Advances in Hydrogen Embrittlement Study

Here, we present a review of the hydrogen embrittlement behavior of face-centered cubic (FCC) alloys with short-range order (SRO) of solute atoms. In this paper, three types of FCC alloys are introduced: Fe–Mn–C austenitic steels, high-nitrogen steels, and CoCrFeMnNi high-entropy alloys. The Fe–Mn–C austenitic steels show dynamic strain aging associated with Mn–C SRO, which causes deformation localization and acceleration of premature fracture even without hydrogen effects. The disadvantageous effect of dynamic strain aging on ductility, which is associated with the deformation localization, amplify plasticity-assisted hydrogen embrittlement. Cr–N and Co–Cr–Ni SRO effects in high-nitrogen austenitic steels and high-entropy alloys enhance the dislocation planarity, which causes stress concentration in the grain interior and near the grain boundaries. The stress concentration coupled with hydrogen effects causes quasi-cleavage and intergranular fractures.

Investigations of hydrogen concentrations and acoustic anisotropy in single-crystal nickel-based specimens were carried out. The growth of creep and thermal fatigue cracks for different modes of thermomechanical loading was studied. Experimental data and theoretical estimates of acoustic anisotropy in specimens with crystallographic direction \( \langle 011 \rangle \) of face-centered cubic lattice were obtained. It was found that anisotropy of elastic modulus provides a main contribution to acoustic anisotropy in the case of single-crystal alloys. Measurements of hydrogen concentrations revealed its accumulation after thermomechanical loading in a weakly bound state along edges of specimens to the level of 4 ppm. It indicates a significant degradation of mechanical properties and the presence of developed hydrogen embrittlement. The obtained results allow one to develop an integrated approach for estimating the residual life of single-crystal structures by analyzing hydrogen concentrations and acoustic anisotropy parameters.

The work is devoted to study the influence of damaged surface layer on mechanical properties of metal structures. Comparative studies of acoustic anisotropy distributions and dissolved hydrogen concentrations measured according to the vacuum heating method were carried out. The correlation of distributions in rolled steel and aluminum specimens after elasto-plastic and fatigue destruction was revealed. The obtained results indicate the possibility of using the acoustoelasticity method for detecting localized plastic deformations, surface microcracking, and zones with increased concentrations of dissolved hydrogen in metal. It can be used to develop new nondestructive ultrasonic approaches in technical diagnostics of metal structures.

In the framework of the diffusion equation, we discuss the influence of hydrogen distribution in the sample on thermal desorption spectroscopy. We show that non-uniform hydrogen distribution after precharging may significantly affect the Choo-Lee plot. We demonstrate that taking into account influence of hydrogen distribution is important for understanding experimental results. Good comparison of experimental and modeling data is also shown.

Understanding the interaction of hydrogen with a steel microstructure is key toward further material development and a potential future hydrogen based economy. A reliable determination of the hydrogen diffusivity and trapping are crucial hereto. Electrochemical permeation is mainly used for the former, while thermal desorption spectroscopy (TDS) is opted for the latter. Combination of both, together with a detailed microstructural evaluation, provides fundamental insights for the engineering of suitable hydrogen traps and diffusion barriers. Finally, in-situ mechanical testing enables to evaluate the hydrogen embrittlement susceptibility and identifies the active deformation mechanism. This chapter summarizes some recent experimental advances and developments of our research group. At first, focus lies on the electrochemical permeation technique, which has been expanded to apply a constant load to the materials to evaluate the influence of stresses on hydrogen diffusivity during in-situ hydrogen permeation. Elastic load on dual-phase steel increases hydrogen diffusion due to crystal lattice expansion, while plastic deformation decreases diffusion due to the formation of lattice discontinuities, e.g., dislocations. Next, the ability to assess hydrogen trapping in austenite-containing materials is critically assessed for a duplex stainless steel, revealing that the TDS data are dominated by hydrogen diffusion in these low diffusivity materials. In-situ interrupted tensile testing on these materials is further complemented with scanning electron microscopy—electron backscatter diffraction analysis. \(\varepsilon \)- and \(\alpha \)’-martensite are found in austenite of the hydrogen-charged tensile specimens, while these martensitic transformation do not show in the uncharged samples. This is, among others, explained by a reduction in stacking fault energy due to the presence of hydrogen. Hydrogen-assisted cracks also initiate in these materials, mainly in the austenite phase. Finally, the hydrogen sensitivity is evaluated for high strength-low ductility Fe–C steels. Due to their brittle nature, a novel in-situ three-point bending setup is developed to evaluate their sensitivity to hydrogen. Hydrogen causes a transition from a microvoid (Fe–0.2C), intergranular (Fe–1.1C), or mixed (Fe–0.4C) fracture surface (air-tested samples), to a hydrogen-induced cleavage fracture appearance. This is accredited by the Hydrogen Enhanced Plasticity Mediated Decohesion mechanism, proposing that hydrogen is preferentially trapped at packet or block boundaries in high carbon steels, while lath martensitic boundaries play a minor role in the crack development.

Macroscopic testing of the hydrogen embrittlement (HE) resistivity of ultra and advanced high-strength steels is still a difficult task. Different testing procedures are recommended in literature, such as the slow strain rate (SSR) test, the constant load (CL) test, or the incremental step load (ISL) test. Nevertheless, a direct comparison of the results of the different testing procedures is challenging and the influence of the microstructure is not well understood. Therefore, the present work contributes to a deeper understanding of the role of internal hydrogen diffusion and trapping at microstructural defects during SSR testing of notched samples using physical reasonable diffusion-mechanical finite element (FE) simulations. The modeling approach allows a detailed study of the role of macroscopic strength and multiple trapping sites on the local hydrogen accumulation at the notch.

The chapter focuses on calculation of the effective diffusion coefficient of a porous material accounting for the volume fraction, shape of pores, and their distribution over orientations in a three-dimensional solid. The existing pores are considered as embedded inhomogeneities possessing a high diffusivity in comparison with a matrix. The segregation effect is taken into account. Maxwell homogenization schemes in terms of diffusivity and resistivity contribution tensors are used. Inhomogeneities are assumed to have a spheroidal shape. The paper considers diverse microstructural patterns, namely, (1) arbitrary orientation distribution of pores, (2) orientational scatter of pores about a preferential orientation, (3) arbitrary orientation distribution of rotational axes of spheroidal pores in one plane. Application of the model to problems related to hydrogen damage is discussed.

In this work, we carry out experiments on the extraction of hydrogen from amorphous titanium hydrides by Vacuum Hot Extraction method. Based on the obtained experimental data, we construct thermal desorption spectra with a stepwise change in the extraction temperature. Using the Kissinger model for decomposition of a solid as for a chemical reaction of the first order, we construct the Arrhenius dependences to calculate the activation energy for the decomposition of titanium hydrides. For the same temperature ranges, the hydrogen binding energies determined for each of the samples differ several times, and the activation energy decreases with increasing temperature. At the same time, for a temperature range of 350–370 \(^\circ \)C, the activation energy tends to infinity. This effect commonly is explained by the influence of traps corresponding to the chemical composition and microstructure of the material. We question this explanation, since we study various samples of the same chemical compound, and the resulting activation energies are in the range that does not correspond to the value of the chemical bond energies.

Within the framework of linear nonequilibrium thermodynamics, we construct a new model of the diffusion of a gas component into a solid under thermo-mechanical loads. Assuming that we have a linear elastic behaviour of the solid, we obtain a local balance equation for the diffusion of the gas component, which takes into account the stress–strain state of the solid and its mutual influence on the diffusion process, the temperature in the system, and the concentration of the gas component infiltrated into the solid. We specify the model for the case of hydrogen diffusion into metal. The solution of the obtained differential equation shows that taking into account the stress–strain state strongly affects the distribution of hydrogen inside the metal. We found that the concentration quickly increases at the boundary layer, in which the hydrogen concentration exceeds the amount in bulk by more than a hundred times, which is consistent with experimental data on the skin effect when metals are saturated with hydrogen.

During the last few decades, keen attention has been paid to the advanced steels with the ultra-fine-grained (UFG) microstructure manufactured by severe plastic deformation (SPD) techniques. Although these materials often demonstrate prominent mechanical properties, the detrimental environmentally induced effects, such as hydrogen embrittlement (HE), which may appear during their service life, have been just scarcely studied. In particular, the influence of the hydrogen concentration and strain rate, which are among the main factors controlling HE, in general, has not been considered in UFG ferritic steels as yet. Thus, the objective of the present study was to examine the effect of these factors on the mechanical behaviour and fracture mode of the low-alloy steel processed by ECAP in comparison with the conventionally fabricated counterparts. The ECAPed and as-received specimens of the low-alloy steel grade 09G2S were cathodically hydrogen charged at different current densities and then subjected to tensile testing at two different strain rates. The diffusible hydrogen concentration in the specimens before tensile testing was assessed by the hot extraction method. After hydrogen charging both as-received and ECAPed specimens demonstrate HE the extent of which increases with the increasing hydrogen concentration and decreasing strain rate. It is found that the ECAPed steel occludes much higher hydrogen concentration than the as-received one. At the given hydrogen concentration, the ECAPed specimens demonstrate stronger hydrogen-induced ductility loss as well as a fundamentally different fracture mode in comparison to the as-received counterparts.

The models of the wave description of the hydrogen concentration in materials are discussed and compared. Special attention is paid to the role of nonlinear effects.

Hydrogen interaction with steels and metallic alloys, in general, is an old issue, but the interest in the phenomenon is incredibly increased in recent years. From the ’90s of the last century up to today, the papers about Hydrogen Embrittlement (Scopus, Elsevier, Amsterdam, [1]) are almost tripled! This establishes the growing attention on this topic, due also to the development of hydrogen-based economy. In Oil & Gas industry, hydrogen–steel interaction and related phenomena are often related to corrosion reactions, a consequence of the severe sour environments typical of this industrial sector. This is the reason why corrosion is the second most frequent cause of pipeline failures (Yang et al., Reliab Eng Syst Saf 159, 214–222, [2]), with the peculiar result of dangerous substances released in the environment, and it has translated into a continuous development of new technologies to monitor and control the ‘corrosion state’. The present work aims at characterizing the hydrogen susceptibility of X60 steel, a High-Strength Low-Alloy (HSLA) steel, widely used in Oil & Gas industry. The study is carried out by means of a rigorous approach based on traditional scientific techniques; moreover, an innovative solution was developed, validated and proposed to approach the possibility of on-field monitoring of operating pipelines.

Aluminum alloys are very popular in a variety of technical applications. The strong influence of hydrogen on the properties of aluminum alloys is known, however, as in the case of steels; it is continuously increasing as new alloys with extreme properties are developed and introduced. Scientific research in the field of the hydrogen effect on the properties of aluminum alloys is mainly focused on the fundamental aspects such as the diffusion coefficients of hydrogen in aluminum, possible types of hydrogen traps, and their effect on the microstructure of alloys. At the same time, the industry has a problem of cracking ingots and semi-finished products (sheets, pipes, and plates), including their further processing and welding. In contrast to the high-strength steels, scientific research does not actually provide specific values for critical hydrogen concentration. The problem of separating the hydrogen adsorbed on the surface and dissolved during measurements has not been solved. There are only a few types of aluminum alloy reference specimens. The article is intended to partially fill this gap. It provides specific examples of the study of technological problems and proposes the measurement methods that allow the separation of hydrogen dissolved and adsorbed on the surface.