The working conditions of oil and gas fields with high temperature, high pressure and high concentration of corrosive medium have put forward strict requirements for the corrosion resistance of steels and alloys in service. In terms of common sense, martensitic stainless steel has become an economical and effective alternative to expensive corrosion-resistant alloys in oil and gas fields due to its good corrosion resistance and mechanical properties. This paper mainly introduces various martensitic stainless steels for oil and gas fields and their corrosion resistance characteristics and relevant mechanisms, summarizes their corrosion failure modes and the factors affecting their corrosion resistance, sort out the measures to improve and optimize their corrosion resistance, and summarize the current research status at home and abroad for improving the corrosion resistance of martensitic stainless steels used in oil and gas fields, in terms of the alloy composition, microstructure, anti-corrosion coating and corrosion inhibitor etc. Finally, look forward to the research directions of improving their corrosion resistance. The purpose of this study is to provide a reference for the development and production of martensitic stainless steels with better corrosion resistance for the application in oil and gas fields.

As a high-strength alloy steel, 42CrMo steel is extensively used in the fields of machinery manufacturing, automotive engineering, petrochemicals, and aerospace et al. due to its remarkable mechanical properties. Nevertheless, in order to cope with the harsher service environments, it is imperative to further enhance its wear resistance and corrosion resistance. This paper comprehensively reviews the research progress of laser cladding technology applied to 42CrMo steel at home and abroad. It examines the recent progress and existing problems in aspects such as the cladding materials, optimization of process parameters, microstructure and microhardness, wear resistance and wear mechanisms, corrosion resistance and anticorrosion mechanism of the clad coatings. Moreover, it looks forward to the development trend of laser cladding technology for the surface modification of 42CrMo steel, aiming to provide a theoretical basis and technical reference for enhancing the comprehensive performance of 42CrMo steel.

In order to clarify the performance of marine steel in real service conditions of polar ice seawater with microorganisms at low temperature, herein, the corrosion and wear corrosion behavior of a F-class marine steel FH40 at low temperatures in simulated polar seawater solution, which is a mixture of artificial seawater with Psychrophilic cibarius containing 2216E culture medium was studied via immersion test, electrochemical measurement and reciprocating friction and wear test. The results showed that FH40 steel consisted primarily of ferrite and a small amount of pearlite, with minor common inclusions containing Al, Ti, and Si. The corrosion rate of the steel in the simulated polar seawater was (0.238 ± 0.005) mm/a. Corrosion products composed of γ-FeOOH, α-FeOOH, Fe₂O₃/Fe₃O₄, and a microbial biofilm of Psychrophilic cibarius. These loose and porous corrosion product film, along with localized coverage of polar microorganisms, synergistically induced the formation of pits. The friction coefficient of steel in simulated polar seawater was 0.41 with a specific wear rate of 4.1 × 10^-5 g/(N·m·s) and a wear volume of 0.019 mm³. The mechanism related with the wear-corrosion was identified as a hybrid model involving mechanical removal and corrosion removal. In addition, friction exacerbated localized corrosion and compromised the corrosion protection of the rust layer, while the post continued corrosion of the worn steels helped alleviate pitting corrosion in the wear scar area and reduced the width of the wear scar.

Peanut shell extract was prepared by reflux method using forestry and agricultural residue of peanut shell as raw materials. The corrosion inhibition properties of the peanut shell extract (PSE) on cold-rolled steel (CRS) in hydrochloric acid (HCl) solution was studied using mass loss measurement, potentiodynamic polarization curve (PDP) and electrochemical impedance spectroscopy (EIS), metallographic microscopy (MM), and scanning electron microscopy (SEM). Additionally, the relationship between the surface tension and conductivity of the corrosion inhibitor solution and the performance of PSE was also investigated. The results indicate that PSE exhibits excellent inhibition properties for CRS in 1.0 mol/L HCl solution, with the inhibition efficiency (η_w) increasing as the concentration of PSE increases. The inhibition efficiency (η_w) can reach up to 93.15% with the addition of 200 mg/L PSE at 40 ℃. However, the inhibition efficiency decreases with higher acid concentration and with longer inhibition time. The adsorption of PSE on the CRS surface follows the Langmuir monolayer adsorption model, with |ΔG⁰| in the range of 20 kJ/mol to 40 kJ/mol. This indicates that the adsorption of PSE on the CRS surface involves a combination of physical and chemical interactions. PSE acts as a mixed inhibitor, effectively inhibiting both the cathodic hydrogen evolution reaction and the anodic dissolution reaction. The Nyquist diagram features a single capacitive reactance arc, indicating that the corrosion of CRS in an acidic medium is primarily inhibited by charge transfer resistance. The microtopography analysis using MM and SEM confirmed that PSE effectively prevented the corrosion of CRS by HCl. In comparison to the bare surface, the surface hydrophobicity of CRS increased after inhibition test. The conductivity of the solution decreased after inhibition test, and the surface tension decreased with increasing PSE concentration. The surface tension of the solution after inhibition test was higher than that before.

Under actual operating conditions of wind turbine blades, rain erosion causes extremely severe damage to the coatings on wind turbine blades. Polytetrafluoroethylene (PTFE) is often used to enhance the wear resistance, hydrophobicity, anti-icing, and anti-sand erosion properties of coatings. However, research on the impact of PTFE on the rain erosion resistance of coatings is lacking. Therefore, this study investigates the impact of PTFE on the wear resistance and rain erosion resistance of polyurethane (PU) protective coatings on wind turbine blades, as well as the damage mechanisms of these coatings. This study prepared PU coatings with different PTFE contents, tested the basic properties of the PU coatings. Additionally, the study explored the impact of varying amounts of PTFE on the erosion resistance of PU coatings under two different erosion conditions using a high-speed liquid drop erosion device. The study used a profilometer to characterize the macroscopic morphology of the coatings and measure the volume loss. It employed scanning electron microscopy (SEM) to observe the microstructure of the coatings, and combined with energy-dispersive X-ray spectroscopy (EDS) to analyze how PTFE influences the wear resistance and rain erosion resistance of the coatings. The wear resistance tests showed that the coating's wear resistance improved with increasing PTFE content, with the best performance observed at a mass fraction of 5%. The liquid drop erosion tests revealed that, compared to coatings without PTFE, coatings with 1%-2%PTFE exhibited little change in erosion resistance. However, coatings with 3%-5%PTFE experienced a sharp decrease in erosion resistance. SEM and EDS analysis indicated that fluorine (F) elements accumulated at specific locations on the coating surface, leading to the formation of defects such as pinholes, peeling, and delamination pits. Moreover, higher PTFE content in the coating correlated with an increased presence of surface defects.

When navigating in polar ice regions, ships are subject simultaneously to both ice friction and seawater corrosion. However, the interaction behavior between wear and corrosion of shipbuilding steels remains unclear. In this study, the corrosion-wear behavior in seawater of three types of shipbuilding steels, EH40, FH40, and 921A was studied via mechanical-electrochemical approach. The results indicate that the three shipbuilding steels all suffered from abrasive wear, while different clusters composed of abrasive dusts and corrosion products co-exist on the worn surfaces. Among them, 921A demonstrated the best wear and corrosion resistance due to its high hardness and stable martensitic structure, followed by FH40, while the EH40 exhibiting the poorest performance. Although the volume loss directly caused by corrosion accounts for a relatively small proportion of the total volume loss, corrosion can significantly accelerate the wear of steel. For FH40 and EH40, the total corrosion wear is dominated by the portion of pure mechanical friction, and the corrosion induced wear increments accounts for 18.5% and 32.8%, respectively. In contrast, the corrosion induced wear increment for 921A was twice the proportion of pure mechanical friction, indicating a marked corrosion acceleration effect on mechanical wear.

Ti-alloy has widely used in the manufacture of advanced marine equipment. However, in practical applications, galvanic corrosion may tend to happen when Ti-alloy is coupled with dissimilar metallic materials, which significantly threatens the reliability and service lifetime of marine equipment. In present work, the galvanic corrosion behavior of coupling pairs of Ti80 alloy with four commonly-used metallic materials for marine engineering, such as 921A steel, B10 Cu-alloy, 6061 Al-alloy and 40Cr steel respectively, in NaCl solution was studied via weight change measurement, open circuit potential measurement, potentiodynamic polarization measurement and electrochemical impedance spectroscopy as well as 3D optical profilometer, Fe-SEM and XRD. It is found that galvanic corrosion may occur when Ti80 alloy is coupled with any one of the four metallic materials, while the galvanic corrosion does not alter the corrosion behavior of the anode material for the four pairs. Even though, the difference of free-corrosion potentials between the two metallic materials of the coupling pair will play the role as driving force for electron transfer of the coupling system, which may lead to the accelerated dissolution of the metallic material acted as the anode. By taking the free-corrosion rate of the four test metallic materials as reference, after being coupled with Ti80 alloy the increment in corrosion rate of the four metallic materials can be ranked as follows: 6061 > 40Cr > 921A > B10. Besides, it is noted that there is not positively correlation between the galvanic corrosion effect with the potential difference of the coupling pairs.

The inhibition performance of nitrobarbituric acid (NBA) on AZ31B and AZ91D alloys in 3.5%NaCl solution was comparatively evaluated using weight loss method, hydrogen evolution measurement, and electrochemical tests. The results revealed that NBA significantly could inhibit the corrosion of AZ31B in 3.5%NaCl solution, whereas it promoted the corrosionof AZ91D alloy. The inhibition mechanisms of NBA on the two Mg-alloys were elucidated through SEM-EDS, XRD, and XPS analyses. The acidic NBA reduced the pH value of 3.5%NaCl solution, initially dissolving Mg matrix of AZ31B alloy. For AZ31B alloy, the dissolution of the Mg matrix released Mg²⁺ ions, facilitating the formation of a dense Mg(OH)₂ scale on the alloy surface, which effectively inhibited the further corrosion. Conversely, the inherent corrosion resistance of AZ91D hindered the rapid formation of a protective scale Mg(OH)₂, allowing NBA to dissolve the substrate, thus promoting the corrosion of AZ91D alloy.

The effectiveness of cathodic protection on rotating equipment, such as drum filters is influenced by rotation parameters. Herein, a test set, on which test-pieces made of Q345B steel can be inserted, was designed to simulate the rotation circumstance of drum filters in an artificial seawater. Then, the effectiveness of cathodic protection on the test-pieces of Q345B steel was assessed according to the known orthogonal experiment procedure in terms of the varying parameters such as protection potential, duty cycle, and rotation frequency etc. The results show that as the rotation frequency increases from 0.010 r/d to 0.020 r/d, the degree of cathodic protection effectiveness first increases and then decreases, with the best protection effectiveness emerges at the frequency of 0.015 r/d, where the protection degree reaches up to 90.67%. This may be related to the flow rate and the morphology of corrosion products. As the duty cycle increases from 0.25 to 0.75, the degree of cathodic protection gradually increases. Regarding the protection potential, when the set protection potential negatively increases from -0.80 V to -1.25 V (vs. SSC), the degree of cathodic protection increases from 12.43% to 90.67%. This may be related to the proportion of cathodic polarization products CaCO₃ and Mg(OH)₂. When the proportion of CaCO₃ is low and that of Mg(OH)₂ is high, the Ca-containing deposition layer becomes tighter, resulting in better cathodic protection effectiveness.

The pickling process is a crucial step in the production of tinplate, and alterations in process parameters can affect the corrosion behavior of tinplate, which varies with changes in the tin coating mass. Currently, there is a lack of systematic research on the coupled influence mechanism of the pickling process and tin coating mass on the corrosion behavior of tinplate. Herein, the influence of electrolytic pickling and chemical pickling on the corrosion resistance of tinplates with different tin coating mass was assessed by means of neutral salt spray (NSS) testing, electrochemical testing methods and scanning electron microscopy (SEM), in terms of the variation of corrosion resistance and microstructure of coatings with varying tin coating weights and pickling processes. The results indicate that as the tin coating mass increases, the negative impact of switching to a chemical pickling process on the properties of tinplate gradually diminishes, which may be ascribed to the improved coating microstructure and property with the increasing tin mass. Furthermore, in case of high tin coating mass, the tinplate being subjected to chemical pickling can provide corrosion resistance comparable with that being subjected to electrolytic pickling.

Nickel based 718 alloy is commonly used to fabricate grid springs for pressure water reactor, due to its excellent mechanical properties, relative ease of manufacturing, and good corrosion resistance. There is a risk of stress corrosion cracking (SCC) for nickel based 718 alloy in harsh environments such as irradiation, stress, and high temperature and pressure water in the primary circuit. In recent years, fuel rod damage caused by SCC of nickel based 718 alloy grid springs has emerged both domestically and internationally, which has a significant impact on the safety, reliability, and economy of nuclear power plants. Herein, the SCC initiation behavior of nickel based 718 alloy strips, being subjected to standard heat treatment, in a simulated pressurized water environment of primary circuit of nuclear power plant was assessed, while the evolution of crack initiation on the alloy surface was observed through intermittent sampling under different strain conditions. It is found that the cracking of 718 alloy emerged mainly on grain boundaries, meanwhile, the precipitates of (Nb, Ti)C tend to be oxidized into brittle Nb containing oxides. The oxidized (Nb, Ti)C and TiN are easy crack under the action of stress. With the increase of strain, cracks at grain boundaries and on particles (Nb, Ti)C tend to further propagating, and the cracks at TiN tend to expanding towards grain boundaries. Therefore, (Nb, Ti)C and TiN may play a detrimental role to the SCC resistance of nickel based 718 alloy.

The effect of self-generated magnetic field produced by electric current on the corrosion behavior of Cu in simulated marine atmospheric environments was studied via a novel lab-made electrochemical test set, which consists of that a current-carrying copper conductor is covered with T2 pure Cu foil, and a thin electrolyte layer (TEL) on top of the Cu foil. The surface morphology and composition of the corrosion products were characterized by using scanning electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy techniques. The results showed that with the increasing intensity of the self-generated magnetic field, both the cathodic and anodic processes of the copper were accelerated, jointly leading to an increase in the corrosion rate. During long term corrosion exposure, the composition of the corrosion products on the copper surface changes with the increasing intensity of the self-generated magnetic field, while weakening its protective ability for the subsequent corrosion of Cu substrate, thus, pitting corrosion occurs on the Cu surface. At the same time, it is found that the corrosion degree of the Cu surface is closely related to the direction of the electric current and locations of the test piece, namely where the current input the corrosion degree is higher than that the current output. Herewith, the influence mechanism of the self-generated magnetic field on the atmospheric corrosion of Cu is further discussed.

The marine corrosive environment is complex, and the marine structure itself is also subjected to stress and other effects, which gradually highlights the corrosion and performance degradation problems of high-strength Al-alloy welded joints used in marine equipment. Herein, the corrosion behavior and performance degradation of welded joints of 7-series high-strength Al-alloy under different stresses, while immersion in Qingdao natural seawater at 5 ℃ for different times was studied via a lab simulation set, electrochemical measurement, universal test machine, SEM and XPS, in terms of the corrosion morphology, corrosion products, and degradation regularity of welded joints. The results show that as stress increases and immersion time prolongs, the corrosion tendency of high-strength Al-alloy welded joints increases, and their corrosion resistance gradually decreases; while the corrosion potential of the welded joint becomes more negative, the charge transfer resistance decreases, resulting in lower potential, higher corrosion sensitivity, and poorer corrosion resistance. When subjected to tensile stress exceeding 25%σ_s, as the pre stress increases, the proportion of oxygen in the corrosion products continues to increase, the corrosion product film is damaged, and the corrosion becomes more severe. With the increase of stress and immersion time, the elongation and cross-sectional shrinkage of the welded joint after fracture decrease, and thus the sensitivity to stress corrosion increases.

Herein, the influence of cyclic planar molecular structure and linear molecular structure of polyaspartic ester polyurea amino component on the microstructure of polyurea coatings and the diffusion behavior of corrosive media within the coating was studied by means of molecular dynamics simulation. The results indicate that compared with linear molecular structures, cyclic planar molecular structures have greater steric hindrance, resulting larger free volume and lower density of the polyurea system; The increase in molecular branching can further increase the free volume of the coating, leading to a decrease in the density of the system; The increase in molecular chain segment length has a relatively small impact on the compactness of the system; Water molecules can form hydrogen bonds with polyurea molecules and tend to exist in an aggregated state inside the coating. Regarding the corrosion resistance of the formed coating, linear molecular structures are more conducive to formation of dense coating structures and enhancement of coating corrosion resistance. Finally, this article conducts a study on the correlation mechanism between coating structure and performance through molecular simulation methods, providing a new means of molecular simulation screening for coating formulation design.

The Al_0.5CoCrFeNi high-entropy alloy was smelted by vacuum medium frequency induction melting, followed by homogenization heat-treatment and cold rolling with 40% reduction, and then post-heat treatment at 800, 1000 and 1200 ℃ respectively. The microstructure and mechanical properties, as well as the corrosion behavior in solutions of 0.5 mol/L H₂SO₄, 0.5 mol/L NaOH and 3.5%NaCl of as the cast alloy and the rolled + post heat-treated alloys were studied by XRD, SEM, EDS, AFM, universal testing machine and electrochemical corrosion test. The microstructure analysis shows that the as-cast high entropy alloy has a typical dendrite structure composed of fcc-phase and bcc-phase (B2) with precipitates of flocculent structure-like fine fcc-phase within the B2-phase, however after rolling+heat treatment, the fine fcc-phase within the B2 phase is completely dissolved, while certain amount of acicular B2-phase is precipitated within the fcc-phase. Mechanical analysis shows that the precipitation of the hard and brittle acicular B2-phase increases the yield strength and hardness of the alloy. After rolling + heat treatment, the potential difference within the B2 phase is eliminated, but the potential difference between B2-phase and fcc-phase is increased, nevertheless, which gradually decreases with the increase of heat treatment temperature. The electrochemical corrosion test results show that in 0.5 mol/L H₂SO₄ solution, the corrosion properties of the alloy at different temperatures are linearly related to the Cr content in B2-phase. In 0.5 mol/L NaOH solution, the as-cast alloy and rolled + 1000 ℃ heat treated alloy showed excellent corrosion resistance. In contrast, the rolled + 1200 ℃ heat treated alloy has the best corrosion resistance in 3.5%NaCl solution.

The influence of build-up direction and post annealing treatment on corrosion properties of the selective laser melting (SLM) Ti6Al4V alloy were investigated in terms of its microstructure evolution and corrosion performance versus processing conditions. The passivation and corrosion behavior of the SLM alloy with different morphology of α/α′ phases was assessed in Hanks solution. The build-up directions and post annealing treatments of the SLM-Ti6Al4V alloy significantly result in differences of its corrosion resistance in Hanks solution. The corrosion resistance in the XZ plane of the SLM-Ti6Al4V alloy heat-treated below 800 ℃ is better than that of the XY plane, showing obvious anisotropy. The size of the α/α′ phase increases with the increasing annealing temperatures, correspondingly, the anisotropy of the corrosion resistance weakens. The SLM-Ti6Al4V alloy after annealing at temperatures below 800 ℃ presents the pitting corrosion, but the corrosion along boundaries in the alloy after annealing at temperatures above 900 ℃. The excellent corrosion resistance was obtained for the alloy annealed at 800 ℃ due to a desired α/α′ phase size and the density of boundaries.

The localized corrosion behavior of EH690, a 690 MPa grade low alloy steel in an artificial chloride containing acidic seawater was assessed via immersion test, optical microscope, laser confocal microscope, and scanning electron microscope with energy dispersive spectroscope, in terms of the effect active inclusions on the localized corrosion of the steel. It is found that the inclusions in EH690 steel are similar in shape, mainly spherical or ellipsoidal, with a diameter of 1-4 μm. The types of inclusions in steel plates of different thickness are basically the same, which may be divided into three categories: (Mn,Ca)S-MgO·Al₂O₃, (Mn,Ca)S-MgO·Al₂O₃-TiN, and (Mn,Ca)S. The density of the corrosion-active inclusion is higher on the surface area of the thick plate. The dissolution of corrosion-active inclusions first occurs at the interface between the inclusion and the matrix, meanwhile causes corrosion of matrix. However, in case when immersion in the same medium for the same period, these inclusions exhibit different corrosion activities, which may be due to the different diffusion capabilities of aggressive particles in the pits and the micro-galvanic corrosion within the pits.

The long-term corrosion behavior of test pieces and cooling plate of laser additive manufactured AlSi10Mg Al-alloy in commercial ethylene glycol coolant was assessed via isothermal test at 88 ℃ and thermal cyclic test, meanwhile the degradation of ethylene glycol coolant was examined along with the corrosion process. The results showed that the pH value and reserve alkalinity of the coolant decreased with the increasing time, while the content of Al ions, mechanical impurities, and acidic oxidation products of ethylene glycol in the coolant increased, and glyoxylic acid was the main acidic oxidation product of ethylene glycol. The monitoring parameters of coolant degradation displayed different trends in thermal cycling test and constant temperature test, with a clear time turning point in thermal cycling test, and the corrosion rate of aluminum alloy in thermal cycling test was significantly higher than that in isothermal test. The corrosion products on the surface of Al-alloy were composed of Al₂O₃, Al-ethylene glycol, Al-ethylene glycol oxidation products, and precipitates of corrosion inhibiting components.

The internal and external corrosion protection of oil and gas pipelines mainly depends on highly corrosion-resistant coatings. However, it remains a challenge to assess the protective performance of existing coatings non-destructively. In this work, a double-electrode electrochemical impedance probe was designed to estimate the degradation of coatings. The lab tests show that the EIS measured by the double-electrode probe agrees well with that by conventional three-electrode cells. In addition, the |Z|_{0.01 Hz} increases first and then becomes stable with the increasing distance between the two electrodes. Through the simulation of COMSOL electrostatic field, it shows that the coating impedance measured by the double-electrode probe is twice that by a single-electrode probe. Although, the coating degradation state can be revealed using either probe, but the use of double-electrode probe can avoid the troubles of requiring to find out the iron-related leaking spot emerged on the coating during field tests. Eventually, a portable impedance meter for in situ non-destructive monitoring of coating is designed based on the double-electrode probe. Through online evaluation of coating degradation state, the impedance meter may provide guidance for the determination of preventive maintenance cycle and maintenance area of degraded coatings for pipeline or large tank.

As the key equipment connecting the primary and secondary circuits of PWR nuclear power plants, the corrosion behavior of heat transfer tubes of steam generator (SG) would be affected by different water chemistry. Herein, the effect of dissolved oxygen (DO) and dissolved hydrogen (DH) on the corrosion performance of Nickel-based alloy 690 used as SG tubes in high temperature pressurized water were studied. In comparison with the formed oxide scale of the alloy formed in the high temperature water containing 1 μg/L DO, in the high temperature water containing 3 mg/L DO, the Cr-rich oxides in the formed oxide scale tend to be unstable and easily soluble in water, thus resulting in a thickened scale of loose, porous and non-protective NiO oxides. Furthermore, in the high temperature water containing 3 mg/L DH, DH leads to an increase of Cr(OH)₃ and a decrease of Cr₂O₃ in the formed oxide scales, as a result, the protectiveness of the oxide scales deteriorated, and the oxide scales grew thicker.

AlSiN nano-composite coatings were prepared on TC4 Ti-alloy substrate by using multi-arc ion plating technique. The influence of N₂ flow rate and target-substrate distance on their microstructure, mechanical properties and corrosion resistance in 3.5%NaCl solution was investigated. The results show that the variation of plating process parameters influence the crystalline growth mode of the AlSiN coating. By longer target-substrate distances and higher N₂ gas flow the prepared AlSiN coatings exhibited higher crystallinity via a columnar grain growth mode, while a dense coating of finer grains or amorphous structure was obtained by shorter distances and lower N₂ gas flow rates. Comparatively, the AlSiN coating of higher crystallinity exhibits higher microhardness and excellent mechanical properties. The corrosion resistance of the coatings was influenced by the combined effects of crystallization growth mode and mechanical properties, namely the crystallization mode may affect the penetration of the corrosive medium and the formation of the surface oxide scale, while the mechanical properties may be related with the strength and the generation of defects of the coating. Electrochemical data indicate that the AlSiN nanocomposite coating prepared by a N₂ flow of 0.15 L/min and a target-substrate distance of 180 mm exhibited the optimal corrosion resistance, showing one order of magnitude reduction in corrosion current density compared to that of the TC4 substrate.

7075 Al-alloy suffered often from corrosion damages during service in coastal area environments, due to seawater splash or salt atmosphere corrosion. Therefore, for the problem of high strength but poor corrosion resistance of 7075 Al-alloy, a cyclic strengthening (CS) process at ambient temperature is adopted to improve its strength and corrosion resistance. Compared with the traditional peak aging T6, the cyclic strengthening treated 7075 Al-alloy shows better corrosion resistance with higher free-corrosion potential and higher impedance value in electrochemical test. In NaCl solution, the intergranular corrosion depth of the T6 treated alloy was 58 μm, while that of the CS treated one was only 15 μm. The corrosion pits and corrosion microcracks formed for the CS alloy are smaller than that of the T6 ones in salt spray corrosion test. The corrosion products of both T6 and CS alloy contain Zn(OH)₂ and ZnCl₂, the formation of which is due to the electrochemical reaction between the η′(MgZn₂) phase at the grain boundaries of the T6 alloy, and the clusters of atoms in the CS alloy and the Al-matrix, respectively. After the CS process, a large number of dislocations and clusters of atoms are generated within the 7075 Al-alloy, which hinders the dislocation movement and increases the free-corrosion potential, thereby improving the strength and corrosion resistance of the 7075 Al-alloy.

Maine Carbon Capture, Utilization and Storage (CCUS) is one of the effective methods to solve the problems caused by the excess emission of CO₂. However, the pipelines face serious corrosion problems in the process of CO₂ transport. Aiming at marine corrosion problems under supercritical CO₂ conditions, this work investigated the corrosion behavior of A106 carbon steel with different water contents and temperature by mass loss, scanning electron microscope (SEM), X-ray diffractometer (XRD) and three-dimensional stereoscopic microscope. Results indicate that the corrosion rate of A106 steel increased with the increase of water content in CO₂ environment at 10 MPa and 35 ℃. When the water content exceeded 2000 μL/L, the corrosion rate was significantly accelerated. A106 steel reached the maximum corrosion rate, i.e., 0.16 mm/a at the water content of 3000 μL/L. However, the localized corrosion rate of A106 steel was the highest with the value of 0.73 mm/a at the water content of 2000 μL/L. In the CO₂ environment at 10 MPa, the corrosion rate of A106 steel decreased from 25 to 60 ℃ and then increased with the increase of temperature. At 60 ℃, the corrosion rate reached a minimum value, i.e., 0.025 mm/a. Therefore, temperature and water content are the key factors affecting the corrosion of steel materials in supercritical CO₂ environment.

Hydrogen vessels and pipelines with cracks are at risk of hydrogen-induced cracking (HIC) failure. Predicting or assessing HIC requires accurate knowledge of hydrogen concentration at the crack tip. Due to the difficulty related with directly detecting hydrogen atoms, numerical methods are commonly used to acquire the hydrogen diffusion and concentration distribution. However, the chosen diffusion constitutive model can significantly influence the calculation results of hydrogen concentration. Herein, for two selected hydrogen diffusion models, namely a model of hydrogen diffusion coupled with hydrogen trapping and another model of considering only the hydrostatic stress-induced hydrogen diffusion, an Abaqus subroutine was proposed to calculate the hydrogen diffusion around a mode I crack tip during loading and load-holding periods. The differences in hydrogen concentration evolution between the two models were evaluated under various conditions. The results showed that differences in diffusible hydrogen concentration evolution between the two models during loading became more pronounced when the diffusion rate was slower or the material had lower strength. If only the diffusible concentration is needed and the diffusion rate is fast, both diffusion models are applicable. The steady-state hydrogen concentration distribution in low-strength steels was strongly influenced by hydrogen trapping, whereas in high-strength steels, stress effects gradually dominated as the initial hydrogen concentration increased. Therefore, for low-strength steels, the hydrogen trapping effect must be considered, whereas for high-strength steels, it can be neglected. The effect of hydrogen trapping on steady-state hydrogen concentration distribution increased significantly with higher trap binding energy. When the trap binding energy was relatively low, the two models produced comparable results, allowing the use of the trapping-free diffusion model. However, the model with hydrogen trapping was more appropriate when hydrogen-induced softening was also considered. These results provide a valuable reference for selecting a diffusion model when analyzing the HIC behavior of metals.

Ferritic Fe-Cr-Al based alloys have been considered as one of the most promising candidates as clad material for the accident tolerant fuel (ATF) owing to their excellent high temperature oxidation and corrosion resistance. The corrosion performance of Fe-Cr-Al alloys in highly oxidizing environments (such as high temperature, high pressure hydrothermal conditions) was very important to determine their suitability served as ATF cladding materials, especially for the domestic Fe-Cr-Al alloys. Herein, the corrosion behavior of domestic ferritic Fe-13Cr-4Al-2Mo-0.65Nb-0.4Ta-0.05Y alloy (mass fraction, %, designated as M2 hereafter) was examined via an autoclave at 360 ℃ in the condition of saturated vapor pressure with different dissolved-oxygen contents: namelytotal deoxidization (DEO), dissolved-oxygen concentration of 100 μg/L O₂ (DO100) and saturated dissolved-oxygen exposures (SDO) respectively for a long term. Then the formed oxide scales on M2 alloy were characterized by using XRD and SEM combined with EDS, and TEM in terms of their morphology and phase constituents, as well as elemental distribution and microstructure. The results indicated that the thickness of oxide scales on FeCrAl based alloy was 1.4, 2.3 and 0.1 μm in conditions DEO, DO100 and SDO, respectively. And with the increasing of dissolved oxygen contents, the phase constituent of the formed oxide scale changes from a mixed structure of spinel-like ((Fe, Cr)₃O₄), M₃O₄ and M₂O₃ in DEO conditions to the mixture of hematite-like (Fe, Cr)₃O₄ and (Fe, Cr)₂O₃ in DO100 conditions, and then a thin and dense monolayer structure of hematite (Fe, Cr)₂O₃ in SDO conditions. Correspondingly, the corrosion kinetics also changed from mass loss into mass gain. All the above results indicated that dissolved-oxygen had a significant influence on the corrosion of domestic FeCrAl based alloy in high temperature water, and it is worth noted that the domestic FeCrAl based alloy revealed an excellent corrosion resistance especially in SDO condition.

The intergranular corrosion behavior of friction stir welded joints of semi-solid 7075 Al-alloy in solution of 10 mL H₂O₂ + 57 g NaCl + 1000 mL H₂O was assessed by means of immersion test, optical microscope, scanning electron microscope (SEM) and energy spectroscopy (EDS) etc. The results show that the entire welded joint can be differentiated as four zones: the base metal (BM) zone, the heat-affected (HAZ) zone, the thermo-mechanically affected (TMAZ) zone and the nuclear weld (NZ) zone. Among them, the corrosion degree of the weld center (NZ) is the lightest, the heat-affected (HAZ) zone is the most serious; while the corrosion degree of the four zones of the weld joint may be ranked in an order from low to high as follows NZ < BM < TMAZ < HAZ. In general, with the increase of corrosion time, the corrosion forms of every zone of the friction stir welded joint of semi-solid 7075 Al-alloy conform to the same characteristics of pitting corrosion, intergranular corrosion and spalling corrosion. The difference of corrosion performance of different zones of semi-solid 7075 Al-alloy friction stir welded joints may be attributed to the different microstructure and distribution of second-phase particles in various zones of the joint.

Regarding the microbial corrosion issue in polymer flooding pipelines for oil fields, the corrosion behavior and patterns of pipeline steel in a polymer flooding environment containing anaerobic sulfate reducing bacteria (SRB) and aerobic iron bacteria (IOB) were assessed by means of electrochemical measurement, and characterization in surface morphology, composition and phase constutients of corrsion products. The results indicate that both SRB and IOB attend to adhere and grow on the surface of pipeline steel in polymer flooding media, and a loose microbial film can be seen on the steel surface, significantly affecting the corrosion electrochemical process of pipeline steel. In the early stage of biofilm growth in SRB and IOB environments, open circuit potential of the steel increased about 20 mV, indicating the physical barrier effect of extracellular polymeric EPS on electrochemical processes. The corrosion rate in IOB environment is relatively low, and the corrosion current density significantly increases in SRB and SRB/IOB environments. In the coexistence environment of SRB and IOB, IOB consumes dissolved oxygen to create an anaerobic environment for SRB, which is conducive to the growth of fixed SRB, thereby promoting cathodic and anodic reactions, transforming the corrosion form from non-uniform corrosion to localized corrosion, and forming corrosion pits with peculiar characteristics.

The corrosion behavior of five commonly used power grid materials: carbon steel, zinc, galvanized steel, aluminum, and copper in natural environment of a typical coastal area at Zhejiang province was assessed via year-long exposure testing. Meanwhile, electrochemical performance, the surface and cross-sectional morphology and phase composition of the corrosion products were systematically analyzed. Additionally, by integrating four months of online corrosion current monitoring data, the corrosion rates and mechanisms of different materials were explored. The results indicate that the coastal environment significantly affects the corrosion of different materials, with noticeable differences in morphology and thickness of the rust scale. Copper and aluminum exhibited better corrosion resistance, while carbon steel and galvanized steel had higher corrosion rates, and zinc showed strong corrosion resistance in the initial stage.

NdFeB magnets of poor corrosion resistance was subjected to surface Mg-alloying via magnetron sputtering technique and followed by thermal diffusion treatment, so that to improve the corrosion resistance of the magnets. The corrosion resistance of the surface Mg alloying NdFeB magnets in 3.5%NaCl solution is investigated by static immersion test corrosion electrochemical measurements and accelerated aging tests to optimize the preparation parameters of the surface Mg alloying. The surface Mg alloying NdFeB magnets before and afer corrosion test are characterized by X-ray diffractometer, X-ray photoelectron spectrometer and scanning electron microscope, as well as by atomic force microscope for determining the potential difference between the phases within the magnets during corrosion process. Results show that the magnets subjected to Mg-sputtering and then diffusion treated at 550 ℃ for 105 min shows the best corrosion resistance, with E_corr of -0.684 V and I_corr of 1.055 × 10^-6 A·cm^-2, which is an order of magnitude lower than that of the bare magnets (6.896 × 10^-5 A·cm^-2). The mechanism related with the enhancement of corrosion resistance may be that the Mg atoms diffuse into the intergranular of the magnets, stabilizing the Nd-rich phase in grain boundaries and relieving the potential difference between the matrix and the intergranular, thus reducing the free-corrosion tendency of NdFeB magnets.

Zn-alloys are regarded as promising biodegradable metallic materials due to their low corrosion rates and favorable cytocompatibility. To address the challenges associated with the Zn-0.4Mn alloy, which exhibits better ductility but lower surface hardness, wear resistance, and cytocompatibility etc., herein, the effect of surface laser remelting on the microstructure, microhardness, wear resistance, corrosion resistance, and cytocompatibility of the Zn-0.4Mn alloy was assessed. The findings revealed that the surface hardness and wear resistance of the remelted Zn-0.4Mn alloy were significantly enhanced. Furthermore, a reduction in corrosion current density and an increase in impedance indicated that laser remelting improved the corrosion resistance of the Zn-0.4Mn alloy. Additionally, L929 cytotoxicity tests demonstrated that the biocompatibility of the Zn-alloy was enhanced due to improved corrosion resistance and reduced leaching of Zn ions. Consequently, laser remelting emerges as an effective method for improving the mechanical properties, degradation characteristics, and biosafety of Zn-alloys.

As raw materials, polyurea resin (PU) and hexadecyltrimethoxysilane (HDTMS) were diluted with ethanol, then PU paints with concentrations of 3% to 100%, and HDTMS paints with concentrations of 1% to 30% were prepared respectively, of which the contact angles for water were comparatively examined. Meanwhile, a composite paint of PU-HDTMS based on the optimal concentrations of the above two paints was prepared. Further, coatings of PU, HDTMS and PU-HDTMS were applied on mortar blocks respectively. The anti-icing performance of the coatings was comprehensively evaluated by measuring the static freezing time on the coatings, the amount of ice accumulation on the coatings at various tilt angles, and the bond strength between the formed ice and the coatings at -20 ℃. The anti-icing durability of the coatings was assessed through multiple icing-deicing circles. The results indicated that the optimal concentrations for PU and HDTMS coatings were 7% and 5%, respectively. The surface of the 100%PU coating was smooth and exhibited low ice bond strength; however, its effectiveness in delaying freezing time was not significant, and the icing resistance of PU coatings decreased upon dilution. In contrast, the 5%HDTMS coating effectively delayed the freezing time while also demonstrating low ice bond strength. The contact angle of the PU-HDTMS coating was measured as 153.38°, which was superior to that of both the PU and HDTMS coatings.