Dense Oxide Film Research Articles

A novel Co–Cr–Fe–Ni–Mo–Si MPEA-based Laves phase alloy with high strength and high-temperature wear-resistance

In this work, a novel Co–Cr–Fe–Ni–Mo–Si multi-principal element alloy (MPEA)-based Laves phase alloy (T-MPEA) is designed and fabricated. The microstructure, mechanical properties and dry sliding wear properties of the new alloy are investigated, and compared to those of T-800 (Co-based) and T-700 (Ni-based) Tribaloy alloys. Hard intermetallic Laves phases disperse in face-centered-cubic solid solution in T-MPEA, and the Mo- and Si-rich Laves phase reaches a fraction of ∼60%. The compressive strength of T-MPEA reaches 1912 MPa, which is higher than that of T-700 and close to that of T-800. T-MPEA exhibits a mean hardness of 624 HV0.3, and maintains a high hardness above 500 HV0.3 even at 800 °C. Owing to its high strength and hardness, T-MPEA exhibits higher wear-resistance, compared to that of T-700 in all dry sliding wear tests, from room temperature to 600 °C. Owing to the high resistance to softening and dense oxide film formation at high temperatures, T-MPEA exhibits excellent high-temperature wear-resistance.

Microstructure and Corrosion Property of Prepared CoCrW Coatings on the TC4 Surface by Laser Cladding

Ti6Al4V (TC4) is widely used in aerospace, marine equipment, and the petrochemical industry. However, the dense oxide film on the surface of this alloy will be destroyed in reducing acid solution, resulting in surface corrosion in practical application. To enhance the corrosion resistance of TC4 in marine environments, this study employed laser cladding technology to deposit a CoCrW cladding layer on the TC4 alloy surface. Experimental results validated the successful preparation of a dense, crack-free CoCrW layer. The microstructure of the CoCrW layer was characterized by predominant bulk grains and minor equiaxed crystal constituents, demonstrating a robust metallurgical bond to the matrix. Notably, the corrosion resistance of the TC4 surface witnessed a marked improvement, evident from the CoCrW coating’s increased open circuit potential, elevated electrochemical impedance spectroscopy (EIS) radius, phase angle, and impedance modulus values. The corrosion rates of both the TC4 and CoCrW cladding layers escalated with extended immersion time and increased immersion corrosion temperature. However, the CoCrW cladding layer reported minimal mass loss and the least corrosion rate. In summary, the CoCrW coating, when prepared via laser cladding on the TC4 surface, markedly bolstered corrosion resistance.

MICROSTRUCTURE AND PROPERTIES OF LASER CLADDED TiNiCoCrVSi HIGH ENTROPY ALLOY COATING

A TiNiCoCrVSi high entropy alloy (HEA) coating was prepared on Ti–6Al–4V alloy by laser cladding. Then, the microstructure, phase composition, hardness, wear resistance and high-temperature oxidation resistance of the prepared coatings were investigated. The wear behavior of the TiNiCoCrVSi coating against a Si3N4 ball was evaluated under dry sliding conditions. The high-temperature oxidation resistance was tested at 800∘C. The results show that the phase structure of the TiNiCoCrVSi coating was mainly composed of a body-centered cubic (BCC) (Ni,Co)Ti2 and (Ti,V)5Si3. The TiNiCoCrVSi coating has a high hardness, and the highest surface hardness was 1357 HV. The wear volume of the coating was 1/7 of that of Ti–6Al–4V. The wear mechanism was abrasive wear and oxidative wear. The TiNiCoCrVSi coating exhibited good high-temperature oxidation resistance at 800∘C. A dense oxide film (TiO2, Cr2O3 and NiCr2O4) was formed on the surface of the coating. The dense oxide film prevented oxidation. The high-temperature oxidation resistance of the coating was 1/12 of that of the substrate.

Enhancing the wear and high-temperature oxidation behavior of NiCrBSi coatings by collaboratively adding WC and Cr3C2

A composite coating was deposited by collaborative modification with tungsten carbide (WC) and Cr3C2 ceramic particles to improve the wear resistance of NiCrBSi coating over a wide temperature range. The original NiCrBSi coating and the composite coatings with WC and Cr3C2 collaboratively (NiCrBSi +20 wt% WC–Cr3C2–Ni) and exclusively (NiCrBSi +20 wt% WC and NiCrBSi +20 wt% Cr3C2–NiCr) added were designed and deposited by plasma spraying. The microhardness of the composite coatings added with the ceramic phase was higher than that of the NiCrBSi coating. The composite coating with the addition of WC showed the maximum microhardness (896.8 HV). The wear mechanism of the four coatings at room temperature was dominated by fatigue spalling, whereas oxidative and abrasive wear prevailed at 700 °C. The composite coating (NiCrBSi +20 wt% WC–Cr3C2–Ni) showed excellent abrasion resistance at room temperature and 700 °C. The wear volume of the composite coating (NiCrBSi +20 wt% WC–Cr3C2–Ni) decreased by 83.5 % and 46.9 % at room temperature and 700 °C, respectively, compared with the wear volume of the NiCrBSi coating. In general, high WC hardness was favorable for improving the microhardness of the coating. The preferential oxidation of Cr3C2 instead of WC promoted the formation of a dense oxide film on the surface of the coating and reduced oxidation within the coating. This study revealed the mechanism of the collaborative enhancement of NiCrBSi coatings by WC and Cr3C2 and the improved wear resistance of the NiCrBSi coatings at room and high temperatures.

The research on the high strength and anti-arc ablation coatings applied in steel conductive rail

In order to enhance the ablation-resistant performance of stainless-steel conductive rails, Mo coating, 410 stainless steel coating and 15 wt% Cr2AlC particles reinforced 410 stainless steel composite coating were prepared and evaluated. Different from the weak interfacial strength caused by the dissimilar metals between Mo and steel rails, 410 stainless steel coating has better interfacial contact with steel rails. The introduction of Cr2AlC into 410 stainless steels further strengthened the mechanical properties of coating by alloy strengthening effect and particle strengthening effect, as the decomposition of Cr2AlC into nano CrC particles is accompanied with the diffusion of Al atoms into 410 stainless steels. It was found that the composite coating can still resist arc erosion at 150 A current, as a dense oxide film formed during the ablation process and the decomposition of Cr2AlC contributed to the heat absorption.

Hot corrosion behavior of a novel TiC/GTD222 nickel-based composite prepared by selective laser melting

In this study, a novel TiC/GTD222 nickel-based composite with enhanced hot corrosion resistance was designed by incorporating appropriate amounts of C, Al, and Ti elements into the GTD222 superalloy. The composite was successfully prepared using the selective laser melting (SLM) technique. The hot corrosion behavior of GTD222 superalloy and the TiC/GTD222 composite in a salt mixture of 75% Na2SO4 + 25% NaCl (wt%) at 900 °C was systematically studied. The results show that the TiC/GTD222 composite exhibits much better hot corrosion resistance than the GTD222 superalloy. This is because a continuous and dense double-layer oxide film is formed in the composite (The inner layer is TiO2 and the outer layer is Cr2O3), while oxide film of the superalloy is loose and porous, and has a discontinuous TiO2 and Al2O3 distribution. The adding alloy elements can promote the formation of more γ' phase and TiC particles in the TiC/GTD222 composite, and also result in the refined grain and formation of more dislocations. The above microstructures increase the diffusion channels of elements, and the higher contents of Al and Ti can enhance the diffusion potential energy of these elements, leading to the formation of continuous and dense double-layer oxide film of the composite. This work provides new ideas for the design of additive manufactured superalloy.

Effect of oxide layer on the electrochemical corrosion behavior of a Ni-based superalloy in 3.5 wt% NaCl

The recycle technology of superalloy is a research hotspot and difficulty in the filed of superalloy. Recovery of superalloy bulk material is a major focus. Purification smelting after surface impurity removal is an application trend of superalloy regeneration technology. During the use and processing of superalloy, the surface will form a dense oxide layer. The oxide layer of superalloy scrap is difficult to remove by traditional mechanical method. However, the oxide layer on the superalloy surface can be efficiently removed by electrochemical dissolution. Based on the background above, we investigated the electrochemical corrosion behavior of GH4738 superalloy which oxidized for different time in 3.5 wt% NaCl. The effect of oxide layer on the electrochemical corrosion behavior of GH4738 was studied by potentiodynamic polarization and electrochemical impendence spectroscopy(EIS). The morphology and phase composition of the alloy were analyzed by scanning electron microscope (SEM), electron probe X-ray Micro-Analyzer (EPMA) and X-ray diffraction (XRD). The results indicated that the dense oxide film not only has a protective effect on the oxidation corrosion of the alloy, but also has a protective effect on the electrochemical corrosion of the alloy. The oxide layer impedes the electrochemical dissolution of the alloy.

High-temperature oxidation behavior of Inconel 693 alloy at 900 °C–1200 °C

Inconel 693 alloy is a potential nuclear waste vitrification electrode material. The resistance to oxidation at high temperatures can affect the service life of the vitrification process equipment. The high-temperature oxidation behavior of Inconel 693 alloy has been investigated at temperatures of 900 °C, 1050 °C, and 1200 °C. The results show that the kinetic curves obeyed the parabolic-rate law at different oxidation temperatures without abnormal turning points. The oxide film showed a multilayer structure and the oxidation products were similar at different temperatures. Differently, a new product of AlN was generated at 1050 °C and 1200 °C compared with that at 900 °C. At 900 °C, the surface of the alloy was covered with relatively dense and complete oxide films. As the temperature increased, the oxide films were flaked seriously. The oxidation provided effective oxidation protection after 50 h at 1200 °C. In addition, part of the internal oxidation products Al2O3 acted as an effect of pegging Cr2O3 films.

Improving corrosion resistance of Mg–Li alloys by Sn microalloying

It is well known that the corrosion resistance of ultra-light Mg–Li alloys is inferior to traditional Mg alloys due to the rapid oxidation of reactive Li on the surface. In this study, microalloying Sn has been found to improve the corrosion resistance of Mg–Li alloys due to the formation of Mg2Sn on the corrosion pits and reduction of electro-potential difference. Indeed, the addition of Sn not only reduced the corrosion rate to the minimum value of 4.27 mmpy but also promote the formation of dense corrosion oxide films. The volt potential difference between the matrix (α-Mg and β-Li) and Al-X (Gd, Y, Mn) phases has also been measured to reduce from 260 mV (α-Mg) and 343 mV (β-Li) to 220 mV (α-Mg) and 220 mV (β-Li). After homogenization, pitting was significantly reduced, as shown by the in-situ observation of the corrosion process using X-ray tomography. By quantifying the secondary phases, it has been found that the corrosion expansion was restricted by the Mg2Sn and Al-X phases. The corrosion products are primarily MgO, SnO, and Li2O oxides and the corrosion mechanism follows three stages: I. Breakthrough of MgO protective layer by corrosive fluid; II. Hydrogen evolution reaction (HER) between matrix phase and water immersion; III. Segregation of secondary phases and corrosion products. It has been found that all three processes are highly dependent on the Sn solutes and Mg2Sn precipitates, showing the bright future development of corrosion-resistant Mg–Li alloys by Sn microalloying.

Surface polishing and modification of Ti-6Al-4V alloy by shear thickening polishing

In this study, a comparison of three newly developed polishing techniques namely, shear thickening polishing (STP), Chemistry enhanced STP (C-STP) and Electrolysis enhanced STP (E-STP) was made to investigate their suitability to Ti-6Al-4V biomaterials polishing and modification, which can produce Beilby layer after polishing and enhance mechanical and biological performance. The surface roughness Sa after STP was about 13.8 nm with a material removal rate of 54.3 nm/min. The C-STP showed the lowest surface roughness of 7.2 nm which was almost half that of STP and the MRR during C-STP was almost 2.1 times that of the conventional STP. The STP did not lead to any change of the surface composition, whereas a 136 nm thick Beilby layer was observed to form during the C-STP which revealed a lower friction coefficient of 0.04 as well as improved osteoblast cell activity. The E-STP showed an intermittent improvement as it provided a surface roughness of 10.2 nm and 1.6 times MRR than that obtained from conventional STP. Due to the dense oxide film of about 60 nm, the E-STP processed surface showed the best wettability and corrosion resistance. Overall, we reveal an important pathway for achieving scalable finishing on Ti-6Al-4V with desirable surface characteristics.

Hydrolytic Hydrogen Production from Severely Plastic Deformed Aluminum-Based Materials: An Overview

The development of hydrogen energy will help to reduce the use of nonrenewable energy sources and achieve global carbon neutrality. The aluminum-water reaction is an important method of producing hydrogen because aluminum has abundant reserves, a high yield, and no pollution. However, the dense passive oxide film on the surface of aluminum, on the other hand, often obstructs this reaction, which is the primary issue limiting the development of aluminum-based hydrolytic materials. Mechanochemical activation by processing severely plastic deformed aluminum-based materials is one effective approach and has been developed in recent years. This article reviews recent progress of hydrogen production from hydrolysis of severely plastic deformed aluminum-based materials. The kinetic model of aluminum-water reaction, aging protection of the materials, catalytic mechanism and stable rate control for the hydrolysis of aluminum-based materials are reviewed. Furthermore, some existing problems as well as some suggestions for future research on hydrogen production from aluminum-based materials are also discussed.

Alkali assisted water treatment of aluminum promoting the growth of hydrated oxide film for energy conservation

Aluminum anodizing process consumes a lot of energy for ions migration in solid phase. Commonly, the aluminum foil is treated by boiling water to form crystalline γ'-Al2O3 for reducing the energy consumption. In order to improve water treatment, the alkaline buffer solution was used for promoting the growth of hydrated oxide film and contributed to formation of crystalline alumina. As a result, the obtained samples consumed 12.08% less energy during anodizing process compared with that of water treated samples. The hydrated oxide film was detected by means of morphological and electrochemical analysis, which indicated the alkaline treatment promoted generation of hydrated oxide film as well as formed dense anodic oxide film after anodizing. Furthermore, the pretreated samples owned denser anodic oxide film verified by X-ray diffraction and electrochemical analysis, which implied less production of alumina on the same electrical performance. Therefore, the alkaline solution treatment of aluminum/hydrated oxide film has a good prospect for getting rid of the limitation of high energy consumption in electrolytic capacitors industry.

Film-forming investigation of NbC-modified HfC coating based on oxyacetylene ablation and argon-atmosphere heating above 2000 °C

Ablation test of NbC-modified HfC coatings using an oxyacetylene flame and heat treatment of HfO2–Nb2O5 plates up to 2100 °C were performed. The results indicate that HfC-30 mol% NbC coating forms a dense oxide film comprising HfO2 columnar crystals, achieving the best ablation property. At 2100 °C in an argon atmosphere, the solubility of niobium suboxide in HfO2 is in the range 27–30 mol%, and the stable phases are HfO2, Nb, and NbO. NbO liquids improve the transport of Hf and produce gradients of temperature and oxygen concentration, promoting the formation of a composite film under an oxyacetylene flame.

Effect of carbides on the electrochemical dissolution behavior of solid-solution strengthened cobalt-based superalloy Haynes 188 in NaNO3 solution

The electrochemical dissolution behavior of cobalt-based superalloy Haynes 188 was observed by an in-situ observation device. The results showed that at low current density, a dense oxide film was formed on the carbide surface to protect its dissolution. But at high current density, carbide dissolved and produced CO bubbles until falling off. The dissolution of carbide at high current density resulted in the reduction of the high ten-point mean roughness (Rz) and the improvement of surface quality. A dissolution model under different current densities was established to reveal the mechanism of influence of carbide on surface quality under different current densities.

Effects of tartaric acid on the structure and corrosion resistance for anodizing films of aerospace aluminium alloys

ABSTRACT Anodising films are obtained by anodising 2099 aluminium-lithium alloys in tartaric acid-sulphuric acid solutions with different concentrations. The microscopic surface morphology of the anodic-oxide film is observed by field emission scanning electron microscope (FG-SEM), and the corrosion resistance of the film was investigated by open-circuit potential, electrochemical experiments and neutral salt spray experiments. The results show that the aluminium-lithium alloy can form a uniform and dense anodic oxide film in different concentrations of tartaric acid-sulphuric acid solution. Tartaric acid does not change the film formation mechanism of the anodic oxide film, but reduced the dissolution rate of the oxide film, so that the growth rate and thickness of the oxide film increased first and then decreased with the increase of the tartaric acid concentration in the experimental study. This result generally indicates that the addition of tartaric acid can also significantly improve the corrosion resistance of the anodic-oxide film, and the more detailed features are discussed.

Oxidation Property of a Fourth-Generation Powder Metallurgy FGH4108 Nickel-Based Superalloy

Isothermal oxidation kinetics of a fourth-generation powder metallurgy FGH4108 nickel-based superalloy is investigated at 800 °C to 1100 °C by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDS). At 800 °C and 900 °C, the oxidation kinetic curves of the FGH4108 superalloy follow parabolic law. At 1000 °C, the oxidation kinetic curve follows cubic law. At 1100 °C, the oxidation kinetic curve has two distinct parts: the first part follows a parabolic law, and the second one obeys a linear law. Cross-sectional morphologies and elemental distributions show that the oxide film consists of two parts at 800 °C: the outer layer is a continuous dense protective Cr2O3 oxide film, and the inner layer is a discontinuous Al2O3 oxide layer. At 900–1100 °C, the oxides consist of three layers: the outermost is the oxides of Cr2O3 and TiO2, the middle is a continuous oxide of Al2O3, and the innermost is dotted oxides of TiO2. The thickness of the inner TiO2 oxide layer increases with the increase of oxidation temperature. On this basis, the oxidation behavior of the FGH4108 superalloy at high temperatures is confirmed to be controlled by the diffusion of Cr, Al, Ti, and O. From the aspect of oxidation resistance, the long-term service temperature of the FGH4108 superalloy should not exceed 1000 °C.

Study on exothermic effect of surface modified porous aluminum

Aluminum powder is widely used in the field of energy materials due to its high energy density. However, the combustion of aluminum powder is limited by the dense oxide film on the surface. In this study, surface modified porous aluminum (TFA@Al) was prepared by a simple chemical method. The morphology and structure of the TFA@Al surface were characterized by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The thermal oxidation and thermal nitridation processes of TFA@Al were analyzed by thermal analyzer (TG-DSC). The results show that the etched holes on the surface of TFA@Al can effectively promote the oxidation of aluminum and improve the exothermic effect of aluminum. The coupling reaction mechanism between Al core and oxygen at the etched holes is proposed. The explosion heat and combustion of thermite composed of TFA@Al and CuO (TFA@Al/CuO) and thermite composed of Al and CuO (Al/CuO) were also studied. The results show that TFA@Al/CuO has higher explosion heat value and emission spectral intensity than Al/CuO. Surface modified porous aluminum is expected to be used in the field of aluminum-containing energy materials.

Effect of laser remelting on high-temperature oxidation resistance of AlCoCrFeNi high-entropy alloy coating

To reveal the effect of laser remelting on the high-temperature oxidation resistance of high-entropy alloy (HEA) coating, an AlCoCrFeNi HEA coating was prepared on AISI 1045 steel by plasma spraying technology and then remelted by laser remelting process. The microstructure of the coatings before and after remelting was characterized, and oxidation experiment was carried out at 900 °C for 100 h. The results showed that, after laser remelting, the porosity of AlCoCrFeNi HEA coating decreased from 4.8 % to 0.3 %. Moreover, the phase compositions of the coating after remelting were the same as that before remelting, which were still dominated by a single BCC solid solution structure. After oxidation, the oxidation weight gain of the remelted coating was slightly greater than that of the as-sprayed coating. Nevertheless, uniform and dense multilayer oxide films were formed on the remelted coating surface, leading to the lower oxygen content in the remelted coating and at the interface of remelted coating/substrate. Therefore, laser remelting can effectively improve the ability of AlCoCrFeNi HEA coating to hinder oxygen at high temperature and prevent the substrate from oxidation.

The tribocorrosion resistance of TiN+TiB /TC4 composite coatings and the synergistic strengthening effects of multi-level reinforcements

The Ti-based composite coating of TiN + TiB /TC4 is successfully fabricated by laser cladding. The results show that the addition of BN promotes the in-situ formation of an elliptic TiN phase at the micron level and fibrous TiB phase at the nanometer level, forming a new structure of the hard TiN surrounded and pinned by coherent TiB. No obvious plastic deformation occurs with the increase of TiN and TiB phases, and the dense TiO2-MoO3 oxide film forms during tribocorrosion. The tribocorrosion rate is much reduced and drops to the lowest rate of 246.93 ± 14 µm/yr.

Coronary Au@Bi Nanospheres for Highly Impedance‐Sensitive Immunosensing toward CEA

AbstractNovel coronary Au@Bi nanospheres (NSs) are simply synthesized by sparkling gold nanoparticles (Au NPs) on the surface of bismuth (Bi) NSs and successfully used as highly impedance‐sensitive immunosensing platform to develop a new label‐free electrochemical immunosensor for the detection of carcinoembryonic antigen (CEA). Firstly, Bi NSs are prepared by one‐pot hydrothermal method, showing uniform sphere morphology with a dense oxide film formed outside Bi NSs due to the easy oxidation of Bi in the air. The oxide film significantly hinders the transmission of electrons and effectively improves the sensitivity of the proposed electrochemical impedance immunosensor. The surface functionalization of Bi NSs with Au NPs enhances the biocompatibility, stability, as well as active surface area of the produced Au@Bi NSs, preferable for the efficient loading of antibody molecules. The electrochemical impedance spectroscopy (EIS) is selected as the optical technique to measure CEA with the constructed immunosensor based on Au@Bi NSs. Because of the excellent impedance‐responsive performance, this new immunosensor displays highly sensitive detection toward CEA in a linear range of 50 fg mL−1–100 ng mL−1 with an extremely low detection limit of 9.83 fg mL−1 and could be potentially used in early clinical detection of cancer.