Local Hydrogen Content Research Articles

Role of grain size and anisotropy of neighboring grains in hydrogen‐assisted intergranular fatigue crack initiation in austenitic stainless steel

AbstractThis study explores the impact of microstructural features on fatigue crack initiation in poly‐crystalline materials, emphasizing hydrogen‐induced complexities. Grain anisotropy, misorientations, grain size variations, and elastic–plastic inhomogeneities concentrate stress at grain boundaries, making them susceptible to crack initiation during fatigue loading. The presence of hydrogen compounds this process, due to complications of characterization of local hydrogen content and activating embrittling mechanisms. Building upon a model for nickel, this research investigates 316L austenitic stainless steel specimens with varying grain sizes, both uncharged and hydrogen‐charged. In situ low‐cycle fatigue loading experiments establish correlations between fatigue crack initiation and microstructural features. The study reveals specific combinations of features crucial in the initiation process, undergoing alterations in the presence of hydrogen. A proposed qualitative model links microstructural features with accumulated plastic shear strain during fatigue and prevalent hydrogen embrittlement mechanisms like hydrogen‐enhanced local plasticity and hydrogen‐enhanced decohesion.

Design of high-strength martensitic steels by novel mixed-metal nanoprecipitates for high toughness and suppressed hydrogen embrittlement

To obtain a fundamental understanding of mechanisms of hydrogen embrittlement (HE) and its prevention in advanced high-strength steels containing novel nanoscale mixed-metal precipitates, it is necessary to study local microstructure, H trapping, and crack path with new multiscale experimental and simulation approach. Spatially resolved hydrogen mapping via SKPFM is used together with investigation of the crack path using high-resolution EBSD and HMPT, and global trapping behavior of the alloys by TDS. These results are combined with newly introduced method to elucidate real-time distribution of hydrogen in the alloy using high-energy synchrotron X-ray diffraction (HES-XRD). Mixed-metal precipitates improves HE resistance of the alloy, due to nature of the trapping sites, e.g. irreversible H-trapping by carbon vacancies inside novel nanoprecipitates and high total length of PAGBs. This is because of lower possibility of build-up of critical local hydrogen content at PAGBs for intergranular hydrogen-assisted cracking due to hydrogen-enhanced decohesion mechanism. Less weakly trapped hydrogen also reduces frequency of dislocation activation and enhanced dislocation slip in {011} slip plane due to hydrogen-enhanced localized plasticity in regions with affinity for transgranular hydrogen-assisted cracking at lower local hydrogen content. Direct evidence of carbon vacancies in novel nanoprecipitates is observed for the first time via HAADF-STEM.

Calibration of NASA’s Neutron Spectrometer System (NSS) for landed measurements of hydrogen content of the lunar subsurface

NASA Ames Research Center and the Lockheed Martin Advanced Technologies Center have developed a rugged, low-resource neutron spectrometer instrument to characterize the near-surface hydrogen content of the lunar surface. This Neutron Spectrometer System (NSS) monitors local thermal and epithermal neutron rates to provide information about the depth-dependent distribution of hydrogen to depths of a few tens of cm. As of mid-2022, NSS is currently slated to fly on two NASA Commercial Lunar Payload Services (CLPS) missions; the Astrobotic Peregrine-1 lander to a near-side equatorial location, and the VIPER lunar rover to explore the polar terrain around Nobile crater. We report the results of a science calibration campaign that characterized the performance of the NSS sensors. These measurements were used to benchmark the accuracy of Geant4 radiation transport simulations that provide the energy- and angle-dependent neutron sensitivity of the NSS sensors. This information is a necessary input for converting NSS measurements of the thermal and epithermal neutron leakage flux to constraints on local hydrogen content in regions with otherwise known geochemical composition.

Effects of local stress, strain, and hydrogen content on hydrogen-related fracture behavior in low-carbon martensitic steel

The present study investigated the hydrogen-related fracture behavior of specimens with different stress concentration factors through microstructure observation, finite element (FE) simulation, and digital image correlation (DIC) analysis. The alloy studied was a simple model alloy (Fe-0.2C binary alloy) with fully martensite structure. When the hydrogen content was large (2.21 mass ppm (121 at ppm)), the crack initiation and propagation occurred along the prior austenite grain boundaries. Through the FE simulations, we found that the crack initiation sites corresponded to the region with high stress and high hydrogen content. Although the stress concentration factors were different, the stress level and the hydrogen content at the crack initiation sites were almost the same, indicating that the hydrogen-related intergranular fracture originated from stress-controlled decohesion at the prior austenite grain boundaries. For the specimen with small hydrogen content (0.41 mass ppm (22.5 at ppm)), the quasi-cleavage cracks formed at the surface of the notch root and propagated along the {011} planes. The FE simulations revealed that the plastic strains were maximum at the initiation sites of the quasi-cleavage cracks. Moreover, we confirmed that hydrogen enhanced the local plastic deformation by DIC analysis. As the local values of maximum principal stress, plastic strain, and hydrogen content at the initiation sites of the quasi-cleavage cracks were different depending on the stress concentration factor, the critical quantitative condition for the initiation of quasi-cleavage cracking was not simple compared to that of the case of intergranular cracking.

Combined Deformation and Solidification-Driven Porosity Formation in Aluminum Alloys

In die-casting processes, the high cooling rates and pressures affect the alloy solidification and deformation behavior, and thereby impact the final mechanical properties of cast components. In this study, isothermal semi-solid compression and subsequent cooling of aluminum die-cast alloy specimens were characterized using fast synchrotron tomography. This enabled the investigation and quantification of gas and shrinkage porosity evolution during deformation and solidification. The analysis of the 4D images (3D plus time) revealed two distinct mechanisms by which porosity formed; (i) deformation-induced growth due to the enrichment of local hydrogen content by the advective hydrogen transport, as well as a pressure drop in the dilatant shear bands, and (ii) diffusion-controlled growth during the solidification. The rates of pore growth were quantified throughout the process, and a Gaussian distribution function was found to represent the variation in the pore growth rate in both regimes. Using a one-dimensional diffusion model for hydrogen pore growth, the hydrogen flux required for driving pore growth during these regimes was estimated, providing a new insight into the role of advective transport associated with the deformation in the mushy region.

Empirical Formulae to Predict Hardness, Hydrogen Diffusion Coefficient and Tensile Properties of Steel HAZ

Weld cold cracking is categorized as hydrogen cracking. To assess cold cracking susceptibility of steel HAZ (heat affected zone), it is necessary to estimate local hydrogen content and residual stress at a weld root that are ... | Find, read and cite all the research you need on Tech Science Press

Beating hydrogen with its own weapon: Nano-twin gradients enhance embrittlement resistance of a high-entropy alloy

High-entropy alloys have shown exceptional damage tolerance at cryogenic temperatures. Here we report that this essential property can be maintained even when exposing the equiatomic CoCrFeMnNi alloy to the most detrimental environmental condition known to metals, hydrogen. This is enabled by a self-accommodation mechanism: the higher the local hydrogen content, the higher the twin formation rate as hydrogen reduces the stacking fault energy. Thus, the hydrogen’s through thickness diffusion gradient translates into a nano-twin gradient that counteracts material weakening by enhanced local strengthening. The concept targets applications under harsh and cryogenic conditions, such as encountered in arctic, offshore, energy and liquid gas chemical processing, and transport operations. The new mechanism opens a pathway to the design of alloys that withstand heavy mechanical loading under cryogenic and hydrogen-containing conditions.

Hydrogenation behavior on 30 nm vanadium thin films with two different adhesion conditions

The influence of a thin polycarbonate de-adhesion layer on the hydrogen concentration is studied on 30 nm vanadium films deposited on glass substrates, using electrochemical hydrogenography in an optical microscopy and scanning tunneling microscopy. It is shown that the optical reflection provides information about the de-adhesion morphology (buckles) while the optical transmission signal gives information about concentration and film thickness changes. Artificially patterned samples allow simultaneous studying adhered and de-adhered film parts, for similar mean concentrations. The optical data clearly show a different hydrogen behavior of the two parts. Data interpretation suggests higher local hydrogen content in the adhered film parts than for the detached films parts. Strong changes in the optical transmission of the adhered film parts can be attributed to strong morphological changes at the film surface. These changes are mainly attributed to grain sliding processes in the vanadium film.

122 応力測定によるステンレス鋼の局所的水素量評価法の提案(材料工学・材料力学II)

122 応力測定によるステンレス鋼の局所的水素量評価法の提案(材料工学・材料力学II)

Influence of hydrogen content and microstructure on the fatigue behaviour of steel SAE 52100 in the VHCF regime

The fatigue life of the bearing steel 52100 (100Cr6) in bainite and martensite conditions was investigated up to 2×109 cycles. The tests were performed under cycling tension (R=0.1) and tension–compression (R=−1) on a piezo-electric ultrasonic testing equipment. The specimens are designed with a cylindrical part in the highly stressed centre. Due to grinding, compressive residual stresses are found at the surface, hence crack initiation solely occurs subsurface. Prior testing half of the specimens was charged with hydrogen. The hydrogen content varies from 0.6 as initial condition to 3ppm after charging. The increased hydrogen content decreased the endurance limit to nearly half of the value of uncharged conditions and crack initiation changed: Conditions with low hydrogen content failed from chromium carbides, titanium nitrides or slag agglomerations. Conditions with 3ppm hydrogen failed from slag agglomerations, often in combination with aluminium magnesium oxides, and manganese sulphides. Next to the inclusions a fine granular area (FGA) could be observed in some cases, and nearly all fractured surfaces showed a fisheye surrounded by an Optically Bright Zone (OBZ) with the crack initiating inclusion in its centre. Furthermore, selected specimens where analysed using secondary ion mass spectroscopy in a time of flight setup (ToF-SIMS) to ascertain the local hydrogen content. From the results it is assumed that hydrogen accumulates in the cavity at inclusions or bonds to the inclusion if it contains silicon.

水素侵入による980MPa級溶接金属の低温割れ限界条件

Prevention of weld cracking is primely important for ensuring the integrity of steel construction. Especially, for high strength steel weld, which is susceptible to hydrogen cold cracking, it is important to clarify the critical condition for cracking in order for expanding use of high strength steel applications. In this study, critical conditions of hydrogen content and residual stress in the high strength steel weld with tensile strength level of over 980MPa were investigated. Cold cracking test was conducted using Y-grooved constraint weld joint by intentionally introducing hydrogen gas, and critical hydrogen content in the weld metal to cold cracking was determined. Cold cracking occurred in the weld metal from the root, bottom portion in the weld metal, when hydrogen content exceeds about 2ppm, and fracture surface was typical grain boundary fracture caused by hydrogen embrittlement. Then, residual stress distribution in the weld meal was measured by neutron diffraction technique. Same Y-grooved weld joint with no cold cracking was used for stress measurement. Neutron beam was filtered by 2mm×2mm slit to measure the residual stress in the small region. Reference sample without residual stress was prepared by introducing multiple saw cuts with small intervals in the same weld joint, and lattice spacing of stress free condition was first measured. Then, lattice spacing in the three different directions along the centerline of the weld metal were measured to calculate residual stress in the three directions. All portions in the weld metal center showed tensile residual stress. The root portion showed highest tensile stress of over 1110MPa in the transverse direction, which is the same as the crack opening direction. Therefore, it is considered that high level of tensile residual stress is the key factor for cold cracking. Hydrogen concentration to the root region by pressure stress was discussed in terms of local hydrogen content condition for cracking.

Investigating the Nucleation and Growth of Electrodeposited Pt on Polycrystalline Diamond Electrodes

The nucleation and growth of electrochemically formed Pt adlayers on highly boron-doped, polycrystalline diamond thin-film electrodes were investigated using chronoamperometry. The experimental curves measured at different fixed potentials were analyzed and compared to theoretical curves for the two limiting cases of three-dimensional nucleation and growth, as described by Scharifker and Hills [ Electrochim. Acta , 28 , 879 (1983)] : instantaneous and progressive. Metal phase formation at short times proceeded via a more instantaneous nucleation mechanism at lower overpotentials on both microcrystalline and ultrananocrystalline diamonds. However, there was a transition on both diamond types to a progressive mechanism at higher overpotentials. Based on the results, apparently, there exists a relatively constant nucleation site density on these conducting polycrystalline films at lower overpotentials, with new nucleation sites developing over time at higher overpotentials. We suppose that the initial nucleation is strongly related to heterogeneities in the density of electronic states (DOS) across a film brought about by variations in the local boron and hydrogen content more so than variations in the physicochemical properties. The shift to a more progressive nucleation and growth mechanism is consistent with an increased DOS at more negative overpotentials. Some comparison measurements are reported for glassy carbon and highly oriented pyrolytic graphite.

Identification and quantification of hydride phases in Zircaloy-4 cladding using synchrotron X-ray diffraction

Zirconium hydrides precipitate in fuel cladding alloys as a result of hydrogen uptake from the high-temperature corrosion environment of light water reactors. Synchrotron X-ray diffraction was performed at room temperature on stress-relieved Zircaloy-4 cladding with two distributions of hydrides – (1) uniformly distributed hydrides across the entire cladding wall and (2) hydride rim next to the outer surface. The δ-hydride phase was found to be the predominant hydride phase to precipitate for hydrogen contents up to 1250 weight parts per million (wt ppm). At a higher content, about 3000 wt ppm, although δ-hydride is still the majority phase, a significant amount of γ-hydride is also observed. At even higher hydrogen contents, in excess of approximately 6000 wt ppm, such as can occur in a highly dense hydride layer, peaks associated with the ε-hydride phase are also observed in the diffraction pattern. The volume fraction of hydrides was estimated as a function of hydrogen content using the integrated intensities of select diffraction peaks corresponding to the α-Zr matrix and the hydride phases. These estimated values agree well with calculated values from the independently measured concentrations. The results of this study indicate that hydride precipitation in Zircaloy-4 is a complex process of evolving hydride phases with increasing local hydrogen content.

Numerical Modelling of Cold Cracking Initiation and Propagation in S 1100 QL Steel Root Welds

Although the phenomenon of hydrogen assisted cold cracking (HACC) and respective avoidance procedures have extensively been investigated in the seventies and eighties, the reasons for recent failures are still a lack of knowledge about the basic hydrogen effects on steel microstructures and, in particular, a lack of welding procedure specifications and standards accounting directly and consistently for cold cracking avoidance in modern high strength structural steels with yield strengths of up to 1 100 MPa. In previous several contributions the consequences of various heat treatment procedures targeted at HACC avoidance have been shown, as for instance their effects on stress-strain build up and on hydrogen diffusion in high strength steel welds. But, a principal interaction of three local influences on hydrogen assisted cold cracking, i.e. local microstructure; local mechanical load and local hydrogen content have not yet been studied in detail for these materials. For this, a numerical model for HACC has been developed, accounting particularly for crack-initiation and crack-propagation criteria, like the hydrogen redistribution during the process of cracking. The numerical model has been used to investigate HACC in such materials, i.e. in the weld microstructures of an S 1100 QL steel, under severe restraint and various hydrogen levels. The results were achieved by in depth thermal and structural finite element simulations combined with numerical hydrogen diffusion modelling. By such procedure, HACC in single-layer welded plates with thickness of 20.0 mm at realistic restraints has been studied. As a particular result, it turned out that the crack-initiation location is typically in the centre of the weld metal (WM), where only a single crack is initiated at hydrogen contents of up to 10.0 Nml/100 g Fe. But, it was evidently shown by such analyses that the crack-initiation location is shifted into the HAZ and that multiple cracking occurs at higher hydrogen contents of up to 15.0 Nml/100 g Fe.

Investigation of Local Hydrogen Distribution Around Fatigue Crack Tip of a Type 304 Stainless Steel with Secondary Ion Mass Spectrometry and Hydrogen Micro-Print Technique

In order to establish an appropriate method for measuring the local hydrogen content distribution around a fatigue crack tip in austenitic stainless steels, secondary ion mass spectrometry (SIMS) and the hydrogen micro-print technique (HMPT) were applied to a fatigue crack in a type 304 stainless steel fatigued in a hydrogen gas environment. The main results in this study are as follows. In the SIMS method, it is visualized that a high content of hydrogen exists in the plastic zone at a fatigue crack tip propagated in hydrogen gas, compared to that on a smooth area fatigued in hydrogen, though there is a measurement error based on false detection due to the edge effect regarding hydrogen in water vapor on the fatigue crack surface. On the other hand, hydrogen in the plastic zone is difficult to detect by HMPT. This is attributed to the difficulty for hydrogen atoms to be emitted from the sample in this case. To detect hydrogen, it is necessary to sputter the atoms forcibly. In addition, it is considered that to analyze the local hydrogen distribution around a fatigue crack tip with SIMS not only qualitatively but also quantitatively, reduction of the false detection due to the edge effect is necessary.

Investigation of Local Hydrogen Distribution Around Fatigue Crack Tip on a Type 304 Stainless Steel with Secondary Ion Mass Spectrometry and the Hydrogen Micro-print Technique

In order to establish an appropriate method for measuring the local hydrogen content distribution around a fatigue crack tip in austenitic stainless steels, secondary ion mass spectrometry (SIMS) and the hydrogen micro-print technique (HMPT) were applied to a fatigue crack in a type 304 stainless steel tested in a hydrogen gas environment. The main results obtained in this study are as follows. In the SIMS method, there is a measurement error based on the edge effect regarding hydrogen in water vapor on the fatigue crack surface, though it is visualized that a high content of hydrogen exists in the plastic zone at a fatigue crack tip propagated in hydrogen, compared to that on a smooth area fatigued in hydrogen. On the other hand, this hydrogen in the plastic zone is difficult to detect with HMPT. In this case, this is attributed to the difficulty for hydrogen atoms to be emitted from the sample. To detect the hydrogen, it is necessary to sputter atoms forcibly. In addition, it is understood that to analyze the local hydrogen distribution around a fatigue crack tip with SIMS not only qualitatively but also quantitatively, reduction of the error based on the edge effect is necessary.

Nanoscopic fatigue and stress corrosion crack growth behaviour in a high‐strength stainless steel visualized in situ by atomic force microscopy

ABSTRACT In situ atomic force microscope (AFM) imaging of the fatigue and stress corrosion (SC) crack in a high‐strength stainless steel was performed, under both static and dynamic loading. The AFM systems used were (1) a newly developed AFM‐based system for analysing the nanoscopic topographies of environmentally induced damage under dynamic loads in a controlled environment and (2) an AFM system having a large sample stage together with a static in‐plane loading device. By using these systems, in situ serial clear AFM images of an environmentally induced crack under loading could be obtained in a controlled environment, such as in dry air for the fatigue and in an aqueous solution for the stress corrosion cracking (SCC). The intergranular static SC crack at the free corrosion had a sharp crack tip when it grew straight along a grain boundary. The in situ AFM observations showed that the fatigue crack grew in a steady manner on the order of sub‐micrometre. The same result was obtained for the static SC crack under the free corrosion, growing straight along a grain boundary. In these cases, the crack tip opening displacement (CTOD) remained constant. However, as the static SC crack was approaching a triple grain junction, the growth rate became smaller, the CTOD value increased and the hollow ahead of the crack tip became larger. After the crack passed through the triple grain junction, it grew faster with a lower CTOD value; the changes in the CTOD value agreed with those of the crack growth rate. At the cathodic potential, the static SC crack grew in a zigzag path and in an unsteady manner, showing crack growth acceleration and retardation. This unsteady crack growth was considered to be due to the changes in the local hydrogen content near the crack tip. The changes in the CTOD value also agreed with those of the crack growth rate. The CTOD value in the corrosive environment was influenced by the microstructure of the material and the local hydrogen content, showing a larger scatter band, whereas the CTOD value of the fatigue crack in dry air was determined by the applied stress intensity factor, with a smaller scatter band. In addition, the CTOD value in the corrosive environment under both static and dynamic loading was smaller than that of the fatigue crack; the environmentally induced crack had a sharper crack tip than the fatigue crack in dry air.

Ductility of Zircaloy-4 Fuel Cladding and Guide Tubes at High Fluences

Abstract Zircaloy fuel cladding suffers progressive degradation of ductility as its neutron exposure and hydrogen uptake increase with burnup. The loss of ductility appears to be the key property governing the cladding integrity in service. We report ductility data of Zircaloy-4 fabricated in stress-relief annealed (SRA) and recrystallized (RXA) conditions, covering a range of fluence, hydrogen content, and irradiation and test temperature. The testing was performed on unirradiated and irradiated Zircaloy-4 cladding and guide tubes in SRA and RXA conditions, respectively, in the temperature range 25–350°C. These materials had been exposed to an estimated neutron fluence of ∼8 to 10 × 1025 n/m2 (E > 1 MeV) over four cycles of PWR operation. Due to its RXA fabrication condition, the guide tube material was also believed to represent BWR cladding. The hydrogen contents in the irradiated cladding was in the range of ∼200–600 ppm, exhibiting typical radial distribution of circumferential hydrides. By comparison, the hydrogen content in the irradiated guide tube material was in the range of ∼250–1800 ppm, exhibiting fairly uniform through-wall distribution of circumferential hydrides. Tensile tests and hydraulic burst tests were conducted on 130–150 mm long tubular specimens. In addition, smaller specimens machined in the form of 55 mm long curvilinear dog-bone and 10 mm slotted semicircular arc were tested in plane stress and plane strain configurations. Corresponding unirradiated archive materials in as-received condition and with uniform hydrogen charging up to 1200 ppm were also tested by identical methods. In all tests the fracture mode was examined by SEM fractography. The investigations revealed a decrease in ductility of Zircaloy-4, mainly caused by irradiation and only partly by increasing hydrogen content. Unlike the elongation data, the strength data remained nearly constant with increasing hydrogen content in both materials at all test temperatures. The irradiated RXA material showed better ductility than irradiated SRA material at equivalent hydrogen levels, and exhibited a clearer correlation of ductility with hydrogen content, mainly due to its uniform hydrogen distribution. The paper will provide these and other quantitative data, e.g., those correlating ductility with the local (near fracture surface) hydrogen content. The paper synthesizes the experimental results and discusses their possible application to the criteria for hydrogen concentration and ductility limits in high burnup fuel.

Fracture toughness of alloy 690 and EN52 welds in air and water

The effect of low- and high-temperature water with high hydrogen on the fracture toughness of alloy 690 and its weld, EN52, was characterized using elastic-plastic JIC methodology. While both materials display excellent fracture resistance in air and elevated-temperature (>93 °C) water, a dramatic degradation in toughness is observed in 54 °C water. The loss of toughness is associated with a hydrogen-induced intergranular cracking mechanism, where hydrogen is picked up from the water. Comparison of the cracking behavior in low-temperature water with that for hydrogen-precharged specimens tested in air indicates that the critical local hydrogen content required to cause low-temperature embrittlement is on the order of 120 to 160 ppm. Loading-rate studies show that cracking resistance is improved at rates above ∼ 1000 MPa √m/h, because there is insufficient time to produce grain-boundary embrittlement. Electron fractographic examinations were performed to correlate cracking behavior with microstructural features and operative fracture mechanisms.

高強度鋼の水素割れ感受性評価におけるWeibull形状パラメータの決定方法

An experimental method to obtain the shape parameter m in the Weibull stress for evaluation of hydrogen embrittlement (HE) was examined in a commercial JIS SCM440 steel with the tensile strength of 1403 MPa. The stepwise HE tests were performed by using circumferentially notched round-bar specimens with the stress concentration factor of 4.9 after hydrogen pre-charging and homogenization treatments. The applied stress of the first step loading was set at 702 MPa and the stress increment from the second step was 14 MPa. The holding time was over 12 h for the first step and over 2 h for each step from the second step. It was conformed by acoustic emission measurement that the first cracking and final fracture occurred in the same step. The diffusible hydrogen content was measured by thermal desorption analysis immediately after fracture. The distribution of stress and hydrogen content near notch root was calculated by FE-analysis. By this procedure, it was able to obtain the distribution of critical Weibull stress under the condition that the local diffusible hydrogen content in fracture process zone was constant. The shape parameter m was determined to be 46 for the present steel. In the discussion part, it was confirmed that the evaluation of the HE susceptibility based on the local approach is appropriate and it was pointed out that the hydrogen content distribution in the fracture process zone must be taken into account for evaluating the HE.