Compact Oxide Film Research Articles

Oxidation Behavior of Pre-Strained Polycrystalline Ni3Al-Based Superalloy.

The harsh service environment of aeroengine hot-end components requires superalloys possessing excellent antioxidant properties. This study investigated the effect of pre-strain on the oxidation behavior of polycrystalline Ni3Al-based superalloys. The growth behaviors of oxidation products were analyzed by scanning electron microscope, transmission electron microscope, X-ray Photoelectron Spectroscopy and Raman spectroscopy. The results indicated that the 5% pre-strained alloys exhibited lower mass gain, shallower oxidation depth and more compact oxide film structures compared to the original alloy. This is mainly attributed to the formation of rapid diffusion paths for Al atoms diffusing to the surface under 5% pre-strain, which promotes the faster formation of protective Al2O3 film while continuing to increase the pre-strain to 25% results in less protective transient oxidation behavior being aggravated due to the increase in dislocation density within the alloy, which prevents the timely formation of the protective Al2O3 film, resulting in uneven oxidation behavior on the alloy.

The enhanced high-temperature oxidation resistance of additively manufactured GH4169 by adding small amounts of 304L

Enhancing the high-temperature oxidation resistance of nickel-based alloys is critical for expanding their industrial applications. Herein, we report a novel strategy for enhancing the high-temperature oxidation resistance of the GH4169 nickel-based alloy by adding small amounts of 304L stainless steel using selective laser melting technology. The oxidation property of GH4169 with various 304L additions (2 wt.%, 4 wt.%, and 6 wt.%) at 900 °C for 45 h was investigated. Results show that the addition of 304L significantly improves the oxidation resistance of GH4169. The thickness of the oxide film and the intergranular oxidation depth of GH4169 with 6 wt.% 304L added are reduced by 61% and 69%, respectively. The addition of 304L increases Cr and decreases Ni in the matrix, which facilitates the formation of a more compact oxide film. The Nb in Laves phase will be increased with 304L addition, which effectively inhibits oxygen penetration and metallic element diffusion.

Tribocorrosion and Mechanical Properties of Nanotubes Grown on Ti–35Nb Alloy by Anodization

Abstract In this study, we evaluated the tribocorrosion and mechanical properties of nanotubes grown on a Ti–35Nb alloy. The nanotube arrays, approximately 2.0 µm thick, were formed through controlled anodization and annealing, composed of Ti and Nb oxides. The compact oxide film at the nanotube/substrate interface provided corrosion resistance, lubricating properties in worn tracks, and improved wear resistance. The nanotubes exhibited a lower coefficient of friction, hardness, and elastic modulus compared to untreated Ti–35Nb. The crystalline structure of the nanotubes and the oxide interface layer enhanced adhesion, preventing plastic deformation and improving tribocorrosion resistance.

Corrosion behavior and oxide layer of selective-laser-melted Al-Mg-Sc-Zr alloy in marine atmospheric environment with different Cl−concentration

In this study, the corrosion response of the Al-Mg-Sc-Zr alloy produced by selective laser-melting in marine atmospheric environments with different Cl− concentrations was studied by electrochemical and immersion. Microstructural observations showed the microstructural of Al-Mg- Sc -Zr alloy featured a double grain microstructure, making up a coarse and fine grain area. TEM showed that some white precipitates enriched with Zr and Sc were dispersed in the samples. The potentiodynamic polarization test indicated increasing the Cl− concentration led to a negative shift of corrosion potential and narrowed the potential range of the passive zone, which also caused the increase of corrosion current density value. The electrochemical impedance spectroscopy showed that higher Cl− concentration was greatly detrimental to generating a compact and dense oxide film on the Al-Mg-Sc-Zr alloys, as indicated by decreasing the resistance of the corrosion product layer and charge transfer resistance. The immersion test demonstrated that the samples suffered serious pit corrosion when the Cl− content increased to 1.5 and 3.5 wt%, showing a larger size and more depth of corrosion pits. This study is expected to provide data to determine the reliability of the SLM-manufactured Al-Mg-Sc-Zr alloy in marine atmospheric conditions.

Tailoring the corrosion behavior and mechanism of Mg-Gd-Zn alloys via Sc microalloying

The Sc microalloying can decrease the corrosion rates of Mg-Gd-Zn alloys by about two orders of magnitude, and thus significantly improving corrosion resistance of Mg-Gd-Zn alloys. Notably, the Sc microalloying can inhibit the precipitation of (Mg, Zn)3Gd phase with high potential while promote the precipitation of 14H-LPSO phase with low potential under the premise of reducing the total amount of second phases. Thus, the micro-galvanic corrosion effect can be effectively weakened. Additionally, the Sc microalloying can lead to the grain refinement, which can act as barriers to corrosion propagation and promote the nucleation and growth of oxides. Also, the activity of Gd, Zn and Sc in α-Mg phase can be increased with the Sc microalloying, which facilitates the formation of related continuous and compact oxide films. The continuous and compact films can effectively protect the alloy matrix from corrosion. Furthermore, the stacking faults distributed in different grains with different orientations in Sc-contained alloys can lead to a more uniform corrosion. The synergistic effects resulted by Sc microalloying contribute to the significantly improved corrosion resistance of Mg-Gd-Zn alloys.

Interfacial microstructures and corrosion behavior of tungsten heavy alloy/superalloy dissimilar joints: design, regulation and mechanism

The interfacial microstructures and corrosion behavior of tungsten heavy alloy/superalloy dissimilar joints brazed with various Cu–Ti based multicomponent amorphous alloys were investigated by time-varying chemical bath immersion tests and electrochemical measurements. The longitudinal analysis of corrosion behavior differences in different regions of dissimilar joints was conducted, and the horizontal analysis of the influence of compositional variation in filler materials on corrosion behavior was investigated. Importantly, the brazed joint with CuTiNiZrV filler material (CT3 joint) exhibited the noblest Ecorr (−0.911 VSCE) and the highest charge transfer resistance (1610.5 Ω cm2). From the compositional and microstructural effects on the corrosion resistance, the enhancing anti-corrosion performance was mainly attributed to the tailoring of the microstructures and corrosion potential of the brazing seam, and the formation of protective compact oxide film (Fe2O3-NiO-CoO-VO).

Improved corrosion inhibition of calcium disodium EDTA for mild steel in chloride-contaminated concrete pore solution

The corrosion inhibition of EDTA-Ca for mild steel in chloride-contaminated concrete pore solution, with EDTA-Na as comparison, was investigated via several electrochemical methods and surface characterizations. Results show that corrosion inhibition efficiency of EDTA-Ca is higher than that of EDTA-Na. Corrosion inhibition efficiency increased with an increase in EDTA-Ca concentration while decreased with the increased EDTA-Na concentration. EDTA-Ca adsorbs physiochemically on surface of mild steel which obeys Langmuir isotherm, while adsorption of EDTA-Na is physical obeying Freundluich isotherm. A much thinner and more compact oxide film with higher Fe2+ content formed in the presence of EDTA-Ca compared to EDTA-Na. The availability of coordinate bonds for chelation in EDTA-Ca or EDTA-Na plays a critical role in determining the corrosion inhibition efficiency.

Unusually high corrosion resistance in Mo CrNiCo medium entropy alloy enhanced by acidity in aqueous solution

• A series of ultra-corrosion-resistant medium entropy alloys were developed. • The corrosion resistance of our alloys unusually increases with acidity in Cl − containing solutions. • The unique anti-corrosion behaviour results from the formation of a protective and compact medium entropy oxide film, which can be attributed to the synergic effect of the chemical complexity on absorption of H 2 O and O 2 . High corrosion resistance of alloys is essential for their structural applications; however, most alloys suffer from degradation of their corrosion resistance with the increasing acidity of their surroundings. Nonetheless, we developed a series of medium-entropy alloys (MEAs) in this work, which exhibit high strength, superior fracture toughness and ultra-high corrosion resistance, outperforming the variety of corrosion resistant alloys hitherto reported. Most interestingly, our MEAs exhibit an unusual anti-corrosion behavior and their corrosion resistance increases with acidity in Cl − containing solutions. Through extensive thermodynamic calculations, density functional theory (DFT) simulations and experiments, we reveal that the unusual anti-corrosion behavior of our MEAs can be attributed to their surface chemical complexity, which facilitates the physio-chemical-absorption of H 2 O and O 2 and thus the rapid formation of metastable medium entropy passive films that contain the lowest amount of defects, as compared to the passive films on conventional alloys reported in the literature.

A study of the growth mechanism of large-diameter double-wall TiO2 nanotube arrays fabricated by high voltage anodization.

Research on the growth mechanism of titanium dioxide (TiO2) nanotube arrays fabricated by anodic oxidation is essential to achieve artificial control of the microstructure and to expand their applications. In our previous work, we reported the preparation of highly ordered large-diameter double-wall TiO2 nanotube arrays prepared by high voltage anodization. In this paper, we observed and analyzed the initial growth process of large-diameter double-wall TiO2 nanotube arrays anodized at 120 V in ethylene glycol electrolyte containing aluminum fluoride (NH4F) and water (H2O), such as the evolution of surface and cross-sectional morphologies, the influence of current density on growth rate, the transition process from nanoholes to nanotubes, and the evolution of dimples on the remaining substrate. On the basis of our observations and inspirations from the existing viewpoints, we established growth models of large-diameter double-wall TiO2 nanotube arrays corresponding to different growth stages to explain the growth process. The growth rate of anodic oxide film changes accordingly with the current density. The compact anodic oxide film formed initially actually contains outer layer and inner layer, with no obvious interface between them. Then, the bottom even levels of the inner layer and outer layer bulge towards the substrate and become individual hemisphere-like structures. The inner layer becomes the outer wall, and the outer layer becomes inner wall. Eventually, V-shaped large-diameter and double-wall TiO2 nanotube arrays form. The results presented in this work are significant and provide a better understanding of the growth mechanism of large-diameter double-wall TiO2 nanotube arrays anodized by high voltage.

Modification of the Ni-NiO-oxidant system by thermo-chemical oxidation with accelerated growth of the p-type dielectric oxide layer, by the action of substituted V2O5 on the system

Nickel is covered with very thin oxide film and is stable against corrosion under normal conditions. Nickel, as Ni-NiO-oxidant system, can make much thicker (even a thousand times) and more corrosion unstable oxides. With certain new oxidation process parameters, nickel can undergo so-called accelerated oxidation. The subject and goal of this work is to find the most favorable conditions for performing of accelerated - catastrophic Ni oxidation process, when substitution of V2O5 is carried out into NiO (2V (Ni)), with significant electron concentration increase and oxygen surplus. Unlimited main and secondary charge carriers transfer is significantly facilitated if oxide film with non-stoichiometric composition and defects is formed. The aim is to avoid compact oxide film formation by chemical-thermal treatments and to obtain porous and defective NiO. By using oxidized system Ni - NiO - oxidant in glass, ceramics and evaporated metal technology, extraordinary usable value of this work is ensured.

Characterisation of AlCrCuFeMo x high entropy alloys for nuclear fuel cladding

High entropy alloys (HEAs) have great potential used for accident-tolerant fuel (ATF) due to their excellent properties. The ATF properties of AlCrCuFeMo x HEAs were systematically investigated. The AlCrCuFeMo x had the typical dendrite morphology and Cu and Al elements segregated in the interdendrite region. After 1200°C water vapour oxidation, compact and continuous α-Al2O3 oxide film formed on the surface and effectively protected the inner from further oxidation. When x = 1, the HEA had the best oxidation resistance (59 mg/dm2 weight gain after 1 h), two orders lower than that of the traditional Zr-1Nb alloy for nuclear fuel cladding. Under normal operation water condition, the performance of the present HEAs is not as good as Zr-1Nb due to the segregation of Cu and dispersed Al2O3 formed on the surface.

Tailoring the microstructure and enhancing the corrosion resistance of extruded dilute Mg-0.6Al-0.5Mn-0.25Ca alloy by adding trace Ce

The effect of trace Ce addition on the microstructure evolution and corrosion behavior of dilute Mg-0.6Al-0.5Mn-0.25Ca-xCe (x = 0.1–0.3 wt%) alloys were investigated using immersion tests and electrochemical measurements. The Ce addition caused the formation of Al8Mn4Ce and Al11Ce3, which were less noble than Al8Mn5. Strikingly, the alloy containing 0.3 wt% Ce exhibited the lowest average corrosion rate of 4.13 mm y−1, which was 6.5 times lower than that of Ce-free alloy. The outstanding anti-corrosion properties were attributed to the low potential difference between Ce-containing phases and matrix, the compact composite oxide film (MgO-CeO2-Al2O3), and the enrichment of Fe in Ce-containing phases.

Corrosion behaviors and mechanism of CrFeNi2 based high-entropy alloys

Herein, a novel CrFeNi2-based multi-component alloy system was designed and the corrosion behaviors were investigated in 3.5 wt% NaCl solution. The single-phase FCC solid solution was observed in CrFeNi2 and CoCrFeNi2 alloys, while the lamellar eutectic structure composed of dual-phase formed in the AlCoCrFeNi2 alloy. The electrochemical results showed that the CrFeNi2-based alloys, with higher Epit and lower Icorr, displayed better corrosion resistance, outperforming previously reported conventional alloys and some other high entropy alloys, due to the compact and stable oxide films composing of protective oxide/hydroxide. In the CrFeNi2-based alloy system, all examined specimens were suffered localized corrosion. The Co-free CrFeNi2 alloy possessed the best corrosion resistance, demonstrating the widest passivation region (approximately 1035 mVAg/AgCl), the highest pitting potential (954 mVAg/AgCl), and an outstanding repassivation ability. In addition, the corrosion mechanism was investigated and discussed. This research will sight light on the comprehending of corrosion behaviors through different phases and the effect of element on corrosion resistance.

Effect of Nb on the surface composition of FeCrAl alloys after anodic polarization

XPS combined with AFM have been used to investigate the surface modifications of nuclear grade FeCrAl-xNb (x= 0, 0.5, 1.0, 1.5 wt.%) alloys, induced by anodic polarization in a simulated primary coolant. Electrochemical tests were performed to study the role of the minor element Nb on the corrosion potential and composition. The optimal content of Nb, obtained after the comparative analysis of the UHV-sputtered surface, native oxide-covered surface and anodic polarized surface, is 0.5 wt.%. This alloy presents a more compact Al-enriched oxide film consistent with a higher corrosion potential at −89 mV. The protectiveness of oxide film against the active dissolution can be improved by Nb addition, but does not increases linearly with Nb content. High resolution XPS analysis details the changes of Nb oxidized states, and provides the stratification of the oxide film containing the (hydr) oxides of Fe, Al and Cr.

Effect of Ce addition on the high‐temperature oxidation resistance of Mg–Gd alloys

AbstractIn the present study, the oxidation resistance of magnesium alloyed with Gd and Ce was investigated. The high‐temperature oxidation resistance of Mg–3.5Gd–xCe (x = 0, 0.2, 0.4, 0.7 and 1.0 wt%) alloys was evaluated at temperatures between 550°C and 650°C. Results indicate that adding less than 0.7 wt% Ce resulted in high oxidation resistance, whereas the Ce addition exceeding 0.7 wt% deteriorated the oxidation resistance. The high oxidation resistance phenomenon is attributed to the formation of compact oxide films primarily composed of MgO, Gd2O3, and a small amount of CeO2 on the surface of Mg–3.5Gd–0.2Ce and Mg–3.5Gd–0.4Ce alloys. These compact oxide films can prevent the matrix from experiencing further oxidation. The deteriorated oxidation resistances of Mg–3.5Gd–0.7Ce and Mg–3.5Gd–1Ce alloys were found to be due to the severe internal oxidation caused by the distributed Mg12Ce phases along the grain boundaries.

Tuning microstructure and improving the corrosion resistance of Ti-6Al-3Nb-2Zr-1Mo alloy using the electron beam freeform fabrication

Herein, the microstructure and corrosion behavior of Ti-6Al-3Nb-2Zr-1Mo alloy manufactured by the electron beam freeform fabrication (EBF3) have been thoroughly investigated. The evident prior-β grain boundary, the inside of which is composed of predominant α-lath and slight β-phase, is achieved. The EBF3-manufactured alloy displays a significantly improved corrosion resistance compared to the wrought alloy, especially the XY-plane. The X-ray photoelectron spectroscopy results reveal the formation of a more stable oxide film for the EBF3-manufactured alloy due to a higher fraction of phase boundaries induced by the fine α-laths; besides, the heterogeneous distribution of compositions between α- and β-phases can be effectively alleviated, resulting in the absence of the strong galvanic corrosion, which has been illustrated combined experiments and ab-initio calculations. The electrochemical analyses indicate that all samples exposed to the artificial seawater exhibit a typical spontaneous passive behavior, deriving from the presence of a compact oxide film, while a active–passive transition behavior is observed in 5 M HCl, stemming from the formation of a non-protective porous oxide film, which is well interpreted using the mixed potential theory. In addition, the oxygen reduction reaction, determined by diffusion and charge-transfer processes, is the predominant cathodic reaction in the artificial seawater, whereas, in 5 M HCl, the cathodic reaction is primarily associated with the hydrogen evolution reaction controlled by the discharge step.

Corrosion resistance of Mg-Al-Zn magnesium alloy concrete formwork in Portland cement paste

Corrosion resistance of Mg-Al-Zn magnesium alloy (AZ41) embedded in PC paste was investigated with 6061 aluminium alloy (AA6061) as s control. Electrochemical methods were adopted to assess the corrosion resistance of AZ41 and AA6061 and surface characterizations were carried out to obtain the morphology and composition of oxide films formed. Results show that the corrosion resistance of AZ41 is obviously higher than that of AA6061 in PC paste due to the formation of a much more compact and thinner oxide film on AZ41. The oxide films on AZ41 and AA6061 are both n-type semiconductors. The oxide film formed on AZ41 mainly consists of uniform Mg(OH)2 layer and Mg(OH)2 + Ca2SiO5 particles on AZ41 substrate as well as manganese oxide on Al-Mn second phase, while the oxide film formed on AA6061 is mainly composed of AlOOH, Ca2Al2O4 and Ca2SiO5.

Effect of Chromium on Microstructure and Oxidation Wear Behavior of High-Boron High-Speed Steel at Elevated Temperatures.

In order to investigate the effect of Cr content on the microstructures and oxidation wear properties of high-boron high-speed steel (HBHSS), so as to explore oxidation wear resistant materials (e.g., hot rollers), a scanning electron microscope, an X-ray diffractometer, an electron probe X-ray microanalysis and an oxidation wear test at elevated temperatures were employed to investigate worn surfaces and worn layers. The results showed that the addition of Cr resulted in the transformation of martensite into ferrite and pearlite, while the size of the grid morphology of borides in HBHSSs was refined. After oxidation wear, oxide scales were formed and the high-temperature oxidation wear resistance of HBHSSs was gradually improved with increased additions of Cr. Meanwhile, an interaction between temperature and load in HBHSSs during oxidation wear occurred, and the temperature had more influence on the oxidation wear properties of HBHSSs. SEM observations indicated that a uniform and compact oxide film of HBHSSs in the worn surface at elevated temperatures was generated on the worn surface, and the addition of Cr also reduced the thickness of oxides and inhibited the spallation of worn layers, which was attributed to improvements in microhardness and oxidation resistance of the matrix in HBHSSs. A synergistic effect of temperature and load in HBHSSs with various Cr additions may dominate the oxidation wear process and the formation and spallation of oxide films.

The Applications of Ultra-Thin Nanofilm for Aerospace Advanced Manufacturing Technology.

With the development of industrial civilization, advanced manufacturing technology has attracted widespread concern, including in the aerospace industry. In this paper, we report the applications of ultra-thin atomic layer deposition nanofilm in the advanced aerospace manufacturing industry, including aluminum anti-oxidation and secondary electron suppression, which are critical in high-power and miniaturization development. The compact and uniform aluminum oxide film, which is formed by thermal atomic layer deposition (ALD), can prevent the deep surface oxidation of aluminum during storage, avoiding the waste of material and energy in repetitive production. The total secondary electron yield of the C/TiN component nanofilm, deposited through plasma-enhanced atomic layer deposition, decreases 25% compared with an uncoated surface. The suppression of secondary electron emission is of great importance in solving the multipactor for high-power microwave components in space. Moreover, the controllable, ultra-thin uniform composite nanofilm can be deposited directly on the complex surface of devices without any transfer process, which is critical for many different applications. The ALD nanofilm shows potential for promoting system performance and resource consumption in the advanced aerospace manufacturing industry.

Effect of Iron Content on Corrosion Properties of Pure Titanium as Grain Refiner.

Microstructures and corrosion properties of pure titanium were characterized when iron was used as a grain refiner. The added Fe element acted as a strong grain refiner for pure titanium by forming β Ti phase at grain boundaries, and 0.15 wt% Fe was revealed to be a sufficient amount to make the grain size of pure titanium below 20 μm, which was the requirement for the desired titanium cathode. However, corrosion resistance was decreased with the Fe amount added. From the open circuit potential (OCP) results, it was obvious that the TiO2 stability against the reducing acid environment was deteriorated with the Fe amount, which seemed to be the main reason for the decreased corrosion resistance. Electrochemical impedance spectroscopy (EIS) results showed that both the decrease in the compact oxide film’s resistance (Rb) and the appearance of the outer porous film occurred as a result of the dissolution of the TiO2 layer, whose phenomena became more apparent as more Fe was added.