Search

The microstructures and corrosion properties of selective laser-melted (SLM) 304L stainless steel (SS) were investigated after vacuum heat treatment. The electrochemical analysis showed that heat treatment was able to improve the pitting resistance of SLM 304L SS, which was even better than that of wrought 316L SS after vacuum heat treatment at 1100 °C for 2 hours. The microstructure analysis showed that the 1100 °C heat treatment eliminated the melt pool boundaries, reduced the defect density, optimized the micro-interfaces of the material, and weakened the agglomeration of nano-oxide particles. In addition, the heat treatment increased the content of Cr2O3 in the passive film, which enhanced the stability of the passive film. [ABSTRACT FROM AUTHOR]

Jet electrochemical micromilling (JEMM) exhibits significant potential for high-efficiency and high-quality machining of titanium alloy microstructures. However, during the JEMM process, the machined surface of the workpiece inevitably experiences stray current attacks at low current levels. Due to the formation of a dense passive film on the surface of the titanium alloy under electrochemical action, stray corrosion occurs on the machined surface. Hence, the electrochemical dissolution behavior of titanium alloys at low current densities directly impacts both machining efficiency and quality. This study first analyzed the effects of electrolyte composition and current density on the transpassive potential, breakdown of the passive film, current efficiency, and the dissolved surface on Ti-6Al-4V. The transpassive potential and electrochemical impedance of Ti-6Al-4V were found to be lower in NaCl solution than in NaNO3 solution. In addition, lower current densities enabled higher current efficiency and resulted in a more uniform and flat dissolution surface. Subsequent experiments used these two solutions for JEMM of complex-shaped microstructures on Ti-6Al-4V. The findings demonstrated that, compared to the NaNO3 solution, the use of NaCl solution increases the material removal rate by approximately 30%, enhances the aspect ratio by about 26%, and reduces surface roughness by roughly 58%. This indicates that employing NaCl solution can lead to superior machining efficiency and quality. [ABSTRACT FROM AUTHOR]

The corrosion resistance and passivation property of CoCrNi MEA in NaCl solution containing various concentrations of NaHSO3 were systematically investigated. The results reveal that the presence of HSO3− increases defects within the passive film, thins its thickness and disrupts the stability and integrity of the film. Increasing HSO3− concentration reduces the passivity of the MEA, facilitates the nucleation of metastable pitting and increases the tendency of metastable pitting to evolve into stable pitting, as well the corrosion rate increases significantly. Moreover, the corrosion of the MEA is aggravated by the micro-galvanic corrosion cells constituted between the substrate and the oxide inclusion. In addition, the MEA suffers a significant selective dissolution. [ABSTRACT FROM AUTHOR]

In historical reinforced concrete buildings, square ribbed rebars, round ribbed rebars and square twisted rebars are the main steel rebars. In order to determine the corrosion behavior of such historical steel rebars, we investigated the deterioration mechanisms of steel rebars in historical architecture in simulated concrete pore solution using various electrochemical tests and microscopic examination of corrosion products. The hot-rolled ribbed bar (HRB)335 rebars used in modern buildings were used as a control sample. The results demonstrated that the corrosion process of the historical rebars was similar to that of HRB335 rebars. Nevertheless, there were some differences in the chemical composition, microstructure, passive film characteristics, critical chloride ion concentration, and corrosion products. In the passivation stage, the stability order of the passive film generated on the surface of the rebars was as follows: square ribbed rebars > square twisted rebars > HRB335 rebars > round ribbed rebars. In the Cl− corrosion stage, the damaging effect order of Cl− on the passive film is square ribbed rebars > HRB335 rebars > square twisted rebars > round ribbed rebars. The critical chloride ion concentration was between 0.5% and 2.0% by weight. The corrosion products were mainly Fe2O3 , α -FeOOH, γ -FeOOH. β -FeOOH, and protective Fe3O4. The corrosion products of HRB335 rebars were mainly nonprotective crystallized FeOOH with various morphologies. The results of this study provide a scientific foundation for the conservation design and residual life prediction of historic reinforced concrete buildings. [ABSTRACT FROM AUTHOR]

Herein, the effect of bovine serum albumin (BSA) on the corrosion resistance of high nitrogen stainless steel (HNS) is systematically investigated based on experimental characterizations and first-principle calculations. Electrochemical measurements firstly prove that the anodic dissolution rate of HNS has significantly increased due to BSA adsorption and the potential deterioration of the passive film. By subsequent morphology and composition characterizations, it is demonstrated that BSA forms a 1.9 μm porous adsorption layer on HNS surface via the peptide bond mostly in α-helix and β-turn structure. Furthermore, Mott-Schottky tests confirm that the carrier (cation vacancy) density in the passive film has dramatically risen from 6.29 × 1021 cm−3 to 1.97 × 1022 cm−3 after BSA adsorption, which could be ascribed to the detachment of Cr atom from its original lattice due to the preference interaction between BSA molecule and Cr atom. Most importantly, such an increased defects will further promote the dissolution process of both the passive film and HNS matrix according to point defect model (PDM), which will definitely undermine the protective ability of the passive film and eventually result in the declined corrosion resistance of HNS in BSA-contained solution.

Liquid droplet impingement (LDI) treatment changes the roughness and introduces residual compressive stress on 321 stainless steel (SS). Compared to untreated 321 SS, 1 h of LDI treatment with 100, 150 and 175 m/s gradually increases the pitting potential of 321 SS, while 1 h of LDI treatment with 200 m/s decreased the pitting potential of 321 SS. The passive films grown on the 321 SS after LDI treatment with 100, 150 and 175 m/s show a decreased receptor density, an increased Cr content and an increased thickness, whereas a dense passive film with good corrosion resistance cannot be formed on the 321 SS after LDI treatment with 200 m/s. The effect of the change in surface state due to LDI treatment on the electrochemical passivation behavior is explained in detail.

This study systematically investigated the electrochemical corrosion and static immersion corrosion behavior of the novel Ti6422 (Ti–6Al–4V–2Mo–2Fe) alloy with equiaxed (EM) and lamellar structure (LM) in HCl solution. The differences in corrosion performance between EM and LM samples were analyzed based on the characteristics of the passive film and substrate microstructure. Results indicated that the LM sample contained higher contents of TiO₂, Al₂O₃, and MoO₃ with higher stability compared with the EM sample, and the thickness of passive film was approximately twice that of the EM sample. Additionally, the donor density of LM sample was lower than EM sample. These findings indicate that the passive film on LM samples is thicker, with fewer defects and higher density. Electrochemical corrosion results revealed that the corrosion current of LM samples was lower and the polarization resistance was higher than these of EM samples, both suggesting superior corrosion resistance of LM samples. Immersion corrosion further confirmed that the LM sample had a lower corrosion rate. The enhanced corrosion resistance in LM samples was primarily due to higher content of corrosion-resistant β phase. Conversely, the numerous micro-galvanic cells between αs precipitates and adjacent β phase in EM samples weakened the corrosion resistance. Overall, these results demonstrated that regulating microstructure through heat treatment is an effective strategy for improving corrosion resistance of titanium alloys.

Most research on the corrosive CoCrFeNi high-entropy alloy (HEA) has mainly modulated element species and atomic concentration recently. However, the corrosive resistance of the passive film in the elevated temperatures environment inevitably need to be extensively explored for application. In this work, the microstructure and corrosion behavior in the elevated temperatures of face-centered cubic (FCC) CoCrFeNiWx (x = 0 and 0.2) HEAs are investigated. The mechanism of passivation layers on the corrosion behavior of HEAs is further discussed for comparison to the alloy of addition tungsten. Through potentiodynamic polarization curves in 3.5 wt% NaCl solution from 25 °C to 70 °C, the addition of tungsten can raise the critical pitting temperature, while maintaining a lower passivation current density and a larger passivation range at the same time. The high resolution X-ray photoelectron spectrometer (HRXPS), electrochemical impedance spectroscopy (EIS) and scanning electrochemical microscopy (SECM) are all conducted to analyze the passivation composition and chemical reaction of the present alloys detailly. The CoCrFeNiW0.2 HEA exhibits the uniform Cr2O3 layer on the FCC matrix; the proportion of dispersive WO3 layer on the μ phase precipitates form a double-layer passive film under elevated temperature in 3.5 wt% NaCl. It shows that the synergistic effect of the double-layer passive film significantly enhances the pitting and corrosive resistance in this HEA.

The pitting mechanism of 7 series high-strength aluminum (Al) alloys (7xxx) is investigated experimentally and numerically (finite element method, FEM) by comparing the characteristics of passive films and pitting kinetics of two types of 7xxx Al alloys. The point defect model (PDM) is used to evaluate the passive film properties in the two varieties of 7xxx Al alloy, and the FEM is employed to calculate the point defect diffusion process in detail. The results reveal that the two 7xxx Al alloys exhibit various microstructures, particularly the 7xxx-1, characterized by a robust (111) fiber texture and a lower proportion of low-angle grain boundaries than the 7xxx-2. The diffusivity D of point defects in 7xxx-1 (3.85 × 10−18–52.74 × 10−18 cm2 s−1) is lower than that in 7xxx-2 (5.47 × 10−18–66.61 × 10−18 cm2 s−1) and the diffusion duration of 7xxx-1 is longer than 7xxx-2, which is closely associated with the rupture of passive film. Additionally, FEM proved that the initial shapes of pits dictate the progression of pitting, manifesting that the shallow dish shape grows laterally while the deep hole shape grows longitudinally.

This study investigates the corrosion characteristics of Co30Cr20Ni20Fe20Mo10 (Co30HEA), Co40Cr20Ni15Fe15Mo10 (Co40HEA), and Co50Cr20Ni10Fe10Mo10 (Co50HEA), designed as Co-rich high entropy alloys, compared to 316 L stainless steel and L605. Co30HEA has a single FCC phase, whereas the other two alloys exhibit a dual phase of FCC + (Cr, Mo) σ phase. The presence of high Cr and Mo content in the σ phase results in Cr depletion zones. Co30HEA shows the highest corrosion resistance in Ringer's solution, which diminishes with increasing Co content. Its passive film exhibits ideal capacitive behavior at low frequencies, indicating strong passivation. The films, primarily composed of Cr oxides and hydroxides, vary in thickness, with Co30HEA having a film about twice as thick as the others. All three alloys demonstrate pitting corrosion; however, Co30HEA shows the smallest pits mainly at grain boundaries, while the others show pits near the σ phase due to unstable passive films in the Cr and Mo-depleted zones, acting as anodic sites for galvanic corrosion.

The oxidation behavior of as-cast AlCoFeNiCux (x = 0.6–3.0) high entropy alloys was studied by isothermal annealing in flowing synthetic air at 1000 °C. A formation of an external protective Al2O3 scale has been found. The oxidation kinetics followed a parabolic rate law. The rate constants were increasing with increasing Cu concentration in the alloys. A scale spallation on the alloys with higher Cu concentration was observed. The spallation facilitated a penetration of oxygen through the scale and promoted the formation of CuO and CuAl2O4. The oxidation mechanism of the AlCoFeNiCux alloys is discussed and compared with previously studied high entropy alloys.

In this study, the effect of electro-pulsing combining laser shock peening (EP-LSP) treatment on the microstructure and corrosion resistance of Ti-6Al-4V alloys was investigated, and the hardness, surface roughness, microstructure, and electrochemical properties of Ti-6Al-4V alloys after EP-LSP treatment were studied and compared with those of single EPed and LSPed samples. Also, to investigate the effect of the number of laser impacts on microstructure and corrosion resistance, changes in samples after one and three laser impacts were compared. The results showed that all treatments improved the hardness of as-received sample and three EP-LSPed (3 EP-LSP) samples had the maximum hardness which increased 24.3% compared with the as-received sample. As the number of laser impacts increased from one to three, the surface hardness increased, but the surface quality decreased, and the surface showed periodic protrusions. The one EP-LSPed (1 EP-LSP) sample showed the best corrosion resistance, with a 73.2% reduction in corrosion current density compared to the as-received sample. This is due to the grain refinement and the transformation of the α to β phase in the EP-LSPed samples. It has a beneficial effect on the formation of dense passive film. In addition, the sample surface with one impact has lower surface roughness and better surface quality compared to that of three impacts. [ABSTRACT FROM AUTHOR]

The purpose of this study was to investigate the composition of oxide films formed on SA106 Gr.B carbon steel in nitrite solutions at 35 °C for 1000 h. The product of the reduction of nitrite during the corrosion inhibition process was also examined. The X-ray photoelectron spectroscopy results revealed that a thin Fe3O4 film was formed and ammonium ions were adsorbed on the outermost surface of the oxide film. The presence of ammonium ions was also demonstrated by ion chromatography. These results indicate that nitrites are reduced to ammonium ions, which in turn promotes the formation of the protective Fe3O4 film. [ABSTRACT FROM AUTHOR]

This work covers the formation of a passive state for two different alloys used in the aeronautical industry. The aim of this study is to investigate the effectiveness of passivation treatments on 17-7PH and 410 SS (stainless steel) samples, specifically when performed with citric and nitric acid solutions at 49 °C using an immersion time of 90 min and subsequent exposure in 3.5 wt.% NaCl solution. Employing the cyclic potentiodynamic polarization (CPP) technique, the corrosion properties of the passivated material were evaluated according to the ASTM G65-11 standard. A microstructural analysis was performed using scanning electron microscopy (SEM). The passivated layer was characterized via X-ray photoelectron spectroscopy. In the results, the CPP curves showed positive hysteresis, indicating pitting localized corrosion, and 17-7PH steel passivated at 49 °C for 90 min in citric acid exhibited lower corrosion rate values equivalent to ×10−3 mm/year. [ABSTRACT FROM AUTHOR]

Electrochemical impedance spectroscopy, potentiodynamic polarization curves, and the Mott–Schottky method were used to study the corrosion behaviors of vermicular graphite cast iron and gray cast iron and the characteristics of the passive films on the surfaces of vermicular graphite cast iron and gray cast iron in engine coolant. The results showed that the passive film formed on the surface of vermicular graphite cast iron exhibited a low density of defects and had a higher protective property compared to that on gray cast iron under the same conditions. Flake graphite was conducive to the formation of the passive film on the surface of cast iron, but the dissolution rate of the passive film on the surface of gray cast iron was higher than that of vermicular graphite cast iron. Vermicular graphite cast iron showed better corrosion resistance than gray cast iron in engine coolant. The charge transfer resistance of the anodic reaction of vermicular graphite cast iron and gray cast iron in engine coolant was much greater than that of the cathodic reaction, and the control step of the corrosion process in the system was the anodic reaction process. [ABSTRACT FROM AUTHOR]

In this study, SEM, AFM, TEM, XPS, and electrochemical tests are used to study the passivation behavior of chromium alloyed high-strength rebar in simulated concrete pore (SCP) solutions with different pH values. The results show that after passivation in SCP solution with different pH values, the passivating film on the surface of the chromium alloyed rebar primarily consists of a layer of nanoscale oxide particles, which makes the passive film exhibit a p-n type semi-conductor, and the passive film presents a rhombohedral crystal structure. As the pH value of the SCP solution decreases, the nanoscale oxide particles on the surface of the rebar become denser, which leads to a reduction in the carrier density (Nq and Na) of the passive film and an increase in film resistance (R2) and charge transfer resistance (R3), thus increasing the corrosion resistance of the passive film. The passive film on the surface of the chromium alloyed high-strength rebar predominantly exhibits a three-layer structure, the outer passive film layer is composed of Fe oxides, the stable layer of the passive film is composed of Fe oxides and Cr oxides, and the growth layer of inner passive film is composed of Cr oxides. Compared with passivation 10 d in SCP solutions with pH 13.5 and pH 12.5, the passive film on the surface of the rebar has good stability at pH 10.5, which indicates that the addition of Cr is beneficial to promote the corrosion resistance of the rebar. [ABSTRACT FROM AUTHOR]

The effect of the recrystallization degree on the properties of passive films formed in 0.1 M HNO3 solution for super ferritic stainless steel S44660 was examined in this study. The initial specimens, in their cold-rolled state, showed a high dislocation density, as observed through electron backscatter diffraction (EBSD) experiments. Analysis of potentiodynamic polarization (PDP) curves and electrochemical impedance spectroscopy (EIS) measurements suggested that with the increase of recrystallization degree, the corrosion current density reduced and the corrosion potential increased. As revealed by Mott–Schottky analysis, the passive film showed a dual structure of n-type and p-type semiconductors, with the carrier density of the passive film decreasing as the recrystallization degree increased. X-ray photoelectron spectroscopy (XPS) provided insights into the film composition, indicating that the Fe2O3 and Cr2O3 content, which improved the stability of the passive film, increased with the degree of recrystallization. In summary, the increase in recrystallization degree reduced the number of defects in the microstructure, thereby creating favorable conditions for the formation of highly protective passive films. The passive film formed after complete recrystallization exhibited enhanced corrosion resistance. [ABSTRACT FROM AUTHOR]

This paper is aimed to study the corrosion resistance of Cr10Mo1 alloy corrosion-resistant steel (CR) in the seawater–sea sand concrete pore solution (SWSSCPS), compared with low-carbon steel (LC) and stainless steel (SS). X-ray photoelectron spectroscopy (XPS), SEM, atomic force microscope, and Mott–Schottky curve tests are applied to obtain information on the composition, structure, and morphology of the corrosion-resistant (CR) passive film. Finally, the difference between CR passive film and the other two kinds of steels under chloride attack is investigated, and the apparent morphology, microstructure, and chemical composition of the CR passive film during the attack are analyzed. With the exposure time increased, the passive film and interfacial integrity of CR are approximately equivalent to that of SS in terms of phase angle in the midband and low-frequency band modulus, indicating the anticorrosion performance of CR has a much better effect than that of LC and close to that of SS. The results reveal that the FeO in the passive film outer layer and a high amount of Cr2O3/Cr(OH)3 in the inner layer prevent CR from further corrosion by chloride ions. [ABSTRACT FROM AUTHOR]

This work systematically studied the corrosion behavior and passivation property of CoCrFeNi high‐entropy alloys (HEAs) in a simulated seawater environment. The results reveal that the addition of CO32−/HCO3− results in the secondary passivation of the HEA in NaCl solution, and secondary passivation film possesses higher dissolution rate in comparison with primary passive film. H+ ions ionized by HCO3− facilitate the charge transfer process, thin the thickness of passive film, and increase the disordered degree of the film. Moreover, the presence of HCO3− promotes the nucleation and growth of metastable pits, and enhances the pitting sensitivity. Furthermore, an increase in CO32− concentration accelerates the dissolution of passive film, weakens the compactness and protective performance of the film, and increases the probability that metastable pitting evolves into stable pitting, as well aggravates the corrosion of the HEA. In addition, the corrosion resistance of the HEA is diminished due to the formation of microgalvanic corrosion cells between matrix and inclusion. The selective dissolution of elements occurred in the HEA. [ABSTRACT FROM AUTHOR]

In this paper, the passive behavior of 304 stainless steel (SS) in NaCl solution is studied by electrochemical methods and surface analysis. The polarization measurement results show that the pitting potential (Ep) has a simple linear relationship with the temperature increase. Scanning Kelvin probe results show that the surface potential difference on the surface of 304 SS is well correlated with the temperature. Scanning electron microscope results show that the rupture of the passive film accelerates with the increase of temperature. The X‐ray photoelectron spectroscopy analysis shows that the high temperature causes more oxidation on the surface of 304 SS, leading more Cr3+ oxidized to Cr6+ at high temperature. [ABSTRACT FROM AUTHOR]

The influence of grain size on the corrosion behavior of pure aluminum and the defect density and diffusion coefficient of surface passive films were investigated using electron backscatter diffraction (EBSD) and electrochemical testing techniques, based on the point defect model (PDM). Samples with three different grain sizes (23 ± 11, 134 ± 52, and 462 ± 203 μm) were obtained by annealing at different temperatures and times. The polarization curves and electrochemical impedance spectroscopy results for the pure aluminum in the 3.5% NaCl solution showed that with decreasing grain size, the corrosion current (icorr) decreased monotonously, giving rise to a noble corrosion potential and a large polarization resistance. The Motte–Schottky results showed that the passive films that formed on pure aluminum with fine grains of 23 ± 11 μm had a low density (3.82 × 1020 cm−3) of point defects, such as oxygen vacancies and/or metal interstitials, and a small diffusion coefficient (1.94 × 10−17 cm2/s). The influence of grain size on corrosion resistance was discussed. This work demonstrated that grain refinement could be an effective approach to achieving high corrosion resistance of passive metals. [ABSTRACT FROM AUTHOR]

Early CO2 curing acting as a new curing technique is an effective way to cut down on carbon footprint in cement industry. It also improves the strength development and long-term durability of concrete without reinforcement. Given the fact that reinforcement concrete is most widely used in construction and building fields, the carbon sequestration potential will be enhanced remarkably if this curing technology can be used in reinforced concrete. However, the impacts of early CO2 curing on the corrosion behavior of steels, which is the major concern for reinforced concrete exposure to chloride, is unclear yet. In this work, the permeability of chloride, threshold chloride value and corrosion behaviors of steels in cement mortar were determined to comprehensively study the effect of early CO2 curing on the chloride induced corrosion of steels. Early CO2 curing lowers the chloride ions permeability of mortars, in particular for the mortars with 28 day curing ages. Steels take longer time to form stable passive films in early CO2-cured mortar than in conventional moist-cured ones. Early CO2 curing reduces the chloride threshold concentration of mortar, in particular for the mortars that the whole cross section is carbonated, the reduction reaches ∼50%. However, it exerts few effects on corrosion induction phase of steel rebar. Moreover, early CO2 curing decreases the corrosion rate of steel bars in corrosion propagation phase and thus the overall corrosion rate of steels during the whole testing process due to slower chloride ingress rate. Thus, early CO2 curing can act as an alternative curing technique in the production of pre-cast reinforced concrete exposed to chloride. [ABSTRACT FROM AUTHOR]

This work systematically studied the corrosion behavior and passivation property of CoCrFeNi high‐entropy alloys (HEAs) in a simulated seawater environment. The results reveal that the addition of CO32−/HCO3− results in the secondary passivation of the HEA in NaCl solution, and secondary passivation film possesses higher dissolution rate in comparison with primary passive film. H+ ions ionized by HCO3− facilitate the charge transfer process, thin the thickness of passive film, and increase the disordered degree of the film. Moreover, the presence of HCO3− promotes the nucleation and growth of metastable pits, and enhances the pitting sensitivity. Furthermore, an increase in CO32− concentration accelerates the dissolution of passive film, weakens the compactness and protective performance of the film, and increases the probability that metastable pitting evolves into stable pitting, as well aggravates the corrosion of the HEA. In addition, the corrosion resistance of the HEA is diminished due to the formation of microgalvanic corrosion cells between matrix and inclusion. The selective dissolution of elements occurred in the HEA. [ABSTRACT FROM AUTHOR]

The influence of B and Sb on the microstructure and corrosion behavior of T6-treated Al–Si–Mg alloys has been specifically studied. It is found that the addition of 0.03 wt% B to Al–Si–Mg alloys results in the lowest corrosion rate (0.02451 mm/y) when immersed in 3.5 wt% NaCl solution for 3 days. This improvement can be attributed to the transformation of coarse dendritic α-Al grains into refined equiaxed grains, which is beneficial for the formation of uniform and compact passive film. In contrast, the Al–Si–Mg alloy with addition of 0.2 wt% Sb shows the highest corrosion rate (0.05795 mm/y), which can be attributed to two reasons. First, the addition of Sb contributes to the transformation of rod-like eutectic Si particles into a spherical morphology, increasing the number of micro-galvanic corrosion sites and thus accelerating the corrosion process. Second, the generated Mg3Sb2 phase, being more noble than the eutectic Si phase, strengthens the micro-galvanic corrosion.

In this work, CoCrFeNiSix coatings were fabricated by magnetron sputtering at the negative bias voltage ranging from 0 to 100 V. The effect of negative bias voltage on the composition, microstructure and corrosion performance was studied. The results show that all CoCrFeNiSix coatings consisted of amorphous and nanocrystalline FCC phases. However, the ratio of both amorphous/nanocrystalline phases and Si/(Co + Cr + Fe + Ni) atoms decreased with increasing negative bias voltage. Applying negative bias voltage also led to the improved surface quality. Accordingly, the corrosion rate of CoCrFeNiSix coatings in 0.5 mol/L H2SO4 solution exhibited a decreasing trend. Meanwhile, the CoCrFeNiSix coating deposited at 100 V had the lowest passive current density, highest coating resistance and lowest carrier density. This was because that Si competed with Cr to suppress the formation of Cr2O3 in the compact inner layer, and thus the decreasing Si content caused by increasing negative bias voltage led to the improved protection effect of the passive film.

Abstract The mechanism of interaction between magnesite mineral and phosphoric acid (0.001–0.5 M) in addition to the determination of the protective properties for Ti alloy (working electrode) in phosphoric acid both with and without an inhibitor have been investigated by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization measurements. Results of electrochemical tests show that the corrosion resistance of titanium alloy in phosphoric acid solution only increased and hydrogen production decreased by either decreasing acid concentration or increasing immersion time associated with the thickening of the oxide film formed on the alloy surface. On adding magnesite, the corrosion resistance of Ti alloy is enhanced by increasing the phosphoric acid concentration (0.001–0.5 M) due to the formation of sparingly soluble magnesium phosphate film on the alloy surface that inhibits the effect of increasing hydrogen evolution reaction due to the pH value decreases. The increasing adsorption behavior of the magnesite inhibitor and decreasing its diffusion were deduced from EIS measurements. Thus, the addition of 3% magnesite minimizes the corrosion by forming a new protective film (Mg3(PO4)2), which differs from the traditional passive film and prevents the effect of the increase of hydrogen evolution. The surface morphology and chemical composition of the tested alloy were determined using scanning electron microscopy (SEM), Fourier transform Infra-Red spectroscopy (FTIR), X-ray diffraction (XRD), X-ray Fluorescence (XRF) and In situ Raman spectroscopy.

In the current investigation, X70 pipeline steel plate was welded using submerged-arc welding. Thereafter, a (Fe0.5Ni0.2)61Cr9Co6Si1.5B17.5Nb5 amorphous alloy coating with a thickness of 400 ± 30 μm was successfully deposited on the surface of welded X70 pipeline steel by high velocity oxy-fuel (HVOF). The corrosion resistance of the substrate and coating in acidic environments was discussed, and the corrosion mechanisms were analyzed. The results show that the coating is completely amorphous with a dense microstructure, showing a typical thermal spray laminar flow-like structure. The corrosion potential (Ecorr) and self-corrosion current density (Icorr) are − 396 mV and 2.061 × 10−6 A/cm2, respectively. The Ecorr of all coatings is better than that of substrate. The coating A, where the BM zone is located, has the largest capacitance resistance arc radius and the smallest Icorr (1.427 × 10−7 A/cm2), which provides the best corrosion resistance. The maximum Icorr of the coating (Icorr = 2.320 × 10−7 A/cm2) is one order of magnitude lower than the minimum Icorr of the substrate (Icorr = 2.061 × 10−6 A/cm2), which indicates that the coating has better corrosion resistance than the substrate. The corrosion mechanism of the coating in H2SO4 solution is active dissolution of metal elements in the coating (initial stage) and passivation film protection coating (later stage). This work provides a very valuable idea to solve the problem of corrosion failure of X70 pipeline steel. [ABSTRACT FROM AUTHOR]

Personalized laser powder bed fusion (PBF-LB/M) Ti-6Al-4V (TC4) has a broader application prospect than that of traditional casting. In this paper, the composition and corrosion resistance of the passive film formation mechanism of TC4 prepared by optimization of PBF-LB/M techniques and traditional casting were systematically studied in 0.9 wt.% NaCl at 37 °C by electrochemical technique and surface analysis. The rates of the passive film formation process, corrosion resistance and composition of TC4 show different characteristics for the different preparation processes. Although the rate of passive film formation of cast-TC4 was higher at the initial immersion, the open circuit potential was more positive, and the film thickness was larger after stabilization, those facts show no positive correlation with corrosion resistance. On the contrary, with no obvious defects on the optimized PBF-LB/M-TC4, the passive film resistance is 2.5 times more, the defect concentration is reduced by 30%, and the TiO2 content is higher than that of the cast-TC4, making the martensitic-based PBF-LB/M-TC4 exhibit excellent corrosion resistance. This also provides good technical support for the further clinical application of PBF-LB/M-TC4. [ABSTRACT FROM AUTHOR]

Repassivation characteristics of carbon steel experienced thermal cycles in tropical marine environments were investigated in a simulated concrete pore solution (SCPS). The results suggested that the damage of passive films on the carbon steel mainly occurred during the cooling process in thermal cycles. The damaged passive films gradually recovered in the SCPS, and the duration of repassivation extended with the amplitude of thermal cycles and cyclic number in the high-amplitude thermal cycles (20–60 °C and 20–70 °C), while it was not significantly affected by the cyclic number in the low-amplitude thermal cycles (20–40 °C and 20–50 °C). [ABSTRACT FROM AUTHOR]

High-entropy alloys (HEAs) are special type of alloy suitably developed for use in petroleum exploration, energy storage devices, medical implants, etc. This is because they possess excellent corrosion, thermal, and mechanical properties. Corrosion characteristic of HEAs prepared via spark plasma sintering is a top notch as the technique generates corrosion resistant phases and homogenous microstructure. This study was aimed at reviewing recent publications on corrosion characteristics of HEAs processed by SPS in order to develop ways of improving their anti-corrosion properties. The resource materials were obtained from Scopus-indexed journals and Google Scholar websites of peer-reviewed articles published within the last 5 years. From the study, it was revealed that incorporation of some elements (Al, Cr, Ti) into HEAs can improve their corrosion resistance, while addition of some others can reduce their brittleness and enhance their stability and formability. It was recommended that optimization of SPS parameters was one of the strategies of generating better corrosion characteristics in HEAs. [ABSTRACT FROM AUTHOR]

Passive films on the superaustenitic stainless steel 1.4652 were studied using angular resolved hard X‐ray photo‐electron spectroscopy (HAXPES), which provides an increased information depth compared to conventional X‐ray photo‐electron spectroscopy (XPS). Elemental depth profiles in the oxide as well as gradients in the underlying metal were established using a dedicated algorithm. The utility was exemplified for three different conditions of film formation: (i) as polished and as polarized to the high passive end in (ii) 1 M H2SO4 and (iii) 1 M NaOH. The use of a superaustenitic material ascertained that metal signals from the main contributors to film formation: Fe, Cr, Ni, and Mo remained above the detection limit throughout the data set. With the dual‐source technique (XPS, HAXPES), it was possible to investigate metal gradients underneath the passive film. For polarizations in an acidic environment, a metallic nickel enrichment of the order of 5 Å was found. For a corresponding polarization in an alkaline environment, the metal region closest to the oxide/metal interface was enriched in iron, followed by concentration gradients down to about 50 Å into the metal. [ABSTRACT FROM AUTHOR]

The mechanism of interaction between magnesite mineral and phosphoric acid (0.001–0.5 M) in addition to the determination of the protective properties for Ti alloy (working electrode) in phosphoric acid both with and without an inhibitor have been investigated by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization measurements. Results of electrochemical tests show that the corrosion resistance of titanium alloy in phosphoric acid solution only increased and hydrogen production decreased by either decreasing acid concentration or increasing immersion time associated with the thickening of the oxide film formed on the alloy surface. On adding magnesite, the corrosion resistance of Ti alloy is enhanced by increasing the phosphoric acid concentration (0.001–0.5 M) due to the formation of sparingly soluble magnesium phosphate film on the alloy surface that inhibits the effect of increasing hydrogen evolution reaction due to the pH value decreases. The increasing adsorption behavior of the magnesite inhibitor and decreasing its diffusion were deduced from EIS measurements. Thus, the addition of 3% magnesite minimizes the corrosion by forming a new protective film (Mg3(PO4)2), which differs from the traditional passive film and prevents the effect of the increase of hydrogen evolution. The surface morphology and chemical composition of the tested alloy were determined using scanning electron microscopy (SEM), Fourier transform Infra-Red spectroscopy (FTIR), X-ray diffraction (XRD), X-ray Fluorescence (XRF) and In situ Raman spectroscopy. [ABSTRACT FROM AUTHOR]

This research examines the behavior of electrochemical passivation and the chemistry of surface films on 654SMO super austenitic stainless steel and C276 nickel-based alloy in simulated condensates from flue gas desulfurization in power plant chimneys. The findings indicate that the resistance to polarization of the protective film on both materials initially rises and then falls with either time spent in the solution or the potential of anodic polarization. Comparatively, 654SMO exhibits greater polarization resistance than C276, indicating its potential suitability as a chimney lining material. Mott–Schottky analysis demonstrates that the density of donors in the passive film formed on 654SMO exceeds that on C276, potentially due to the abundance of Fe oxide in the passive film, which exhibits the characteristics of an n-type semiconductor. The primary components of the passive films on both materials are Fe oxides and Cr oxides. The formation of a thin passive film on C276 in the simulated condensates is a result of the low Gibbs free energy of nickel oxide and low Cr content. The slower diffusion coefficient of point defects leads to the development of a thicker and more compact passive film on the surface of 654SMO. [ABSTRACT FROM AUTHOR]

6Mo super austenitic stainless steel (SASS) with nitrogen contents of 0.2 and 0.4 (wt.%) was melted, and solution treatments at 1100, 1180, and 1250 °C for 30 min were performed. The effects of nitrogen on the microstructure and pitting resistance of the two steels that signed as 0.2N and 0.4N samples were investigated. At a heat-treatment temperature of 1180 °C, the alloy demonstrates the highest corrosion resistance, attributed to the combined effects of grain size and precipitates. The structure of the passivation film changes with increasing nitrogen content, with the Cr/Fe ratio is significantly higher in the 0.4N sample compared to the 0.2N sample. Moreover, the increase in nitrogen content results in thicker Cr and Mo oxide layers and higher levels of NH3 and NH4+, thereby improving the corrosion resistance of the stainless steel. [ABSTRACT FROM AUTHOR]

The corrosion resistance of Cr reinforced HRB400 rebar in the marine environment was investigated. The addition of Cr increases the amount of Cr(OH)3 and α-FeOOH in the passivate film, resulting in a denser passivate film structure. This enhanced passivation film inhibits localized corrosion. The pitting potential and critical chloride concentration (CTL) of the steel increased with the increase in chromium content, indicating improved corrosion resistance of the steel. On the other hand, an increase in the concentration of Cl- in solution leads to a decrease in the pitting potential and resistance of the steel, which reduces the corrosion resistance. At higher Cl- concentrations, the Cl- ions form an electrochemical interface with the steel surface, resulting in a sharp decrease in the Rf value. In addition, the gradual decrease in solution pH leads to a decrease in the pitting potential and CTL of HRB400 and 1.5Cr steel. The corrosion resistance was also found to be reduced, pH reduction accelerated the intrusion of chloride ions, which led to a severe breakdown of the passivation film.

In order to elucidate the impact of Cl- and CO2 on the corrosion behavior of 316L stainless steel in the produced water environment of the Liaohe oilfield, the effects of varying Cl- concentrations and CO2 partial pressures on 316L stainless steel were investigated through immersion tests, electrochemical impedance spectroscopy(EIS) and polarization curve techniques. The Cl- concentration gradients were 0, 0.030 0, 0.051 5, 0.070 0 mol/L, while the CO2 partial pressures were set at 0.2, 0.4, 0.6 MPa. Additionally, X-ray diffraction(XRD) technology was employed to analyze the corrosion products. Results showed that with the increase of Cl- concentration, the diameter of the capacitive reactance arc decreased, the dispersion index decreased, and the corrosion was intensified. With the increase of CO2 partial pressure, the diameter of the capacitive reactance arc first decreased and then increased, the dispersion index first decreased and then increased, and the corrosion first intensified and then slowed down. This was due to the fact that Cl- would destroy the passive film on the surface of 316L, while CO2 would react with the substrate to form FeCO3. With the increase of CO2 partial pressure, the FeCO3 protective film became denser.

In order to identify the causes of black line defects in thin specification hot-dip Al-Zn sheets, a ZEISS Merlin Compact field emission scanning electron microscope (SEM) and an attached OXFORD X-max N type energy spectrometer were utilized to analyze the surface and cross-section of black line defects in hot-dip Al-Zn steel plates, as well as the microstructure observation and chemical composition of the steel substrate surface after corrosion and removal of the coating. Analysis was also conducted on the steel substrate surface after the coating had been removed by corrosion. Results showed that the black line defects on the upper surface of the hot-dip Al-Zn steel sheet were caused by a thicker passive film due to scratches on the steel substrate. On the lower surface of the hot-dip Al-Zn sheet, the black line defects were attributed to a thicker passive film resulting from concave micro-deformations of the lower surface coating. Scratches on the surface and depressions of the coating of the Al-Zn steel sheet were found to cause different reflections of light from the rest of the surrounding area, forming a visually perceived black line defect.

Flotation separation of apatite from calcite is difficult due to their same active calcium atoms on the surface. Flotation is mainly used to separate calcite and apatite minerals from each other and this can be done by knowing the interaction mechanism for each which is our aim here. Phosphoric acid is used to separate apatite and calcite. The outcomes showed that phosphoric acid had a strong depression ability to apatite but it does not for calcite. Herein, the interaction mechanism between minerals like calcite (36–100 μm) and fluorapatite of two size fractions (36–100 μm) and (20–100 μm) with phosphoric acid on 316L stainless steel, at 25 °C, was studied. Both materials are easily available, natural product, cheap and environmentally acceptable. Each mineral works with a different mechanism and this is confirmed by changing the shape for both Nyquist and Tafel plots after adding each mineral to phosphoric acid. Electrochemical impedance spectroscopy (EIS) showed that calcite materials work with both diffusion and adsorption mechanism, however, fluorapatite interaction mechanism is controlled by adsorption. Also, the dissolution of calcite material is higher than fluorapatite as confirmed by EIS and potentiodynamic polarization techniques. Results show that either increasing in concentration of the phosphoric acid or immersion time or size of particles, decreases passivation for both materials.

Abstract This study employs advanced electrochemical and surface characterization techniques to investigate the impact of electrochemical hydrogen charging on the corrosion behavior and surface film of the Ti-6Al-4V alloy. The findings revealed the formation of γ-TiH and δ-TiH2 hydrides in the alloy after hydrogen charging. Prolonging hydrogen charging resulted in more significant degradation of the alloy microstructure, leading to deteriorated protectiveness of the surface film. This trend was further confirmed by the electrochemical measurements, which showed that the corrosion resistance of the alloy progressively worsened as the hydrogen charging time was increased. Consequently, this work provides valuable insights into the mechanisms underlying the corrosion of Ti-6Al-4V alloy under hydrogen charging conditions.