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Austenitic stainless steels are used widely in many fields due to their good mechanical properties and high resistance to corrosion. This work focuses on the reconstruction of the passive film after scratching. The purpose of the study was to compare changes in the rate of passive layer reconstruction and to discuss the effect of both the type of material and its electrochemical treatment on the reconstruction of the passive layer for two types of stainless steel: 304 and 316. The XPS tests performed indicate a significantly higher Cr/Fe ratio for the samples after the electropolishing process of 1.41–1.88 compared to the as-received samples of 0.82–0.86. After 2–3 min of sputtering the surface with Ar+ ions, a decrease in chromium content can be observed, with a simultaneous increase in nickel content, visible especially for the electropolished samples. A new approach in the conducted research was to scratch the test samples under controlled conditions, then evaluate the dynamics of the passive layer reconstruction using the AFM method, and then confront the obtained results with XPS measurements for the corresponding samples. For the as-received samples (2B finish) and those after surface treatment, regardless of the level of contamination of the electropolishing process bath, the reconstruction time was similar, which was approximately 2 h, although certain differences in the process dynamics were noticeable. [ABSTRACT FROM AUTHOR]

Duplex stainless steels, known for their excellent corrosion resistance, are employed in a variety of chloride solutions—acidic, neutral, and alkaline—due to a stable passive film that forms on their surfaces. This study involved polarization tests, EIS (Electrochemical Impedance Spectroscopy) measurements, Mott–Schottky plots, and XPS (X-Ray Photoelectron Spectroscopy) analyses in both static and dynamic conditions across acidic (1NaCl + 0.1N HCl, pH 1.0), neutral (1N NaCl, pH 6.7), and alkaline (1N NaCl + 0.1N NaOH, pH 13.2) chloride solutions to confirm that duplex stainless steels exhibit similar passivation behavior (0.79 μA/cm2 > ip > 0.2 μA/cm2 and 590 kΩ·cm2 < Rp < 651 kΩ·cm2). Regardless of the pH of the solution, p-type and n-type semiconductive properties were observed, but the balance of the semiconductive tendencies was different. Comparing passive films formed under dynamic conditions, through real-time HCl injection into a neutral chloride solution, with those formed under static conditions, revealed that both conditions yield similar structural and property characteristics in the films, as well as comparable electrochemical behaviors. These findings suggest that the passive film on the stainless steel surface adjusts to the environment and can be spontaneously repassivated in response to environmental changes. [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]

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]

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]

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]

Localized corrosion behaviors of Hastelloy X and stainless steel 316 in Persian Gulf coastal water were compared fundamentally using cyclic potentiodynamic polarization (CPC), electrochemical impedance spectroscopy (EIS), Mott–Schottky analysis. X-ray diffraction spectroscopy and scanning electron microscopy techniques. The results showed that passive films that are formed on Hastelloy X and stainless steel 316 are mainly include nickel and chromium oxides that exhibit p-type semiconducting behavior. The films that are formed on the surface of former include less crystal defects than those on the latter one surface. In both cases, films with more crystal defects will form when their respective formation temperature increases. Such passive films' characteristics lead to find Hastelloy X to be more resistant to localized corrosion than stainless steel 316 in Persian Gulf water as was proved by the CPC and EIS test results; i.e. as the temperature increases from 25 to 75°C, pitting corrosion resistance (Rpit) and film resistance (Rfilm) values decreased in the case of Hastelloy X and stainless steel 316 samples while the former is more resistant to corrosion than the latter. [ABSTRACT FROM AUTHOR]

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]

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]

Electrochemical and passive film evolution peculiarities including compositional alternation, film thickening and diffusion process of oxygen vacancies of Fe48Cr15Mo14C15B6Y2 amorphous/nanocrystalline composite coating were investigated in borate buffer solution with different solution temperatures. A lower stability of the passive film could occur at a higher temperature as manifested by a greater corrosion current density and passive current density. The formation of metal mechanical mixtures as the corrosion products could cause inner stress and deteriorate the stability of passive film, which were also active sites easily invaded by corrosive ions. This effect would induce metastable pitting in these active sites due to the dissolution of large amounts of metal mechanical mixtures into the solution accompanied with local rupture of passive film and initiation of pitting. Reduction in impedance value at elevated temperatures was caused by the increment in Fe-containing n-type semiconducting species and depletion of Mo-containing oxides, which can suppress the growth of insoluble oxide Cr2O3. AFM topographic images indicated that the distribution of agglomerated oxides with larger size on the surface gradually dispersed in larger region with increasing temperature, suggesting that the micro/nanoscale hierarchical structures of passive films were changed. The promoted annihilation effect of oxygen vacancies at the passivated substances/electrolyte interface resulted in the acidification effect by accelerating the production of more hydrogen ions at a higher temperature. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this study is to investigate the corrosion resistance of superalloys subjected to ultrasonic impact treatment (UIT). The passive film growth on the superalloys' surface is analyzed to illustrate the corrosion mechanism. Design/methodology/approach: Electrochemical tests were used to investigated the corrosion resistance of GH4738 superalloys with different UIT densities. The microstructure was compared before and after the corrosion tests. The passive film characterization was described by electrochemical impedance spectroscopy (EIS) and X-ray photoelectron spectroscopy (XPS) tests. Findings: The compressive residual stress and corrosion resistance of the specimens significantly increased after UIT. The order of corrosion resistance is related to the UIT densities, i.e. 1.96 s/mm2 > 1.71 s/mm2 > 0.98 s/mm2 > as-cast. The predominant constituents of the passive films are TiO2, Cr2O3, MoO3 and NiO. The passive film on the specimen with 1.96 s/mm2 UIT density has the highest volume fraction of Cr2O3 and MoO3, which is the main reason for its superior corrosion resistance. Originality/value: This study provides quantitative corrosion data for GH4738 superalloys treated by ultrasonic impact. The corrosion mechanism is explained by the passive film's characterization. [ABSTRACT FROM AUTHOR]

The corrosion behavior of 6082 aluminum alloy in deicing salt was investigated by electrochemical impedance spectra combined with an X‐ray diffractometer, scanning electron microscopy, electron backscatter diffraction, and transmission electron microscope. The experiment results showed that the corrosion tendency of 6082 aluminum alloy in deicing salt strongly depends on its different matrix and grain boundary precipitates, which also show the characteristics of transformation during the corrosion process. The Nyquist plot exhibits the characteristics of double capacitive resistance arcs, and the capacitive resistance arcs were affected by corrosion characteristics and corrosion products on aluminum alloy surface. The nucleation and development of pitting and the formation of a passive film were closely related to the Si phase in the 6082 aluminum alloy. [ABSTRACT FROM AUTHOR]

In the proton exchange membrane water electrolysis (PEMWE), the titanium bipolar plate coated with noble metals is usually used, which puts forward higher requirements for costs. This study investigates the cathode plasma electrolytic deposition (CPED) for the titanium and obtains TiN and TiN/CrN coatings. The TiN coating exhibits the diffusion resistance in the anode PEMWE environment, resulting in an increase in the interfacial contact resistance (ICR). The denser TiN/CrN coating eliminates the diffusion resistance and increases the polarization resistance (R p) value from 3873 Ω cm2 of TiN coating to 12,320 Ω cm2 of TiN/CrN. After long-term potentiostatic polarization, the ICR of TiN/CrN coating is 8.5 mΩ cm2, which is 3.5 times lower than that of TiN coating. Therefore, the low-cost TiN/CrN coating obtained by CPED has brought a good application prospect for bipolar plates in PEMWE. • The TiN and TiN/CrN coatings improve electrical conductivity after long-time service. • The dense TiN/CrN coating avoids the diffusion resistance of the TiN coating. • The corrosion mechanism of TiN/CrN coating in PEMWE environment was revealed. • The passive film properties of TiN and TiN/CrN coatings on TA1 were studied. [ABSTRACT FROM AUTHOR]

The effects of varying Cr and Mo concentrations on the pitting corrosion resistance of super austenitic stainless steels in Cl− solutions were investigated using a combination of immersion experiments, electrochemical measurements, X-ray photoelectron spectroscopy, and first-principles computational simulations. The surface characteristics, impedance, and defect concentration of the passive film were changed, and this eventually resulted in a decrease in the number of pitting pits. Due to a decrease in active sites within the passive film, a delayed beginning of pitting, and the combined effect of MoO42− inhibitors, it was discovered that an increasing Mo concentration slows the rate of pitting extension, resulting in reduced maximum pitting area and depth. Additionally, Mo increased the adsorption energy of nearby atoms, whereas Cr raised the adsorption energy of itself. Interestingly, compared with individual doping, co-doping of Cr and Mo increased work function and adsorption energy, indicating a synergistic impact in enhancing resistance to Cl− corrosion. [ABSTRACT FROM AUTHOR]

The corrosion behaviour and mechanism of CoCrNi medium-entropy alloy (MEA) imposed by alternating current (AC) in HCO3−/CO32− solution with various pH were systematically investigated via a series of corrosion tests. The results showed that with the augment of pH value, the polarisation resistance of the MEA decreased significantly, Ep shifted negatively, and ipI value increased, as well as corrosion rate was enhanced, revealing that the corrosion resistance was weakened. As solution pH increased, the formation of secondary passivation zone became easier, which may be attributed to the reaction conversion process of Cr(III) to Cr(VI) species. Moreover, the increase in pH led to an increase in defect density and a thinning of passivation film, facilitating the corrosion of the MEA. AC interference accelerated the ion exchange process and promoted the formation possibility of stable pitting. Higher iAC and pH inhibited the repassivation of metastable pitting, and increased the pitting susceptibility. Highlights The effect of pH on the corrosion behaviour of CoCrNi MEA with imposed AC was clarified. High pH and iAC accelerated the nucleation and growth of metastable pits. With increased pH and iAC, the stability and protective ability of passive film were weakened. The secondary passivation of the MEA was mainly due to the conversion of Cr(III) to Cr(VI) species. [ABSTRACT FROM AUTHOR]

X‐ray photoelectron spectroscopy (XPS) is a technique that is widely used to study thin oxide films because of its extremely high surface sensitivity. Utilizing the QUASES (Quantitative Analysis of Surfaces by Electron Spectroscopy) software package developed by Sven Tougaard (University of Southern Denmark), a user can obtain additional information that is not extracted in conventional XPS analysis, specifically the composition as a function of depth. Presented here is the QUASES analysis of four Ni‐Cr‐Mo alloys performed while testing various inelastic mean free path (IMFP) determination methods in the context of providing a framework for the analysis of complex oxides in QUASES. Ni‐Cr‐Mo alloys are often used to replace conventional materials under aggressive conditions, because of their exceptional corrosion resistance. Their corrosion resistance is conferred by the formation of an inert surface oxide film that protects the underlying metal. Using the QUASES software, the thickness of the air‐formed oxide on four Ni‐Cr‐Mo alloys was found to lie within the range of 2.5–3.6 nm. They were found to be composed of an inner Cr2O3 layer and an outer Cr (OH)3 layer, with a transition zone where the two coexisted. Oxidized Mo species, MoO2 and MoO3, were found in trace amounts at the boundary between the Cr2O3‐only and mixed Cr2O3/Cr (OH)3 regions of the oxide. We also determined that using 20% reduced IMFP values gave results similar to those obtained using electron effective attenuation length (EAL) values. Auger depth profiles showed comparable trends to the QUASES models. [ABSTRACT FROM AUTHOR]

In this study, an Al–Mn–Zr alloy was designed and its microstructure and corrosion behavior compared after laser welding to that of AA3003. As the results of immersion and electrochemical tests showed, both alloys had a faster corrosion rate in the fusion zone than in the base metal. Laser welding caused interdendritic segregation, and spread the intermetallic compounds (IMCs) evenly throughout in the fusion zone. This increased the micro-galvanic corrosion sites and destabilized the passive film, thus increasing the corrosion rate of the fusion zone. However, Zr in the Al–Mn alloy reduced the size and number of IMCs, and minimized the micro-galvanic corrosion effect. Consequently, Al–Mn–Zr alloy has higher corrosion resistance than AA3003 even after laser welding. [ABSTRACT FROM AUTHOR]

Ni‐based alloy coatings are sprayed on 304 stainless steel substrates using a high velocity oxygen fuel spraying (HVOF) method. The corrosion‐wear behavior was analyzed using a "block on ring" corrosion‐wear system. This study mainly discusses the effect of different applied potentials on corrosion and wear interaction using scanning electron microscopy, transmission electron microscopy and X‐ray photoelectron spectroscopy (XPS). The results show that as the applied potential increases, the weight loss and corrosion current density of the nickel‐based alloy coating increase accordingly. Increasing the applied potential, the total loss of corrosion‐wear (Wtotal) of the coating increased significantly. Under high applied potential, the main factor for the serious damage is the interaction of corrosion and wear. In addition, the friction coefficient of the coating first increases and then decreases with increasing applied potential. The surface morphology of the passivation layer and the thickness of corrosion oxide can have an important influence on the corrosion‐wear process. Based on the XPS analysis results, the composition of the passive film formed on the surface of the coating in the process of corrosion‐wear includes NiO, Cr2O3, MoO2, and MoO42−. [ABSTRACT FROM AUTHOR]

The corrosion behavior and surface conductivity of type 446 stainless steel were investigated in the simulated cathode environment of proton exchange membrane fuel cell with 0.0005 M H2SO4 + 0.1 ppm F− solution at 80 °C under different polarization potentials by using electrochemical measurement methods, X-ray photoelectron spectroscopy (XPS) and inductively coupled plasma optical emission spectroscopy (ICP-OES). The 446 stainless steel passivates spontaneously in the simulated environment. The current density and interface contact resistance (ICR) enlarge slightly with increasing the anodic polarization potential in the passive region. As the potential changes from 0.7 to 1.5 V vs. SCE, the current density and ICR increase markedly due to the occurrence of transpassivation, secondary passivation, and oxygen evolution. The ICR values are larger by about 24 mΩ cm2 after the polarization above 0.7 V vs. SCE. The polarization potential shifts from the passive region to oxygen evolution region, resulting in higher oxidized Fe and Mo contents in the product film on specimen surface and relatively more release of alloying constituents (especially Cr and Mo) into the solution. These are mainly responsible for the degradation of corrosion and surface conductivity properties. [ABSTRACT FROM AUTHOR]

The effect of hydrogen on the passivation behavior and electrochemical characteristics of selective laser melted (SLMed) 316L stainless steel in a simulated anode environment for a proton exchange membrane water electrolyzer (PEMWE) was studied. The results indicate that hydrogen charged into the sample increased the ratio of superficial Fe2+/Fe3+ and OH−/O2−, increased the concentration of point defects, reduced the film thickness, and weakened its protective effect. The film near 0.6 V SCE showed n-type semiconductor behavior. Hydrogen charging resulted in a higher defect density and thinner space charge layer in the film, which promoted the invasion of aggressive ions. • The relationship between the hydrogen charging and Electrochemical behavior of the passive film were established. • Hydrogen charging led to the change of the semiconductor type of the passive film. • Hydrogen accelerated the charge transfer process and led to the thinning of the space charge layer of the passive film. [ABSTRACT FROM AUTHOR]

It is important to investigate the susceptibility of passive film stability to pore defect in amorphous metal coatings (AMCs). To clarify the correlation, Fe-based AMCs with different porosities were prepared by high velocity air fuel (HVAF) spraying, and their electrochemical properties, semiconductor characteristics, and surface chemistry of the passive film were determined in detail. The results showed that the passivation current density exhibited obvious sensitivity to porosity. It could increase by more than an order of magnitude while the porosity increased by only a factor of 1 (from 0.35 to 0.78 vol.%). This sensitivity was attributed to the increase in point defect density and the decrease in electronic work of the passive film. In addition, the positive shift in the film-forming potential could also increase the passivation current density. This is due to the fact that the passive film inside the pore defects degrades more at a higher film-forming potential. This work inspires us that the porosity should be strictly controlled to ensure a stable passive film in amorphous metal coatings. [ABSTRACT FROM AUTHOR]

In this work, the effect of grain size variation on the pitting corrosion as well as the passivation behavior of the Alloy 600H has been critically assessed by various electrochemical techniques. The grain size modifications have been achieved by a series of thermal and thermo‐mechanical processing. The potentiodynamic polarization study has revealed that the coarse‐grained specimens exhibit higher corrosion and pitting resistance than the fine‐grained ones. This has been attributed to the greater extent of random high‐angle grain boundary (RHAGB) surface area in the fine‐grained specimens, which acted as favorable locations for pit initiation. The electrochemical impedance spectroscopy (EIS) result has indicated the formation of more imperfect (nonstoichiometric) passive layers in fine‐grained specimens due to the predominant presence of high energy and defective RHAGBs surface. Moreover, the Mott–Schottky analysis has revealed that the fine‐grained specimens generate higher defect densities at the interfaces, which leads to passive film instability due to increased mobility of cation interstitial and cation vacancies at the interfaces. [ABSTRACT FROM AUTHOR]

The corrosion behavior and mechanism of CoCrFeNi HEA under AC application were systematically studied in 3.5 wt.% NaCl solution containing different concentrations of NaHSO3. The results showed that the existence of HSO3− increased the defect density within the passivation film on the surface of the HEA. With the increase of HSO3− concentration, the passivation zone became narrow, Ep shifted negatively, and ip increased, which indicated that the corrosion resistance of the HEA was weakened. When the HSO3− concentration increased to 0.1 M, a clear transition zone appeared, indicating that the increase in concentration reduced the passivity of the HEA, and its corrosion behavior changed from the typical passivation characteristic to the activation state with increasing iAC. The imposed AC promoted the nucleation of metastable pitting, which was indicated by a remarkable increase in the average pitting number density (Navg) from 5 to 17 mm−2 with the enhancement of iAC. [ABSTRACT FROM AUTHOR]

Among various materials available for alleviating the corrosion-related degradation, thermal sprayed Fe-based metallic glass coatings (MGCs) have received huge attention from the scientific community due to the exceptional combination of mechanical and corrosion properties, along with commercially attractive low material cost of this particular alloy system. Emerging reports on the thermal sprayed Fe-based MGCs outperforming conventional corrosion-resistant materials and coatings have accelerated further exploration of this domain, resulting in an immense increase of research activities over the last few decades producing fascinating results. This review takes a holistic approach encompassing an in-depth assessment of all the relevant salient work till date, including corrosion properties, corresponding degradation mechanisms, metallurgical and environmental factors with reference to passive film dynamics and/or formation of corrosion products. Moreover, various strategies for improved corrosion properties and recent research progress have been reviewed with an attempt to identify the present knowledge gaps and the future research directions. [ABSTRACT FROM AUTHOR]

A nanosecond pulsed fiber laser was used to modify the surface of 304 stainless steel. The compactness, microstructure, chemical composition, and corrosion resistance of the stainless steel passive film were observed by the blue dot detection method, scanning electron microscopy, x‐ray photoelectron spectroscopy, and electrochemical methods. The influence of different laser fluences on the stability and corrosion resistance of the stainless steel passive film was studied. The results show that with increasing laser fluence, the discoloration reaction time of the stainless steel surface increases first and then decreases, while the surface roughness decreases first and then increases. When the laser fluence is lower than 11.19 J/cm2, a compact and uniform passive film is formed. When the laser fluence is larger than this value, the stainless steel substrate is prone to secondary corrosion. Chromium oxides are enriched in the passive film, and the anodic dissolution rate decreases, which promotes a positive shift in the corrosion potential of the stainless steel, decreases the corrosion current density and increases the polarization resistance and the corrosion resistance. The surface corrosion resistance is thus significantly improved. [ABSTRACT FROM AUTHOR]

The aim of this work was to revisit second‐harmonic generation (SHG) as a technique for the in situ analysis of oxide film formation on steel samples immersed in aqueous solutions and during electrochemical experiments. The measurements were compared to active reflectance spectroscopy (ARS), which is a more established in situ spectroscopy technique. Carbon steel electrodes were subjected to polarization in pH neutral and mild‐alkaline electrolytes to provoke the formation of passive films. In situ SHG measurements allowed monitoring of compositional changes in the formed film, as the SHG intensity increased in the domain of stability of Fe3O4 and decreased in the domain of stability of Fe2O3 during potentiodynamic polarization. ARS, on the other hand, is suitable to monitor film thickness. ARS absorption increased along with film growth when moving in the anodic direction during potentiodynamic polarization. During 30 min cathodic polarization at −0.9 VAg/AgCl sat. KCl in initially pH neutral the combination of SHG and ARS revealed the presence of an oxide film that was primarily composed of Fe3O4 and with a thickness up to 0.7 nm. [ABSTRACT FROM AUTHOR]

In this study, an Fe-Cr-Mo-C-B (FeCrMoCB) metallic glass coating was prepared by atmospheric plasma spraying. The composition and morphology of the as-sprayed FeCrMoCB metallic glass coating were characterized by x-ray diffraction and scanning electron microscopy. A potentiostatic polarization study was performed for different times to evaluate the changes in the growth process of the passive film. The impedance value of the passive film and the passivation time were found to be in good agreement with the logarithmic relationship within 24 h of passivation. After 24 h of potentiostatic polarization, the impedance value of the passive film was significantly improved to 1.54 × × 105 Ω⋅cm2 and the carrier concentration was increased to 1.10 × 1021 cm−3. The results of x-ray photoelectron spectroscopy analysis showed that the increase in oxide content, especially Cr2O3, and the decrease in hydroxide content in the passive film may be the main reason for the improved corrosion resistance of the passive film. [ABSTRACT FROM AUTHOR]

The effect of chloride threshold (CT = [Cl−]/[SO42−]) on the pitting behaviors of 316LN in the sour water was studied by using electrochemical tests. The result shows that the pitting resistance of 316LN decreases with the increase in CT and temperature. The critical chloride threshold (CCT) decreases from 3 at 40°C to 1.5 at 70°C and then remains unchanged when further increases the temperature. The EIS experiment manifests that the protectiveness of the passive film reduces with the increase of CT, and the variation of the charge transfer resistance (Rct) is in keeping with the pitting potential (Epit). Increasing the CT or raising the temperature from 40°C to 80°C enhances the donor (point defect) density, resulting in a thinning of the protective film. Methods to raise the value of the CCT, that is, to improve the chlorine corrosion resistance of the pipelines were proposed. [ABSTRACT FROM AUTHOR]

The quest for stainless steel coatings suitable for demanding marine structural components has long centered on achieving a delicate balance between heightened hardness and corrosion resistance. Traditionally, this pursuit has posed significant challenges. Nitrogen alloying has emerged as a promising avenue for enhancing both properties simultaneously in martensitic stainless steel. However, its limited solubility in martensite has stood as a formidable obstacle for its widespread adoption. In this work, we have successfully developed a high nitrogen martensitic stainless steel coating via laser cladding under a N 2 atmosphere, utilizing 410L powder incorporated with nitrides as the raw material. The resulting coating boasted a nitrogen content of up to 0.221 wt%, essentially reaching the thermodynamic solubility limit of nitrogen in the 410L liquid phase. Remarkably, the introduction of nitrogen led to a substantial 145 % increase in the pitting potential of 410L stainless steel, complemented by a notable elevation in hardness. Despite the potential risk posed by chromium enrichment in the martensitic matrix, a hazard that may exacerbate corrosion, the presence of nitrogen in solid solution effectively mitigated these adverse effects. Instead, nitrogen facilitated accelerated passive film formation, bolstered passive film stability, and suppressed the growth of stable pits. Our findings are expected to offer valuable insights into the design and fabrication of high corrosion- and wear-resistant martensitic stainless steels. [Display omitted] • An in-suit nitrogen alloying method for martensitic stainless steel was proposed. • The high nitrogen martensitic stainless steel coating had 0.221 wt% of nitrogen. • Simultaneous improvements in hardness, wear resistance and corrosion resistance. • The effects of structural characteristics on corrosion behavior were elucidated. [ABSTRACT FROM AUTHOR]

[Display omitted] • Effect of Nb content on NiTi SMAs' passivity behavior was studied. • NiTi SMA is susceptible to pitting and crevice corrosion in 3.5 wt% NaCl solution. • Incorporation of Nb 2 O 5 into TiO 2 passive film improves localized resistance. • The addition of 9 at.% Nb makes NiTi SMA immune to localized corrosion. This study explores the passivity and localized corrosion behavior of Ni(100-x)/2Ti(100-x)/2Nbx shape memory alloys (where x = 3, 6, and 9 at.%) through potentiodynamic and potentiostatic polarization tests in 3.5 wt% NaCl solution. The results reveal a significant dependence of the surface passive film's stability on the Nb concentration. Using X-ray photoelectron spectroscopy (XPS), the chemical composition of the passive films formed on the NiTiNb alloys was characterized. Microstructural analysis showed that increasing Nb content affects the volume fraction of the eutectic microconstituent, leading to the suppression of martensite and secondary Ni-Ti phases in the microstructure with higher Nb additions. The findings demonstrate that localized corrosion resistance improves with Nb additions, attributed to the incorporation of Nb 2 O 5 into the TiO 2 passive film, enhancing its protective capacity. Remarkably, the NiTi shape memory alloy exhibits immunity to localized corrosion when 9 at.% Nb is added. [ABSTRACT FROM AUTHOR]

This study presents a novel non-linear heating ageing (NLHA) strategy which is capable of regulating the mechanical properties and corrosion resistance of the Al-Mg-Zn(-Ag) alloy effectively. Compared to the linear heating ageing (LHA), the NLHA technology induces a more pronounced hardening response. Under the action of NLHA technology, the addition of Ag promotes the co-precipitation of T′-Mg 32 (Al, Zn, Ag) 49 and η'-MgZn 2 phases. In addition, Ag promotes the discontinuous distribution of grain boundary precipitates and increases the thickness of passive film. As a result, the Ag-bearing Al-Mg-Zn-Ag alloy presents better mechanical properties and corrosion resistance than that of Al-Mg-Zn alloy. • NLHA promotes the precipitation of nanoparticles. • Ag-additions increase the thickness of passive film. • Ag-bearing Al-Mg-Zn-Ag alloy presents better corrosion resistance. [ABSTRACT FROM AUTHOR]

• Stress concentration induces micro-cracks at the bottom of pitting after the passive film damage. • Mechano-electrochemical effects at the crack tip location promote AD and HE. • Proposed a novel stress corrosion cracking mechanism model for 316L stainless steel. This paper analyzes the failure mechanisms of stress corrosion cracking (SCC) in 316L stainless steel flow promoter strings in corrosive oilfield environments. Electrochemical tests and passive film analysis techniques were employed to elucidate the degradation behavior of the 316L stainless steel passive film. The fracture characteristics were analyzed using slow strain rate tensile tests, scanning electron microscopy, and electron backscatter diffraction techniques to clarify the SCC mechanisms. The results indicate that the SCC of 316L stainless steel is controlled by anodic dissolution due to passive film breakdown in the oilfield environment. The degradation of the passive film, induced by Cl- and CO 2 , promotes SCC in 316L stainless steel, with cracks propagating in a trans granular manner. [ABSTRACT FROM AUTHOR]

The corrosion performance of high-strength FeNiCrAl medium-entropy alloy compared with that of 304 stainless steel was investigated in 1 mol/L KOH solution. The electrochemical results indicated that the FeNiCrAl medium-entropy alloy has a better corrosion resistance and lower corrosion rate. The immersion tests confirmed that the degree of corrosion of the FeNiCrAl medium-entropy alloy was less severe than that of 304 stainless steel. X-ray photoelectron spectroscopy results revealed that the higher corrosion resistance of the FeNiCrAl medium-entropy alloy results from the difference in composition of the passive films. The FeNiCrAl medium-entropy alloy promotes the enrichment of Al and Ni with an oxidation state on the surface, and it suppresses the formation of iron oxidation, inducing effective passive films with increased compactness, higher charge transfer resistance, and lower defect density. Our results are meaningful for designing and applying medium-entropy alloys with excellent corrosion resistance in alkaline media. [Display omitted] • FeNiCrAl medium-entropy alloy has a higher corrosion resistance in KOH media. • Passive films on MEA are compact with a higher impedance and lower defect density. • Al and Ni with an oxidation state are enriched in passive films of MEA. • The formation of less protective iron oxides is suppressed in passive films of MEA. [ABSTRACT FROM AUTHOR]

This study examined how varying B element concentrations (x = 0, 0.04, 0.1, and 0.2 at.%) affect the microstructure, corrosion resistance, and characteristics of passive films in AlCrFe 2 Ni 2 B x high-entropy alloys. The findings indicated that as-cast AlCrFe 2 Ni 2 B x alloys transitioned from distinct grain structures to dendritic structures. Increased B content significantly enhanced inter-dendritic regions, resulting in notable grain refinement during this transition. In a 3.5 wt.% NaCl solution, B content increase from 0 at.% to 0.1 at.% improved corrosion resistance, while a 0.2 at.% concentration slightly reduced resistance. These effects stemmed from microstructural changes and variations in passive film composition. [ABSTRACT FROM AUTHOR]

Mechanical properties, passivation behaviors and corrosion resistance of biomedical Ti15Mo alloy with ultra-finer twins were investigated. Cyclic deformation was conducted to activating more {332} twin variants via periodic changes of tension and compression. Microstructural refinement via numerous twins with the stable boundaries is different from other mechanisms, resulting in a higher hardness and maintaining the low elastic modulus after deformation and annealing. The results of electrochemical impedance spectroscopy and X-ray photoelectron spectroscopy tests, revealed that twin boundaries are beneficial to enhancing passivation behaviors via forming a thicker oxide film in PBS solution. The alloy with ultra-finer {332} twins exhibit a better corrosion resistance due to a lower passivation current. The expected biomedical performance was obtained in the alloy after ±3 % amplitude cyclic deformation and 730 °C/7 min annealing, in contrast to the initial alloy with coarse grains, increasing 8.8 % of the hardness, decreasing 46 % of the corrosion current and maintaining the low elastic modulus. • Ti-15Mo alloy after cyclic deformation is activated more {332} twin variants. • Twins in β-Ti alloy is beneficial to obtain excellent mechanical properties. • Twin boundaries enhance passivation behaviors via forming a thicker oxide film. [ABSTRACT FROM AUTHOR]

[Display omitted] • As-build specimen showed superior corrosion resistance than heat treated specimen. • Multiple shot LSP could improve the corrosion resistance significantly. • Microstructure-phase played foremost role in the corrosion behaviour of 15–5 PH SS. • LSP resulted in enrichment of passive layer with Cr and Fe oxides. The emerging applications of metal additive manufacturing (AM) in various industries calls upon the post-processing treatment to homogenize the microstructure which also improves its corrosion properties, specifically for the materials to be used in the corrosive marine environments. In the present study, the electrochemical corrosion properties of 15–5 precipitation hardening (PH) stainless steel specimens developed by laser powder bed fusion (L-PBF) technique in as-build state, and the same after heat treatment and laser shock peening (LSP) were evaluated and compared with the wrought specimens. The effect of LSP parameters on the residual stress, surface topography and corrosion kinetics were evaluated in details. Repetitive LSP shots demonstrated as being a significant factor controlling the corrosion behaviour of L-PBF 15–5 PH stainless steel. Though heat treatment was found to deteriorate the corrosion resistance of the as-build 15–5 PH stainless steel specimen, LSP improved the corrosion resistance of the heat treated specimen by 2 fold making it superior to the as-build specimens. Utilizing the X-ray photoelectron spectroscopy (XPS) analysis, passive layer composition on the specimens were compared. A corrosion mechanism elucidating the overall influence of microstructure and surface condition on the formation of stable Cr and Fe rich passive film were demonstrated. [ABSTRACT FROM AUTHOR]

• 2205DSS forms a double layer passivation film in 30–70 °C, the outer layer is rich in chromium and iron hydroxides, and the inner layer is mainly iron and chromium oxides. • The temperature increase is beneficial to the reaction kinetic rate, accelerates the speed of the film forming reaction, and increases the thickness of the passive film. • The protective properties of passive films depend on the chromium and iron xides/hydroxides content and defect concentration, rather than its thickness. The effects of mine water from 30 to 70 °C on the corrosion mechanism and passive film properties of 2205 DSS was investigated. The results show that the breakdown potential of stainless steel decreases with the increase of temperature, and critical pitting temperature within the range of 50–60 °C.The results show that with the increase of temperature, the breakdown potential decreases from 1.164 V SCE to 0.902 V SCE , and corrosion resistance of stainless steel decrease gradually. The thickness of passive film increases from 0.73 nm to 4.73 nm with the temperature increasing from 30 °C to 70 °C, the defect concentration also increases gradually, and the oxide/hydroxide ratio of Cr and Fe decreased. It was also found that protective properties of the passive film decreased with increasing temperature. The thickness of passive film is not an absolute factor for the protective properties. On the contrary, the content of chromium oxides/hydroxides and the defect concentration in the passive film are the determining factors for the its protective properties. The results of this work provide new insights into the corrosion protection of equipment during the treatment of mine water by LT-MED. [Display omitted] [ABSTRACT FROM AUTHOR]

Titanium aluminides (TiAl) are distinguished by their exceptional strength-to-weight ratio, making them ideal for aerospace and medical applications. Notably, TiAl alloys offer a unique combination of high-temperature resistance and corrosion resilience, contributing to their growing prominence in advanced engineering and biomedical fields. Although initially developed for aerospace applications, TiAl alloys have demonstrated promising potential as implant materials over time. Hence, this research focuses on producing γ-TiAl alloy through electron beam powder bed fusion (EB-PBF) technology, utilising a powder with a composition of Ti-48Al-2Cr-2Nb. For comparative purposes, the corrosion characteristics of Ti6Al4V produced via EB-PBF were also evaluated under identical conditions. The findings indicate that the EB-PBF γ-TiAl exhibits exceptional resistance to corrosion. This is supported by the significantly high polarisation resistance and corrosion potential values, as well as the notably low corrosion current value. However, based on the analysis of the polarisation and impedance curves, it can be observed that the γ-TiAl sample displayed a less protective passive film formation. This occurrence can be attributed to the presence of aluminium ions within the passive layer, resulting in the formation of unstable oxides. As a consequence, it can be inferred that γ-TiAl exhibits inferior resistance to pitting corrosion when compared to Ti6Al4V alloy. The point defect model and Mott-Schottky test further revealed that the γ-TiAl alloy exhibited increased oxygen vacancies. Additionally, the presence of aluminium ions as impurities or dopants led to their substitution for titanium ions, creating cationic vacancies within the passive film. The accumulation of excessive cation vacancies ultimately led to the initiation of pitting corrosion. • Electrochemical behaviour of γ-TiAl produced by the electron beam powder bed fusion process is investigated. • The corrosion potential and current density of the γ-TiAl intermetallic alloy are comparable to the Ti6Al4V sample. • γ-TiAl alloy exhibits excellent corrosion resistance when exposed to 0.9 % NaCl solutions. • The concentration of Al ions released from the γ-TiAl was higher than Ti6Al4V. • Higher Al content in γ-TiAl sample increases the density of cationic vacancies within the passive films. [ABSTRACT FROM AUTHOR]

This paper reviews the formation and breakdown of passive film on the surface of reinforcement steel in alkali-activated materials (AAMs) considering the characteristics of reaction product and pore solution chemistry. The literature review shows that the pore solution of AAMs has higher concentrations of OH−, Na+, silica and aluminium compared to Portland cement (PC). This relatively high alkalinity contributes to the generation of a passive film, which has positive effects on the corrosion resistance of reinforcement steel embedded in AAMs. The silica-aluminium zeolite layer present on the surface of passive film adsorbs chloride ions and effectively inhibits chloride-induced depassivation. Generally, lower ratios of [Cl−]/[SO 4 2−] and [Cl−]/[S 2 O 3 2−] potentially inhibit the depassivation of reinforcement steel. The high pH value and the elevated concentrations of HS− of AAMs contribute to the increase of critical chloride content (C crit). However, the higher content of reduced sulfide mainly dissolved from slag results in the consumption of dissolved oxygen, which is necessary for the formation of passive film. Generally, the presence of reduced sulfide forms Fe-S complexes on the surface of reinforcement steel in AAMs. Even so, higher corrosion resistance for AAMs is mostly expected with longer depassivation time due to finer microstructure and lower chloride penetration rates compared to PC-based materials. The decrease in pH value in the pore solution of the AAMs is the main factor affecting carbonation-induced depassivation of reinforcement steel, while high concentrations of bicarbonate and carbonate ions inhibit depassivation. • Fe-S complexes forms on the reinforcement steel in simulated pore solution of alkali-activated slag. • The higher content of slag in alkali-activated materials delays the formation of passive film. • High pH value of alkali-activated materials increases the chloride threshold value. [ABSTRACT FROM AUTHOR]

The vital role of hydrogen on lead-induced localized corrosion of Alloy 690TT in the simulated secondary crevice chemistries of pressurized water reactor at 25 °C is investigated by using surface analysis techniques and calculations. Density functional theory (DFT) calculation reveals that there is a coupling effect between lead and hydrogen on inhibiting the kinetic diffusion of oxygen vacancies. Experimental results show that hydrogen causes the change of most easily-corroded location from the grain/carbide interface to the TiN/nucleus interface in the lead-induced corrosion process, which provides a new interpreting sight as for lead-induced stress corrosion cracking mode of nickel-based Alloys. • The kinetic diffusion of oxygen vacancies in oxide layer is inhibited by the coupling effect of lead and hydrogen. • Lead promotes the preferential corrosion at the grain/carbides interface of passivated Alloy 690TT. • Hydrogen causes the change of most easily-corroded location from the grain/carbide interface to the TiN/nucleus interface for Alloy 690TT in the lead-induced corrosion process. [ABSTRACT FROM AUTHOR]

This work reports the mechanism of corrosion resistance enhancement of 316 L stainless steel after Te-RE alloying. The individual MnS inclusions are replaced by composite inclusions, resulting in a reduced risk of pitting corrosion. The decrease of inclusion amount and Volta potential difference between inclusion and matrix induced by the addition of Te/La promoted the stability of the inclusions and lessened the active sites for pitting corrosion. TeO 2 formed in the passive film with Te treatment could be easily reduced by Cr and Mo, and resulting in a significant increasing of MoO 2 and Cr 2 O 3 content in the passive film. This enhanced the stability of the passive film. Te and RE exhibited a synergistic effect on the increase of Cr and Mo in the passive film, resulting in a further improvement of the passive film. However, RE could not exist in the passive film stably due to its poor thermodynamic stability of the rare earth oxides, and only acted as a bridge for the formation of Cr and Mo oxides. • 316 L stainless steel with RE-Te exhibited superior corrosion resistance. • MnS was replaced by stable RE-TE-containing inclusions. • RE-Te promoted the increase of Cr 2 O 3 and TeO 2 content in the passive film. • Rare earths are not directly involved in the generation of passive film. [ABSTRACT FROM AUTHOR]

The effect of microstructure on the corrosion behavior and film properties of strengthened AlCoCrFeNi 2.1 eutectic high-entropy alloy (EHEA) was investigated. Annealing of the 80 % cold-rolled AlCoCrFeNi 2.1 EHEA at 650–1200 ℃ effectively improved the stable passive region to 930 mV, and decreased the passive current density by 25 % to 3.5 μA/cm2 compared with the cast alloy in 0.1 M H 2 SO 4 solution. The improved corrosion resistance of the annealed AlCoCrFeNi 2.1 EHEA was attributed to the increasing oxides proportion and thickness of passive film and the reduced composition difference between FCC and B2 phases. The B2 phase in lamellae suffered the severest corrosion. • The tailored microstructure regulation improved the corrosion resistance of AlCoCrFeNi 2.1 EHEA. • The passive region of the annealed AlCoCrFeNi 2.1 EHEAs increased by 120 mV compared with the cast in 0.1 M H 2 SO 4 solution. • The B2 phase in lamellae region suffered the severest corrosion in the sulfuric acid solution. • The mechanism of the improved corrosion resistance of the annealed AlCoCrFeNi 2.1 EHEA was revealed. [ABSTRACT FROM AUTHOR]