Problem Of Hydrogen Embrittlement Research Articles

Study of Hot-Dip Aluminium Plating Based on Micro-Morphology and Coating Bond Strength

Hydrogen barrier coatings with Al2O3 as the main component are a good choice for solving the hydrogen embrittlement problem during hydrogen transportation in long-distance pipelines. However, the difference in the coefficients of thermal expansion between the substrate and the Al2O3 coating limits its further utilisation and development. In this study, rare earth oxides were added to the molten aluminium solution, and a Fe-Al transition layer was introduced on the surface of X80 steel by hot-dip plating to solve the thermal mismatch. Here, the microstructure and bonding strength of the hot-dip aluminium layer were investigated. It is found that the hot-dip aluminium coating consists of the outermost aluminium-rich layer and the inner Fe-Al alloy layer, and the microstructure of the two will change with the change in dip plating parameters. The best overall performance of the hot-dip aluminium layer was obtained from X80 steel substrate at a dip plating temperature of 700 °C and a dip plating time of 5 min. This coating has a good interface, moderate thickness, and a bond strength of 49 N. This study provides a reference value for solving the thermal mismatch between the steel substrate and the Al2O3 hydrogen barrier coating generated by subsequent anodising.

Study on the permeability behaviour of hydrogen doped natural gas in polyethylene pipeline

The use of non-metallic PE pipes to transport hydrogen energy can avoid the problem of hydrogen embrittlement in metal pipes, but due to material characteristics, PE pipes exhibit gas leakage behavior. Therefore, this article conducted a study on the permeability of polyethylene (PE100) as a gas pipeline material for hydrogen-doped gas, mainly analyzing the effects of hydrogen content and gas pressure on the permeability of PE100 gas. We ensure that the raw materials are uniform and free from pore defects through microstructure observation and industrial CT characterization. The experimental results show that with the increase of hydrogen content in the hydrogen-doped gas, the gas permeability coefficient of the sample significantly increases. When the hydrogen content is 60%, the gas permeability coefficient increases by 83% compared to when no hydrogen is added. Further increase in hydrogen content results in no significant change in the gas permeability coefficient; As the gas pressure increases, the gas permeability coefficient of the s ample gradually decreases. This study will provide data support for the safe transportation of hydrogen energy and promote the development of the hydrogen energy industry.

Effect of Coating on Stress Corrosion Performance of Bridge Cable Steel Wire

Hot galvanization on steel surfaces can isolate the steel from corrosive environments and alleviate the stress corrosion cracking caused by the anodic dissolution mechanism. However, the cathodic protection potential of the coating is excessively negative, which may aggravate the hydrogen embrittlement problem. The effect of a coating on the stress corrosion performance of bridge cable wire was studied by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive spectrometry (EDS), a thermal desorption analysis (TDA), an electrochemical workstation, and an FIP test. The results show that hot-dip ZnAl and ZnAlMg alloy coatings can significantly prolong the stress corrosion fracture time of steel wire substrates. From a macroscopic perspective, the stress corrosion cracking fracture is a brittle fracture caused by hydrogen embrittlement. Moreover, the coating type has little effect on the fracture morphology of bridge cable wire. In NH4SCN solution (50 °C, 20 wt.%), a corrosion product layer composed of ZnS and Al2O3 was formed on the surface of the coated steel wire. The electrochemical analysis showed that the corrosion resistance of the ZnAlMg coating was better than that of the ZnAl coating, which was the main reason for the improvement of the stress corrosion performance.

Simulations on the thermal and mechanical performance of the rotating target system of accelerator-driven neutron source for Boron Neutron Capture Therapy(BNCT)

The development of an accelerator-based BNCT facility, X-BNCT, at Xi’an Jiaotong University was introduced. The 30 mA protons were accelerated to 2.8 MeV by a linear RFQ accelerator, then the lithium target was bombarded to produce neutrons required for treatment through 7Li(p, n)7Be reaction, and a large amount of energy was deposited on the target. To remove the heat on the target, the design and analysis of the rotating target system was discussed in this paper. The channels with a small size in the target flap were studied and an interlayer was added to avoid the problem of hydrogen embrittlement. The heat transfer simulation was carried out with Gaussian beam or uniform beam in the rotating target system by the CFD method. The maximum temperatures of lithium were lower than the melting point, indicating the advancement of the rotating target structure in cooling. And it was concluded that the uniform scheme should be considered even for the rotating target system. Finally, the stress analysis of each component of the rotating target in the process of rotation was simulated, and the results showed that the design met the material requirements.

Effect of Mo addition on hydrogen segregation at α-Fe grain boundaries: A first-principles investigation of the mechanism by which Mo addition improves hydrogen embrittlement resistance in high-strength steels

The development of high-strength steels is essential for realizing a decarbonized society; however, to achieve this, the problem of hydrogen embrittlement must be solved. The effectiveness of adding Mo has been demonstrated to address this issue, but its underlying mechanism has not yet been clarified. To investigate this mechanism, we developed a calculation method to evaluate the effect of adding alloying elements on the grain boundary segregation of H using parameters calculated via first-principles calculations. Accordingly, the segregation energies of H with and without Mo segregation near the grain boundary were calculated. Based on the obtained segregation energies, the concentration of H at the grain boundary was calculated for a given amount of Mo under the heat treatment conditions normally assumed. The results showed that a small amount of Mo segregates to α-Fe grain boundaries and significantly reduces the grain boundary concentration of H owing to repulsive interactions between Mo and H. This indicates that Mo addition improves the resistance to hydrogen embrittlement by reducing the grain boundary H concentration. The physical origin of these repulsive interactions was further investigated by decomposing them into mechanical and chemical contributions; we found that these repulsive interactions are mainly caused by the chemical contribution. Furthermore, the crystal orbital Hamiltonian population indicated that the chemical contribution can be attributed to the large core repulsion between Mo–H at α-Fe grain boundaries (in comparison to that between Fe–H) owing to the larger atomic orbital of Mo. The proposed calculation method as well as the information obtained from our evaluations can help in the development of high-strength steels with excellent resistance to hydrogen embrittlement and in the improvement the resistance to hydrogen embrittlement of various metallic materials.

Study on the Effect of Microstructure Gradients Caused by Heat Gradients on Hydrogen Embrittlement Sensitivity in Heavy Forgings

The hydrogen embrittlement problem of alloy steel heavy forgings not only has the common properties of general hydrogen embrittlement, but also has the characteristics brought by its scale characteristics. The research of hydrogen embrittlement, combined with its characteristics and commonness, is of vital importance for the service safety of engineering structures. The temperature field and microstructure distribution in the machining process were investigated through the simulation of a finite element. On this basis, the physical simulation experiments were carried out to obtain the microstructure of heavy forgings in radial directions. The hydrogen embrittlement sensitivity was characterized by electrochemical hydrogen charging and slow strain rate tests (SSRT). The microstructure and fracture morphology of the samples were characterized to explore the law and mechanism of hydrogen embrittlement sensitivity gradient distribution along the axial direction. It is helpful to understand the hydrogen embrittlement of heavy forgings in order to guide engineering practice.

The Potential of the Internal Friction Technique to Evaluate the Role of Vacancies and Dislocations in the Hydrogen Embrittlement of Steels

Hydrogen embrittlement of steels is known to have considerable impact in many engineering sectors. To be able to mitigate the hydrogen embrittlement problem, a profound comprehension of the interaction of hydrogen with the steel microstructure is required. Especially the interaction of hydrogen with dislocations and vacancies is very relevant as these defects are known to play an important role in hydrogen embrittlement. At present, thermal desorption spectroscopy is mostly used to study hydrogen–defect interactions. However, information obtained solely by this technique is insufficient to obtain a full understanding of the interaction of hydrogen with these defects in the steel microstructure. Herein, the use of internal friction, as a complementary technique to thermal desorption spectroscopy, to reveal the interaction of hydrogen with dislocations and vacancies, is reviewed based on the present understanding in the literature. Furthermore, the opportunities to use internal friction to characterize the interaction between hydrogen and these defects and to give more insight into the hydrogen embrittlement mechanism are discussed. It is demonstrated that internal friction has not yet been used to its full potential for this purpose, although it entails the opportunity to develop fundamental insights into the hydrogen embrittlement phenomenon.

(Invited) Corrosion Behavior and Hydrogen Permeation of Steel Materials Under Wet-Dry Cyclic Environment

Higher strength steels have been required from the viewpoint of safety and energy saving in the fields of transportation equipment and infrastructure. However, it is known that the higher the strength of steels, the higher the risk of hydrogen embrittlement. It has been reported that hydrogen embrittlement occurs even in atmospheric corrosive environment, and solving the problem of hydrogen embrittlement will be the key to the future hydrogen energy society. For that purpose, it is necessary to clarify the hydrogen embrittlement behavior due to atmospheric corrosion. We focused on surface potential measurement as a technique to visualize permeated hydrogen. The purpose of this study is to clarify the hydrogen permeation behavior of steel materials under atmospheric corrosive environment.A 50 x 50 x 0.5t mm of pure iron plate was used as the sample. After grinding both surfaces of samples and degreasing with ethanol, nickel plating was applied to the hydrogen detective side of the sample. Hydrogen penetration was accelerated by a wet-dry cyclic corrosion test using a droplet of 0.5 M NaCl solution. The distilled water was added after second cycles to avoid the accumulation of NaCl. The potential of the hydrogen detective surface was measured with time in the drying process by surface potential device. The surface potential probe is set on the XY stage and the surface potential distribution can be obtained by scanning the probe. In this study, the surface potential of the copper plate in contact with the sample was adjusted at 0V as the reference potential.Although the corrosion occurred on the surface in the drying process after dropping the NaCl solution, no surface potential change was observed on the hydrogen detective side of the sample in that process. The surface potential started to change in a part of the surface of the sample immediately after the droplet was completely dried, and after 1hour, the size and shape of the potential changed area became almost the same as those of the corrosion products. No corrosion occurred on the hydrogen detective side of samples during the surface potential measurement, indicating that the surface potential change is attributed to the atomic hydrogen penetrated through the samples. The surface potential changed area gradually disappeared, and almost no potential change was observed on the surface after 72 hours. The change in surface potential after the second cycle of wet and dry cyclic corrosion test showed the same tendency as in the first cycle, and a potential distribution close to the shape of corrosion products was observed.

Key technologies for thermodynamic cycle of precooled engines: A review

The precooled combined cycle engines were proposed to overcome the limitation of Mach number due to high-temperature inlet. However, there has been little discussion about the thermodynamic cycle of these engines. Therefore, the current research progress and key technologies in the precooled engine thermodynamic cycle are analyzed and summarized in detail in this study. The main precooled engines, specifically ATREX and SABRE, are compared. The engine precooling cycle can be divided into direct and indirect precooling cycles. By comparing the performance of the direct precooling cycle ATREX engine in the non-precooling and precooling modes, the advantages of this engine in terms of specific thrust, compressor boost ratio, and flight Mach number are examined. The SABRE engine with an indirect precooling cycle not only solves the problem of hydrogen embrittlement of the precooler, but also achieves higher thrust and specific impulse than the ATREX engine. However, the ATREX engine with a direct precooling cycle is simpler in structure and has less adjusting variables, and thus, it is suitable for application in high-speed aircraft with a low flow rate. In addition, comparing the precooling cycle working mediums, the hydrogen medium shows excellent performance but has a limited aircraft flight range. Conversely, the use of a hydrocarbon fuel in the aircraft results in a longer flight range but with relatively low performance. Therefore, a development trend toward multi-fuel hybrid use can be expected.

The stressed state of a titanile shell operating in a medium with hydrogen

Improving reliability in the operation of equipment operating in a water-containing environment is associated with solving the problem of hydrogen embrittlement of metals. In the absence of a rigorous physical theory, it becomes necessary to predict the carrying capacity of various structures based on the available experimental data showing a decrease in the mechanical properties of materials in contact with hydrogen. In this paper, a solution is given to a physically nonlinear problem of determining stresses in a titanium shell. When integrating resolving equations, the method of SK Godunov’s discrete orthogonalization is applied. Due to the fact that hydrogen most noticeably reduces the plastic properties of metals, the construction has revealed a dangerous point with a maximum intensity value of tangential stresses. The regularities of changes in the intensity of shear deformations at the dangerous point of the shell during an emergency pressure increase in the apparatus have been found. It is shown that an emergency pressure increase in the shell may lead to the appearance of plastic deformation zones, and the effect of hydrogen is manifested in the reduction of the breaking load.

Hydrogen embrittlement and notch tensile strength of pearlitic steel: a numerical approach

This paper offers a numerical approach to the problem of hydrogen embrittlement and notch tensile strength of sharply notched specimens of high-strength pearlitic steel supplied in the form of hot rolled bars, by using the finite element method in order to determine how the notch depth influences the concentration of hydrogen in the steady-state regime for different loading values. Numerical results show that the point of maximum hydrostatic stress (towards which hydrogen is transported by a mechanism of stress-assisted diffusion) shifts from the notch tip to the inner points of the specimen under increasing load, with numerical evidence of an elevated inwards gradient of hydrostatic stress “pumping” hydrogen inside the sample.

Finite Element Modeling of the Behavior of a Hollow Cylinder in a Hydrogen-Containing Environment

The two main research orientations on the problem of hydrogen embrittlement are examined: the study of fundamental principles and the disclosure of micromechanisms and the relation between hydrogen embrittlement and metal aging; the development of models and methods for predicting the kinetics of change in stress-strain state and for evaluating the longevity of structures subjected to hydrogen embrittlement. The state of the problem of hydrogen embrittlement of metals in the first direction is briefly analyzed. More attention is paid to the importance of predicting the behavior of charged metal structures under the influence of hydrogen embrittlement. We then examine the use of finite element modeling using the ANSYS software to compute the calculation analysis of a hollow cylinder subjected to internal and external pressures and hydrogen embrittlement. The cylinder material is nonlinear elastic and its properties depend on the hydrogen concentration at each point of the cylinder. Consideration is given to the influence of the rigidity of the stress state and the hydrogen concentration on the diffusion kinetics of hydrogen in the cylinder body. The problem is solved in time steps. The distributions of the hydrogen concentration and the stresses for a quarter of the volume of the cylinder are given, as well as the graphs of these values ​​according to the thickness of the wall of the cylinder at different times. It is shown that the ANSYS software package adapted to the resolution of such problems can model the behavior of different structures in a hydrogen-containing environment, taking into account the effects caused by both the influence of hydrogen on mechanical properties of the material and by the stress state of the structures, as well as by the influence of the stress state on the interaction kinetics of hydrogen with the structures.

Investigation of Mechanical Tests for Hydrogen Embrittlement in Automotive PHS Steels

The problem of hydrogen embrittlement in ultra-high-strength steels is well known. In this study, slow strain rate, four-point bending, and permeation tests were performed with the aim of characterizing innovative materials with an ultimate tensile strength higher than 1000 MPa. Hydrogen uptake, in the case of automotive components, can take place in many phases of the manufacturing process: during hot stamping, due to the presence of moisture in the furnace atmosphere, high-temperature dissociation giving rise to atomic hydrogen, or also during electrochemical treatments such as cataphoresis. Moreover, possible corrosive phenomena could be a source of hydrogen during an automobile’s life. This series of tests was performed here in order to characterize two press-hardened steels (PHS)—USIBOR 1500® and USIBOR 2000®—to establish a correlation between ultimate mechanical properties and critical hydrogen concentration.

Phenomenon of embrittlement in titanium shells from hydrogen exposure

Increasing the reliability of equipment used for production, transportation, storage and utilization of hydrogen is directly related to solving the problem of hydrogen embrittlement of metals. Without a fundamental physical theory, it is necessary to predict the bearing capacity of metal structures on the basis of obtained experimental data on the effect which hydrogen have on metal properties. This paper presents a solution (based on the method of discrete orthogonalization proposed by S.K. Godunov) of a physically-nonlinear problem of stress distribution in a titanium shell. Since hydrogen, most notably, reduces plastic properties of metals utilized in structural elements, a critical point was determined where the intensity of shear deformation is maximal. It was found how the intensity changes at a critical point of a shell if the pressure within the device rises to an emergency level. Such a rise of the pressure in the shell could lead to appearance of plastic deformation regions, and hydrogen exposure is manifested in reduced breaking stress and changed fracture pattern.

Hydrogen Embrittlement of Dissimilar Steel Welding Joints

Aiming at the problem of hydrogen embrittlement in dissimilar steel welded joints, the hydrogen permeation behavior and stress corrosion sensitivity of the material in sea water were studied by hydrogen permeation test, electrochemical test and slow strain rate tensile test (SSRT), and the fracture morphology was observed with SEM. The results show that the corrosion resistance and hydrogen permeation characteristics of dissimilar steel welded joints are obviously different. The corrosion resistance of the weld zone is between two parent materials. The corrosion resistance of A side HAZ is the worst, and hydrogen evolution reaction is easy. Under the condition of different polarization potential, the material gradually changes from ductile fracture to brittleness with the negative shift of the polarization potential. When the cathodic polarization potential is negative to -950 mV, the welding joints have obvious characteristics of hydrogen embrittlement.

Positron Spectroscopy of Defects in Hydrogen-Saturated Zirconium

Zirconium alloys, such as Zr-1Nb are widely used as cladding materials for nuclear fuel elements of light water reactors. Hydrogen embrittlement problem causes degradation of these parts of nuclear reactors. It is known, that hydrogen uptake causes changes in microstructure and defect structure of metals. The aim of this work is study of Zr-1Nb alloys’ defect structure after hydrogen saturation up to the concentration of 600 ppm. Saturation of hydrogen was carried out from the gas phase under high temperature and pressure. This study reveals the increase of average positron lifetime with the increase of hydrogen concentration. Value of the average positron lifetime achieves plateau when the concentration of hydrogen is about 600 ppm. Also the following effects were detected in the material after hydrogen uptake up to different concentrations: crystal lattice expansion, dislocations and vacancy-like defects formation, as well as the defect-hydrogen complexes formation.

AE Monitoring of Hydrogen Embrittlement Crack in Maraging Steel

AE (Acoustic Emission) result from initiation and propagation of cracks in materials. Then AE monitoring can detect the micro cracks. Maraging steels witch have superior strength are used as structural materials. However, these have hydrogen embrittlement problem under humid air. Hydrogen embrittlement resistance of maraging steels is usually estimated by visual testing (VT) which checks whether rupture or not in laboratory. However the testing method is batch style testing. Then it is difficult to estimate the exact rupture time through VT. Then the AE monitoring applied to detect hydrogen embrittlement of maraging steel. Hydrogen embrittlement crack accelerated by a droplet of NaCl solution that was set on the center of the maraging steel thin plate. In this case, the droplet was too small to determine the hydrogen embrittlement crack through the electrochemistry method.AE sensor also set on the plate and detected AE signals.AE signals were classified as to amplitude, frequency, and wave form. AE event rate was also focused. The surface crack propagation was also recorded by digital camera. Crack growth was confirmed from the pictures. AE event counts separate 3 regions. At first region, AE event counts detect before surface cracks were able to be observed. In this region, cracks may initiate under the droplet. At Second region, AE event counts were constantly increased. In this region it was observed that increment by crack growth was constant by digital camera. It shows that means the second region was the crack growth stage. At third region, AE event rate was increased twice. The second crack growth was observed in digital camera images. Then AE event rate reflected the number of cracks. There was good relation between crack propagation and AE event rate. AE event rates were difference between types of steels. The other steel which has high hydrogen embrittlement resistance tend to have low AE events rate.

404 プラズマチャージしたアルミニウム合金中の水素挙動(OS4-(1),OS4 オーガナイズドセッション《材料・組織と加工》)

In recent years, environmental problems such as drain on fossil fuels and global warming has been growing serious problems. Auto manufacturers are making in the development of fuel cell vehicles using hydrogen as clean energy. A high pressure storage is a mainstream method to store hydrogen in the fuel cell vehicles, but aluminum alloy that is used for high pressure container as liner material has the problem of hydrogen embrittlement. To elucidate mechanism for the hydrogen embrittlement, it is effective to charge the metallic specimen with large amount of hydrogen and to observe the behavior of the hydrogen in laboratory level. There is plasma charging method as one method for hydrogen charging. It is reported to introduce a large amount of hydrogen and not to make oxide film. In this study, the behavior of hydrogen in three aluminum alloys whose compositions are close to 2024 and 7075 has been investigated by mean of hydrogen microprint technique (HMPT) and thermal desorption spectroscopy (TDS).

DC Magnetron Sputtering of B2 Phase Feal(111) Single-Crystal-Like Films and Hydrogen Damage Behavior

B2 ordered FeAl intermetallic is an important candidate for high-temperaturestructural materials, and its hydrogen embrittlement problem has attracted wide attentions in recent decades. In this paper, we prepared single-crystal-like B2-FeAl (111) thin films on Si (111) substrate using the conventional magnetron sputtering method, and studied the phase composition and the influences of hydrogen on FeAl (111) films by X-ray diffraction (XRD), scanning electron microscopy (SEM), Atomic force microscope (AFM) and transmission electron microscope (TEM) analysis. The preffered growth mechanism of FeAl (111) film and its hydrogen induced modification were discussed.

Effect of Hydrogen and Magnetic Field on the Mechanical Behavior of High Strength AISI 4340 Steel

Presence of hydrogen in materials is known to affect their mechanical properties due to hydrogen embrittlement problem. Steels used in various applications are prone to be exposed to aqueous electrochemical environments, which may introduce hydrogen into the alloy. These alloys are also prone to be simultaneously exposed to magnetic field, which may affect the hydrogen embrittlement susceptibility of these alloys. Therefore, it is important to examine the effect of hydrogen and magnetic field on the mechanical behavior of iron-based alloys. In this work, the effect of hydrogen and magnetic field on the fracture behavior of high strength AISI 4340 steel was examined. Three-point bend test was used to study the fracture behavior. In all the cases, the samples tested with hydrogen charging show a drastic reduction in ductility and fracture stress values. The effect of magnetic field was seen to be negligible. The hydrogen embrittlement was characterized by a change in the fracture surface from a ductile-type fracture to a brittle cleavage-type fracture. Acoustic emission signals collected during the test corresponds to the fracture behavior.