Coatings

11 pages, 5061 KiB

Open AccessEditor’s ChoiceArticle

Interface Engineering Induced N, P-Doped Carbon-Shell-Encapsulated FeP/NiP₂/Ni₅P₄/NiP Nanoparticles for Highly Efficient Hydrogen Evolution Reaction

by Ting Zhang, Jianguo Zhong, Wei Gao and Yuxin Wang

Coatings 2024, 14(7), 817; https://doi.org/10.3390/coatings14070817 - 1 Jul 2024

Cited by 2 | Viewed by 1566

Abstract

Modifying the electronic structure of a catalyst through interface engineering is an effective strategy to enhance its activity in the hydrogen evolution reaction (HER). Interface engineering is a viable strategy to enhance the catalytic activity of transition metal phosphides (TMPs) in the HER [...] Read more.

Modifying the electronic structure of a catalyst through interface engineering is an effective strategy to enhance its activity in the hydrogen evolution reaction (HER). Interface engineering is a viable strategy to enhance the catalytic activity of transition metal phosphides (TMPs) in the HER process. The interface-engineered FeP/NiP₂/Ni₅P₄/NiP multi-metallic phosphide nanoparticles confined in a N, P-doped carbon matrix was developed by a simple one-step low-temperature phosphorization treatment, which only requires 72 and 155 mV to receive the current density of 10 mA/cm² in acid and alkaline electrolyte, respectively. This enhanced performance can be primarily attributed to the heterointerface of FeP/NiP₂/Ni₅P₄/NiP multi-metallic phosphides, which promotes electron redistribution and optimizes the adsorption/desorption strength of H* on the active sites. Furthermore, the N, P-doped carbon framework that encapsulates the nanoparticles inhibits their aggregation, leading to an increased availability of active sites throughout the reaction. The results of this study open up a straightforward and innovative approach to developing high-performance catalysts for hydrogen production. Full article

(This article belongs to the Section Surface Engineering for Energy Harvesting, Conversion, and Storage)

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12 pages, 4831 KiB

Open AccessEditor’s ChoiceArticle

Lifetime Extension of Atmospheric and Suspension Plasma-Sprayed Thermal Barrier Coatings in Burner Rig Tests by Pre-Oxidizing the CoNiCrAlY Bond Coats

by Jens Igel, Walter Sebastian Scheld, Daniel Emil Mack, Olivier Guillon and Robert Vaßen

Coatings 2024, 14(7), 793; https://doi.org/10.3390/coatings14070793 - 26 Jun 2024

Viewed by 1833

Abstract

Oxidation of the bond coat during turbine operation leads to additional stresses in the thermal barrier coating (TBC) system that promotes spalling of the thermal insulation. Therefore, the oxidation behavior of a TBC system plays an important role in the thermal cycling of [...] Read more.

Oxidation of the bond coat during turbine operation leads to additional stresses in the thermal barrier coating (TBC) system that promotes spalling of the thermal insulation. Therefore, the oxidation behavior of a TBC system plays an important role in the thermal cycling of a TBC system. To delay the loss of thermal insulation, research has typically focused for a long time on the composition and microstructure of the ceramic topcoats and metallic bond coats. More recently, heat treatment for the diffusion annealing of the bond coat has also become a focus of research. Several studies have shown that pre-oxidation of the bond coat prior to the application of the ceramic topcoat slows down the subsequent oxidation of the bond coat in service. The improved thermal cyclability has been demonstrated in studies for systems with atmospheric plasma-sprayed (APS), suspension plasma-sprayed (SPS) or electron beam physical vapor deposition (EB-PVD) top coatings. However, no study has directly compared the effects of pre-oxidation on different topcoats. Therefore, this study compared the effect of pre-oxidation on APS and SPS coatings with the same bond coat. For both topcoats, pre-oxidation slowed the subsequent TGO growth and thus increased the lifetime of the coatings. The improvement in lifetime was particularly pronounced for the systems with an SPS topcoat. Overall, the lifetime of the coatings with an APS topcoat was higher as the critical energy release rate within the coating was not exceeded in these coatings. Full article

(This article belongs to the Section Plasma Coatings, Surfaces & Interfaces)

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19 pages, 11634 KiB

Open AccessEditor’s ChoiceArticle

Tribological Properties and Surface Wettability of Coatings Produced on the Mg-AZ31B Alloy by Plasma Electrolytic Oxidation

by Mateusz Niedźwiedź, Marek Bara, Joanna Korzekwa, Sławomir Kaptacz, Maciej Sowa, Aleksander Olesiński and Wojciech Simka

Coatings 2024, 14(7), 780; https://doi.org/10.3390/coatings14070780 - 21 Jun 2024

Cited by 4 | Viewed by 1784

Abstract

This paper presents the influence of plasma electrolytic oxidation parameters (peak current density, process time, pulse frequency) on the tribological properties and surface wettability of the produced coatings. The process parameters were selected in accordance with Hartley’s research plan for three input variables [...] Read more.

This paper presents the influence of plasma electrolytic oxidation parameters (peak current density, process time, pulse frequency) on the tribological properties and surface wettability of the produced coatings. The process parameters were selected in accordance with Hartley’s research plan for three input variables with three variable values. Oxide coatings were made on the AZ31B magnesium alloy using a trapezoidal voltage waveform and a two-component alkaline electrolyte. The tribological properties of the coatings were determined as a result of tribological tests carried out on the T-17 tester in reciprocating motion. The tribological partner for the coatings was a PEEK/HPV pin. As a result of tribological tests, the friction coefficient µ, the mass wear of the pin and the average change in sample mass were determined. The tests showed changes in both the friction coefficient and pin wear. Before and after tribological tests, profilographometric measurements of the coatings were performed. The tests allowed for the determination of roughness parameters and the load–bearing curve of the sample surfaces. Surface wettability tests were carried out by determining the contact angles. Full article

(This article belongs to the Special Issue Surface Engineering, Coatings and Tribology)

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21 pages, 21058 KiB

Open AccessEditor’s ChoiceArticle

Tribocatalytic Reaction Enabled by TiO₂ Nanoparticle for MoDTC-Derived Tribofilm Formation at ta-C/Steel Contact

by Daiki Matsukawa, Jae-Hyeok Park, Woo-Young Lee, Takayuki Tokoroyama, Jae-Il Kim, Ryoichi Ichino and Noritsugu Umehara

Coatings 2024, 14(6), 773; https://doi.org/10.3390/coatings14060773 - 19 Jun 2024

Cited by 2 | Viewed by 1909

Abstract

Tribochemically produced triboproducts are becoming increasingly important in tribosystems and serve to improve system performance by preventing friction or wear. Diamond-like carbon (DLC) is chemically stable, which features a trade-off with tribological pros and cons. Chemically stable DLC is thermally stable and suppresses [...] Read more.

Tribochemically produced triboproducts are becoming increasingly important in tribosystems and serve to improve system performance by preventing friction or wear. Diamond-like carbon (DLC) is chemically stable, which features a trade-off with tribological pros and cons. Chemically stable DLC is thermally stable and suppresses surface damage in a high-temperature operating environment; however, it causes a detrimental effect that hinders the formation of a competent tribofilm. In this study, we dispersed highly reactive TiO₂ nanoparticles (TDONPs) in molybdenum dithiocarbamate (MoDTC)-containing lubricant for adhering triboproducts on the DLC surface. In addition, TDONPs contributed to the decomposition of triboproducts by promoting the decomposition of MoDTC through its catalytic role. Rutile TDONPs were more helpful in reducing friction than anatase TDONPs and improved the friction performance by up to ~100%. Full article

(This article belongs to the Special Issue Advanced Tribological Coatings: Fabrication and Application)

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19 pages, 21066 KiB

Open AccessEditor’s ChoiceArticle

The Influence of Bias Voltage and Gas Pressure on Edge Covering during the Arc-PVD Deposition of Hard Coatings

by Otmar Zimmer, Tim Krülle and Thomas Litterst

Coatings 2024, 14(6), 732; https://doi.org/10.3390/coatings14060732 - 7 Jun 2024

Cited by 1 | Viewed by 1525

Abstract

The edge area is especially essential for cutting tools, since this is the contact zone between the work piece and the tool. Hard coatings (PVD or CVD coatings) can protect the edge against wear and they are commonly used. The geometries of the [...] Read more.

The edge area is especially essential for cutting tools, since this is the contact zone between the work piece and the tool. Hard coatings (PVD or CVD coatings) can protect the edge against wear and they are commonly used. The geometries of the cutting edges change during the coating process, with the edge radius increasing. Therefore, the film thickness is limited and the initial radius of the uncoated tool must be smaller than the target radius of the coated edge. A new coating process based on vacuum arc PVD was developed to overcome this limitation. The film growth at the edges can be properly controlled by means of selected coating materials and process conditions. Thus, it is possible to grow edges sharper than the initial edge geometry. Different substrates were coated with different coating systems. Parameters such as the bias voltage, coating pressure, and initial radius were varied within this work. It was found that the application of a bias voltage is crucial for the generation of sharp edges. It was also found that the edge sharpening caused by coatings works best on samples with an initial radius of around 15 µm. Full article

(This article belongs to the Special Issue Advanced Coating Technology by Physical Vapor Deposition and Applications)

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18 pages, 6375 KiB

Open AccessEditor’s ChoiceArticle

Automated Crack Detection in 2D Hexagonal Boron Nitride Coatings Using Machine Learning

by Md Hasan-Ur Rahman, Bichar Dip Shrestha Gurung, Bharat K. Jasthi, Etienne Z. Gnimpieba and Venkataramana Gadhamshetty

Coatings 2024, 14(6), 726; https://doi.org/10.3390/coatings14060726 - 6 Jun 2024

Cited by 3 | Viewed by 2493

Abstract

Characterizing defects in 2D materials, such as cracks in chemical vapor deposited (CVD)-grown hexagonal boron nitride (hBN), is essential for evaluating material quality and reliability. Traditional characterization methods are often time-consuming and subjective and can be hindered by the limited optical contrast of [...] Read more.

Characterizing defects in 2D materials, such as cracks in chemical vapor deposited (CVD)-grown hexagonal boron nitride (hBN), is essential for evaluating material quality and reliability. Traditional characterization methods are often time-consuming and subjective and can be hindered by the limited optical contrast of hBN. To address this, we utilized a YOLOv8n deep learning model for automated crack detection in transferred CVD-grown hBN films, using MATLAB’s Image Labeler and Supervisely for meticulous annotation and training. The model demonstrates promising crack-detection capabilities, accurately identifying cracks of varying sizes and complexities, with loss curve analysis revealing progressive learning. However, a trade-off between precision and recall highlights the need for further refinement, particularly in distinguishing fine cracks from multilayer hBN regions. This study demonstrates the potential of ML-based approaches to streamline 2D material characterization and accelerate their integration into advanced devices. Full article

(This article belongs to the Special Issue Advances in Nanostructured Thin Films and Coatings, 2nd Edition)

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17 pages, 10024 KiB

Open AccessEditor’s ChoiceArticle

Exploring the Impact of Spray Process Parameters on Graphite Coatings: Morphology, Thickness, and Tribological Properties

by Adedoyin Abe, Josue A. Goss and Min Zou

Coatings 2024, 14(6), 714; https://doi.org/10.3390/coatings14060714 - 5 Jun 2024

Cited by 3 | Viewed by 2213

Abstract

This study explores, through a full factorial experimental design, the effects of graphite concentration and spray flow rate on the morphology, thickness, and tribological performance of graphite coatings for potential tribological applications. Coatings were applied to rough substrates using varying concentrations and flow [...] Read more.

This study explores, through a full factorial experimental design, the effects of graphite concentration and spray flow rate on the morphology, thickness, and tribological performance of graphite coatings for potential tribological applications. Coatings were applied to rough substrates using varying concentrations and flow rates, followed by analysis of their morphological characteristics, roughness, thickness, coefficient of friction (COF), and wear behavior. The results revealed distinct differences in the coating morphology based on flow rate, with low-flow-rate coatings exhibiting a porous structure and higher roughness, while high-flow-rate coatings displayed denser structures with lower roughness. A COF as low as 0.09 was achieved, which represented an 86% reduction compared to uncoated steel. COF and wear track measurements showed that thickness was influential in determining friction and the extent of wear. Flow rate dictated the coating structure, quantity of transfer film on the ball, and the extent of graphite compaction in the wear track to provide a protective layer. SEM and elemental analysis further revealed that graphite coatings provided effective protection against wear, with graphite remaining embedded in the innermost crevices of the wear track. Low flow rates may be preferable for applications requiring higher roughness and porosity, while high flow rates offer advantages in achieving denser coatings and better wear resistance. Overall, this study highlights the importance of optimizing graphite concentration and spray flow rate to tailor coating morphology, thickness, and tribological performance for practical applications. Full article

(This article belongs to the Special Issue Friction, Wear, Lubrication and Mechanics of Surfaces and Interfaces)

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16 pages, 6415 KiB

Open AccessEditor’s ChoiceArticle

Comparative Study of Multilayer Hard Coatings Deposited on WC-Co Hardmetals

by Mateja Šnajdar, Danko Ćorić and Matija Sakoman

Coatings 2024, 14(6), 674; https://doi.org/10.3390/coatings14060674 - 27 May 2024

Cited by 1 | Viewed by 1817

Abstract

This paper examines the impact of a multilayered gradient coating, applied via plasma-activated chemical vapor deposition (PACVD), on the structural and mechanical attributes of nanostructured WC-Co cemented carbides. WC-Co samples containing 5 and 15 wt.% Co were synthesized through a hot isostatic pressing [...] Read more.

This paper examines the impact of a multilayered gradient coating, applied via plasma-activated chemical vapor deposition (PACVD), on the structural and mechanical attributes of nanostructured WC-Co cemented carbides. WC-Co samples containing 5 and 15 wt.% Co were synthesized through a hot isostatic pressing (HIP) process using nanoparticle powders and coated with two distinct multilayer coatings: titanium nitride (TiN) and titanium carbonitride (TiCN). Nanosized grain formation without microstructural defects of the substrates, prior to coating, was confirmed by magnetic saturation and coercivity testing, microstructural analysis, and field emission scanning electron microscope (FESEM). Nanoindentation, fracture toughness and hardness testing were conducted for uncoated samples. After coatings deposition, characterizations including microscopy, surface roughness determination, adhesion testing, coating thickness measurement, and microhardness examination were conducted. The impact of deposited coatings on wear resistance of produced hardmetals was analyzed via scratch test and dry sliding wear test. Samples with higher Co content exhibited improved adhesion, facilitating surface cleaning and activation before coating. TiN and TiCN coatings demonstrated similar roughness on substrates of identical composition, suggesting Co content’s minimal influence on layer growth. Results of the mechanical tests showed higher microhardness, higher elastic modulus, better adhesion, and overall superior tribological properties of the TiCN coating. Full article

(This article belongs to the Special Issue Advances in Deposition and Characterization of Hard Coatings)

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12 pages, 6042 KiB

Open AccessEditor’s ChoiceArticle

Influence of Flow Rates and Flow Times of Plasma-Enhanced Atomic Layer Deposition Purge Gas on TiN Thin Film Properties

by Ju Eun Kang, Surin An and Sang Jeen Hong

Coatings 2024, 14(6), 673; https://doi.org/10.3390/coatings14060673 - 27 May 2024

Viewed by 1989

Abstract

This study investigated the effect of purge gas flow rate and purge gas flow time on the properties of TiN thin films via chemical reaction simulation and the plasma-enhanced atomic layer deposition (PEALD) process along purge gas flow rates and time settings. Chemical [...] Read more.

This study investigated the effect of purge gas flow rate and purge gas flow time on the properties of TiN thin films via chemical reaction simulation and the plasma-enhanced atomic layer deposition (PEALD) process along purge gas flow rates and time settings. Chemical reaction simulation unveiled an incremental increase in generating volatile products along purge gas flow rates. In contrast, increased purge gas flow times enhanced the desorption of physically adsorbed species flow time in the film surface. Subsequent thin film analysis showed that the increased Ar purge gas flow rate caused a shift of 44% in wafer non-uniformity, 46% in carbon composition, and 11% in oxygen composition in the deposited film. Modulations in the Ar purge gas flow time yielded variations of 50% in wafer non-uniformity, 46% in carbon composition, and 15% in oxygen content. Notably, 38% of the resistivity and 35% of the film thickness occurred due to experimental variations in the Ar purge step condition. Increased purge gas flow rates had a negligible impact on the film composition, thickness, and resistivity, but the film’s non-uniformity on a 6-inch wafer was notable. Extended purge gas flow times with inadequate flow rates resulted in undesired impurities in the thin film. This study employed a method that utilized reaction simulation to investigate the impact of purge gas flow and verified these results through film properties analysis. These findings can help in determining optimal purge conditions to achieve the desired film properties of PEALD-deposited TiN thin films. Full article

(This article belongs to the Special Issue Application of Advanced Plasma Technology in Coatings, Films and Etching)

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17 pages, 3740 KiB

Open AccessEditor’s ChoiceArticle

Magnetron-Sputtered Long-Term Superhydrophilic Thin Films for Use in Solid-State Cooling Devices

by Maria Barrera, Olaf Zywitzki, Thomas Modes and Fred Fietzke

Coatings 2024, 14(5), 622; https://doi.org/10.3390/coatings14050622 - 14 May 2024

Cited by 2 | Viewed by 1554

Abstract

Pulse-magnetron-sputtered long-term superhydrophilic coatings have been synthesized to functionalize the surfaces of solid-state cooling devices, e.g., electrocaloric heat pumps, where not only a complete wetting of the surface by a fluid is intended, but also fast wetting and dewetting processes are required. The [...] Read more.

Pulse-magnetron-sputtered long-term superhydrophilic coatings have been synthesized to functionalize the surfaces of solid-state cooling devices, e.g., electrocaloric heat pumps, where not only a complete wetting of the surface by a fluid is intended, but also fast wetting and dewetting processes are required. The coatings consist of a (Ti,Si)O₂ outer layer that provides lasting hydrophilicity thanks to the mesoporous structure, followed by an intermediate WO₃ film that enables the reactivation of the wettability through visible light irradiation, and a W underlayer which can work as a top electrode of the electrocaloric components thanks to its suitable electrical and thermal conductivity properties. Process parameter optimization for each layer of the stack as well as the influence of the microstructure and composition on the wetting properties are presented. Finally, water contact angle measurements, surface energy evaluations, and a contact line dynamics assessment of evaporating drops on the coatings demonstrate that their enhanced wetting performance is attributed not only to their intrinsic hydrophilic nature but also to their porous microstructure, which promotes wicking and spreading at the nanometric scale. Full article

(This article belongs to the Section Thin Films)

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16 pages, 5011 KiB

Open AccessEditor’s ChoiceArticle

Effect of Electrolytic Plasma Polishing on Surface Properties of Titanium Alloy

by Dongliang Yang, Huanwu Sun, Gangqiang Ji, Yuxia Xiang and Juan Wang

Coatings 2024, 14(5), 615; https://doi.org/10.3390/coatings14050615 - 13 May 2024

Cited by 6 | Viewed by 2065

Abstract

Electrolytic plasma polishing (EPPo) is an advanced metal surface finishing technology with high quality and environmental protection that has broad application prospects in the biomedical field. However, the effect of EPPo on surface properties such as corrosion resistance and the wettability of biomedical [...] Read more.

Electrolytic plasma polishing (EPPo) is an advanced metal surface finishing technology with high quality and environmental protection that has broad application prospects in the biomedical field. However, the effect of EPPo on surface properties such as corrosion resistance and the wettability of biomedical titanium alloys remains to be investigated. This paper investigated the changes in surface roughness, surface morphology, microstructure, and chemical composition of Ti6Al4V alloy by EPPo and their effects on surface corrosion resistance, wettability, and residual stress. The results showed that Ra decreased from 0.3899 to 0.0577 μm after EPPo. The surface crystallinity was improved, and the average grain size increased from 251 nm to more than 800 nm. The oxidation behavior of EPPo leads to an increase in surface oxygen content and the formation of TiO₂ and Al₂O₃ oxide layers. EPPo can significantly improve the corrosion resistance and wettability of titanium alloy in simulated body fluid and eliminate the residual stress on the sample surface. The surface properties are enhanced not only by the reduction in surface roughness but also by the formation of a denser oxide film on the surface, changes in the microstructure, an increase in surface free energy, and the annealing effect developed during EPPo. This study can provide guidance and references for applying EPPo to biomedical titanium alloy parts. Full article

(This article belongs to the Section Plasma Coatings, Surfaces & Interfaces)

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21 pages, 3508 KiB

Open AccessEditor’s ChoiceArticle

Exploring TMA and H₂O Flow Rate Effects on Al₂O₃ Thin Film Deposition by Thermal ALD: Insights from Zero-Dimensional Modeling

by Júlia Karnopp, Nilton Azevedo Neto, Thaís Vieira, Mariana Fraga, Argemiro da Silva Sobrinho, Julio Sagás and Rodrigo Pessoa

Coatings 2024, 14(5), 578; https://doi.org/10.3390/coatings14050578 - 7 May 2024

Cited by 2 | Viewed by 3860

Abstract

This study investigates the impact of vapour-phase precursor flow rates—specifically those of trimethylaluminum (TMA) and deionized water (H₂O)—on the deposition of aluminum oxide (Al₂O₃) thin films through atomic layer deposition (ALD). It explores how these flow rates [...] Read more.

This study investigates the impact of vapour-phase precursor flow rates—specifically those of trimethylaluminum (TMA) and deionized water (H₂O)—on the deposition of aluminum oxide (Al₂O₃) thin films through atomic layer deposition (ALD). It explores how these flow rates influence film growth kinetics and surface reactions, which are critical components of the ALD process. The research combines experimental techniques with a zero-dimensional theoretical model, designed specifically to simulate the deposition dynamics. This model integrates factors such as surface reactions and gas partial pressures within the ALD chamber. Experimentally, Al₂O₃ films were deposited at varied TMA and H₂O flow rates, with system conductance guiding these rates across different temperature settings. Film properties were rigorously assessed using optical reflectance methods and attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy. The experimental findings revealed a pronounced correlation between precursor flow rates and film growth. Specifically, at 150 °C, film thickness reached saturation at a TMA flow rate of 60 sccm, while at 200 °C, thickness peaked and then declined with increasing TMA flow above this rate. Notably, higher temperatures generally resulted in thinner films due to increased desorption rates, whereas higher water flow rates consistently produced thicker films, emphasizing the critical role of water vapour in facilitating surface reactions. This integrative approach not only deepens the understanding of deposition mechanics, particularly highlighting how variations in precursor flow rates distinctly affect the process, but also significantly advances operational parameters for ALD. These insights are invaluable for enhancing the application of ALD technologies across diverse sectors, including microelectronics, photovoltaics, and biomedical coatings, effectively bridging the gap between theoretical predictions and empirical results. Full article

(This article belongs to the Special Issue Functional Films/Coatings Processing Technologies: Deposition and Process)

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20 pages, 13537 KiB

Open AccessEditor’s ChoiceArticle

Influence of Selected Parameters of Zinc Electroplating on Surface Quality and Layer Thickness

by Jozef Mascenik, Tomas Coranic, Jiri Kuchar and Zdenek Hazdra

Coatings 2024, 14(5), 579; https://doi.org/10.3390/coatings14050579 - 7 May 2024

Cited by 2 | Viewed by 4462

Abstract

Surface treatment technologies are pivotal across diverse industrial sectors such as mechanical engineering, electrical engineering, and the automotive industry. Continuous advancements in manufacturing processes are geared towards bolstering efficiency and attaining superior product quality. This study aimed to empirically compare practical outcomes with [...] Read more.

Surface treatment technologies are pivotal across diverse industrial sectors such as mechanical engineering, electrical engineering, and the automotive industry. Continuous advancements in manufacturing processes are geared towards bolstering efficiency and attaining superior product quality. This study aimed to empirically compare practical outcomes with theoretical insights. Employing galvanic zinc plating under constant voltage with varying plating durations unveiled a correlation between coating thickness and electrolyte composition alongside plating duration. The graphical representation delineated the optimal electrolyte composition conducive to maximal coating thickness. Notably, an evident decrease in leveling ability was noted with prolonged plating durations. The experiment corroborated the notion that theoretical formulas for coating thickness estimation possess limited accuracy, often resulting in measured values surpassing theoretical predictions. These findings underscore the imperative for refined theoretical models to comprehensively grasp galvanic surface treatment processes. Full article

(This article belongs to the Special Issue Advances in Electrodeposited Composite Coatings: Diversity, Applications and Challenges)

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16 pages, 49708 KiB

Open AccessEditor’s ChoiceArticle

Effect of Quenching Cooling Rate on Hydrogen Embrittlement of Precipitation-Hardened Martensitic Stainless Steels

by Sicong Shen, Xingyu Ma, Xiaolong Song, Wenwen Zhao and Yong Shen

Coatings 2024, 14(5), 572; https://doi.org/10.3390/coatings14050572 - 6 May 2024

Cited by 1 | Viewed by 2450

Abstract

Heat treatment plays a decisive role in the microstructure of metallic materials. The effect of cooling rate changes caused by the quenching medium on the microstructure of steel materials should be clarified. In this study, the effect of the quenching cooling rate on [...] Read more.

Heat treatment plays a decisive role in the microstructure of metallic materials. The effect of cooling rate changes caused by the quenching medium on the microstructure of steel materials should be clarified. In this study, the effect of the quenching cooling rate on the microstructure of two precipitation-hardened martensitic stainless steels was investigated. The mechanical properties and hydrogen embrittlement susceptibility effected by the changes in the microstructure were also analyzed. A slow tensile test and hydrogen pre-charging were carried out to obtain the hydrogen embrittlement susceptibility parameters of the specimens. The results show that the quenching cooling rate only affects specific microstructures, including the twin structure and misorientation angle. Before hydrogen charging, the mechanical properties of the precipitation-hardened martensitic stainless steels were not affected by changing the quenching cooling rate. After hydrogen charging, the hydrogen embrittlement susceptibility decreased as the quenching cooling rate increased. Full article

(This article belongs to the Special Issue Deposition, Characterization and Application of Anti-corrosion and Lubricating Coatings)

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15 pages, 2681 KiB

Open AccessEditor’s ChoiceArticle

Utilizing Metal Oxide Thin Films for Device Engineering of Solution-Processed Organic Multi-Junction Solar Cells

by Afshin Hadipour

Coatings 2024, 14(5), 525; https://doi.org/10.3390/coatings14050525 - 24 Apr 2024

Cited by 2 | Viewed by 1834

Abstract

Electron and hole transporting layers play a major role in high-performance and stable organic-based optoelectronic devices. This paper demonstrates detailed device engineering of multi-junction organic photovoltaics built on two different metal oxide-based electron and hole transport (buffer) layers prepared by thermal or solution-processed [...] Read more.

Electron and hole transporting layers play a major role in high-performance and stable organic-based optoelectronic devices. This paper demonstrates detailed device engineering of multi-junction organic photovoltaics built on two different metal oxide-based electron and hole transport (buffer) layers prepared by thermal or solution-processed methods. The main focus is on the device processing parameters as well as practical details of preparation of buffer layers to give the research community a clear, step-by-step recipe to successfully replicate and build series and parallel connected multi-junction solution-based organic solar cells for their needs. Here, the recipes and deposition conditions of two metal oxide buffer layers are presented in detail, based on basic commercially available materials and tools, to achieve well-engineered tandem (multi-junction) solution-processed organic solar cells. The buffer layers have appropriate energy levels for electrical selectivity of anode and cathode electrodes, and they are highly stable and chemically compatible with processing of solution-based polymer solar cells. To demonstrate the engineering steps of multi-junction devices, the PCE10:PC70BM blend is used as the active layer for all subcells. Then, to improve the power conversion efficiency of the single-junction photovoltaic device, PCE10:PC70BM blend is used in combination with DPPx:PC70BM with different absorption spectra for bottom and top subcell active layers. An optimized series tandem device with 10.6% power conversion efficiency is demonstrated. Generally, the device structures reported here can also be used for other types of optoelectronic devices, such as light emitting diodes and photodetectors. Full article

(This article belongs to the Special Issue Advanced Metal Oxide Films: Materials and Applications)

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12 pages, 3792 KiB

Open AccessEditor’s ChoiceArticle

Controlling the Superconducting Critical Temperature and Resistance of NbN Films through Thin Film Deposition and Annealing

by Yang Pei, Qian Fan, Xianfeng Ni and Xing Gu

Coatings 2024, 14(4), 496; https://doi.org/10.3390/coatings14040496 - 17 Apr 2024

Cited by 2 | Viewed by 2545

Abstract

This study investigated the relationship between the superconducting properties, electrical properties, sputtering process parameters, and post-growth annealing of NbN films. Four series of NbN films were deposited by DC magnetron sputtering using different process parameters. With the assistance of a four-probe method, the [...] Read more.

This study investigated the relationship between the superconducting properties, electrical properties, sputtering process parameters, and post-growth annealing of NbN films. Four series of NbN films were deposited by DC magnetron sputtering using different process parameters. With the assistance of a four-probe method, the superconducting performance presented first an increase and then a decreasing trend as the resistance of the prepared films increased, which could be attributed to the variation of the N/Nb ratio in the films. This correlation implied that it is very challenging to fabricate films with both high Tc and high resistance or high Tc and low resistance by adjusting the sputtering process parameters. In order to overcome these bottlenecks, a series of films were deposited on Si, GaN/Si, SiN/Si, AlN/Si, and AlN/sapphire substrates, and the film deposited on Si was annealed at 900 °C. Annealing reduced the stress of the films on the buffer layer and increased the grain size and crystallinity of the films, except for the films on the GaN/Si substrates. This resulted in a significant decrease in the resistivity of the film and a significant increase in the superconducting transition temperature. Full article

(This article belongs to the Section Thin Films)

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11 pages, 3973 KiB

Open AccessEditor’s ChoiceArticle

The Effect of Intumescent Coating Containing Expandable Graphite onto Spruce Wood

by Elena Kmeťová, Danica Kačíková and František Kačík

Coatings 2024, 14(4), 490; https://doi.org/10.3390/coatings14040490 - 16 Apr 2024

Cited by 6 | Viewed by 2419

Abstract

Wood, one of the materials predominantly employed in construction, possesses various advantageous properties alongside certain drawbacks, such as susceptibility to thermal degradation. To enhance wood fire resistance, one approach involves the application of flame retardants. This study compared the fire-retardant effectiveness of expandable [...] Read more.

Wood, one of the materials predominantly employed in construction, possesses various advantageous properties alongside certain drawbacks, such as susceptibility to thermal degradation. To enhance wood fire resistance, one approach involves the application of flame retardants. This study compared the fire-retardant effectiveness of expandable graphite, bonded with water glass, as a coating for spruce wood against commercially available fire-retardant treatments. Spruce wood samples (Picea abies (L.) H. Karst) underwent treatment with three distinct retardants: expandable graphite in combination with water glass, Bochemit Antiflash, and Bochemit Pyro. The fire-technical characteristics of the samples were examined by a non-standard test method—a test with a radiant heat source. The experiment evaluated the fire-retardant properties by recording changes in sample mass, burning rate, and temperature difference. The best results among all flame retardants were achieved by expandable graphite in combination with water glass, in all evaluation criteria. Among all the flame retardants used, expandable graphite in combination with water glass achieved the best results in all evaluation criteria. Full article

(This article belongs to the Special Issue Advances in Surface Modification and Coatings of Wood and Wood Composites)

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13 pages, 2626 KiB

Open AccessEditor’s ChoiceArticle

Electrolyte Influence on Properties of Ultra-Thin Anodic Memristors on Titanium

by Dominik Knapic, Elena Atanasova, Ivana Zrinski, Achim Walter Hassel and Andrei Ionut Mardare

Coatings 2024, 14(4), 446; https://doi.org/10.3390/coatings14040446 - 9 Apr 2024

Cited by 1 | Viewed by 1333

Abstract

Titanium anodic memristors were prepared in phosphate buffer (PB) and citrate buffer (CB) electrolytes. Studying their I-U sweeps, the memristors presented self-rectifying and volatile behaviors. Transmission electron microscopic analysis revealed crystalline protrusions inside a semi-crystalline Ti oxide. Grounded in this, a hybrid interfacial [...] Read more.

Titanium anodic memristors were prepared in phosphate buffer (PB) and citrate buffer (CB) electrolytes. Studying their I-U sweeps, the memristors presented self-rectifying and volatile behaviors. Transmission electron microscopic analysis revealed crystalline protrusions inside a semi-crystalline Ti oxide. Grounded in this, a hybrid interfacial memristive switching mechanism relaying on partial filaments was proposed. Moreover, both analyzed memristor types demonstrated multilevel switching capabilities. The memristors anodized in the PB and CB showed high-to-low resistance ratios of 4 × 10⁴ and 1.6 × 10², respectively. The observed (more than two order of magnitude) ratio improvement of the PB memristors suggests their better performance, in spite of their modestly high resistive state instabilities, attributed to the thermal stress caused by consecutive switching. The endurance and retention of both the PB and CB memristors was measured over up to 10⁶ cycles, indicating very good lifetimes. Phosphate incorporation into the anodic oxide was confirmed by photoelectron spectroscopy analysis and was related to the improved memristive behavior of the PB sample. The presence of phosphate inside the memristively active layer modifies the availability of free O species (vacancies and ions) in the oxide. Taking all this into consideration, Ti anodic memristors anodized in PB are emphasized as candidates for neuromorphic computing. Full article

(This article belongs to the Special Issue Thin Films and Nanostructures for Electronics)

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14 pages, 29865 KiB

Open AccessEditor’s ChoiceArticle

The Use of PVD Coatings for Anti-Wear Protection of the Press-In Connection Elements

by Sławomir Kowalski

Coatings 2024, 14(4), 432; https://doi.org/10.3390/coatings14040432 - 4 Apr 2024

Cited by 5 | Viewed by 1352

Abstract

Press-in connections are the commonly used methods for connecting machinery components. In relation to that wide use, those connections are liable to various types of damage and wear. Therefore, this article proposes one of the methods which may improve the life of the [...] Read more.

Press-in connections are the commonly used methods for connecting machinery components. In relation to that wide use, those connections are liable to various types of damage and wear. Therefore, this article proposes one of the methods which may improve the life of the press-in connection. CrN+OX, TiN, and ZrN coatings made in the PVD technology were used. The coatings were applied on shafts mating with sleeves and subjected to a rotational bending moment. Tests and observations were conducted that enabled the assessment of the influence of those coatings on the development of wear, in particular fretting, in the tribological kinematic pair. The tests showed the development of wear on all the observed shaft surfaces, with a lower intensity of damage recorded on coated shafts compared to uncoated ones. The traces of fretting wear were noted each time at the edges of the connection, which is due to the mechanism of wear development under rotational bending conditions. In the case of uncoated shafts, wear occurs at the entire circumference of the axle seat in the form of a 3–4 mm wide ring; however, that width is different on either side. In the case of coated shafts, wear occurs on the circumference of the axle seat in the form of a thin ring 1–3 mm wide, depending on the coating. In the case of a ZrN coating, fretting wear appears locally. The largest surface area occupied by wear is 0.75 cm². Fretting wear comprises mainly material build-ups, pits, and surface scratches. In addition to fretting wear, damage resulting from the process of forcing the sleeve onto the shaft was observed on the tested surfaces. Full article

(This article belongs to the Section Corrosion, Wear and Erosion)

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12 pages, 2651 KiB

Open AccessEditor’s ChoiceArticle

Bioinspired Living Coating System for Wood Protection: Exploring Fungal Species on Wood Surfaces Coated with Biofinish during Its Service Life

by Faksawat Poohphajai, Ana Gubenšek, Anja Černoša, Karen Butina Ogorelec, Lauri Rautkari, Jakub Sandak and Anna Sandak

Coatings 2024, 14(4), 430; https://doi.org/10.3390/coatings14040430 - 3 Apr 2024

Cited by 2 | Viewed by 1931

Abstract

Biofinish is an innovative wood protection system inspired by biological processes. It enhances the hydrophobicity of wood through oil treatment, resulting in improved dimensional stability. Living cells of the fungus Aureobasidium pullulans effectively protect wood from deterioration caused by other decaying fungi. The [...] Read more.

Biofinish is an innovative wood protection system inspired by biological processes. It enhances the hydrophobicity of wood through oil treatment, resulting in improved dimensional stability. Living cells of the fungus Aureobasidium pullulans effectively protect wood from deterioration caused by other decaying fungi. The melanin pigment produced by the fungus provides an appealing dark surface and additionally protects the wood substrate against UV radiation. The significant advantage of Biofinish is its remarkable self-healing ability, which distinguishes it from conventional wood protection methods. This research aimed to explore fungal species colonising surfaces exposed to natural weathering and assess the survival of A. pullulans on wood surfaces coated with Biofinish during its in-service period. This study was performed on a facade composed of European larch wood (Larix decidua) treated with linseed oil and coated with Biofinish at the InnoRenew CoE building in Izola, Slovenia, following a 9-month exposure period. The majority of the detected species belonged to the genera Aureobasidium. The results indicated the survival and effective antagonistic action of A. pullulans, the living and active ingredient of the coating, against other wood-decaying fungi. Full article

(This article belongs to the Special Issue New Challenges in Wood Adhesives and Coatings, 2nd Edition)

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15 pages, 4800 KiB

Open AccessEditor’s ChoiceArticle

Dual Strategy Based on Quantum Dot Doping and Phenylethylamine Iodide Surface Modification for High-Performance and Stable Perovskite Solar Cells

by Shulan Zhang, Renjie Chen, Mujing Qu, Biyu Long, Nannan He, Sumei Huang, Xiaohong Chen, Huili Li and Tongtong Xuan

Coatings 2024, 14(4), 409; https://doi.org/10.3390/coatings14040409 - 29 Mar 2024

Cited by 1 | Viewed by 1461

Abstract

High-quality perovskite films (PFs) are crucial for achieving high-performance perovskite solar cells (PSCs). Herein, we report a dual-modification strategy via incorporating CsPbBr₃ QDs into MAPbI₃ perovskite bulk and capping the interface of the perovskite/hole transport layer (HTL) with phenylethylamine iodide (PEAI) [...] Read more.

High-quality perovskite films (PFs) are crucial for achieving high-performance perovskite solar cells (PSCs). Herein, we report a dual-modification strategy via incorporating CsPbBr₃ QDs into MAPbI₃ perovskite bulk and capping the interface of the perovskite/hole transport layer (HTL) with phenylethylamine iodide (PEAI) to improve perovskite crystallinity and interface contact properties to acquire high-quality PFs with fewer defects. CsPbBr₃ QDs promoted perovskite grain growth and reduced bulk defects, while PEAI surface modification passivated interfaces, improved hydrophobic properties, and prevented carrier recombination at the perovskite/HTL interface. Benefiting from growth control and the effective suppression of both bulk and interface carrier recombination, the resulting devices show a greatly improved photoelectric conversion efficiency (PCE) from 17.21% of the reference cells to 21.04% with a champion Voc of 1.15 V, Jsc of 23.30 mA/cm², and fill factor (FF) of 78.6%. Furthermore, the dual-modification strategy endows PFs with promoted moisture tolerance, and the nonencapsulated PSCs retain 75% of their initial efficiency after aging for 30 days at 40% relative humidity and room temperature, which is significantly higher than the 59% value of the original PSCs. Good operational stability and the maintained efficiency of the target device over time suggest the potential for future commercialization. Full article

(This article belongs to the Special Issue Perovskite Photovoltaics: From Materials to Device Applications)

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24 pages, 8097 KiB

Open AccessEditor’s ChoiceArticle

CoCrFeMnNi_0.8V/Cr₃C₂-Ni₂₀Cr High-Entropy Alloy Composite Thermal Spray Coating: Comparison with Monolithic CoCrFeMnNi_0.8V and Cr₃C₂-Ni₂₀Cr Coatings

by Stavros Kiape, Maria Glava, Emmanuel Georgatis, Spyros Kamnis, Theodore E. Matikas and Alexandros E. Karantzalis

Coatings 2024, 14(4), 402; https://doi.org/10.3390/coatings14040402 - 28 Mar 2024

Cited by 2 | Viewed by 1816

Abstract

High-entropy alloys (HEAs) are revolutionizing the field of surface engineering, challenging traditional alloy frameworks with their superior mechanical attributes and resistance to corrosion. This investigation delves into the properties of the CoCrFeMnNi_0.8V HEAs, both as a standalone material and when blended [...] Read more.

High-entropy alloys (HEAs) are revolutionizing the field of surface engineering, challenging traditional alloy frameworks with their superior mechanical attributes and resistance to corrosion. This investigation delves into the properties of the CoCrFeMnNi_0.8V HEAs, both as a standalone material and when blended with Cr₃C₂-Ni₂₀Cr, to evaluate their efficacy as cutting-edge surface treatments. The addition of vanadium to the CoCrFeMnNi_0.8V alloy results in a distinctive microstructure that improves hardness and resistance to abrasion. The incorporation of Cr₃C₂-Ni₂₀Cr particles enhances the alloy’s toughness and longevity. Employing high-velocity oxy-fuel (HVOF) thermal spray methods, these coatings are deposited onto steel substrates and undergo detailed evaluations of their microstructural characteristics, abrasion, and corrosion resistance. Findings reveal the CoCrFeMnNi_0.8V coating’s exceptional ability to withstand corrosion, especially in environments rich in chlorides. The hybrid coating benefits from the combination of the HEA’s inherent corrosion resistance and the enhanced wear and corrosion resistance provided by Cr₃C₂-Ni₂₀Cr, delivering comprehensive performance for high-stress applications. Through the fine-tuning of the application process, the Cr₃C₂-Ni₂₀Cr reinforced high-entropy alloy coating emerges as a significant advancement in protective surface technology, particularly for use in marine and corrosive settings. This study not only highlights the adaptability of HEAs in surface engineering but also prompts further investigation into innovative material pairings. Full article

(This article belongs to the Special Issue Modern Methods of Shaping the Structure and Properties of Coatings)

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17 pages, 8868 KiB

Open AccessEditor’s ChoiceArticle

Effect of Conformal Coating on Electrochemical Migration Behavior of Multi-Layer Ceramic Capacitor for Automotives Based on Water Drop Test

by Young-Ran Yoo, Seokyeon Won and Young-Sik Kim

Coatings 2024, 14(3), 359; https://doi.org/10.3390/coatings14030359 - 18 Mar 2024

Cited by 2 | Viewed by 2329

Abstract

A large amount of multi-layer ceramic capacitor (MLCC) is mounted inside a printed circuit board (PCB) constituting electronic components. The use of MLCC in electric vehicles and the latest mobile phones is rapidly increasing with the latest technology. Environments in which electronic components [...] Read more.

A large amount of multi-layer ceramic capacitor (MLCC) is mounted inside a printed circuit board (PCB) constituting electronic components. The use of MLCC in electric vehicles and the latest mobile phones is rapidly increasing with the latest technology. Environments in which electronic components are used are becoming more diverse and conformal coatings are being applied to protect mounted components from these environments. In particular, MLCCs in electronic components mainly have voltage applied. They might be used in environments where humidity exists for various reasons. In a humid environment, electrochemical migration (ECM) will occur, with the cathode and anode on the surface of the MLCC encountering each other. This can result in product damage due to a short circuit. In this study, the effects of voltage, NaCl concentration, and distance between electrodes on a non-mount MLCC, surface mount MLCC, and solder pad pattern were evaluated using a water drop test (WDT). Based on the analysis of the effects of the presence of conformal coating, applied voltage, concentration of NaCl, and the distance between electrodes, a mechanism model for ECM behavior in MLCCs was proposed. Full article

(This article belongs to the Special Issue Recent Advances in Surface Functionalisation)

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19 pages, 33776 KiB

Open AccessEditor’s ChoiceArticle

Properties of Diamond-like Tungsten-Doped Carbon Coatings Lubricated with Cutting Fluid

by Krystyna Radoń-Kobus, Monika Madej, Joanna Kowalczyk and Katarzyna Piotrowska

Coatings 2024, 14(3), 342; https://doi.org/10.3390/coatings14030342 - 13 Mar 2024

Cited by 3 | Viewed by 1976

Abstract

In this paper, the authors investigated the impact of DLC coatings doped with tungsten (a-C:H:W) coatings obtained using plasma-assisted physical vapor deposition (PVD) on the properties of the 100Cr6 steel. The results of the 100Cr6 steel specimens with and without the coating were [...] Read more.

In this paper, the authors investigated the impact of DLC coatings doped with tungsten (a-C:H:W) coatings obtained using plasma-assisted physical vapor deposition (PVD) on the properties of the 100Cr6 steel. The results of the 100Cr6 steel specimens with and without the coating were compared. Scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) analysis were used to observe the morphology of the coating surfaces and cross-sections and identify the elements in the coating composition. The contact angle of the investigated surfaces was measured with a tensiometer. Additionally, the effect of the coatings on the tribological properties of lubricated friction pairs was evaluated. Friction tests were performed on a ball-on-disc tribometer under lubrication with cutting fluid. The surface texture of the samples before and after the tribological tests was measured using a confocal profilometer. The results obtained from the tests and analysis allow for the conclusion that the use of DLC coatings a-C:H:W increases the hardness of 100Cr6 steel by three times. The values of the contact angles were indicative of surface hydrophilic characteristics. The tungsten-doped diamond-like coating under friction conditions reduced the coefficient of friction and wear. DLC coatings a-C:H:W lubricated with the cutting fluid improve the mechanical and tribological properties of 100Cr6 steel sliding surfaces under friction. Full article

(This article belongs to the Special Issue Advances in Deposition and Characterization of Hard Coatings)

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13 pages, 3731 KiB

Open AccessEditor’s ChoiceArticle

Fabrication of Thin TEG (Bi-Ni) Using Magnetron Sputtering Technology and Investigations

by Žydrūnas Kavaliauskas, Arūnas Baltušnikas, Mindaugas Milieška and Vitas Valinčius

Coatings 2024, 14(3), 335; https://doi.org/10.3390/coatings14030335 - 12 Mar 2024

Viewed by 1412

Abstract

As the industry develops more and more, heat is produced during fabrication processes, resulting in an excess of heat. One of the ways to solve the problem can be the conversion of excess heat into electricity using a thermoelectric generator (TEG). The authors [...] Read more.

As the industry develops more and more, heat is produced during fabrication processes, resulting in an excess of heat. One of the ways to solve the problem can be the conversion of excess heat into electricity using a thermoelectric generator (TEG). The authors of this paper propose a method of using thin-film TEGs for electricity generation, a procedure that has been given little attention to in the literature. In this study, thin TEGs (about 50–100 nm thick) were obtained from Bi-Ni, using magnetron sputtering technology. This type of TEG can be used not only as a device that generates electricity, but also as a protective layer for various systems, protecting them from environmental influences. In addition, such TEGs can be formed on a complex, uneven surface, with various details changing their geometric shape. As shown from XRD studies, the obtained Bi-Ni layer is polycrystalline. XRD studies help to determine whether the layer obtained is composed of pure layers of Bi and Ni metals or whether metal oxides have formed (metal oxides have a negative effect on electrical conductivity). An increase in the temperature from 80 to 120 K, respectively, increases the voltage generated by the TEG from 0.01 to 0.03 V. Meanwhile, the efficiency of such TEG element changes from 1 to 4.5% when the temperature change increases from 30 to 119 K. Full article

(This article belongs to the Section Surface Characterization, Deposition and Modification)

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16 pages, 6487 KiB

Open AccessEditor’s ChoiceArticle

An Edge Detection Algorithm for SEM Images of Multilayer Thin Films

by Wei Sun, Fang Duan, Jianpeng Zhu, Minglai Yang and Ying Wang

Coatings 2024, 14(3), 313; https://doi.org/10.3390/coatings14030313 - 5 Mar 2024

Cited by 3 | Viewed by 3615

Abstract

In processing multilayer thin film materials, scanning electron microscopy (SEM) is commonly employed for observation. In images of SEM, backscattered electron (BSE) images is particularly suitable for distinguishing different components and layers of the films. However, at high magnification levels, BSE images often [...] Read more.

In processing multilayer thin film materials, scanning electron microscopy (SEM) is commonly employed for observation. In images of SEM, backscattered electron (BSE) images is particularly suitable for distinguishing different components and layers of the films. However, at high magnification levels, BSE images often have blurriness and noise, leading to low edge sharpness. This study proposes a method for improving the integrity and accuracy of the edges. First, we segment the image into different contrast regions using the masking algorithm. Second, we enhance the images in separate regions by the enhancement algorithm. Finally, we combine the regions by logical operations. In instantiation, we implement our approach on SEM-BSE images. It was found that the edges are significantly sharpened through the assessment of the edge evaluation algorithm. Full article

(This article belongs to the Section Thin Films)

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19 pages, 6241 KiB

Open AccessEditor’s ChoiceArticle

Investigating the Impact of Physical Vapour Deposition (PVD)-Coated Cutting Tools on Stress Corrosion Cracking Susceptibility in Turning Super Duplex Stainless Steel

by Edinei Locks, Qianxi He, Jose M. DePaiva, Monica Guimaraes, Abul Fazal Arif, Stephen C. Veldhuis and Joey R. Kish

Coatings 2024, 14(3), 290; https://doi.org/10.3390/coatings14030290 - 28 Feb 2024

Cited by 6 | Viewed by 2168

Abstract

This work aimed to ascertain the corresponding influences of several PVD-coated cutting tools on the susceptibility of the machined surface of super duplex stainless steel (SDSS) to stress corrosion cracking. Coatings comprised of AlCrN, AlCrN/TiSiN, and AlTiN were applied to cemented carbide cutting [...] Read more.

This work aimed to ascertain the corresponding influences of several PVD-coated cutting tools on the susceptibility of the machined surface of super duplex stainless steel (SDSS) to stress corrosion cracking. Coatings comprised of AlCrN, AlCrN/TiSiN, and AlTiN were applied to cemented carbide cutting tools using the PVD method; these were then used to turn the outer surface of the SDSS tube section. During the cutting process, the material presents the following combination of features: (i) a tendency for strain hardening, reflected in microstructural modifications and residual stresses of the machined surface and (ii) high temperatures in the cutting region, reducing the tool life. The goal of this work was to evaluate the surface integrity (work hardening and corrosion behaviour) of the SDSS obtained after the machining process (finish turning) with cemented carbide tools coated with three different PVD coatings. Full article

(This article belongs to the Special Issue Corrosion/Wear Mechanisms and Protective Methods)

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8 pages, 3398 KiB

Open AccessEditor’s ChoiceCommunication

The Facile Construction of Anatase Titanium Dioxide Single Crystal Sheet-Connected Film with Observable Strong White Photoluminescence

by Tao He, Dexin Wang, Yu Xu and Jing Zhang

Coatings 2024, 14(3), 292; https://doi.org/10.3390/coatings14030292 - 28 Feb 2024

Cited by 1 | Viewed by 1464

Abstract

Deposited by a reactive atmospheric pressure non-thermal TiCl₄/O₂/Ar plasma, anatase TiO₂ single crystal sheet-connected film exhibits two large exposed {001} facets and a high concentration of oxygen defects. Strong white photoluminescence centered at 542 nm has been observed [...] Read more.

Deposited by a reactive atmospheric pressure non-thermal TiCl₄/O₂/Ar plasma, anatase TiO₂ single crystal sheet-connected film exhibits two large exposed {001} facets and a high concentration of oxygen defects. Strong white photoluminescence centered at 542 nm has been observed with naked eyes, whose internal quantum efficiency is 0.62, and whose intensity is comparable to that of commercial fluorescent lamp interior coatings. Based on the simulation results of a hybrid global–analytical model developed on this atmospheric pressure non-equilibrium plasma system, the mechanism of a self-confined growth of single crystal sheets was proposed. A high concentration of oxygen defects is in situ incorporated into the anatase crystal lattice without damaging its crystallographic orientation. This method opens a new way to construct 3D porous metal-oxide single crystal sheet-connected films with two exposing high energy surfaces and a large concentration of oxygen defects. Full article

(This article belongs to the Special Issue Recent Advances in the Development of Thin Films)

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22 pages, 40607 KiB

Open AccessEditor’s ChoiceArticle

Influence of the Al Content on the Electrochemical Behavior of Zn-Al Cold-Sprayed Coatings in the Context of the Deep Geological Disposal of Radioactive Waste

by Alice Martin, Gaëlle Charrier, Valérie Maillot, Didier Crusset, Fanny Gouraud, Christophe Verdy, Egle Conforto, René Sabot, Juan Creus and Philippe Refait

Coatings 2024, 14(3), 261; https://doi.org/10.3390/coatings14030261 - 22 Feb 2024

Viewed by 1364

Abstract

For high-level radioactive waste, the French National Radioactive Waste Management Agency is currently developing a 500 m deep geological disposal facility called Cigéo. Carbon steel containers will be used to contain the wastes in the specific conditions of the disposal. The use of [...] Read more.

For high-level radioactive waste, the French National Radioactive Waste Management Agency is currently developing a 500 m deep geological disposal facility called Cigéo. Carbon steel containers will be used to contain the wastes in the specific conditions of the disposal. The use of a sacrificial coating was studied as an additional protection for the containers against corrosion. A previous work had shown the possibility to use Zn-Al coatings in this specific medium. To optimize the coatings’ performance, the cold-spraying process was considered instead of the previously used wire arc spraying because it can increase the cohesion between the particles in the coating. Moreover, three aluminum contents, i.e., 5, 15 and 25 wt.%, were considered. The characterization of the obtained coatings revealed a strongly heterogeneous composition for the lower Al content (5 wt.%), with local Al contents from 1.3 wt.% Al to 44.5 wt.% Al. The corrosion study was carried out in a specific solution mimicking the pore solution of the surrounding cementitious material designed for disposal at a temperature of 50 °C. First, the polarization curves acquired with coated steel electrodes revealed the pseudo-passive behavior of the 25 wt.% Al coating, while for the other compositions, the coating remained active. Moreover, the higher aluminum content (25 wt.%) induced an important decrease in potential, with a possible risk of hydrogen embrittlement for the protected steel. Secondly, the sacrificial properties were investigated through 6 months of experiments using coated electrodes with cross-like defects and coated electrodes coupled with bare steel electrodes. Whatever the composition of the coating, the protection was maintained, with the 15 wt.% Al coating giving the best performance. Full article

(This article belongs to the Section Corrosion, Wear and Erosion)

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16 pages, 4495 KiB

Open AccessEditor’s ChoiceReview

On Numerical Modelling and an Experimental Approach to Heterojunction Tandem Solar Cells Based on Si and Cu₂O/ZnO—Results and Perspectives

by Laurentiu Fara, Irinela Chilibon, Ileana Cristina Vasiliu, Dan Craciunescu, Alexandru Diaconu and Silvian Fara

Coatings 2024, 14(3), 244; https://doi.org/10.3390/coatings14030244 - 20 Feb 2024

Cited by 1 | Viewed by 1598

Abstract

A comparative analysis of three advanced architectures for tandem solar cells (SCs) is discussed, respectively: metal oxide, thin film, and perovskite. Plasmonic solar cells could further increase solar cell efficiency. Using this development, an innovative PV technology (an SHTSC based on metal oxides) [...] Read more.

A comparative analysis of three advanced architectures for tandem solar cells (SCs) is discussed, respectively: metal oxide, thin film, and perovskite. Plasmonic solar cells could further increase solar cell efficiency. Using this development, an innovative PV technology (an SHTSC based on metal oxides) represented by a four-terminal Cu₂O/c-Si tandem heterojunction solar cell is investigated. The experimental and numerical modelling study defines the main aim of this paper. The experimental approach to SHTSCs is analysed: (1) a Cu₂O layer is deposited using a magnetron sputtering system; (2) the morphological and optical characterization of Cu₂O thin films is studied. The electrical modelling of silicon heterojunction tandem solar cells (SHTSCs) is discussed based on five simulation tools for the optimized performance evaluation of solar devices. The main novelty of this paper is represented by the following results: (1) the analysis suggests that the incorporation of a buffer layer can improve the performance of a tandem heterojunction solar cell; (2) the effect of interface defects on the electrical characteristics of the AZO/Cu₂O heterojunction is discussed; (3) the stability of SHTSCs based on metal oxides is studied to highlight the degradation rate in order to define a reliable solar device. Perspectives on SHTSCs based on metal oxides, as well as Si perovskite tandem solar cells with metal oxides as carrier-selective contacts, are commented on. Full article

(This article belongs to the Special Issue Optical Thin Film and Photovoltaic (PV) Related Technologies, Volume II)

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11 pages, 23726 KiB

Open AccessEditor’s ChoiceArticle

Microstructure, Wear Resistance and Corrosion Resistance of CrN Coating with Platinum-Iridium Co-Doping

by Di Yang, Feng Yan, Weilun Zhang and Zhiwen Xie

Coatings 2024, 14(2), 238; https://doi.org/10.3390/coatings14020238 - 18 Feb 2024

Cited by 2 | Viewed by 2041

Abstract

A novel Pt-Ir co-doping strategy was devised to enhance the corrosion resistance of CrN coating. The deposited CrN coating exhibits a coherent growth pattern, resulting in significant mechanical strength and large grain sizes. However, during the corrosion process, corrosive fluids infiltrate through growth [...] Read more.

A novel Pt-Ir co-doping strategy was devised to enhance the corrosion resistance of CrN coating. The deposited CrN coating exhibits a coherent growth pattern, resulting in significant mechanical strength and large grain sizes. However, during the corrosion process, corrosive fluids infiltrate through growth defects, leading to inadequate corrosion resistance of the coating. By incorporating Pt-Ir atoms as dopants, coherent grain growth is effectively hindered, yielding a uniformly smooth surface. Simultaneously, localized non-coherent lattice growth occurs due to co-doping in the coatings, impacting the mechanical properties of CrN-PtIr coatings and causing multidirectional fracture. Nevertheless, this dense coating surface impedes the penetration of corrosive fluids and enhances the corrosion resistance of the coating to some extent. Full article

(This article belongs to the Special Issue Advances in Corrosion Resistant Coatings)

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11 pages, 12013 KiB

Open AccessEditor’s ChoiceCommunication

Interface Modulation of CoNi Alloy Decorated with Few-Layer Reduced Graphene Oxide for High-Efficiency Microwave Absorption

by Hai Xie, Jinmei Li, Yaoming Zhang, Juan Yang, Tingmei Wang and Qihua Wang

Coatings 2024, 14(2), 228; https://doi.org/10.3390/coatings14020228 - 15 Feb 2024

Cited by 2 | Viewed by 1804

Abstract

Metal-organic frameworks (MOFs)-derived microwave absorbers with tunable components and microstructures show great potential in microwave absorption. Herein, we report a facile thermal reduction approach for synthesizing CoNi alloy/reduced graphene oxide (CoNi/rGO) composites from bimetallic CoNi-MOFs. By tuning the ratio of graphene oxide (GO) [...] Read more.

Metal-organic frameworks (MOFs)-derived microwave absorbers with tunable components and microstructures show great potential in microwave absorption. Herein, we report a facile thermal reduction approach for synthesizing CoNi alloy/reduced graphene oxide (CoNi/rGO) composites from bimetallic CoNi-MOFs. By tuning the ratio of graphene oxide (GO) in the precursors, the resulting CoNi/rGO-2 composite demonstrates optimal microwave absorption performance with a minimum reflection loss (RL_min) of −66.2 dB at 7.6 GHz in the C band. Moreover, the CoNi/rGO-2 with 50 wt% filler loading achieves a maximum effective absorption bandwidth (EAB) of 6.8 GHz (10.6–17.4 GHz) at a thickness of 2.5 mm, almost spanning the entire Ku band and a portion of the X band. The outstanding performance of CoNi/rGO-2 is ascribed to the high magnetic loss from the CoNi alloy and the incorporation of rGO, which induces interfacial polarization to enhance the dielectric loss and improve the impedance matching of composite. These favorable findings highlight the considerable potential and superiority of the CoNi/rGO-2 composite as an electromagnetic wave absorption material. This work sets forth a viable strategy for designing high-efficiency alloy/rGO absorbers. Full article

(This article belongs to the Special Issue Functional Magnetic and Dielectric Composites: Fabrication, Properties and Applications)

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17 pages, 9908 KiB

Open AccessEditor’s ChoiceArticle

Enhanced Osteogenic Activity and Antibacterial Properties of Graphene Oxide-Poly(Lactic Acid) Films for the Repair of Cranial Defects in Rats

by Kai Liu, Wen Lai, Jianyong Wu and Yongjian Lu

Coatings 2024, 14(2), 223; https://doi.org/10.3390/coatings14020223 - 12 Feb 2024

Cited by 5 | Viewed by 1989

Abstract

The failure of bone defect repair caused by bacterial infection is a significant clinical challenge. However, the currently utilized bone graft materials lack antibacterial properties, necessitating the development of bone repair materials with both osteoinductive and antibacterial capabilities. Graphene oxide (GO) has garnered [...] Read more.

The failure of bone defect repair caused by bacterial infection is a significant clinical challenge. However, the currently utilized bone graft materials lack antibacterial properties, necessitating the development of bone repair materials with both osteoinductive and antibacterial capabilities. Graphene oxide (GO) has garnered considerable attention due to its distinctive physical, chemical, and biological characteristics. In this study, we prepared a graphene oxide-poly(lactic acid) (GO-PLA) film with exceptional biological properties. In vitro investigations demonstrated that the GO-PLA film substantially enhanced the adhesion and proliferation capacity of rat bone marrow mesenchymal stem cells (rBMSCs). Furthermore, we observed augmented alkaline phosphatase activity as well as increased expression levels of osteogenic genes in rBMSCs cultured on the GO-PLA film. Additionally, we evaluated the antibacterial activity of our samples using gram-positive Streptococcus mutans (Sm) and gram-negative Actinobacillus actinomycetemcomitans (Aa). Our findings revealed that GO doping significantly inhibited bacterial growth. Moreover, implantation experiments conducted on rat skull defects demonstrated excellent guided bone regeneration performance exhibited by the GO-PLA film. Overall, our results indicate that the GO-PLA film possesses outstanding osteogenic and antibacterial properties, making it a promising biomaterial for bone tissue regeneration. Full article

(This article belongs to the Section Thin Films)

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10 pages, 3330 KiB

Open AccessEditor’s ChoiceArticle

Microstructure and Dry-Sliding Wear Resistance of CoCrFeNiMoTi_x High Entropy Alloy Coatings Produced by Laser Cladding

by Hui Liang, Jinxin Hou, Li Jiang and Zhiqiang Cao

Coatings 2024, 14(2), 221; https://doi.org/10.3390/coatings14020221 - 12 Feb 2024

Cited by 5 | Viewed by 3208

Abstract

The new-type CoCrFeNiMoTi_x high-entropy alloy coatings were successfully devised and prepared on Q235 steel using laser cladding. Influence of Ti content on their microstructure and wear-resistance was studied systematically; the relevant mechanisms were deeply revealed. The CoCrFeNiMoTi_x coatings consisted of NiTi, [...] Read more.

The new-type CoCrFeNiMoTi_x high-entropy alloy coatings were successfully devised and prepared on Q235 steel using laser cladding. Influence of Ti content on their microstructure and wear-resistance was studied systematically; the relevant mechanisms were deeply revealed. The CoCrFeNiMoTi_x coatings consisted of NiTi, FCC, and BCC phases, and with the increasing of Ti content, contents of BCC phase and FCC phase gradually increased and decreased, respectively. The CoCrFeNiMoTi₀.₇₅ coating had the highest hardness (950 HV), which was about 6.5 times higher than the substrate (Q235 steel, 150 HV). According to Archard law, metal materials’ wear resistance is generally proportional to hardness; thus, the CoCrFeNiMoTi₀.₇₅ high entropy alloy coating with the highest hardness showed the best wear resistance, exhibiting a wear mechanism of slight abrasive wear. Full article

(This article belongs to the Special Issue Advances in Wear-Resistant Coatings)

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17 pages, 4918 KiB

Open AccessEditor’s ChoiceArticle

The Antibacterial Properties of a Silver Multilayer Coating for the Prevention of Bacterial Biofilm Formation on Orthopedic Implants—An In Vitro Study

by Sanne W. G. van Hoogstraten, Janine Fechter, Rainer Bargon, Julia L. van Agtmaal, Laura C. W. Peeters, Jan Geurts and Jacobus J. C. Arts

Coatings 2024, 14(2), 216; https://doi.org/10.3390/coatings14020216 - 9 Feb 2024

Cited by 2 | Viewed by 2993

Abstract

The prevention of biofilm formation on orthopedic implants is essential, as biofilms are the main challenge in the effective treatment of periprosthetic joint infection (PJI). A silver multilayer (SML) coating was developed to prevent biofilm formation on the implant surface. Previous studies have [...] Read more.

The prevention of biofilm formation on orthopedic implants is essential, as biofilms are the main challenge in the effective treatment of periprosthetic joint infection (PJI). A silver multilayer (SML) coating was developed to prevent biofilm formation on the implant surface. Previous studies have already demonstrated its antibacterial properties without cytotoxic effects. However, the coating has not been previously tested when applied to common titanium surfaces used in total joint arthroplasty implants. These surfaces often have increased roughness and porosity in the case of cementless implants, which can alter the antibacterial effect of the coating. In this study, we assessed the antibacterial and anti-biofilm properties of the SML coating on corundum-blasted and plasma-sprayed microporous-coated titanium alloy surfaces, using S. aureus, S. epidermidis, and E. coli. An antibacterial activity test following the principles of ISO 22196, ASTM E2180-18, and JIS Z 2801 standards was performed, as well as a biofilm proliferation assay investigating bacterial adhesion and biofilm formation. The SML coating exhibited strong antibacterial effects for all bacterial strains. After 24 h biofilm culture, a >4-log reduction in CFU was induced by the SML coating for S. epidermidis and E. coli on the corundum-blasted and plasma-sprayed microporous-coated titanium surfaces, respectively, when compared to the uncoated surfaces. The coating showed bactericidal properties against Gram-positive bacteria on the corundum-blasted discs. The SML coating on two common titanium surfaces demonstrates significant potential as an effective strategy in combating PJI across a wide range of orthopedic implants. Full article

(This article belongs to the Special Issue Advances in Antibacterial Coatings: From Materials to Applications)

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19 pages, 10815 KiB

Open AccessEditor’s ChoiceArticle

The Influence of TiO₂ Nanoparticles on the Physico–Mechanical and Structural Characteristics of Cementitious Materials

by Carmen T. Florean, Horatiu Vermesan, Gyorgy Thalmaier, Bogdan V. Neamtu, Timea Gabor, Cristina Campian, Andreea Hegyi and Alexandra Csapai

Coatings 2024, 14(2), 218; https://doi.org/10.3390/coatings14020218 - 9 Feb 2024

Cited by 8 | Viewed by 2049

Abstract

The urgent need for sustainable construction that corresponds to the three pillars of sustainable development is obvious and continuously requires innovative solutions. Cementitious composites with TiO₂ nanoparticles (NT) addition show potential due to their improved durability, physico–mechanical characteristics, and self-cleaning capacity. This [...] Read more.

The urgent need for sustainable construction that corresponds to the three pillars of sustainable development is obvious and continuously requires innovative solutions. Cementitious composites with TiO₂ nanoparticles (NT) addition show potential due to their improved durability, physico–mechanical characteristics, and self-cleaning capacity. This study aimed to evaluate the influence of NT on cementitious composites by comparing those with 2%–5% nanoparticles with a similar control sample without nanoparticles, as well as an analysis of cost growth. The experimental results showed an increase in bulk density of the material (4.7%–7.4%), reduction in large pore sizes by min. 12.5%, together with an increase in cumulative volume and cumulative specific surface area of small pore sizes, indicating densification of the material, also supported by SEM, EDS, and XRD analyses indicating acceleration of cement hydration processes with formation of specific products. The changes at microstructural level support the experimental results obtained at macrostructural level, i.e., modest but existent increases in flexural strength (0.6%–7.9%) and compressive strength (0.2%–2.6%) or more significant improvements in abrasion resistance (8.2%–58%) and reduction in water absorption coefficient (37.5%–81.3%). Following the cost–benefit analysis, it was concluded that, for the example case considered of a pedestrian pavement with a surface area of 100 m², using 100 mm thick slabs, if these slabs were to be made with two layers, the lower layer made of cementitious composite as a reference and the upper layer with a thickness of 10 mm made of cementitious composite with 3% NT or 4% NT, the increase in cost would be acceptable, representing less than 15% compared to the cost for the exclusive use of cementitious composite without NT. Full article

(This article belongs to the Special Issue Development and Characterization of New Construction Materials and Coatings)

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34 pages, 17972 KiB

Open AccessEditor’s ChoiceReview

Plasma Electrolytic Oxidation (PEO) as a Promising Technology for the Development of High-Performance Coatings on Cast Al-Si Alloys: A Review

by Patricia Fernández-López, Sofia A. Alves, Jose T. San-Jose, Eva Gutierrez-Berasategui and Raquel Bayón

Coatings 2024, 14(2), 217; https://doi.org/10.3390/coatings14020217 - 9 Feb 2024

Cited by 15 | Viewed by 5454

Abstract

Cast Al-Si alloys, recognized for their excellent mechanical properties, constitute one of the most widely employed non-ferrous substrates in several sectors, and are particularly relevant in the transport industry. Nevertheless, these alloys also display inherent limitations that significantly restrict their use in several [...] Read more.

Cast Al-Si alloys, recognized for their excellent mechanical properties, constitute one of the most widely employed non-ferrous substrates in several sectors, and are particularly relevant in the transport industry. Nevertheless, these alloys also display inherent limitations that significantly restrict their use in several applications. Among these limitations, their low hardness, low wear resistance, or limited anti-corrosion properties, which are often not enough when the component is subjected to more severe environments, are particularly relevant. In this context, surface modification and the development of coatings are essential for the application of cast Al-Si alloys. This review focuses on the development of coatings to overcome the complexities associated with improving the performance of cast Al-Si alloys. Against this background, plasma electrolytic oxidation (PEO), an advanced electrochemical treatment that has revolutionized the surface modification of several metallic alloys in recent years, emerges as a promising approach. Despite the growing recognition of PEO technology, the achievement of high-performance coatings on cast Al-Si is still a challenge nowadays, for which reason this review aims to provide an overview of the PEO treatment applied to these alloys. In particular, the impact of the electrolyte chemical composition on the properties of the coatings obtained on different alloys exposed to harsh environments has been analyzed and discussed. By addressing the existing gaps and challenges, this paper contributes to a better understanding of the intricacies associated with the development of robust PEO coatings on cast Al-Si alloys. Full article

(This article belongs to the Special Issue Plasma Electrolytic Oxidation (PEO) Coatings, 2nd Edition)

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17 pages, 3199 KiB

Open AccessEditor’s ChoiceArticle

The Wavelet Transform for Feature Extraction and Surface Roughness Evaluation after Micromachining

by Daniel Grochała, Rafał Grzejda, Arkadiusz Parus and Stefan Berczyński

Coatings 2024, 14(2), 210; https://doi.org/10.3390/coatings14020210 - 6 Feb 2024

Cited by 14 | Viewed by 1986

Abstract

Miniaturization is a dominant trend in machine building which requires the use of advanced techniques of manufacturing and control. Apart from dimensional and shape precision of miniaturized components, surface geometry, particularly roughness and so-called microroughness that results from the use of advanced treatment [...] Read more.

Miniaturization is a dominant trend in machine building which requires the use of advanced techniques of manufacturing and control. Apart from dimensional and shape precision of miniaturized components, surface geometry, particularly roughness and so-called microroughness that results from the use of advanced treatment techniques, plays an important role in correct assembly, reliable operation and durability of the whole machine. The selection of filtration method in surface geometry of micro-objects can be a substantial problem. The authors of the paper propose to use wavelet filtration in digital processing of a point cloud to remove measurement noise and not to change the surface character of the measured object. Also, the authors propose, in this paper, some criteria for selecting the number of wavelet filtration levels based on minimalization of the RMS value. It is supposed to improve the efficiency of low-pass filtration of small areas of the surface, particularly compared to traditional λs Gaussian filtration. Full article

(This article belongs to the Special Issue Recent Trends in Precision Measurement of Metals and Alloys)

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10 pages, 2233 KiB

Open AccessEditor’s ChoiceArticle

Coconut-Solid-Waste-Derived Hard-Carbon Anode Materials for Fast Potassium Ion Storage

by Yi Ma, Wenhao Liu, Wenhan Liu, Guangwan Zhang, Yu Wang, Haokai Wang, Wei Chen, Meng Huang and Xuanpeng Wang

Coatings 2024, 14(2), 208; https://doi.org/10.3390/coatings14020208 - 6 Feb 2024

Cited by 6 | Viewed by 2033

Abstract

Hard carbon, which features recyclability, low costs, and environmental friendliness, is an attractive anode material for K⁺ storage. Nevertheless, the state-of-the-art hard carbon is still unsatisfactory due to its poor multiplication performance and unclear energy storage mechanism. In this study, a one-pot [...] Read more.

Hard carbon, which features recyclability, low costs, and environmental friendliness, is an attractive anode material for K⁺ storage. Nevertheless, the state-of-the-art hard carbon is still unsatisfactory due to its poor multiplication performance and unclear energy storage mechanism. In this study, a one-pot carbonisation method using coconut solid waste biomass is applied to obtain high-performance hard-carbon (CHC) anode materials. The microstructure and electrochemical properties of the CHC are investigated at different carbonisation temperatures (1100–1500 °C). The CHC materials prepared at 1300 °C (CHC1300) have a high capacity of 265.8 mAh g⁻¹ at a current density of 25 mA g⁻¹ and a superior cyclability of 1000 cycles at 1.0 A g⁻¹ with a capacity retention of 96.6%. This approach, referred to as the “biomass-to-application” strategy, holds promise for advancing the development of cost-effective and sustainable KIBs. Full article

(This article belongs to the Section Surface Engineering for Energy Harvesting, Conversion, and Storage)

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15 pages, 7136 KiB

Open AccessEditor’s ChoiceArticle

Friction Evolution of Graphite Bearing Impregnated with Polymer Subjected to Vibration Fretting at High Temperature

by Hamid Zaïdi, Stéphane Tournis, Leila Deville, Caroline Richard, Mohamed Aissa and Kaouthar Bouguerra

Coatings 2024, 14(2), 207; https://doi.org/10.3390/coatings14020207 - 6 Feb 2024

Cited by 1 | Viewed by 1629

Abstract

To address friction and wear challenges in dry contacts, manufacturers often employ self-lubricating materials. Graphite and its derivatives stand out as particularly suitable due to their exceptional tribological properties. However, under intense friction conditions, graphite can experience a decline in lubricating efficiency due [...] Read more.

To address friction and wear challenges in dry contacts, manufacturers often employ self-lubricating materials. Graphite and its derivatives stand out as particularly suitable due to their exceptional tribological properties. However, under intense friction conditions, graphite can experience a decline in lubricating efficiency due to severe abrasive wear. This abrasive damage results in elevated activated carbon surfaces with increased surface energy, fostering greater adhesion between sliding surfaces. The low friction coefficient of graphite is not an inherent property but rather a consequence of water vapor adsorption by the material. Beyond 150 °C, desorption of the vapor occurs, leading to a transition in the friction coefficient from µ = 0.1 to µ = 0.6. To address this issue, impregnation solutions for self-lubricating materials have been developed, with various compositions tailored to specific objectives. Common types include molybdenum disulfide, soft metals and polymers. In this predominantly experimental study, the impact of polymer impregnation on the evolution of friction force and wear rate in graphite material bearings subjected to a dry fretting contact under severe thermal stresses at 270 °C was investigated. Additionally, the mechanical stresses in the bearings throughout different phases of our tests were analyzed using a numerical model. Full article

(This article belongs to the Section Corrosion, Wear and Erosion)

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44 pages, 6271 KiB

Open AccessEditor’s ChoiceReview

Recent Advances in the Application of Metal Oxide Nanomaterials for the Conservation of Stone Artefacts, Ecotoxicological Impact and Preventive Measures

by Marwa Ben Chobba, Maduka L. Weththimuni, Mouna Messaoud, Clara Urzi and Maurizio Licchelli

Coatings 2024, 14(2), 203; https://doi.org/10.3390/coatings14020203 - 4 Feb 2024

Cited by 6 | Viewed by 3230

Abstract

Due to the ongoing threat of degradation of artefacts and monuments, the conservation of cultural heritage items has been gaining prominence on the global scale. Thus, finding suitable approaches that can preserve these materials while keeping their natural aspect of is crucial. In [...] Read more.

Due to the ongoing threat of degradation of artefacts and monuments, the conservation of cultural heritage items has been gaining prominence on the global scale. Thus, finding suitable approaches that can preserve these materials while keeping their natural aspect of is crucial. In particular, preventive conservation is an approach that aims to control deterioration before it happens in order to decrease the need for the intervention. Several techniques have been developed in this context. Notably, the application of coatings made of metal oxide nanomaterials dispersed in polymer matrix can be effectively address stone heritage deterioration issues. In particular, metal oxide nanomaterials (TiO₂, ZnO, CuO, and MgO) with self-cleaning and antimicrobial activity have been considered as possible cultural heritage conservative materials. Metal oxide nanomaterials have been used to strengthen heritage items in several studies. This review seeks to update the knowledge of different kinds of metal oxide nanomaterials, especially nanoparticles and nanocomposites, that have been employed in the preservation and consolidation of heritage items over the last 10 years. Notably, the transport of nanomaterials in diverse environments is undoubtedly not well understood. Therefore, controlling their effects on various neighbouring non-target organisms and ecological processes is crucial. Full article

(This article belongs to the Special Issue Heritage Conservation and Restoration: Surface Characterization, Cleaning and Treatments)

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18 pages, 5323 KiB

Open AccessEditor’s ChoiceArticle

Interface Interaction between MoO₃ and Carbon Dots Derived from Chitosan Promoted the Photocurrent Extraction Ability of Carriers in a Wide Range of the Light Spectrum

by Xingfa Ma, Mingjun Gao, Xintao Zhang, You Wang and Guang Li

Coatings 2024, 14(2), 171; https://doi.org/10.3390/coatings14020171 - 29 Jan 2024

Cited by 3 | Viewed by 1922

Abstract

Due to the large number of defects at the grain boundaries of nanocomposites, defects have a significant effect on the physico-chemical properties of a material. Therefore, controlling the charging behaviour of functional nanocomposites in a non-contact manner with a light field can improve [...] Read more.

Due to the large number of defects at the grain boundaries of nanocomposites, defects have a significant effect on the physico-chemical properties of a material. Therefore, controlling the charging behaviour of functional nanocomposites in a non-contact manner with a light field can improve their physical and chemical properties. Chitosan-derived carbon dots were synthesised by exploiting the abundant N element in chitosan. In order to passivate the defects of chitosan-derived carbon dots, a MoO₃/carbon dot nanocomposite was constructed in this study to tailor the band gap and improve the extraction ability of carriers through light induction. The results showed that the strong interfacial interaction between MoO₃ and carbon dots enhanced the optical absorption and interfacial charge transfer in the visible and some near-infrared regions. The resulting MoO₃/carbon dot heterostructure was coated on A4 printing paper, and electrodes were integrated in the coating film. The photocurrent signals of the thick film were investigated using 405, 532, 650, 808, 980 and 1064 nm light sources. The results indicated that the phenomenon of photocurrent switching to the visible light and some near-infrared light regions was observed. The charge carrier extraction ability of the MoO₃/carbon dot nanocomposite through light triggering was much better than that of chitosan-derived carbon dots. The on/off ratio and response speed of the MoO₃/carbon dot nanocomposite were significantly improved. The physical mechanism was discussed based on the ordered and disordered structures of polymer-derived carbon nanomaterials. This material could be applicable to the development of broadband flexible photosensors, artificial vision or light-utilising interdisciplinary fields. Full article

(This article belongs to the Section Surface Engineering for Energy Harvesting, Conversion, and Storage)

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24 pages, 5414 KiB

Open AccessEditor’s ChoiceArticle

Study of the Geochemical Decay and Environmental Causes of Granite Stone Surfaces in the Built Heritage of Barbanza Peninsula (Galicia, NW Spain)

by Ana C. Hernandez, Jorge Sanjurjo-Sánchez, Carlos Alves and Carlos A. M. Figueiredo

Coatings 2024, 14(2), 169; https://doi.org/10.3390/coatings14020169 - 28 Jan 2024

Cited by 5 | Viewed by 4240

Abstract

In Galicia (NW Spain), granite was the most used stone material in historical buildings. Despite the good properties of granite as a construction material, it overcomes several physical and chemical weathering processes that cause decay, resulting in a loss of value in building [...] Read more.

In Galicia (NW Spain), granite was the most used stone material in historical buildings. Despite the good properties of granite as a construction material, it overcomes several physical and chemical weathering processes that cause decay, resulting in a loss of value in building materials, architectural elements and details. This is caused by a range of processes, from aesthetic damage to stone erosion. The causes of such decay are well known from case studies of historical buildings, being correlated with atmospheric agents, air pollution and aggregate materials, among others. In this work, we studied 15 historical monuments built with granite blocks of the architectural Heritage of the Barbanza Peninsula (Galicia). Because of the geographic features of this area, there is a steep rainfall and sea spray gradient that allows us to study historical buildings exposed to different environmental conditions in a short distance from the shoreline to inland. We used geochemical, petrological and microscopic tools to assess the decay of the granites and compared the results with environmental factors to assess the role of humidity (rainfall) and sea spray on the decay. Both the observation of coatings and the assessment of weathering have shown that buildings close to the shoreline are more affected by sea salts, while buildings far from the coast are mostly affected by biological weathering. Surprisingly, chemical weathering is higher in a strip area some hundreds of meters away from the sea shore and at lower altitudes (between 10 and 30 m). Indeed, very good correlation is observed for weathering indices, such as CIA, MWPI, VR, Si-Ti index, Kr, CAN and AKN, with a distance to the shoreline from 0.5 km, with linear correlation values ranging from −0.91 to 0.80. Full article

(This article belongs to the Section Surface Characterization, Deposition and Modification)

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17 pages, 916 KiB

Open AccessEditor’s ChoiceArticle

Temperature Coefficient of Electronic Polarizability in Thin Polymer Films Deposited on Si and SiO₂ Substrates Determined via Spectroscopic Ellipsometry

by Henryk Bednarski, Barbara Hajduk, Paweł Jarka and Pallavi Kumari

Coatings 2024, 14(2), 166; https://doi.org/10.3390/coatings14020166 - 27 Jan 2024

Cited by 2 | Viewed by 1822

Abstract

Ellipsometry is widely used to determine the thermo-optical properties of thin polymer films. However, if the thermo-optic coefficient (TOC) and the linear thermal expansion coefficient (LTEC) are to be used to determine the temperature coefficient of electronic polarizability (TCEP) in thin polymer films, [...] Read more.

Ellipsometry is widely used to determine the thermo-optical properties of thin polymer films. However, if the thermo-optic coefficient (TOC) and the linear thermal expansion coefficient (LTEC) are to be used to determine the temperature coefficient of electronic polarizability (TCEP) in thin polymer films, their values must be determined with the greatest possible accuracy, as both have the opposite effect. In this article, we analyze changes in ellipsometric parameters resulting from changes in the thin film temperature in order to develop a data analysis method for temperature-dependent spectroscopic ellipsometry that will facilitate the accurate determination of thermo-optical parameters, including the TCEP, in polymer thin films. As practical application examples, we identified optimal spectral windows to accurately determine the thermo-optical parameters of 50 to 150 nm-thick PMMA thin films deposited on Si and SiO₂ substrates. The influence of thin-film thickness on the accuracy of TOC and LTEC determination is discussed. Full article

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

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17 pages, 4276 KiB

Open AccessEditor’s ChoiceArticle

Revolutionizing Construction Safety with Geopolymer Composites: Unveiling Advanced Techniques in Manufacturing Sandwich Steel Structures Using Formwork-Free Spray Technology

by Van Su Le and Kinga Setlak

Coatings 2024, 14(1), 146; https://doi.org/10.3390/coatings14010146 - 21 Jan 2024

Viewed by 1999

Abstract

The article discusses the fabrication of sandwich steel and geopolymer structures using spray technology without the need for formwork. In the article, the effects of high temperatures on geopolymer materials are analyzed and their mechanical properties and durability are examined. The importance of [...] Read more.

The article discusses the fabrication of sandwich steel and geopolymer structures using spray technology without the need for formwork. In the article, the effects of high temperatures on geopolymer materials are analyzed and their mechanical properties and durability are examined. The importance of geopolymer coatings for steel protection is also highlighted, and specific features such as the setting time, application process, attachment strength, fire testing, and production costs are analyzed. The materials and methods used in the study are described, including the composition of geopolymer binders and the process of applying geopolymer coatings to steel plates. The research includes test methods such as strength tests, density tests, thermal conductivity tests, accelerated aging tests, microstructure analyses, pore size analyses, and fire resistance tests. The research section concludes with a summary of the chemical and phase composition of the materials and a discussion of the fire resistance of the geopolymer composites (GCs). The results show that GC foams offer excellent thermal insulation, providing up to 75 min of fire resistance with a 6 mm coating, reducing temperatures by 150 °C compared to uncoated steel. GC foams have a density of 670 kg/m³, a thermal conductivity of 0.153 W/m∙K, and a cost effectiveness of USD 250 per cubic meter. Full article

(This article belongs to the Section Surface Characterization, Deposition and Modification)

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12 pages, 5843 KiB

Open AccessEditor’s ChoiceArticle

Influence of the Gas Flow Rate on the Crack Formation of AlCoCrNi High-Entropy Metallic Film Fabricated Using Magnetron Sputtering

by Young-Soon Kim, Hae-Jin Park, Young-Seok Kim, Sung-Hwan Hong and Ki-Buem Kim

Coatings 2024, 14(1), 144; https://doi.org/10.3390/coatings14010144 - 21 Jan 2024

Cited by 2 | Viewed by 1755

Abstract

In the present study, the AlCoCrNi high-entropy metallic film was deposited on a Si wafer using a magnetron sputtering system. To capture the effects of the sputtering parameters on the microstructure and mechanical properties of the film, the flow rate of Ar gas [...] Read more.

In the present study, the AlCoCrNi high-entropy metallic film was deposited on a Si wafer using a magnetron sputtering system. To capture the effects of the sputtering parameters on the microstructure and mechanical properties of the film, the flow rate of Ar gas injected into the chamber (5, 7, and 8 sccm) was controlled. All films were identified as being of BCC phase with compositions of near equiatomic proportions, regardless of the gas flow rates. Nano-scale clusters were observed on the surfaces of all films, and nano-cracks were found in the film deposited at the Ar gas flow rate of 8 sccm, unlike the films deposited at the gas flow rates of 5 and 7 sccm. Detailed microstructural analysis of film deposition at an Ar gas flow rate of 8 sccm indicated that the void boundaries contribute to the formation of nano-cracks. The nano-indentation results indicated that the Ar gas flow rate 5 sccm specimen, with the smallest cluster size at the topmost surface, showed the highest hardness (12.21 ± 1.05 GPa) and Young’s modulus (188.1 ± 11 GPa) values. Full article

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

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13 pages, 3189 KiB

Open AccessEditor’s ChoiceArticle

Exploring the Influence of the Deposition Parameters on the Properties of NiTi Shape Memory Alloy Films with High Nickel Content

by André V. Fontes, Patrícia Freitas Rodrigues, Daniela Santo and Ana Sofia Ramos

Coatings 2024, 14(1), 138; https://doi.org/10.3390/coatings14010138 - 20 Jan 2024

Cited by 2 | Viewed by 2096

Abstract

NiTi shape memory alloy films were prepared by magnetron sputtering using a compound NiTi target and varying deposition parameters, such as power density, pressure, and deposition time. To promote crystallization, the films were heat treated at a temperature of 400 °C for 1 [...] Read more.

NiTi shape memory alloy films were prepared by magnetron sputtering using a compound NiTi target and varying deposition parameters, such as power density, pressure, and deposition time. To promote crystallization, the films were heat treated at a temperature of 400 °C for 1 h. For the characterization, scanning electron microscopy, energy dispersive X-ray spectroscopy, atomic force microscopy, synchrotron X-ray diffraction, and nanoindentation techniques were used on both as-deposited and heat-treated films. Apart from the morphology and hardness of the as-deposited films that depend on the deposition pressure, the power applied to the target and the deposition pressure did not seem to significantly influence the characteristics of the NiTi films studied. After heat treatment, austenitic (B2) crystalline superelastic films with exceptionally high nickel content (~60 at.%) and vein-line cross-section morphology were produced. The crystallization of the films resulted in an increase in hardness, Young’s modulus, and elastic recovery. Full article

(This article belongs to the Special Issue Advances in Metal Matrix Composite Coatings and Layers: Microstructure, Physicochemical and Mechanical Properties)

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11 pages, 3861 KiB

Open AccessEditor’s ChoiceArticle

Preparation of Metal–Organic-Framework-Derived Fe-CN@CoCN Nanocomposites and Their Microwave Absorption Performance

by Shuning Ren, Pengfei Ju, Haojie Yu, Bohua Nan, Li Wang, Aizhen Lian, Xusheng Zang and Hongyu Liang

Coatings 2024, 14(1), 133; https://doi.org/10.3390/coatings14010133 - 19 Jan 2024

Cited by 4 | Viewed by 1779

Abstract

Microwave technology is commonly used in many fields such as wireless communication and medical treatment, which are closely related to social development. However, electromagnetic pollution caused by microwaves is gradually increasing and the demand for high-performance microwave absorption materials is also increasing. Porous [...] Read more.

Microwave technology is commonly used in many fields such as wireless communication and medical treatment, which are closely related to social development. However, electromagnetic pollution caused by microwaves is gradually increasing and the demand for high-performance microwave absorption materials is also increasing. Porous materials obtained by the pyrolysis of metal–organic frameworks (MOFs) at high temperatures exhibit good conductivity and magnetism, and the original skeleton structure of MOFs can be maintained; thus, MOF-derived materials can be considered viable candidates of microwave absorption materials. In this paper, Fe-CN@CoCN materials were prepared by pyrolyzing a ferrocene (Fc)-doped core–shell zeolite imidazole framework (Fc-ZIF-8@ZIF-67) at 700, 800, and 900 °C for 2 h in an Ar atmosphere. The obtained Fe-CN@CoCN-0.25-700 nanocomposite exhibited excellent microwave absorption (MA) performance with a minimum reflection loss (RL_min) of −42.27 dB at 5.68 GHz and an effective absorption bandwidth (EAB, RL < −10 dB) of 4.80 GHz at a thickness of 2.5 mm. The Fe-CN@CoCN-0.25-800 nanocomposite possessed optimized MA properties with an RL_min of −40.78 dB at 12.56 GHz and an EAB of 4.16 GHz at relatively low thickness of 2 mm. Fe-CN@CoCN nanocomposites are expected to be efficient materials for microwave absorption coatings. Full article

(This article belongs to the Section Surface Engineering for Energy Harvesting, Conversion, and Storage)

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11 pages, 3617 KiB

Open AccessEditor’s ChoiceArticle

Improved Heat Dissipation of Dip-Coated Single-Walled Carbon Nanotube/Mesh Sheets with High Flexibility and Free-Standing Strength for Thermoelectric Generators

by Katsuma Miura, Takuya Amezawa, Saburo Tanaka and Masayuki Takashiri

Coatings 2024, 14(1), 126; https://doi.org/10.3390/coatings14010126 - 18 Jan 2024

Cited by 5 | Viewed by 2011

Abstract

Single-walled carbon nanotubes (SWCNTs) are promising thermoelectric materials used in thermoelectric generators (TEGs) to power sensors. However, the limitation of SWCNTs is their high thermal conductivity, which makes it difficult to create a sufficient temperature difference. In this study, we fabricated dip-coated SWCNT/mesh [...] Read more.

Single-walled carbon nanotubes (SWCNTs) are promising thermoelectric materials used in thermoelectric generators (TEGs) to power sensors. However, the limitation of SWCNTs is their high thermal conductivity, which makes it difficult to create a sufficient temperature difference. In this study, we fabricated dip-coated SWCNT/mesh sheets using an SWCNT dispersion. Several types of mesh materials were tested, and the most suitable material was polyphenylene sulfide (PPS). SWCNTs were uniformly deposited on the PPS mesh surface without filling the mesh openings. The SWCNT/PPS mesh sheets exhibited flexibility and free-standing strength. When the edge of the SWCNT/PPS mesh sheets were heated, a higher temperature gradient was produced compared with that of the conventional SWCNT film owing to the increase in heat dissipation. A flexible and free-standing TEG with an area of 1200 mm², fabricated using SWCNT/PPS mesh sheets, exhibited an output voltage of 31.5 mV and maximum power of 631 nW at a temperature difference of 60 K (T_low: 320 K). When the TEG was exposed to wind at 3 m/s, temperature difference further increased, and the performance of the TEG increased by a factor of 1.3 for output voltage and 1.6 for maximum power. Therefore, we demonstrated that the TEG’s performance could be improved using SWCNT/PPS mesh sheets. Full article

(This article belongs to the Special Issue Thermoelectric Thin Films for Thermal Energy Harvesting)

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12 pages, 11049 KiB

Open AccessEditor’s ChoiceArticle

High-Temperature Heat Treatment of Plasma Sprayed Ti–Si–C–Mo Coatings

by Jining He, Jialin Liu, Hongjian Zhao, Yanfang Qin and Jiawei Fan

Coatings 2024, 14(1), 109; https://doi.org/10.3390/coatings14010109 - 15 Jan 2024

Cited by 1 | Viewed by 1400

Abstract

In this work, the effect of 800 °C and 1100 °C post-heat treatment on the plasma spraying of Ti–Si–C–xMo (x = 1.0, 1.5) composite coatings was investigated. The composite coatings were composed of TiC, Ti₃SiC₂, Ti₅Si₃ [...] Read more.

In this work, the effect of 800 °C and 1100 °C post-heat treatment on the plasma spraying of Ti–Si–C–xMo (x = 1.0, 1.5) composite coatings was investigated. The composite coatings were composed of TiC, Ti₃SiC₂, Ti₅Si₃ and Mo₅Si₃ reacted phases. After heat treatment, the Ti₃SiC₂ and Mo₅Si₃ phases increased. The coating microhardness decreased by 16% and 18% for Ti–Si–C–1.0Mo and Ti–Si–C–1.5Mo coatings, respectively, after heat treatment at 1100 °C. Fracture toughness increased by 16% for the Ti–Si–C–1.5Mo coating after heat treatment at 1100 °C, which was mainly due to the heat treatment promoting Ti₃SiC₂ formation, healing micro-cracks, reducing the internal stress and making the microstructure dense. The coating friction coefficient before and after heat -treatment was between 0.4 and 0.6. After heat treatment, the wear amount of the coating was first reduced and then increased, and the minimum wear loss occurred after heat treatment at 800 °C. The wear mechanism was mixed abrasive wear, adhesive wear and tribo-oxidation wear. Full article

(This article belongs to the Special Issue Advanced Materials and Surface Protection)

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