Dual-layer Coatings Research Articles

Surface modification of WE43 Mg alloy via combination of cold spray and micro-arc oxidation for wear related applications at high temperatures

This study investigates the high temperature wear behaviour of a WE43 Mg alloy after covering it with single and dual layer coatings. For this purpose, cold spray and micro-arc oxidation processes were employed individually and sequentially. Single-layer coatings fabricated by cold spray and micro-arc oxidation processes were Al/Al2O3 composite and MgO-based ceramic, respectively. Sequential application of cold spray and micro arc oxidation processes induced dual layer coating upon synthesizing an external Al2O3–based layer over the Al/Al2O3 composite layer. Results of the wear tests conducted under the load of 2 N revealed the superior resistance of the dual layer coated sample against the rubbing action of the counterface compared to single layer coatings. Thus, the presence of a relatively hard and tough external Al2O3-based layer over the Al/Al2O3 composite layer sustained protection up to the temperature of 320 °C, where the dominant wear mechanism was fatigue wear. However, the increase in the test temperature to 350 °C caused detachment of the external Al2O3-based layer. Reduction of the wear test load from 2 to 1 N resulted in the remaining of external Al2O3-based layer intact with the underlying Al/Al2O3 composite layer even at a test temperature of 350 °C. It is therefore concluded that the combination of cold spray and micro-arc oxidation processes is promising to broaden the reliable use of WE43 and other Mg alloys in wear related applications at high service temperatures.

Tailored micro-arc oxidation coatings to match with parylene for enhanced tribological performance of Ta-12W alloys

To improve the tribological properties of tantalum-tungsten alloys, dual-layer composite coatings are designed using micro-arc oxidation (MAO) and chemical vapor deposition (CVD) techniques. By adjusting the concentrations of NaOH and NaF additives as well as the oxidation mode (constant current/voltage) of MAO process, the microstructure and properties of underlying MAO layers are tailored for better matching with the top parylene layer, aiming to develop composite coatings capable of service under heavy loads. A comprehensive study is conducted to evaluate the effect of these parameters on the growth, microstructure, bond strength, and mechanical properties of MAO coatings, along with their subsequent impact on the friction and wear behavior under various loads for composite coatings. The findings reveal that increasing the concentration of either NaOH or NaF significantly increases the coating thickness, surface porosity, crystallinity, and hardness of MAO coatings, by promoting the spark discharge activities. However, distinct interfacial growth behavior is observed due to anionic effects caused by OH− and F−. The oxidation mode plays a crucial role in determining the mechanical quality of coatings; the constant voltage mode facilitates dense coatings with high adhesion due to its self-repairing mechanism. Furthermore, wear tests confirm that the enhanced mechanical properties and open-porosity of the MAO coatings markedly improve the tribological performance of composite coatings. This improvement is attributed to the excellent load-bearing capacity provided by hard MAO layers, as well as the anchoring and storage capabilities of the textural porous surfaces. The optimized composite coating demonstrates long-lasting low friction even under heavy loads up to 80 N.

The Effect of a Dual-Layer Coating for High-Capacity Silicon/Graphite Negative Electrodes on the Electrochemical Performance of Lithium-Ion Batteries

Silicon-based electrodes offer a high theoretical capacity and a low cost, making them a promising option for next-generation lithium-ion batteries. However, their practical use is limited due to significant volume changes during charge/discharge cycles, which negatively impact electrochemical performance. This study proposes a practical method to increase silicon content in lithium-ion batteries with minimal changes to the manufacturing process by using dual-layer electrodes (DLEs). These DLEs are fabricated with two slurries containing silicon and graphite as active materials. Notably, the electrode with the silicon as the outermost layer on top of the graphite layer (Si-on-top) demonstrated a superior initial capacity of 935 mAh/g and retained 70% of its capacity (537 mAh/g) after 100 cycles at 0.5 C. In contrast, a single-layered electrode (SLE) with a silicon–graphite mixture retained only 50.3% of its capacity (370 mAh/g) under the same conditions. These findings suggest that DLEs, particularly with the silicon layer located on top, effectively increase silicon content in the negative electrode while remaining compatible with existing manufacturing processes. This approach offers a realistic strategy for enhancing the performance of lithium-ion batteries without significant process modifications.

Construction of dual-layer composite coatings using MAO and CVD to enhance the tribological properties of tantalum–tungsten alloys

Construction of dual-layer composite coatings using MAO and CVD to enhance the tribological properties of tantalum–tungsten alloys

Enhancing osteointegration and antibacterial properties of PEEK implants via AMP/HA dual-layer coatings

Polyetheretherketone (PEEK) is a widely used engineering plastic in orthopedic and dental implants, but its bioinertness leads to poor bone integration. To overcome this, a sulfonation treatment was applied to PEEK first to create a rough, microporous surface enhancing cellular adherence and integration. Subsequently, amorphous magnesium phosphate (AMP) nanosheets were produced through microwave-assisted synthesis, and hydroxyapatite (HA) was generated using a bionic solution hydrothermal method. A dual-layer coating system composed of an interlayer AMP and a top layer HA on the surface of PEEK was developed to enhance osteointegration. Surface analysis confirms the creation of increased surface area, improved hydrophilicity with introduced hydrophilic groups, and enhanced protein attraction. In vitro assessments on mouse embryonic osteoblasts (MC3T3-E1) demonstrate the non-toxicity of these coatings and their efficacy in promoting cell proliferation. Moreover, antimicrobial evaluations against E. coli and S. aureus highlight the potential of these composite coatings in preventing implant-related infections. The AMP/HA dual-layer coating on sulfonated PEEK emerges as a potent method for enhancing osteointegration and antibacterial properties, offering a promising approach to improve bone repair efficiency in clinical applications.

Comparison of the effects of two biodegradable coatings on the characteristics of white-top linerboard used in packaging food materials in cold environments

Effects of two biodegradable coatings were compared relative to the characteristics of white-top linerboard. To coat the surface of the paperboard, nano-polyurethane was sprayed onto the surface using a nozzle. Subsequently, the samples were placed inside a refrigerator and freezer for a period of 2 and 4 months. In the second stage, nano-polyurethane was again sprayed onto the surface, using a nozzle, to improve the performance of the coating material. To further enhance the coating, the surfaces of the coated white-top linerboard were coated with a nanoclay using a laboratory coater. Subsequently, the samples were placed inside a refrigerator and freezer for a period of 2 and 4 months. The properties of the samples were measured thereafter. The results showed a reduction in water absorption of the samples after coating and freezing. This can be attributed to the penetration of the coating solution into the paper pores, resulting in a decrease in pore diameter and, consequently, a decrease in water permeability through the paper pores. In the coated and frozen samples, an increase in thickness and surface smoothness was observed, but most of the mechanical strength properties decreased. These changes were more pronounced in the dual-layer coatings.

Magnetically controlled interface weaving of dual-layer heterogeneous coatings with active and passive anti-corrosion protection

Polydimethylsiloxane (PDMS) elastomer exhibiting remarkable corrosion resistance and fouling release properties. However, their performances are often compromised due to the weak interfacial adhesion with rigid substrates. Herein, we have developed an innovative dual-layer heterogeneous coating via magnetic-controlled interface weaving technology, achieving a seamless integration of PDMS with a rigid epoxy (EP) substrate. Magnetic nanoparticles (Fe3O4@MPDA-MBT) were strategically incorporated into the coating system, guided by a magnetic field to facilitate their interfacial migration. This controlled migration of nanoparticles resulted in the formation of interface layer between the EP primer and PDMS topcoat, leading to a sharp increase in PDMS adhesion strength (3.0 MPa), which is over 7 times greater than that of control counterpart (0.4 MPa). Additionally, Fe3O4@MPDA-MBT were selectively enriched adjacent to the metal substrate, thereby endowing the coating with outstanding corrosion resistance, due to the quick releasing of enough MBT inhibitors, as confirmed by electrochemical tests with high corrosion resistance value (2.2 × 108 Ω·cm2). Also, the topcoat PDMS enabled the dual-layer heterogeneous coating to achieve fouling-release and cavitation resistance.

Dual-Lifetime Referencing (t-DLR) Optical Fiber Fluorescent pH Sensor for Microenvironments.

The pH behavior in the μm to cm thick diffusion boundary layer (DBL) surrounding many aquatic species is dependent on light-controlled metabolic activities. This DBL microenvironment exhibits different pH behavior to bulk seawater, which can reduce the exposure of calcifying species to ocean acidification conditions. A low-cost time-domain dual-lifetime referencing (t-DLR) interrogation system and an optical fiber fluorescent pH sensor were developed for pH measurements in the DBL interface. The pH sensor utilized dual-layer sol-gel coatings of pH-sensitive iminocoumarin and pH-insensitive Ru(dpp)3-PAN. The sensor has a dynamic range of 7.41 (±0.20) to 9.42 ± 0.23 pH units (95% CI, T = 20 °C, S = 35), a response time (t90) of 29 to 100 s, and minimal salinity dependency. The pH sensor has a precision of approximately 0.02 pHT units, which meets the Global Ocean Acidification Observing Network (GOA-ON) "weather" measurement quality guideline. The suitability of the t-DLR optical fiber pH sensor was demonstrated through real-time measurements in the DBL of green seaweed Ulva sp. This research highlights the practicability of optical fiber pH sensors by demonstrating real-time pH measurements of metabolic-induced pH changes.

High temperature oxidation and hot corrosion behaviors of PEO and PEO/polysilazane preceramic-based dual-layer coatings on Ti6Al4V alloy

The high temperature oxidation and corrosion behaviors of a plasma electrolytic oxidation (PEO) coating and a PEO/polysilazane (PEO/PSZ) dual-layer coating are investigated. After exposure in NaCl+Na2SO4 salt at 600 ℃ for 240 h, PEO coating tends to generate porous and loose scales, causing cracking or even complete peeling off from the substrate, and corrosion scales follow the law of formation-shedding-reformulation. After exposure in NaCl+Na2SO4 salt at 600 ℃ for 480 h, the PEO/PSZ coating exhibits a three-layer structure including the outermost corroded layer with sandwich structures, uncorroded Al2O3 particles-containing interlayer, and PEO bottom layer, which retards the continuous penetration of corrosive media and further diffusion of oxygen to the inner bulk alloy, resulting in a remarkable reduction of oxidation and corrosion rate.

Mitigating the Capacity Degradation by Ion-Electron-Conducting Dual-Layer Coating on a Layered Oxide Cathode Material for Sodium Ion Batteries

A high-capacity and long-life layered P2-Na0.7[Ni0.35Mn0.60Co0.05]O2 (NMC) cathode material, dually coated with Na-ion-conducting Na2SiO3 and electron-conducting RGO, has been successfully synthesized and tested for half-cell as well as full-cell applications. The first coating layer of Na2SiO3 provides a three-dimensional (3D) diffusion channel for Na-ion migration, while the second coating layer of RGO offers the electron-conducting pathways to enhance the charge transfer. Moreover, Si4+ migration in the NMC lattice during Na2SiO3 coating causes the enhancement in the interlayer spacing, which significantly increases the Na+-diffusion rate. The structural, morphological, electronic, and electrochemical analyses of the prepared cathode materials have been performed. The synergic effect of dual-layer modification and Si4+ doping not only protects the cathode particles but also improves the Na-ion kinetics as well as charge transfer rate, resulting in superior electrochemical performance. The dually surface-modified cathode shows a maximum discharge capacity of 171 mAh g–1 at ∼13 mA g–1 and 62 mAh g–1 at ∼1300 mA g–1 with 76% capacity retention and ∼98% coulombic efficiency over 500 cycles at 1C rate (260 mA g–1) for the half cell, while for the full cell, it delivers an initial discharge capacity of ∼91 mAh g–1 and 66% capacity retention over 1000 cycles at 1C rate.

Effect of Si content on microstructure, mechanical properties, and cutting performance of TiSiN/AlTiN dual-layer coating

Ti1-xSixN/AlTiN dual-layer coatings with different Si content were prepared by cathode arc evaporation to study the effect of Si-doping on the coatings. The composition, morphology, and microstructure of the coatings were characterized using SEM, XRD, and XPS. The hardness, elastic modulus, and adhesion strength were measured by nano-indentation and micro-scratch. Results show that coatings all consist of TiN grains and Si3N4 amorphous phases. Ti1-xSixN/AlTiN dual-layer coating has the highest hardness of 43.07 GPa at a Si content of 0.19 and the lowest elastic modulus of 314.46 GPa at a Si content of 0.25. High-speed milling of Ti-6Al-4V alloy was performed to evaluate the cutting performance of the coated tools. The value and amplitude of the cutting force were collected to analyze the wear condition of tools. When cutting speed at 120 m/min, the coating with a Si content of 0.19 shows the best cutting performance, having the lowest cutting force and flank wear. The higher silicon content increases the bonding of titanium alloy, influencing the stability during cutting. The lower silicon content reduces the wear resistance of the coating and shorten tool life. Suitable Si content of the coating has been proved effective in improving the cutting performance on Ti-6Al-4V alloy.

Design and fabrication of enhanced corrosion-resistant LDH-Zn-G/Ni dual-layer structural coatings on magnesium alloys

A particular dual-layer structure of reinforced anti-corrosion magnesium aluminum-layered double hydroxide - Zn-G/Ni coating (LDH-ZGN), grown in situ the magnesium aluminum-layered double hydroxide coating (LDH) on the surface of the magnesium alloy, and a Zn-G/Ni composite coating was deposited on the LDH coating by low-pressure cold gas spraying (LPCGS). The LDH-ZGN was characterized by XRD, XPS, SEM, EDS, etc. The coating's corrosion protection and enhancement effect were explored through the electrochemical test of polarization curve, EIS, and coating immersion test. LDH-ZGN exhibited excellent corrosion resistance, mainly attributed to the synergy between reduced graphene oxide (rGO) and magnesium aluminum-layered double hydroxides (MgAl-LDH) and the enhancement effect of the coating under the particular dual-layer structure. • Build a dual-layer structural coating on the surface of the Mg alloy. • The cooperation of MgAl-LDH and rGO improves corrosion resistance. • rGO and Ni synergistically enhance the protective effect of the LDH-ZGN coating.

Copper-Based Nanocatalysts with SiO2 and Carbon Dual-Layer Coatings and Metallic Ni/CuNi Decoration toward Highly Efficient Nitroaromatics Reduction.

Nanocomposites with novel architectures and multifunctional properties have attracted extensive attention among related researchers. Herein, we develop a magnetically responsive Ni/CuNi nanoparticle (NP) decoration of Cu-based composites that could serve as recoverable nanocatalysts for nitroaromatics reduction. The nanocatalysts consist of an inner copper core and abundant tiny satellite Ni/CuNi NPs, which are tightly combined as a stable whole part by a silica interlayer and a carbon outer layer. In addition to the high catalytic activity, the outer Ni/CuNi NPs exhibit a strong magnetic response toward the external magnetic field, thereby offering a convenient way to separate the composites from the reaction solution. Moreover, characterization results reveal that high annealing temperature (above 700 °C) favors the construction of yolk-shell nanostructures and the formation of outer bimetallic CuNi NPs. As a result, owing to the excellent catalytic performance of the Cu inner cores, the high coverage of outer Ni or CuNi NPs, and the unique sandwich-like structure, the resultant Cu@SiO2@C-Ni composites show the use of such magnetically responsive recoverable nanocatalysts for the 4-nitrophenol reduction. Hence, this research could provide new guidelines for designing and synthesizing novel and efficient copper-based composites for other fields, such as carbon dioxide reduction, energy storage, and batteries.

Facile fabrication of graphene oxide and MOF-based superhydrophobic dual-layer coatings for enhanced corrosion protection on magnesium alloy

Corrosion is an inevitable and thorny problem when magnesium (Mg) alloys are used in marine environments. Superhydrophobic coatings have great potential for metal corrosion protection due to their superhydrophobicity and self-cleaning properties. However, the poor mechanical stability of the surface seriously hinders the practical application. Herein, a robust superhydrophobic graphene oxide (GO)/polypyrrole (PPy)-zeolitic imidazolate framework-8 (ZIF-8) dual-layer coating was prepared on the surface of magnesium (Mg) alloy by electrodeposition and spraying method, which was composed of a bottom GO layer and a upper superhydrophobic PPy/ZIF-8 layer. The GO layer extends the transmission path of corrosion ions and the superhydrophobic coating prevents the contact between the Mg alloy and the corrosive solution. In addition, the dual-layer superhydrophobic coating has excellent self-cleaning and mechanical properties. More importantly, the as-prepared coating can withstand 3.5 wt% NaCl solutions for 120 h and still maintain good corrosion resistance. Furthermore, the GO layer and the superhydrophobic layer have a synergistic effect, which significantly improves the corrosion resistance of Mg alloys. The facile method and superhydrophobic dual-layer coatings will have good application prospects on a variety of metal substrates.

Micromechanical characterization and dynamic wear study of DC-Arc coated cemented carbide cutting tools for dry titanium turning

The present study investigates the micromechanical properties of ceramic coated WC/Co tools and their influence on wear performance during dry Ti6Al4V turning. Physical and micromechanical characterization have been performed for the evaluation of the PVD coating properties. Higher hardness, elastic modulus, and adhesion strength have been obtained for dual-layer (AlTiN/AlCrN) coated tool than monolayer AlTiN and AlCrN coated tools. Micromechanical properties influence the wear mechanisms in thermally activated and abrasion dominant crater zones. Dual-layer coated tools reduced the flank wear at the corner radius and crater wear by 35–50% and 40%, respectively. Dynamic wear and abrasion-dissolution wear mechanisms have been explored over the tool rake face. Dual-layer coatings have improved wear performance by diminishing delamination, micro-fracturing of WC grains, binder dissolution and fractured interface boundaries.

Biologically Inspired Scalable-Manufactured Dual-layer Coating with a Hierarchical Micropattern for Highly Efficient Passive Radiative Cooling and Robust Superhydrophobicity.

Bioinspired materials for temperature regulation have proven to be promising for passive radiation cooling, and super water repellency is also a main feature of biological evolution. However, the scalable production of artificial passive radiative cooling materials with self-adjusting structures, high-efficiency, strong applicability, and low cost, along with achieving superhydrophobicity simultaneously remains a challenge. Here, a biologically inspired passive radiative cooling dual-layer coating (Bio-PRC) is synthesized by a facile but efficient strategy, after the discovery of long-horned beetles' thermoregulatory behavior with multiscale fluffs, where an adjustable polymer-like layer with a hierarchical micropattern is constructed in various ceramic bottom skeletons, integrating multifunctional components with interlaced "ridge-like" architectures. The Bio-PRC coating reflects above 88% of solar irradiance and demonstrates an infrared emissivity >0.92, which makes the temperature drop by up to 3.6 °C under direct sunlight. Moreover, the hierarchical micro-/nanostructures also endow it with a superhydrophobic surface that has enticing damage resistance, thermal stability, and weatherability. Notably, we demonstrate that the Bio-PRC coatings can be potentially applied in the insulated gate bipolar transistor radiator, for effective temperature conditioning. Meanwhile, the coverage of the dense, super water-repellent top polymer-like layer can prevent the transport of corrosive liquids, ions, and electron transition, illustrating the excellent interdisciplinary applicability of our coatings. This work paves a new way to design next-generation thermal regulation coatings with great potential for applications.

Adhesion, structure, and mechanical properties of Cr HiPIMS and cathodic arc deposited coatings on SiC

Chromium deposited by high-power impulse magnetron sputtering (HIPIMS) versus cathodic arc (CA) processes exhibits very different mechanical properties. Combining the two can result in a single-phase with superior performance that can be tailored for use in coating SiC for advanced nuclear fuel cladding. Coating morphology, residual stress, elemental depth profiles, and mechanical testing by scratch, pull-off adhesion, and microcantilevers are shown for HiPIMS, CA, and combined coatings. CA coatings were likely to spall and had lower adhesion strength due to tensile residual stresses but had desirable material properties. By depositing an initial layer of Cr by HiPIMS followed by a layer of Cr by CA, a more adherent coating was achieved and some of the stress issues with CA morphology were resolved. Combined coatings withstood at least 80 MPa in pull-off adhesion tests and had maximum failure stress values of 5GPa in microcantilever tests. These results were better than either individual deposition method and point to a hybrid approach being a path forward for a more robust coating. • Cr coatings were deposited by HiPIMS and cathodic arc on model SiC substrates. • Properties of both individual and hybrid dual layer coatings were studied. • A hybrid coating benefitted both adhesion and mechanical properties.

Advanced iron boride coatings to enhance corrosion resistance of steels in geothermal power generation

ABSTRACT Iron boride coatings obtained by the CVD-based thermal diffusion process are proposed and evaluated for the first time for high-temperature corrosion and scaling conditions in geothermal power generation. The testing results in different corrosion environments are presented. The influence of structure and surface composition on the materials’ performance is demonstrated. The dual-layer boride-based coatings successfully withstand the actions of high temperature/high pressure water and steam with a presence of H2S, CO + CO2, chlorides and hydrocarbons in simulating conditions and strong acidic environments. They demonstrated minimal scaling and corrosion when the materials were immersed into the modelling mixes of chloride salt solutions with SiO2 or SiO2+Fe2O3 at elevated temperatures and into the brine solution at boiling. These advanced ceramic coatings and technology should promote significant extension of the steels’ service life in harsh geothermal-related corrosion environments.

Superhydrophobic ZIF-8-Based Dual-Layer Coating for Enhanced Corrosion Protection of Mg Alloy.

Magnesium (Mg) and its alloys are regarded as the most promising engineering materials because of their unique property. However, the Mg alloys were easily corroded in humid environments, which restricted their wider applications. Herein, the superhydrophobic ZIF-8/PVDF/LDH (SZPL) double-layered coating was fabricated on Mg alloys via electrodeposition and dip-coating methods, which consisted of the underlying layered double hydroxide (LDH) transition structure and top superhydrophobic zeolitic imidazolate framework-8 (ZIF-8) layer. Besides, the LDH transition structure not only worked as a protection shield but also strengthened the binding force between the substrate and the top superhydrophobic ZIF-8 layer. The top superhydrophobic ZIF-8 layer could serve as an armor on the LDH layer to further prevent the corrosive ions from infiltrating the microporous defects. In addition, the as-prepared SZPL double-layered coating showed robust superhydrophobic and self-cleaning properties, which could block the electrolyte invasion. Furthermore, the electrochemical tests demonstrated that the SZPL coating highly enhanced the corrosion protection ability of Mg alloys. Moreover, the superhydrophobic ZIF-8-based coating could still retain excellent anticorrosion property after immersion in 3.5 wt % NaCl solution for 7 days. The enhanced anticorrosion ability was ascribed to the fact that a synergistic effect of the underlying LDH transition layer hindered the transmission of aggressive ions and the top superhydrophobic ZIF-8-based coating decreased the contact area of the substrate with corrosive solution. Therefore, such coatings offer a new strategy for fabricating excellent anticorrosive coatings with robust superhydrophobicity and self-cleaning performance on metal substrates.

Food-Safe Chitosan–Zein Dual-Layer Coating for Water- and Oil-Repellent Paper Substrates

Coated paper substrates are used for a wide range of applications. The biggest challenge that remains unsolved with regard to coated paper is its recyclability. Herein, we report a unique approach that relies on 100% biobased and biodegradable food-safe materials for water- and oil-resistant papers. A 35-liner paper was coated with an oil-resistant chitosan solution and subsequently by a hydrophobic zein solution. The resultant chitosan–zein-coated paper showed remarkable water resistance (Cobb 60 value of 4.88 g/m2) and oil repellency (kit rating 12/12). Scanning electron microscopy (SEM) analysis was used to determine the changes in the surface texture of the paper before and after coating treatment. The excellent mechanical properties of the coated paper were retained after the coating treatment. In addition, the pulp was recycled from the chitosan–zein-coated paper to validate the recyclability of this novel approach.