Coatings

19 pages, 9335 KiB

Open AccessArticle

Spectroscopic and Physicochemical Studies on 1,2,4-Triazine Derivative

by Arwa Alrooqi, Zahra M. Al-Amshany, Laila M. Al-Harbi, Tariq A. Altalhi, Moamen S. Refat, Ali M. Hassanien, Gaber A. M. Mersal and Ahmed A. Atta

Coatings 2022, 12(5), 714; https://doi.org/10.3390/coatings12050714 - 23 May 2022

Cited by 3 | Viewed by 1679

Abstract

A novel 5-(5-Bromo-2-hydroxybenzylidene)-6-oxo-3-phenyl-5,6-dihydro-1,2,4-triazine-2(1H)-carbothioamide (4) “compound 4” was synthesized. The chemical structure of compound 4 was confirmed with spectroscopic techniques. Thermal analysis (TGA/dTGA) studies were conducted for identifying the kinetic thermodynamic parameters and the thermal stability of the synthesized compound 4. Cyclic [...] Read more.

A novel 5-(5-Bromo-2-hydroxybenzylidene)-6-oxo-3-phenyl-5,6-dihydro-1,2,4-triazine-2(1H)-carbothioamide (4) “compound 4” was synthesized. The chemical structure of compound 4 was confirmed with spectroscopic techniques. Thermal analysis (TGA/dTGA) studies were conducted for identifying the kinetic thermodynamic parameters and the thermal stability of the synthesized compound 4. Cyclic voltammetric studies were performed for recognizing electrochemical characteristics of the synthesized compound 4. The calculated highest occupied molecular orbital (HOMO), lowest unoccupied molecular orbital (LUMO), and the band gap were found to be −3.61, −5.32, and 1.97 eV, respectively. Using a diffused reflectance spectroscopy (DRS) technique, the estimated values of the optical band transitions of compound 4 in powder form were found to be 2.07 and 2.67 eV. The structural properties of thermally evaporated compound 4 thin films were analyzed using field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), and Fourier transform infrared (FTIR) spectroscopy. It was found that compound 4 has a triclinic crystal structure. The optical transitions and the optical dispersion factors of compound 4 thin films were investigated using a UV-Vis spectroscopy technique. From the UV-Vis spectroscopy technique,

E_{g}^{i n d} = 3.6 V

was estimated for both the as-deposited and annealed thin films. For the as-deposited film, there were two photoluminescence (PL) emission peaks centered at 473 and 490 nm with a shoulder at 422 nm. For the annealed film at 423 K, there were five PL emission peaks centered at 274, 416, 439, 464, and 707 nm with a shoulder at 548 nm. The dark electrical conduction of compound 4 thin film was through a thermally activated process with activation energy equaling 0.88 eV. Full article

(This article belongs to the Topic Optical and Optoelectronic Materials and Applications)

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14 pages, 5866 KiB

Open AccessArticle

Study on the Corrosion Behavior and Mechanism of ER8 Wheel Steel in Neutral NaCl Solution

by Cheng-Gang He, Zhi-Bo Song, Yao-Zhe Gan, Rong-Wei Ye, Run-Zhi Zhu, Ji-Hua Liu and Zhi-Biao Xu

Coatings 2022, 12(5), 713; https://doi.org/10.3390/coatings12050713 - 23 May 2022

Cited by 3 | Viewed by 1729

Abstract

This paper analyzed the corrosion behavior and corrosion performance of ER8 wheel steel through a full immersion test. The average corrosion rate of the ER8 wheel specimen in 2.0% NaCl solution shows a gradual increase over the whole corrosion cycle. Although the corrosion [...] Read more.

This paper analyzed the corrosion behavior and corrosion performance of ER8 wheel steel through a full immersion test. The average corrosion rate of the ER8 wheel specimen in 2.0% NaCl solution shows a gradual increase over the whole corrosion cycle. Although the corrosion rate showed fluctuations at 3.5% and 5.0% concentration before 576 h, the corrosion rate also showed a steady increase after 576 h. The corrosion rates of specimens at different concentrations after 2160 h were over 0.12 mm/year. With increasing immersion times or concentrations of NaCl solution, the coverage area of the corrosion products dominated by iron oxides gradually increased, and the corrosion products on the surface became denser. The corrosion products were primarily γ-FeOOH, α-FeOOH and Fe₃O₄. As the density of the surface corrosion products increased, cracks and holes appeared on the surface of the rust layers, which made the rust layer unable to protect the substrate from further corrosion. After removing the corrosion products, pitting corrosion appeared on the surface of the substrate. The radius of the capacitive reactance arc gradually decreased with the increasing immersion time. The impedance modulus in the low-frequency region decreases and then increases with increasing NaCl solution concentration, which is the highest in 3.5% NaCl solution. I_corr increased with an increasing Cl⁻ concentration, which was similar to the mechanism of catalytic electrolysis due to Cl⁻. The specimens with rust layers have worse corrosion resistance when the immersion time is extended. The corrosion product did not protect the substrate but accelerated the corrosion process. Full article

(This article belongs to the Special Issue Friction and Corrosion Properties of Steels)

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10 pages, 271 KiB

Open AccessArticle

Effect of Intraoral Humidity on Dentin Bond Strength of Two Universal Adhesives: An In Vitro Preliminary Study

by Sarah Dabbagh, Louis Hardan, Cynthia Kassis, Rim Bourgi, Walter Devoto, Maciej Zarow, Natalia Jakubowicz, Maroun Ghaleb, Naji Kharouf, Mouhammad Dabbagh, Heber Isac Arbildo-Vega and Monika Lukomska-Szymanska

Coatings 2022, 12(5), 712; https://doi.org/10.3390/coatings12050712 - 23 May 2022

Cited by 3 | Viewed by 3704

Abstract

This study investigated the effect of intraoral humidity on microtensile bond strength (μTBS) to dentin of two universal adhesives applied in self-etch (SE) mode. Forty extracted human molars were selected for this study. Dentin specimens were allocated into four groups, standardized and then [...] Read more.

This study investigated the effect of intraoral humidity on microtensile bond strength (μTBS) to dentin of two universal adhesives applied in self-etch (SE) mode. Forty extracted human molars were selected for this study. Dentin specimens were allocated into four groups, standardized and then bonded with two commercial multimode adhesives, according to two humidity conditions (50% relative humidity (RH) and 90% RH). Following composite resin build-up and 24 h of water storage, the μTBS of the bonded interface was analyzed. The 50% RH was higher for Scotchbond Universal (SBU) than Prime&Bond Universal (PBU), while for 90% RH, SBU had significantly lower values than PBU. With PBU, the mean bond strength was not significantly different between both humidity settings tested (p > 0.05), while for SBU, the mean bond strength was significantly different between both conditions tested (p < 0.05); μTBS was significantly higher for 50% RH than for the other group. Within the limitation of this in vitro study, it can be concluded that: 1) the bonding performance of adhesives systems depends on the humidity settings; 2) increased RH exerts a detrimental effect on the bond strength of 2-hydroxyethyl methacrylate (HEMA)-containing adhesive tested. However, this phenomenon was not observed for HEMA-free adhesive tested; 3) further research in this area is needed to investigate different adhesive systems, temperatures and humidity settings. Full article

(This article belongs to the Special Issue Surface Properties of Dental Materials and Instruments)

13 pages, 2684 KiB

Open AccessArticle

High-Temperature Aroma Mitigation and Fragrance Analysis of Ethyl Cellulose/Silica Hybrid Microcapsules for Scented Fabrics

by Zuobing Xiao, Bin Zhang, Xingran Kou, Yunwei Niu, Liu Hong, Wei Zhao, Haocheng Cai and Xinyu Lu

Coatings 2022, 12(5), 711; https://doi.org/10.3390/coatings12050711 - 23 May 2022

Cited by 1 | Viewed by 2402

Abstract

Microencapsulation can improve the thermal stability of a fragrance, and composite wall materials are one way to further improve the thermal stability of microcapsules. This paper presents a facile approach for cotton fabric coatings by using cellulose/silica hybrid microcapsules. Lavender fragrance oil-loaded cellulose/silica [...] Read more.

Microencapsulation can improve the thermal stability of a fragrance, and composite wall materials are one way to further improve the thermal stability of microcapsules. This paper presents a facile approach for cotton fabric coatings by using cellulose/silica hybrid microcapsules. Lavender fragrance oil-loaded cellulose/silica hybrid microcapsules were one-step synthesized via emulsion solvent diffusion. The prepared microcapsules were found to be spherical in shape with a particle size distribution between 500 to 1000 nm. Due to the slow releasing of lavender fragrance oil in the capsules, the fragrance loss rate of (3-aminopropyl)triethoxysilane (APTES)-, triethoxy(3-glycidyloxypropyl)silane (GPTES)-, and (3-aercaptopropyl)trie-thoxysilane (MPTES)- modified cellulose/silica hybrid microcapsules are 25.2%, 35.1%, and 16.7% after six hours at 120 °C. E-nose and gas chromatography–mass spectrometry (GCMS) studies found that the fragranced cotton fabrics had good retention of characteristic aromas. It provides the basis for the application of the heating treatment of cotton fabrics in sterilization, bleaching, printing, and other processes. Full article

(This article belongs to the Topic Nanofibers and Thin Coatings with Special Physicochemical Properties)

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15 pages, 5615 KiB

Open AccessArticle

The Influence of Negative Voltage on Corrosion Behavior of Ceramic Coatings Prepared by MAO Treatment on Steel

by Mingzhe Xiang, Tianlu Li, Yun Zhao and Minfang Chen

Coatings 2022, 12(5), 710; https://doi.org/10.3390/coatings12050710 - 23 May 2022

Cited by 5 | Viewed by 1712

Abstract

In this study, the 10B21 steel was treated by micro-arc oxidation (MAO) in the electrolyte consisting of aluminate and phosphate to enhance its corrosion resistance. The effect of negative voltage on corrosion resistance of the MAO coating obtained has mainly been analyzed through [...] Read more.

In this study, the 10B21 steel was treated by micro-arc oxidation (MAO) in the electrolyte consisting of aluminate and phosphate to enhance its corrosion resistance. The effect of negative voltage on corrosion resistance of the MAO coating obtained has mainly been analyzed through their phase composition, microstructure, interfacial bonding strength, salt spray and electrochemical testing. The result indicates that with negative voltages applied to the MAO coating, Fe-Al transition layers arise between coating layer and matrix. Furthermore, different negative voltages bring forward different α-Al₂O₃ contents contained in the MAO coatings and when it reaches −100 V, the amount of α-Al₂O₃ appears as the largest. The surface porosity of the coating was also significantly decreased. In addition, the corrosion current density of the coating is only 3.64 μA·cm⁻², which is two orders of magnitude lower than that of the substrate. After 72 h of salt spray corrosion, it is found that the coating substrate is less corroded when the negative voltage of 100 V is applied. Therefore, −100 V has been proven as the optimum performance for improving the corrosion resistance of 10B21 steel. Full article

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11 pages, 3076 KiB

Open AccessArticle

ZnO Piezoelectric Films for Acoustoelectronic and Microenergetic Applications

by Egor Golovanov, Vladimir Kolesov, Vladimir Anisimkin, Victor Osipenko and Iren Kuznetsova

Coatings 2022, 12(5), 709; https://doi.org/10.3390/coatings12050709 - 23 May 2022

Cited by 8 | Viewed by 1825

Abstract

Zinc oxide is one of the most popular materials for acoustoelectronic sensors and vibro-piezo-transducers used in nano-piezo-generators. In the present paper, thick piezoelectric ZnO films are fabricated on both sides of various substrates using magnetron sputtering technique. It is shown that the main [...] Read more.

Zinc oxide is one of the most popular materials for acoustoelectronic sensors and vibro-piezo-transducers used in nano-piezo-generators. In the present paper, thick piezoelectric ZnO films are fabricated on both sides of various substrates using magnetron sputtering technique. It is shown that the main problem for double film deposition is the difference in thermal expansion coefficients of the ZnO films and the substrate materials. The problem is solved by decreasing the plate temperature up to 140 °C, reducing the growing rate up to 0.8 ± 0.05 μm/h, and diminishing the oxygen content in Ar mixture up to 40%. Using the modified sputtering conditions, the ZnO films with thickness up to 15 μm, grain size 0.3 μm, and piezoelectric module as large as 7.5 × 10⁻¹² C/N are fabricated on both faces of quartz and lithium niobate plates as well as on flexible polyimide flexible film known as Kapton. The films are characterized by chemical composition, crystallographic orientation, piezoelectric effect, and acoustic wave generation. They are applied for vibro-piezo-transducer based on flexible ZnO/Kapton/Al/ZnO/Al structure. When the structure is mechanical excited, the variable electric voltage of about 35 mV is generated. The value of the voltage is sufficient for an unstable energy source used in autonomic micro-energetic energy-store systems. Full article

(This article belongs to the Special Issue Functional Films for Surface Acoustic Wave (SAW) Based Chemical and Biological Sensor Applications)

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14 pages, 5535 KiB

Open AccessArticle

Numerical Simulation and Multi-Objective Parameter Optimization of Inconel718 Coating Laser Cladding

by Sirui Yang, Haiqing Bai, Chaofan Li, Linsen Shu, Xinhe Zhang and Zongqiang Jia

Coatings 2022, 12(5), 708; https://doi.org/10.3390/coatings12050708 - 23 May 2022

Cited by 9 | Viewed by 1835

Abstract

Aiming at the difficulty of temperature control in the laser cladding process of high-temperature nickel-based alloys, the influence of cladding parameters on the temperature of the molten pool, and the quality of the cladding layer were explored. Firstly, through the analysis of the [...] Read more.

Aiming at the difficulty of temperature control in the laser cladding process of high-temperature nickel-based alloys, the influence of cladding parameters on the temperature of the molten pool, and the quality of the cladding layer were explored. Firstly, through the analysis of the finite element method, the Inconel718 single-pass cladding model was established on the surface of 45 steel by using parametric language and life–death element technology, the influence of different laser power and scanning speed on the temperature of the molten pool center was explored, and reasonable process parameters scope were selected. Secondly, taking the cladding parameters as independent variables, and taking the dilution rate and forming coefficient of the cladding layer as the response variables, using BBD (Box–Behnken Design) to design experiments the response surface analysis method was used to establish the regression prediction model of the cladding process parameters and response indicators, and the genetic algorithm was used to carry out multi-objective optimization to obtain the best results. The optimal parameter combination is a laser power of 1756 W, a scanning speed of 19.43 mm/s, and a powder feeding rate of 19.878 g/min. Finally, a multi-pass lap joint experiment was carried out with the optimal parameters, and it was found that the cladding layer has a dense and fine structure and a good metallurgical bond with the matrix, which can effectively guide the actual production. Full article

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11 pages, 2965 KiB

Open AccessArticle

Influence of Prevailing Wind Direction on Sapping Quantity of Rammed Earth Great Wall of the Ming Dynasty

by Na Su, Bo Yang, Wenwu Chen, Linrong Xu and Yongwei Li

Coatings 2022, 12(5), 707; https://doi.org/10.3390/coatings12050707 - 22 May 2022

Cited by 1 | Viewed by 1602

Abstract

Sapping caused by prevailing wind erosion is one of the most significant factors in the deterioration of earthen sites located in Datong County, Qinghai Province, China. Long-term effects of wind may cause surface erosion, or even serious damage to the Great Wall of [...] Read more.

Sapping caused by prevailing wind erosion is one of the most significant factors in the deterioration of earthen sites located in Datong County, Qinghai Province, China. Long-term effects of wind may cause surface erosion, or even serious damage to the Great Wall of Ming Dynasty. Difference of sapping quantity should be attributed to variability of the prevailing wind directions. To better understand the effects of wind direction on erosion, meteorological data in the study area for fifty-two years (from 1961 to 2013) were collected and statistically analyzed. Sapping quantity of earthen structure was measured by field investigation on the Wall along the ridge whose azimuth ranges from 95°–244° and mainly concentrated in 140°–210°. Results showing obvious difference of sapping quantity could be observed at both sides of the Wall under the prevailing wind directions (ESE, SE and SSE). Further, the Wall was divided into small segments with a length of 20 m for comparison and maximum sapping quantity could be found at the Wall whose azimuth is at an angle of 30° to the prevailing wind. The aim of this study is to provide reference for the deterioration of the Wall under long-term wind pressure, and provide a targeted conservation method for earthen structure. Full article

(This article belongs to the Special Issue Coatings for Cultural Heritage: Cleaning, Protection and Restoration)

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15 pages, 6502 KiB

Open AccessArticle

Van der Waals Epitaxial Growth of ZnO Films on Mica Substrates in Low-Temperature Aqueous Solution

by Hou-Guang Chen, Yung-Hui Shih, Huei-Sen Wang, Sheng-Rui Jian, Tzu-Yi Yang and Shu-Chien Chuang

Coatings 2022, 12(5), 706; https://doi.org/10.3390/coatings12050706 - 20 May 2022

Cited by 4 | Viewed by 2164

Abstract

In this article, we demonstrate the van der Waals (vdW) epitaxial growth of ZnO layers on mica substrates through a low-temperature hydrothermal process. The thermal pretreatment of mica substrates prior to the hydrothermal growth of ZnO is essential for growing ZnO crystals in [...] Read more.

In this article, we demonstrate the van der Waals (vdW) epitaxial growth of ZnO layers on mica substrates through a low-temperature hydrothermal process. The thermal pretreatment of mica substrates prior to the hydrothermal growth of ZnO is essential for growing ZnO crystals in epitaxy with the mica substrates. The addition of sodium citrate into the growth solution significantly promotes the growth of ZnO crystallites in a lateral direction to achieve fully coalesced, continuous ZnO epitaxial layers. As confirmed through transmission electron microscopy, the epitaxial paradigm of the ZnO layer on the mica substrate was regarded as an incommensurate van der Waals epitaxy. Furthermore, through the association of the Mist-CVD process, the high-density and uniform distribution of ZnO seeds preferentially occurred on mica substrates, leading to greatly improving the epitaxial qualities of the hydrothermally grown ZnO layers and obtaining flat surface morphologies. The electrical and optoelectrical properties of the vdW epitaxial ZnO layer grown on mica substrates were comparable with those grown on sapphire substrates through conventional solution-based epitaxy techniques. Full article

(This article belongs to the Special Issue Recent Advances in the Growth and Characterizations of Thin Films)

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20 pages, 2414 KiB

Open AccessFeature PaperArticle

Modeling of Imperfect Viscoelastic Interfaces in Composite Materials

by Oscar Luis Cruz-González, Reinaldo Rodríguez-Ramos, Frederic Lebon and Federico J. Sabina

Coatings 2022, 12(5), 705; https://doi.org/10.3390/coatings12050705 - 20 May 2022

Cited by 2 | Viewed by 1713

Abstract

The present work deals with hierarchical composites in three dimensions, whose constituents behave as non-aging linear viscoelastic materials. We model the influence that imperfect viscoelastic interfaces have on the macroscopic effective response of these structures. As an initial approach, the problem of two [...] Read more.

The present work deals with hierarchical composites in three dimensions, whose constituents behave as non-aging linear viscoelastic materials. We model the influence that imperfect viscoelastic interfaces have on the macroscopic effective response of these structures. As an initial approach, the problem of two bodies in adhesion is studied and in particular the case of soft viscoelastic interface at zero-order is considered. We deduce the integral form of the viscoelastic interface by applying the matched asymptotic expansion method, the correspondence principle, and the Laplace–Carson transform. Then, by adapting the integral form previously obtained, we address a heterogeneous problem for periodic structures. Here, theoretical results obtained for perfect interfaces are extended to the formal viscoelastic counterpart of the spring-type imperfect interface model. Finally, we show the potential of the proposed approach by performing calculations of effective properties in heterogeneous structures with two- and three-scale geometrical configurations and imperfect viscoelastic interfaces. Full article

(This article belongs to the Special Issue Recent Developments in Interfaces and Surfaces Engineering)

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24 pages, 3301 KiB

Open AccessArticle

Optimum Selection of Coated Piston Rings and Thrust Bearings in Mixed Lubrication for Different Lubricants Using Machine Learning

by Anastasios Zavos, Konstantinos P. Katsaros and Pantelis G. Nikolakopoulos

Coatings 2022, 12(5), 704; https://doi.org/10.3390/coatings12050704 - 20 May 2022

Cited by 4 | Viewed by 2594

Abstract

The purpose of this study is to build a parametric algorithm combining analytical results and Machine Learning in order to improve the tribological performance of coated piston rings and thrust bearings in mixed lubrication using different synthetic lubricants. The friction models for piston [...] Read more.

The purpose of this study is to build a parametric algorithm combining analytical results and Machine Learning in order to improve the tribological performance of coated piston rings and thrust bearings in mixed lubrication using different synthetic lubricants. The friction models for piston ring conjunction and pivoted pad thrust bearing consider the basic lubrication theory, the detailed contact geometry and the complete lubricant action for a wide range of speeds. The data produced from the analytical solutions are used as input for the training of regression models. The effect of TiN, TiAlN, CrN and DLC coatings on friction coefficient are investigated through multi-variable quadratic regression and support vector machine models. The optimum selection is considered when the minimum friction coefficient is predicted. Smooth TiN2 and TiAlN coatings seem to affect better the ring friction coefficient than rougher steel, TiN1 and CrN coatings using an uncoated or coated Nickel Nanocomposite (NNC) cylinder. Using an NNC cylinder for better durability, the friction coefficients were found to be higher by 31.3−58.8% for all the studied rings due to the rougher surface morphology. On the other hand, the results indicate that pads coated with DLC show lower friction coefficients compared to the common steel and TiAlN, CrN, and TiN applications. The multi-variable second-order polynomial regression models were demonstrated to be 1−6% more accurate than the quadratic support vector machine models in both tribological contacts. Full article

(This article belongs to the Special Issue Selection of Lubricants and Coatings for Engine Components Using Machine Learning)

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23 pages, 11652 KiB

Open AccessArticle

Immune Optimization of Welding Sequence for Arc Weld Seams in Ship Medium-Small Assemblies

by Mingxin Yuan, Suodong Liu, Yunqiang Gao, Hongwei Sun, Chao Liu and Yi Shen

Coatings 2022, 12(5), 703; https://doi.org/10.3390/coatings12050703 - 20 May 2022

Viewed by 1313

Abstract

The arc weld seam is a common form in ship medium-small assemblies. In order to reduce the deformation of the welded parts with an arc weld seam, and then improve the welding quality, research on the optimization of welding sequences based on the [...] Read more.

The arc weld seam is a common form in ship medium-small assemblies. In order to reduce the deformation of the welded parts with an arc weld seam, and then improve the welding quality, research on the optimization of welding sequences based on the artificial immune algorithm is carried out in this paper. First, the formation mechanism of welding deformation is analyzed by the thermo-elastic-plastic finite element method; next, the reduction in the welding deformation is taken as the optimization goal, and the welding sequence optimization model for the arc weld seam is constructed under the condition of boundary constraints; then, an immune clonal optimization algorithm based on similar antibody similarity screening and steady-state adjustment is proposed, and its welding sequence optimization ability is improved through antibody screening and median adjustment. Finally, the welding sequence optimization tests are carried out based on the Ansys platform. Numerical tests of a typical arc weld seam show that different welding sequences will cause different welding deformations, which verifies the importance of welding sequence optimization. Furthermore, the numerical test results of four different types of welds in ship medium-small assemblies demonstrated that the use of distributed optimization algorithms for welding sequence optimization can help reduce the amount of welding deformations, and the immune clonal algorithm, based on antibody similarity screening and steady-state adjustment, achieves the optimal combination of the welding sequence. Compared with the other three optimization algorithms, the maximum welding deformation caused by the welding sequence optimized by the proposed immune clonal algorithm is reduced by 3.1%, 4.0%, and 3.4%, respectively, the average maximum welding deformation is reduced by 3.5%, 5.5%, and 4.7%, respectively, and the convergence generation of the optimization algorithm is reduced by 16.8%, 13.1% and 14.5%, respectively, which further verifies the effectiveness and superiority of the proposed immune clonal algorithm in the optimization of welding sequences. Full article

(This article belongs to the Special Issue Progress in Coatings Deposition by Advanced Welding and Welding-Related Processes)

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20 pages, 5427 KiB

Open AccessArticle

Physicochemical and Biological Evaluation of Chitosan-Coated Magnesium-Doped Hydroxyapatite Composite Layers Obtained by Vacuum Deposition

by Daniela Predoi, Carmen Steluta Ciobanu, Simona Liliana Iconaru, Steinar Raaen, Monica Luminita Badea and Krzysztof Rokosz

Coatings 2022, 12(5), 702; https://doi.org/10.3390/coatings12050702 - 20 May 2022

Cited by 13 | Viewed by 1783

Abstract

In the present work, the effectiveness of vacuum deposition technique for obtaining composite thin films based on chitosan-coated magnesium-doped hydroxyapatite Ca_10−xMg_x(PO₄)₆ (OH)₂ with x_Mg = 0.025 (MgHApCh) was proved for the first time. The [...] Read more.

In the present work, the effectiveness of vacuum deposition technique for obtaining composite thin films based on chitosan-coated magnesium-doped hydroxyapatite Ca_10−xMg_x(PO₄)₆ (OH)₂ with x_Mg = 0.025 (MgHApCh) was proved for the first time. The prepared samples were exposed to three doses (0, 3, and 6 Gy) of gamma irradiation. The MgHApCh composite thin films nonirradiated and irradiated were evaluated by scanning electron microscopy (SEM), atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS) studies. The biological evaluation of the samples was also presented. All the results obtained from this study showed that the vacuum deposition method allowed for obtaining uniform and homogeneous layers. Fine cracks were observed on the MgHApCh composite thin films’ surface after exposure to a 6 Gy irradiation dose. Additionally, after gamma irradiation, a decrease in Ca, P, and Mg content was noticed. The MgHApCh composite thin films with doses of 0 and 3 Gy of gamma irradiation showed a cellular viability similar to that of the control. Samples with 6 Gy doses of gamma irradiation did not cause significantly higher fibroblast cell death than the control (p > 0.05). On the other hand, the homogeneous distribution of pores that appeared on the surface of coatings after 6 Gy doses of gamma irradiation did not prevent the adhesion of fibroblast cells and their spread on the coatings. In conclusion, we could say that the thin films could be suitable both for use in bone implants and for other orthopedic and dentistry applications. Full article

(This article belongs to the Collection Feature Paper Collection in Bioactive Coatings and Biointerfaces)

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13 pages, 3756 KiB

Open AccessArticle

Damage Characteristics of Aluminum-Coated Grating Irradiated by Nanosecond Pulsed Laser

by Jiamin Wang, Kuo Zhang, Yanhui Ji, Jinghua Yu, Jirigalantu, Wei Zhang, Wenhao Li, Changbin Zheng and Fei Chen

Coatings 2022, 12(5), 701; https://doi.org/10.3390/coatings12050701 - 20 May 2022

Viewed by 1398

Abstract

An aluminum-coated grating (ACG) is a core component of laser systems and spectrometers. Understanding damage to the ACG induced by nanosecond lasers is critical for future high-power laser applications. In this study, we applied finite element simulation and practical experimentation to investigate the [...] Read more.

An aluminum-coated grating (ACG) is a core component of laser systems and spectrometers. Understanding damage to the ACG induced by nanosecond lasers is critical for future high-power laser applications. In this study, we applied finite element simulation and practical experimentation to investigate the characteristics of ACG damage. Based on a coupling model using fluid heat transfer with the level-set method, we simulated the damage caused to an ACG by a 1064 nm nanosecond single pulse laser. The theoretical modeling showed that the ridge and bottom corners of the grid will be preferentially damaged, and the simulated damage threshold will range from 0.63 J/cm² to 0.95 J/cm². We performed a one-on-one damage test according to the ISO21254 standard to investigate the failure condition of 1800 l/mm ACGs; the laser-induced damage threshold (LIDT) was 0.63 J/cm² (1064 nm, 6.5 ns). Microscopy images showed that the damaged area decreased with decreasing laser fluence, and scanning electron microscopy measurements showed that the main damage mechanism was thermodynamic damage, and that damage to the grid occurred first. The results of the experiments and simulations were in good agreement. Full article

(This article belongs to the Section Laser Coatings)

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16 pages, 5470 KiB

Open AccessArticle

Effects of W Content on Structural and Mechanical Properties of TaWN Films

by Li-Chun Chang, Chin-Han Tzeng and Yung-I Chen

Coatings 2022, 12(5), 700; https://doi.org/10.3390/coatings12050700 - 20 May 2022

Cited by 8 | Viewed by 1527

Abstract

In this study, TaWN films were fabricated through co-sputtering. The effects of W addition on the structural variation and mechanical properties of these films were investigated. TaWN films formed face-centered cubic (fcc) solid solutions. With the increase in the W content, the fcc [...] Read more.

In this study, TaWN films were fabricated through co-sputtering. The effects of W addition on the structural variation and mechanical properties of these films were investigated. TaWN films formed face-centered cubic (fcc) solid solutions. With the increase in the W content, the fcc phase varied from TaN-dominant to W₂N-dominant, which was accompanied by a decrease in the lattice constant and alterations in material characteristics, such as the chemical bonding and mechanical properties. The phase change was further correlated with the bonding characteristics of films examined by X-ray photoelectron spectroscopy. The hardness increased from 21.7 GPa for a Ta₅₄N₄₆ film to 23.2–31.9 GPa for TaWN films, whereas the Young’s modulus increased from 277 GPa for the Ta₅₄N₄₆ film to 302–391 GPa for the TaWN films. The enhancement in films’ mechanical properties was attributed to the strengthening of the solid solution and the phase change. The wear behavior of the fabricated TaWN films was evaluated using the pin-on-disk test. The Ta₁₇W₅₅N₂₈ and Ta₃₆W₂₄N₄₀ films exhibited an abrasive wear behavior and low wear rates of 4.9–7.6 × 10⁻⁶ mm³/Nm. Full article

(This article belongs to the Special Issue Physical Vapor Deposition II)

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17 pages, 1826 KiB

Open AccessReview

Gas Sensors Based on Titanium Oxides (Review)

by Simonas Ramanavicius, Arunas Jagminas and Arunas Ramanavicius

Coatings 2022, 12(5), 699; https://doi.org/10.3390/coatings12050699 - 19 May 2022

Cited by 31 | Viewed by 3346

Abstract

Nanostructured titanium compounds have recently been applied in the design of gas sensors. Among titanium compounds, titanium oxides (TiO₂) are the most frequently used in gas sensing devices. Therefore, in this review, we are paying significant attention to the variety of [...] Read more.

Nanostructured titanium compounds have recently been applied in the design of gas sensors. Among titanium compounds, titanium oxides (TiO₂) are the most frequently used in gas sensing devices. Therefore, in this review, we are paying significant attention to the variety of allotropic modifications of titanium oxides, which include anatase, rutile, brukite. Very recently, the applicability of non-stoichiometric titanium oxide (TiO_2−x)-based layers for the design of gas sensors was demonstrated. For this reason, in this review, we are addressing some research related to the formation of non-stoichiometric titanium oxide (TiO_2−x) and Magnéli phase (Ti_nO_2n−1)-based layers suitable for sensor design. The most promising titanium compounds and hetero- and nano-structures based on these compounds are discussed. It is also outlined that during the past decade, many new strategies for the synthesis of TiO₂ and conducting polymer-based composite materials were developed, which have found some specific application areas. Therefore, in this review, we are highlighting how specific formation methods, which can be used for the formation of TiO₂ and conducting polymer composites, can be applied to tune composite characteristics that are leading towards advanced applications in these specific technological fields. The possibility to tune the sensitivity and selectivity of titanium compound-based sensing layers is addressed. In this review, some other recent reviews related to the development of sensors based on titanium oxides are overviewed. Some designs of titanium-based nanomaterials used for the development of sensors are outlined. Full article

(This article belongs to the Special Issue Conducting Polymers Based Coatings for Sensors and Other Technological Applications)

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10 pages, 2924 KiB

Open AccessArticle

Hydrodynamic Analysis of the Thickness Variation in a Solid Film Formed by a Spin Coating Process

by Heesung Park

Coatings 2022, 12(5), 698; https://doi.org/10.3390/coatings12050698 - 19 May 2022

Cited by 1 | Viewed by 1887

Abstract

The surface profile of the film formed by spin coating is experimentally investigated in this paper. The unavoidable wavy form at the surface was observed when the ultraviolet curable resin was used. In addition, the surface thickness variation was directly related to the [...] Read more.

The surface profile of the film formed by spin coating is experimentally investigated in this paper. The unavoidable wavy form at the surface was observed when the ultraviolet curable resin was used. In addition, the surface thickness variation was directly related to the viscosity, disk rotation speed, and disk size. Fluid dynamic theory with non-dimensional analysis was conducted to describe the surface profile after the spin coating process. It was found that the film had been thickened until the viscosity force and Coriolis force were balanced. The Coriolis force, however, also affected the flow instability during the spinning of the disk. The film thickness variation is successfully described by using the non-dimensional factors. In addition, the edge bump which is induced by hydraulic jump is expressed by the relation of power law of Ekman, Weber, and Reynolds numbers. In this paper, the thickness variation and edge bump position are expressed by using hydrodynamic theory. It is also reveals that the Coriolis force acts based on the magnitude of thickness variation, and the surface tension affects the edge bump position. The presented relationships will contribute further understanding of the spin coating process. The outcome of this paper supports the cost-effective productions of electronic microcircuits and solar cells. Full article

(This article belongs to the Topic Inorganic Thin Film Materials)

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14 pages, 5026 KiB

Open AccessArticle

Enhanced Anti-Tribocorrosion Performance of Ti-DLC Coatings Deposited by Filtered Cathodic Vacuum Arc with the Optimization of Bias Voltage

by Yongqing Shen, Jun Luo, Bin Liao, Lin Chen, Xu Zhang, Yuanyuan Zhao, Pan Pang and Xinmiao Zeng

Coatings 2022, 12(5), 697; https://doi.org/10.3390/coatings12050697 - 19 May 2022

Cited by 6 | Viewed by 1614

Abstract

To improve the anti-tribocorrosion property, and decrease the metal dissolution and wear of stainless-steel components caused by the synergistic action of corrosion and friction in marine environments, Ti-DLC coatings were obtained on steel substrate using a filtered cathodic vacuum arc (FCVA) system by [...] Read more.

To improve the anti-tribocorrosion property, and decrease the metal dissolution and wear of stainless-steel components caused by the synergistic action of corrosion and friction in marine environments, Ti-DLC coatings were obtained on steel substrate using a filtered cathodic vacuum arc (FCVA) system by adjusting bias voltage. The structure, mechanical properties, corrosion, and tribocorrosion behavior were investigated. Increasing the bias voltage from −50 V to −300 V, Ti content decreased from 23.9 to 22.5 at.%, and grain size decreased first, and then increased. Obvious TiC grains embedded in the amorphous carbon matrix were observed in the coating from the TEM result. Hardness increased from 30.23 GPa to 34.24 GPa with an increase in bias voltage from −50 to −200 V. The results of tribocorrosion testing showed that the Ti-DLC coatings at −200 V presented the best anti-tribocorrosion performance with the smallest friction coefficient of 0.052, wear rate of 2.48 × 10⁻⁷ mm³/N∙m, and high open-circuit potential, which is mainly due to the dense structure, high value of H/E* and H³/E*², and great corrosion resistance. Obtained results suggest that the Ti-DLC coating with nanocomposite structure is a potential protective material for marine equipment. Full article

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17 pages, 6531 KiB

Open AccessReview

Intumescent Coatings for Fire Resistance of Steel Structures: Current Approaches for Qualification and Design

by Donatella de Silva, Iolanda Nuzzo, Emidio Nigro and Antonio Occhiuzzi

Coatings 2022, 12(5), 696; https://doi.org/10.3390/coatings12050696 - 19 May 2022

Cited by 9 | Viewed by 3947

Abstract

Intumescent coatings (ICs) are often used for protecting steel buildings during a fire when the structural, aesthetic, and architectural features of the structural members should be preserved. Indeed, ICs form a thin protective layer on the steel surface, that if exposed to fire [...] Read more.

Intumescent coatings (ICs) are often used for protecting steel buildings during a fire when the structural, aesthetic, and architectural features of the structural members should be preserved. Indeed, ICs form a thin protective layer on the steel surface, that if exposed to fire or elevated temperatures, expands in volume with a consequent reduction in density. Hence, the protective layer captivates heat and protects the structural member from damage or elevated deformation. This reactive fire protection is designed using prescriptive tables, in which the IC thickness is chosen according to the required fire resistance, critical temperature, and section factor of the steel element. These tables are elaborated on the basis of the tests results according to the UNI EN 13381-8 standard, which is the reference for characterizing reactive systems such as ICs. For its reactive nature, this fire protection has to be applied to the structure in a controlled manner, and it is good practice to verify its correct application by measuring thickness and adhesion in situ through regulated methods. The qualification process of IC systems in Italy can be realized through a voluntary certification within the scope of a European technical assessment or by means of a national technical assessment certificate that is mandatory. All these aspects related to qualification, assessment, and design of ICs are often ignored by both designers and manufacturers, especially in Italy. Therefore, this paper describes all the approaches, introducing the main technical differences, in order to provide a sort of guideline on the use of these reactive fire protections. Full article

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13 pages, 2978 KiB

Open AccessArticle

Synthesis of the Porous ZnO Nanosheets and TiO₂/ZnO/FTO Composite Films by a Low-Temperature Hydrothermal Method and Their Applications in Photocatalysis and Electrochromism

by Xusong Liu, Gang Wang, Hui Zhi, Jing Dong, Jian Hao, Xiang Zhang, Jing Wang, Danting Li and Baosheng Liu

Coatings 2022, 12(5), 695; https://doi.org/10.3390/coatings12050695 - 19 May 2022

Cited by 16 | Viewed by 3133

Abstract

In this paper, porous zinc oxide (ZnO) nanosheets were successfully prepared by a simple low-temperature hydrothermal method. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Brunauer–Emmett–Teller (BET) tests showed that the synthesized product was ZnO with porous sheet structure. [...] Read more.

In this paper, porous zinc oxide (ZnO) nanosheets were successfully prepared by a simple low-temperature hydrothermal method. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Brunauer–Emmett–Teller (BET) tests showed that the synthesized product was ZnO with porous sheet structure. The diameter of porous nanosheets was about 100 nm and the thickness was about 8 nm. As a photocatalyst, the degradation efficiencies of porous ZnO nanosheets for methyl orange (MO), methylene blue (MB) and Rhodamine B (RhB) were 97.5%, 99% and 96.8%, respectively. In addition, the degradation efficiency of ZnO for mixed dyes (Mo, MB and RhB) was satisfactory, reaching 97.7%. The photocatalytic stability of MB was further tested and remained at 99% after 20 cycles. In the experiment, ZnO/FTO (fluorine-doped tin oxide) composites were prepared by using ZnO as the conductive layer. Titanium dioxide (TiO₂) was deposited on the surface of ZnO/FTO by electrodeposition, so as to obtain a TiO₂/ZnO/FTO composite. By studying the electrochromic properties of this composite, it was found that the TiO₂/ZnO/FTO composite shows a large light modulation range (55% at 1000 nm) and excellent cycle stability (96.6% at 200 cycles). The main reason for the excellent electrochromic properties may be the synergistic effect between the porous structure and the polymetallic oxides. This study is helpful to improve the photocatalytic efficiency and cycling stability of metal oxides, improve the transmittance of thin films and provide a new strategy for the preparation of ZnO composite materials with excellent photocatalytic and electrochromic properties. Full article

(This article belongs to the Special Issue Smart Coatings for Energy Saving Applications)

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16 pages, 6137 KiB

Open AccessArticle

Sandwich Structure to Enhance the Mechanical and Electrochemical Performance of TaN/(Ta/Ti)/TiN Multilayer Films Prepared by Multi-Arc Ion Plating

by Rong Tu, Mai Yang, Yang Yuan, Rui Min, Qizhong Li, Meijun Yang, Baifeng Ji and Song Zhang

Coatings 2022, 12(5), 694; https://doi.org/10.3390/coatings12050694 - 19 May 2022

Cited by 3 | Viewed by 2054

Abstract

TaN/(Ta/Ti)/TiN multilayer films at various target to substrate distances (d_ts), composed of hexagonal TaN, (t-Ta/fcc-Ti) and fcc-TiN with a sandwich structure, were prepared via multi-arc ion plating. With increasing d_ts, the deposition rate of the films first increased [...] Read more.

TaN/(Ta/Ti)/TiN multilayer films at various target to substrate distances (d_ts), composed of hexagonal TaN, (t-Ta/fcc-Ti) and fcc-TiN with a sandwich structure, were prepared via multi-arc ion plating. With increasing d_ts, the deposition rate of the films first increased and then decreased, and the average grain size increased from 11.9 to 13.9 nm and then decreased to 10.4 nm. The TaN/(Ta/Ti)/TiN multilayer films have a high ratio of hardness to elastic modulus (H/E*) and H³/E*² ratios, displaying an outstanding level of both hardness and toughness compared with Ta-related films. The nano-multilayer TaTi interlayers inhibited the columnar structure and prolonged the corrosion diffusion path by increasing stable interfaces. The TaN/(Ta/Ti)/TiN multilayer film at d_ts = 220 mm exhibited comprehensive properties, including a high hardness of 25 GPa, strong adhesion strength of 68 N, low coefficient of friction of 0.41, low wear rate of 2.7 × 10⁻⁶ mm³(mN)⁻¹ and great corrosion resistance in 3.5 wt% NaCl solution, showing promising application as a protective coating. Full article

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7 pages, 8534 KiB

Open AccessArticle

Tribological Behaviors of Polycrystalline Cubic Boron Nitride Sliding against Bearing Steel in Vacuum Conditions

by Fan Yang, Zhe Wu, Dezhong Meng, Wenbo Qin and Dingshun She

Coatings 2022, 12(5), 693; https://doi.org/10.3390/coatings12050693 - 18 May 2022

Cited by 1 | Viewed by 1363

Abstract

In order to understand the surface and interface conditions of polycrystalline cubic boron nitride (PcBN) sliding against bearing steel in vacuum environments, the effects of different loads on the tribological behaviors of PcBN and bearing steel AISI 52100 were studied deeply in a [...] Read more.

In order to understand the surface and interface conditions of polycrystalline cubic boron nitride (PcBN) sliding against bearing steel in vacuum environments, the effects of different loads on the tribological behaviors of PcBN and bearing steel AISI 52100 were studied deeply in a vacuum tribometer. Furthermore, the wear tracks of PcBN and the wear scars of AISI 52100 were characterized by scanning electron microscopy and energy dispersive X-ray spectroscopy. The results show that the stable coefficient of friction (CoF) of the tribopair experiences a decrease first and then an increase with the increase in loads from 2 N to 15 N. The adhesive layer increases with the increase in loads, and the formation of adhesive layer contributes to the change of CoF and wear rate of counterpart balls. The adhesive layer is formed due to the combination of high contact stress and high temperature. Meanwhile, the exfoliated cubic boron nitride grains are embedded into the adhesive layer as abrasive grains, resulting in abrasive wear. Thus, the main wear mechanisms are adhesive wear and abrasive wear. Full article

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17 pages, 4200 KiB

Open AccessArticle

Influence of Rust Inhibitors on the Microstructure of a Steel Passive Film in Chloride Concrete

by Qun Guo, Xiaozhen Li, Nan Lin and Junzhe Liu

Coatings 2022, 12(5), 692; https://doi.org/10.3390/coatings12050692 - 18 May 2022

Cited by 6 | Viewed by 1475

Abstract

To compare the corrosion inhibition behaviors of rust inhibitors with different mechanisms on steel bars, the rust resistance effect of sodium molybdate (Na₂MoO₄), sodium chromate (Na₂CrO₄), benzotriazole (BTA), N-N dimethyl ethanolamine, sodium molybdate (Na₂ [...] Read more.

To compare the corrosion inhibition behaviors of rust inhibitors with different mechanisms on steel bars, the rust resistance effect of sodium molybdate (Na₂MoO₄), sodium chromate (Na₂CrO₄), benzotriazole (BTA), N-N dimethyl ethanolamine, sodium molybdate (Na₂MoO₄) + benzotriazole (BTA), and sodium chromate (Na₂CrO₄) + benzotriazole (BTA) on steel bars in a simulated chloride concrete pore solution was studied. The rust resistance effects of different types of rust inhibitors were assessed by electrochemical impedance spectroscopy (EIS), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and scanning electron microscopy (SEM). The effects of different types of rust inhibitors on the film formation characteristics of a passive film on a steel bar surface were expounded. The results show that: When sodium molybdate (Na₂MoO₄) and benzotriazole (BTA) acted together, the impedance value and the capacitive reactance arc radius were the largest, and the density of the passive film and the inhibition efficiency were the highest. The composition of the passive film was primarily composed of iron compounds, and it also contained oxide and adsorption films that were formed on the steel bar surface by the rust inhibitors. The rust resistance effect was proportional to the compactness of the passive film. Full article

(This article belongs to the Special Issue Interface and Surface Modification for Durable Concretes)

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35 pages, 12446 KiB

Open AccessFeature PaperReview

High-Entropy Coatings (HEC) for High-Temperature Applications: Materials, Processing, and Properties

by Muhammad Arshad, Mohamed Amer, Qamar Hayat, Vit Janik, Xiang Zhang, Mahmoud Moradi and Mingwen Bai

Coatings 2022, 12(5), 691; https://doi.org/10.3390/coatings12050691 - 18 May 2022

Cited by 19 | Viewed by 5972

Abstract

High-entropy materials (HEM), including alloys, ceramics, and composites, are a novel class of materials that have gained enormous attention over the past two decades. These multi-component novel materials with unique structures always have exceptionally good mechanical properties and phase stability at all temperatures. [...] Read more.

High-entropy materials (HEM), including alloys, ceramics, and composites, are a novel class of materials that have gained enormous attention over the past two decades. These multi-component novel materials with unique structures always have exceptionally good mechanical properties and phase stability at all temperatures. Of particular interest for high-temperature applications, e.g., in the aerospace and nuclear sectors, is the new concept of high-entropy coatings (HEC) on low-cost metallic substrates, which has just emerged during the last few years. This exciting new virgin field awaits exploration by materials scientists and surface engineers who are often equipped with high-performance computational modelling tools, high-throughput coating deposition technologies and advanced materials testing/characterisation methods, all of which have greatly shortened the development cycle of a new coating from years to months/days. This review article reflects on research progress in the development and application of HEC focusing on high-temperature applications in the context of materials/composition type, coating process selection and desired functional properties. The importance of alloying addition is highlighted, resulting in suppressing oxidation as well as improving corrosion and diffusion resistance in a variety of coating types deposited via common deposition processes. This review provides an overview of this hot topic, highlighting the research challenges, identifying gaps, and suggesting future research activity for high temperature applications. Full article

(This article belongs to the Special Issue Advanced High-Entropy Materials and Coatings)

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11 pages, 3141 KiB

Open AccessArticle

The Effect on Energy Efficiency of Yttria-Stabilized Zirconia on Brass, Copper and Hardened Steel Nozzle in Additive Manufacturing

by Hasan Demir and Atıl Emre Cosgun

Coatings 2022, 12(5), 690; https://doi.org/10.3390/coatings12050690 - 17 May 2022

Cited by 6 | Viewed by 1716

Abstract

This study aimed to investigate if a thermal barrier coating (TBC) affected the energy efficiency of 3D printers. In accordance with this purpose, the used TBC technique is clearly explained and adapted to a nozzle in a simulation environment. Brass, copper, and hardened [...] Read more.

This study aimed to investigate if a thermal barrier coating (TBC) affected the energy efficiency of 3D printers. In accordance with this purpose, the used TBC technique is clearly explained and adapted to a nozzle in a simulation environment. Brass, copper, and hardened steel were selected to be the materials for the nozzles. The reason for the usage of a thermal barrier coating method is that the materials are made with low thermal conductivity, which reduces the thermal conductivity and energy losses. Yttria-stabilized zirconia was used to coat material on brass, copper, and hardened steel. To prevent temperature fluctuations, yttria-stabilized zirconia together with a NiCRAl bond layer was used and, thus, heat loss was prevented. Additionally, the paper addressed the effects of the coating on the average heat flux density and the average temperature of the nozzles. In addition, by means of the finite element method, steady-state thermal analyses of the coated and uncoated nozzles were compared, and the results show that the thermal barrier coating method dramatically reduced energy loss through the nozzle. It was found that the average heat flux was reduced by 89.4223% in the brass nozzle, 91.6678% in the copper nozzle, and 79.1361% in the hardened steel nozzle. Full article

(This article belongs to the Special Issue Energy Efficient Coatings)

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15 pages, 6332 KiB

Open AccessFeature PaperArticle

Overcoming the Dilemma between Low Electrical Resistance and High Corrosion Resistance Using a Ta/(Ta,Ti)N/TiN/Ti Multilayer for Proton Exchange Membrane Fuel Cells

by Rong Tu, Rui Min, Mai Yang, Yang Yuan, Long Zheng, Qizhong Li, Baifeng Ji, Song Zhang, Meijun Yang and Ji Shi

Coatings 2022, 12(5), 689; https://doi.org/10.3390/coatings12050689 - 17 May 2022

Cited by 5 | Viewed by 2296

Abstract

Bipolar plates in proton exchange membrane fuel cells (PEMFCs) are confronted by the dilemma of low contact resistance and high corrosion resistance; this study aimed to simultaneously satisfy these dimensions in a harsh environment. Using thick multilayer coatings can improve the corrosion resistance, [...] Read more.

Bipolar plates in proton exchange membrane fuel cells (PEMFCs) are confronted by the dilemma of low contact resistance and high corrosion resistance; this study aimed to simultaneously satisfy these dimensions in a harsh environment. Using thick multilayer coatings can improve the corrosion resistance, but the contact resistance would be largely compromised. To address this challenge, we propose compatible tantalum/titanium-based coatings on 316L stainless steel (SS316L) as bipolar plates for PEMFCs. With the transition layer, the optimal TaN/(Ta,Ti)N/TiN/Ti coating exhibits an ultralow corrosion current density of 0.369 μA·cm⁻² (at +0.6 V vs. SCE) and a contact resistance of 6 mΩ cm² at 138 N/cm² after 5 h of potentiostatic polarization, both of which meet the standard of the U.S. Department of Energy. Electrochemical impedance spectroscopy (EIS) and an equivalent electrical circuit model further elucidated that TaN/(Ta,Ti)N/TiN/Ti coating significantly impedes the oxidation reaction and dissolution of metals and provides good protection for the SS316L. Full article

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11 pages, 42446 KiB

Open AccessArticle

Effect of Electromagnetic Pulses on the Microstructure and Abrasive Gas Wear Resistance of Al_0.25CoCrFeNiV High Entropy Alloy

by Olga Samoilova, Nataliya Shaburova, Valeriy Krymsky, Vyacheslav Myasoedov, Ahmad Ostovari Moghaddam and Evgeny Trofimov

Coatings 2022, 12(5), 688; https://doi.org/10.3390/coatings12050688 - 16 May 2022

Cited by 3 | Viewed by 1752

Abstract

High entropy alloys (HEAs) are among the most promising materials, owing to their vast chemical composition window and unique properties. Segregation is a well-known phenomenon during the solidification of HEAs, which negatively affects their properties. The electromagnetic pulse (EMP) is a new technique [...] Read more.

High entropy alloys (HEAs) are among the most promising materials, owing to their vast chemical composition window and unique properties. Segregation is a well-known phenomenon during the solidification of HEAs, which negatively affects their properties. The electromagnetic pulse (EMP) is a new technique for the processing of a metal melt that can hinder segregation during solidification. In this study, the effect of an EMP on the microstructure and surface properties of Al_0.25CoCrFeNiV HEA is studied. An EMP, with an amplitude of 10 kV, a leading edge of 0.1 ns, a pulse duration of 1 ns, a frequency of 1 kHz, and pulse power of 4.5 MW, was employed for melt treatment. It was found that the microstructure of Al_0.25CoCrFeNiV HEA changes significantly from dendritic, for an untreated sample, to lamellar “pearlite-like”, for an EMP treated sample. Moreover, EMPs triggered the formation of a needle-like σ-phase within the solid solution grains. Finally, these microstructural and compositional changes significantly increased the microhardness of Al_0.25CoCrFeNiV HEA, from 343 ± 10 HV_0.3 (without the EMP) to 553 ± 15 HV_0.3 (after the EMP), and improved its resistance against gas-abrasive wear. Finally, an EMP is introduced as an effective route to modify the microstructure and phase formation of cast HEAs, which, in turn, opens up broad horizons for fabricating cast samples with tailorable microstructures and improved properties. Full article

(This article belongs to the Special Issue Surface Properties of Multi-Component Materials)

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11 pages, 3072 KiB

Open AccessArticle

Dual-Band Terahertz Perfect Absorber Based on Metal Micro-Nano Structure

by Zehai Guan, Yanxiu Liu, Ye Li, Peng Zhao, Yubin Zhang and Sheng Jiang

Coatings 2022, 12(5), 687; https://doi.org/10.3390/coatings12050687 - 16 May 2022

Cited by 6 | Viewed by 1846

Abstract

We propose a sub-wavelength range-based dual-band tunable ideal terahertz metamaterial perfect absorber. The absorber structure consists of three main layers, with the absorber layer consisting of a metal I-shaped structure. By simulating the incident wave absorbance of the structure, we found that the [...] Read more.

We propose a sub-wavelength range-based dual-band tunable ideal terahertz metamaterial perfect absorber. The absorber structure consists of three main layers, with the absorber layer consisting of a metal I-shaped structure. By simulating the incident wave absorbance of the structure, we found that the structure has more than 99% absorption peaks in both bands. In addition, we have investigated the relationship between structural absorbance and the structural geometrical parameters. We have studied the relationship between the thickness of the metal absorber layer

h_{b}

and the absorbance of the metamaterial structure in the 4–14 THz band. Secondly, we have studied the relationship between the thickness of the SiO₂ dielectric layer and structural absorbance. Afterwards, we have studied the relationship between the incident angle of the incident electromagnetic wave and structural absorbance. Finally, we have studied the relationship between the length of the metal structure and structural absorbance. The structure can be effectively used for detectors, thermal emitters, terahertz imaging and detection. Full article

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13 pages, 6976 KiB

Open AccessArticle

Cutting Performance of Multicomponent AlTiZrN-Coated Cemented Carbide (YG8) Tools during Milling of High-Chromium Cast Iron

by Hu Yang, Renxin Wang, Ziming Guo, Rongchuan Lin, Shasha Wei and Jianchun Weng

Coatings 2022, 12(5), 686; https://doi.org/10.3390/coatings12050686 - 16 May 2022

Cited by 2 | Viewed by 1761

Abstract

In order to improve the cutting performance of cemented-carbide (YG8) tools during the milling of high-chromium cast iron, AlTiZrN coating was deposited on the surface of YG8 samples and milling tools by physical vapor deposition (PVD) technology. The micromorphology and mechanical properties of [...] Read more.

In order to improve the cutting performance of cemented-carbide (YG8) tools during the milling of high-chromium cast iron, AlTiZrN coating was deposited on the surface of YG8 samples and milling tools by physical vapor deposition (PVD) technology. The micromorphology and mechanical properties of the coating were studied by the experimental method, and the cutting performance of the coated tools was tested by a milling machining center. The results show that the AlTiZrN coating presents the face-centered cubic (fcc) structure of TiN. The average microhardness is 3887 HV_0.05. The bonding strength between the coating and the substrate meets the standard HF3 and is up to the requirements. The coefficient of friction (COF) of the coating is about 0.32. AlTiZrN coating can significantly improve the life of cemented-carbide tools. At cutting speeds of 85, 105, and 125 mm/min, the lives of the AlTiZrN-coated tools increased by 20.7%, 22.4%, and 35.2%, respectively, compared with the uncoated tools. Under the same cutting condition, AlTiZrN-coated tools have better cutting and chip-breaking performance than uncoated tools. With the increase in cutting speed, the workpiece chips produced by AlTiZrN-coated tools are smaller and more uniform, and the scratches on the machined surface are smoother. Therefore, at higher cutting speeds, AlTiZrN-coated tools have more advantages in life and cutting performance than that of uncoated tools. During the cutting process, the wear mechanisms of the AlTiZrN-coated tools mainly included friction, oxidation, and bonding, while oxidation and bonding wear were the main wear mechanisms in the later stage of wear. Full article

(This article belongs to the Topic Surface Engineered Materials)

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18 pages, 2236 KiB

Open AccessEditor’s ChoiceArticle

Synthesis and Characterization of Boron Thin Films Using Chemical and Physical Vapor Depositions

by Bart Schurink, Wesley T. E. van den Beld, Roald M. Tiggelaar, Robbert W. E. van de Kruijs and Fred Bijkerk

Coatings 2022, 12(5), 685; https://doi.org/10.3390/coatings12050685 - 16 May 2022

Cited by 3 | Viewed by 2859

Abstract

Boron as thin film material is of relevance for use in modern micro- and nano-fabrication technology. In this research boron thin films are realized by a number of physical and chemical deposition methods, including magnetron sputtering, electron-beam evaporation, plasma enhanced chemical vapor deposition [...] Read more.

Boron as thin film material is of relevance for use in modern micro- and nano-fabrication technology. In this research boron thin films are realized by a number of physical and chemical deposition methods, including magnetron sputtering, electron-beam evaporation, plasma enhanced chemical vapor deposition (CVD), thermal/non-plasma CVD, remote plasma CVD and atmospheric pressure CVD. Various physical, mechanical and chemical characteristics of these boron thin films are investigated, i.e., deposition rate, uniformity, roughness, stress, composition, defectivity and chemical resistance. Boron films realized by plasma enhanced chemical vapor deposition (PECVD) are found to be inert for conventional wet chemical etchants and have the lowest amount of defects, which makes this the best candidate to be integrated into the micro-fabrication processes. By varying the deposition parameters in the PECVD process, the influences of plasma power, pressure and precursor inflow on the deposition rate and intrinsic stress are further explored. Utilization of PECVD boron films as hard mask for wet etching is demonstrated by means of patterning followed by selective structuring of the silicon substrate, which shows that PECVD boron thin films can be successfully applied for micro-fabrication. Full article

(This article belongs to the Special Issue Thin-Film Synthesis, Characterization and Properties)

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