Effect Of Hydrogen Content Research Articles

Molecular investigation on physical and tensile properties of polyethylene (PE) under high-pressure hydrogen environments

Polymer liners are key components of high-pressure hydrogen storage tanks, and understanding their behaviour under such environments is crucial for safety. This study employs molecular dynamics (MD) simulation to investigate the physical and tensile properties of amorphous polyethylene (PE) under the effects of hydrogen content, pressure, temperature. It is found that hydrogen molecules decrease glass transition temperature by approximately 3%, while pressure have no noticeable impact. Meanwhile, hydrogen molecules enhance diffusivity, while pressure suppresses diffusivity and exhibits a more pronounced impact, resulting in an overall decrease of 44% in diffusivity under high-pressure hydrogen. Tensile stress also increases the diffusivity by 17%. Hydrogen molecules weaken the non-bonded molecular interactions of PE, which reduces the percentage of trans conformation and orientation parameters. Meanwhile, hydrogen also suppresses the internal energy change of PE induced by tensile deformation. Therefore, hydrogen molecules lead to a decrease in tensile properties. Comparatively, pressure causes PE to produce more trans conformations under tension, which improves orientation, entanglement parameters, and the internal energy change of PE, and finally enhances the tensile properties of PE. The effect of pressure surpasses that of hydrogen, which results in an approximately 40% increase in tensile properties under high-pressure hydrogen. This study provides molecular-level insights into the individual and coupled effects of hydrogen and pressure, forming a foundation for predicting polymer behaviour under high-pressure hydrogen conditions.

Effect of hydrogenation on fatigue crack growth resistance of diffusion bonded TC4 titanium alloy laminates

A method was proposed to improve the fatigue crack growth (FCG) resistance of TC4 (Ti6Al4V) titanium alloy laminate by hydrogenation/low-temperature diffusion bonding/dehydrogenation (H-DB-DH) combined process. Effects of hydrogen contents and different dehydrogenation temperatures on FCG behaviors and tensile properties as well as microstructures were investigated. Residual hydrogen contents beneath fatigue fracture surfaces were measured to determine the safe dehydrogenation temperature. The hydrogen content of 0.3 wt% and dehydrogenation temperature of 780 °C are optimal to produce TC4 laminate with a 9.87 % improvement of FCG life compared with the diffusion bonded one without hydrogenation. FCG rate decrease results from the comprehensive effect of recrystallization volume fraction increase, grain refinement, mean geometrically necessary dislocations (GNDs) density decrease and texture intensity weakness as well as texture diversity improvement. This paper provides theoretical support for fatigue property improvement of titanium alloy by hydrogen diffusion bonding process.

Hydrogen embrittlement and strain rate sensitivity of electrodeposited copper: part I – the effect of hydrogen content

Slow strain rate tensile testing was conducted on electrodeposited copper, which is a candidate coating material for used nuclear fuel containers. Embrittlement was observed in electrodeposited copper containing 26.4 ± 1.0 ppm hydrogen, with a strain rate sensitivity such that the embrittlement was exacerbated at lower strain rate (5 × 10−7 s−1). Tensile tests conducted at 100° and 200 °C also intensified embrittlement when compared with tests conducted at room temperature. In contrast, electrodeposited copper containing only 5.25 ± 0.97 ppm hydrogen exhibited ductile behavior at all tested strain rates and temperatures. These findings suggest that a previously unexplained slow strain rate hydrogen embrittlement can operate in electrodeposited copper provided that the hydrogen concentration is sufficiently high. Further analyses revealed that the deformation of embrittled copper is achieved by the formation of internal microcracks which coalesce at the point of failure.

Effect of hydrogen content on the high-temperature compressive deformation behavior and microstructure evolution of TC17 alloy

Thermo-hydrogen process (THP) has been an important research direction of the titanium alloy heat treatment process. However, the effect of THP on the thermal deformation behavior and microstructure evolution of TC17 alloy during hot compression has not been investigated. In this study, a series of isothermal compression experiments were carried out on hydrogenated TC17 alloy specimens in the temperature range covering the α+β phase region and β phase region of TC17 alloys with different hydrogen contents, to investigate the effect of hydrogen on the high-temperature flow behavior and microstructure evolution. The results show that the primary α phase of the hydrogenated TC17 alloy is significantly reduced. Observing the XRD pattern, the substitutional solution effect of hydrogen causes the β phase lattice to expand, resulting in a shift of the β phase toward a small angle as the hydrogen content increases. The flow stress shows a tendency to decrease and then increase with increasing hydrogen content. This is attributed to the softening effect of hydrogen on the α phase and the hardening effect on the β phase. This also leads to the deformation activation energy showing the same trend. When the hydrogen content increases to 0.4 wt%, the activation energy decreases to the lowest point by about 24 %. Finally, the appropriate hydrogen concentration can effectively reduce the destabilization region in the hot working map and expand the processing window of TC17 alloy.

Hydrogen Embrittlement of 27Cr-4Mo-2Ni Super Ferritic Stainless Steel.

The effect of hydrogen content on the deformation and fracture behavior of 27Cr-4Mo-2Ni super ferritic stainless steel (SFSS) was investigated in this study. It was shown that the plasticity and yield strength of SFSS were very susceptible to hydrogen content. The introduction of hydrogen led to a significant decrease in elongation and a concurrent increase in yield strength. Nevertheless, a critical threshold was identified in the elongation reduction, after which the elongation remained approximately constant even with more hydrogen introduced, while the yield strength exhibited a monotonic increase with increasing hydrogen content within the experimental range, attributed to the pinning effect of the hydrogen Cottrell atmosphere on dislocations. Furthermore, the hydrogen-charged SFSS shows an apparent drop in flow stress after upper yielding and a reduced work hardening rate during the subsequent plastic deformation. The more hydrogen is charged, the more the flow stress drops, and the lower the work hardening rate becomes.

Bayesian statistical model for cladding high-temperature burst under loss-of-coolant accident conditions

ABSTRACT This study developed a probabilistic determination model with respect to cladding high-temperature burst conditions based on the Bayesian statistical method to reasonably evaluate fuel behaviors under loss-of-coolant accident conditions, including fuel fragmentation, relocation, and dispersal. The candidate models (correlations) were based on the widely accepted empirical model established based on nonirradiated fuel cladding data. Explanatory variables were added to improve the applicability of these models with respect to irradiated materials and generalization performance. The posterior predictive distribution of each candidate model was evaluated using Bayesian estimation comprising 238 sets of high-temperature burst test data. The generalization performance was evaluated using information criteria. The results of model evaluation showed improved predictive performance by considering the effect of hydrogen content. A comparison with burnup as an alternative explanatory variable confirmed that hydrogen content was the better parameter and other burnup-associated effects, such as irradiation hardening of the metal matrix and oxide growth (reduction of the metal matrix), were less dominant under burst conditions.

Effects of hydrogen content on laminar burning velocity and Markstein length in outwardly propagating spherical SNG–air premixed flames

As the hydrogen content of the five synthetic natural gas (SNG) fuels fixed with the Wobbe index increases, the unstretched laminar burning velocity and Markstein length also increase. For the addition of hydrogen to natural gas pipelines, an experiment was conducted using up to 19% hydrogen gas (SNG H19). By comparing the error rates with the measured laminar burning velocities and the four reaction mechanisms, Aramco 2.0 was selected as the optimized mechanism for the SNG mixtures. The unstretched laminar burning velocities were compared with those of Aramco 2.0 for SNG–air premixed flames under elevated pressures up to 0.5 MPa for equivalence ratios (ϕ) of 0.7–1.4. The results showed that the measured laminar burning velocities were consistent with the numerical values under lean and stoichiometric conditions; however, the deviations increased under rich conditions as the hydrogen content increased. The laminar burning velocities estimated using the four mixing laws were evaluated under elevated pressure and rich conditions. Consequently, the results predicted by mass-fraction mixing and Q/k models were in good agreement with the measured values. The Markstein length decreases linearly as the hydrogen content increases, but all Markstein lengths are positive; therefore, no instability occurs in the SNG–air premixed flames. The measured Markstein lengths were compared with the theoretical Markstein lengths and reasonably traced well to the isothermal surface at 600 K. When the hydrogen content reaches up to SNG H19, the theoretical Markstein lengths overpredict the results, except for ϕ values of 0.7 and 1.4.

Effect of hydrogen content on superconductivity in La–H compounds

Finding room-temperature superconductors is one of the most important subjects in scientific search. Due to its hydrogen clathrate structures, LaH10 has become one of the widely known room-temperature superconductors under pressure. So exploring the role of hydrogen content would help understanding the mechanism of superconductivity in the hydrides. Here, we explore the evolution of hydrogen content in lanthanum hydrides based on the first-principles calculations. We found new lanthanum hydrides at pressures, such as Cmcm-LaH. The electronic properties and electron–phonon coupling have been studied and found that Fm3¯m-LaH obtained an unexpected low Tc of ∼ 0.001 K. The superconductive mechanism has been studied in LaHx (x = 0, 1, 2, 3, 8, 10), where LaH0 means elemental lanthanum. We found that low content of hydrogen depresses the electron–phonon interaction in La–H compounds before H–H bonds formed. But with the increases of H content, the strong electron–phonon coupling of H atoms would help the compounds obtain high Tc. This result would explain the lanthanum hydrides with lower H content obtain weaker electron–phonon coupling and could not became potential high-temperature superconductors.

Effect of Hydrogen Content on Pollutant Emissions and Combustion Characteristics of a Methane-Hydrogen Mixture Fueled Multi-Nozzles Array Model Combustor

Effect of Hydrogen Content on Pollutant Emissions and Combustion Characteristics of a Methane-Hydrogen Mixture Fueled Multi-Nozzles Array Model Combustor

Molecular understanding of the effect of hydrogen on graphene growth by plasma-enhanced chemical vapor deposition.

Plasma-enhanced chemical vapor deposition (PECVD) provides a low-temperature, highly-efficient, and catalyst-free route to fabricate graphene materials by virtue of the unique properties of plasma. In this paper, we conduct reactive molecular dynamics simulations to theoretically study the detailed growth process of graphene by PECVD at the atomic scale. Hydrocarbon radicals with different carbon/hydrogen (C/H) ratios are employed as dissociated precursors in the plasma environment during the growth process. The simulation results show that hydrogen content in the precursors significantly affects the growth behavior and properties of graphene (e.g., the quality of obtained graphene, which is indicated by the number of hexagonal carbon rings formed in the graphene sheets). Moreover, increasing the content of hydrogen in the precursors is shown to reduce the growth rate of carbon clusters, and prevent the formation of curved carbon structures during the growth process. The findings provide a detailed understanding of the fundamental mechanisms regarding the effects of hydrogen on the growth of graphene in a PECVD process.

Effects of hydrogen content in films on the etching of LPCVD and PECVD SiN films using CF4/H2 plasma at different substrate temperatures

AbstractThe dependences of etching characteristics on substrate temperature (Ts, from –20 to 50°C) of the plasma‐enhanced chemical vapor deposition (PECVD) SiN films (PE‐SiN) and low‐pressure chemical vapor deposition (LPCVD) SiN films (LP‐SiN) with CF4/H2 plasma were investigated. The Fourier‐transform infrared spectroscopy shows that both film types were N–H bond‐rich films, but in different hydrogen contents (PE‐SiN 22.7 at% and LP‐SiN 3.8 at%) from the Rutherford backscattering spectroscopy analyses. A higher hydrogen content led to a thinner fluorocarbon thickness because of the reaction between hydrogen outflux and C and N to form an HCN byproduct. The etch rates (ER) for the PE‐SiN were higher than that of the LP‐SiN at all Ts, due to the different FC thickness and etching mechanisms proposed. The formation of the N−Hx layer on PE‐SiN at low temperature caused the decrease in ER. For the LP‐SiN, the weak dependences of Ts on surface structure and ER were observed.

DLC coated spur gears – Part II: coating properties and potential for industrial use

PurposeThis paper aims to address the coating and compound analysis of diamond-like carbon (DLC) on steel, to understand the frictional behavior in tribological gear systems presented in paper Part I. Here, the Ti and Zr modified DLC coating architectures are analyzed regarding their chemical, mechanical and thermophysical properties. The results represent a systematic analysis of the thermal insulating effect in tribological contact of DLC coated gears.Design/methodology/approachThe approach was to evaluate the effect of the substitution of Zr through Ti at the reference coating ZrCg to TiCg and the effect on thermophysical properties. Furthermore, the influence of different carbon and hydrogen contents on the coating and compound properties was analyzed. Therefore, different discrete Ti or Zr containing DLC coatings were deposited on an industrial coating machine. Thereby the understanding of the microstructure and chemical composition of the reference coatings is increased.FindingsResults prove comparable mechanical properties of metal modified DLC independent of differences in chemical compositions. Moreover, the compound adhesion between TiCg/16MnCr5E was improved compared to ZrCg/16MnCr5E. The effect of hydrogen content Ψ and carbon content xc on the thermophysical properties is limited by Ψ = 18 at.% and xc = 90 at.%.Practical implicationsThe findings of the combined papers Part I and II show a high potential for industrial application of DLC on gears. Based on the results DLC coatings and gears can be tailored to each other.Originality/valueSystematic analysis of DLC coatings were conducted to evaluate the effect of titanium, carbon and hydrogen on thermophysical properties.

The effect of hydrogen content and yield strength on the distribution of hydrogen in steel: a diffusion coupled micromechanical FEM study

In this study, we investigate the effect of the heterogeneous micromechanical stress fields resulting from the grain-scale anisotropy on the redistribution of hydrogen using a diffusion coupled crystal plasticity model. A representative volume element with periodic boundary conditions was used to model a synthetic microstructure. The effect of tensile loading, initial hydrogen content and yield strength on the redistribution of lattice (CL) and dislocation trapped (Cx) hydrogen was studied. It was found that the heterogeneous micromechanical stress fields resulted in the accumulation of both populations primarily at the grain boundaries. This shows that in addition to the well-known grain boundary trapping, the interplay of the heterogeneous micromechanical hydrostatic stresses and plastic strains contribute to the accumulation of hydrogen at the grain boundaries. Higher yield strength reduced the amount of Cx due to the resulting lower plastic deformation levels. On the other side, the resulting higher hydrostatic stresses increased the depletion of CL from the compressive regions and its diffusion toward the tensile ones. These regions with increased CL are expected to be potential damage initiation zones. This aligns with the observations that high-strength steels are more susceptible to hydrogen embrittlement than those with lower-strength.

Effect of hydrogen content on dielectric strength of the silicon nitride film deposited by ICP-CVD* *Project supported by the Natural Science Foundation of Jiangsu Higher Education Institutions of China (Grant Nos. 19KJD140002 and 19KJB140008), the Key Projects of Ministry of Science and Technology of China (Grant No. SQ2020YFF0407077), Postgraduate Research & Practice Innovation Program of Jiangsu Province, China (Grant Nos.

The inductively coupled plasma chemical vapor deposition (ICP-CVD) deposited silicon nitride (SiN x ) thin film was evaluated for its application as the electrical insulating film for a capacitor device. In order to achieve highest possible dielectric strength of SiN x , the process parameters of ICP-CVD were carefully tuned to control hydrogen in SiN x films by means of tuning N2/SiH4 ratio and radio frequency (RF) power. Besides electrical measurements, the hydrogen content in the films was measured by dynamic secondary ion mass spectrometry (D-SIMS). Fourier transform infrared spectroscopy (FTIR) and micro Raman spectroscopy were used to characterize the SiN x films by measuring Si–H and N–H bonds’ intensities. It was found that the more Si–H bonds lead to the higher dielectric strength.

Tensile properties evolution of hydrogen-induced TA10 titanium alloy welded joints

Hydrogen embrittlement of titanium alloy weldments often occur at low hydrogen concentrations. The effect of hydrogen content on tensile properties of titanium alloy welded joints and its mechanism were studied. The results show that with the increase of hydrogen content, the room temperature strength was significantly improved, the plasticity was significantly deteriorated. At 0.05 wt.% H, solid solution hydrogen had a limited effect on tissue strengthening and a slight increase in tensile strength; solid solution hydrogen reduced the pinning effect of solute atom on dislocation movement, yield strength decreased; solid solution hydrogen only depend on the diffusion and accumulation to cause the local micro-region hydrogen concentration to increase, which had a little effect on the plasticity. After 0.12 wt.% H, the pinning effect of the hydride was strengthened, the hydrogen-induced dislocation cross-slip was more difficult, and the strength at room temperature was significantly increased; the brittle hydride itself fractured, precipitated, or accelerated separation from the matrix, resulting in significant plasticity decline. When not charged with hydrogen or 0.05 wt.% H, the ductile fracture occurred in the welded joint; After 0.12 wt.% H, the brittle fracture was the main; solid solution hydrogen and the hydride had a direct effect on fracture mode transformation.

Effects of hydrogen content that alters damage evolution mechanisms in SUH 660 precipitation-strengthened Fe–Cr–Ni steel

This study aims at understanding the change of the hydrogen embrittlement mechanism with respect to hydrogen content of a precipitation-strengthened Fe–Ni–Cr-based steel. Hydrogen was electrochemically introduced with different current densities. The hydrogen-charging deteriorated crack initiation and propagation resistances as well as the crack tip blunting capability. Further, with increasing hydrogen content, the primary cracking sites changed from coarse carbides to slip bands, and then to grain boundaries. Moreover, because the crack initiation probability increased and the resistance to trans-granular crack propagation decreased with hydrogen content, the crack coalescence associated with slip localization occurred more frequently.

In-situ investigation of the fatigue crack initiation and propagation behavior of Zircaloy-4 with different hydrogen contents at RT and 300 °C

In this paper, the effects of hydrogen content and temperature on the fatigue crack initiation and propagation behavior of Zircaloy-4 are investigated by in-situ scanning electron microscope observation. The results show that, at room temperature, with the increase of hydrogen content, the tensile strength increases and the elongation decreases, but the fatigue lifetime (fatigue crack initiation lifetime and fatigue failure lifetime) first increases and then decreases. The cut-off point is at about 200 ppm hydrogen content. The fatigue crack growth rate increases with the increase of hydrogen content. At 300 °C, with the increase of the hydrogen content, tensile strength, elongation and fatigue lifetime of Zircaloy-4 alloys exhibit the same variations as those at room temperature. However, the fatigue crack growth rate is less affected by the hydrogen content. The results also show that, with the same hydrogen content, the fatigue lifetime at 300 °C is longer than that at room temperature, and the fatigue crack growth threshold at 300 °C is lower than that at room temperature. The fatigue crack propagation path is strongly affected by the hydride and grain boundaries. The hydrogen content has a significant effect on the fatigue crack initiation mechanism. For the un-hydrided sample, the fatigue cracks initiate at the sub-surface. With the increase of hydrogen content, the fatigue cracks tend to initiate at the surface of the sample.

Influence of hydrogen embrittlement on impact property and microstructural characteristics in aluminum alloy weld

As a light-weighting structural material, aluminum alloy is being applied in the automobile and high-speed train, the property of which however is affected by the content of hydrogen, and much importance has been attached to the impact property of aluminum alloy. In this study, hydrogen was determined in ER5183 welding wire and afterwards the effect of hydrogen content on the impact property of Al–Mg MIG weld is investigated to clarify the mechanism of hydrogen action which provided a reasonable control range of hydrogen content in aluminum welding wire. The results show that the impact toughness of the weld is decreased with the increasing hydrogen content. In addition, the decohesion of impurities from the matrix and the formation of porosity are also observed in the weld. The morphology of impact fracture appears facet and porosity due to the “hydrogen-enhanced localized plasticity” effect on plasticity. Considering the good impact property as well as the fine microstructure of the weld, hydrogen content of the ER5183 welding wires should be controlled below 0.18 μg/g.

Effect of hydrogen content in ER5183 welding wire on the tensile strength and fracture morphology of Al–Mg MIG weld

In this study, hydrogen was determined in the ER5183 wires for MIG welding, and the effect of hydrogen in the wires on the tensile strength as well as the fracture behavior of Al–Mg MIG weld were investigated in order to clarify the affecting mechanism by hydrogen, which provided a reasonable range of hydrogen content in ER5183 welding wires. The results showed that, with the increasing hydrogen content, the tensile strength of the corresponding welds decreased accordingly. During the fracture process of the weld, hydrogen played serious roles as follows, accelerating the fracture process, promoting the formation of pores and causing the decohesion of the inclusion and matrix. By the mechanisms mentioned above, hydrogen changed the feature of fracture morphology from dimples to various defects. Considering the high tensile strength as well as the fine microstructure of the welds, the hydrogen content of the ER5183 welding wires should be controlled below 0.18 μg/g.

Low-temperature direct diffusion bonding of hydrogenated TC4 alloy and GH3128 superalloy

Bonding at high temperatures can cause many problems, such as an induction of high stress, grain coarsening and strict requirements for bonding equipments, etc.. In this paper, a hydrogenation approach was utilized for the TC4 alloy before the dissimilar materials bonding process. Effects of hydrogen contents on the diffusion behavior of the TC4/GH3128 joints were investigated. Particularly, the mechanism that the hydrogenation affected the low-temperature bonding process of the TC4/GH3128 joints was discussed. By regulating the bonding temperatures, holding durations and hydrogen contents, a maximum of 92 MPa was achieved. The formation mechanism of the diffusion bonded TC4/GH3128 joint was proposed. This novel metal hydrogenation idea can offer new insights on the development of the low-temperature joining particularly suitable for dissimilar materials joining.