Metal Embrittlement Research Articles

The Effect of Grain Boundary Misorientation on Hydrogen Flux Using a Phase‐Field‐Based Diffusion and Trapping Model

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.

High temperature creep and embrittlement in metals and alloys under conditions of the long-term usage

High temperature creep and embrittlement in metals and alloys under conditions of the long-term usage

A new approach for in situ electrochemical nanoindentation: Side charging as a promising alternative

Understanding hydrogen embrittlement in metals is an essential task for the energy transition, where hydrogen plays a key role. Besides the economic consequences of embrittlement, safety aspects are a very important factor to consider. Therefore, materials need to be screened in order to evaluate their mechanical response under hydrogen influence. Besides macroscopic mechanical testing, in situ electrochemical nanoindentation and micromechanical testing —in general— represent promising methods as they allow to characterize individual microstructural features. In the established “front-side” charging approach, hydrogen enters the sample at the same surface on which indentation tests are performed. An alternative is “back-side” charging, where hydrogen is introduced at the opposite side of the indentation location. In the present study, a novel “side” charging cell was designed and the results were compared to those obtained by “front-side” charging. For this purpose, a ferritic steel with high chromium content (X6Cr17) underwent a grain coarsening heat treatment to ensure that multiple nanoindentation experiments can be performed within a single grain. A similar grain orientation was tested with both charging approaches. The novel “side” charging cell design outperforms the stiffness of the reference front-side charging cell by 60 %. Both cell designs yielded constant Young's moduli before, during and several hours after charging. The hardness increased during charging due to hydrogen uptake, whereas the hardness settled several hours after charging to the values before charging started. The presence of hydrogen at the indentation side was confirmed by in situ X-ray diffraction using a self-reporting titanium film.

Hydrogen trapping and embrittlement in metals – A review

Hydrogen embrittlement in metals (HE) is a serious challenge for the use of high strength materials in engineering practice and a major barrier to the use of hydrogen for global decarbonization. Here we describe the factors and variables that determine HE susceptibility and provide an overview of the latest understanding of HE mechanisms. We discuss hydrogen uptake and how it can be managed. We summarize hydrogen trapping and the techniques used for its characterization. We also review literature that argues that hydrogen trapping can be used to decrease HE susceptibility. We discuss the future research that is required to advance the understanding of HE and hydrogen trapping and to develop HE-resistant alloys.

A thermo-chemo-mechanically coupled peridynamics for investigating crack behavior in solids

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.

Diagnostic complex «MicroLab-Z2» for non-destructive evaluation of structural and deformation parameters of metal conscructions

The behavior of the construction under the influence of external factors is determined by three key groups of parameters of the metal composition (chemical, structural and deformation). Obtaining information about these parameters directly on the construction will effectively solve the problem of assessing its actual technical condition. The problem of non-destructive evaluation of the chemical composition of a metal is solved using portable spectrometers. The MicroLab-Z2 diagnostic complex has been developed to evaluate the other two groups of parameters. It has two functional blocks. The surface preparation unit ensures that the surface of the construction site has a roughness, flatness and level of applied mechanical hardening corresponding to the laboratory preparation of metallographic grinds. The research unit is a platform on which a metallographic microscope and a portable microhardness tester are installed. It allows metallographic researches with magnification up to x1000, surface microindentation, measurement of microhardness values at load of 0—200 gs and optical study of the morphology of imprints in any spatial position. The reliability of the data obtained by the MicroLab-Z2 diagnostic complex has been confirmed during comparative tests with stationary equipment. With the help of the developed device, an assessment of the structure parameters, contamination of metal with non-metallic inclusions, assessment of the degree of hardening and embrittlement of metal, detection of aging processes can be performed. The use of the MicroLab-Z2 diagnostic complex for operational non-destructive evaluation of structural and deformation parameters of metal constructions will allow us to reach a qualitatively different level of efficiency in performing production and input control of manufactured products, assessing the maintainability of defects, planning repairs and other compensating measures, and industrial safety expertise.

Anisotropy and grain size dependence of the effects of hydrogen on the shock-induced spallation in iron

Hydrogen (H) embrittlement in metals has long been a source of concern in academia and industry. However, the fundamental mechanisms remain not well understood in dynamic events. Using atomic simulations, shock responses of monocrystalline α-Fe along the [100] and [111] crystal orientations and nanocrystalline Fe with and without H atoms are investigated systematically. For the first time, the anisotropic dependences of the effects of H atoms on the spall strength are revealed. In the case of the [100] crystal orientation, H atoms prevent the phase transition of α-iron under shock compression, further slowing down the growth of voids during spall fracture and enhancing the spall strength at high strain rates. While in the case of [111] crystal orientation, H atoms promote dislocation formations under shock compression which is consistent with the known hydrogen-enhanced local plasticity (HELP) mechanism; H atoms accelerate the growth of voids during the spallation and reduce loads-bearing capacity, which finally lowers the spall strength of α-iron. In nanocrystalline samples, voids favor along GBs. The presence of H atoms would cause a local disturbance at the GB but block the long-distance movement of the surrounding atoms resulting in a slight increase in spall strength. The combined effects of H atoms and GBs influence the void evolution. This work provides deep insights into the hydrogen effect on metals under dynamic loading and should benefit a wide broad of research communities in materials and mechanics.

Hydrogen storage alloys for stationary applications

• An alternative option to store hydrogen in a more compact and safer way than compressed gas systems, applied to a hybrid H2 – Li-ion Power-to-Power plant built in an off-grid site. In off grid locations the energy supply has always been a problem in terms of infrastructures and costs. Power-to-Power (P2P) energy systems could assume an important role especially in these sites, in order to make these places energetically independent and mostly based on renewable sources exploitation. P2P have in fact a great potential to help fixing the problem of intermittent production of RES like wind and PV. This paper aims to describe a real hybrid H 2 -battery P2P system with special focus on the topic of hydrogen storage. Today, H 2 is conventionally stored in high-pressurized vessels and this solution is linked to several technical and regulatory problems (encumbrance, safety, metal embrittlement, too large volumes going above regulatory limits in some cases, etc.). Instead, hydrogen can be absorbed in large quantities using metal hydrides, reaching volumetric density values often higher than liquid hydrogen. Discovered in the late 70 s and extensively studied in the last decades, this kind of solution has never reached a proper commercialization principally due to the limited gravimetric density values, making them unsuitable for automotive and transport purposes. But hydrogen storage alloys (HSA) can raise significant interest for stationary applications. Two of the most promising alloys are considered as applicable in a real P2P plant that will be built in Italy (Ginostra – Sicily) in the framework of the H2020 project REMOTE, modelled, designed and compared to the state-of-the-art solution based on a compressed hydrogen vessel. The final part of the paper covers the preliminary economic assessment of this new kind of plant and a future (optimistic) price trend, plotting a hypothetic learning curve.

Review of Hydrogen Embrittlement in Metals: Hydrogen Diffusion, Hydrogen Characterization, Hydrogen Embrittlement Mechanism and Prevention

Hydrogen dissolved in metals as a result of internal and external hydrogen can affect the mechanical properties of the metals, principally through the interactions between hydrogen and material defects. Multiple phenomena such as hydrogen dissolution, hydrogen diffusion, hydrogen redistribution and hydrogen interactions with vacancies, dislocations, grain boundaries and other phase interfaces are involved in this process. Consequently, several hydrogen embrittlement (HE) mechanisms have been successively proposed to explain the HE phenomena, with the hydrogen-enhanced decohesion mechanism, hydrogen-enhanced localized plasticity mechanism and hydrogen-enhanced strain-induced vacancies being some of the most important. Additionally, to reduce the risk of HE for engineering structural materials in service, surface treatments and microstructural optimization of the alloys have been suggested. In this review, we report on the progress of the studies on HE in metals, with a particular focus on steels. It focuses on four aspects: (1) hydrogen diffusion behavior; (2) hydrogen characterization methods; (3) HE mechanisms; and (4) the prevention of HE. The strengths and weaknesses of the current HE mechanisms and HE prevention methods are discussed, and specific research directions for further investigation of fundamental HE mechanisms and methods for preventing HE failure are identified.

Quality Of Restored Steel Gas Pipes For Re-Application In Construction

The structure and mechanical properties of eight steel gas pipeline single-seam and double-seam pipes that were in operation were studied. It is shown that the degree of corrosion damage to pipe surfaces depends on the chemical composition of the steels. In the studied steels, a significant variation in the hydrogen content between neighboring volumes and the studied pipes was revealed. According to electron-fractographic analysis , there is no significant difference in the degree of embrittlement of the base metal, the weld and the zone of thermal influence. A noticeable effect of hydrogen absorption of steels on the coefficient of anisotropy of the impact toughness has been established, which causes a decrease in the impact toughness on transverse samples to a greater extent than on longitudinal ones. According to the results of mechanical tests for tensile and impact bending, it was found that the restored welded pipes are suitable for use in structures from the first to the fourth groups for the construction, repair and reconstruction of industrial and civil facilities. Naturally, this implies the need for their restoration repair.

Application of Machine Learning to Predict Grain Boundary Embrittlement in Metals by Combining Bonding-Breaking and Atomic Size Effects.

The strengthening energy or embrittling potency of an alloying element is a fundamental energetics of the grain boundary (GB) embrittlement that control the mechanical properties of metallic materials. A data-driven machine learning approach has recently been used to develop prediction models to uncover the physical mechanisms and design novel materials with enhanced properties. In this work, to accurately predict and uncover the key features in determining the strengthening energies, three machine learning methods were used to model and predict strengthening energies of solutes in different metallic GBs. In addition, 142 strengthening energies from previous density functional theory calculations served as our dataset to train three machine learning models: support vector machine (SVM) with linear kernel, SVM with radial basis function (RBF) kernel, and artificial neural network (ANN). Considering both the bond-breaking effect and atomic size effect, the nonlinear kernel based SVR model was found to perform the best with a correlation of r2 ~ 0.889. The size effect feature shows a significant improvement to prediction performance with respect to using bond-breaking effect only. Moreover, the mean impact value analysis was conducted to quantitatively explore the relative significance of each input feature for improving the effective prediction.

Grain Boundary Embrittlement of Steels of Vver-1000 Reactor Vessels Under Long-Term Operation

Results of fractographic analysis and Auger electron spectroscopy of materials of vessels of VVER-1000 reactors obtained at the “Kurchatov Institute” Research Center are systematized. Comparative analysis of the effect of the operating factors on the level of grain boundary embrittlement in the matrix metal and welded joints is performed. The contribution of grain boundary embrittlement into the total radiation-induced embrittlement of the weld metal of the vessels is determined.

Solvent-mediated extraction of fatty acids in bilayer oil paint models: a comparative analysis of solvent application methods

The impact of solvent exposure on oil paintings and the differences between solvent application methods are longstanding topics in cleaning studies. Solvent exposure is ideally kept to a minimum, because solvent swelling can lead to the extraction and displacement of reactive paint components. In particular, important concerns are fatty acids displacement resulting in metal soap formation and embrittlement of paint due to solvent exposure. In this study, the extraction of a saturated fatty acid (SFA) marker and the formation of zinc soaps were monitored to measure the impact of solvent cleaning on tailored bilayer model systems for aged oil paint. Three methods of solvent application were compared: cotton swab, rigid gel and Evolon tissue (with different solvent loading). The samples were analysed by surface acoustic wave nebulization mass spectrometry (SAWN-MS) and thermally-assisted hydrolysis and methylation pyrolysis gas chromatography mass spectrometry (THM-Py-GC/MS) by comparing the calculated margaric:palmitic acid (text {C}_{17}{:}text {C}_{16}) ratio determined in the extracts (taken from the swab, gel or Evolon tissue). We conclude that both swab cleaning and squeezed Evolon tissue application result in comparable SFA extraction. The rigid gel and Evolon with controlled solvent-loading limit the amount of SFA extraction. The distribution of text {C}_{17} after solvent application was visualised using static Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) on cross sections, showing that text {C}_{17} redistribution took place in all cases where solvent was applied. Crystalline zinc soaps formation was not observed after 5 min of ethanol exposure in the embedded cross-sections with imaging ATR-FTIR, indicating that solvent exposure does not immediately trigger the formation of crystalline metal soaps. However, significant zinc soap formation was found after 30 min of ethanol exposure using Evolon tissue without controlled loading. This study contributes to a better understanding of the impact of different methods of solvent application on oil paintings and highlights important differences between these methods.

Quantification of solute deuterium in titanium deuteride by atom probe tomography with both laser pulsing and high-voltage pulsing: influence of the surface electric field

Atom probe tomography (APT) has been increasingly used to investigate hydrogen embrittlement in metals due to its unique capacity for direct imaging of H atoms interacting with microstructural features. The quantitativeness of hydrogen measurements by APT is yet to be established in views of erroneous compositional measurements of bulk hydrides and the influence of spurious hydrogen, e.g. residual gas inside the analysis chamber. Here, we analyzed titanium deuteride (approx. 65.0 at%–66.6 at% D) in lieu of hydride to minimize the overlap with residual gas, both with laser pulsing and high-voltage (HV) pulsing. Strategies were deployed to prevent H pick-up during specimen fabrication, including preparing specimens at cryogenic temperature. The measured composition of deuterium by APT with laser pulsing decreases significantly with the applied laser pulse energy, which is interpreted with regards to the strength of the corresponding surface electrostatic field, as assessed by the evolution of charge-state ratio. In contrast, compositional analyses with HV pulsing are roughly independent of the applied experimental parameters, although approx. 15 at%–20 at% off the nominal composition. Aided by plotting paired mass-to-charge correlations, the mechanisms of composition bias in both pulsing modes are discussed. A special emphasis is placed on the local variations of the measured composition as a function of the local electric field across the specimen’s surface, which is not uniform due to asymmetric heat distribution related to the localized laser absorption and the faceted nature of surface caused by the crystallographic structure. Our investigations demonstrate the challenges of quantitative analysis of solute deuterium by APT but nevertheless provide insight to achieving the best possible experimental protocol.

Atomistic simulations of hydrogen effects on tensile deformation behaviour of [0 0 1] twist grain boundaries in nickel

Hydrogen (H) embrittlement of metals is a common phenomenon but the exact atomic mechanisms responsible for H-induced plasticity process and ultimate failure are not clarified. In this work, the impacts of H on tensile deformation behaviour of different types of twist grain boundaries (TGBs) have been systematically studied by molecular dynamics (MD) simulations. Different deformation mechanisms are reported, depending on grain boundary types and bulk H concentrations, including easier dislocation nucleation due to the presence of H, H-enhanced dislocation dissociation, and H-induced slip planarity. The simulations indicate that the interactions between H-enhanced dislocation plasticity and TGBs play a crucial role in the ultimate fracture path. The decohesion of the TGBs is considerably promoted by the presence of H under conditions where dislocation accommodation and emission process on the TGBs causes the changes of grain boundary structures and local stress state. Our results advance a mechanistic understanding for experimentally-observed H embrittlement and provide a viable path to engineering microstructure with high resistance to H embrittlement in new materials.

Hydrogen embrittlement of tungsten induced by deuterium plasma: Insights from nanoindentation tests

Abstract

On the Nature of Similarity in Embrittlement of Metals by Hydrogen and Surfactants

A mechanism for a similar effect of hydrogen and surface active elements surfactants on the structure and properties of metals is discussed based on studies of austenitic steels and using the ab initio calculations and experimental measurements of the electron structure mechanical spectroscopy and tension tests The similarity is originated from the local enhancement of the metallic character of interatomic bonds The obtained results are interpreted within the frame of the electron approach to the hydrogen enhanced localized plasticity phenomenon HELP in hydrogen embrittlement The surfactants increase the density of electron states at the Fermi level and correspondingly the concentration of free electrons As a response a local decrease of the shear modulus resulted in the initiation of dislocation sources decrease of the line tension of dislocations and distance between their assembles is expected which facilitates the opening and propagation of cracks and mechanical degradation The comparison with the adsorption induced dislocation emissionhypothesis AIDE for hydrogen and liquid metal embrittlements is carried out

Impact Property of Low-Activation Vanadium Alloy NIFS-HEAT-2 After Electron Beam Welding and Neutron Irradiation

In order to investigate the effect of post-weld heat treatment (PWHT) and post-irradiation annealing (PIA), electron-beam-weld specimens of the reference low activation vanadium alloy, NIFS-HEAT-2, were neutron-irradiated to a fluence of 7.62 × 1023 neutron m−2 (E > 1 MeV) at 563 K in Belgian Reactor-2. In the present experiments, unexpected oxidation of the surface of the samples occurred during the neutron irradiation, and significantly degraded impact properties of the weld metal, while the degradation was not significant for the base metal. The removal of the oxidized layer by electro-polishing improved the impact properties of the weld metal. Although complete removal of the oxidized layer could not be confirmed, it is revealed that impact absorbed energy of the weld metal with post-weld heat treatment at 1073 K was comparable to that of the base metal after the post-irradiation polishing. In other words, irradiation embrittlement of the weld metal was successfully suppressed by the PWHT. PIA at 773 K and above was effective to recover the irradiation hardening and irradiation embrittlement. Mechanisms of the irradiation hardening, irradiation embrittlement and its recovery were discussed.

Influence of gaseous components and pressures on hydrogen embrittlement of natural gas pipeline

Hydrogen usually penetrates metals through defects such as dislocations, vacancies, and crystalline imperfections and causes embrittlement, leading to cleavage fracture and intergranular fracture. Synthetic natural gas produced by coal gasification, biogas, and landfill gas inevitably contain hydrogen. Therefore, hydrogen embrittlement of pipeline materials should be considered when they are mixed with conventional natural gas and supplied to customers. To analyze hydrogen embrittlement of base metals and girth weld metals of API 5L X70 and X65 gas pipelines, a specimen was treated in 100 % hydrogen environment at 10 MPa to determine the hydrogen concentration in it. Small punch (SP) tests were performed under various gaseous components and pressures. When SP tests were performed at very low speed, hydrogen embrittlement could be observed. Specimens became very susceptible to hydrogen embrittlement with increasing hydrogen partial pressure in the hydrogen/methane gas mixture, and the SP energy also decreased dramatically.

Effect of Damaging Irradiation on Low-Temperature Embrittlement of Metals

The effect of low-temperature damaging irradiation on the high-temperature embrittlement (cold shortness) in metals was investigated in a previously proposed model. The cold shortness state with possible brittle fracture in metals is not formed in the irradiation process because of the dynamical radiation processes arising.