Hydrogen Pre-charging Research Articles

Synergistic Effects of Pre-charged Hydrogen and Tensile Stress on the Stress Corrosion Cracking of 2024-T351 Aluminum Alloy

Synergistic Effects of Pre-charged Hydrogen and Tensile Stress on the Stress Corrosion Cracking of 2024-T351 Aluminum Alloy

Very high cycle fatigue properties of ultrahigh strength steels in the presence of hydrogen

The very high cycle fatigue (VHCF) properties of 2000 MPa ultrahigh strength martensitic steels after hydrogen pre-charging were investigated by means of ultrasonic fatigue tests. Results showed that the VHCF lives of the experimental steels were drastically decreased by about two orders after pre-charged with a hydrogen concentration of CH = 1.23 wppm. The experimental steel tempered at a higher temperature of 300 °C with some epsilon-carbides and a lower density of dislocations showed higher VHCF lives in the presence of hydrogen. It could be attributed to the lower hydrogen diffusion coefficient since hydrogen might accelerate fatigue crack propagation in the granular bright facet (GBF) area.

Hydrogen Embrittlement Detection Technology Using Nondestructive Testing for Realizing a Hydrogen Society.

Crack detection in high-pressure hydrogen gas components, such as pipes, is crucial for ensuring the safety and reliability of hydrogen infrastructure. This study conducts the nondestructive testing of crack propagation in steel piping under cyclic compressive loads in the presence of hydrogen in the material. The specimens were hydrogen-precharged through immersion in a 20 mass% ammonium thiocyanate solution at 40 °C for 72 h. The crack growth rate in hydrogen-precharged specimens was approximately 10 times faster than that in uncharged specimens, with cracks propagating from the inner to outer surfaces of the pipe. The fracture surface morphology differed significantly, with flat surfaces in hydrogen-precharged materials and convex or concave surfaces in uncharged materials. Eddy current and hammering tests revealed differences in the presence of large cracks between the two materials. By contrast, hammering tests revealed differences in the presence of a half size crack between the two materials. These findings highlight the effect of hydrogen precharging on crack propagation in steel piping and underscore the importance of early detection methods.

Grain refinement's effect on hydrogen embrittlement of 304 austenitic stainless steel: A comparative investigation of hydrogen in-situ charging vs. pre-charging

Controversy surrounds the potential of grain refinement in suppressing metal hydrogen embrittlement (HE). The literature presents two methods for introducing hydrogen into metals: hydrogen pre-charging (HPC) and hydrogen in-situ charging (HISC). This study compares the effect of grain refinement on HE under electrochemical HPC and HISC conditions, focusing on type 304 austenitic stainless steel with a grain size range of 0.5–35 μm. HE behaviors were evaluated through tensile testing and fracture morphology analyses, while hydrogen diffusion and concentration were examined using hydrogen uptake amount measurements and hydrogen permeation tests, complemented by finite element (FE) simulations. Results indicate that coupling with plastic deformation significantly accelerated hydrogen transport in the HISC condition, leading to higher apparent hydrogen diffusivity compared to the HPC condition, with grain boundaries (GBs) act as hydrogen traps. Under the HISC, grain refinement reduced HE susceptibility by decreasing the apparent diffusivity due to an increased trapping effect of GBs and suppressing intergranular fracture by reducing the hydrogen amount distributed to each GB (hydrogen occupancy of the GBs). However, grain refinement to below 1 μm increased HE under the HPC condition. Hydrogen permeation tests showed that under the HPC, grain refinement slightly decreased hydrogen diffusivity. In the ultrafine-grained specimen, as GBs trapped more hydrogen atoms, they not only provided hydrogen to stress-concentrated lattices and newly-formed dislocations by detrapping but also maintained a higher hydrogen occupancy of the GBs, thus increasing HE. It is concluded that whether grain refinement suppresses HE depends primarily on the resulting hydrogen occupancy of the GBs, which is influenced by the charging conditions rather than the quantity of traps.

Unveiling the roles of initial phase constituents and phase metastability in hydrogen embrittlement of TRIP‐assisted VCrCoFeNi medium‐entropy alloys

Medium-entropy alloys (MEAs) that exhibit transformation-induced plasticity (TRIP) from face-centered cubic (FCC) to body-centered cubic (BCC) are considered promising for liquid hydrogen environments due to their remarkable cryogenic strength. Nonetheless, studies on hydrogen embrittlement (HE) in BCC-TRIP MEAs have not been conducted, although the TRIP effect and consequent BCC martensite usually deteriorate HE susceptibility. In these alloys, initial as-quenched martensite alters hydrogen diffusion and trap behavior, and deformation-induced martensitic transformation (DIMT) provides preferred crack propagation sites, which critically affects HE susceptibility. Therefore, this study aims to investigate the HE behavior of BCC-TRIP MEAs by designing four V10Cr10Co30Fe50–xNix (x = 0, 1, 2, and 3 at%) MEAs, adjusting both the initial phase constituent and phase metastability. A decreased Ni content leads to a reduced fraction and mechanical stability of FCC, which in turn increases HE susceptibility, as determined through electrochemical hydrogen pre-charging and slow-strain rate tests The permeation test and thermal desorption analysis reveal that the hydrogen diffusivity and content are affected by initial BCC fraction, interconnectivity of BCC, and refined FCC. As these initial phase constituents differ between the alloys with FCC- and BCC- dominant initial phase, microstructural factors affecting HE are unveiled discretely among these alloy groups by correlation of hydrogen-induced crack behavior with hydrogen diffusion and trap behavior. In alloys with an FCC-dominant initial phase, the initial BCC fraction and DIMT initiation rate emerge as critical factors, rather than the extent of DIMT. For BCC-dominant alloys, the primary contributor is an increase in the initial BCC fraction, rather than the extent or rate of DIMT. The unraveled roles of microstructural factors provide insights into designing HE-resistant BCC-TRIP MEAs.

Effect of Quenching Cooling Rate on Hydrogen Embrittlement of Precipitation-Hardened Martensitic Stainless Steels

Heat treatment plays a decisive role in the microstructure of metallic materials. The effect of cooling rate changes caused by the quenching medium on the microstructure of steel materials should be clarified. In this study, the effect of the quenching cooling rate on the microstructure of two precipitation-hardened martensitic stainless steels was investigated. The mechanical properties and hydrogen embrittlement susceptibility effected by the changes in the microstructure were also analyzed. A slow tensile test and hydrogen pre-charging were carried out to obtain the hydrogen embrittlement susceptibility parameters of the specimens. The results show that the quenching cooling rate only affects specific microstructures, including the twin structure and misorientation angle. Before hydrogen charging, the mechanical properties of the precipitation-hardened martensitic stainless steels were not affected by changing the quenching cooling rate. After hydrogen charging, the hydrogen embrittlement susceptibility decreased as the quenching cooling rate increased.

Experimental and numerical study on high-cycle fatigue performance of austenitic stainless steel with pre-charged hydrogen

High-cycle fatigue performance is one of the crucial issues for hydrogen diaphragm compressors, as hydrogen embrittlement affects the components in a high pressure hydrogen environment. In this study, the high-cycle fatigue response of MP7, a novel material of austenitic stainless steel designed for hydrogen diaphragm compressors, is investigated by tests and by numerical ways using the Crystal Plasticity Finite Element Method (CPFEM). The uniaxial tensile tests and fatigue tests are carried out on MP7 specimens with different levels of pre-charged hydrogen. The analysis indicates that, even for MP7 with the improved hydrogen resistance performance, both the ductility and the fatigue limit are still affected by the pre-charged hydrogen in a considerable way. Based on the principles of crystal plasticity theory, a CPFEM model is established and a fatigue life prediction model for austenitic stainless steel with pre-charged hydrogen is proposed. This model successfully predicts the fatigue life under different hydrogen contents and stress amplitudes, and the predicted fatigue lives are well-fitted to S-N curves within a two-fold error band.

Comprehensive effect of grain boundaries and grain boundary carbides on the hydrogen embrittlement of GH3536

In this work, the effects of the grain boundaries (GBs) and GB carbides on the hydrogen embrittlement (HE) of GH3536 superalloy were investigated. The GBs and (Cr, Mo)-enriched M23C6 carbides at GBs would lead to the dominating intergranular brittle fractures after electrochemical hydrogen pre-charging. The GBs and GB carbides act as hydrogen traps to promote the hydrogen-assisted crack initiation and further propagation at the interfaces between the GB carbides and matrix, which ultimately leads to the brittle fracture. With decreasing the solid solution temperature from 1150 °C to 950 °C, the average grain size refined from 23.9 ± 1.3 μm to 14.5 ± 0.3 μm, resulting in the superior HE resistance and less brittle fracture region. The study may be instructive for designing HE-resistant superalloys for hydrogen-fueled gas turbines in the future.

Effect of precharging methods on the hydrogen embrittlement of 304 stainless steel

Electrochemical and gaseous hydrogen precharging are representative methods for evaluating hydrogen embrittlement in metallic materials. In this study, the effects of these methods on the tensile properties and microstructural deformation behaviors of austenitic stainless steel (304 L) were investigated. The tensile properties and microstructural deformation behaviors of precharged and unprecharged specimens were compared through conventional and in situ tensile tests, and the resulting differences were verified. Hydrogen precharging causes ductility reduction and changes in the fracture mode of 304 L stainless steel. Microcrack nucleation and propagation were unrelated to the hydrogen precharging method. However, the precharging methods differed in terms of the penetration depth of hydrogen and trapping sites. In the case of electrochemical hydrogen precharging, the hydrogen concentrations on the surface and at the center differed, and hydrogen was mainly trapped in grain boundaries. However, in the case of gaseous hydrogen precharging, the interior had a uniform hydrogen concentration, and hydrogen was mainly trapped inside the lattice. The hydrogen precharging methods induced differences in mechanical properties and microstructures. The effect of hydrogen on the deformation behavior of 304 L stainless steel was the same regardless of the precharging method. However, the effect of hydrogen was observed at different elongated displacement levels depending on trapping sites.

Hydrogen induced cracking behavior of the dual-phase Co30Cr10Fe10Al18Ni30Mo2 eutectic high entropy alloy

In this paper, the hydrogen induced cracking behavior of the Co30Cr10Fe10Al18Ni30Mo2 eutectic high entropy alloy was studied. The results showed that the strength and ductility of the alloy decreased after hydrogen pre-charging, and quasi-cleavage fracture features and hydrogen-induced cracks were found. Moreover, the cracks induced by hydrogen pre-charging were found to propagate along the two-phase interface and inside the BCC phase.

Extraction of reversible hydrogen trapped on prior austenite grain boundaries and promoting intergranular fracture in the elastic region of tempered martensitic steel by utilizing frozen-in hydrogen distribution at -196 °C

Factors that promote hydrogen-related intergranular (IG) fracture in the elastic region of tempered martensitic steel have been identified utilizing frozen-in hydrogen distribution and tensile tests in liquid nitrogen at -196 °C. Tensile test results at room temperature (R.T.) after precharging with 12.1 mass ppm of hydrogen showed hydrogen embrittlement associated with IG fracture. Although tensile test results at -196 °C after precharging with the same amount of hydrogen did not show hydrogen embrittlement with IG fracture, those at -196 °C after preloading with elastic stress just before fracture strength at R.T. showed hydrogen embrittlement with IG fracture. As preloading stresses increased and preloading speeds decreased, subsequent hydrogen embrittlement susceptibility at -196 °C increased. In addition, although tensile testing at -196 °C after hydrogen precharging, preloading at R.T., and unloading at -196 °C resulted in IG fracture, testing conducted after unloading at R.T. did not. It is noted that reversible hydrogen that accumulates on prior austenite grain boundaries (PAGBs) in the presence of load and desorbs in the absence of load in the elastic region at R.T. is directly responsible for IG fracture. These findings revealed that hydrogen-related IG fracture in the elastic region of tempered martensitic steel was not caused by stress-free hydrogen distribution, but was promoted by reversibly accumulated hydrogen mainly due to stress-induced diffusion onto PAGBs during stress loading at R.T.

Hydrogen embrittlement prompt fracture in Ni-based single crystal superalloy

Hydrogen-fueled and hydrogen-hybridized aircraft engines are a new trend in the aviation industry for environmental reasons. Single crystalline Ni-based superalloys are the most commonly used engine materials and their hydrogen embrittlement properties need urgent investigation. In this study, the hydrogen embrittlement behavior and underlying fracture mechanism of a second-generation Ni-based single crystal superalloy with electrochemical hydrogen pre-charge were investigated. The superalloy showed tremendous susceptibility to hydrogen embrittlement with reduced strength and ductility. A large number of micropores and cracks on the fracture surface are found in hydrogen-charged specimens, leading to embrittlement and ultimate cracking. More dislocations, stacking faults and DSBs are observed in specimens with hydrogen uptake. Hydrogen-induced micropores first form at the γ/γ′ interface and then propagate into the γ′ phase, leading to cracking, which was analyzed using in situ environmental studies with a transmission electron microscope. Hydrogen reduces the cohesive strength between the γ- and γ′-phase and accelerates crack propagation along the voids. Hydrogen embrittlement fracture in Ni-based single crystal superalloys is due to synergistic hydrogen-enhanced local plasticity, strain-induced vacancies and decohesion in the hydrogen-induced cracking process.

Enhancing the hydrogen embrittlement resistance with cementite/VC multiple precipitates in high-strength steel

The superior hydrogen embrittlement (HE) resistance and satisfied work hardening capacity are achieved in high-strength spring steel after hydrogen pre-charging with dispersed multiple precipitates via the multi-microalloying of 1.04 wt% Cr and 0.14 wt% V. The precipitates are determined to be the triplex microstructures, i.e., the isolated (Mn, Cr, V)-enriched cementite, isolated V-enriched VC, and the co-precipitation of cementite and VC. These multiple precipitates could act as the effective hydrogen traps to achieve more potent irreversible hydrogen trapping capacity, thus inhibiting the HE susceptibility by ∼23%. Hence, the strategy of cementite/VC multiple precipitates is beneficial in designing the high-strength and HE-resistant automotive steels.

Insight into Intergranular Corrosion of the Aluminum Alloy 2024-T3: Effect of Pre-Charged Hydrogen

2024-T3 aluminum alloy has been widely applied in aviation fields, whilst the accumulation of hydrogen at grain boundaries deteriorates the mechanical properties and corrosion resistance. The intergranular corrosion of 2024-T3 related to hydrogen permeation was investigated. Atom probe tomography was used to observe the precise position of hydrogen atoms in relation to grain boundaries. The ionic current density of the H pre-charged surface was studied by in situ scanning vibrating electrode technique. Results show that the distribution of H is highly related to the S-phase at grain boundaries and the H pre-charging significantly improves the charge transfer efficiency at the initial period of intergranular corrosion process while the enhancement effect is then gradually weakened. The study provided new insight into hydrogen distribution at grain boundaries and its impact on the intergranular corrosion of 2024-T3 aluminum alloy, which can be informative and instructive for the research of corrosion in aluminum alloy.

Effects of laser powder bed fusion process parameters on microstructure and hydrogen embrittlement of high-entropy alloy

Hydrogen embrittlement behavior, micro-deformation, and crack propagation mechanism of CoCrFeNiMn high-entropy alloy (HEA) fabricated by laser powder bed fusion (LPBF) under different parameters were investigated by slow strain rate tensile tests (at room temperature) with/without electrochemical hydrogen pre-charging. The LPBF CoCrFeNiMn HEA shows excellent resistance to hydrogen embrittlement. Unsuitable LPBF parameters are accompanied by many microcracks and holes, resulting in a slight decrease in the hydrogen embrittlement resistance of the material. The electron backscatter diffraction (EBSD), electron channeling contrast image (ECCI) techniques, and transmission electron microscope (TEM) were carried out to research the main influencing factors of hydrogen on the deformation mechanism and crack propagation. Compared with un-charged samples, a larger number of deformation twins (DTs) appear in the deformation process of hydrogen-charged LPBF CoCrFeNiMn, attributing to the reduction of stacking fault energy (SFE) due to the ingress of hydrogen. The nano DTs and crossing twin system contribute to the extra work hardening, and a strain hardening platform is observed for all hydrogen-charged samples, resulting in the increase of strain hardening rate or the mitigation of the loss of strain hardening. Although unsuitable process parameters will trigger fabrication defects and reduce mechanical properties, the cellular structure can bring a hydrogen-induced strain hardening platform for LPBF CoCrFeNiMn to reduce the damage caused by hydrogen embrittlement.

Micro-mechanisms of deformation accommodation in AA7050 alloy in the presence of hydrogen

The interaction of hydrogen with dislocations in AA 7050 alloy heat treated to produce different matrix precipitates is studied using interrupted micro-tensile tests of pre-charged specimens and electron back scattered diffraction (EBSD). Hydrogen promoted slip planarity as well as sub-grain formation in the overaged condition having incoherent ƞ (MgZn2) precipitates, while it enhanced dislocation looping and pitting in case of higher density Mg-Zn precipitates (GP II) dominated alloy. For the first time, a semi-quantitative analysis on the extent of the effect of hydrogen on micro-mechanisms of deformation evolution is carried out using sufficient statistics through large area scans in EBSD. It is shown that the interaction of pre-charged hydrogen with the microstructure was unaffected by recrystallization as well as texture till 6% strain.

Crack growth rate in hydrogen pre-charged martensitic steels during slow strain rate tests

Crack growth rate in two high strength martensitic steels with the Mo contents of 0.43 wt.% and 1.06 wt.% was investigated by means of slow strain rate tests (SSRT) on compact tensile specimens after hydrogen pre-charging. It was found that the crack growth rate increased and the values of stress intensity factors KIH and KImax decreased with the increase of pre-charged hydrogen concentration. The steel with higher Mo content showed much lower crack growth rate than the steel with lower Mo content. It could be attributed to more nano-sized precipitates that can act as the hydrogen trapping sites and mitigate hydrogen deleterious effects on crack growth rate and the KIH and KImax values.

Hydrogen induced microstructure, mechanical properties and cracking evolution in a novel CoCrNiMo medium-entropy alloy

Medium-entropy alloys (MEAs) have shown exceptional hydrogen tolerance. Here we systematically investigated the hydrogen resistance evolution of a non-equiatomic Co35Ni36Cr23Mo6 MEA from microstructure, trapping site, mechanical properties and cracking. The ultimate tensile strength and ductility of Co35Ni36Cr23Mo6 at room temperature were about 840 MPa and 71%, respectively. In the case of hydrogen pre-charging for 12 h, the above values were almost unchanged, indicating excellent hydrogen resistance. Grain boundaries were the main initiation and propagation paths for hydrogen-induced secondary cracks, while no secondary crack was on the Co35Ni36Cr23Mo6 alloy without hydrogen. We also found that the non-ductile region in the fracture morphology could be generated only when the hydrogen concentration reached a certain threshold. Moreover, hydrogen not only had negative effect on the MEA, but also promoted the formation of nanotwins during deformation process in this alloy.

Hydrogen-Induced Intergranular Fracture Behavior Accelerated by Needle-like MC Carbide in IN740H Superalloy

Hydrogen embrittlement of a Ni-based superalloy, IN740H, was evaluated after gas-phase hydrogen pre-charging. Specimens with different grain sizes were prepared to induce different precipitation behavior under annealing treatment; the formation of needle-like MC carbide was found only in a specimen with a larger grain size and incoherent twin boundaries after annealing treatment at 1173 K. While other parameters including the grain size and annealing treatment turned out not to undermine the resistance to hydrogen embrittlement, the needle-like MC carbide was found to induce premature failure after hydrogen absorption.

Continuousness of interactions between hydrogen and plastic deformation of ultra-high strength steel sheet consisting of ferrite and nanometer-sized precipitates

ABSTRACT The continuousness of the interactions between hydrogen and plastic deformation of an ultra-high strength steel sheet consisting of ferrite and nanometer-sized precipitates has been investigated by tensile tests after or during cathodic hydrogen charging. In the tensile test in the air after hydrogen pre-charging, a hydrogen thermal desorption analysis shows that the amount of hydrogen desorbed decreases with increasing applied tensile strain from room temperature to 50 °C, but increases in the high temperature region. Upon tensile straining to 0.06, no hydrogen is desorbed in the low temperature region, and the change in desorption behaviour when strain exceeds 0.06 is negligible. This suggests that substantial interactions between hydrogen and plastic deformation in the test with hydrogen pre-charging occur only in the early stages of deformation. In contrast, in the tensile test during hydrogen charging, the hydrogen desorption which begins from room temperature continues even upon tensile straining to 0.06, suggesting continuous interactions, and a unique dislocation structure resembling sub-grain boundaries is observed. Upon aging at room temperature after tensile straining to 0.06 during hydrogen charging, all hydrogen desorption lower than 100 °C shifts to the high temperature region, but the recovery of elongation is not necessarily complete. When tensile strain is applied during hydrogen charging, continuous interactions presumably induce anomalous damage, thereby enhancing the degradation of ductility. The results of the present study strongly support the conclusion that the continuousness of the dynamic interactions between hydrogen and plastic deformation plays essential roles in hydrogen embrittlement of ferritic steel.