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Coatings, Volume 11, Issue 8 (August 2021) – 142 articles

Cover Story (view full-size image): During the 17th and 18th century, hundreds of valuable musical instruments were made in the workshops of the most important Cremonese violin makers. The unique opportunity to investigate three coeval violins made by Giuseppe Guarneri “del Gesù” in 1734, namely Spagnoletti, Stauffer, and Principe Doria, allowed us to observe similarities and differences among the violins. The non-invasive approach through X-ray fluorescence (XRF) and reflection FTIR spectroscopy was combined with a 3D laser scanner to characterize the chemical composition of the materials used in coating systems and to obtain preliminary valuable information about the design peculiarities adopted by the great violin maker in Cremona. View this paper
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Article
Effect of Deformation on the Microstructure of Cold-Rolled TA2 Alloy after Low-Temperature Nitriding
Coatings 2021, 11(8), 1011; https://doi.org/10.3390/coatings11081011 - 23 Aug 2021
Cited by 1 | Viewed by 674
Abstract
In order to improve the low hardness and poor wear resistance of TA2, this paper proposes a composite process of cold-rolling and low-temperature plasma nitriding with recrystallization. This composite modification process can effectively achieve the dual goals of modifying the matrix structure and [...] Read more.
In order to improve the low hardness and poor wear resistance of TA2, this paper proposes a composite process of cold-rolling and low-temperature plasma nitriding with recrystallization. This composite modification process can effectively achieve the dual goals of modifying the matrix structure and surface of TA2 alloy simultaneously. The cold-rolling experimental results indicate that when the deformation rate increases, the small-sized grains in the sample increase significantly, and the grain orientation changes from TD (transverse direction) to RD (rolling direction) and then to TD. The nitriding experimental results indicate that the {0001} basal surface texture deflected from the TD direction to the RD direction, {10-10} cylindrical texture components gradually increased, and the special orientation phenomenon of cylindrical and conical texture disappeared, it can be seen that an increase in the deformation rate promotes recrystallization. The XRD test results indicate that after low-temperature nitriding, metastable nitriding phase TiN0.26 is formed on the surface of TA2. The SEM morphology of the cross-section shows that a relatively special nitrided zone is formed, and mechanical performance test results indicate the wear resistance and hardness of the alloy increased. Full article
(This article belongs to the Special Issue Surface Engineering of C/N/O Functionalized Materials)
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Article
Fabrication of Mg Coating on PEEK and Antibacterial Evaluation for Bone Application
Coatings 2021, 11(8), 1010; https://doi.org/10.3390/coatings11081010 - 23 Aug 2021
Cited by 2 | Viewed by 784
Abstract
Polyetheretherketone (PEEK) is an alternative biomedical polymer material to traditional metal and ceramic biomaterials. However, as a bioinert material, its wide application in the medical field is seriously restricted due to its lack of bioactivity. In this research, pure Mg was successfully deposited [...] Read more.
Polyetheretherketone (PEEK) is an alternative biomedical polymer material to traditional metal and ceramic biomaterials. However, as a bioinert material, its wide application in the medical field is seriously restricted due to its lack of bioactivity. In this research, pure Mg was successfully deposited on a PEEK substrate by vapor deposition to improve the antibacterial properties of PEEK implants. The morphology and elemental composition of the coating were characterized by scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS). The higher the deposition temperature, the larger the Mg particle size. The Mg coating possesses a hydrophilic surface and a higher surface free energy that create its good biocompatibility. The Mg coating on a PEEK substrate withstands up to 56 days’ immersion. The antibacterial test showed that the antibacterial rate of coated PEEK is 99%. Mg-coated PEEK demonstrates promising antibacterial properties. Full article
(This article belongs to the Special Issue Biofunctional Surfaces and Coatings of Biomaterials)
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Article
Analytical Simulation for Magnetohydrodynamic Maxwell Fluid Flow Past an Exponentially Stretching Surface with First-Order Velocity Slip Condition
Coatings 2021, 11(8), 1009; https://doi.org/10.3390/coatings11081009 - 23 Aug 2021
Cited by 5 | Viewed by 1125
Abstract
The study of fluid flow upon an exponentially stretching surface has significant importance due to its applications in technological phenomena at the industrial level. These applications include condensing process of fluid film, heat exchanger processes, extrusion of plastic sheet in aerodynamics, cooling process [...] Read more.
The study of fluid flow upon an exponentially stretching surface has significant importance due to its applications in technological phenomena at the industrial level. These applications include condensing process of fluid film, heat exchanger processes, extrusion of plastic sheet in aerodynamics, cooling process of metal sheet, and growth of crystals, etc. Keeping in view all these applications, in this paper, we have discussed the magnetohydrodynamic flow of Maxwell fluid past an exponentially stretching sheet. The stretching surface is considered to be slippery by imposing the velocity slip condition. The magnetic field impact is taken into consideration. Furthermore, heat radiation, Joule heating, Brownian motion, and thermophoresis are also considered. The modeled system is reduced to ordinary differential equations with the help of similarity variables. For the analytical solution, we have used the homotopy analysis method. Furthermore, HAM is compared with the shooting method and found to be in great agreement. The squared residual error of the fluid flow problem at 15th order of approximations for Newtonian and non-Newtonian cases has been investigated. It is found that the fluid flow problem converges quickly for the case of non-Newtonian fluid as compared to Newtonian fluid. In addition, the velocity profile increases while the thermal and concentration profiles reduce with greater values of Darcy number. The thermal profile is the increasing function of the Brownian motion parameter and Eckert number whereas the concentration profile is the reducing function of the Brownian motion parameter and Eckert number. With the augmentation in Darcy number, the permeability strength of porous medium increases which concludes the increasing conduct of thermal and mass transportation. Full article
(This article belongs to the Special Issue Nanofluidics: Interfacial Transport Phenomena)
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Article
Hierarchical Two-Dimensional Layered Double Hydroxide Coated Polydopamine Nanocarriers for Combined Chemodynamic and Photothermal Tumor Therapy
Coatings 2021, 11(8), 1008; https://doi.org/10.3390/coatings11081008 - 23 Aug 2021
Cited by 3 | Viewed by 1178
Abstract
The combination of chemodynamic therapy (CDT) and photothermal therapy (PTT) has proven to be successful in combating the challenges associated with cancer therapy. A combination of these therapies can maximize the benefits of each therapeutic modality through endogenous reduction-oxidation (redox) reaction and external [...] Read more.
The combination of chemodynamic therapy (CDT) and photothermal therapy (PTT) has proven to be successful in combating the challenges associated with cancer therapy. A combination of these therapies can maximize the benefits of each therapeutic modality through endogenous reduction-oxidation (redox) reaction and external laser power induction. In the current work, we have designed a copper-aluminum layered double hydroxide (CuAl-LDH) loaded doxorubicin (DOX) by a co-precipitation method; the surface was coated with polydopamine (PDA). The synthesized [email protected]@PDA nanocarrier (NC) served as a Fenton-like catalyst with photothermal properties. It is well known that metal ion incorporated NCs can induce intracellular depletion of reduced glutathione (GSH) levels along with the reduction of Cu2+ to Cu+. The Cu+ ions in turn react with DOX leading to the generation of intracellular hydrogen peroxide (H2O2) molecules to produce the highly toxic hydroxyl radicals (•OH) through a Fenton-like reaction. The enhanced absorption of [email protected]@PDA at 810 nm, greatly improved the photothermal efficiency in comparison with bare CuAl-LDH and [email protected] In vitro studies revealed the tremendous CDT/PTT efficacy of [email protected]@PDA in suppressing A549 cancer cells. Furthermore, reactive oxygen species (ROS) assays and intracellular levels of various ROS cascade biomolecules support our findings in the efficient destruction of cancer cells through synergistic CDT/PTT therapy. Full article
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Article
Hydrostatic Bearing Characteristics Investigation of a Spherical Piston Pair with an Annular Orifice Damper in Spherical Pump
Coatings 2021, 11(8), 1007; https://doi.org/10.3390/coatings11081007 - 23 Aug 2021
Viewed by 649
Abstract
The spherical pump is a totally new hydraulic concept, with spherical piston and hydrostatic bearing, in order to eliminate the direct contact between the piston and cylinder cover. In this paper, the governing Reynolds equation under spherical coordinates has been solved and the [...] Read more.
The spherical pump is a totally new hydraulic concept, with spherical piston and hydrostatic bearing, in order to eliminate the direct contact between the piston and cylinder cover. In this paper, the governing Reynolds equation under spherical coordinates has been solved and the hydrostatic bearing characteristics are systematically investigated. The operating sensitivities of the proposed spherical hydrostatic bearing, with respect to the piston radius, film beginning angle, film ending angle, film thickness, and temperature, are studied. The load carrying capacity, pressure drop coefficient, stiffness variation of the lubricating films, leakage properties, and leakage flow rates are comprehensively discussed. The related findings provide a fundamental basis for designing the high-efficient spherical pump under multiple operating conditions. Besides, these related results and mechanisms can also be utilized to design and improve other kinds of annular orifice damper spherical hydraulic bearing systems. Full article
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Review
Review on Surface Treatment for Implant Infection via Gentamicin and Antibiotic Releasing Coatings
Coatings 2021, 11(8), 1006; https://doi.org/10.3390/coatings11081006 - 23 Aug 2021
Cited by 2 | Viewed by 1066
Abstract
Surface treatment of metallic implants plays a crucial role in orthopedics and orthodontics. Metallic implants produce side-effects such as physical, chemical/electro-chemical irritations, oligodynamic/catalytic and carcinogenic effects. These effects cause bacterial infections and account for huge medical expenses. Treatment for these infections comprises repeated [...] Read more.
Surface treatment of metallic implants plays a crucial role in orthopedics and orthodontics. Metallic implants produce side-effects such as physical, chemical/electro-chemical irritations, oligodynamic/catalytic and carcinogenic effects. These effects cause bacterial infections and account for huge medical expenses. Treatment for these infections comprises repeated radical debridement, replacement of the implant device and intravenous or oral injection antibiotics. Infection is due to the presence of bacteria in the patient or the surrounding environment. The antibiotic-based medication prevents prophylaxis against bacterial colonization, which is an emphatic method that may otherwise be catastrophic to a patient. Therefore, preventive measures are essential. A coating process was developed with its drug infusion and effect opposing biofilms. Modification in the medical implant surface reduces the adhesion of bacterial and biofilms, the reason behind bacterial attachment. Other polymer-based and nanoparticle-based carriers are used to resolve implant infections. Therefore, using an implant coating is a better approach to prevent infection due to biofilm. Full article
(This article belongs to the Special Issue Recent Advances in Bio-Composite Coatings)
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Article
Preparation and Application of Polyurethane Coating Material Based on Epoxycyclohexane-Epoxychloropropane Protective for Paper
Coatings 2021, 11(8), 1005; https://doi.org/10.3390/coatings11081005 - 23 Aug 2021
Cited by 1 | Viewed by 734
Abstract
Paper historic relics are of great value to research and preserve. However, with the change of environment, paper cultural relics are constantly aging and damaged. Therefore, the reinforcement and conservation of the paper is an important topic in the field of cultural relics [...] Read more.
Paper historic relics are of great value to research and preserve. However, with the change of environment, paper cultural relics are constantly aging and damaged. Therefore, the reinforcement and conservation of the paper is an important topic in the field of cultural relics protection; thus, it is a crucial and arduous task to discover high-performance protective materials. The coating reinforcement method is a kind of commonsense method to strengthen the paper. Additionally, it is key to select appropriate reinforcing resins. Polyurethane has influence on the improvement of paper strength, stability, and appearance. The epoxycyclohexane-epoxychloropropane polyether polyol was prepared with epoxycyclohexane and epoxychloropropane as materials, glycerol as the initiator, boron trifluoride diethyl etherate as the catalyst, and dichloromethane as the solvent. Infrared (IR) spectroscopy as well as proton nuclear magnetic resonance (1HNMR) spectroscopy were adopted to characterize the structure of the synthetic copolyether. Then, polyurethane based on epoxycyclohexane-epoxychloropropane was prepared by the synthetic copolyether reacting with hexamethylene diisocyanate (HDI) trimer. The effect of the mass concentration of polyurethane on the tensile strength, elongation, folding endurance, and the tearing strength of paper samples were tested. When 10% polyurethane solution was applied to paper, not only were the mechanical properties greatly improved, but the gloss and brightness also changed slightly, which conformed to the principle of “repair as old”. The above results indicate that the synthetic polyurethane combines the advantages of epoxycyclohexane-poxychloropropane polyether polyol along with polyurethane, presenting excellent properties in paper reinforcement or conservation. Full article
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Article
Computational Fluid Dynamics Analysis of Particle Deposition Induced by a Showerhead Electrode in a Capacitively Coupled Plasma Reactor
Coatings 2021, 11(8), 1004; https://doi.org/10.3390/coatings11081004 - 23 Aug 2021
Cited by 1 | Viewed by 862
Abstract
Defect formation in the deposition of thin films for semiconductors is not yet sufficiently understood. In a showerhead-type capacitively coupled plasma (CCP) deposition reactor, the showerhead acts as both the gas distributor and the electrode. We used computational fluid dynamics to investigate ways [...] Read more.
Defect formation in the deposition of thin films for semiconductors is not yet sufficiently understood. In a showerhead-type capacitively coupled plasma (CCP) deposition reactor, the showerhead acts as both the gas distributor and the electrode. We used computational fluid dynamics to investigate ways to enhance cleanliness by analyzing the particle deposition induced by the showerhead electrode in a CCP reactor. We analyzed particle transport phenomena using a three-dimensional complex geometry, whereas SiH4/He discharges were simulated in a two-dimensional simplified geometry. The process volume was located between the RF-powered showerhead and the grounded heater. We demonstrated that the efficient transportation of particles with a radius exceeding 1 μm onto the heater is facilitated by acceleration inside the showerhead holes. Because the available space in which to flow inside the showerhead is constricted, high gas velocities within the showerhead holes can accelerate particles and lead to inertia-enhanced particle deposition. The effect of the electrode spacing on the deposition of particles generated in plasma discharges was also investigated. Smaller electrode spacing promoted the deposition of particles fed from the showerhead on the heater, whereas larger electrode spacing facilitated the deposition of particles generated in plasma discharges on the heater. Full article
(This article belongs to the Special Issue Surface Modification by Plasma-Based Processes)
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Article
Modeling and Simulation of Vacuum Low Pressure Carburizing Process in Gear Steel
Coatings 2021, 11(8), 1003; https://doi.org/10.3390/coatings11081003 - 23 Aug 2021
Cited by 2 | Viewed by 903
Abstract
A combination of simulation and experimental approaches to optimize the vacuum carburizing process is necessary to replace the costly experimental trial-and-error method in time and resources. In order to accurately predict the microstructure evolution and mechanical properties of the vacuum carburizing process, a [...] Read more.
A combination of simulation and experimental approaches to optimize the vacuum carburizing process is necessary to replace the costly experimental trial-and-error method in time and resources. In order to accurately predict the microstructure evolution and mechanical properties of the vacuum carburizing process, a multi-field multi-scale coupled model considering the interaction of temperature, diffusion, phase transformation, and stress was established. Meanwhile, the improved model is combined with the heat treatment software COSMAP to realize the simulation of the low-pressure vacuum carburizing process. The low-pressure vacuum carburizing process of 20CrMo gear steel was simulated by COSMAP and compared with the experimental results to verify the model. The results indicated that the model could quantitatively obtain the carbon concentration distribution, Fe-C phase fraction, and hardness distribution. It can be found that the carbon content gradually decreased from the surface to the center. The surface carbon concentration is relatively high only after the carburizing stage. With the increase in diffusion time, the surface carbon concentration decreases, and the carburized layer depth increases. The simulated surface carbon concentration results and experimental results are in good agreement. However, there is an error between calculations and observations for the depth of the carburized layer. The error between simulation and experiment of the depth of carburized layer is less than 6%. The simulated surface hardness is 34 HV lower than the experimental surface hardness. The error of surface hardness is less than 5%, which indicates that the simulation results are reliable. Furthermore, vacuum carburizing processes with different diffusion times were simulated to achieve the carburizing target under specific requirements. The results demonstrated that the optimum process parameters are a carburizing time of 42 min and a diffusion time of 105 min. This provides reference and guidance for the development and optimization of the vacuum carburizing process. Full article
(This article belongs to the Special Issue Surface Modification and Functionalization for Advanced Materials)
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Article
The Relationship between Cyclic Multi-Scale Self-Organized Processes and Wear-Induced Surface Phenomena under Severe Tribological Conditions Associated with Buildup Edge Formation
Coatings 2021, 11(8), 1002; https://doi.org/10.3390/coatings11081002 - 22 Aug 2021
Viewed by 959
Abstract
This paper presents experimental investigations of various interrelated multi-scale cyclic and temporal processes that occur on the frictional surface under severe tribological conditions during cutting with buildup edge formation. The results of the finite element modeling of the stress/temperature profiles on the friction [...] Read more.
This paper presents experimental investigations of various interrelated multi-scale cyclic and temporal processes that occur on the frictional surface under severe tribological conditions during cutting with buildup edge formation. The results of the finite element modeling of the stress/temperature profiles on the friction surface are laid out. This study was performed on a multilayer coating with the top alumina ceramic layer deposited by CVD (chemical vapor deposition) on a WC/Co carbide substrate. A detailed analysis of the wear process was conducted by 3D wear evaluation, scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM/EDS) and electron backscattered diffraction (EBSD), as well as X-ray photoelectron spectroscopy (XPS) methods. The following cyclic phenomena were observed on the surface of the tribo-system during the experiments: a repetitive formation and breakage of buildups (a self-organized critical process) and a periodical increase and decrease in the amount of thermal barrier tribo-films with a sapphire structure (which is a self-organization process). These two processes are interrelated with the accompanying progression of cratering, eventually resulting in the catastrophic failure of the entire tribo-system. Full article
(This article belongs to the Special Issue Coatings for Cutting and Stamping Tools: Recent Advances)
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Article
Low-Temperature Large-Area Zinc Oxide Coating Prepared by Atmospheric Microplasma-Assisted Ultrasonic Spray Pyrolysis
Coatings 2021, 11(8), 1001; https://doi.org/10.3390/coatings11081001 - 22 Aug 2021
Cited by 1 | Viewed by 908
Abstract
Zinc oxide (ZnO) coatings have various unique properties and are often used in applications such as transparent conductive films in photovoltaic systems. This study developed an atmospheric-pressure microplasma-enhanced ultrasonic spray pyrolysis system, which can prepare large-area ZnO coatings at low temperatures under atmospheric-pressure [...] Read more.
Zinc oxide (ZnO) coatings have various unique properties and are often used in applications such as transparent conductive films in photovoltaic systems. This study developed an atmospheric-pressure microplasma-enhanced ultrasonic spray pyrolysis system, which can prepare large-area ZnO coatings at low temperatures under atmospheric-pressure conditions. The addition of an atmospheric-pressure microplasma-assisted process helped improve the preparation of ZnO coatings under atmospheric conditions, compared to using a conventional ultrasonic spray pyrolysis process, effectively reducing the preparation temperature to 350 °C. A program-controlled three-axis platform demonstrated its potential for the large-scale synthesis of ZnO coatings. The X-ray diffraction results showed that the ZnO coatings prepared by ultrasonic spray pyrolysis exhibited (002) preferred growth orientation and had a visible-light penetration rate of more than 80%. After vacuum treatment, the ZnO reached a 1.0 × 10−3 Ωcm resistivity and a transmittance of 82%. The tribology behavior of ZnO showed that the vacuum-annealed coating had a low degree of wear and a low coefficient of friction as the uniformly distributed and dense coating increased its load capacity. Full article
(This article belongs to the Special Issue Intelligent Tribological and Functional Coatings)
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Article
Sound-Absorption Performance and Fractal Dimension Feature of Kapok Fibre/Polycaprolactone Composites
Coatings 2021, 11(8), 1000; https://doi.org/10.3390/coatings11081000 - 22 Aug 2021
Cited by 2 | Viewed by 763
Abstract
This article introduces a kind of composite material made of kapok fibre and polycaprolactone by the hot-pressing method. The effects of volume density, mass fraction of kapok fibre, and thickness on the sound-absorption performance of composites were researched using a single-factor experiment. The [...] Read more.
This article introduces a kind of composite material made of kapok fibre and polycaprolactone by the hot-pressing method. The effects of volume density, mass fraction of kapok fibre, and thickness on the sound-absorption performance of composites were researched using a single-factor experiment. The sound-absorption performance of the composites was investigated by the transfer function method. Under the optimal process parameters, when the density of the composite material was 0.172 g/cm3, the mass fraction of kapok was 40%, and the thickness was 2 cm, the composite material reached the maximum sound-absorption coefficient of 0.830, and when the sound-absorption frequency was 6300 Hz, the average sound-absorption coefficient was 0.520, and the sound-absorption band was wide. This research used the box dimension method to calculate composites’ fractal dimensions by using the Matlab program based on the fractal theory. It analysed the relationships between fractal dimension and volume density, fractal dimension and mass fraction of kapok fibre, and fractal dimension and thickness. The quantitative relations between fractal dimension and maximum sound-absorption coefficient, fractal dimension, and resonant sound-absorption frequency were derived, which provided a theoretical basis for studying sound-absorption performance. The results showed that kapok fibre/polycaprolactone composites had strong fractal characteristics, which had important guiding significance for the sound-absorption performance of kapok fibre composites. Full article
(This article belongs to the Special Issue Natural Fiber Based Composites)
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Article
Enhancement of Cleanliness and Deposition Rate by Understanding the Multiple Roles of the Showerhead Electrode in a Capacitively Coupled Plasma Reactor
Coatings 2021, 11(8), 999; https://doi.org/10.3390/coatings11080999 - 21 Aug 2021
Cited by 2 | Viewed by 698
Abstract
Increasing the productivity of a showerhead-type capacitively coupled plasma (CCP) reactor requires an in-depth understanding of various physical phenomena related to the showerhead, which is not only responsible for gas distribution, but also acts as the electrode. Thus, we investigated how to enhance [...] Read more.
Increasing the productivity of a showerhead-type capacitively coupled plasma (CCP) reactor requires an in-depth understanding of various physical phenomena related to the showerhead, which is not only responsible for gas distribution, but also acts as the electrode. Thus, we investigated how to enhance the cleanliness and deposition rate by studying the multiple roles of the showerhead electrode in a CCP reactor. We analyzed the gas transport in a three-dimensional complex geometry, and the SiH4/He discharges were simulated in a two-dimensional simplified geometry. The process volume was installed between the showerhead electrode (radio frequency powered) and the heater electrode (grounded). Our aim of research was to determine the extent to which the heated showerhead contributed to increasing the deposition rate and to reducing the size of the large particles generated during processing. The temperature of the showerhead was increased to experimentally measure the number of particles transported onto the heater to demonstrate the effects thereof on the decrease in contamination. The number of particles larger than 45 nm decreased by approximately 93% when the showerhead temperature increased from 373 to 553 K. Full article
(This article belongs to the Special Issue Surface Modification by Plasma-Based Processes)
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Article
Multi-Objective Optimization of MIG Welding and Preheat Parameters for 6061-T6 Al Alloy T-Joints Using Artificial Neural Networks Based on FEM
Coatings 2021, 11(8), 998; https://doi.org/10.3390/coatings11080998 - 21 Aug 2021
Cited by 1 | Viewed by 1037
Abstract
To control the welding residual stress and deformation of metal inert gas (MIG) welding, the influence of welding process parameters and preheat parameters (welding speed, heat input, preheat temperature, and preheat area) is discussed, and a prediction model is established to select the [...] Read more.
To control the welding residual stress and deformation of metal inert gas (MIG) welding, the influence of welding process parameters and preheat parameters (welding speed, heat input, preheat temperature, and preheat area) is discussed, and a prediction model is established to select the optimal combination of process parameters. Thermomechanical numerical analysis was performed to obtain the residual welding deformation and stress according to a 100 × 150 × 50 × 4 mm aluminum alloy 6061-T6 T-joint. Owing to the complexity of the welding process, an optimal Latin hypercube sampling (OLHS) method was adopted for sampling with uniformity and stratification. Analysis of variance (ANOVA) was used to find the influence degree of welding speed (7.5–9 mm/s), heat input (1500–1700 W), preheat temperature (80–125 °C), and preheat area (12–36 mm). The range of research parameters are according to the material, welding method, thickness of the welding plate, and welding procedure specification. Artificial neural network (ANN) and multi-objective particle swarm optimization (MOPSO) was combined to find the effective parameters to minimize welding deformation and stress. The results showed that preheat temperature and welding speed had the greatest effect on the minimization of welding residual deformation and stress, followed by the preheat area, respectively. The Pareto front was obtained by using the MOPSO algorithm with ε-dominance. The welding residual deformation and stress are the minimum at the same time, when the welding parameters are selected as preheating temperature 85 °C and preheating area 12 mm, welding speed is 8.8 mm/s and heat input is 1535 W, respectively. The optimization results were validated by the finite element (FE) method. The error between the FE results and the Pareto optimal compromise solutions is less than 12.5%. The optimum solutions in the Pareto front can be chosen by designers according to actual demand. Full article
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Article
Study on Laser Surface Hardening Behavior of 42CrMo Press Brake Die
Coatings 2021, 11(8), 997; https://doi.org/10.3390/coatings11080997 - 21 Aug 2021
Viewed by 610
Abstract
Laser surface hardening is a promising surface technology to enhance the properties of surfaces. This technology was used on the 42CrMo press brake die. Its hardening behavior was investigated by using scanning electron microscopy and electron backscattering diffraction. The results indicated that the [...] Read more.
Laser surface hardening is a promising surface technology to enhance the properties of surfaces. This technology was used on the 42CrMo press brake die. Its hardening behavior was investigated by using scanning electron microscopy and electron backscattering diffraction. The results indicated that the martensite in the hardening zone was significantly finer than that in the substrate. There were many low-angle grain boundaries in the martensite of the hardening zone, and the kernel average misorientation and grain orientation spread in the hardening zone grains were obviously greater, which further improved the hardness of the hardening zone, especially near the substrate. The microstructure and the properties of the blade maintained excellent uniformity with treatment by single-pass laser surface hardening with a spot size of 2 mm, scanning speed of 1800 mm/min, and power of 2200 W. The hardness of the hardening zone was 1.6 times higher than that of the base material, and the thickness of the hardening zone reached 1.05 mm. Full article
(This article belongs to the Special Issue Surface Modification and Functionalization for Advanced Materials)
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Article
A Note on the Influence of Smectite Coating on the Coefficient of Restitution of Natural Sand Particles Impacting Granitic Blocks
Coatings 2021, 11(8), 996; https://doi.org/10.3390/coatings11080996 - 20 Aug 2021
Cited by 4 | Viewed by 829
Abstract
The study of the collision behavior of solid objects has received a significant amount of research in various fields such as industrial applications of powders and grains, impacts of proppants and between proppant and rocks during hydraulic fracturing, and the study of debris [...] Read more.
The study of the collision behavior of solid objects has received a significant amount of research in various fields such as industrial applications of powders and grains, impacts of proppants and between proppant and rocks during hydraulic fracturing, and the study of debris flows and avalanches and the interactions of landslide materials with protective barriers. This problem has predominantly been studied through the coefficient of restitution (COR), which is computed from the dropping and rebound paths of particles; its value corresponds to 1 for perfectly elastic impacts and 0 for perfectly plastic impacts (i.e., at the collision there is no rebound of the particle). Often, the colliding particles (or particle–block systems) are not perfectly clean, and there is debris (or dust) on their surfaces, forming a coating, which is a highly possible scenario in the debris flows of natural particles and fragments; however, the topic of the influence of natural coatings on the surfaces of particles on the collision behavior of particle–block systems has been largely overlooked. Thus, the present study attempts to provide preliminary results with respect to the influence of natural coating on the surfaces of sand grains in the COR values of grain–block systems using a stiff granitic block as an analogue wall. Montmorillonite powder, which belongs to the smectite clay group, was used and a sample preparation method was standardized to provide a specific amount of clay coating on the surfaces of the sand grains. The results from the study showed a significant influence of the smectite coating in the COR values of the grain–block systems, which was predominantly attributed to the dissipation of energy at the collision moment because of the compression of the soft coating of microparticles. Additionally, the method of analysis for calculating the COR values based on one and two high-speed cameras was explored, as the impacts of natural grains involve deviations from the vertical, which influences the rebound paths. Thus, a sensitivity analysis was performed investigating the differences in the COR values in two-dimensional and three-dimensional analysis of the impact tests. Full article
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Article
Tailoring Al–Li Alloy Surface Wettability with a Femtosecond Laser and Its Effect on Bonding Performance
Coatings 2021, 11(8), 995; https://doi.org/10.3390/coatings11080995 - 20 Aug 2021
Viewed by 742
Abstract
In this study, a femtosecond laser was used to pretreat the surface of the Al–Li alloy, the surface micromorphology, roughness, contact angle, and surface wettability of which were adjusted by changing the laser scanning speed, and the sample was bonded into a single [...] Read more.
In this study, a femtosecond laser was used to pretreat the surface of the Al–Li alloy, the surface micromorphology, roughness, contact angle, and surface wettability of which were adjusted by changing the laser scanning speed, and the sample was bonded into a single joint with polyether ether ketone (PEEK) adhesive. The mechanism of the laser surface treatment affecting the bonding strength of the Al–Li alloy was explored through tensile and shear experiments. The results indicated that optimizing the laser surface treatment parameters could change the surface roughness and surface micromorphology of the Al–Li alloy, so as to change its surface free energy and bonding strength. Compared with the untreated sample, the bonding strength of the Al–Li alloy increased by 81%, 95%, 107%, 91%, and 78% under the treatment of laser scanning at 25, 20, 15, 10, and 5 mm/s, respectively. As a whole, femtosecond laser etching of the Al–Li alloy surface had an important influence on its wettability and bonding performance. Full article
(This article belongs to the Special Issue Laser Surface Engineering)
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Article
Effect of Lime Stabilization and Partial Clinoptilolite Zeolite Replacement on the Behavior of a Silt-Sized Low-Plasticity Soil Subjected to Freezing–Thawing Cycles
Coatings 2021, 11(8), 994; https://doi.org/10.3390/coatings11080994 - 20 Aug 2021
Cited by 6 | Viewed by 707
Abstract
Soil stabilization, through either physical or chemical techniques of coating-cementation development, is a commonly adopted practice in geotechnical and transportation engineering projects used to strengthen soils and mitigate negative geo-environmental impacts. This can be particularly important in enhancing the mechanical properties of soils [...] Read more.
Soil stabilization, through either physical or chemical techniques of coating-cementation development, is a commonly adopted practice in geotechnical and transportation engineering projects used to strengthen soils and mitigate negative geo-environmental impacts. This can be particularly important in enhancing the mechanical properties of soils which are prone to degradation of their response because of freezing and thawing actions. It was attempted in this research study to examine the effect of lime–zeolite stabilization on the behavior of a silt-sized natural soil of low plasticity, by performing standard compaction tests as well as unconfined compressive experiments evaluating the strength of the composite samples. The natural soil mixed with various contents of lime and zeolite partial replacement was subjected to consecutive freezing and thawing cycles. The results from the study showed significant improvement of the mechanical performance of the treated soil when mixed with lime partially replaced with zeolite in terms of strength and durability and, based on scanning electron microscopic images, additional insights were attempted to be obtained on the microstructure of the specimens subjected to temperature changes. Full article
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Article
Ion and Radical Characteristics (Mass/Energy Distribution) of a Capacitively Coupled Plasma Source Using Plasma Process Gases (CxFy)
Coatings 2021, 11(8), 993; https://doi.org/10.3390/coatings11080993 - 20 Aug 2021
Viewed by 667
Abstract
We constructed a capacitively coupled plasma (CCP) source and installed various diagnostic tools to perform process diagnosis using a plasma process gas (CxFy). We obtained the energy and mass distributions of the ions and radicals from Ar, C4F8/Ar, and [...] Read more.
We constructed a capacitively coupled plasma (CCP) source and installed various diagnostic tools to perform process diagnosis using a plasma process gas (CxFy). We obtained the energy and mass distributions of the ions and radicals from Ar, C4F8/Ar, and C4F6/Ar plasmas. The energy distribution of the ions incident on the substrate was controlled using the self-bias voltage, and the ion energy was found to be inversely proportional to the mass. The measured species and density of the ions and radicals can help understand plasma process results as they provide information about the ions and radicals incident on the substrate. Full article
(This article belongs to the Special Issue Surface Modification by Plasma-Based Processes)
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Article
The Relationship between Coating Property and Solid Particle Erosion Resistance of AIP-Deposited TiAlN Coatings with Different Al Contents
Coatings 2021, 11(8), 992; https://doi.org/10.3390/coatings11080992 - 20 Aug 2021
Cited by 1 | Viewed by 710
Abstract
TiAlN coatings with different Al ratios were deposited by the cathodic arc ion plating (AIP) method, and the relationship between solid particle erosion resistance and structural, mechanical properties was investigated by a micro slurry-jet erosion (MSE) test. The crystal structure of TiAlN coating [...] Read more.
TiAlN coatings with different Al ratios were deposited by the cathodic arc ion plating (AIP) method, and the relationship between solid particle erosion resistance and structural, mechanical properties was investigated by a micro slurry-jet erosion (MSE) test. The crystal structure of TiAlN coating changes depending on the Al ratio. The coating shows a B1 single cubic phase between the Al ratio of 0 and 0.58; above this ratio, formation of a B4 hexagonal phase is observed. The mechanical properties such as hardness and Young’s modulus of the TiAlN coating also depend on the Al ratio and the crystal structure. The erosion rate decreases by increasing the Al ratio up to 0.58, as the coating is a cubic single phase. The TiAlN coating shows the lowest erosion rate at an Al ratio of 0.58. The erosion rate increases drastically as the crystalline phase changes from the B1 cubic to B4 hexagonal phase at the Al ratio of more than 0.58. The change in erosion rate is also discussed in connection with mechanical properties such as erodent particle hardness to coating hardness ratio and coating hardness to Young’s modulus ratio. Full article
(This article belongs to the Special Issue Hard Coatings for Surface Engineering Solutions)
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Article
Improvement of the Tribological Properties of Alumina Coatings by Zirconia Addition
Coatings 2021, 11(8), 991; https://doi.org/10.3390/coatings11080991 - 20 Aug 2021
Viewed by 753
Abstract
Al2O3 and Al2O3-ZrO2 coatings were deposited on stainless steel using atmospheric plasma spraying. The influence of arc current and zirconia addition on the surface morphology of the coating, phase composition and tribological properties under dry [...] Read more.
Al2O3 and Al2O3-ZrO2 coatings were deposited on stainless steel using atmospheric plasma spraying. The influence of arc current and zirconia addition on the surface morphology of the coating, phase composition and tribological properties under dry sliding conditions were investigated. The addition of zirconia reduced the surface roughness of the coatings. The X-ray diffraction measurements indicated that the Al2O3 coatings were composed of β-Al2O3, α-Al2O3, and γ-Al2O3 phases. The addition of zirconia led to the formation of tetragonal and monoclinic phases of zirconia in the as-sprayed coatings. The friction coefficients of Al2O3 and Al2O3-ZrO2 coatings were similar and varied in the range of 0.72–0.75. The specific wear rates of the as-sprayed coatings were reduced with the increase of arc current. It was obtained that the wear rates of the Al2O3-ZrO2 coatings were at least three times lower compared to Al2O3 coatings. Full article
(This article belongs to the Section Ceramic Coatings and Engineering Technology)
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Review
The Use of Nanocellulose in Edible Coatings for the Preservation of Perishable Fruits and Vegetables
Coatings 2021, 11(8), 990; https://doi.org/10.3390/coatings11080990 - 19 Aug 2021
Cited by 3 | Viewed by 1244
Abstract
The usage of edible coatings (ECs) represents an emerging approach for extending the shelf life of highly perishable foods, such as fresh and fresh-cut fruits and vegetables. This review addresses, in particular, the use of reinforcing agents in film-forming solutions to tailor the [...] Read more.
The usage of edible coatings (ECs) represents an emerging approach for extending the shelf life of highly perishable foods, such as fresh and fresh-cut fruits and vegetables. This review addresses, in particular, the use of reinforcing agents in film-forming solutions to tailor the physicochemical, mechanical and antimicrobial properties of composite coatings. In this scenario, this review summarizes the available data on the various forms of nanocellulose (NC) typically used in ECs, focusing on the impact of their origin and chemical or physical treatments on their structural properties (morphology and shape, dimension and crystallinity) and their functionality. Moreover, this review also describes the deposition techniques of composite ECs, with details on the food engineering principles in the application methods and formulation optimization. The critical analysis of the recent advances in NC-based ECs contributes to a better understanding of the impact of the incorporation of complex nanoparticles in polymeric matrices on the enhancement of coating properties, as well as on the increase of shelf life and the quality of fruits and vegetables. Full article
(This article belongs to the Special Issue Biopolymer Coatings for Food Packaging Applications)
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Article
Features and Functionality of the Optical Interference Meter for Measurement of Surface Displacements of Control Objects
Coatings 2021, 11(8), 989; https://doi.org/10.3390/coatings11080989 - 19 Aug 2021
Viewed by 554
Abstract
This article presents in detail the methodology and results of test studies of the functionality of a prospective optical setup for measuring the surface linear displacements of control objects, developed on the basis of a new interference measurement method, namely the “luminous point” [...] Read more.
This article presents in detail the methodology and results of test studies of the functionality of a prospective optical setup for measuring the surface linear displacements of control objects, developed on the basis of a new interference measurement method, namely the “luminous point” method. The dependencies of the changes in intensity of the optical field of interference patterns are obtained, characterizing the features of the functional capabilities of the setup. It is experimentally confirmed that with significant changes in the angle of incidence of radiation on the surface of the control object, the sensitivity of the investigated setup does not change. The noted research results are most appropriate for use in the development of new contactless optical setups for measuring the displacements of the surfaces of control objects, and for use in various experimental works in the processes of the creation and production of machines and equipment, as well as in the diagnosis of the state of structural materials and power elements of machines and equipment during operation. Full article
(This article belongs to the Special Issue Micro-Nano Optics and Its Applications)
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Article
Corrosion Behavior of Amorphous Sol–Gel TiO2–ZrO2 Nano Thickness Film on Stainless Steel
Coatings 2021, 11(8), 988; https://doi.org/10.3390/coatings11080988 - 19 Aug 2021
Cited by 3 | Viewed by 1106
Abstract
In this work, a single-layer TiO2–ZrO2 thin film is deposited on the AISI 316L austenitic stainless steel by the sol–gel process and the dip coating method to improve its corrosion resistance properties. For the sol preparation, titanium isopropoxide and zirconium [...] Read more.
In this work, a single-layer TiO2–ZrO2 thin film is deposited on the AISI 316L austenitic stainless steel by the sol–gel process and the dip coating method to improve its corrosion resistance properties. For the sol preparation, titanium isopropoxide and zirconium butoxide are used as the precursors, yttrium acetate hydrate is used for the ZrO2 stabilization, i-propanol as the solvent, nitric acid as the catalyst, acetylacetone as the chelating agent, and the distilled water for the hydrolysis. The deposited films are annealed at 400 °C or 600 °C. Morphology and phase composition of the sol–gel TiO2–ZrO2 films and powders are analyzed by scanning electron microscopy (SEM) equipped with EDX detector and X-ray diffraction (XRD), respectively. The thickness of the sol–gel TiO2–ZrO2 films deposited on the stainless steel is determined by glow discharge optical emission spectrometry (GD-OES). The corrosion behavior of the stainless steel, coated by amorphous films, is evaluated in 3 wt% NaCl and 0.5 mol dm−3 HCl by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques. It is found that the sol–gel TiO2–ZrO2 films with the amorphous structure, deposited by the sol–gel process, and calcined at 400 °C significantly enhance the corrosion properties of AISI 316L in both chloride media. Full article
(This article belongs to the Special Issue Metal Oxide Films and Their Applications)
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Review
Structural Changes of Hydroxylapatite during Plasma Spraying: Raman and NMR Spectroscopy Results
Coatings 2021, 11(8), 987; https://doi.org/10.3390/coatings11080987 - 19 Aug 2021
Cited by 1 | Viewed by 758
Abstract
Functional osseoconductive coatings based on hydroxylapatite (HAp) and applied preferentially by atmospheric plasma spraying to medical implant surfaces are a mainstay of modern implantology. During contact with the hot plasma jet, HAp particles melt incongruently and undergo complex dehydration and decomposition reactions that [...] Read more.
Functional osseoconductive coatings based on hydroxylapatite (HAp) and applied preferentially by atmospheric plasma spraying to medical implant surfaces are a mainstay of modern implantology. During contact with the hot plasma jet, HAp particles melt incongruently and undergo complex dehydration and decomposition reactions that alter their phase composition and crystallographic symmetry, and thus, the physical and biological properties of the coatings. Surface analytical methods such as laser-Raman and nuclear magnetic resonance (NMR) spectroscopies are useful tools to assess the structural changes of HAp imposed by heat treatment during their flight along the hot plasma jet. In this contribution, the controversial information is highlighted on the existence or non-existence of oxyapatite, i.e., fully dehydrated HAp as a thermodynamically stable compound. Full article
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Article
Electrochemical Corrosion Behavior of Pure Mg Processed by Powder Metallurgy
Coatings 2021, 11(8), 986; https://doi.org/10.3390/coatings11080986 - 19 Aug 2021
Cited by 1 | Viewed by 876
Abstract
Pure Mg samples were prepared by powder metallurgy using the cold and hot compacting methods. Cold compacted pure Mg (500 MPa/RT) was characterized by 5% porosity and the mechanical bonding of powder particles. Hot compacted samples (100 MPa/400 °C and 500 MPa/400 °C) [...] Read more.
Pure Mg samples were prepared by powder metallurgy using the cold and hot compacting methods. Cold compacted pure Mg (500 MPa/RT) was characterized by 5% porosity and the mechanical bonding of powder particles. Hot compacted samples (100 MPa/400 °C and 500 MPa/400 °C) exhibited porosity below 0.5%, and diffusion bonding combined with mechanical bonding played a role in material compaction. The prepared pure Mg samples and wrought pure Mg were subjected to corrosion tests using electrochemical impedance spectroscopy. Similar material corrosion behavior was observed for the samples compacted at 500 MPa/RT and 100 MPa/400 °C; however, hot compacted samples processed at 500 MPa/400 °C exhibited longer corrosion resistance in 0.9% NaCl solution. The difference in corrosion behavior was mainly related to the different binding mechanisms of the powder particles. Cold compacted samples were characterized by a more pronounced corrosion attack and the creation of a porous layer of corrosion products. Hot compacted samples prepared at 500 MPa/400 °C were characterized by uniform corrosion and the absence of a layer of corrosion products on the specimen surface. Powder-based cold compacted samples exhibited lower corrosion resistance compared to the wrought pure Mg, while the corrosion behavior of the hot compacted samples prepared at 500 MPa/400 °C was similar to that of wrought material. Full article
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Article
The Action Difference of Lasiodiplodia theobromae on Infecting and Dyeing Poplar Wood in Spatial Growth
Coatings 2021, 11(8), 985; https://doi.org/10.3390/coatings11080985 - 19 Aug 2021
Viewed by 623
Abstract
Many factors affect the driving force of fungal growth and secretion. To compare the differences of Lasiodiplodia theobromae infected poplar wood, the changes of physical and chemical properties of vertically and horizontally infected poplar wood before and after dyeing were analyzed, and the [...] Read more.
Many factors affect the driving force of fungal growth and secretion. To compare the differences of Lasiodiplodia theobromae infected poplar wood, the changes of physical and chemical properties of vertically and horizontally infected poplar wood before and after dyeing were analyzed, and the infection characteristics were studied in this paper. The horizontal infection was more effective than the vertical infection in terms of infection depth, color depth, and microscopic hyphal invasion. The mycelium first intruded into the earlywood tissue and began to secrete a large amount of pigment after twenty days. The crystallinity of mycelium decreased slightly, and the difference in weight loss rate was negligible. The initial contact angle of the dyed specimen on the horizontal infection increased drastically in distilled water, but there was almost no difference between varnish and natural coating. The horizontal infection was more efficient than the vertical infection and had a higher color depth and a better induction effect, which is crucial in future microbial dyeing. Full article
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Editorial
Special Issue “Surface Treatment of Textiles”
Coatings 2021, 11(8), 984; https://doi.org/10.3390/coatings11080984 - 19 Aug 2021
Viewed by 616
Abstract
Textiles are commonly composed of natural and synthetic fibers for normal applications [...] Full article
(This article belongs to the Special Issue Surface Treatment of Textiles)
Review
Amine-Rich Coatings to Potentially Promote Cell Adhesion, Proliferation and Differentiation, and Reduce Microbial Colonization: Strategies for Generation and Characterization
Coatings 2021, 11(8), 983; https://doi.org/10.3390/coatings11080983 - 18 Aug 2021
Viewed by 936
Abstract
Biomaterial surface modification represents an important approach to obtain a better integration of the material in surrounding tissues. Different techniques are focused on improving cell support as well as avoiding efficiently the development of infections, such as by modifying the biomaterial surface with [...] Read more.
Biomaterial surface modification represents an important approach to obtain a better integration of the material in surrounding tissues. Different techniques are focused on improving cell support as well as avoiding efficiently the development of infections, such as by modifying the biomaterial surface with amine groups (–NH2). Previous studies showed that –NH2 groups could promote cell adhesion and proliferation. Moreover, these chemical functionalities may be used to facilitate the attachment of molecules such as proteins or to endow antimicrobial properties. This mini-review gives an overview of different techniques which have been used to obtain amine-rich coatings such as plasma methods and adsorption of biomolecules. In fact, different plasma treatment methods are commonly used with ammonia gas or by polymerization of precursors such as allylamine, as well as coatings of proteins (for example, collagen) or polymers containing –NH2 groups (for example, polyethyleneimine). Moreover, this mini-review will present the methods used to characterize such coatings and, in particular, quantify the –NH2 groups present on the surface by using dyes or chemical derivatization methods. Full article
(This article belongs to the Special Issue Functional Surfaces for Biomedical Applications)
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Article
Preparation and Characterization of PU/PET Matrix Gradient Composites with Microwave-Absorbing Function
Coatings 2021, 11(8), 982; https://doi.org/10.3390/coatings11080982 - 18 Aug 2021
Cited by 1 | Viewed by 755
Abstract
In the field of microwave-absorbing materials, functional powder has always been the focus of research. In order to fabricate lightweight and flexible garment materials with microwave-absorbing function, the current work was carried out. Firstly, the general properties of polyurethane (PU) matrix composites reinforced [...] Read more.
In the field of microwave-absorbing materials, functional powder has always been the focus of research. In order to fabricate lightweight and flexible garment materials with microwave-absorbing function, the current work was carried out. Firstly, the general properties of polyurethane (PU) matrix composites reinforced with various microwave-absorbing powders were studied, and the carbon nanotubes (CNTs)/Fe3O4/PU film was proven to have the best general properties. Secondly, the needle-punched polyester (PET) nonwoven fabrics in 1 mm-thickness were impregnated into PU resin with the same composition of raw material as Fe3O4/CNTs/PU film, thereby the microwave-absorbing nonwovens with gradient structure were prepared. Moreover, the absorbing properties of the CNTs/Fe3O4/PU/PET gradient composites were tested and analyzed. Finally, the relationship between the mass ratio of CNTs and Fe3O4, and the microwave-absorbing properties was studied. The results show that the mass ratio of CNTs/Fe3O4 has a significant effect on the microwave-absorbing property of CNTs/Fe3O4/PU/PET. When the mass ratio of CNTs/Fe3O4 is 1:1, the prepared CNTs/Fe3O4/PU/PET gradient composite can achieve effective reflection loss in the range of more than 2 GHz in Ku-band (12–18 GHz), and the minimum reflection loss reaches −17.19 dB. Full article
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