Coatings

1 pages, 119 KiB

Open AccessCorrection

Correction: Liu et al. Synthesis and Characterization of Silane-Coupled Sodium Silicate Composite Coatings for Enhanced Anticorrosive Performance. Coatings 2025, 15, 428

by Minghui Liu, Zhiwen Tan, Shengda Xu, Yuantao Zhao, Haoran Wang, Shitao Zhang, Rong Ma, Tao Jiang, Zhen Ma, Ning Zhong and Wenge Li

Coatings 2025, 15(5), 515; https://doi.org/10.3390/coatings15050515 (registering DOI) - 25 Apr 2025

Abstract

In the original publication [...] Full article

13 pages, 843 KiB

Open AccessArticle

Effect of Climatic and Thermal Aging on Friction of Frost-Resistant Rubber With and Without Ultra-High Molecular Weight Polyethylene Coating

by Ivan Shkalei, Jeng-Haur Horng, Elena Torskaya, Pavel Bukovsky, Aleksey Morozov, Fedor Stepanov, Natalia Petrova, Afanasy Dyakonov and Vasilii Mukhin

Coatings 2025, 15(5), 514; https://doi.org/10.3390/coatings15050514 - 24 Apr 2025

Abstract

The polymer composite frost-resistant rubber–UHMWPE (ultra-high molecular weight polyethylene) has simultaneously damping, anti-wear and anti-friction properties. To use it in seals operating in northern climatic conditions, it is necessary to study the effect of climatic aging on mechanical, strength and tribological properties of [...] Read more.

The polymer composite frost-resistant rubber–UHMWPE (ultra-high molecular weight polyethylene) has simultaneously damping, anti-wear and anti-friction properties. To use it in seals operating in northern climatic conditions, it is necessary to study the effect of climatic aging on mechanical, strength and tribological properties of the composite. In this study, climatic aging of rubber and UHMWPE separately was made at testing ground in Yakutsk (Russia), as well as accelerated thermal aging of the composite in laboratory conditions. Comparison of the results of climatic and laboratory aging showed that climatic aging has a negative effect on the properties of both rubber and UHMWPE. Accelerated aging, on the contrary, leads to an improvement in the anti-friction properties of the composite with a small (about 10 percent) increase in its stiffness. Thus, with prolonged use in friction units, the composite should be protected from radiation and ozone. Full article

(This article belongs to the Special Issue Wear and Tribology Properties of Materials, Films and Coatings)

12 pages, 6490 KiB

Open AccessArticle

Research on the Correlation of Physical Properties Between NbN Superconducting Thin Films and Substrates

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

Coatings 2025, 15(5), 513; https://doi.org/10.3390/coatings15050513 - 24 Apr 2025

Abstract

This paper investigates the relationship between the physical properties of NbN thin films and a series of different substrates/buffer layers used for the thin film growth. Substrates, including 4H-SiC, AlN/Si, AlN/sapphire, and annealed AlN/sapphire, were selected for NbN film deposition via DC magnetron [...] Read more.

This paper investigates the relationship between the physical properties of NbN thin films and a series of different substrates/buffer layers used for the thin film growth. Substrates, including 4H-SiC, AlN/Si, AlN/sapphire, and annealed AlN/sapphire, were selected for NbN film deposition via DC magnetron sputtering. Post-deposition annealing was also employed to study its impact on the films’ quality. Comprehensive characterizations were performed on NbN films, focusing on superconducting critical temperature (T_C), transition width (ΔT_C), crystalline quality, and surface roughness. The results demonstrate that the annealed NbN films grown on 4H-SiC substrates with the highest crystalline quality exhibit optimal crystalline quality, achieving a T_C of 16.3 K. Experimental results reveal intrinsic correlations between the critical properties of NbN superconducting thin films and substrate structural characteristics; the impact of post-growth annealing on the T_C is also studied. Full article

(This article belongs to the Special Issue Electrochemical Properties and Applications of Thin Films)

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18 pages, 5060 KiB

Open AccessArticle

Highly Sensitive and Tunable Graphene Metamaterial Perfect Absorber in the Near-Terahertz Band

by Siwen Zhang, Kele Chen, Tangyou Sun, Qianju Song, Zao Yi and Yougen Yi

Coatings 2025, 15(5), 512; https://doi.org/10.3390/coatings15050512 - 24 Apr 2025

Abstract

This paper presents a highly sensitive and tunable graphene-based metamaterial perfect absorber (MPA) operating in the near-terahertz band. The structure features a unique flower-like graphene pattern, consisting of a Au substrate, a SiO₂ dielectric layer, and the patterned graphene. Multiple reflections of [...] Read more.

This paper presents a highly sensitive and tunable graphene-based metamaterial perfect absorber (MPA) operating in the near-terahertz band. The structure features a unique flower-like graphene pattern, consisting of a Au substrate, a SiO₂ dielectric layer, and the patterned graphene. Multiple reflections of incident light between the gold and graphene layers increase the duration and intensity of the interaction, resulting in efficient absorption at specific frequencies. The design utilizes surface plasmon resonance (SPR) to achieve near-perfect absorption of 99.9947% and 99.6079% at 11.7475 THz and 15.8196 THz, respectively. By tuning the Fermi level and relaxation time of graphene, it is possible to precisely control the frequency and absorptivity of the absorption peak, thereby demonstrating the dynamic tunability of the absorber. The high symmetry and periodic arrangement of the structure ensures insensitivity to the polarization angle of the incident light in the range of 0° to 90°, making it extremely valuable in practical applications. In addition, the absorber exhibits very high sensitivity to changes in ambient refractive index with a maximum sensitivity of 3.205 THz/RIU, a quality factor (FOM) of 11.3011 RIU⁻¹, and a Q-Factor of 48.61. It has broad application prospects in the fields of sensors, optoelectronic devices, and terahertz imaging. Full article

(This article belongs to the Section Thin Films)

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19 pages, 6268 KiB

Open AccessArticle

Performance of Micronized Biowax Powders Replacing PTFE Fillers in Bio-Based Epoxy Resin Coatings

by Pieter Samyn, Chris Vanheusden and Patrick Cosemans

Coatings 2025, 15(5), 511; https://doi.org/10.3390/coatings15050511 - 24 Apr 2025

Abstract

In view of sustainable-by-design issues, there is an urgent need for replacing harmful coating ingredients with more ecological, non-toxic alternatives from bio-based sources. In particular, fluorine derivatives such as polytetrafluoroethylene (PTFE) powders are frequently applied as coating additives because of their versatile role [...] Read more.

In view of sustainable-by-design issues, there is an urgent need for replacing harmful coating ingredients with more ecological, non-toxic alternatives from bio-based sources. In particular, fluorine derivatives such as polytetrafluoroethylene (PTFE) powders are frequently applied as coating additives because of their versatile role in rendering hydrophobicity and lubrication. In this research, a screening study is presented regarding the performance of alternative micronized biowax powders, produced from various natural origins, when used as functional additives in protective epoxy coatings for wood. The micronized wax powders from bio-based sources (carnauba wax, rice bran wax, amide biowax) and reference fossil sources (PE wax/PTFE, PE wax, PTFE), of large (8 to 11 µm) and small sizes (4 to 6 µm), were added into fully bio-based epoxy clear coat formulations based on epoxidized flaxseed oil and proprietary acid hardener. Within concentration ranges of 0.5 to 10 wt.-%, it was observed that rice bran micropowders present higher hardness, scratch resistance, abrasion resistance, and hydrophobicity when compared to the results for PTFE. Moreover, the proprietary mixtures of biowax combined with PTFE micropowders provide synergistic effects, with PTFE mostly dominating in regards to the mechanical and physical properties. However, the granulometry of the micronized wax powders is a crucial parameter, as the smallest biowax particle sizes are the most effective. Based on further analysis of the sliding interface, a more ductile surface film forms for the coatings with rice bran and carnauba wax micropowders, while the amide wax is more brittle in parallel with the synthetic waxes and PTFE. Infrared spectroscopy confirms a favorable distribution of biowax micropowders at the coating surface in parallel with the formation of a protective surface film and protection of the epoxy matrix after abrasive wear. This study confirms that alternatives to PTFE for the mechanical protection, gloss, and hydrophobicity of wood coatings should be critically selected among the available grades of micronized waxes, depending on the targeted properties. Full article

(This article belongs to the Section Functional Polymer Coatings and Films)

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12 pages, 3950 KiB

Open AccessArticle

Electrochemical One-Step Synthesis of Cu₂O with Tunable Oxygen Defects and Their Electrochemical Performance in Li-Ion Batteries

by Yu Zheng, Lanxiang Huang, Feiyu Jian, Shujia Zhao, Wu Tang and Hui Tang

Coatings 2025, 15(5), 510; https://doi.org/10.3390/coatings15050510 - 24 Apr 2025

Abstract

We report a facile galvanic oxidation corrosion method for the preparation of cuprite nanocrystals (Cu₂O) with controllable oxygen vacancies. The Cu₂O microspheres have been employed as active anode materials in lithium-ion batteries (LIBs), exhibiting excellent electrochemical performance. The effect [...] Read more.

We report a facile galvanic oxidation corrosion method for the preparation of cuprite nanocrystals (Cu₂O) with controllable oxygen vacancies. The Cu₂O microspheres have been employed as active anode materials in lithium-ion batteries (LIBs), exhibiting excellent electrochemical performance. The effect of oxygen vacancies on the electrochemical properties was studied. The oxygen vacancy-rich Cu₂O electrodes exhibited a high specific discharge capacity (1002.3 mAh g⁻¹ at 0.1 C) and remarkable reversibility. Oxygen vacancies in Cu₂O not only promote high electronic conductivity but also provide additional active sites for lithiation/delithiation, further enhancing electrochemical performance. Furthermore, the formation mechanism of Cu₂O during the galvanic oxidation–corrosion process has been proposed. Full article

(This article belongs to the Special Issue Energy Storage and Conversion: From Materials, Devices to Applications)

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13 pages, 13782 KiB

Open AccessArticle

Electrodeposited CoFeNi Medium-Entropy Alloy Coating on a Copper Substrate from Chlorides Solution with Enhanced Corrosion Resistance

by Katarzyna Młynarek-Żak, Monika Spilka, Krzysztof Matus, Anna Góral and Rafał Babilas

Coatings 2025, 15(5), 509; https://doi.org/10.3390/coatings15050509 - 24 Apr 2025

Abstract

Medium-entropy alloys (MEAs) exhibit properties comparable or even superior to high-entropy alloys (HEAs). Due to their very good resistance in thermomechanical conditions and corrosive environments and unique electrical and magnetic properties, medium-entropy alloys are good candidates for coating applications. One of the most [...] Read more.

Medium-entropy alloys (MEAs) exhibit properties comparable or even superior to high-entropy alloys (HEAs). Due to their very good resistance in thermomechanical conditions and corrosive environments and unique electrical and magnetic properties, medium-entropy alloys are good candidates for coating applications. One of the most economically effective methods of producing metallic coatings is electrodeposition. In this work, the structure of an electrodeposited CoFeNi medium-entropy alloy coating on a copper substrate from a metal chlorides solution (FeCl₂ ∙ 4H₂O + CoCl₂ ∙ 6H₂O + NiCl₂ ∙ 6H₂O) with the addition of boric acid (H₃BO₃) was investigated. The coating was characterized by a nanocrystalline structure identified by transmission electron microscopy examination and X-ray diffraction methods. Based on XRD and TEM, the face-centered cubic (FCC) phase of the CoFeNi MEA coating was identified. The high corrosion resistance of the MEA coating in a 3.5% NaCl environment at 25 °C was confirmed by electrochemical tests. Full article

(This article belongs to the Special Issue Advances of Ceramic and Alloy Coatings, 2nd Edition)

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19 pages, 6948 KiB

Open AccessArticle

Shielding Effect of Rubber Disbond on DCVG Signal Magnitude for Coating Defect Detection in Pipes Buried in Soil: A Simulation Analysis

by Young-Ran Yoo, Seung-Heon Choi, Ki-Tae Kim, Bu-Teak Lim, Dae-Young Lee, Young-Cheon Kim and Young-Sik Kim

Coatings 2025, 15(5), 508; https://doi.org/10.3390/coatings15050508 - 24 Apr 2025

Abstract

Many pipelines are buried and operated underground in nuclear and chemical plants. Since these pipelines are welded on-site and subsequently coated, ensuring the integrity of these coatings is crucial. Over time, rubber coatings can disbond due to factors such as soil pressure, creating [...] Read more.

Many pipelines are buried and operated underground in nuclear and chemical plants. Since these pipelines are welded on-site and subsequently coated, ensuring the integrity of these coatings is crucial. Over time, rubber coatings can disbond due to factors such as soil pressure, creating gaps that lead to defects and may expose weld joints to electrolytes locally. Thus, effective detection of coating defects in buried pipelines is crucial for maintaining pipelines’ structural integrity and preventing corrosion. This study examines the shielding effect of rubber disbond on DCVG signal magnitude using the Direct Current Voltage Gradient (DCVG) technique. Simulations conducted with COMSOL Multiphysics^®, considering variables such as soil resistivity (1–19 kΩ·cm), defect exposure size (100 cm² and 1 cm²), detection electrode distance, and applied voltage, show that the DCVG signal generally increases as soil resistivity decreases and as defect size and electrode spacing increase. This is due to a stronger current distribution resulting from the higher applied voltages. However, shielded defects consistently produce lower DCVG signals than unshielded ones, a phenomenon that stems from the insulating shielding layer around the defect, which restricts the flow of the inspection current. These findings highlight how the shielding layer significantly influences the distribution of the inspection current. Full article

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12 pages, 3562 KiB

Open AccessArticle

Stabilization of Epitaxial NiO(001) Ultra-Thin Films on Body-Centered-Cubic Ni(001)-p(1x1)O

by Andrea Picone, Franco Ciccacci, Lamberto Duò and Alberto Brambilla

Coatings 2025, 15(5), 507; https://doi.org/10.3390/coatings15050507 - 23 Apr 2025

Abstract

Ultrathin NiO films, ranging from 1 to 16 monolayers (ML) in thickness, have been stabilized via reactive molecular beam epitaxy on the (001) surface of a metastable body-centered cubic (BCC) Ni film. Low-energy electron diffraction (LEED) confirms that NiO grows as a crystalline [...] Read more.

Ultrathin NiO films, ranging from 1 to 16 monolayers (ML) in thickness, have been stabilized via reactive molecular beam epitaxy on the (001) surface of a metastable body-centered cubic (BCC) Ni film. Low-energy electron diffraction (LEED) confirms that NiO grows as a crystalline film, exposing the (001) surface. Auger electron spectroscopy (AES) reveals a slight oxygen excess compared to a perfectly stoichiometric NiO film. Scanning tunneling microscopy (STM) shows that at low coverages the film exhibits atomically flat terraces, while at higher coverage a “wedding cake” morphology emerges. Scanning tunneling spectroscopy (STS) reveals a thickness-dependent evolution of the electronic band gap, which increases from 0.8 eV at 3 ML to 3.5 eV at 16 ML. The center of the band gap is approximately 0.2 eV above the Fermi level, indicating that NiO is p-doped. Full article

(This article belongs to the Special Issue Accelerated Development of Nanomaterials, Coatings, and Thin Films for Optical and Electronic Applications)

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21 pages, 11310 KiB

Open AccessArticle

Experimental and Numerical Studies on the Tribological Properties of Bearing Steel 20GrNi2MoV Against W2Mo9Cr4VCo8 Steel Under Dry Sliding Process

by Li Cui, Donghui Wang, Xingyu Ma, Bo Zhang and Xin Wang

Coatings 2025, 15(5), 506; https://doi.org/10.3390/coatings15050506 - 23 Apr 2025

Abstract

In this paper, the wear characteristics of 20GrNi2MoV bearing steel under different working conditions were investigated by finite element simulation considering microscopic grain size and pin-on-disk friction experiments, and the wear mechanism during friction and wear was explained, along with a finite element [...] Read more.

In this paper, the wear characteristics of 20GrNi2MoV bearing steel under different working conditions were investigated by finite element simulation considering microscopic grain size and pin-on-disk friction experiments, and the wear mechanism during friction and wear was explained, along with a finite element model that took initial grain size and material organization into account to predict the process of subsurface crack initiation during friction. The results show that high-speed and large-load conditions have a significant effect on the wear characteristics of dry friction of pinned disks. The effect of high speed and load will greatly reduce the time of the grinding stage, and the friction coefficient can quickly reach a stable state; the roughness of the surface of the friction pair increases with the increase in load, but the roughness shows a tendency to first increase and then decrease with the increase in sliding speed. Martensitic phase transformation occurs in the friction subsurface, and the decrease in Mn element content is one of the causes of cracks on the subsurface of the material; with the increase in load and speed, the damage form of the sample disk material is changed from abrasive wear and adhesive wear to the mixture of three kinds of wear: abrasive wear, adhesive wear, and cracks. In addition, the simulation of crack initiation and growth agrees well with the experiment, which proves the accuracy of crack prediction. This study provides a reference for crack initiation prediction in the study of pinned disk friction vises. Full article

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16 pages, 8504 KiB

Open AccessArticle

Synergistic Corrosion Inhibition and UV Protection via TTA-Loaded LDH Nanocontainers in Epoxy Coatings

by Qiuli Zhang, Yaning Yu, Jingjing Li, Chengxian Yin, Feng Tian, Jiahui Liu and Jun Zhou

Coatings 2025, 15(5), 505; https://doi.org/10.3390/coatings15050505 - 23 Apr 2025

Abstract

To address the issue of metal corrosion in marine environments, we developed a nanofiller with corrosion resistance and UV absorption capabilities. This nanofiller is prepared using a coprecipitation hydrothermal method and consists of TTA intercalated into an LDH structure with an outer layer [...] Read more.

To address the issue of metal corrosion in marine environments, we developed a nanofiller with corrosion resistance and UV absorption capabilities. This nanofiller is prepared using a coprecipitation hydrothermal method and consists of TTA intercalated into an LDH structure with an outer layer containing CeO₂, forming a layered double hydroxide (LDH) sandwich structure nanocontainer. TTA can be successfully released in corrosive environments, and the filler exhibits excellent corrosion inhibition and interlayer ion exchange properties. Polarization curve analysis shows that the corrosion inhibition efficiency of MgAl-TTA LDH@CeO₂ reaches 89.87%. After immersion in a corrosion solution for 60 days, the EP/MgAl-TTA LDH@CeO₂ coating maintains a high impedance of 3.88 × 10⁸ Ω·cm² in the low-frequency region, which is 166 times that of the pure EP coating. Even after 240 h of UV aging, the impedance of the EP/MgAl-TTA LDH@CeO₂ coating remains high at 3.10 × 10⁸ Ω·cm² (20,000 times higher than the pure EP coating). This significantly enhances the coating’s anti-aging and corrosion resistance, providing a feasible method for creating new long-lasting corrosion-resistant coatings in challenging environments. Full article

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12 pages, 5039 KiB

Open AccessArticle

Enhancement of Energy Storage Performance in NaNbO₃-Modified BNT-ST Ceramics

by Erping Wang, Hongjun Yang, Haizhou Guo, Hongxia Li, Haosong Zhang, Jinyu Li, Mingsai Gu, Tao Yang and Yangyang Zhang

Coatings 2025, 15(5), 504; https://doi.org/10.3390/coatings15050504 - 23 Apr 2025

Abstract

Relaxor ferroelectrics based on sodium bismuth titanate (Bi_0.5Na_0.5TiO₃, BNT) have attracted more interest recently as potential ecologically acceptable materials for pulse power technology because of their excellent full-energy storage capabilities. This paper formed (1 − x){0.97[0.98(BNT-ST)-0.02CN]-0.03AlN}- [...] Read more.

Relaxor ferroelectrics based on sodium bismuth titanate (Bi_0.5Na_0.5TiO₃, BNT) have attracted more interest recently as potential ecologically acceptable materials for pulse power technology because of their excellent full-energy storage capabilities. This paper formed (1 − x){0.97[0.98(BNT-ST)-0.02CN]-0.03AlN}-xNN ceramics through a traditional solid-state reaction process. It was noted that the incorporation of NaNbO₃ enhances the property of energy storage by elevating the breakdown strength and causing the creation of an ergodic relaxation state. The effective energy storage density (W_rec) and the energy storage efficiency (η) are 1.09 J/cm³ and 85%, respectively. The breakdown field strength E_b reached 155 kV/cm at x = 40%. These ceramics have excellent temperatures and frequency stabilities from 0.5 to 50 Hz and 20 to 60 °C. Full article

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10 pages, 3771 KiB

Open AccessArticle

Effects of Tempering Temperature on the Microstructure and Mechanical Properties of Vanadium-Microalloyed Medium-Carbon Bainitic Steel

by Litang Geng, Zhiwen Tian, Dongyun Sun, Xiaoyong Feng and Fucheng Zhang

Coatings 2025, 15(5), 503; https://doi.org/10.3390/coatings15050503 - 23 Apr 2025

Abstract

This study examined the impact of tempering temperature on the microstructure and properties of vanadium (V)-microalloyed medium-carbon bainitic steel. A series of heat treatments were performed on the steel, and the microstructural evolution and mechanical properties were systematically investigated through X-ray diffraction (XRD), [...] Read more.

This study examined the impact of tempering temperature on the microstructure and properties of vanadium (V)-microalloyed medium-carbon bainitic steel. A series of heat treatments were performed on the steel, and the microstructural evolution and mechanical properties were systematically investigated through X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and mechanical testing systems (MTS). The findings revealed that tempering temperature has a significant influence on microstructural changes. Specifically, at 350–450 °C, retained austenite begins to decompose and carbides start to precipitate. At 550–600 °C, bainitic ferrite laths undergo coarsening. Regarding mechanical properties, both tensile strength and yield strength initially increase with tempering temperature before decreasing as the temperature continues to rise. The diffusion and redistribution of carbon atoms during tempering enhance the elongation of all tempered samples compared to their untempered counterparts. Optimal comprehensive mechanical properties are achieved at 450 °C, where precipitation strengthening from vanadium, enhanced stability of retained austenite, and synergistic strengthening effects of decomposition products are most pronounced. This research provides a theoretical foundation for optimizing the heat treatment process of such steels and offers insights into the synergistic effects of V-microalloying and tempering. Full article

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19 pages, 28935 KiB

Open AccessReview

Progress in Surface Engineering Techniques for Magnesium–Lithium-Based Alloys

by Ningning Li, Zhenjie Hao, Yaya Feng, Yan Shang, Yuping Tong, Fan Lu, Lei Xu, Xi Chen, Shuai Li and Jin Peng

Coatings 2025, 15(5), 502; https://doi.org/10.3390/coatings15050502 - 23 Apr 2025

Abstract

Magnesium–lithium alloys, currently the lightest metallic structural materials, exhibit exceptional specific strength, superior damping capacity, and remarkable electromagnetic shielding properties. These characteristics endow them with significant potential for engineering applications in automotive, aerospace, satellite, and military industries. However, their poor corrosion resistance severely [...] Read more.

Magnesium–lithium alloys, currently the lightest metallic structural materials, exhibit exceptional specific strength, superior damping capacity, and remarkable electromagnetic shielding properties. These characteristics endow them with significant potential for engineering applications in automotive, aerospace, satellite, and military industries. However, their poor corrosion resistance severely restricts practical implementation. This review systematically examines recent advances in surface engineering techniques for magnesium–lithium alloys, with a focus on corrosion protection strategies. Key approaches are critically analyzed, including chemical conversion coatings, electroless plating, anodization, and advanced coating technologies. Furthermore, emerging hybrid methods combining multiple surface treatments are highlighted. Finally, future research directions are proposed to address existing challenges in surface protection of magnesium–lithium alloys. Full article

(This article belongs to the Special Issue Advanced Corrosion Protection through Coatings and Surface Rebuilding)

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21 pages, 23863 KiB

Open AccessArticle

Application of AC-DC-AC Accelerated Aging to Assess the Galvanic Corrosion Risk of Mild Steel Coated with Graphene-Embedded Epoxy Coatings

by Kazem Sabet-Bokati and Kevin Paul Plucknett

Coatings 2025, 15(5), 501; https://doi.org/10.3390/coatings15050501 - 23 Apr 2025

Abstract

This study presents a novel approach to evaluate the galvanic corrosion risk of mild steel coated with graphene-embedded epoxy coatings. The potential for graphene platelets to promote anodic dissolution of the underlying steel substrate via galvanic corrosion mechanisms was systematically assessed through the [...] Read more.

This study presents a novel approach to evaluate the galvanic corrosion risk of mild steel coated with graphene-embedded epoxy coatings. The potential for graphene platelets to promote anodic dissolution of the underlying steel substrate via galvanic corrosion mechanisms was systematically assessed through the accelerated alternating current-direct current-alternating current (AC-DC-AC) technique and cathodic disbondment testing. The possible risk of displacing cathodic reactions from the coating–steel interface to the dispersed graphene platelets within the epoxy matrix was investigated by evaluating the degradation trend of the graphene-containing coating under the AC-DC-AC test. The degradation behaviour of both pure epoxy and graphene-embedded epoxy coatings during accelerated aging was characterized using electrochemical impedance spectroscopy (EIS) measurements. The finding highlighted the negligible catalytic effect of incorporated graphene platelets on the anodic dissolution of steel substrate. On the other hand, as an inert filler, graphene platelets contributed to the enhancement of the structural integrity of the epoxy matrix during the AC-DC-AC test and natural immersion in NaCl 3.5 wt % solution by enhancing the barrier performance of the coating. Despite their spectacular barrier performance, damaged graphene-containing coatings performed inferiorly against corrosion-induced delamination compared to pure epoxy. Samples underwent the cathodic disbondment test to eliminate the effect of substrate anodic dissolution from corrosion-induced delamination. The accelerated delamination of graphene-embedded epoxy coatings was attributed to the destructive impact of graphene platelets on the interfacial adhesion of the epoxy matrix to the steel substrate. Full article

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

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18 pages, 4364 KiB

Open AccessArticle

Frictional Behavior of MoS₂ Coatings: A Comparative Study of Dynamic and Static Friction in Vacuum and Inert Gases

by Hamid Zaidi, Caroline Richard, Hong Son Bui, Stéphane Tournis, Mohamed Aissa and Kaouthar Bouguerra

Coatings 2025, 15(5), 500; https://doi.org/10.3390/coatings15050500 - 22 Apr 2025

Abstract

The tribological behavior of molybdenum disulfide (MoS₂) coatings was systematically investigated under various controlled gas environments in a vacuum chamber. A hemispherical steel pin was slid cyclically over a MoS₂-coated steel disk, prepared via high-speed powder spraying. The study [...] Read more.

The tribological behavior of molybdenum disulfide (MoS₂) coatings was systematically investigated under various controlled gas environments in a vacuum chamber. A hemispherical steel pin was slid cyclically over a MoS₂-coated steel disk, prepared via high-speed powder spraying. The study measured both dynamic and static friction coefficients under different gaseous atmospheres, including high vacuum, helium, argon, dry air, and water vapor. In high vacuum (10⁻⁵ Pa), an ultra-low dynamic friction coefficient (µ ≈ 0.01) was observed, while increasing values were recorded with helium (µ ≈ 0.03), argon (µ ≈ 0.04), dry air (µ ≈ 0.17), and water vapor (µ ≈ 0.30). Static friction coefficients followed a similar trend, decreasing significantly upon evacuation of water vapor or injection of inert gases. Surface analyses revealed that friction in vacuum or inert gases promoted smooth wear tracks and basal plane alignment of MoS₂ crystallites, while exposure to water vapor led to rougher, more disordered wear surfaces. Mass spectrometry and energetic modeling of physisorption interactions provided further insights into gas–solid interfacial mechanisms. These results demonstrate that the tribological performance of MoS₂ coatings is highly sensitive to the surrounding gas environment, with inert and vacuum conditions favoring low friction through enhanced basal plane orientation and minimal gas–surface interactions. In contrast, water vapor disrupts this structure, increasing friction and surface degradation. Understanding these interactions is crucial for optimizing MoS₂-based lubrication systems in varying atmospheric or sealed environments. Full article

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

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14 pages, 2440 KiB

Open AccessArticle

Assistance to Determine the Stability State of a Reactive Sputtering Process Based on the Analytical Solution of the Classical Berg Model

by Marcell Gajdics, Nikolett Hegedűs, Dániel Olasz and Miklós Serényi

Coatings 2025, 15(5), 499; https://doi.org/10.3390/coatings15050499 - 22 Apr 2025

Abstract

In this study, we propose simple analytical formulas for reactive sputtering technology, which can be used to assist in the selection of appropriate sputtering parameters during the deposition of thin films. Radio frequency (RF) sputtered alumina (Al₂O₃) was used [...] Read more.

In this study, we propose simple analytical formulas for reactive sputtering technology, which can be used to assist in the selection of appropriate sputtering parameters during the deposition of thin films. Radio frequency (RF) sputtered alumina (Al₂O₃) was used to evaluate the results. Layers with O/Al ratios ranging from 24/76 to 54/73 were deposited. Following effective deposition, the equations of the Berg model describing the process were studied. The achieved stoichiometry and the associated technological parameters are of critical importance for the analysis of the equations; consequently, this established the primary guiding principle when selecting the analytical approximations. A straightforward graph of the processing parameters (pumping speed, partial pressure) has been constructed, with the objective of avoiding the hysteresis that is an inherent feature of the reactive sputtering process. In addition, we have extended the classical Berg model to examine how the biased substrate can influence deposition. It was found that applying a substrate bias can decrease target coverage, while it does not alter substrate coverage. Full article

(This article belongs to the Section Thin Films)

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19 pages, 7992 KiB

Open AccessArticle

Effect of the Fluoride Species and Content of the PEO Electrolyte on the Corrosion Properties of the Layers Obtained on AZ31 for Biomedical Purposes

by Isis Tournay-Dufrenne, Célia Pasté, Alexandre Mégret, Lisa Dangreau and Marie-Georges Olivier

Coatings 2025, 15(5), 498; https://doi.org/10.3390/coatings15050498 - 22 Apr 2025

Abstract

This study aims to investigate the effects of different fluoride salts added in the PEO bath on the corrosion resistance and morphology of AZ31 magnesium alloy coatings. The PEO process was performed using a bipolar cycle with varying durations (4 and 30 min) [...] Read more.

This study aims to investigate the effects of different fluoride salts added in the PEO bath on the corrosion resistance and morphology of AZ31 magnesium alloy coatings. The PEO process was performed using a bipolar cycle with varying durations (4 and 30 min) in baths containing different fluoride salts (NaF, LiF, Na₂SiF₆) and a reference bath without fluoride. The coatings were characterised using SEM-EDS, XRD, and electrochemical impedance spectroscopy (EIS) to assess their morphology, chemical composition, and corrosion resistance. The results indicate that the presence of fluorides significantly influences the coating properties. NaF and Na₂SiF₆ coatings exhibited better corrosion resistance and more compact microstructures compared to LiF and the fluoride-free reference. The study highlights the importance of the fluoride counter ion in the PEO bath, demonstrating that NaF and Na₂SiF₆ provide superior protection against corrosion, making them suitable for biomedical applications where both porosity and corrosion resistance are critical. Full article

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19 pages, 5055 KiB

Open AccessArticle

Parametric Study of Inverse Heat Source Model Based on Molten Pool Morphology for Selective Laser Melting

by Longchao He, Ruixiang Bai, Zhenkun Lei, Da Liu, Hao Jiang, Yaoxing Xu and Jinjing Zhu

Coatings 2025, 15(5), 497; https://doi.org/10.3390/coatings15050497 - 22 Apr 2025

Abstract

Selective laser melting is a commonly employed additive manufacturing technique that facilitates the fabrication of intricate geometries through the laser-induced melting of powder materials. The quality of the produced parts is significantly influenced by the molten pool morphology, which is affected by parameters [...] Read more.

Selective laser melting is a commonly employed additive manufacturing technique that facilitates the fabrication of intricate geometries through the laser-induced melting of powder materials. The quality of the produced parts is significantly influenced by the molten pool morphology, which is affected by parameters such as laser power, scanning rate, and powder characteristics. However, the selection of unknown parameters within the heat source model significantly impacts the simulation outcomes and must be carefully considered. This study addresses this issue by proposing an inversion method for accurately determining the parameters of the Goldak double ellipsoid heat source model using molten pool morphology as a reference. A pattern search algorithm combined with Bayesian inference was employed to invert and estimate the heat source parameters. The results demonstrated that the inversed parameters significantly improved the prediction accuracy of molten pool geometry. The inverse parameters χ₀, χ₁, and χ₂ were 1.17, 1.00, and 2.08, respectively. The study provides valuable insights into the use of image-based methods for parameter inversion and offers a more reliable tool for improving the precision of simulations. These findings have important implications for optimizing processing conditions and enhancing the overall quality of additively-manufactured components. Full article

(This article belongs to the Special Issue Laser Surface Engineering and Additive Manufacturing)

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22 pages, 22206 KiB

Open AccessArticle

Research on the Formation Behaviour and Tribological Service Mechanism of Ni-Based Composite Coatings Prepared by Thermal Spraying Assisted with Alternating Current Magnetic Field

by Qingwen Yun, Jun Xiong, Ying Dong, Xi Zhu, Zhiyuan Wang, Fengyuan Bao, Jinyu Li and Yunan Jin

Coatings 2025, 15(5), 496; https://doi.org/10.3390/coatings15050496 - 22 Apr 2025

Abstract

In this paper, an alternating current (AC) magnetic field-assisted device was employed to enhance the preparation process of supersonic plasma spraying coatings. The phase structure and mechanical service characteristics of the five types of coatings were tested. The research found that the porosity [...] Read more.

In this paper, an alternating current (AC) magnetic field-assisted device was employed to enhance the preparation process of supersonic plasma spraying coatings. The phase structure and mechanical service characteristics of the five types of coatings were tested. The research found that the porosity of the coating decreased from 3.93% to 1.58%, the hardness increased from 702.88 to 921.12 HV, the bonding strength increased from 26 MPa to 38.3 MPa, and the tribological coefficient decreased from 0.6859 to 0.4670. The mechanism is that the AC magnetic field enhances the internal structure of the coating through electromagnetic stirring, electromagnetic oscillation and other effects. It also stirs the solidification process of the powder particles, improves the melting behaviour of the coating particles at the interface, and enhances the bonding quality of the coating. The improvement of the microstructure and mechanical properties further improves the tribological properties of the coating. At the same time, it is found that the higher the intensity of the AC magnetic field is not necessarily better for the improvement of the coating performance. When the AC magnetic field voltage reaches the peak of the device, the coating formation process is disturbed by the AC magnetic field, and the coating quality formed under the same spraying process is poor. Appropriate control of the AC magnetic field can effectively improve the internal structure and service quality of the coating. This provides a new technical idea and theoretical research basis for the development of advanced equipment surface engineering protection. Full article

(This article belongs to the Special Issue Advanced Coating and Surface Engineering for Tribology and Corrosion Resistance)

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Coatings, Volume 15, Issue 5 (May 2025) – 20 articles

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