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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]

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 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]

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 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]

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]

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]

Effect of temperature on the corrosion behavior of CoCrNi medium-entropy alloy (MEA) in 3% NH4Cl solution was investigated by means of electrochemical measurements, immersion test and statistics analysis. The results show that increasing temperature makes it more difficult to form stable passive film on the MEA surface, accelerates the rupture of the film and reduces the anti-corrosion resistance of the MEA. Particularly at higher temperature, the corrosion rate of the MEA increases, as well the size and number of pits increase. In addition, NH4+ is further hydrolyzed with increasing solution temperature, which promotes the initiation and propagation of metastable pitting, slows down the re-passivation process and enhances the possibility of transition from metastable pitting to stable pitting. [ABSTRACT FROM AUTHOR]

The comparison of corrosion resistance between CoCrFeMnNi high entropy alloy (HEA) and 2205 duplex stainless steel (DSS) in a simulated concrete pore solution was investigated. The results reveal that compared with 2205 DSS, the passive film produced on CoCrFeMnNi HEA possesses a stronger protective ability with a thicker and more stable structure. The initiation frequency, lifetime and peak current value of metastable pitting of the HEA are lower than those of 2205 DSS, indicating that the metastable pitting corrosion is more difficult to occur in HEA. Moreover, the HEA suffers from scattered small-sized pitting, whereas dense and large pits are generated on 2205 DSS. Thus, the HEA exhibits a superior corrosion resistance in comparison with the DSS. [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]

A comparative study on the corrosion behavior of CoCrNi medium-entropy alloy (MEA) with CoCrFeMnNi high-entropy alloy (HEA) in SO2-polluted marine environment was investigated by a series of tests. Results indicate that CoCrNi MEA possesses smaller passive current density, larger polarization resistance and lower corrosion rate compared with those of CoCrFeMnNi HEA, which demonstrates that the MEA possesses better anti-corrosion performance than the HEA. This could be ascribed to the detail difference in the microstructure and passive film of the two alloys. Compared with the MEA, the smaller grain size and the larger number of oxides reduce the anti-corrosion performance of the HEA. Moreover, the oxide and matrix constitute the micro-galvanic corrosion cell, which promotes the generation of pits. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

In this study, cyclic potentiodynamic polarization, potentiodynamic–potentiostatic–potentiodynamic (PD–PS–PD) impedance, and semiconductor performance tests, combined with SEM/energy spectroscopy and XPS detection were used to systematically study the crevice corrosion behavior of SS904L, SS2205, SS2507, and SS254SMO stainless steels with synthetic crevice electrodes in simulated mixture solution of NaCl (10 g/L) and Na2SO4 (5.7 g/L) at 60 °C and pH = 3.5. The results showed that the corrosion behavior among the four stainless steels was most severe at the crevice mouth position, and the SS2507 formed passive films with better stability. Through the discussion of four stainless steels crevice corrosion mechanisms, the crevice geometry restricts the diffusion of metal ions and produces an autocatalytic effect to promote the development of crevice corrosion. Cr, Mo and N have a synergistic effect that improves resistance to crevice corrosion. The crevice corrosion resistance of the four stainless steels decreased in order of SS2507 > SS254SMO > SS904L > SS2205. [ABSTRACT FROM AUTHOR]

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The corrosion behavior of CoCrFeMnNi high entropy alloy in 3.5 wt.% NaCl solution with and without 0.05 M NaHSO3 was studied by electrochemical measurement, immersion test, and atomic force microscope. The results show that with the addition of HSO3−, the state of activation indicated by the anodic reaction evolves to the passivation state. Corrosion resistance is related to the state of the film on the HEA surface. The addition of HSO3− may produce a protective composition that transforms the corrosion product film into passive film. With the presence of HSO3−, the dense and highly protective passive film is formed, which improves the corrosion resistance of the HEA. Without HSO3−, the loose, incompact and incomplete corrosion product film produced on the surface of the HEA exhibits a low protective effect. [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 current study investigates the effect of long-term immersion on the corrosion response and the consequent passive film formation process of lean duplex stainless steel 2101 in 3.5 wt% NaCl solution. The corrosion behavior of the alloy has been monitored through long term immersion tests at different time intervals, viz. 0, 3, 5, 10, 20, 40, and 70 days. The electrochemical tests, such as potentiodynamic polarization and electrochemical impedance spectroscopy, have been performed after each immersion period to understand the change in corrosion rate and passivation behaviour, respectively, with respect to immersion duration. With the increase in immersion duration, the pitting potential (Epit) gradually shifts towards a nobler direction with a simultaneous reduction in corrosion rate (rcorr). This has been attributed to the gradual increase in the thickness of the passive film with the increase in duration of immersion, as revealed through the EIS analysis. The passive film is found to become nearly stable after 40 days of immersion of the specimen in 3.5 wt% NaCl solution. Interestingly, the thickness and stability of the passive film obtained after 40 days of immersion in 3.5 wt% NaCl solution are comparable to the passive film that is formed in mildly passivating media, namely borate buffer solution. An investigation of post immersion surface morphology has also confirmed the gradual improvement in the uniformity and compactness of the oxide-rich passive layer with increase in immersion period, which eventually led to improved corrosion resistance of the alloy in the saline environment. [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 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 corrosion behavior of 2507 super duplex stainless steel (SDSS) in H2S-free and H2S-containing acidic environments was investigated. In N2 environment, the dissolution of Fe was intensified with potential, resulting in the increase in the current density. The presence of H2S decreased the corrosion resistance of 2507 SDSS. As the potential rose between − 0.45 and − 0.37 V(SCE), the selective dissolution of the ferrite was declined due to the increase in the content of Cr and Fe species in the corrosion product layer. Interestingly, when the potential was above − 0.37 V(SCE), the formation of pits in the ferritic region at the phase boundary interface extended toward the ferritic region with the increasing potential under the synergistic effect of H2S. [ABSTRACT FROM AUTHOR]

The effect of stabilizing additions of Ti and Nb on corrosion performance of austenitic stainless steel welds was studied. Multipass multilayer austenitic stainless steel weld pads comprising filler combinations of AISI 316L, AISI 347, and AISI 321 were fabricated and different weld compositions were obtained from these weld pads. Among all weld metals, as-deposited weld with Ti content of 0.12 wt.% and Nb content of 0.48 wt.% exhibited the lowest degree of sensitization and superior pitting corrosion performance in contrast to other Ti + Nb stabilized, Nb stabilized and AISI 316L deposited welds. Thermal aging at 750 °C for 24 h increased corrosion susceptibility for different welds where the presence of Ti and Nb in austenitic stainless steel weld facilitated higher Ni retention characteristics and lesser Cr depletion at dendritic regions as compared with Nb stabilized and AISI 316L deposited weld metals. The passive film formed on Ti + Nb stabilized weld was relatively thinner (3.61 nm) and denser by virtue of the presence of higher content of Ni, Cr, and O that enhanced its passive film protectiveness as determined from electrochemical impedance spectroscopy results. Thus, Ti and Nb played a combined role in lowering the segregation of vital elements such as Cr, C, Ni in austenitic stainless steel welds thereby improving their corrosion performance. [ABSTRACT FROM AUTHOR]

Zirconium is a prospective metal to replace stainless steel in nuclear energy, aerospace, medicine, and chemical fields owing to its excellent comprehensive properties. However, microfabrication of zirconium metal by existing machining methods suffers from severe tool wear, low machining efficiency, and poor machining quality. Electrochemical machining has advantages for processing zirconium metal microstructures, but related studies have been rarely reported due to superpassivation of zirconium. The aim of this study was to evaluate the feasibility and processing trends of masked jet electrochemical machining of Zr702 sheet microdimple array. The dissolution behavior of Zr702 was analyzed in different concentrations of sodium nitrate and polyaluminum chloride electrolytes. The electrolyte was optimized, and the electrochemical corrosion mechanism of Zr702 was explained. Then, the effect of main processing parameters, including the mask aperture, machining gap, electrolyte pressure, jet scan speed, and pulse voltage, on machining performance was investigated in detail. After optimizing the parameters, a good synthesized quality of microdimple array was obtained with an average diameter of 157.60 μm, an average depth of 79.25 μm, a depth/diameter ratio of 0.503, a lateral corrosion coefficient of 2.043, a diameter variable coefficient of 1.72, and a depth variable coefficient of 2.90. [ABSTRACT FROM AUTHOR]

The effect of different AC current densities on the corrosion behavior and mechanism of CoCrNi MEA in carbonate/bicarbonate solution was evaluated by a series of corrosion test methods. The results reveal that the interference of AC damages the internal structure of the passive film, increases its defect amount, and reduces the stability and protection of the film. With the increase in iAC, the corrosion rate of the MEA apparently increases, and the corrosion form is evoluted from pitting corrosion to general corrosion. In particular, the more severe corrosion occurs at 150 A/m2, which is attributed to a large number of H atoms distributed on the surface of the MEA. In addition, the formation of pitting is mainly due to the selective dissolution of Co element, while Co and Ni elements in the oxide are selectively dissolved in the corrosion process. [ABSTRACT FROM AUTHOR]

The influence of microstructure and passive film on the corrosion behavior of CoCrFeMnNi high-entropy alloy (HEA) prepared by different cooling methods in alkaline soil simulation solution was investigated by electrochemical measurements, immersion test, atomic force microscopy, and x-ray photoelectron spectrometry. The results show that the corrosion resistance of the HEA decreases with decreasing cooling rate, and the water-cooled sample exhibits the best anti-corrosion property. The corrosion behavior of the HEA is closely related to σ-phase, grain size, oxide, and passive film. The micro galvanic corrosion effect between grain boundary (GB) and inner-grain reduces as the grain size increases. σ-phase distributed at GBs and the oxide increases the susceptibility to pitting corrosion. The increasing number of σ-phase significantly reduces the corrosion resistance of HEA. And pits around GB regions and σ-phase are attributed to the selective dissolution of Fe, Co, and Cr elements. The pits generated in the interior of σ-phase are mainly caused by the selective dissolution of Cr. The passive film of the water-cooled sample contains higher contents of Cr2O3, Fe2O3, and bound water, and lower contents of Mn oxide and FeO, which has better protection ability to the matrix. Moreover, a dense passive film is formed on the water-cooled sample as indicated by the fact that the donor density (ND) of passive film on the furnace-cooled sample is approximately 1.65 times that of water-cooled sample. [ABSTRACT FROM AUTHOR]

As part of promoting eco-friendly research & development, corrosion chemistry encourages green inhibitors for metal corrosion prevention. Thespesia Linoleic acid, n-Hexadecanoic acid, trans-Squalene, Phytol were identified as the active components responsible for corrosion inhibition. The optimum concentration of 500 ppm could deliver protection with efficiency in the range of 97%–98%. Additionally, we extended the study to evaluate the extract's capability for its use in the paint industry. The remarkable potential of the TiO2-TP composite coating thus developed was illustrated by physico-chemical, electrochemical, and surface analyses. According to the electrochemical impedance spectroscopy (EIS) study, the applied leaf extract loaded coatings resist corrosion of CS at efficiencies of 97.9%, 91.6%, and 98.5% in 1 M HCl, 1 M HCl at 80 °C, and rainwater mediums, respectively. The proposed composite coating is undoubtedly promising for industrial application and is also recommended by green protocols. [ABSTRACT FROM AUTHOR]

With the continuous tightening of marine exhaust emission standards, removing nitric oxide (NO) by Fe(II)EDTA solution complex adsorption is regarded as a promising method. In order to evaluate the feasibility and risk of the corrosion failure for candidate metal in the Fe(II)EDTA-based liquid-phase denitrification system, the corrosion behavior of 316L stainless steel (SS) in Fe(II)EDTA, Fe(III)EDTA, and Fe(II)EDTA-NO was investigated using open circuit potential (OCP), electrochemical impedance spectroscopy (EIS), potentiodynamic polarization, Mott-Schottky method, and X-ray photoelectron spectroscopy (XPS). The experimental results reveal that 316L SS is applicable to the liquid-phase denitrification environment, because of a passive film produced on the 316L SS surface which can protect effectively itself from further corrosion. Thereinto, the homogeneity and thickness of the passive film formed in the Fe(III)EDTA secure the maximum value. Beyond all doubt, the corrosion rate of 316L SS in Fe(III)EDTA is minimum only 0.001 mm·year−1. Meanwhile, the passive film was found to have semiconductive characteristics. The XPS results provide strong evidences for the above electrochemical measurements that the different electrochemical properties including variation of n/p-type semiconductor behavior are attributed to its chemical component. The passive film mainly consists of Cr2O3, Fe3O4, and MoOx, and FeO, CrO3, NiO, and MoO2 are not detected in the passive film formed in Fe(III)EDTA. These phenomena reasonably explain why the Mott-Schottky plot in Fe(III)EDTA only showed one n/p-type transformation rather than two in Fe(II)EDTA and Fe(II)EDTA-NO. [ABSTRACT FROM AUTHOR]

In order to investigate the influence of the preparation method on the electrochemical dissolution behavior of the typical superalloy Inconel 718, we employed various test methods to determine the composition and structure of the passive film. Test results show that the film is mainly composed of Cr2O3 and NiO, which have an obvious impact on the electrochemical and physical properties of the surface. The electrochemical machining experiments indicate that wrought Inconel 718 contains large amounts of pitting and selective corrosion, while hot-rolled Inconel 718 exhibits finer grains and a more uniform distribution, which results in a more even dissolution and a better surface quality. [ABSTRACT FROM AUTHOR]

Being an exclusive construction material for lightweight rail vehicles, protection from pitting corrosion in harsh marine atmospheric environment in high humidity and Cl− ion concentration is critical for austenitic SUS 301L stainless steel (SS), especially when it inevitably suffers from mechanical damages during post disposals. Herein, an innovative dry passivation method for austenitic SUS 301L SS was established in a closed air atmosphere at low temperature and constant pressure. The process parameters were optimized, and the passivation mechanism was explained using polarization curve, electrochemical impedance spectroscopy (EIS), X-ray photoelectron spectroscopy (XPS), and contact angle measurement. The pitting corrosion susceptibility of the passive film prepared in a closed air chamber under 1.0×105 Pa at 80 °C for 80 min was evaluated in 3.5% NaCl solution and exhibited higher pitting potential and corrosion resistance, lower passivity-maintaining current density, and wettability when compared with conventional nitric acid treatment. Besides, dry passivation facilitated the repairing of the surface structural defect itself and the post-processing damage, similar to the accelerated aging of film. The decrease in oxygen concentration and convection-diffusion strengthened the preferential chromium oxidation to form a compact chromium-rich passive film to resist the aggression of Cl− ion. [ABSTRACT FROM AUTHOR]

The superior corrosion resistance of high-entropy alloys (HEA) has attracted much attention from researchers in recent years. In this study, with minor additions of passivation elements into a CoCrFeNi matrix, a (CoCrFeNi)94Ti1.5Al4.5 HEA coating was prepared by a plasma cladding method. This coating has a single FCC phase structure and uniform microstructure, which is expected to form a uniform and compact passive film on the corrosion surface. After adding Ti and Al elements, the passive film became more compact due to the decrease in the proportion of porous hydroxide, which increased the impedance of the passive film, thereby improving the corrosion resistance of the whole HEA coating. After potentiostatic polarization for 4 h, a stable passive film was formed on the (CoCrFeNi)94Ti1.5Al4.5 coating surface in a 0.5-M H2SO4 solution. The corrosion current density was only 175 nA/cm2, which was much lower than that of 304 stainless steel and pure titanium. This indicated that minor additions of Ti and Al can promote the formation of corrosion-resistant high-performance passive films without forming deleterious second phases, and that this phenomenon is more obvious in sulfuric acid solution than in hydrochloric acid solution. [ABSTRACT FROM AUTHOR]

Electrochemical characteristics and semiconducting behavior of additively manufactured electron beam melted (EBM) and wrought (WR) Ti–6Al–4V (Ti-G5) are compared in Ringer's physiological solution. X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM) confirmed the α + β structure of the tested materials, with two different microstructure types of "bimodal" and "basket-weave" for WR and EBM, respectively. Potentiodynamic polarization (PDP) revealed that the corrosion current density for EBM (icorr = 0.27 ± 0.06 μA cm−2) is less than the WR (icorr = 0.70 ± 0.05 μA cm−2). Moreover, potentiostatic polarization (PS) that was employed to form the passive layers at three different potentials of 300, 500, and 700 mVAg/AgCl, showed that the passive films on the EBM sample are thinner. This finding was confirmed by electrochemical impedance spectroscopy (EIS). Furthermore, through Mott–Schottky (M–S) analysis, donor densities on WR passive films were found to be ~ 1.5 times larger than EBM. Although PS and EIS confirmed that the passive layer on EBM is thinner, it provides higher corrosion resistance than WR. The passive layer on both samples were found to have n-type characteristics with a duplex structure. [ABSTRACT FROM AUTHOR]

The electrochemical behavior of titanium (Ti) was investigated before and after anodic polarization at different potentials in simulated seawater solutions. The results showed that the Ti anodically polarized at 3.2 VSCE was much more stable than those at 0.5 VSCE and the open-circuit potential (OCP), and the passive film formed at the low potentials could be transformed to a more protective film after polarization at the high potential. The polarization at the high anodic potential could effectively enhance the long-term durability of Ti under natural immersion conditions. Nitzschia closterium f. minutissima could only slightly influence the electrochemical behavior of Ti. The film formed at the 3.2 VSCE on Ti appeared to have very limitedly better antifouling performance than those formed at the 0.5 VSCE and OCP. [ABSTRACT FROM AUTHOR]

The electrochemical corrosion behavior of an aged Fe-18Cr-15Mn-0.66 N high-nitrogen austenitic stainless steel in 3.5 wt.% NaCl solution was studied using the measurements of polarization curves and electrochemical impedance spectroscopy, and the composition of the passive films formed on the HNSS was investigated using x-ray photoelectron spectroscopy (XPS). XPS analyses results showed that the passive films formed in this solution were composed of Cr oxide/hydroxide (mainly) and iron oxides (partially). The XPS depth profile suggested that near the passive film /HNSS interface, both Cr and Fe contents increased, but the Cr and Fe oxide/hydroxide contents decreased. [ABSTRACT FROM AUTHOR]

The effect of aging time on corrosion behavior of 2507 super duplex stainless steel (SDSS) under a 3.5wt.% NaCl solution was explored by electrochemical tests, atomic force microscopy (AFM), x-ray photoelectron spectroscopy (XPS), and immersion test. The experimental results indicate that with an increasing aging time, the anti-corrosion property of 2507 SDSS aged at 850 °C decreases significantly. The SDSS aged for 5 min contains two precipitated phases (χ, γ2). As aging time increases, the quantity of σ phase precipitates significantly increases, which seriously reduces the corrosion resistance of SDSS due to the increasing number of micro-galvanic corrosion cells. In addition, the passive film of SDSS aged for 60 min exhibits the minimum values of Rct and Rf, as well as the maximum carrier densities. For the aging time of 5 min, the passive film consists of higher contents of Cr2O3 and H2O, as well as less FeO, while also demonstrating good stability and compactness. The precipitated phases seriously decrease the protective ability of passive film, especially the σ phase. [ABSTRACT FROM AUTHOR]

The corrosion behavior of an Inconel 718 alloy fabricated using the selective laser melting (SLM) technique in a 3.5 wt.% NaCl solution is determined. The corrosive effect of the NaCl solution on the Inconel 718 alloy is investigated using potentiodynamic polarization curve measurements, Mott-Schottky plots, electrochemical impedance spectroscopy, atomic force microscopy, and x-ray photoelectron spectroscopy (XPS) and is compared with that on a commercially rolled Inconel 718 alloy (R 718). Electrochemical results suggest that the application of SLM to the Inconel 718 alloy lowers its corrosion resistance. The passive films formed on both alloys show p-type and n-type semiconductor behaviors. However, the concentrations of the defects in the passive films formed on the surface of the SLM Inconel 718 alloy are higher than those on the surface of the commercially rolled R 718. XPS shows that the passive film formed on the SLM Inconel 718 alloy has a higher NiO content, leading to the deterioration of its protective properties. [ABSTRACT FROM AUTHOR]

The microstructure of two sets of 316L alloys (SLM and wrought structure) is determined using SPECTROMAXx stationary metal analyzer, FE-SEM/EDS and XRD. The physical–chemical properties of the passive films are also investigated by means of XPS, Auger after sputtering and electrochemical impedance spectroscopy measurements. Differences and similarities between the two sets of alloys are then identified. The corrosion behavior of alloys is investigated in NaCl solution at the macro- and microscale (microcapillary technique). It was found that the inclusion/particles cleanliness is the first-order parameter explaining differences between 316L(WS) and 316L(SLM). In the absence of particles (pure matrix), the two sets of alloys have the same corrosion behavior. Residual stresses, the average grain size, the PREN and the passive films properties are of second order. [ABSTRACT FROM AUTHOR]

In this work, the stability of passive film for long-time immersed Cu-bearing L605 (L605-Cu) alloy in the phosphate buffer solution (PBS) was studied by potentiodynamic polarization and electrochemical impedance spectroscopy. The results showed that the impedance of passive film for L605-Cu alloy experienced an initial increase and subsequent stabilization with the increase in the immersion time. In addition, the plate count method was employed to assess the antibacterial durability of L605-Cu alloy against Escherichia coli after long-time immersion. The results indicated that the antibacterial rate of L605-Cu alloy presented a declining tendency with the immersion time prolonging. X-ray photoelectron spectroscopy (XPS) was used to analyze the change of the chemical composition in the passive film on L605-Cu alloy immersed in the PBS for different time. The results showed that Cu content and its compounds in the passive film gradually increased with the immersion time prolonging, hinting declined activity of Cu ions penetrating into the passive film, which resulted in a decrease in the antibacterial performance. [ABSTRACT FROM AUTHOR]

As a material with good corrosion resistance, 5083 aluminum alloy has a great application prospect in marine environment. In this work, the corrosion characteristics of 5083 aluminum alloy in seawater containing phosphate were investigated with Potentiodynamic Polarization, Electrochemical Impedance Spectroscopy (EIS), Scanning Electron Microscope (SEM), Energy Dispersive Spectroscopy Analysis (EDSA), X-ray Photoelectron Spectroscopy (XPS) and Laser Confocal Microscope. The results indicated that the effects of phosphate in seawater were two-fold. Firstly, phosphate slightly accelerated the corrosion of 5083 in seawater in the early stage of corrosion. HPO42− competed with OH− in the adsorption process on the alloy surface, which weakened the contact between OH− and Al3+ near the interface of the alloy, and inhibited the formation as well as the self-repair of the passive film, thus accelerating the activation dissolution process. Compared with the natural seawater, the charge transfer resistance of 5083 in the seawater containing phosphate decreased faster during the early stage of corrosion, and the corrosion current density icorr was higher in seawater containing phosphate. On the other hand, the addition of phosphate would not affect the cluster distribution of the second phase of 5083 in seawater, but it changed the composition of the corrosion product layer and had an obvious inhibitory effect on the local corrosion of 5083 in seawater. After 16-day exposure, shallower and more sparsely distributed pits could be observed on the derusted surface of 5083 in the seawater containing phosphate, and the pitting coefficient in the seawater containing phosphate was significantly lower than that in natural seawater. The reduction of pitting tendency could be realized mainly through two ways. First, the HPO42− adsorbed on the surface of the passive film in the early stage of corrosion and repeled the corrosive anions such as Cl−. Second, phosphate participated in the construction of the CaHPO4 precipitation film, which acted as a barrier and protection. [ABSTRACT FROM AUTHOR]

Properties of a passive film formed on pure nickel in an anaerobic alkaline solution are investigated by a first-principles calculation and electrochemical experiments in this work, and both results show agreement with each other. The formation energy of nickel vacancies is lower than that of oxygen vacancies in the NiO film, which is consistent with the deduction of the point defect model in which nickel vacancies impart p-type semiconducting character to the passive film, as confirmed by Mott–Schottky analysis. The density of nickel vacancies (approximately 1021 cm−3) in the passive film increases with temperature but decreases with the film-formation potential. The thickness of the passive film increases linearly with the film-formation potential, as verified both by Auger electron spectroscopy and electrochemical impedance spectroscopy. The diffusion coefficient of the nickel vacancies increases from 10−18 to 10−16 cm2/s as the temperature rises from 298 to 348 K, respectively, in experiments using high-field equations and first-principles calculation. [ABSTRACT FROM AUTHOR]

The effect of room temperature deformation on the microstructure and corrosion behavior of selective laser-melted (SLM) 316L steel in 0.9 wt.% NaCl medium was explored by electrochemical tests, microstructural analysis, and passive film characterization. The irregular evolution of corrosion behavior was first found in the deformed SLM 316L steel. The corrosion resistance of SLM 316L steel improved with increasing room temperature deformation level reached the maximum at 20% deformation, and then weakened with further increasing deformation below 40%. Microstructural analysis indicated that the deformation twins passed through the molten pool boundaries when the deformation was 20%, but not when the deformation was 40%. The dislocation density, Σ3, and low-angle grain boundaries increased slightly with increasing deformation below 20%, but they increased distinctly with deformation level greater than 20%. Besides, room temperature deformation modified the oxide content of the surface passive film, especially for the chromium oxide, which affected the corrosion resistance of passive film. Above results indicate that low room temperature deformation level of SLM 316L stainless steel is feasible to improve its corrosion resistance and optimize the passive film. [ABSTRACT FROM AUTHOR]

Effect of passive potential on the protective capacity of passive film formed on CoCrFeMnNi high-entropy alloy was investigated in carbonate/bicarbonate solution by using electrochemical measurements, atomic force microscopy and x-ray photoelectron spectroscopy (XPS). The results reveal that the protective ability of passive film is sensitive to the applied potential, and the anti-corrosion property of passive film at high potential is significantly enhanced as indicated by the high film resistance and the low donor densities. The Cr2O3 content and the ratios of Mn/Mnox as well as O2−/OH− in the secondary passive film are greater than those in the primary passive film. Moreover, increasing the potential facilitates the formation of a homogeneous and thick passive film, which considerably improves the protective ability of the film. [ABSTRACT FROM AUTHOR]

In order to improve the mechanical system performances such as wear resistance and vibration damping behavior, it was focused on the micro-topography of the surface machined by electro-chemical mechanical finishing (ECMF) in this paper. The ECMF was applied in this investigation as a result of it providing more controllable process parameters including the electric potential gradient (EPG), current density, mechanical force, and passive film. The simulation based on the finite element method was applied to analyze the influence of the EPG and the current density on the surface micro-topography under the different magnitudes of mechanical pressure and thicknesses of the passive film. It was shown that the mechanical pressure and the mass percent of the electrolyte which had been controlled are profitable and necessary to gain the feature of arc-like micro-topography on the surface and the growth in material removal rate. The unusual micro-topography of the surface with Ra0.2024μm was finished by using ECMF within 2 min on the condition of 20% NaNO3 electrolyte and 0.2 MPa of mechanical pressure. The investigation on dynamic pressure effect was carried out to confirm the influence of the unusual micro-topography on the thickness in the oil film. The result indicated that compared with the surface machined by fine grinding (FG), the surface finished by ECMF can make an increase in the average film thickness of 3% and a reduction in the square deviation of 46.5%. A discussion was set up to determine the cause of the difference in the results of the experiment. It was shown that the reason for the difference is the distinction in the micro-topography of the surface obtained by ECMF and FG. The micro-topography of the surface finished by ECMF is more favorable to establish a stranger and stable dynamic pressure effect as the result of its fractal dimension, scale coefficient, kurtosis and skewness. The discussion indicated that the finish method impacts the surface topography, and the machining accuracy affects the cross-scale effect of the surface dynamic pressure effect. [ABSTRACT FROM AUTHOR]

The effects of Cl− concentration and applied alternating current (AC) on the corrosion behavior of 2507 super duplex stainless steel (SDSS) were studied in a saturated Ca(OH)2 solution by electrochemical measurements, immersion test, and x-ray photoelectron spectroscopy. The results show that the presence of Cl− ions accelerates the corrosion of 2507 SDSS in the saturated Ca(OH)2 solution. The protective ability of passive film decreases as Cl− concentration increases, especially at the concentration of 10% Cl−. As the applied iAC increases, the ip value increases, and the Ep value decreases. The applied AC increases the number of defects within the passive film, affects the electronic property of the surface film, which results in a harmful effect on the passive film, and weakens its anti-corrosion property. The higher the iAC, the more severe the damage influence is. Moreover, imposed AC promotes the pitting corrosion sensitivity of SDSS and enhances its corrosion rate. The applied AC and the addition of Cl− exert a combined effect, reducing the corrosion resistance of passive film formed on 2507 SDSS. [ABSTRACT FROM AUTHOR]

The effect of warm pre-strain on the corrosion behavior of 304 and 316 steels in 3.5% NaCl solution was first explored by electrochemical tests, passive film characterization, and structural analysis. The pitting corrosion resistance of 304 steel decreases with the increase of strain level below 20% and increases with the strain at a higher strain level, while the pitting corrosion resistance of 316 steel increases slightly with the increase of strain level below 20% and decreases with the strain at a higher strain level. The random grain boundaries in 304 steel are interrupted with the increase of strain level higher than 20%; this does not occur in 316 steel, which exhibits more dislocations. The coupling effect of microstructure changes induced by warm pre-strain affects the oxide content of the passive film, especially for the chromium oxide, which results in abnormal corrosion behavior. Knowing the corrosion mechanism is of value for academic research and enables the design of advanced stainless steel with high strength and corrosion resistance. [ABSTRACT FROM AUTHOR]

In absorption chillers using LiBr aqueous solution, corrosion problems of carbon steel heat exchangers become more serious as the temperature of the generator increases. To reduce the corrosion problems, various surface treatment methods are applied such as a shot-peening. In this study, corrosion characteristics were investigated for untreated and shot-peened surfaces. Pyrex tube samples containing the specimens and LiBr aqueous solution with Li2MoO4 were made and put into a high temperature oven at 200 °C After 2000 hours, the surface and cross section of carbon steel specimens were observed using field emission scanning electron microscope (FE-SEM) and energy dispersive spectroscopy (EDS). It was found that the passive films have the characteristic of a double layer consisting of a thick MoO2 layer and thin Fe3O4 layer. Thicker passive films were observed on the shot-peened surface than the untreated one. As a result of corrosion depth measurement, the shot-peened specimens showed a slightly smaller uniform corrosion depth, however, they showed a much smaller pitting corrosion depth than the untreated ones. It is supposed that the shot-peened surface is more effective in preventing the pitting corrosion than uniform corrosion. The results of this study are expected to be applied effectively to the absorption chillers using LiBr aqueous solution to estimate and reduce the corrosion. [ABSTRACT FROM AUTHOR]

The present study investigates the microstructural and passivation behavior of surface mechanical attrition treated (SMAT) AISI 304 stainless steel in a 0.6 M NaCl solution at room temperature. SMAT process, which is more advanced than the classical shot-peening, causes 2-3 times improvement in surface hardness of the steel. Ball size, a vital SMAT parameter, plays a significant role in controlling the microstructure and corrosion behavior of the steel. Larger diameter (6 mm) balls induce thicker deformed layer (450 μm), a higher proportion of deformation-induced martensite (~ 50%), a higher density of dislocations and twins, and higher lattice strain. TEM results confirm the presence of {111} twins throughout the deformed layer. SMAT enhances the corrosion properties of the steel. Specimen SMATed with 4-mm-diameter-balls displays the lowest corrosion rate (1.80 × 10−4 mmpy). SMAT increases the pitting resistance of the steel surface. XPS is utilized to understand the passivation mechanism of steel comprehensively. SMAT alters the proportion of Cr2O3, Cr(OH)3, Fe2O3, and FeO compounds in the passive layer. SMAT increases the thickness of the passive layer. [ABSTRACT FROM AUTHOR]

The effect of microstructure and passive film on the corrosion resistance of 2507 super duplex stainless steel (SDSS) in simulated marine environment was investigated by electrochemical measurements, periodic wet-dry cyclic corrosion test, scanning Kelvin probe force microscopy, atomic force microscopy, and X-ray photoelectron spectrometry. The results show that the occupation ratio of γ phase increases with the decrease in cooling rate, whereas the content of α phase reduces gradually. In addition, the σ precipitated phase only emerges in the annealed steel. The pitting sensitivity and corrosion rate of 2507 SDSS reduce first and then increase as the cooling rate decreases. The σ precipitated phase drastically reduces the protective ability of the passive film and facilitates micro-galvanic corrosion of the annealed steel. For various microstructures, the pits are preferentially distributed within the σ and γ phases. The corrosion resistance of 2507 SDSS prepared by different cooling methods is closely related to the microstructure and structure (stability and homogeneity) of the passive film. Normalized steel shows an optimal corrosion resistance, followed by the quenched and annealed steels. [ABSTRACT FROM AUTHOR]

The influence of predeformation temperature (100-400 °C) on the corrosion property of the predeformed 304 austenitic stainless steel (SS) in 3.5 wt.% NaCl medium was studied by electrochemical and microstructural characterization. The degradation of pitting corrosion resistance of the predeformed 304 SS can be inhibited by decreasing the deformation temperature. The increase in special (low-Σ coincidence site lattice) boundaries, the decrease in low angle and random grain boundaries improve the pitting corrosion resistance. The corrosion property of the predeformed 304 SS is controlled by the coupling effect of grain boundary and dislocation, while it is little affected by the residual stress. The microstructures induced by adjusting predeformation temperature change the characteristics of the passive film on the SS surface, which affects the pitting corrosion resistance. The achieved results distinctly demonstrate that high-strength and corrosion-resistant metallic materials are possible to be developed by controlling predeformation temperature. [ABSTRACT FROM AUTHOR]

In this study, the effects of protein adsorption on the electrochemical corrosion behavior of commercially pure niobium in phosphate-buffered saline (PBS) solutions with several concentrations (0–4 g L–1) of bovine serum albumin (BSA) were investigated via both electrochemical measurements and surface characterization. For low concentrations of BSA, the adsorbed protein molecules are insufficient to form a barrier layer, resulting in slight decrease in the cathodic reaction via the inhibition effect. Meanwhile, the anodic reaction is accelerated by the chelation effect between the protein molecule and metal ions. When the added BSA reaches saturation capacity, the adsorbed protein amount is approximately 1.8 μg cm–2, corresponding to approximately 1.2 adsorbed layers, facilitating the formation of a complete barrier layer. The inhibition effect of adsorbed protein molecules becomes more dominant for both cathodic and anodic reactions. The results of this study will help provide a better understanding of the mechanism of protein adsorption on the corrosion behavior of biometallic alloys. [ABSTRACT FROM AUTHOR]

Stainless steel (SS) is one of the most widely used engineering materials in marine engineering. However, its corrosion in the marine atmospheric environment due to the high concentration of Cl− is a problem. The SS corrosion is a threat to the development and security of marine industry; therefore, evaluating the corrosion resistance of SSs is necessary. In this work, atmospheric corrosion detection probes based on a symmetrical electrode system were used to study the corrosion behaviors of 304 SS and 2205 duplex stainless steel (DSS) in a simulated marine atmosphere. A theoretical model for electrochemical noise (EN) data analysis based on the Thevenin electrochemical equivalent circuit (EEC) model was established. The relationship between the EN characteristic parameters and the corrosion rate was obtained. The Thevenin EEC model analysis showed that the relationship between the noise resistance (Rn), the noise impedance [Rsn(f)], and the impedance modulus (|Z(f)|) was R n ≈ R sn = 3 Z (f) . Thus, Rn and Rsn can be used as indicators for quantitative corrosion evaluation. The results of EN detection for the 304 SS and 2205 DSS showed that in a simulated marine atmospheric environment, the passive films on the two SSs were relatively intact at the initial exposure stage, and their dissolution rates were slow. The corrosion resistance of the 2205 DSS was higher than that of the 304 SS. With the deposition of Cl− on the SS surface, pitting was initiated and the dissolution rate increased. The pitting initiation process on the SS surface was random, and part of the active pores could be repassivated. [ABSTRACT FROM AUTHOR]

The purpose of this work was to enhance the corrosion resistance of the passive film on 304 stainless steel (SS) by chemical modification in alkaline phosphate–molybdate solutions. The 304 SS was passivated in both phosphate and phosphate–molybdate mixed solutions to investigate the effect of molybdate on its corrosion resistance. The experimental results indicated that the passive film showed better corrosion resistance in Cl−-containing solutions after modification in phosphate–molybdate solutions than in phosphate-only solutions. Energy-dispersive spectroscopy analyses revealed that the passive film formed in phosphate–molybdate solutions contained Mo and P after modification, which is the reason for the enhanced corrosion resistance. [ABSTRACT FROM AUTHOR]