Yuwan Tian

In marine environments, critical components are susceptible to corrosion failure due to the influence of chloride ions. High-entropy alloys have garnered widespread attention owing to their superior comprehensive properties. This study investigates the corrosion behavior of Co-Fe-Ni-Mo-W high-entropy alloys in seawater and explores the role of chromium (Cr) in modulating their corrosion resistance. Electrochemical methods were employed to compare the corrosion resistance of CoFeNiMo_0.1W_0.2 and CoFeNiMo_0.1W_0.2Cr_0.7 high-entropy alloys in seawater, while modern physical characterization techniques—including XRD, SEM, and XPS—were utilized to elucidate the underlying corrosion resistance mechanisms. The results demonstrate that during prolonged immersion in seawater, the surface of the Cr-free CoFeNiMo_0.1W_0.2 alloy fails to develop a stable protective layer, leading to severe surface corrosion, with corrosion products including crystalline Ni(OH)₂ among others. In contrast, the Cr-containing CoFeNiMo_0.1W_0.2Cr_0.7 alloy exhibits excellent self-passivation characteristics in seawater: its open-circuit potential remains within a relatively positive range throughout a 49 d immersion period, its charge transfer resistance increases by nearly two orders of magnitude compared to the Cr-free counterpart, and no significant pitting pits or corrosion product accumulation are observed on its surface. The corrosion resistance mechanism can be attributed to the introduction of Cr, which promotes the formation of a dense passive film enriched with Cr₂O₃ on the alloy surface. This passive film possesses superior physical barrier and charge-shielding properties, thereby significantly inhibiting the adsorption and penetration of aggressive Cl⁻ ions, and thus effectively protecting the substrate.

Chloride-induced corrosion of steel reinforcements is one of the main factors restricting the durability of reinforced concrete structures. Chromium (Cr) alloying is an effective strategy to enhance the corrosion resistance of steel. However, the appropriate Cr content for different environments remains undetermined. In this study, steels with three different Cr contents of 0, 5, and 10 wt.% were prepared. Electrochemical methods and physical characterization techniques were used to investigate the effects of Cr content on the passive film and corrosion behavior of steels in a simulated concrete pore solution under chloride attack. The results show that Cr alloying increases the critical chloride concentration for steel depassivation, passive film resistance, and charge transfer resistance. Specifically, the critical chloride concentrations of 0Cr, 5Cr, and 10Cr are 0.63, 0.81, and 1.56 mol/L, respectively. In a simulated pore solution with 0.6 mol/L chloride, the charge transfer resistances of 0Cr, 5Cr, and 10Cr are 4.1, 5.8, and 63.4 × 10⁵ Ω·cm², respectively, corresponding to corrosion rates that are 1.39- and 15.31-times lower for 5Cr and 10Cr relative to 0Cr. Therefore, in concrete exposed to marine chloride attacks, the use of high Cr alloying is necessary. Although the cost increases and the weldability deteriorates, the improvement in corrosion resistance is far superior to that of medium Cr alloying. The excellent corrosion resistance of high-Cr steel stems from its passive film mainly composed of stable Cr₂O₃ with a lower oxygen vacancy defect density, while that of 5Cr is dominated by less stable Cr(OH)₃, which weakens the corrosion resistance of the passive film.

The marine atmospheric environment, characterized by a high chloride content, high humidity, and a high corrosion rate of structural steel, urgently demands anticorrosion methods that are compatible with other technologies such as alloy steel and organic coatings. In this study, an inhibitor-loaded conversion film was grown in situ on a steel surface to prevent chloride-induced corrosion. Specifically, a Mg-Fe layered double hydroxide (LDH) conversion film was grown on the steel surface, and p-aminobenzoate (pAB⁻) inhibitor ions were intercalated into the LDH. After half a year of natural corrosion in the actual marine atmospheric environment, the average corrosion rate of steel with the inhibitor@LDH film was 36.20 µm/a, which was 21% lower than that of the steel substrate (45.91 µm/a). The inhibitor@LDH film also effectively suppressed local pitting corrosion, with the density of corrosion pits significantly reduced by 64%. Furthermore, the inhibitor@LDH film promoted the formation of a denser and thinner rust layer on the steel surface, with a smaller crack width, fewer cracks, and an increased α-FeOOH/γ-FeOOH ratio. In summary, the inhibitor@LDH conversion film inhibits general and local corrosion on steel in a marine atmospheric environment.

Measuring the fatigue crack growth rate via the crack growth experiment (a-N curve) is labor-intensive and time-consuming. A machine learning interpolation–extrapolation strategy (MLIES) aimed at enhancing the prediction accuracy of small-data models has been proposed to accelerate fatigue testing. Two specific approaches are designed by transforming a-N curve data from N to ΔN and from a to Δa (S1)/Δa/ΔN (S2) to enrich the data volume and leverage the incremental information. Thus, a simple and fast-responding single-layer neural network model can be trained based on the early-stage data points from fatigue testing and accurately predict the remaining part of an a-N curve, thereby enhancing the experimental efficiency. Through exponential data expansion and data augmentation, the trained neural network model is able to learn the underlying rules governing crack growth directly from the experimental data, requiring no explicit analytical crack growth laws. The proposed MLIES was validated on fatigue tests for aluminum alloy and titanium alloy samples under different experimental parameters. Results demonstrate its effectiveness in reducing testing time/cost by 15–32% while achieving over 30% higher prediction accuracy for the a-N curve compared to a traditional machine learning modeling approach. Our research offers a data-driven recipe for accurate crack growth prediction and accelerated fatigue testing.

The microstructure evolution of Al_0.3FeCoNiCr_x (x = 0, 0.3, 0.5, 1, 1.5) high-entropy alloys (HEAs) were studied using X-Ray diffraction technique and scanning electron microscope equipped with energy dispersive spectrometer. The short-term and long-term corrosion behaviours of these alloys in 3.5 wt.% NaCl solution were studied by electrochemical impedance spectroscopy, potentiodynamic polarisation measurement, immersion test and corrosion morphology analysis. The results show that all the designed HEAs present single-phase FCC structure, and the increase in Cr content changes the microstructural morphology from cellular to a typical dendritic–interdendritic state. Without the influence of phase transformation, the corrosion resistance of Al_0.3FeCoNiCr_x HEAs gradually increases with the increase in Cr content. Our designed alloys exhibit excellent corrosion resistance compared to the existing HEAs in the AlFeCoNiCr composition system.

In this study, the surface of steel was coated with a Mg-Al-pAB-LDH coating in order to enhance its corrosion resistance in the marine environment. The crystal structure, micro-morphology, and chemical composition of the Mg-Al-pAB-LDH coating were characterised using physicochemical techniques. The corrosion protection performance in a simulated marine environment was evaluated through electrochemical methods. The results indicate that the Mg-Al-pAB-LDH coating effectively adsorbs chloride ions from the environment, thereby increasing the corrosion potential of the steel in chloride environments and reducing its corrosion current density. In addition, the Mg-Al-pAB-LDH coating applied to the surface of steel not only enhances the corrosion resistance in the marine environment but also possesses self-healing capabilities in areas of local damage to the steel surface.

Steel reinforcement in marine concrete structures is vulnerable to chloride-induced corrosion, which compromises its structural integrity and durability. This study explores the combined effect of the alloying element Cr and the smart corrosion inhibitor LDH-NO₂ on enhancing the corrosion resistance of steel reinforcement. Employing a machine learning approach with a support vector machine (SVM) algorithm, a predictive model was developed to estimate the polarization resistance of steel, considering Cr content, LDH-NO₂ dosage, environmental pH, and chloride concentration. The model was rigorously trained and validated, demonstrating high accuracy, with a correlation coefficient exceeding 0.85. The findings reveal that the addition of Cr and application of LDH-NO₂ synergistically improve corrosion resistance, with the model providing actionable insights for selecting effective corrosion protection methods in diverse concrete environments.

Marked changes in temperature, pH, dissolved oxygen (DO) content, and nutrient content typically occur in marine thermoclines, which are key factors that affect the corrosion of metals. Offshore platforms require marine metals to be exposed to deep-sea environments and thus increase their penetration into the marine thermocline. This study investigates the galvanic corrosion of E690 steel in a marine thermocline using a simulated marine thermocline (SMT). Specifically, the corrosion of E690 steel was analyzed using the wire beam electrode (WBE) technique, linear polarization (LP), corrosion morphology, and weight loss measurement. Results indicated that the SMT had a stable multilayer structure, and the variations in temperature, DO, pH, and nutrient concentration in the SMT were similar to those in the natural marine thermocline. There were two forms of E690 steel corrosion in the SMT: galvanic corrosion and seawater corrosion. The corrosion rate of seawater corrosion was influenced by the DO concentration. Galvanic corrosion occurred after the intrusion of E690 steel into the marine thermocline. The driver of galvanic corrosion was the difference values for E_corrs of E690 steel at various depths of the marine thermocline. The E_corr of E690 steel was influenced by the temperature, pH, and DO of the seawater, in the following order: DO >> T > pH. The continuous reduction in E_corr with depth contributed to large-scale galvanic corrosion, and the oscillation variation in E_corr with depth was the reason for small-scale galvanic corrosion. The primary anodic regions of galvanic corrosion were located in the area with the fastest temperature variation in the thermocline, and the position of the anodic regions rose with time. The anodic regions gradually expanded with time. The proportion of galvanic corrosion in the average corrosion rate could increase up to approximately 80% in the stable anodic region. There were many hemispherical corrosion pits on the surface of the single electrodes that were at the depths of 75 cm, 105 cm, and 135 cm. These single electrodes comprised a long-term, sustainable anodic region of galvanic corrosion.

Marked changes in temperature, pH, dissolved oxygen (DO) content, and nutrient content typically occur in marine thermoclines, which are key factors that affect the corrosion of metals. Offshore platforms have required marine metals to be exposed to deep-sea environments and have thus increased their penetration into the marine thermocline. This study investigates the galvanic corrosion of E690 steel in a marine thermocline using a simulated marine thermocline (SMT). Specifically, the corrosion of E690 steel was analyzed using the wire beam electrode (WBE) technique, linear polarization (LP), corrosion morphology, and weight loss measurement. Results indicated that the SMT had a stable multilayer structure, and the variations of temperature, DO, pH and nutrient concentration in the SMT were similar to those in the natural marine thermocline. Galvanic corrosion occurred after the intrusion of E690 steel into the marine thermocline. The driver of galvanic corrosion was the of E690 steel at various depths of the marine thermocline. The Ecorr of E690 steel was influenced by the temperature, pH and DO of seawater, and the order was DO >> T > pH. The continuous reduction of Ecorr with depth contributed to the large-scale galvanic corrosion, and the oscillation variation of Ecorr with depth was the reason for small-scale galvanic corrosion. The primary anodic regions of galvanic corrosion were located in the area with the fastest temperature variation in the thermocline. The proportion of galvanic corrosion in the average corrosion rate could increase up to approximately 80% in the stable anodic region. There were many deep corrosion pits in the long-term and stable anodic region of galvanic corrosion.

Using Cr-bearing low-alloy steel is an effective preventive measure for marine structures, as it offers superior corrosion resistance when compared to plain carbon steel. However, it remains unclear how quenching and tempering heat treatment, which is commonly applied to steel reinforcement in some specific environments to improve its mechanical properties, affects its corrosion resistance. In the present work, the impact of heat treatment on the passive film and depassivation behavior of the 0.2C-1.4Mn-0.6Si-5Cr steel are studied. The results reveal that quenching and tempering result in grain refinement of the Cr-bearing steel, which increases its hardness. However, this refinement causes significant degradation in its corrosion resistance. The critical [Cl⁻]/[OH⁻] ratio after quenching and tempering is determined to be approximately 6.6 times lower than that after normalization, and the corrosion rate is 1.6 times higher. After quenching and tempering, the passive film predominantly comprises iron oxides and hydroxides, with relatively high water content and defect density. Additionally, the Fe^II/Fe^III ratio and film resistance are relatively low. In comparison, after normalization, the steel exhibits high corrosion resistance, with the passive film formed offering the highest level of protection.