Formation Of Passive Film Research Articles

Corrosion resistance of additively manufactured aluminium alloys for marine applications

Additive manufacturing opens new possibilities for designing light-weight structures using aluminium alloys. The microstructure of two Al alloys and their corrosion resistance in NaCl and natural seawater environments were investigated. The newly designed Al-Mn-Cr-Zr based alloy showed a higher corrosion resistance than reference AlSi10Mg alloy in both environments in as printed and heat-treated conditions. The corrosion initiated in the Al matrix along the precipitates in the alloys where the Volta potential difference was found the highest. The coarser microstructure and precipitate composition of the new Al-alloy led to the formation of a resistant passive film which extended the passivity region of the Al-Mn-Cr-Zr alloy compared to the AlSi10Mg alloy. The effect of heat treatment could be seen in the microstructure as more precipitates were found in between the melt pool boundaries, which affected the corrosion initiation and slightly the pitting resistance. Overall, this study shows that a newly designed Al-alloy for additive manufacturing has a suitable corrosion resistance for applications in marine environments.

The Effects of Cl− and Selected Deoxidizers on the High-Temperature Corrosion Electrochemistry of Alloy 690 in Nuclear Steam Generator Water

The heat transfer tube in a steam generator serves as a critical heat exchange component in the primary and secondary loops of pressurized water reactor (PWR) nuclear power plants. The corrosion resistance of the heat transfer tube material directly influences the longevity of PWR nuclear power plants. This study investigated the electrochemical corrosion properties of 690 alloy (UNS N06690) in a simulated secondary water environment of PWR, focusing on different chloride ion concentrations and combinations of deoxidizers. The findings reveal a gradual decrease in the corrosion potential of 690 alloy, accompanied by an increase in self-corrosion current and a progressive reduction in the passivation range, ultimately leading to its disappearance as chloride ion concentration rises from 0 µg/L to 500 µg/L. Moreover, the impedance value of the inner film exhibits a declining trend with an increase in chloride ion concentration. Conversely, the resistance value of the outer film remains relatively stable while the size and spacing of oxide particles on the surface of the 690 alloy continuously increase. This observation suggests that chloride ions primarily influence the formation of the inner passivation film, which in turn determines the corrosion resistance of the 690 alloy. Notably, the performance of the 690 alloy is similar when the deoxidizer combination is ammonia (NH3) + erythorbic acid (ERA) or NH3 + hydrazine (N2H4), demonstrating the ability to form a relatively complete passivation film and exhibit improved corrosion resistance compared to NH3+N-isopropyl hydroxylamine, additionally, when the deoxidizer combination is NH3+N2H4, the 690 alloy exhibits lower self-corrosion current density across different chloride ion concentrations, indicating enhanced corrosion resistance.

Enhanced corrosion protection of rebars in alkaline solutions by ferroporphyrin and the mechanisms of electron consumption and lattice reconstruction

Abstract Reinforced concretes are the primary materials in coastal and offshore engineering. In alkaline environment of concrete, the anodic process is passivation of rebars and the conjugated cathodic process is oxygen reduction reaction (ORR). It is proposed that a novel approach to enhance the passivation films through catalyzed ORR by iron meso-tetra(4-carboxyphenyl)porphine (FeTCPP). The ORR catalyst FeTCPP promotes the formation of passivation film, as it accelerates the consumption of abundant electrons generated and accumulated by the anodic formation of passivation films. The passivation films of rebars are highly defective Fe3O4 semiconductor. The dissolution of interstitial ferrous ions and lattice iron ions produces defects of O ion vacancies, Fe ion vacancies and interstitial Fe ions, and they further cause the formation and accumulation of Fe atom vacancies on the metal surface, leading to the collapse of the passivation films. The FeTCPP adsorbs on the surface of passivation films, hindering the dissolution of lattice iron ions and interstitial ferrous ions, thereby inhibiting the generation and accumulation of Fe atom vacancies and improving the integrity and protective ability of the passivation films.

Towards direct superlubricity and negligible wear with polyalcohol lubricant mixtures of ethylene glycol and glycerol for steel tribopairs

Friction and wear remain as the main concerns in the mechanical mobility systems due to the significant energy consumption and the main mode of component failures, and achieving direct superlubricity has attracted enormous attention by fundamentally minimizing friction and wear. In this work, we have prepared polyalcohol lubricant mixtures of ethylene glycol and glycerol to precisely enhance the in-situ formation of passivation film on the friction surfaces, and remarkable direct superlubricity of 0.0057 combined with negligible wear has been successfully achieved at ethylene glycol/glycerol weight ratio of 0.6 for steel tribopairs. Lubrication state analysis indicates that the achieved superlubricity state is in the boundary lubrication regime, and further adsorption analysis indicates that there is a strong interaction between lubricant molecules and friction surfaces via the hydroxyl groups. A sliding simulation of polyalcohol lubricant mixtures of ethylene glycol and glycerol indicates that ethylene glycol could be induced to accumulate near the friction surfaces to form easy-to-shear layers. Furthermore, both the experimental analysis and the molecular dynamics simulation demonstrate that a tribochemical reaction could be induced for the lubricant molecules at the interface, with water molecules formed to further strengthen the formation of easy-to-shear layers and oligomers formed to more effectively passivate the asperity contacts. This work provides a new strategy to direct liquid superlubricity and could advance the application of liquid superlubricity in the industry field.

Study on mechanism underlying the acceleration of pitting corrosion of B30 copper–nickel alloy by sulfate-reducing bacteria in seawater

In this paper, the relationship between the pitting corrosion formation of B30 copper–nickel (CuNi) alloy and the metabolism of sulfate-reducing bacteria (SRB) was investigated. Combined with the influence of temperature during the actual operation of the cooling systems, the evolution law of the alloy passivation film was analyzed, and the mechanism of SRB promoting the accelerated development of B30 CuNi alloy pitting corrosion was revealed. The results show that SRB significantly promoted the pitting formation and development of B30 CuNi alloy. The maximum pitting depth was 3.9 μm in the sterile system and 15.3 μm with SRB, which was 3.9 times higher than that of sterile system. The loose porous Cu2S film formed by SRB metabolites and copper matrix was easily penetrated by corrosive anions, which promoted copper dissolution and led to pit nucleation. The sulfide adsorbed on the surface prevented or delayed the passivation of B30 CuNi alloy by blocking the adsorption site of O atom, and the corrosion nuclei continued to grow. The non-uniformity caused by the film peeling accelerated the longitudinal development of pitting corrosion, and the expansion and coalescence of adjacent pits caused the transverse development of pitting corrosion. Temperature had a certain influence on the SRB and the formation of B30 CuNi alloy passivation film. The passivation film was formed rapidly at 50 °C with poor quality and the passivation property of Cu2O film was weakened. With the increase of temperature, the pitting potential of sterile system negative shifted from 0.447 to 0.360 V (vs. SCE), while SRB system from 0.340 to 0.198 V (vs. SCE), and the pitting resistance decreased. The passivation film with defects and the Cu2S reduced the barrier efficiency of the film and accelerated the pitting corrosion of B30 CuNi alloy.

Comparing Electrochemical Passivation and Surface Film Chemistry of 654SMO Stainless Steel and C276 Alloy in Simulated Flue Gas Desulfurization Condensates.

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.

The effect of B and Sb on the corrosion behavior of T6-treated Al–Si–Mg alloys

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

Cryogenic etching of positively tapered silicon pillars with controllable profiles

Fabrication of high aspect ratio silicon nanopillars is challenging for various applications. A cryogenic silicon etching process using SF6 and O2 plasma is investigated to create silicon nanopillars with 10 μm height and tens of nanometers apex. In the process, fluorine radicals react with silicon atoms, releasing volatile SiFx byproducts and then oxygen atoms interact with SiFx and deposit a SiOxFy film acting as an inhibitor. By adjusting the O2 concentration and the forward radio frequency power, this process modifies the formation of the SiOxFy passivation film and adjusts the bombardment of ions onto the inhibitor, resulting in the desired positive taper angles of silicon pillars. Two etching steps, with higher and lower O2 concentrations, are consecutively combined to create a sharp apex and a wide base. The results demonstrate the high etching rate and controllability of cryogenic etching to obtain high aspect ratio silicon pillars with desired profiles.

Electrochemical oscillation behaviors of gold during its recovery from waste printed circuit boards through slurry electrolysis

Slurry electrolysis is an effective technology for recovering gold from waste printed circuit boards (WPCBs). However, electrochemical oscillation during the gold recovery process is a potential factor affecting power consumption. As a result, the potential oscillation behaviors of gold dissolution at a constant current were studied. These results showed that the periodic formation and dissolution of the Au-OH passive film on the anode induced electrochemical oscillation. The amplitude and frequency of electrochemical oscillation were affected by hydrochloric acid concentration, current intensity, electrode spacing, and sodium chloride concentration, among which the concentration of sodium chloride had a significant inhibitory effect. Under the following conditions: hydrochloric acid concentration of 8 mol/L, current of 0.03 A, and electrode spacing of 1.5 cm, the obtained maximum amplitude potential and frequency were 1.17 V and 0.56 Hz, respectively. The phase space reconstruction results showed that the systems evolved between the near-linear equilibrium region and the periodic oscillation region. Different factors induced two oscillation modes: top-down and bottom-up. The top-down and bottom-up oscillations induced by current intensity, hydrochloric acid concentration, and electrode spacing reduced the relative power consumption by 11.8, 17.2, and 11.8 %, respectively, and increased the relative power consumption by 14.3, 21.2, and 30.1 %, respectively. A critical value was obtained, which varied oscillation patterns and gained a region of lower power consumption. The addition of trisodium citrate and PVP can improve gold recovery rate and current efficiency by regulating process of electrochemical oscillation. This work will provide theoretical support for recovering valuable metals from WPCBs with reduced energy consumption by controlling the external conditions to switch the oscillation mode.

Effect of carbon nanotube content and annealing temperature on corrosion performance of carbon nanotube/Ni composite layer

Adding carbon nanotubes (CNTs) to metal composites changes their corrosion resistance, which is significantly affected by the distribution of CNTs. In this study, the effect of the content and distribution of CNTs on the corrosion resistance of composites was investigated by changing the electrodeposition process. The results indicated that could inhibit grain growth and act as an elemental channel for passivation film formation, which positively enhanced the corrosion resistance of the material. However, the annealing used to improve the bonding strength of CNTs to the matrix increased the grain size of the material, which had a weakening effect on the corrosion resistance. Using ultrasonic in electrodeposition had an obvious promoting effect on the uniform distribution of CNTs. The composites with 0.1 g/l CNT showed the best corrosion resistance after annealing for 30 min at 600 °C.

Synergistic Enhancement of Strength, Ductility, and Corrosion Resistance of Ti6Al4V Alloy Through Low Cu Doping and Hot Extrusion

A Cu-containing Ti6Al4V alloy is considered an ideal biomedical material due to its excellent antibacterial properties. However, the addition of Cu leads to a mismatch in strength, ductility, and corrosion resistance, which hinders their further application. To address this issue, the study utilized low Cu doping and hot extrusion to optimize the material’s properties. The results showed that the primary lamellar structures were transformed into equiaxed grains, with an average grain size reduced from 10 μm to 300 nm. The nanoequiaxed grains had a homogeneous elemental composition and a stronger base texture, with orientations aligned with the extrusion direction. As a result, synergistic strengthening in terms of strength, ductility, and corrosion resistance was achieved. The film resistance increased from 127 kΩ·cm2 to 325 kΩ·cm2, the ultimate tensile strength (UTS) increased from 1,030 MPa to 1,330 MPa, and the elongation increased from 7% to 21%. These improvements were attributed to the nanostructure and basal texture, which facilitated the formation of a thicker passive film and reduced pitting corrosion, thereby enhancing corrosion resistance. Additionally, the nanoequiaxed grains could provide grain boundary strengthening and texture strengthening on UTS and ensure uniform deformation for elongation.

Formation and long-time exposure aging of oxides on Ni-Cr and Ni-Cr-X (X = Mo, W) alloys in acidic chloride solutions: Ramifications towards corrosion resistance

The passivation of Ni-22Cr, Ni-22Cr-6Mo, and Ni-22Cr-6Mo-3W (wt%) was characterized from 100 s to 10 days in 0.1 M NaCl in pH 4 at various potentials in the passive range. The influence of aqueous solution exposure time in NaCl (exposure aging), passivation potential, as well as Ni-Cr-X alloy composition (Mo or W) on passive film growth, composition, oxidation state, molecular identity, and inner versus outer film layering were investigated. Initial passive film formation was dominated by Ni(II). Cr(III) oxides and hydroxides tended to enrich upon formation and exposure aging. Corundum and rock salt are speculated to undergo a solid-state phase transformation to form NiCr2O4 at long times under certain conditions. The concept of the time-potential-transformation diagrams to describe the evolution of passive film phases and protectiveness is introduced. Factors limiting Cr(III) enrichment were discussed. Aliovalent Mo and W ions were detected in passive films, particularly after aging. The roles of Cr enrichment, Ni depletion, and Mo and/or W aliovalent cations after oxide aging towards protectiveness to passive and localized corrosion in chloride (Cl-) solutions were discussed.

Corrosion behavior of metallic coatings on titanium bipolar plates of proton exchange membrane water electrolysis

The corrosion resistance, conductivity, and cost of the metallic bipolar plates are the main limitations for the Proton Exchange Membrane Water Electrolysis (PEMWE) commercialization. In the present study, Ta, Nb, and Ti non-precious metallic coatings were deposited by closed-field unbalanced magnetron sputtering to increase the corrosion resistance and conductivity of titanium bipolar plates in PEMWE, respectively. The coating samples suffer from corrosion in a simulated extreme anode operating environment of PEMWE (0.5 M H2SO4 + 5 ppm HF, 80 °C, O2). The surface of the Ti coating forms the micropores due to the high dissolution rate in initial formation stage of the passivation film, resulting in a higher current density (1.41 × 10−6 A cm−2). The hydrolysis reaction of Ta coating causes the adsorption of sulfide ions, thereby affecting the density of the passivation film. Despite the Ta coating exhibiting a favorable current density (4.82 × 10−7 A cm−2), ICR (463.11 mΩ cm2) is lamentably poor. The surface of Nb coating has been completely covered by Nb2O5 and NbO2 in the simulated PEMWE environment. The reoxidation process of NbO2 promotes the rate of passivation film formation and provides excellent conductivity. Therefore, Nb coating exhibits the lowest current density and interfacial contact resistance of 2.23 × 10−8 A cm−2 and 119.78 mΩ cm2, respectively, which is very low compared to the bare titanium bipolar plates.

Structural and property regulation of double ceramic phase–reinforced AlCoCrFeNiTiZr–based high entropy alloy coatings by pulsed–wave lasers

In-situ synthesis ZrC and TiC reinforced AlCoCrFeNiTiZr–based high entropy alloy (HEA) coatings were successfully synthesized on R60702 using pulsed–laser cladding. The effects of pulse frequency (5, 50, 500, and 5000 Hz) on microstructure evolution, microhardness, wear resistance, and corrosion resistance were investigated. The results demonstrate that the HEA coatings consists of phases including BCC, HCP, and metal carbides (MC). The phase composition and proportion are influenced by changes in pulse frequency. At pulse frequencies of 5 and 50 Hz, the predominant MC phase is ZrC. As the pulse frequency increases, it transitions to a coexistence of ZrC + TiC before ultimately becoming predominantly TiC. Concurrently, the size of the ceramic phase and the proportion of the HCP phase initially decrease, then increase. A pulse frequency of 500 Hz yields optimizations in microhardness, wear resistance, and corrosion resistance. The favorable mechanical properties are attributed to the synergistic effect of solid solution strengthening, fine crystal strengthening, and ceramic phase strengthening. The optimal corrosion resistance is due to the formation of a stable passivation film while local corrosion and galvanic corrosion are weakened.

Key role of gradient-nanostructure and extremely thin amorphous passive film on tribocorrosion behavior of a novel Cr+N alloyed high-Mn austenitic steel

High manganese steel is influenced by the combined effects of corrosion and wear during service under specific conditions, resulting in components with shortened service life. Under harsh service environments, newly developed Cr+N alloyed austenitic high manganese steel (Mn18Cr7C0.6N0.2 steel) as a new type of railway steel has shown promising results. Herein, the tribocorrosion behaviors of Mn18Cr7C0.6N0.2 and Mn13C1.1 steels in artificial acid rain were studied using electrochemical methods, field emission scanning electron microscope (FE-SEM), focused ion beam scanning electron microscopy (FIB-SEM), scanning transmission electron microscopemicroscopy energy dispersive X-ray spectroscopy (STEM-EDS), and high resolution transmission electron microscopy (HR-TEM). The results showed the formation of passive film and gradient-nanostructure on surfaces of both test steels during tribocorrosion. A dense and tightly adhering amorphous passive film was formed on Mn18Cr7C0.6N0.2 steel surface with a superior blocking effect toward invasive ions. The high strain resistance and plasticity of the Mn18Cr7C0.6N0.2 steel resulted in an intact gradient-nanostructure, suitable for obtaining high surface hardness and maintaining the toughness of the matrix, contribute to providing high wear resistance. The oxide film on the Mn13C1.1 steel surface comprised crystal α-FeOOH. Vortex cracks formed in its gradient structure due to strain localization. Meanwhile, the relatively poor corrosion protection ability and vortex cracks of its gradient-nanostructure prevented it from maintaining interface integrity of the gradient nanostructure, resulting in inferior tribocorrosion resistance. In artificial acid rain, the new type of Cr+N alloyed Mn18Cr7C0.6N0.2 steel exhibited higher tribocorrosion resistance than traditional high manganese steel, promising for use as an excellent wear-resistant material under corrosive environments.

Function of Cu-Sb or Al microalloying on the corrosion resistance of 9Cr steel exposed to simulated concrete pore solution

The role of Cu-Sb or Al on the passivation and Cl-induced depassivation of 9Cr steel in simulated concrete pore solution was systematically obtained via electrochemical tests and microstructure characterization. Both microalloying enhanced electrochemical passivation even if the solution pH dropped. Cu and Al participated in the formation of natural passive film, and the properties of passive film were optimized in terms of resistance, composition, and inner film thickness. However, the chloride threshold level (CTL) was not increased with Cu-Sb microalloying and even decreased with Al microalloying, which is understood from the stability of Al-containing products and the hazards of inclusions.

Voltage-controlled finger friction behavior for immersive tactile experience in aqueous environment

To mimicking fingers perceiving the physical world, researchers developed tactile devices to establish a correlation between real and virtual world. This study proposed a new finger friction modulation method based on voltage-controlled technique in aqueous environment. Under continuous or alternate voltages applied to TC4 plate, the effects of NaCl, KCl and CaCl2 on finger friction were characterized with different concentrations. The finger friction was reversibly modulated by the voltages with the maximum friction variation of 110%. This modulation is attributed to the adsorption of OH-, bubbles effect and formation of passive film which affected the boundary lubrication performance of finger-TC4 interface. This study provides a new surface haptics concept for the underwater human-computer interaction or immersive virtual reality haptic technology.

Incorporation of NH4+ in flower-like zinc phosphate pigment to enhance the corrosion resistance of waterborne epoxy

Herein, the three-dimensional (3D) flower-like pigments of micro-nano scaled zinc phosphate (FZP) and ammonium zinc phosphate (FNZP) were successfully synthesized by hydrothermal synthesis method for improving the corrosion resistance of waterborne epoxy (WEP) coating. The micro-structures, chemical compositions and corrosion resistance of the as-obtained specimens were characterized by SEM, XRD, FT-IR, XPS and EIS, respectively. The results indicated that the 3D flower-like FZP and FNZP pigments were comprised of self-assembled nano-micro sheets with an average thickness of 20 nm ∼ 100 nm. Moreover, the remarkable enhancements of compactness and anticorrosion performance, especially for the FNZP-incorporated coating, were principally contributed to the well dispersibility and favourable solubility, which lengthened the permeation pathway and promoted the formation of passivation film.

Mechanical properties and corrosion resistance of laser cladding iron-based coatings with two types of NbC reinforcement

In this work, iron-based alloy coating without NbC (No-NbC), directly added NbC (A-NbC) and in-situ synthesized NbC (I-NbC) reinforced composite coatings were fabricated on the SS304 substrate surface to compare the strengthening effects of two types of NbC introduction mechanisms on the iron-based alloy. All as-clad coatings presented a complete and dense structure, and compared to A-NbC composite coating, I-NbC composite coating achieved a fine dispersion distribution of the reinforcement. Unlike A-NbC coating with α-Fe and NbC, it was revealed that α-Fe, γ-Fe, NbC and Cr23C6 existed in I-NbC composite coating, and the possibility of in-situ synthesized NbC has been confirmed through thermodynamic theory. Additionally, the introduction of NbC notably refined the grain size of iron-based alloy systems and restrained the generation of high angle grain boundaries (HAGBs). Compared to substrate and No-NbC coating, A-NbC and I-NbC composite coating achieved the higher average microhardness value of 524.6 ± 12 HV and 534.9 ± 4 HV, respectively, mainly relying on the precipitation of NbC in the coating. Meanwhile, the results in the dry sliding friction test found that due to the dispersion and uniformity of in situ synthesized reinforcements, I-NbC composite coating presented a satisfactory wear resistance with the lowest specific wear rate of 6.55 × 10−6 mm3/N m and the minimum friction coefficient of 0.627. NbC particles were considered to be detrimental to the corrosion resistance of coatings in electrochemical corrosion tests due to galvanic corrosion between them and the matrix. However, I-NbC composite coating provided a favorable condition for the formation of passivation film by introducing Cr and Nb atoms, with the minimum Icorr of only 7.55 × 10−8 A cm−2, which was much less than that of other as-clad coatings.

Enhanced corrosion resistance and mechanical properties of CrAlON coatings under alternating hydrostatic pressure

CrAlN coatings and CrAlON coatings with varying oxygen content were prepared on the surface of TC4 using multi-arc ion plating. Oxygen introduction resulted in the formation of a (CrAl)(ON) solid solution, leading to finer coating grains and enhanced corrosion resistance. Following a 240-hour immersion in an alternating hydrostatic pressure (AHP) environment, the coatings retained strong adhesion to the substrate. Moreover, they displayed varied improvements in surface hardness and corrosion resistance. The CrAlN coating's improved performance is due to the formation of a surface passivation film, while the high‑oxygen CrAlON coating's enhancement is primarily attributed to filling surface defects with corrosion products under static water pressure.