Materials and Corrosion-werkstoffe Und Korrosion最新文献

Aluminum alloys are widely used in automotive construction, and since the introduction of biogenic ethanol into fuels, the issue of nonaqueous alcoholate corrosion has become an important topic. In this paper, the kinetics of AA1050 temperature-induced alcoholate pitting corrosion are examined experimentally with a specially constructed microreactor. The generated data are utilized to create a phase field model for the pit growth phase. The effects of ethanol-blend composition and water content are quantitatively assessed and simulated. Phase field simulations allow for the first time the mechanistic characterization of the chemical corrosion process with a water content of up to 0.3% and an estimation of relevant reaction parameters at temperatures of up to 150°C. The approach can further be utilized to develop strategies for minimizing corrosion risk in-service.

The corrosion behavior of galvanized steels and zinc components under atmospheric exposure depends mostly on the corrosion product-based cover layer formation under the prevailing conditions. The use of agar-based gel electrolytes makes it possible to use electrochemical methods to obtain a characteristic value from these cover layers that describe their current and future protective capacity. It is shown here that different states of galvanized steel can be distinguished very well under laboratory conditions and that this method is also suitable for use under practical conditions. Based on the characteristic values and assuming future time of wetness, it is very easy to draw up a forecast for the future corrosion rate, which provides plausible values.

The corrosion behavior of two different Cu–Al–Mn–Ni alloys, pseudoelastic and pseudoplastic, was studied in a 0.6 M sodium chloride aqueous solution by monitoring the open circuit potential for 100 h and characterizing the resulting corrosion products. Electrochemical impedance spectroscopy analysis detected three processes related to the electrochemical double layer, a passive film and a diffusive contribution associated with the dissolution/precipitation of corrosion products. Potentiodynamic scans revealed a cathodically controlled corrosion mechanism and the presence of active–passive behavior at anodic potentials for both alloys studied. Polarization of the samples at selected potentials in the anodic branch allowed the investigation of the reactions involved, highlighting an improved corrosion resistance of the pseudoelastic alloy. The corrosion rates of the pseudoelastic and pseudoplastic alloys, after 100 h of immersion, were determined to be 0.007 and 0.011 mmpy, respectively. The post-experiment characterization was carried out by means of scanning electron microscopy, micro-Raman spectroscopy and X-ray diffraction, supporting the electrochemical results.

To investigate the application of Ni₃Al-based superalloys in gas turbine cycle systems, this experiment exposed Ni₃Al-based superalloys to a 600°C/5 MPa environment with 99.995% pure CO₂ gas. The corrosion and carburization behaviors and mechanisms were investigated in detail. The results reveal that with prolonged thermal exposure, the surface oxides of the samples tend to develop a continuous and homogeneous transition state alumina layer. This layer serves as a protective barrier, preventing the penetration and corrosion of external carbon-containing and oxygen-containing substances into the matrix. A small amount of carbon-containing hazardous substances still penetrates the oxide layer or grain boundaries through highly diffusive pathways such as nanochannels, pores, and cracks, because the transition state of alumina is not completely dense. This leads to carbon deposition at the interface between the oxide layer and the matrix, where a mixture of alumina and amorphous carbon is formed at the interface.

In this paper, self-healing microcapsules were prepared by in situ polymerization using poly(vinyl alcohol) as the emulsifier, urea-formaldehyde resin as the shell material, and alkyd resin as the core material. The average diameter of the obtained microcapsules was about 20 μm and the encapsulation rate of alkyd resin was 50.7 wt.%. The self-healing coating was prepared by adding 5 wt.% of microcapsules to the pure polyurethane coating and then coated on AA2024-T3 substrate. The self-healing effect was evaluated by scanning electron microscopy. Electrochemical impedance spectroscopy tests and neutral salt spray tests confirmed that the self-healing coating had good anticorrosion properties.

Structural automotive components are extensively made of aluminum alloy forgings, due to the elevate strength and low weight required. These products are frequently subjected to recrystallization. Recrystallization, often limited to surface or forging portions, is expected to reduce its tensile strength and corrosion resistance, but the literature is scarce on this subject. For a more comprehensive understanding, the present research studied the corrosion behavior of samples collected from EN AW 6082-T6 forged components, designed to expose both recrystallized and not recrystallized surfaces to the corrosive environment. Several standardized corrosion tests (i.e., PV 1113, ISO 11846, and VW 96380) were applied to assess the most representative with respect to real field exposure. Tensile tests were performed in four different conditions, recrystallized and not recrystallized specimens in an as-forged state or after corrosion. The recrystallization led to a reduction in tensile properties, but this gap was compensated by a higher corrosion resistance than the not recrystallized samples. Consequently, the mechanical properties became comparable after the corrosion test.

Tests for assessing prestressing steels' susceptibility to hydrogen-induced stress corrosion cracking are essential for approvals, in-house monitoring, and third-party material testing. According to ISO 15630-3, the time to brittle fracture by constant load under corrosive conditions in thiocyanate test solutions (A or B) at 50°C is measured. In the literature, a high scattering in stress corrosion tests is reported, which questions the integrity of the test procedure. This paper shows the results of studies about the influence of solution composition on hydrogen charging in electrochemical and permeation measurements. Electrochemical experiments show that polished steel surfaces without common drawing layers have more consistent free corrosion currents, polarization resistances, and B-values in solution A with low scattering compared to the solution B experiments. The influence of temperature at 50°C and an ambient temperature of 22°C was also tested.

The assessment of the impact of corrosion defects on the integrity and safe operation of through-wall pipelines is critical. In this work, a finite element-based model was developed to study the mechano-electrochemical (M-E) effects of external corrosion defects on 10CrMoAl steel pipelines. The effects of parameters such as defect sizes and internal pressures on pipeline conditions are also studied. The results show that increased corrosion depth leads to stress concentration at the center of the defect. The increase in internal pressure causes local plastic deformation and anodic current density concentration at the inner edge of the defect and in the adjacent areas of the defect. M-E interaction causes the growth of corrosion defects significantly at higher internal pressures. The corrosion defects increase with time. As the pressure increases, the failure pressure of the pipeline gradually decreases. The influence of defect depth on the corrosion rate at the defect is greater than that of defect width. With increasing in internal pressure and corrosion defect size, it will lead to more severe plastic deformation, resulting in accelerated corrosion.

A self-healing anticorrosion protective was developed for steel st-37 exposed to the marine tidal zone, which is composed of a multi-layer polymer coating. The coating includes zinc-rich epoxy primer, self-healing microencapsulated embedded epoxy, and a top coat consisting of polyurethane incorporated with silica nanoparticles. The size of microcapsules decreased with increasing agitation during encapsulation, which varies from 4 to 43 µm. Good performance was observed for producing the encapsulated particles with a size of up to 5 µm and more than 90% loading of the embedded healing agent, in which a 1680 rpm agitation along with a pH of 3 for the synthesis environment and a 130 min for the synthesis duration is set. The optimal amount of microcapsules and silica nanoparticles was 10 and 1.5 wt%, respectively. Also, the promised self-healing anticorrosion coating leads the damaged areas to be fully healed in almost 12 h in the face of harsh conditions. In contrast to the non-self-healing one, the healing ability of the developed self-healing coating shows good barrier properties and leads to a lesser loss of interface adhesion.