simple microstructure that can exclude the H-trapping effects of grain boundary, c-vacancy, and misfit dislocation. Increasing isothermal aging time increased γ′ precipitate size while maintaining its volume fraction and a fully coherent interface. The magnitude of negative lattice misfit between the γ and γ′ phases increased from −0.08 to −0.22% according to γ′ precipitate coarsening, resulting in a well-developed tensile-strain field within the γ′ precipitate. The increased tensile-strain field enhanced activation energy for H-desorption in the γ′ precipitate from 31.9 to 35.1 kJ/mol. Therefore, H is preferentially distributed along the γ/γ′ interface within the γ′ precipitate even before deformation. H basically promotes the slip planarity through the H-enhanced localized plasticity (HELP) mechanism in Ni-based single crystal alloys, in which slip is the dominant deformation behavior. As the superalloy possesses a larger negative lattice misfit, H becomes trapped as diffusible-state at the tensile-strain field of the γ/γ′ interface, resulting in cuboidal brittle fracture along the {001} planes. In this process, the HELP mechanism facilitated H localization at the γ/γ′ interface. Thus, the HE behavior distinctly transitioned from HELP to an interaction between HELP and H-enhanced decohesion mechanisms (HEDE) with an increase in the magnitude of the lattice misfit. The HE behavior was investigated by correlating microstructural characterization, H-trapping behavior, and crystallographic fracture mechanism analysis.

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

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

Inhibiting stress corrosion cracking of a prefabricated surface‐defective magnesium alloy thanks to biological organic components

AbstractBiomedical magnesium (Mg) alloys remain a challenge for their mainstream application, because the combination of bio‐mechanical stress and corrosive physiological environment leading to stress corrosion cracking (SCC). It is crucial to avoid the sudden brittle fracture of Mg alloys in vivo for predicting their service duration. However, the key factors, such as surface or physiological environment features, determining the origination or propagation of SCC behavior are still unclear. In the present study, a prefabricated surface defects coating was prepared by the phytic acid (PA, C6H18O24P6) conversion treatment. Four mimicking physiological media were used, ranging from simple to equivalent (Dulbecco's Modified Eagle Medium and Protein [DMEM+Pro]). The results showed that the PA film with numerous micro‐cracks provided limited protective ability in synthetic biological media. A striking finding was determined that although initial high corrosion rate of samples in DMEM+Pro led to an increased SCC nucleation, significant ductile fracture with elongation to failure (14.86%) was observed. Combined with the fracture features, the adsorption or deposition of biological composition into the tunnel of SCC cracks significantly inhibited the hydrogen embrittlement (HE) behavior. These results indicate that preventing the propagation of SCC crack by biological composition, rather than nucleation, plays a key role in avoiding the sudden fracture of Mg alloys. It provides a novel perspective to determine the non‐brittle fracture of Mg alloys for biomedical applications.