Environmental Embrittlement Research Articles

Effects of hydrogen pressure on hydrogen-assisted fatigue crack growth of Cr-Mo steel

The fatigue crack growth rates (FCGRs) of 4130X steel in 45, 70, 87.5 and 100 MPa hydrogen were measured, and the hydrogen concentrations at the crack tip of test specimens were analyzed by establishing a hydrogen transport model. This model can describe the hydrogen behaviors in the process of environmental embrittlement. Results show that the FCGR increases with the increase in hydrogen pressure. However, the acceleration reaches the threshold under 87.5 MPa. Hydrogen pressure has the same influence on hydrogen concentration, and the threshold of the effect is probably related to the fact that the hydrogen absorption on the material surface reaches the limit.

Microstructural Evolution and Mechanical Properties Co relation of Cold rolled Ferritic Lightweight Steel with Increasing Carbon

The structure-properties relationship of cold-rolled and annealed Fe-7wt.%Al lightweight steels for varying carbon contents is explored in this work.Unlike Fe-Mn-Al-C based steels, which experienced processing issues, the hot-worked plates of the present steel were successfully cold-rolled to 2mm thick sheets. Various phases present in the steel for different carbon contents as predicted using the ThermoCalc programme are in line with the experimental findings. The basic alloy with 0.01C contains only a ferrite phase, however, the alloys with higher carbon content have a significant quantity of κ-carbide precipitates. The addition of carbon to Fe-7wt.%Al steel has improved its tensile strength significantly (438 to 828MPa). Tensile elongation, on the other hand, has decreased dramatically (26 to 12 percent) with increasing carbon content The reduction in ductility with increasing carbon is mainly ascribed to the increasing κ-carbide precipitates volume fraction with higher hardness, but not due to the environmental embrittlement as observed in case of higher Al containing steels.

Microstructure Sensitivity on Environmental Embrittlement of a High Nb Containing TiAl Alloy under Different Atmospheres

Mechanical properties in different atmospheres, including oxygen, vacuum, air and H2, of high Nb containing TiAl alloys with the compositions of Ti-45Al-8.5Nb-(0.2W, 0.2B, 0.02Y) have been investigated in this work. Three different microstructure types, nearly lamellar, gamma phase increased nearly lamellar and fully lamellar are selected for revealing the microstructure sensitivity of environmental embrittlement. The results show that the three types of microstructures are all affected by the hydrogen-induced environmental embrittlement. Although the fracture mode of the experimental alloy is cleavage fracture in all atmospheres, the proportions of transgranular and intergranular fractures are different, especially comparing the fracture surfaces in oxygen and hydrogen. Performance comparison results show that the nearly lamellar microstructure is the most susceptible to the hydrogen-induced environmental embrittlement, while the gamma phase increased microstructure is the most stable one; the fully lamellar microstructure results in moderate susceptibility to the atmospheres. Combined with the hydrogen absorption kinetic analysis, it indicates that γ phase at the interface of lamellar colony significantly inhibits the hydrogen-induced environmental embrittlement, while the effect of β phase is just the opposite. In addition, the correlation between microstructure and hydrogen-induced environmental embrittlement is revealed and the corresponding mechanism is also discussed in this work.

Embrittlement failure of 51CrV4 leaf springs

High strength quenched and tempered alloys are used in the manufacture of leaf springs, and peening techniques are used to induce compressive residual stresses on the tension surface of the individual leaves to resist fatigue crack growth. However, the extent of such residual stresses is usually limited to around 0.1–0.2 mm deep. Their beneficial effect can therefore be negated by corrosion pitting, while high strength steels are known to also be susceptible to environmental embrittlement in high chloride environments. This case study deals with an interesting example of environmental embrittlement of multileaf springs reportedly made from 60Si2Mn steel, but actually manufactured from 51CrV4 steel. Multiple cracks initiated from corrosion pits and fatigue failures occurred within 6–9 months from service entry of the vehicles. The embrittlement was triggered by the disinfecting and cleaning regime that reflected the use of the trucks for conveying animal feed.

Influence of a fine-grained surface structure on the tensile behaviour of a beta stabilised intermetallic γ-TiAl-based alloy

Intermetallic TiAl-based alloys show a high susceptibility to the consistency of their surface region expressed by, e.g., a tendency to environmental embrittlement. In the present work, the prospects of near surface grain refinement of the β-stabilised TNM alloy and the first results of mechanical tests are presented and discussed. Grain refinement was done by remelting the surface region by a laser-based process. Adjusted parameters result in a refined surface area to a depth of approx. 225 μm and at the same time a smooth surface. Subsequent heat treatment at 900 °C for 6 h leads to a fine-grained duplex microstructure in the remelted area, with an average grain size of about 500 nm compared to 7.3 μm of the initial state. In the heat-affected zone below the remelted region, lamellar grains disappear by dissolving γ-lamellae during remelting. These lamellae are re-formed during heat treatment, but their spacing is significantly refined. Tensile tests reveal an increase of the tensile strength of remelted and heat-treated specimens by about 16% if compared to those with the initial microstructure. Failure in the remelted and heat-treated tensile specimens originates from the refined lamellar grains of the heat-affected zone.

Environmental embrittlement behavior of high-entropy alloys

Microstructures is an international peer-reviewed, open access, online journal. The journal of Microstructures publishes articles covering new research and developments, perspectives, and reviews related to the microstructures of materials, including, but not limited to metals and alloys, ceramics, polymers, composites, crystals, glasses, biomaterials, interfaces and nanomaterials.

Environmental effects on the strength and impact damage resistance of alumina based oxide/oxide ceramic matrix composites

In this study the effects of high temperature and moisture on the impact damage resistance and mechanical strength of Nextel 610/alumina silicate ceramic matrix composites were experimentally evaluated. Composite laminates were exposed to either a 1050°C isothermal furnace-based environment for 30 consecutive days at 6 h a day, or 95% relative humidity environment for 13 consecutive days at 67°C. Low velocity impact, tensile and short beam strength tests were performed on both ambient and environmentally conditioned laminates and damage was characterized using a combination of non-destructive and destructive techniques. High temperature and humidity environmental exposure adversely affected the impact resistance of the composite laminates. For all the environments, planar internal damage area was greater than the back side dent area, which in turn was greater than the impactor side dent area. Evidence of environmental embrittlement through a stiffer tensile response was noted for the high temperature exposed laminates while the short beam strength tests showed greater propensity for interlaminar shear failure in the moisture exposed laminates. Destructive evaluations exposed larger, more pronounced delaminations in the environmentally conditioned laminates in comparison to the ambient ones. External damage metrics of the impactor side dent depth and area directly influenced the post-impact tensile strength of the laminates while no such trend between internal damage area and residual strength could be ascertained.

Effect of nonmetallic inclusions on localized corrosion of spring steel

Certain inclusions in high-strength 60Si2Mn-Cr spring steel result in poor resistance to localized corrosion. In this work, to study the effect of inclusions on the localized corrosion behavior of spring steel, accelerated corrosion tests were performed by immersing spring steel in 3wt% FeCl3 solution for different times. The results show that severe corrosion occurred in areas of clustered CaS inclusions. Sulfide inclusions containing Ca and Mg induced the strongest localized corrosion susceptibility. For the case of (Ca,Mn,Mg)S inclusions, the ability to induce localized corrosion susceptibility is ranked as follows: MgS > CaS > MnS. Moreover, CaS, (Ca,Mn)S, and (Ca,Mn,Mg)S inclusions were mainly responsible for inducing environmental embrittlement.

Quantitative Monitoring of the Environmental Hydrogen Embrittlement of Al-Zn-Mg-Based Aluminum Alloys via Dynamic Hydrogen Detection and Digital Image Correlation

In this study, a novel analytical system was developed to monitor the environmental hydrogen embrittlement of Al-Zn-Mg-based aluminum alloys dynamically and quantitatively under atmospheric air pressure. The system involves gas chromatography using a SnO2-based semiconductor hydrogen sensor, a digital image correlation step, and the use of a slow strain rate testing machine. Use of this system revealed that hydrogen atoms are generated during the plastic deformation of Al-Zn-Mg alloys caused by the chemical reaction between the water vapor in air and the alloy surface without oxide films. Digital image correlation also clarified that the generated hydrogen atoms caused numerous localized grain boundary cracks on the specimen surface, resulting in a localized grain boundary fracture. The amount of hydrogen atoms associated with the grain boundary fracture was calculated to be 737 atoms/nm2.

Grain refinement and mechanical properties for AISI304 stainless steel single-tracks by laser melting deposition: Mathematical modelling versus experimental results

Many of the significant mechanical properties of stainless steel, including ultimate tensile strength, yield strength and hardness, the ductile–brittle transition temperature, and susceptibility to environmental embrittlement, can be improved by grain size refinement. Hall-Petch relation identifies that the improvement can be quantified in a constitutive relation. In this study, a new mathematical model to calculate the number of grains and their average size inside a single printed layer via the laser melting deposition (LMD) process is proposed. The printed layer's thermal history concerning the moving laser beam and co-axial addition of powder debits was analyzed and used to calculate the thermal stress and strain rate. The average grain size within the printed layer was calculated using the Johnson-Mehl-Avrami-Kolmogorov (JMAK) model. The mechanical properties, including ultimate tensile strength, yield strength, and hardness, were estimated using the average grain size. For single depositions of AISI 304 stainless steel powder debits on a steel substrate, dedicated experiments were performed to verify the model’s trustworthiness. Scanning electron microscopy was used to quantify the number and size of grains. Vickers hardness tests were conducted to confirm the mechanical performances predicted by the developed model. It was found that the primary operating parameters strongly influence the grain type, resulting in three varieties of grains: (a) quasi-continuous circular, (b) long lath-shaped, and (c) a combination of the two mentioned above. The deposited layer's thermal history influences the thermal stresses and controls the growing grains' average size. A strong correlation between experimental and computational results, within the range of 10–15 %, and 8–10%, was obtained for the average grain size and Vickers hardness test. The laser scanning speed and laser power were in an inverse relation with the average grain size, while a direct relationship was noticed between the powder feed rate and average grain size. The mechanical computational and experimental results show that the highest yield strength (=208 MPa), ultimate tensile strength (=722 MPa), and hardness (=278 HV) were obtained for the finest grain structure.

Stress concentration affecting hydrogen-assisted crack in API X70 pipeline base and weld steel under hydrogen/natural gas mixture

A sudden change in the geometrical parameters of a material, such as bends, T-branches, and welded joints may increase the stress concentration, which in turn may enhance the diffusible hydrogen concentration. In this study, quantitative evaluations of the effect of stress concentration factors on hydrogen environmental embrittlement (HEE) will be studied based on the mechanical performance of notched tensile specimens with variations in the stress concentration factors (Kt) of the X70 pipeline base and weld metal. To highlight the role of stress concentration, the tests are performed under a 10 MPa gas mixture condition with a low partial hydrogen pressure. The maximum strengths of the notched specimens were nearly consistent across all Kt values. The degree of HEE susceptibility of the base metal increased with increasing Kt value. However, in the weld metal, prominent reductions in the RA occurred at all Kt values. The complex HEE susceptibility of the weld metal can be attributed to the synergistic action of the microstructure heterogeneity and Kt values.

Effects of boron content on environmental embrittlement of ordered Ni3Fe alloys

The effects of boron content (CB = 0–0.14% (mass fraction)) on the tensile properties and environmental embrittlement of ordered Ni-24%Fe (atom fraction)-B (Ni3Fe-B) alloys have been investigated using tensile tests in vacuum and under gaseous hydrogen. The results indicate that, when CB < 0.06% (mass fraction), the tensile strength and elongation of the alloys in vacuum and gaseous hydrogen increase as CB in the ordered Ni3Fe-B alloy increases. The tensile strength and elongation are maximum, and the hydrogen embrittlement factor (IH) is minimum for the ordered Ni3Fe-0.06%B (mass fraction) alloy. Compared with the ordered B-free Ni3Fe alloy, IH of the ordered Ni3Fe-0.06%B (mass fraction) alloy decreases by 98.1%, and the fracture morphology of the alloy changes from fully intergranular to fully transgranular, when tested in gaseous hydrogen. A critical level of boron segregation at the grain boundaries of ordered Ni3Fe-B alloys is observed. The hydrogen embrittlement of ordered Ni3Fe-B alloys in gaseous hydrogen can be completely suppressed by boron atoms when CB $$\geqslant$$ 0.06% (mass fraction).

In situ X-ray tomography investigation of the crack formation in an intermetallic beta-stabilized TiAl-alloy during a stepwise tensile loading

The impact of high temperature exposure on the mechanical damage behavior of the intermetallic TiAl alloy TNM has been investigated by means of high resolution laboratory computer tomography (CT). An in situ testing device was adapted allowing the study of cracking behavior during tensile testing of unnotched samples by CT. Accordingly, failure of exposed and unexposed samples is controlled by the fracture toughness. Unexposed samples reveal crack formation in the interior at only about 1/3 of their plastic elongation to failure. These internal cracks grow gradually with increasing nominal stress and are subjected to significant crack deflection by the microstructure until the crack growth accelerates and the samples fail. After exposure for 1 h at 800 °C cracks originate in the surface region of the samples at almost the same nominal stresses at which internal cracks first appear. However, due to higher fracture mechanical geometry factor, surface cracks become critical almost instantly after their formation resulting in a reduced ductility, which is known as environmental embrittlement in literature. It is supposed that crack formation at the surface after exposure is the result of stress concentrations which are built-up during plastic deformation due to interstitials in the surface layer.

Determinação da fragilidade ambiental de bacia hidrográfica em relação à atividade suinícola utilizando SIG

The intensified use of natural resources started after the industrial revolution, with increasing the disorderly occupation of watersheds and environmental degradation over the past century. Studies of environmental fragilities helps to identify areas with greater or lesser fragility regarding to certain aspect or activity analyzed, contributing to the decision making and adoption of strategies to minimize such impacts. The objective of the study was to evaluate the environmental fragility of Lajeado Erval Novo Watershed front the swine farming in order to subsidize the support of the decision taken for the environmental licensing system. Therefore, was held an integrated environmental assessment of the basin from data processing in Geographic Information System using a model based on qualitative and quantitative variables and adding socio-environmental characteristics to hierarchize areas with higher and lower environmental fragility for swine effluents. The areas to the southwest and northeast of the studied watershed were diagnosed as points of high environmental fragility. This fragility was, mainly, related to higher generation of swine effluent load and the conditions that contribute to the process of environmental embrittlement of areas, such as the use and soil type, slope and proximity to water resources. The mapping of environmental fragilities, by addressing the specifics variables and conditions of areas, proved to be a very important tool for decision-making and the maintenance of swine activities and the environmental balance of the watershed.

Comparative study of the testing approaches for the susceptibility of high-strength fasteners to environmental hydrogen embrittlement (EHE)

Abstract Low-alloyed, high-strength steels with yield strength above 1200 MPa are frequently used in the automotive industry, in order to reduce the weight of the components. However, hydrogen embrittlement susceptibility is often a concern for this group of materials. Hydrogen can be produced on the metal surface, as a result of electrochemical corrosion reaction during service. The aim of this study is to evaluate the impact of the various loading procedures according to the existing technical specifications for environmental hydrogen embrittlement (EHE) testing. The hydrogen embrittlement susceptibility of high strength fasteners (strength class 14.8) was tested according to the well-established testing specifications: DIN 50969-2, DIN EN ISO 7539, ASTM F1624-12 in 5 wt.-% sodium chloride solution acidified to pH 3 with hydrochloric acid. Open circuit potential measurements were carried out during the testing procedure to gain understanding of the damage process in each of the testing approaches. Under the chosen testing conditions, rising step load (RSL) testing approach, specified in ASTM F1624-12, appeared as the most sensitive method for the evaluation of the material's hydrogen embrittlement susceptibility.

Moisture induced environmental embrittlement of a high Nb containing TiAl alloy

This work investigates the mechanical properties in moisture and air environments of a Ti-45Al-8.5Nb-(W, B, Y) high Nb-containing TiAl alloy. The experimental alloys with nearly lamellar, gamma phase increased nearly lamellar and fully lamellar are selected to illustrate the microstructure related environmental sensitivity of mechanical properties. The results give evidence that the experimental high Nb-containing TiAl alloys with different microstructures can be affected by environmental embrittlement, which results in the decrease of mechanical properties in moisture environment. According to the contrast experiments, mechanical properties of fully lamellar alloy decrease significantly, while the performance of gamma phase increased alloy is the most stable one in both air and moisture environments. Fracture morphology characteristics display that transgranular cleavage fracture is the dominant fracture mode and primarily independent of the environmental media. The different performance of experimental alloys indicates that the morphology of γ phase determines the environmental embrittlement of the experimental high Nb-containing TiAl alloy. In addition, the determining factors and the corresponding mechanism of the observed environmental brittleness are also discussed in this work.

Depth resolved near-surface residual stresses in γ-based TiAl before and after high-temperature exposure

The aim of this study was to gain an insight into the development of near-surface stress, which has been proposed to play a role in environmental embrittlement, as a function of depth after exposure. Investigations were performed, using both energy and angle-dispersive X-ray diffraction, to determine the residual stress as a function of depth for flat specimens made from two γ-based TiAl alloys in as-polished and exposed (700 °C/1 h/air) conditions. It has been found that large compressive stresses are present at the surface of as-polished specimens due to sub-surface deformation that remains despite careful grinding/polishing. After exposure the compressive residual stresses at depths below 0.6 μm are significantly reduced, probably due to the annealing out of deformation induced defects, but remain compressive in nature. However, within 0.6 μm from the outer surface, tensile stresses were present and reached a maximum of around +350 MPa at 0.15 μm depth. The extent to which the development of superficial tensile residual stress and reduced deeper compressive stress contribute to embrittlement remains unclear.

FeAl powder fabrication by rapid solidification and water vapour-based process

A fabrication process for FeAl intermetallic compound powders has been developed in the present work. The fabrication process is based on a technique employed to study the environmental embrittlement of AlFe intermetallic systems. In the present process, thin metallic ribbons were produced by rapid solidification, placed in a steel mesh inside a reactor for subsequent exposure to water vapour for their final transformation into metallic powders. The process also showed the possibility to add alloying elements in small quantities (1–4 at.-%) in order to improve FeAl ductility. The results showed that the present process has advantages in cost for industrial applications since the raw material low cost and the use of water vapour instead of employing high cost equipment. Additionally, the technique can fix some important problems in the process fabrication, which are generally presented in other powders processing techniques.

The effect of oxide scale roughness on the plasticity of iron aluminide alloy

Iron aluminides based on the stoichiometric compositions of Fe3Al and FeAl exhibit poor room temperature ductility due to environmental embrittlement. The embrittling agent is hydrogen liberated from water vapour in contact with an aluminium-rich surface. The formation of Al2O3 oxide scale can act as a barrier retarding the hydrogen penetration from the atmosphere inside the alloy. This barrier effectiveness depends on the scale surface roughness caused by the formation of Al2O3 whiskers. This paper presents a way to suppress the growth of these whiskers. The application of a two-stage isothermal oxidation enabled creating at a lower temperature an intermediate layer, consisting of metastable γ and θ oxides, which contributed to the limitation of α-Al2O3 oxide whiskers growth at a higher temperature and this way to reducing the scale roughness. It has been found that a decreased roughness of scale surface has a favourable influence on iron aluminide plasticity at room temperature.

Effects of hydrogen induced delay fracture on high-strength steel plate of automobile and the improvement

Delay fracture is an environmental embrittlement occurring when materials, environment and stress interact with each other and also a form of hydrogen induced material deterioration. It is a leading factor inhibiting the further improvement of strength of steel and iron material. Hence this study analyzed the improved low-carbon Mn-B type ultra-high strength steel plate (1500 MPa) which were processed by conventional heat treatment and heating forming technique and explored the effects of tempering temperature and heating forming technique on the performance of hydrogen induced delay fracture, which provides a reference for the actual application of such kind of steel plate.