Hydrogen Embrittlement Behavior Research Articles

Study on the Hydrogen Embrittlement of Nanograined Materials with Different Grain Sizes by Atomistic Simulation.

Although hydrogen embrittlement (HE) behavior has been extensively studied in bulk materials, little is known about H-related deformation and the fracture of nanograined materials. In this study, H segregation and HE mechanisms of nanograined Fe with different grain sizes are unveiled, following the employment of classical molecular dynamics simulations. The H segregation ratio increased, but the local H concentration at the grain boundaries (GBs) decreased with decreases in the grain size at a given bulk H concentration. The results demonstrate that H atoms increased the yield stress of nanograined models irrespective of the grain size. Furthermore, it is revealed that brittle fractures were inhibited, and the resistance to HE increased as the grain size decreased, due to the fact that the small-grain models had a lower local H concentration at the GBs and an enhanced GB-mediated intergranular deformation. These results are a clear indication of the utility of grain refinement to resist H-induced brittle failure.

Hydrogen Embrittlement of CoCrFeMnNi High-Entropy Alloy Compared with 304 and IN718 Alloys

The hydrogen embrittlement (HE) behaviors of a CoCrFeMnNi high-entropy alloy (HEA), 304 stainless steel (304SS) and IN718 alloys were studied and compared via electrochemical hydrogen pre-charging, slow strain rate tensile tests, and fracture surface analysis. The results demonstrate that the HEA exhibited the greatest HE-resistance, followed by 304SS and then IN718 alloy, when the alloys were charged at 1.79 mA cm−2 for 24 h and 48 h, and 179 mA cm−2 for 2 h. Hydrogen-induced reduction in ductility was observed for 304SS and IN718 alloys, whereas the hydrogen-affected fracture strain of the HEA was dependent on the hydrogen charging time. The resistance to HE was improved at a short hydrogen charging time (24 h), but reduced at a long charging time (48 h). This is attributed to the competing mechanisms between hydrogen-enhanced twin formation and HEDE (hydrogen-enhanced decohesion).

Effect of ultrasonic surface rolling process on hydrogen embrittlement behavior of TC4 laser welded joints

Effect of ultrasonic surface rolling process on hydrogen embrittlement behavior of TC4 laser welded joints

Effect of Grain Orientation on Hydrogen Embrittlement Behavior of Interstitial-Free Steel

In interstitial-free (IF) steel with a certain microtexture, the micro-orientation of grains is essential to understand the occurrence of hydrogen-induced cracking in body-centered cubic (BCC) structural steels. In this study, the hydrogen embrittlement (HE) susceptibility of IF steels was determined by slow strain rate tensile (SSRT) tests and hydrogen microprinting (HMT) experiments from the perspective of crystal orientation. The strength of the specimen with hydrogen was slightly higher than that without hydrogen, while the ductility and toughness were drastically reduced by hydrogen charging during the SSRT test. The HE susceptibility was characterized by the loss of elongation (Iδ) and toughness (Iψ), with losses of 46.3% and 70%, respectively. The microstructural observations indicate that cracks initiated along grains oriented in the {100} || normal direction (ND), and grain boundaries (GBs) around {100}||ND were prone to be enriched in hydrogen atoms; that is, {100} || ND showed poor resistance to intergranular cracking and susceptible to hydrogen segregation. HMT was used to confirm the above viewpoints. Meanwhile, the statistical results showed those high-angle misorientations of 50–60° deviation are the locations most vulnerable to fracture.

Study on hydrogen embrittlement and reversibility of hot-stamped aluminized 22MnB5 steel

This study investigated the hydrogen embrittlement behavior of ultrahigh strength hot-stamped aluminized 22MnB5 steel. Hydrogen was introduced through electrochemical charging under different hydrogen conditions to assess their sensitivity to hydrogen-induced cracking. Then, the hydrogen-charged specimens were subjected to the slow strain-rate tensile tests. The fracture morphologies revealed that the charging current density altered the fracture mechanism translated from ductile (uncharged) to quasi-cleavage (0.001A-2h) and a mixture of intergranular and quasi-cleavage fracture (0.1A-2h). Furthermore, the reversibility of hydrogen embrittlement of aluminized specimen was investigated. At low-current density, the coatings were corroded by electrolyte, resulting in additional hydrogen which facilitated the formation of hydrogen-induced cracking and inhibited the restoring of mechanical properties. However, with high-current density, effective cathodic protection ensured the integrity of the surface coating, effectively prohibiting the hydrogen intrusion and promoting the reversibility of hydrogen embrittlement.

Effect of Nitrate via CVD Coating on Hydrogen Embrittlement in High Strength Steel Treated with Zinc PVD Coating

High strength low alloy steel (HSLAS) is quite sensitive to hydrogen embrittlement due to its different phases. This study investigated the hydrogen embrittlement (HE) behavior of uncoated, physically vapor deposition (PVD) coated, and chemically vapor deposition (CVD) coated HSLAS. The XRD indicates the formation of ZnO, Zn(N3)2, γN and C3N4 phases at the outer coating layer. The results show that combination of surface nitriding and zinc deposition are efficient method against hydrogen embrittlement. This could be attributed to the reduction of hydrogen that is generated by the reaction of surface Zn) N3)2 phase and the low rate of hydrogen transport through the γN phase. The coatings were tested by immersing the tensile samples in a diluted H2SO4 solution with water for 24 hours. Additionally, the result shows that combined coating resulting in higher tensile strength, yield stress, and tensile elongation compared to uncoated samples. Hardness results indicate that the combined coatings (PVD + CVD) has the higher value of about 258 HV, followed by the uncoated sample of about 218 HV, while the PVD only coated sample have the lower hardness value of about 175 HV.

Effect of Heat Treatment and NC Ni Coating on Electrochemical and Hydrogen Embrittlement Behaviour of a High Strength Low Alloy (HSLA) Steel

Effect of Heat Treatment and NC Ni Coating on Electrochemical and Hydrogen Embrittlement Behaviour of a High Strength Low Alloy (HSLA) Steel

Investigation of hydrogen embrittlement properties of Ni-based alloy 718 fabricated via laser powder bed fusion

The hydrogen embrittlement behavior of heat-treated Alloy 718 fabricated by laser powder bed fusion was fundamentally investigated under electrochemical hydrogen charging. The H transitioned the fracture mode from ductile dimpled to transgranular fracture with a flat fracture surface. Crystallographic analysis showed that H promoted the dislocation slip band, and the resulting concentrated strain and H along the slip planes caused cracking regardless of the distribution of additive manufacturing (AM) microstructural features such as sub-grain boundaries. In addition, thermal desorption spectroscopy and H-permeation tests indicated that the AM microstructural features after heat treatment only slightly influenced the H trapping and diffusion.

Studying the effect of multicomponent nano-coating alloy on hydrogen embrittlement of AISI 1018 steel by gas-phase process

The present study is attempted to investigate the influence of multicomponent Ni-alloy (BNi-2) on the hydrogen embrittlement (HE) behaviour of AISI 1018 steel by using cathodic protection and tensile test. The results show that the HE indexes (HEI) decrease notably when AISI 1018 steel is coated with BNi-2 alloy by DC sputtering process. This coating processes leads to decrease in HE susceptibility of the AISI 1018 steel, which can be rationalized to the enhancement in corrosion resistance and the decrease in hydrogen absorption of the AISI 1018 steel after coating. The tensile strengths of bared samples were decreased with increasing charging time until 24 hours when stable at values 350 MPa. while the coated samples showed an increasement in the tensile strength from 570 MPa to 750 MPa. stabilization in strength at value of 600 MPa was observed after exceeding 48 hours. Also, the tensile test for uncoated specimens indicated a clear reduction on the modulus of elasticity compared with other coated ones.

Heat treatment effects on the hydrogen embrittlement of Ti6Al4V fabricated by laser beam powder bed fusion

Hydrogen embrittlement (HE) behavior of Ti6Al4V produced by laser beam powder bed fusion (PBF-LB) was investigated via tensile tests with/without electrochemical H-charging, and the heat treatment (HT, 950 °C for 2 h) effects on HE mechanisms were also explored. Decreased resistance against HE after long-term H-charging is verified for the HT PBF-LB Ti6Al4V and this phenomenon is not obvious for the as-built (AS) PBF-LB counterparts. To understand this observation, we carried out microstructural characterization experiments including backscattered electron (BSE) image, electron backscatter diffraction (EBSD), transmission electron microscope (TEM), and hydrogen analyses based on X-ray diffraction (XRD) and thermal desorption spectrometry (TDS). These results and others reveal that the β phase introduced by the HT process attracts more hydrogen ingress compared with the full acicular α΄ martensitic phase in the AS PBF-LB parts. The lattice expansion of the hydrogenated β phase compels a localized stress field near the phase boundary, leading to an increased work-hardening rate under H-charging for the HT PBF-LB Ti6Al4V. Consequently, brittle titanium hydrides occur along with the α/β interfaces after H-charging, and the micro-voids preferentially initiate therein and coalesce to micro-cracks under plastic deformation. Therefore, a larger ductility loss is verified for the HT PBF-LB Ti6Al4V compared with the AS PBF-LB counterparts under the same H-charging condition.

Hydrogen Embrittlement Behavior of Pure Ni and Ni–20Cr Alloy with Different Grain Sizes

Hydrogen Embrittlement Behavior of Pure Ni and Ni–20Cr Alloy with Different Grain Sizes

Hydrogen embrittlement of high-strength marine steel as a weld joint in artificial seawater under cathodic polarization

Hydrogen embrittlement (HE) behavior of E690 high-strength steel as a weld joint was investigated in artificial seawater. The most vulnerable location and microstructure to HE was verified, and the underlying mechanism was clarified. Results showed that the weld metal with granular bainitic microstructure leads to premature fracture of the entire weld joint under slow strain rate tensile testing with in-situ hydrogen charging. Dislocation slip bands (DSBs) could be preferentially developed in this zone, and HE initiation was induced via dislocation–hydrogen interaction because the weld metal had the lowest local strength among the weld joint. Martensite/austenite (M/A) constituents and carbides could also contribute to crack initiation and propagation through microvoid coalescence and decohesion.

Effect of prior austenite grain morphology on hydrogen embrittlement behaviour under plastic straining in as-quenched 500 HBW steels

Prior austenite grain (PAG) structure is an important factor influencing hydrogen embrittlement (HE) susceptibility of ultrahigh-strength steels. In this study, the effect of PAG shape and size on HE behaviour is investigated using a novel tuning-fork testing method and hydrogen thermal desorption spectroscopy (TDS). Different PAG structures were acquired via re-austenitization (860°C = A860, 960°C = A960) and rapid quenching of an as-received 500 HBW direct-quenched (DQ) steel, which has an auto-tempered lath-martensitic microstructure and elongated PAG morphology. Fractography reveals different crack propagation mechanisms depending on the PAG shape. With the elongated PAG structure, hydrogen-induced crack propagation transverse to elongated PAGs was transgranular quasi-cleavage. Propagation was partially intergranular with the equiaxed PAG structures, regardless of the PAG size, leading to equally faster fracture. The TDS results show that there are no significant differences between the total hydrogen contents, but re-austenitized A860 and A960 steels contain a higher fraction of weakly trapped hydrogen. This indicates that the PAG boundaries are not the dominant hydrogen traps, and the different crack propagation mechanisms are rather linked to the geometrical shape of the grain structure.

析出硬化型高Mnオーステナイト鋼の水素脆化挙動に及ぼすNi含有量および時効熱処理の影響

析出硬化型高Mnオーステナイト鋼の水素脆化挙動に及ぼすNi含有量および時効熱処理の影響

Comparison between the hydrogen embrittlement behavior of an industrial and a lightweight bearing steel

Hydrogen embrittlement (HE) is a widely occurring problem, also in the automotive industry. Therefore, this study compares the resistance to HE of two types of bearing steels: an industrial 100Cr6 steel and an innovative Fe-8Al-1.1C steel. The innovative character of the Fe-8Al-1.1C steel is found in the fact that a high weight fraction of Al is added to a simplified Fe-1.1C alloy which results in a low-cost martensitic steel with a similar hardness but a lower density, compared to the industrial 100Cr6 steel. The density reduction offers the opportunity to reduce the vehicle weight and as such to reduce the CO2 emission of fuel-based cars or extend the driving range of electrical vehicles. Both alloys are subjected to a similar heat treatment resulting in a martensitic matrix with specially induced carbides. (In-situ) H bending tests and subsequent post-mortem fracture surface analysis are performed to investigate the mechanical degradation of both steels in a H rich environment. For the industrial steel grade, the large Cr-based carbides act as fracture initiation sites for H-assisted cracks. In contrast, the fracture behavior of the Fe-8Al-1.1C material is similar in air and in an H containing environment, indicating that the Fe-8Al-1.1C steel has a better resistance to HE. Although these results are very promising, further optimization of the innovative alloy is needed to improve the mechanical behavior in the absence of H since the presence of microcracks cause premature failure when tested in air.

Axial micro-cracking paths and locally anisotropic hydrogen embrittlement behaviour in cold drawn pearlitic steel wires

This paper analyses the anisotropic fracture behaviour exhibited by initially-smooth samples of cold drawn pearlitic steel wires (commercial prestressing steel wires) subjected to tensile tests in aggressive environment promoted by a corrosion cell. Two testing rates were used: one moderately fast (0.1 mm/min) and another moderately slow (0.01 mm/min). The electro-chemical potential ranged between –1100 mV SCE and –1400 mV SCE (cathodic conditions) to promote hydrogen embrittlement (HE). Axial micro-cracking paths (local crack path deflection) and locally anisotropic HE behaviour was exhibited by the specimens but the phenomenon is strictly local, because the triaxiality level is not high enough to produce global crack path deflection in the presence of hydrogen. The anisotropic fracture behaviour shows marked deviations of the fracture path from the initial fracture zone till the fracture end zone, such deviations being higher than those observed in the specimens failing in inert environment.

Hydrogen embrittlement of additively manufactured AlCoCrFeNi2.1 eutectic high-entropy alloy

AlCoCrFeNi2.1 eutectic high-entropy alloy (HEA) was fabricated in as-cast and additively manufactured (AM) states. The hydrogen embrittlement susceptibility of both materials was investigated through in-situ uniaxial tensile test. Combining several advanced high-resolution scanning electron microscopy (SEM)-based techniques, the deformation and hydrogen embrittlement behavior have been intensively discussed. Interfacial cracking along both phase boundaries and grain boundaries are found to be responsible for the hydrogen-assisted fracture of this material. The cracking susceptibility has a dependence on the manufactured phase morphology. The orientation relationship between the phases and the misorientation between grains also have a significant impact on the hydrogen-induced cracks.

Hydrogen embrittlement behaviors at different deformation temperatures in as-quenched low-carbon martensitic steel

The present study investigated hydrogen-related fractures at different deformation temperatures ranging from −100 °C to 100 °C in low-carbon martensitic steel. The sensitivity to hydrogen embrittlement increased as the temperature decreased from 100 °C to 0 °C, while it decreased as the temperature decreased further below 0 °C. We characterized the fracture surface types from the morphological and crystallographic aspects and found that the fraction of hydrogen-embrittled surfaces exhibited a similar temperature dependence on the sensitivity to hydrogen embrittlement. The qualitative discussion suggested that the degree of hydrogen accumulation exhibits a peak value in the medium temperature range, which has the same tendency as the sensitivity to hydrogen embrittlement confirmed experimentally. Thus, we proposed that the effect of deformation conditions on the sensitivity to hydrogen embrittlement could be explained on the basis of the hydrogen accumulation behavior.

Effects of interstitial C and N on hydrogen embrittlement behavior of non-equiatomic metastable FeMnCoCr high-entropy alloys

The hydrogen embrittlement behavior of C-doped and C-N co-doped non-equiatomic FeMnCoCr high-entropy alloys were investigated by slow strain rate tensile tests (1 × 10−5 s−1) under in-situ electrochemical hydrogen charging. Multi-scale microstructural analysis suggests that appropriate phase stability and stacking fault energy adjusted by C-doping provide the alloy with slightly greater resistance to hydrogen embrittlement with the formation of abundant deformation-induced twins and ε-martensite during deformation. The C-N free alloy shows grain boundary and ε/γ interface cracking even though the γ and ε phases have high deformability. C-N co-doping promotes planar dislocation slip, assisting grain- and twin-boundary cracking under deformation in hydrogen.

Investigation on hydrogen embrittlement susceptibility in martensitic steels with 1000 MPa yield strength

Two quenched and tempered cost-saving marine steels with 1000 MPa yield strength were charged with hydrogen by the electrochemical technique to evaluate the hydrogen embrittlement (HE) behavior. The HE susceptibility index (HEI) obtained by slow strain rate tensile tests (SSRT) indicated that the HE resistance of steel A was weaker than that of steel B. Aided by fracture surface analyses, it could be determined that HE was a combination of hydrogen-enhanced decohesion (HEDE) and hydrogen-enhanced localized plasticity (HELP) model. The microstructural characteristics were examined via transmission electron microscopy (TEM) and scanning electron microscope with electron backscattered diffraction analysis (SEM-EBSD). Thermal desorption spectroscopy (TDS) was applied to explore the hydrogen trapping behavior. It was shown that compared to steel A with fine microstructure and low Σ3 fraction, steel B had excellent HE resistance, which could result from the presence of more nano-sized NbC particles. The precipitation of NbC could not only act as an irreversible hydrogen trap to inhibit the hydrogen diffusion, suppressing the HEDE mechanism, but also can restrict hydrogen–dislocation interaction and suppress the HELP mechanism. The role of the interface between carbide and matrix on hydrogen trapping was investigated by density functional theory (DFT) and showed that the hydrogen capture force of NbC was stronger than (Nb,V)C. In addition, with the coarsening of microstructure during tempering at 580 °C, the high-angle grain boundaries (HAGBs) was obviously reduced, led to the HE susceptibility increased, especially steel A.