Stability Of Passive Film Research Articles

Study on microstructure and corrosion resistance of high-hardness Zn-1.0Cu-1.0Ti alloy

In order to develop a high durability building decoration zinc-based alloy materials, the as-cast Zn-1.0Cu-1.0Ti alloy (ZCT-AC) with homogeneous microstructure and high hardness was successfully prepared by induction melting and rapid solidification. Interestingly, almost all Ti element exists in the as-cast alloy in the form of the homogeneous strip-like TiZn 16 phase, and the Cu element is uniformly dissolved in both the η -Zn and TiZn 16 phase in the form of supersaturated solid solution. The hardness of the ZCT-AC alloy was about 79.3% and 52.7% higher than that of pure Zn and a commercial cold-rolled zinc‑titanium alloy (ZCT-CR), respectively. By potentiodynamic polarization tests in NaCl solution with four different mass fractions (0.1, 1.0, 3.5, and 5.0 wt%) at 25 °C and in 3.5 w.t% NaCl solution at four different temperatures (25, 35, 45, and 55 °C), ZCT-AC alloy showed higher corrosion resistance than the two control samples because of both a high formation efficiency and a high structural stability of passive film. Furthermore, Several plausible corrosion mechanisms of the three samples have been further studied systematically by a long-term immersion tests in 3.5 wt% NaCl solution, the results suggested that the corrosion process of ZCT-AC alloy was dominated by uniform corrosion which led to a higher interface uniformity, the corrosion layer of the alloy had higher uniformity and overall density, and the corrosion rate of both micro-galvanic corrosion and intergranular corrosion were inhibited significantly owing to the uniform distribution of Cu element. This study might provide a theoretical guidance for designing the high durability building decoration materials. • High-hardness as-cast Zn-1.0Cu-1.0Ti alloy shows excellent microstructure homogeneity. • Almost all Ti element exist in the form of strip-like TiZn 16 phases. • Cu element is uniformly dispersed into both of the Zn-rich matrix and the TiZn 16 phase. • The passive film on Zn-1.0Cu-1.0Ti alloy shows high formation efficiency and high structural stability. • Zn-1.0Cu-1.0Ti alloy has higher overall corrosion layer density and interface uniformity.

In-Situ Laser Directed Energy Deposition of Biomedical Ti-Nb and Ti-Zr-Nb Alloys from Elemental Powders

In order to achieve the required properties of titanium implants, more resources and research are needed to turn into reality the dream of developing the perfect implant material. The objective of this study was to evaluate the viability of the Laser Directed Energy Deposition to produce biomedical Ti-Nb and Ti-Zr-Nb alloys from elemental powders (Ti, Nb and Zr). The Laser Directed Energy Deposition is an additive manufacturing process used to build a component by delivering energy and material simultaneously. The material is supplied in the form of particles or wire and a laser beam is employed to melt material that is selectively deposited on a specified surface, where it solidifies. Samples with different compositions are characterized to analyze their morphology, microstructure, constituent phases, mechanical properties, corrosion resistance and cytocompatibility. Laser-deposited Ti-Nb and Ti-Zr-Nb alloys show no relevant defects, such as pores or cracks. Titanium alloys with lower elastic modulus and a significantly higher hardness than Ti grade 2 were generated, therefore a better wear resistance could be expected from them. Moreover, their corrosion resistance is excellent due to the formation of a stable passive protective oxide film on the surface of the material; in addition, they also possess outstanding cytocompatibility.

Corrosion performance of additively manufactured bimetallic aluminum alloys

To restore defected AA2618 alloy molds, remanufacturing of the damaged areas using AlSi10Mg alloy through laser powder bed fusion (L-PBF) technique is proposed. This study in particular focuses on the corrosion characteristics of the fabricated L-PBF AlSi10Mg / cast AA2618 bimetal structure in aerated 3.5 wt.% NaCl electrolyte with respect to the individual alloys. The L-PBF AlSi10Mg side of the bimetal sample was characterized with a superior corrosion response and the highest passive film stability compared with the cast AA2618 side and the dissimilar sample (prepared from the interface region), ascribed to its homogeneous microstructure, containing a very fine network of eutectic Si embedded in a fine grained and supersaturated α-Al matrix. The overall corrosion performance of the dissimilar sample was found to be between the cast AA2618 and L-PBF AlSi10Mg part, with no sign of macro-galvanic corrosion effect between the dissimilar alloys. The heavily precipitated microstructure of the cast AA2618 alloy, particularly the anodic Al2CuMg phase and cathodic Fe-containing intermetallics versus the Al-matrix, dictated the inferior corrosion properties of the cast sample and the cast side of the dissimilar sample.

Influence of Ce Addition on Microstructure and Corrosion Resistance of 2101 Duplex Stainless Steel

2101 duplex stainless steel with low Ni content is developed to replace austenitic stainless steel in many corrosive environments. Herein, the effects of Ce addition on the microstructure and corrosion resistance of 2101 duplex stainless steel are studied. The electrochemical corrosion behavior of 2101 duplex stainless steel with Ce contents of 0, 0.005, and 0.020 wt% is studied in 3.5 wt% NaCl solution and 0.05 mol L−1 H2SO4 + 0.05 mol L−1 KSCN solution at 25 °C. The situation is evaluated in 6 wt% FeCl3 solution at 35 °C. The results show that with increasing Ce content, the proportion of α phase in 2101 duplex stainless steel decreases, whereas the proportion of γ phase increases. At 0.005 wt% Ce, the two‐phase ratio is close to 1:1. Moreover, the partition coefficient (K) of elements gradually approaches 1 with increasing Ce, indicating a more uniform element distribution between the two phases. The electrochemical experiments in simulated seawater and acidic environments show that Ce addition gradually increases the corrosion potential and pitting resistance, leading to the formation of more stable passivation film.

The Effect of Ultraviolet Wavelength on Corrosion Behavior of 7075 Aluminum Alloy in the Marine Atmospheric Environment

The influence of ultraviolet rays on the corrosion behavior of 7075 aluminum alloy in the marine atmosphere was studied by salt spray corrosion test. Electrochemical methods and surface analysis techniques were used to analyze and compare the corrosion laws of 7075 aluminum alloy in the marine atmosphere under ultraviolet radiation with wavelengths of 0 nm, 185 nm, 254 nm, and 365 nm. The results showed that ultraviolet light irradiation could promote the corrosion of 7075 aluminum alloy. Oxygen was prone to chemical reactions to form oxygen atoms after being irradiated by ultraviolet rays, and oxygen atoms recombined with oxygen to form ozone in the marine atmosphere. The 7075 aluminum alloy in the marine atmosphere accelerated corrosion due to the increasing ozone content. Although there were passivation films with different degrees of protection on the surface of aluminum alloy under ultraviolet irradiation, the surface of 7075 aluminum alloy in the marine atmosphere failed to form a stable passivation film after pitting, and the corrosion rate was the fastest when the ultraviolet wavelength was 185 nm.

Effect of aluminum reinforcement on the structural, physicochemical, and electrochemical properties of polyaniline-derived polymer/aluminum composites by in situ polymerization

We investigated the structural, conductive, and electrochemical properties of polyaniline-derived polymer/pristine aluminum composites by in situ polymerization. This research focused on the conductivity and electrochemical energy storage effects of Al particles used as reinforcing elements in composites and elucidating the interaction of polyaniline on the surface of Al particles by keeping the HCl acid dopant concentration and monomer-oxidant ratio constant. FTIR results revealed that polymerization was successfully synthesized by showing all the characteristic peaks of polyaniline, and the polymer matrix of composites produced in the presence of aluminum was polyaniline. SEM images also showed that Al particles were completely embedded or enclosed in the polymer matrix. Conductivity measurements revealed that the inclusion of Al particles with different mass ratios in the polyaniline matrix resulted in a decrease in conductivity compared to pure polyaniline, and these results were likely due to the thin yet highly stable and electrically-resistant protective oxide (Al2O3) film layer that rapidly formed on the aluminum surface in solution with low HCl concentration. Electrochemical characterizations of polyaniline and composites were investigated by galvanostatic charge discharge, cyclic voltammetry, and electrochemical impedance spectroscopy method. The results showed that composites produced with different aluminum content did not have good supercapacitor properties compared to pure polyaniline, due to the rapidly-forming surface oxide film layer which prevented an effective interaction between the polymer matrix and Al particles. Consequently, the composite has not contributed to the increase in capacitance with aluminum loading by redox reactions at the interfaces with functional groups. This confirms that the aluminum incorporated does not interact with the matrix structures of the composites, but is found in composites with a stable and protective passive oxide film layer that rapidly forms on its surface, thus having higher corrosion protection effectiveness.

Long-term stability and electronic properties of passive film of lean-duplex stainless steel reinforcements in chloride containing mortar

The corrosion behavior, semiconducting properties and chemical composition of the passive film formed on lean-duplex stainless steel LDSS 2001, LDSS 2304 and AISI 304 reinforcements embedded in OPC mortar containing chloride, 0, 0.4, 2 and 4 wt% Cl−; after 2.5 years were studied. The Ceff,film of LDSS 2001 remained constant at 3 × 10−5 F/cm2 for all Cl− concentrations. Flat-band potential, EFB,A, of LDSS 2001 increased with the Cl− concentration, suggesting a Cr2O3 film more prone to accept electrons, reducing the vacancy density. The enrichment in chromium in the passive film of LDSS 2001 after 2.5 years increases from 44% to 61%.

Passive film composition and stability of CoCrFeNi and CoCrFeNiAl high entropy alloys in chloride solution

In this work, CoCrFeNi and CoCrFeNiAl high entropy alloys (HEAs) were produced by arc melting. The aim was to investigate the correlation of the electrochemical behavior with microstructural features and chemical compositions of the surfaces during the first hours of immersion in 3.5 wt% NaCl solution at room temperature. Scanning electron microscopy (SEM) analysis and X-ray diffraction (XRD) patterns indicated that the CoCrFeNi alloy was comprised of one single face-centered cubic phase with distinct dendritic and interdendritic regions. The CoCrFeNiAl, in turn, was comprised of B2 and body-centered cubic (BCC) crystalline structures. The BCC phase was associated with dendritic regions while the B2+BCC structure was formed in interdendritic regions. The evolution of the electrochemical behavior was monitored by electrochemical impedance spectroscopy (EIS) up to 24 h of immersion. Al addition decreased the corrosion resistance of the CoCrFeNi alloy, as indicated by the lower charge transfer resistance values. X-ray photoelectron analysis of the passive films revealed that the oxide layer on the CoCrFeNi alloy was enriched with Cr2O3, improving its corrosion resistance. Conversely, the Al2O3-rich passive film formed on the CoCrFeNiAl alloy decreased its corrosion resistance.

Hardness, magnetism and passivation of Fe-Si-B-Nb glasses

Nb is a noble and important element for the Fe based glass manufacture. The mechanical properties, magnetic properties and corrosion behavior of (Fe78Si9B13)100-xNbx (x = 0, 7 and 10) glassy ribbons have been studied by various experimental methods. With the addition of Nb element, the hardness of the Fe-based glasses increases and their coercivity decreases, which is attributed to the ordering tendency of atomic structure by adding Nb atoms. In the potentiodynamic polarization and Mott-Schottky plots, Fe-based glassy ribbons with x = 7 and 10 have a wide passivation platform and an n-type semiconductive surface, while the ribbon with x = 0 does not. By XPS analysis, Nb and B tend to segregate beneath the ribbon surface and form the stable passive film. The Nb addition can improve the hardness, soft magnetism and corrosion resistance of Fe based glasses and will help us to seek for the new type Fe based glasses.

In-Situ Detection of Early Corrosion of Ferritic Cr-Mo Steel in Aqueous Solutions of different Anions using Laser Raman Spectroscopy

We report the early-stage corrosion of modified 9Cr-1Mo ferritic steel in aqueous environments at natural corroding conditions. Uniform, pitting, and crevice corrosion was observed in acidic sulphate, neutral chloride, and fresh water environments, respectively. In-situ laser Raman spectroscopy (LRS) studies revealed the formation of Fe3O4, γ−Fe2O3, γ−FeOOH phases, and stable heterogeneous corrosion products of γ−FeOOH and α−FeOOH in all media, except in an alkaline solution. A stable passive film, composed of oxide and oxy-hydroxides of chromium and iron, is formed in an alkaline solution. X-ray photoelectron spectroscopy (XPS) results confirm the presence of Cr and Fe oxide and oxy-hydroxides in all corrosion products and enrichment of Mn and Nb oxides on the corroded surface in neutral chloride solution, but only Mn oxy-hydroxide in acidic solution. Chloride ion in the corroded surface in neutral chloride solution indicates a chloride-induced corrosion attack. In-situ LRS, together with ex-situ XPS enabled the identification of all corrosion products formed on modified 9Cr-1Mo steel. The presence of laminar γ−FeOOH and acicular α−FeOOH phases are confirmed from the FESEM images. Our results indicate that except in alkaline solution, the corrosive ions deteriorate the integrity of native film on modified 9Cr-1Mo steel.

Corrosion resistance of Cu‐bearing 316L stainless steel tuned by various passivation potentials

Three incremental passivation potentials (0.2, 0.5, and 0.8 VSCE) were selected to passivate the 316L‐Cu stainless steel (SS) and the 316L SS in 0.5 M H2SO4 solution, with the aim to investigate the corrosion resistance differences of two SSs in 0.9 wt.% NaCl solution. Various electrochemical tests including potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), and Mott–Schottky analytical method assisted with X‐ray photoelectron spectroscopy (XPS) were employed. The results indicated that 316L‐Cu SS after passivation in 0.5 M H2SO4 solution showed no influence on the double‐layer structure of passive films. Besides, increased passivation potential augmented the electron donor concentration (ND) and the hole accepter concentration (NA) of the passive film on the 316L‐Cu SS, hinting a gradually declined compactness of the passive film. EIS results further affirmed that the passive film stability of 316L‐Cu SS followed the same tendency with increased passivation potential. XPS results hinted that the oxidation reaction of Cu element switching into Cu2+ and Cu+ ions promoted the dissolution of Cu ions and weakened the passive film stability of 316L‐Cu SS.

Corrosion behavior of 13Cr stainless steel under stress and crevice in high pressure CO2/O2 environment

In this work, through the self-developed setup for in situ electrochemical tests, the corrosion behavior of 13Cr stainless steel under the combined effect of stress and crevice in high pressure CO2/O2 environment was investigated. The results show that 13Cr stainless steel presents a self-passivation state. Under the action of stress, the anodic dissolution process of steel inside crevice is expedited. There is a galvanic effect between the stressed steel inside crevice and the unstressed steel outside crevice. The applied stress reduces the induction stage of crevice corrosion and induces a larger galvanic current, i.e., the applied stress promotes the development of crevice corrosion. Meanwhile, adding 0.1 MPa O2 is conducive to forming a more stable passive film but causes a greater galvanic effect.

Effects of Ti addition on microstructure and the associated corrosion behavior of a 22Cr‐5Ni duplex stainless steel

AbstractThe effects of Ti addition on microstructure and the associated electrochemical properties of 22Cr‐5Ni duplex stainless steel were evaluated using X‐ray diffraction, X‐ray electron probe microanalysis, electron backscattered diffraction, scanning Kelvin probe force microscopy, scanning electron microscopy–energy‐dispersive X‐ray spectroscopy, electrochemical techniques, and X‐ray photoelectron spectroscopy. The results indicated that the addition of a minor amount of Ti refined the grains, improved the pitting potential, and lowered passive current densities remarkably. However, excessive content could cause an imbalance of phase proportion of ferrite and austenite phases and precipitation of the coarse TiN particles. The films on the base and Ti‐containing alloy have a similar chemical composition, but the addition of Ti enriched the chromium in the passive film. In particular, the ratio of Cr2O3 and Mo6+ increased, which helped to form a comparatively homogeneous and stable passive film on the duplex stainless steel.

A non-equiatomic FeNiCoCr high-entropy alloy with excellent anti-corrosion performance and strength-ductility synergy

The mechanical behavior and corrosion resistance of a newly developed non-equiatomic Fe40Ni20Co20Cr20 (at.%) high-entropy alloy (HEA) were investigated. Excellent strength-ductility synergy with fracture elongation of more than 70 % was found to be mediated by dislocation activities and nano-twinning. The alloy shows significantly improved corrosion resistance compared to the equiatomic FeMnNiCoCr HEA upon immersion testing, and higher electrochemical corrosion resistance than the 316L stainless steel in 0.1 M H2SO4 solution. Apart from a high content of Cr3+ in the passive film, the interaction between Co and other elements potentially leads to the formation of Co(Fe,Cr)2O4 and enhances the passive film stability.

Cu-Zr-Ti-Al metallic glass: Thermodynamic prediction, synthesis, and biocorrosion studies

In this study, glass forming composition (GFC) in Cu-Zr-Ti-Al system was predicted using thermodynamic guidelines involved model. The GFC was predicted by optimizing the enthalpy of chemical mixing and mismatch entropy in a statistically designed configurational entropy range. As designed composition Cu46Zr40Ti8.5Al5.5, close to eutectic point, was synthesized into metallic glass by melt spun technique. The amorphous nature of metallic glass was verified using XRD, DSC and TEM. The material was subjected to corrosion studies in simulated body fluids (SBF) at 37 °C using electrochemical polarization technique. The material has exhibited better corrosion resistance in comparison to conventional biomaterials. Enhanced corrosion resistance is attributed to amorphous nature of the material and stable passive film predominately containing ZrO2, Al2O3 and AlOOH. Further, it was observed that the substitution of Cu with Al and Zr in Cu-Zr-Ti metallic glass enhances the corrosion resistance in SBF.

Investigating the Corrosion Behavior of Corrosion-Resistant Alloys in Solutions Containing Dilute Fluoride Ions

The ability of fluoride ions, in trace concentrations, to promote film instability and transpassive dissolution was shown for several corrosion-resistant alloys. While the addition of fluoride ion was found to decrease the transpassive dissolution potential by approximately 0.1 V, the decrease was particularly pronounced in mildly acidic media (pH 5). Results suggest that the decreased potential range of stability for the heavily-relied-upon Cr(III)-rich oxide film is a concern in the presence of oxidizing impurities, which may push the corrosion potentials toward the transpassive region. The decreased potential range of passive film stability was observed using both dynamic and static polarization experiments and was supported by solution and surface analyses.

Effects of Laser-Powder Bed Fusion Process Parameters on the Microstructure and Corrosion Properties of AlSi10Mg Alloy

In this study, the effects of microstructural modifications induced by tuning the laser-powder bed fusion (L-PBD) process parameters on electrochemical stability of the L-PBF-AlSi10Mg alloy are investigated. Three groups of L-PBF-AlSi10Mg samples were fabricated utilizing combinations of L-PBF process parameters for their Upskin layers. The implemented process parameters modifications were found to be not only effective in reducing the as-printed surface roughness of the components, but also led to the formation of cyclic small-large melt pools (MPs) in Upskin layers of the fabricated samples. Such consecutive modification in the size of MPs led to the increased inhomogeneity of the microstructure, contributing to the formation of a coarser intercellular eutectic-Si network, larger grain size, and lower density of low angle grain boundaries. Among all fabricated samples, the sample that experienced the fastest cooling during solidification was found to reveal the highest corrosion resistance and the best passive film stability on its Upskin surface both in naturally-aerated and deaerated 3.5 wt.% NaCl electrolyte, owing to the finer Al-Si eutectic structure that forms along its large MP-boundaries. The as-printed microstructure of the L-PBF-AlSi10Mg was found a dominant factor in determining the necessity of applying post-printing surface polishing procedures to attain better corrosion properties.

Study on corrosion behavior and mechanism of CoCrFeMnNi HEA interfered by AC current in simulated alkaline soil environment

The corrosion behavior and mechanism of CoCrFeMnNi HEA interfered by AC current was investigated in carbonate/bicarbonate solution. AC application can destroy the structure of passive film, generate a change in the content of constitutes, and decrease the stability and protective ability of passive film, especially at higher i AC . With increasing i AC , the corrosion form of HEA is evolved from pitting corrosion occurred at low i AC to intergranular corrosion generated at high i AC . At the interference of 200 A/m 2 , more H atoms are distributed at grain boundaries and interior of grains, resulting in the occurrence of severe corrosion. Moreover, the selective dissolution of Co/Mn occurs in the interior of corroded grains of HEA sample. However, selective dissolution of Fe, Co and Cr is occurred at pits and grain boundaries. • AC corrosion behavior of CoCrFeMnNi HEA was investigated in CO 3 2− /HCO 3 − solution. • AC application damaged the structure of passive film, and changed its composition. • An increased i AC reduced the stability and protective ability of passive film. • Corrosion form of the HEA was evolved from pitting corrosion to intergranular corrosion. • Selective dissolution of Fe, Co and Cr was occurred at pit and grain boundary.

A comprehensive investigation of the electrochemical behavior of nickel-aluminum bronze alloy in alkaline solution: The effect of film formation potential

Nickel- aluminium bronze (NAB) is one of the well-known copper-based alloys; it is a well-recognized material in the marine environment thanks to its good corrosion and wear resistance along with its high strength. In this paper, the effect of film-forming potential on the electrochemical behavior of NAB alloy in 0.1 M Na2SO4 solution was evaluated. The study of the stability of passive films formed on NAB alloy was investigated using potentiodynamic and potentiostatic polarizations, Mott–Schottky (MS) and electrochemical impedance spectroscopy (EIS) analysis. The compositions of the passive films were determined by scanning electron microscope (SEM), UV–vis–NIR spectroscopy, and X-ray diffraction (XRD). All electrochemical tests revealed that the anodic potentials had a strong influence on passive films formed on NAB alloy. At intermediate frequencies above 450 mVSCE, the corrosion process is controlled by the adsorption/desorption process along with charge transfer and diffusion processes. Mott–Schottky analysis indicated that the donor density is in the range of 1021 cm−3 and increased with an increase in the film-forming potential. Moreover, the SEM analysis showed that the NAB alloy suffered a severe corrosion attack of the copper-rich α phase leading to the retention of the κ phases of the as-cast NAB in the passive films. The passive films were grown on the NAB alloy and displayed n-type semi-conductor behavior, which is entirely predictable from the main Cu and Al oxide in the film.

Corrosion protection of NiNb metallic glass coatings for 316SS by magnetron sputtering

Metallic glasses (MGs) appear as promising anti-corrosion coating materials due to their microstructural and physicochemical advantages. Herein, we proposed magnetron sputtered NiNb thin film MG coatings (MGCs) with different structures and compositions for corrosion protection of 316 stainless steel in an aggressive saline environment. The properties of monolayered Ni50Nb50 and Ni60Nb40, as well as the multilayered Ni50Nb50/Ni60Nb40 (at.%) MGCs, were characterized in terms of morphology and microstructural properties, as well as the anticorrosion behavior. All the NiNb MGCs presented compact structure and the monolayered coatings exhibited preferable adhesion properties in comparison with the multilayered coating. The electrochemical tests and XPS results imply that the monolayered Ni50Nb50 MGC with high Nb content resisted corrosion mainly due to the formation of stable passive film that contained abundant Nb2O5 species, whereas the Ni60Nb40 MGC with high Ni content showed week corrosion protection performance during long-term service due to the dissolution of Ni cations and the devastation of the coating structure. Though with bit worse adhesion and more vulnerable Ni60Nb40 layers, the multilayered Ni50Nb50/Ni60Nb40 MGC possessed comparable corrosion resistance with the monolayered Ni50Nb50 MG coating, which remained stable even after 32 days of exposure. Such performance should be ascribed to the combined eff ;ect of the repassivation property for the sub-layers, the hindrance of propagation paths of micro-defects, and the obstruction of corrosive species by interfaces in the multilayered coating.