Oxide Coatings Research Articles

Effects of current density on the corrosion resistance of micro-arc oxidation coatings on Ti6Al4V welded joints

Effects of current density on the corrosion resistance of micro-arc oxidation coatings on Ti6Al4V welded joints

The Influence of the Plasma Electrolytic Oxidation Parameters of the Mg-AZ31B Alloy on the Micromechanical and Sclerometric Properties of Oxide Coatings

This manuscript presents the influence of manufacturing process parameters (peak current density, frequency, process time) on the micromechanical and sclerometric properties of oxide coatings. These parameters were selected based on Hartley’s experimental design, considering three variables at three levels. The coatings were produced on the AZ31B magnesium alloy using the plasma electrolytic oxidation (PEO) method. A trapezoidal voltage waveform and an alkaline, two-component electrolyte were used during the process. The micromechanical and sclerometric properties were assessed by measuring the hardness (HIT) and Young’s modulus (EIT) and determining three critical loads: Lc1 (the critical load at which the first coating damage occurred—Hertz tensile cracks within the scratch), Lc2 (the critical load causing the first cohesive damage to the coating), and Lc3 (the load at which the coating was completely destroyed). Scratch tests were supplemented with profilographometric measurements, which were used to generate isometric images. To identify the relationship between micromechanical and sclerometric properties and the manufacturing parameters, statistical analysis was performed. Research has demonstrated that the plasma electrolytic oxidation (PEO) process improves the micromechanical and adhesive properties of oxide coatings on the AZ31B magnesium alloy. The key process parameters, including peak current density, frequency, and duration, are crucial in determining these enhanced properties.

The Effect of In Situ Laser-Assisted Plasma Spraying on the Plasma Etching Resistance of Yttrium Oxide Coating

In recent years, yttrium oxide coatings prepared by atmospheric plasma spraying (APS) have been employed extensively in semiconductor processing equipment. Meanwhile, defects in yttrium oxide coating, such as unmelted particles and pores, reduce the etching resistance of the coating. In this work, two yttrium oxide coatings were prepared by in situ laser-assisted plasma spraying (LAPS) coupled with a 500 W and 600 W laser for comparison with a coating prepared by APS, and the effects of the laser on the coating properties were investigated. The results show that the surface roughness was reduced by 25.7% (500 W) and 25.3% (600 W) and the porosity was reduced by 52.3% (500 W) and 36.9% (600 W) after laser coupling. After being etched by CF4/CHF3 for a long time, it was observed from SEM, EDS and XPS analyses that the intensity ratios of the Y-F bonds in the coating were 1 (APS):1.3 (LAPS+500W):1.1 (LAPS+600W), which indicated that the LAPS+500W coating had a thicker fluorination layer. It was also observed that the fluorination layer at the defect was first eroded; then, the erosion area gradually spread to the surrounding area, and finally, the fluorination layer was etched. This indicated that the defects had a significant impact on the etching resistance. Consequently, the LAPS+500W coating with fewer defects and a thicker fluorination layer showed the lowest etching rate. Therefore, in situ laser-assisted plasma spraying coupled with an appropriate laser power is an effective method to improve the performance of yttrium oxide coatings.

Tribological Properties of 7A04 Aluminum Alloy Enhanced by Ceramic Coating

The 7A04 Al alloy is a commonly used lightweight metal material; however, its low wear resistance limits its application. In this study, the wear resistance of this alloy was improved by preparing micro-arc oxidation (MAO) coatings, MAO/MoS2 composite coatings, and hard-anodized (HA) coatings on its surface. The friction and wear behaviors of these three coatings with diamond-like coated (DLC) rings under oil lubrication conditions were investigated using a ring–block friction tester. The wear rates of the coatings on the block surfaces were determined using laser confocal microscopy, and the wear trajectories of the coatings were examined using scanning electron microscopy. The results indicated that, among the three coatings, the MAO/MoS2 coating had the lowest coefficient of friction of 0.059, whereas the HA coating had the lowest wear rate of 1.47 × 10−6 mm/Nm. The MAO/MoS2 coatings exhibited excellent antifriction properties compared to the other coatings, whereas the HA coatings exhibited excellent anti-wear properties. The porous structure of the MAO coatings stored lubricant and replenished the lubrication film under oil lubrication. Meanwhile, the introduced MoS2 enhanced the densification of the coating and functioned as a solid lubricant. The HA coating exhibited good wear resistance owing to the dense structure of the amorphous-phase aluminum oxide. The mechanisms of abrasive and adhesive wear of the coatings under oil lubrication conditions and the optimization of the tribological properties by the solid–liquid synergistic lubrication effect were investigated. This study provides an effective method for the surface modification of Al alloys with potential applications in the aerospace and automotive industries.

Synthesis of a Hard Anodic Oxide Coating with a Structure Allowing for Its Modification by Nanoparticles

A hard anodic oxide coating’s characteristic porous structure allows for its modification by the incorporation of nanoparticles. However, achieving an appropriate microstructure requires an optimal pore arrangement and shape, which is influenced by the electrolyte composition, current densities, temperature, and processing time. To achieve pores with a diameter of about 50 nm and the most regular structure, a range of these parameters were tested. Using a two-stage manufacturing process had a beneficial effect on increasing the microporosity of the coating. The addition of phthalic acid at 0 °C did not increase the pore diameter, but allowed for the process to be carried out at higher temperatures. However, the coating produced at 20 °C had a larger pore diameter, but numerous defects. The coating obtained from the three-component solution had the most regular structure, but the smallest pore diameter.

Hydrogen resistance of reduced graphene oxide coatings prepared by electrophoretic deposition on duplex stainless steel

In this study, reduced graphene oxide (rGO) coatings were fabricated on duplex stainless steel (DSS) substrates using the electrophoretic deposition (EPD) method to evaluate their hydrogen resistance performance. The successful fabrication of rGO coatings was confirmed using Fourier Transform Infrared Spectroscopy (FT-IR) and X-ray Photoelectron Spectroscopy (XPS). The structural characteristics were characterized using Raman spectroscopy and X-ray Diffraction (XRD). The results indicate that the EPD voltage is a crucial factor affecting the surface quality of and hydrogen resistance performance of rGO. Lower voltages resulted in lower degrees of rGO reduction and higher surface wrinkle density, while higher voltages caused bubble formation, significantly degrading the coating quality and hydrogen resistance performance. The optimal hydrogen resistance was achieved at an EPD voltage of 7.5V and a deposition time of 6 minutes. Electrochemical hydrogen charging tests and thermal desorption analysis (TDA) demonstrated that rGO coatings prepared under optimal conditions exhibited excellent hydrogen resistance efficiency, significantly reducing hydrogen atom penetration in hydrogen environments. The study further revealed that bubble formation significantly reduces the hydrogen resistance of rGO, which is attributed to increased interlayer spacing and the loss of the “labyrinth effect”.

Simultaneous improvement of wear and corrosion resistance of microarc oxidation coatings on ZK61 Mg alloy by doping with ZrO2 nanoparticles

Simultaneous improvement of wear and corrosion resistance of microarc oxidation coatings on ZK61 Mg alloy by doping with ZrO2 nanoparticles

Review of Electrical Parameters Influence on Characteristics of Plasma Electrolytic Oxide Coating on Zircaloy

<p>Zircaloy-4 (Zr-4) is used as a fuel cladding material in Pressurized Water Reactor (PWR). Zr-4 as a cladding material works in extreme conditions in pressurized water up to 150 atm at 325 ˚C. In addition, the refuelling process in the reactor requires surface protection of the clay material to minimize corrosion and wear. One of the raising methods to enhance the corrosion resistance of the Zr-4 is by plasma electrolytic oxidation (PEO). Characteristics of the ceramic oxide layer produced by PEO are influenced by current density, type and composition of the electrolyte, and voltage mode. One of the challenges in the PEO development on the Zr-4 substrate is a high porosity with a range of 5%-20% and the low number (below 6%) of t-ZrO<sub>2</sub> phases in the inner and outer layers. Optimizing the electrical parameters is necessary to overcome this problem. The results of the literature study show that the cathodic current at the AC voltage plays an important role in determining the resulting plasma characteristics. Low duty cycle (cathodic current> 50%) produce plasma with high density, resulting in a low porosity layer. Oppositely, high duty cycle (cathodic current <50%) produced high content of t-ZrO<sub>2</sub> increase the mechanical resistance. Two-step PEO is beneficial in combining the low and high duty cycle to obtain the benefit of each step. </p>

Synergistic Effect of Polyurethane on Pore-Sealing and Lubrication of Microarc Oxidation Coating.

Microarc oxidation (MAO) is a widely used surface treatment technology. However, its processing inevitably leads to the presence of micropores, microcracks, and other defects in the MAO coating. These defects lead to suboptimal tribological performance and diminished corrosion resistance of the MAO coating. Thus, this study proposed a new pore-sealing method with environmental protection and high efficiency. Polyurethane reactive (PUR) composite coating was prepared on the surface of MAO coating. The sealing effect of the PUR sample was analyzed using scanning electron microscopy (SEM). The molecular structure and elemental changes of the coating were analyzed using X-ray photoelectron spectroscopy (XPS). The tribological properties were analyzed using a tribological testing machine, and the corrosion resistance was tested using an electrochemical workstation. The test results show that the lubricity and corrosion resistance of PUR sample are improved significantly compared with MAO coating. When the mass fraction of PUR is 3 wt %, the PUR sample shows the best lubrication performance, and the coefficient of friction decreases by 70.8%. Compared with the traditional sealing technology, this experimental method is simple and low-cost and has a wide application prospect, which promotes the development of MAO technology.

Study of TaN and Ta2O5 coatings obtained by sputtering with non-self-sustained gas discharge for biomedical implant modification

Tantalum nitride (TaN) and tantalum oxide (Ta2O5) coatings were manufactured by using sputtering with sustained gas discharge in Bulat-type facility. Characteristics of the obtained coatings, including surface morphology, nanohardness, surface wettability, Young's modulus, and biocompatibility, were investigated. Different surface roughness of TaN and Ta2O5 made the main contribution to the transition to hydrophobic surface properties, which led to different conditions for cell adhesion. According to the test results, the average value of the elastic modulus for the sample coated with TaN was 426.1 GPa and Ta2O5 - 172.4 GPa, respectively. The maximum nanohardness was obtained for the TaN nitride coating and reached 37.8 GPa. The biocompatibility of the samples was assessed in vitro by the susceptibility of the surface of the material to cells, since cell attachment and proliferation are closely related to the surface characteristics of the implant. The Ta2O5 coating has shown appropriate biocompatibility profile, as it provides an ideal environment for Mesenchimal Stem Cells (MSC) adhesion from day 1, followed by cell proliferation until the end of the experiment. The TaN coating did not support cell attachment and proliferation during the experiment.

Combination of Plasma Jet and Magnetron Sputtering─A New Method for Preparing Thin Ni–Co–Mn Oxide Coatings on Stainless Steel Meshes and Their Efficiency in the Total Oxidation of Volatile Organic Compounds

Combination of Plasma Jet and Magnetron Sputtering─A New Method for Preparing Thin Ni–Co–Mn Oxide Coatings on Stainless Steel Meshes and Their Efficiency in the Total Oxidation of Volatile Organic Compounds

Effect of Artificial Saliva Modification on Corrosion Resistance of Metal Oxide Coatings on Co-Cr-Mo Dental Alloy.

Surface modifications not only improve the corrosion resistance of Co-Cr-Mo dental alloys (Bego Wirobond® C) but also ensure their long-term performance and reliability in dental applications. This paper describes the preparation of single-layer TiO2-ZrO2 sol-gel coatings on the Co-Cr-Mo dental alloy using the method of dip-coating. The TiO2-ZrO2 sol-gel coatings were sintered at 300 and 500 °C. SEM analysis shows that sintering at 300 °C produces a uniform, slightly dense structure without micro-cracks, while sintering at 500 °C results in a denser structure with micro-cracks due to higher stress and shrinkage. EDS confirms that sintering temperature affects the elemental composition of the coating, with higher temperatures causing the volatilization or diffusion of Ti and Zr. Roughness measurements indicate that the Ra value increases with the sintering temperature, meeting dental application requirements. Electrochemical measurements by open-circuit potential, EIS, and cyclic potentiodynamic curves demonstrate that sintering temperature and saliva composition affect corrosion resistance, with NaF and mouthwashes (Listerine Total Care Teeth Protection® and Meridol®) generally increasing charge transfer resistance and double-layer capacitance. The ceramic TiO2-ZrO2 coatings significantly reduce pitting corrosion susceptibility at physiological and acidic pH, with the 500 °C sintered coating showing better protective properties. These findings highlight the potential of TiO2-ZrO2 coatings in enhancing the performance of Co-Cr-Mo dental alloys.

Enhancing reflectivity of tantalum oxide coatings through plasma spraying and annealing techniques

Tantalum oxides, widely used as a high-reflectivity infrared material in aerospace and optoelectronics, often experiences a significant reduction in coating performance post-plasma spraying due to the emergence of oxygen defects. To overcome this shortcoming, this study comprehensively examined the effects of spray parameters and annealing processes on coating reflectivity. Our findings revealed that while optimizing spray parameters can modify micromorphology, these changes exert limited improvement on reflectivity (<2%). Conversely, muffle and laser annealing markedly enhance reflectivity by altering the surface composition and the valence of tantalum. Notably, post-laser annealing increased the reflectivity to 57 % from the original 12 % at 1070 nm. These results offer valuable insights into the development of high-reflectivity tantalum oxide coatings.

Graphene reinforced magnesium metal matrix composites by infiltrating coated-graphene preform with melt

Graphene’s exceptional mechanical, electrical, and thermal conductivity capabilities make it an ideal reinforcement for metal matrix composites. However, graphene is hard to be dispersed in the melt metal due to its high surface energy, non-wetting nature, and strong van der Waals interactions between graphene sheets, which weaken the reinforcing efficiency of composites. A novel process by infiltrating the coated-graphene preform with melt magnesium was proposed to improve the dispersion of graphene in the magnesium matrix. Graphene preforms with oriented pores were prepared by a directional freeze-drying method. Magnesium oxide coatings were deposited on the surface of graphene inside the graphene preform using the evaporation of magnesium atoms to enhance the strength as well as the wettability between the preform and magnesium matrix. Magnesium matrix composites were fabricated by liquid-solid pressure infiltrating coated-graphene preform with molten magnesium. The microstructure of graphene preforms and composites and mechanical properties of the composites were characterized. The results show that graphene is uniformly dispersed in the matrix and presents a reticular structure, and the hardness, elastic modulus, and compressive strength of the composite were improved apparently compared to the matrix. This study suggests that the method of preparing composites by infiltration provides a novel strategy for fabricating nano-material reinforced magnesium matrix composites.

Bioactive-Glass-Incorporated Plasma Electrolytic Oxidation Coating on AZ31 Mg Alloy: Preparation and Characterization

Bioactive-Glass-Incorporated Plasma Electrolytic Oxidation Coating on AZ31 Mg Alloy: Preparation and Characterization

Evaluation of imidazole blocking layers for perovskite stability

The prevention of AgI formation is critical for ensuring long term stability of perovskite solar cells. While sputtered metal oxide films are known for uniform dense film formation, solution phase nanoparticle coatings of metal oxides are prone to pinholes through which free iodide can migrate leading to AgI formation at the back contact. Iodide migration can be prevented through the addition of passivator or blocking layers at the perovskite/charge transport or charge transport/Ag interfaces. In this paper we evaluated a series of imidazoles as interfacial layers to prevent iodide migration from the perovskite to the Ag back contact through solution phase deposited Y:SnO2. We identified structural features of the imidazoles that contribute to an effective blocking layer. Specifically, it was found that imidazoles with conjugated planer systems and hydrogen bonding heteroatoms were able to prevent ion migration while retaining device performance. Of the materials evaluated 4-(Imidazol-1-yl)phenol had the best performance with a 60 % increase in stability verse the control under illumination at short circuit conditions.

Effects of PEO and BN-PVD coatings on the wear, corrosion, and surface properties of AZ31 magnesium alloy

This study investigates the effects of Plasma Electrolytic Oxidation (PEO) and subsequent Boron Nitride (BN) coatings applied via Physical Vapor Deposition (PVD) on the wear, corrosion, and surface properties of AZ31 magnesium alloy. The AZ31 alloy samples were first coated using the PEO process, forming a ceramic-like layer that enhances surface properties. However, inherent microcracks and pores in PEO coatings can compromise corrosion resistance. To mitigate these issues, a BN layer was applied over the some of PEO coating using RF-PVD, significantly improving wear resistance, corrosion protection, and surface integrity. The coatings were characterized using x-ray diffraction (XRD), scanning electron microscopy (SEM), x-ray photoelectron spectroscopy (XPS), and electrochemical testing. The results indicate that the PEO-BN coatings provide the highest wear resistance, lowest friction coefficient, and most effective barrier against corrosion among the samples tested. These findings highlight the potential of PEO-BN coatings to enhance the durability and performance of magnesium alloys, making them suitable for demanding applications.

Influences of Sr(OH)2 on the Structure and Corrosion Resistance of Micro‐Arc Oxidation Coatings Formed on TC4 Titanium Alloy

ABSTRACTIn order to improve the comprehensive properties of TC4 titanium alloy, micro‐arc oxidation (MAO) coating is prepared on the surface of a TC4 substrate in a basic electrolyte with varying concentrations of Sr(OH)2. The surface morphology, phase composition, element distribution, and corrosion resistance of MAO coatings are analyzed by scanning electron microscopy, X‐ray diffraction, an energy‐dispersive spectrometer, the electrochemical test, and the erosion–corrosion test. The results show that the voltage of the MAO process increases and then decreases; the surface morphology and density of the coatings are greatly improved after doping Sr(OH)2. When the concentration of Sr(OH)2 is 0.6 g L−1, the thickness, hardness, and adhesion strength of the coating reach the maximum values of 37.04 μm, 836.2 HV, and 21.8 N, respectively. At this time, the wear resistance and corrosion resistance are the best, and the friction coefficient and the corrosion rate are the lowest: 0.3352 and 1.04 × 10−10 mm a−1, respectively.

Effect of adding Sr(OH)2 on the formation process of 2024 aluminum alloy micro-arc oxidation coatings

Micro-arc oxidation coatings with oxidation times of 15 S, 30 S, 60 S, 120 S, 240 S and 1800 S were prepared on 2024 aluminum alloy using silicate-phosphate electrolytes containing 0 g/L and 0.5 g/L Sr(OH)2, respectively. The effects of adding Sr(OH)2 on the oxidation voltage, surface morphology and phase composition of the 2024 aluminum alloy MAO coatings formation process were investigated using SEM, XRD and XPS. The results show that adding Sr(OH)2 increases and then decreases the oxidation voltage compared with that of the unadded Sr(OH)2, which has little effect on the morphology of the oxide coatings, the Sr2+ and PO43- in the solution are jointly involved in the formation of the MAO coatings. The main phase composition of the coating is γ-Al2O3, and the Sr element is uniformly distributed as SrCO3 in the coating.

Multiscale textured solar absorber coatings for next-generation concentrating solar power

A high-temperature stable solar absorber is crucial for next-generation (Gen3) concentrating solar power (CSP) plants, to enable high temperature operation, maximize power generation efficiency, and thereby reduce the levelized cost of energy. This study presents novel, fractal-textured solar absorber coatings whose multiscale feature scales effectively match the visible region of the solar spectrum, leading to superb absorptive properties. Single and bimetallic oxide coatings of copper, cobalt and manganese were prepared on Inconel 625 substrates using electrodeposition. The effect of electrodeposition parameters and annealing temperature are systematically studied to optimize the morphology and properties of the oxide coatings. Multiscale textured bimetallic coatings of copper manganese oxide and copper cobalt oxide demonstrate a superior absorptance of 0.985, a remarkably low emittance <0.45 and an exceptional optical efficiency of ∼96 % under Gen3 CSP operating conditions, surpassing previously reported values in the literature by about 5 %. Durability tests confirmed the coatings’ steadfast endurance of mechanical and environmental stress, making them suitable for long-term application in harsh CSP environments.