Multilayer Coatings Research Articles

Eco-friendly epoxidized Eucommia ulmoides gum based composite coating with enhanced super-hydrophobicity and corrosion resistance properties

Developing a green, non-toxic, and sustainable bio-based anticorrosive coating is significant for achieving the objective of "carbon reduction". In this study, superhydrophobic multilayer coatings based on epoxidized Eucommia ulmoides gum were prepared via a layer-by-layer assembly bottom-up approach, providing comprehensive protection for mild steel. The foundational layer, comprising the epoxidized Eucommia ulmoides gum/industrial lignin composite (EEUG-EHL), exhibited commendable adhesion, impermeability, and corrosion resistance. The intermediate layer was composed of 8-hydroxyquinoline/zeolitic imidazolate framework-8 (8HQ@ZIF-8) nanoparticles, which controlled the release of 8HQ through pH responsiveness and had self-healing properties. Employing a spraying method, a top layer with micro-nanostructured consisting of a modified ZIF-8 nanoparticle was created, inspired by the micro-nano structure observed in cicada wings. The multilayer coating exhibited remarkable super-hydrophobicity (contact angle > 150°, sliding angle < 5°), chemical stability, self-cleaning properties, and anti-fouling properties. Notably, the multilayer coating demonstrated exceptional corrosion resistance, maintaining an impedance modulus of 108 ohm cm2 (at 0.01 Hz) after immersion in a 3.5 wt% NaCl solution for 45 days. This work introduces a novel approach to enhance the corrosion protection of metal equipment, aligning with the "green development" strategy and holding significance in advancing marine anti-corrosion construction.

Evaluating the corrosion and tribological performance of nanostructured CrN/TiN and TiN/CrN configurations applied on 410 stainless steel

ABSTRACT This study aims to compare the corrosion and tribological performance of TiN/CrN and CrN/TiN nanostructured multi-layer coatings deposited through cathodic arc evaporation PVD on 410-grade stainless steel. Both coating configurations were available in smooth (polished) and rough states. For the deposition of multi-layer coatings, a middle layer containing Cr and CrN was deposited to the substrate, followed by alternating nanolayers of TiN and CrN. finally, an upper layer of either CrN or TiN was applied. The nanoindentation test revealed that the hardness, Young’s modulus, H/E, and H3/E2 ratios of the coating with a TiN upper layer were 5.57, 1.42, 3.86, and 85.39 times of the substrate, respectively. At the coating with CrN upper layer, these values were 4.04, 1.13, 3.53, and 51.68 times of the substrate, respectively. Results showed that increasing the H/E and H3/E2 ratios increased wear resistance. Wear rates of smooth and rough TiN coatings and smooth and rough CrN coatings were reduced by 86%, 99%, 53%, and 26%, respectively, compared to the substrate. Results of the corrosion test showed that the rough CrN coating had greater corrosion resistance than the coating with a TiN upper layer and the substrate due to its higher hydrophobicity.

Improving the Wear Resistance Properties of 7A04 Aluminum Alloy with Three Surface Modification Coatings

Multiple advantages, such as good formability, high specific strength, excellent thermal conductivity, and high corrosion resistance, enable aluminum alloy wide application in various fields; however, low surface hardness and poor wear resistance limit its further development. In this study, three surface modification coatings were successfully prepared on the surface of 7A04 aluminum alloy by microarc oxidation (MAO) and a combination of hard anodizing treatment (HA) and physical vapor deposition (PVD), named MAO, HA+W+DLC, and HA+Ti+ta-C, respectively. The microstructure, hardness, and tribological properties of the three coatings and the 7A04 aluminum alloy substrate were studied. The results show that the surface quality and hardness of the coated samples were higher than those of the 7A04 aluminum alloy and that the HA+Ti+ta-C coating possessed the highest hardness of 34.23 GPa. Moreover, the wear resistance of the two multilayer coatings was significantly improved during the ring-block wear tests under oil lubrication, exhibiting a wear rate of 1.51 × 10−7 mm3/N·m for HA+W+DLC and 1.36 × 10−7 mm3/N·m for HA+Ti+ta-C.

Effect of titanium interlayer configurations on residual stresses and performance of titanium/titanium nitride multilayer coatings

Multilayer coatings provide an effective measure to control and optimise of residual stresses, enhance coating adhesion, fracture toughness, wear and corrosion resistance of coating system. In this study, we designed and produced bi-layer and four-layer titanium/titanium nitride magnetron sputtered coating configurations by altering the position of the interlayer. The in-plane residual stresses in different coating configurations are measured by multiple peak grazing incidence X-ray diffraction techniques. Subsequently, the effect of different compressive residual stresses on adhesion, mechanical properties, wear and corrosion resistance of coatings are investigated. Results show that the position of interlayer in multilayer coating configuration has a great impact on relaxation of residual stresses. The residual stresses are relieved by 26% and 46% by lowering the position of titanium interlayer from 800 nm at the top to 1000 nm and 1200 nm, respectively. The nanoindentation hardness is decreased by 11% and 13%, respectively. The wear rate of multilayer coating having interlayer position at 800 and 1000 nm from the top is ≈ 23% lower compared to bilayer however it is increased by ≈ 50% when interlayer coatings position changed to 1200 nm from the top. The interposition of interlayer in multilayer coating configurations decreased the corrosion current density by ≈ 50%. All multilayer coatings including higher residual stresses show better adhesion to the substrate compared to bilayer coatings which shows severe delamination.

Simulation of TiN/Ti Multilayer Coating under the Impact of Multiple Particles Based on Cohesive Element

In order to investigate the damage behavior of TiN/Ti multilayer coating under multi-particle impact and the influence of impact angle on erosion resistance, the ABAQUS 2019 software and the cohesive element technology were used for simulation. The results showed that, during the impact process, the upper surface of the TiN layer that was directly below the impact center was mainly subjected to compressive stress, while the lower surface was subjected to tensile stress. At the impact contact edge, tensile stress appeared on the upper surface of the TiN layer, while compressive stress appeared on the lower surface. The increase in the number of impacts leads to an increase in the maximum S11 stress inside the coating and the maximum displacement of the impact center during the impact process. The plastic damage was greater at the locations with higher strain in the Ti sublayer. During the impact process, severe damage occurred in both the top TiN layer and interface areas, and material failure occurred in the impact area. The increase in impact angle leads to an increase in the plastic strain energy of the entire model after the impact and the maximum S11 stress inside the coating during the impact process.

Hydrogen-Induced Microstructure Changes in Zr/Nb Nanoscale Multilayer Structures

Zr/Nb nanoscale multilayer coatings (NMCs) were studied after hydrogenation in a gaseous environment at 400 °C. The hydrogen distribution and content were determined by pressure and hydrogenation time. Increasing the pressure from 0.2 to 2 MPa resulted in different hydrogen distribution within the Zr/Nb NMCs, while the concentration remained constant at 0.0150 ± 0.0015 wt. %. The hydrogen concentration increased from 0.0165 ± 0.001 to 0.0370 ± 0.0015 wt. % when the hydrogenation time was extended from 1 to 7 h. The δ-ZrH hydride phase was formed in the Zr layers with Zr crystals reorienting towards the [100] direction. The Nb(110) diffraction reflex shifted towards smaller angles and the interplanar distance in the niobium layers increased, indicating significant lateral compressive stresses. Despite an increase in pressure, the nanohardness and Young’s modulus of the Zr/Nb NMCs remained stable. Increasing the hydrogen concentration to 0.0370 ± 0.0015 wt. % resulted in a 40% increase in nanohardness. At this concentration, the relative values of the Doppler broadening variable energy positron annihilation spectroscopy (S/S0) increased above the initial level, indicating an increase in excess free volume due to hydrogen-induced defects and changes. However, the predominant positron capture center remained intact. The Zr/Nb NMCs with hydrogen content ranging from 0.0150 ± 0.0015 to 0.0180 ± 0.001 wt. % exhibited a decrease in the free volume probed by positrons, as demonstrated by the Doppler broadening variable energy positron annihilation spectroscopy. This was evidenced by opposite changes in S and W (S↓W↑). The microstructural changes are attributed to defect annihilation during hydrogen accumulation near interfaces with the formation of hydrogen–vacancy clusters and hydrides.

Tailoring the reaction path: External crack initiation in reactive Al/Ni Multilayers

The influence of intentionally externally induced cracks in reactive Al/Ni multilayer systems is investigated. These cracks affect the reaction dynamics and enable tailoring of the reaction path and the overall velocity of the reaction front. The influence of layer variations onto mechanical crack formation and resulting reaction behavior are investigated. High‐speed camera imaging shows the meandering propagation of the reaction front along the crack paths. Therefore, the mechanical cracking process significantly changes the total velocity of the reaction front and thus offers a possibility to control the self‐propagating high‐temperature synthesis process. It is shown that the phase formation remains unaffected despite the applied strains and cracks. This favorable stability in phase formation ensures predictability and provides insight into the adaptation of RMS for precision applications in joints. The results expand the understanding of mechanical cracking as a tool to influence high temperature synthesis in reactive multilayer coatings and provide an opportunity to expand the range of applications.This article is protected by copyright. All rights reserved.

Enhanced solid particle erosion resistance of nanocrystalline Ni-W coatings through multilayer approach

Electrodeposited nanocrystalline Ni-W alloy coatings are projected as potential alternatives for hard chrome (HCr) coatings owing to their comparable hardness and superior corrosion resistance. However, the limited strain hardening ability of the nanocrystalline Ni-W coatings manifests in their poor resistance towards solid particle erosion involving a high strain-rate (>103 s−1) deformation. In the present study, a novel microstructural engineering strategy has been implemented to enhance the strain hardening ability of the nanocrystalline Ni-W coatings without compromising on their strength/hardness. Ni-W multilayer coatings composed of alternatively stacked soft (2.6 GPa) and hard (8.5 GPa) Ni-W layers were developed using the pulse reverse electrodeposition technique. Further, to investigate the effect of individual layer thickness (λ), multilayer coatings with different λ were deposited. Solid particle erosion testing using the angular SiO2 particles showed that the multilayer coatings (irrespective of λ) exhibit superior erosion resistance compared to the homogeneous nanocrystalline Ni-15W at both oblique (θ = 30°) and normal (θ = 90°) impact conditions. The post-erosion microstructural analysis of the multilayer coatings revealed that the hard Ni-W layers undergo uniform strain (ε > 50 %) without cracking due to the constrained co-deformation imposed by the surrounding soft Ni-W layers. Therefore, the enhanced erosion resistance of the multilayer coatings is attributed to the effective dissipation of impact energy through co-deformation of the individual hard and soft Ni-W layers.

Formation Mechanism of Ti–Si Multi-Layer Coatings on the Surface of Ti–6Al–4V Alloy

Titanium alloys are widely used in aerospace applications due to their high specific strength and exceptional corrosion resistance. In this study, a silicide coating with a multi-layer structure was designed and prepared via a pack cementation process to improve the high-temperature oxidation resistance of titanium alloy. A new theory based on the Le Chatelier’s principle is proposed to explain the generation mechanism of active Si atoms. Taking the chemical potential as a bridge, a functional model of the relationship between the diffusion driving force and the change in the Gibbs free energy of reaction diffusion is established. Experimental results indicate that the depth of the silicide coating increases with the siliconization temperature (1000–1100 °C) and time (0–5 h). The multi-layer coating prepared at 1075 °C for 3 h exhibits a thick and dense structure with a thickness of 23.52 μm. This coating consists of an outer layer of TiSi2 (9.40 μm), a middle layer of TiSi (3.36 μm), and an inner layer of Ti5Si3 (10.76 μm). Under this preparation parameter, increasing the temperature or prolonging the holding time will cause the outward diffusion flux of atoms in the substrate to be much larger than the diffusion flux of silicon atoms to the substrate, thus forming pores in the coating. The calculated value of the diffusion driving force FTiSi = 2.012S is significantly smaller than that of FTiSi2 = 13.120S and FTi5Si3 = 14.552S, which perfectly reveals the relationship between the thickness of each layer in the Ti–Si multi-layer coating.

Efficiency enhancement of ultrathin CIGS solar cells by optimal bandgap grading. Part III: piecewise-homogeneous grading

In Parts I [ Appl. Opt. 58, 6067 (2019)APOPAI0003-693510.1364/AO.58.006067] and II [ Appl. Opt. 61, 10049 (2022)APOPAI0003-693510.1364/AO.474920], we used a coupled optoelectronic model to optimize a thin-film CIGS solar cell with a graded-bandgap photon-absorbing layer, periodically corrugated backreflector, and multilayered antireflection coatings. Bandgap grading of the CIGS photon-absorbing layer was continuous and either linear or nonlinear, in the thickness direction. Periodic corrugation and multilayered antireflection coatings were found to engender slight improvements in the efficiency. In contrast, bandgap grading of the CIGS photon-absorbing layer leads to significant enhancement of efficiency, especially when the grading is continuous and nonlinear. However, practical implementation of continuous nonlinear grading is challenging compared to piecewise-homogeneous grading. Hence, for this study, we investigated piecewise-homogeneous approximations of the optimal linear and nonlinear grading profiles, and found that an equivalent efficiency is achieved using piecewise-homogeneous grading. An efficiency of 30.15% is predicted with a three-layered piecewise-homogeneous CIGS photon-absorbing layer. The results will help experimentalists to implement optimal designs for highly efficient CIGS thin-film solar cells.

Influence of Multilayered Polymer Coatings on the Corrosion Behaviour and Microstructures of Al6061-T6 Alloy

The influence of multilayered polymer coatings on the corrosion and microstructural properties of Al6061-T6 alloy was investigated. The electrochemical properties were determined in chloride solution via corrosion tests and electrochemical impedance spectroscopy (EIS) technique at room temperature. The microstructural properties and corrosion mechanism after polarization were studied by scanning electron microscopy (SEM) and atomic force microscopy (AFM)/Kelvin probe force microscopy (KPFM) techniques. From the SEM-AFM/KPFM analysis, the multilayered polymer coated (using polyacrylic acid - PAA) Al6061-T6 alloy experienced a positive shift in the corrosion potential (-0.648V), signifying a possible corrosion protection ability. With a charge transfer resistance of 2.506×10−6 Ω cm2, and lesser corrosion products featured on the coated sample, the present work demonstrates that the deposition of multilayered polymer PAA coating can enhance the corrosion resistance of Al6061-T6 alloy.

Effects of multilayer structure on the high-speed dry-cutting performance of AlCrBN/AlCrN multilayer coatings

To investigate the effects of different structures on the cutting performance of AlCrBN/AlCrN multilayer coatings, AlCrBN/AlCrN coatings with different multilayer structures (single layer, 10 bilayers, and 20 bilayers corresponding to T1 coating, T10 coating, and T20 coating) were synthesized using multi-arc ion plating technology. Grazing incidence X-ray diffraction (GIXRD) and transmission electron microscopy (TEM) results showed that the coatings were mainly composed of fcc-(Cr, Al) N phases located on the (111) and (200) crystal planes. All coatings exhibited a good indentation adhesion to the substrates. The hardness of the T10 coating (32.6 GPa) and T20 coating (31.2 GPa) was significantly higher than that of the T1 coating (28.0 GPa). Annealing experiments show that no phase composition evolution was revealed at 800 °C. High-speed milling tests imply that the milling life of the T10 coating (13 m) and the T20 coating (10 m) was increased by 62.5% and 25.0% compared to the T1 coating (8 m), respectively. In high-speed dry turning tests, the T10 coated tool also showed the longest lifetime (16 mins), an improvement of 23.1% over T1 or T20 coated tools (13 mins). SEM analyses of wear coated tools indicated that a multilayer structure enhanced their resistance to abrasion and adhesion wear, and led to better cutting performance, probably because of their excellent mechanical properties and thermal stability.

A hybrid finite difference level set–implicit mesh discontinuous Galerkin method for multi-layer coating flows

A mathematical model and numerical framework are presented for computing multi-physics multi-layer coating flow dynamics, with applications to the leveling of multi-layer paint films. The algorithm combines finite difference level set methods and high-order accurate sharp-interface implicit mesh discontinuous Galerkin methods to capture a complex set of multi-physics, incorporating Marangoni-driven multi-phase interfacial flow and the transport, mixing, and evaporation of multiple dissolved species. In particular, we develop several numerical methods for this multi-physics problem, including: high-order local discontinuous Galerkin methods for Poisson problems with Robin boundary conditions on implicitly-defined domains, to capture solvent evaporation; finite difference surface gradient methods, to robustly and accurately incorporate Marangoni stresses; and a coupled multi-physics time stepping approach, to incorporate all the different solvers at play including quasi-Newtonian fluid flow. The framework is applicable to an arbitrary number of layers and dissolved species; here, we apply it in a variety of settings, including multi-solvent evaporative paint dynamics, the flow and leveling of multi-layer automobile paint coatings in both 2D and 3D, and an examination of interfacial turbulence within a multi-layer matter cascade. Our results reproduce several phenomena observed in experiment, such as the formation of Marangoni plumes and Bénard cells. We also use the model to study the impact of long-wave deformational surface modes on immersed interfaces as well as the emergence of the final multi-layer film profile.

Interface Amorphization Controls Maximum Wear Resistance of Multinanolayer DLC/WC Coatings.

Multilayer coatings offer significant advantages in protecting materials' surfaces by shielding the underlying materials hierarchically from damage and wear. The layering morphology and structure of multilayer coatings directly affect their wear resistance capacity. Using a systematic set of experiments and molecular dynamics (MD) simulations, we studied the effect of layering thickness on the macroscale wear response of DLC/WC multinanolayer coatings. Our study revealed the existence of a critical bilayer thickness where maximum scratch hardness and wear resistance can be achieved. Our large-scale MD simulations showed that reducing the WC layer thickness to a certain limit increases the scratch hardness due to the confinement of dislocation motion. However, when the thickness of the WC layers falls below 2 nm, the deformation mechanism transitions from the interface-induced dislocation confinement to the interface-mediated amorphization of WC layers, reducing the scratch hardness of the coating. This finding offers a procedure for optimizing the macroscale wear performance of multinanolayer coatings.

Solid lubrication performance of hybrid Ti3C2Tx/MoS2 coatings

MXenes have gained notable attention in tribology due to their excellent wear resistance based on the formation of beneficial tribofilms. However, studies using MXenes as solid lubricants have mainly focused on multi-layer Ti3C2Tx coatings, while little is known about the tribological performance of MXene composites. Therefore, our study aims at scrutinizing and understanding the tribological behavior of MXenes and MXene composites as solid lubricants under reciprocating sliding conditions. Theoretical predictions regarding the resulting interlayer adhesion and coating-substrate adhesion helped to design the hybrid coatings. Multi-layer Ti3C2Tx, molybdenum disulfide (MoS2) and two hybrid coatings using Ti3C2Tx and MoS2 (random mixture and sandwich-like) were spray-coated onto steel substrates with a coating thickness of about 800 nm. Dry sliding tests using a steel ball as counter-body were carried out at room temperature. The coatings’ morphology and formed tribofilms were holistically characterized by scanning and transmission electron microscopy (SEM, TEM) as well as X-ray photoelectron spectroscopy (XPS). Our results demonstrate that both hybrid coatings notably reduce friction and wear, outperforming their respective pure coatings (Ti3C2Tx and MoS2). This is attributed to synergistic effects between Ti3C2Tx and MoS2, with adhesion forces appearing to be the governing mechanism in enhancing the formation of stable tribofilms. Numerical calculations validate our experimental results, verifying that hybrid coatings exhibit low interlayer friction and high adhesion to ferrous substrates. Consequently, our work reveals the potential of Ti3C2Tx/MoS2 hybrid coatings to further optimize friction and wear.

Multi-layered composite coatings with enhanced corrosion and abrasion resistance for industrial flue gas waste heat recovery

The corrosion and abrasion performance of flue gas heat exchangers is a prominent research focus in the field of industrial flue gas waste heat recovery. In this study, we have developed a multi-layered composite coating containing fluorographene and carborundum fillers, which exhibits excellent anti-corrosion and wear-resistant properties. Electrochemical and abrasion experiments demonstrate that the multi-layered composite coating effectively improves both the corrosion resistance and the mechanical properties of the material. The structure and preparation of this multi-layered composite coating provide a novel approach for design and application of advanced coatings for highly corrosive and dusty flue gas waste heat recovery.

Silica-Containing Phosphorus-Based Sol-Gel Finishing to Improve Flame Retardant Performance of Cotton Fabrics

In this paper, the sol-gel technique was used to design hybrid phosphorus-doped silica structures for improving the thermal stability and flame retardancy of cotton fabrics. To this aim, diethylphosphatoethyltriethoxysilane (DPTS) was employed as phosphate alkoxysilane in a multistep procedure that involved multiple layers (from 1 to 6) depositions. The multi-layer coatings were applied by padding using sols containing appropriate molar ratios of the precursor, anhydrous ethanol, catalyst, and hydrochloric acid. Moreover, the synergism P-N on flame retardancy of cotton was assessed by introducing 3-aminopropyltriethoxysilane (APTES) as an N-donor precursor in DPTS sols. The effects of the catalyst during the alkoxide reaction and the silica amount applied by sol-gel treatment on the thermo-oxidative behavior of the treated fabrics were deeply studied. The creation of the silica skeleton on the cotton surface and the interactions between the cellulosic fibres and the doped layer were investigated using FT-IR ATR spectroscopy. Moreover, thermal and thermo-oxidative stability, flammability properties, and combustion behavior of the sol-gel treated cotton fabrics were also studied, proving the effectiveness of the sol-gel coating in the fire protection of the cellulosic substrate.

Multilayer coatings of periodically co-deposited graphene and ag substrate: Improving the electrified friction interface by modifying the strength-ductility combination

Multifunctional and highly adaptable multilayer coatings are considered the future development trend in the field of protective coating design. To enhance wear resistance when subjected to an electric current and to reduce internal stresses, we developed a multilayer structure in which graphene nanoplatelets (GNPs) were deposited within pure silver using a dual electrolyte alternating deposition technique, resulting in the creation of Ag-Ag/GNP multilayer coatings. In this multilayer coating design, the continuous conductive silver layer enhances the overall electrical properties of the coating, and the soft silver layers absorb part of the internal stress in the coating. The deposited GNPs provide crucial structural reinforcement to the coating, thereby improving its mechanical and tribological properties. These coatings were characterized with respect to their structure and mechanical properties using X-ray diffraction, hardness testing, and electronic tensile testing, and their current-carrying tribological performance was studied. Experiments revealed that the crystal structure of single-layer composite coatings changed with increasing GNP content, whereas the multilayer coatings exhibited improved strength and toughness. In current-carrying tribological tests, the multilayer coatings demonstrated significant adaptability to increasing wear depth and current. The wear mechanism of multilayer coatings transitioned from adhesive to abrasive wear. The results indicate that the multilayer coating design effectively enhances friction stability, reduces electrical contact resistance, and decreases wear volume. The findings of this study provide new insights for the design of multilayer structured coatings and will help reduce the loss of rare metals in electrified friction applications.

Global optimization of multilayer dielectric coatings for precision measurements.

We describe the design of optimized multilayer dielectric coatings for precision laser interferometry. By setting up an appropriate cost function and then using a global optimizer to find a minimum in the parameter space, we were able to realize coating designs that meet the design requirements for spectral reflectivity, thermal noise, absorption, and tolerances to coating fabrication errors. We also present application of a Markov-Chain Monte Carlo (MCMC) based parameter estimation algorithm that can infer thicknesses of dielectric layers in a coating, given a measurement of the spectral reflectivity. This technique can be a powerful diagnostic tool for both commercial coating manufacturers, and the community using dielectric mirrors for precision metrology experiments.

High-reliability infrared broadband thin-film polarizing beam splitter with ZnSe compensation layers.

Thin-film polarizing beam splitters (PBSs) fulfill a pivotal role in laser beam splitting, modulation, shaping and isolation. In this study, a high-reliability infrared broadband thin-film PBS was developed. To correct for tensile stress in Ge/YbF3 multilayer coatings, ZnSe compensation layers were incorporated in the multilayer design. The effects of different symmetrical periods on the spectral properties of the infrared PBS were systematically discussed. The infrared PBS operated at 45° and in the long-wave infrared (LWIR) band. Using the percent of optical extrema monitoring (POEM) strategy combined with the high-temperature optical constants (HTOC) of Ge film, the infrared PBS was precisely fabricated on ZnSe substrates. Subsequently, the spectral performance and film reliability of the infrared PBS were carefully characterized. Specifically, the transmittance of p-polarization surpassed 96%, while the extinction ratio exceeded 100:1 within the 10.6 ± 0.15 µm band. The infrared PBS demonstrated commendable environmental reliability, in addition to exhibiting excellent spectral characteristics.