Coatings

8 pages, 1978 KiB

Open AccessBrief Report

Development of a Prototype of Industrial Installation for the Deposition of Self-Restoring Nitride Coatings on Reed Switch Contacts

by Igor A. Zeltser, Alexander Tolstoguzov and Dejun Fu

Coatings 2025, 15(5), 533; https://doi.org/10.3390/coatings15050533 (registering DOI) - 29 Apr 2025

Abstract

A prototype of an industrial installation for the deposition of self-restoring nitride coatings on the surface of reed switch contacts using electro-spark erosion alloying was developed, manufactured, and tested under the laboratory conditions at LLC Nitron. It was shown that the coatings are [...] Read more.

A prototype of an industrial installation for the deposition of self-restoring nitride coatings on the surface of reed switch contacts using electro-spark erosion alloying was developed, manufactured, and tested under the laboratory conditions at LLC Nitron. It was shown that the coatings are formed inside a bulb of reed switches at the final stage of their production following the impact from the spark breakdown between the contacts, stimulated via alternating magnetic and electric fields. The nitrogen concentration in the surface layers of the nitride coatings, estimated by means of X-ray microanalysis, was ca. 19 at. % and their thickness, measured by time-of-flight secondary ion mass spectrometry via sputter depth profiling, ranged between 250 and 350 nm. The novelty of the presented work consists of the development of an innovative piece of equipment, the operating principle and design of which are protected by intellectual property rights (four Russian patents). The technological approach implemented in this installation differs from the industrial galvanic technology due to its high level of environmental safety and economic efficiency, since it does not require the use of gold, ruthenium, or other high-priced metals. Full article

(This article belongs to the Special Issue Smart Coatings: Adapting to the Future)

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11 pages, 1537 KiB

Open AccessArticle

Study on Densification of Gd₂Zr₂O₇-Based Ceramic Target for EB-PVD Application and Its Effect on Fracture Toughness

by Zhen Luo, Xingqi Wang, Yuyang Liu and Xingming Wang

Coatings 2025, 15(5), 532; https://doi.org/10.3390/coatings15050532 (registering DOI) - 29 Apr 2025

Abstract

In this study, the Gd₂Zr₂O₇-based ceramic target was densified via pressureless sintering which follows well with Kingery’s three-stage sintering theory. Sintering temperature is the key factor affecting the densification of targets. In the initial stage, when the [...] Read more.

In this study, the Gd₂Zr₂O₇-based ceramic target was densified via pressureless sintering which follows well with Kingery’s three-stage sintering theory. Sintering temperature is the key factor affecting the densification of targets. In the initial stage, when the sintering temperature is in the range of 1200–1450 °C, the porosity decreases with the density of targets slowly increasing to 64.71%. Grain boundary diffusion controls the densification process. In the middle stage, at 1450–1500 °C, the density ratio of the target rapidly rises to 77.6%. The competition between grain boundary migration rate and pore shrinkage rate leads to the maximum isolated porosity. In the final stage, when the sintering temperature is above 1500 °C, the density ratio of the target significantly increases to 97.28% at the temperature of 1600 °C. Even when the holding time is extended to 7 h at 1500 °C, the density ratio of the target only reaches 85.72%. With the increase in sintering temperature and prolongation of holding time, the fracture toughness of the ceramic targets exhibited a trend of initial increase followed by a decrease. Density ratio and grain size were identified as key factors influencing fracture toughness. When the density ratio reached approximately 80%, the fracture toughness achieved its maximum value of 2.245 MPa·m^0.5. When the sintering temperature exceeds 1450 °C, both the Young’s modulus and hardness of the targets increase rapidly, which significantly enhances their fracture toughness. However, with the increase in sintering temperature or holding time, the grain grows rapidly. This excessive grain growth reduces grain boundary. Full article

(This article belongs to the Special Issue Advances in Protective Coatings: Materials, Fabrication, Corrosion and Applications)

11 pages, 3082 KiB

Open AccessArticle

Comparison of Color Metallography and Electron Microscopy in Characterizing the Microstructure of H59 Brass Alloy

by Shidan Yuan, Ye Ma, Hui Yang, Zhen Ma and Lei Chen

Coatings 2025, 15(5), 531; https://doi.org/10.3390/coatings15050531 (registering DOI) - 29 Apr 2025

Abstract

Color metallographic samples of H59 brass alloy have been prepared by aqua regia etching. In this paper, combined with XRD (X-ray diffraction), traditional metallographic analysis, FE-SEM (field emission scanning electron microscopy), and EBSD (electron backscattering diffraction), the effect of the color metallographic method [...] Read more.

Color metallographic samples of H59 brass alloy have been prepared by aqua regia etching. In this paper, combined with XRD (X-ray diffraction), traditional metallographic analysis, FE-SEM (field emission scanning electron microscopy), and EBSD (electron backscattering diffraction), the effect of the color metallographic method on the microstructure characterization of the H59 brass alloy was analyzed. The experimental results showed that α phases and β phases could be distinguished clearly, and the phase morphology, distribution, and content could be expressed accurately with an average error value of 5.25% for the α phase and 4.71% for the β phase. The average error rate of the phase content characterization was 4.98% (less than 5%) with the color metallographic method. In addition, it was also found in the study that the brightness and darkness of the β phase would be related to the grain orientation, and the bright grains would correspond to the low-index surface, and the dark grains to the high-index surface. As a low-cost, fast, and efficient characterization technique, the experimental results show that color metallography (CM) could replace electron backscattering diffraction (EBSD) for the analysis of the phase composition, phase distribution, phase content, and grain orientation of brass alloys, which would provide an experimental basis for optimizing alloy properties and expanding applications. Full article

19 pages, 1687 KiB

Open AccessArticle

The Effect of CeO₂ Content on the Microstructure and Properties of TiC/WC/Co Composite Cladding Layers

by Wenhui Tong, Qingqi Xu, Yunyi Liu, Zi’ao Qi, Jie Wang and Jiadong Liu

Coatings 2025, 15(5), 530; https://doi.org/10.3390/coatings15050530 (registering DOI) - 29 Apr 2025

Abstract

To address the issue that the insufficient surface hardness and wear resistance of ductile iron under harsh working conditions are likely to lead to early failure, using a cladding layer with dual hard phases is an effective method to improve the surface properties. [...] Read more.

To address the issue that the insufficient surface hardness and wear resistance of ductile iron under harsh working conditions are likely to lead to early failure, using a cladding layer with dual hard phases is an effective method to improve the surface properties. However, the issue that a large amount of hard phases decompose under the action of a high-energy laser to generate brittle phases in the microstructure is quite troublesome. Therefore, by adding CeO₂ to the cladding layer, a TiC/WC/Co composite cladding layer containing CeO₂ is prepared on the substrate by means of a fiber laser. Through OM, SEM-EDS, XRD, and Rockwell hardness tests, the effects of the CeO₂ content on the microstructure, phase composition, and hardness of the coating were studied to determine the optimal addition amount. The results show that the secondary dendrite arm spacing (SDAS) of the γ-Co phase and the sizes of TiWC₂ and WC dendrites exhibit a non-monotonic trend of first decreasing and then increasing with the increase in the CeO₂ content, and the morphology of TiWC₂ evolves from a cross shape to a granular shape and then to a dendritic shape. When the CeO₂ content is 2 wt.%, the WC dendrites are completely inhibited, and the SDAS of γ-Co reaches the minimum value; when the content increases to 4 wt.%, WC dendrite coarsening occurs, and at the same time, the γ-Co dendrite packing density increases significantly, and the eutectic fraction decreases obviously. The hardness of the coating first increases and then decreases with the increase in the CeO₂ addition amount, and reaches a peak value of 91.4 HRC when the CeO₂ content is 4 wt.%, which is approximately 2.57 times the hardness of the substrate. Full article

(This article belongs to the Section Laser Coatings)

11 pages, 3212 KiB

Open AccessArticle

Effect of Pre-Formed Microstructure on Mechanical Properties of Bainitic Steel

by Yu Zhang, Xiaoyan Long, Yanguo Li, Xiaoyong Feng and Zeliang Liu

Coatings 2025, 15(5), 529; https://doi.org/10.3390/coatings15050529 (registering DOI) - 29 Apr 2025

Abstract

Achieving high strength, high toughness, and high plasticity in bainitic steel to meet the needs of economic and industrial development is the direction and driving force for researchers. The reinforcement technology of bainitic steel has become very well developed, with research conducted on [...] Read more.

Achieving high strength, high toughness, and high plasticity in bainitic steel to meet the needs of economic and industrial development is the direction and driving force for researchers. The reinforcement technology of bainitic steel has become very well developed, with research conducted on microstructure, dislocation density, and alloying elements. While improving strength, some plasticity and toughness are inevitably sacrificed. Therefore, achieving high strength, high plasticity, and high toughness in bainitic steel has always been a research focus. Existing research has shown that pre-transformation before the bainitic transformation can help increase the bainitic transformation rate and thereby regulate the microstructure. This paper will conduct a detailed analysis of the influence of pre-phase transformation microstructure on the strength, toughness and plasticity of bainitic steel. Full article

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11 pages, 1852 KiB

Open AccessArticle

Optimizing Parameter Sets for Laser-Textured Piston Rings Using Design of Experiments and Multibody Dynamics Calculations

by Gábor Laki, Dominika Pintér, László Boros and András Lajos Nagy

Coatings 2025, 15(5), 528; https://doi.org/10.3390/coatings15050528 (registering DOI) - 28 Apr 2025

Abstract

Friction and wear reduction in internal combustion engines are crucial for improving efficiency and durability. This study investigates the effect of microtextured surfaces on friction power loss in an engine’s piston ring-cylinder system. A numerical analysis was conducted on piston rings equipped with [...] Read more.

Friction and wear reduction in internal combustion engines are crucial for improving efficiency and durability. This study investigates the effect of microtextured surfaces on friction power loss in an engine’s piston ring-cylinder system. A numerical analysis was conducted on piston rings equipped with dimple-shaped microtextures using AVL Excite Piston & Rings, modelling a hard chromium-coated piston ring and a cast iron cylinder. The goal was to determine the optimal surface texture parameters that minimize friction power loss under typical urban driving conditions with SAE 0W-30 oil. A two-step Design of Experiments (DoE) approach was employed, where the first step involved mapping the effects of texture parameters, i.e., dimple depth (A = 0.5, 1, 1.5 µm), dimple distance (B = 120, 160, 240 µm), and dimple diameter (C = 50, 60, 70 µm), to identify influential factors. The second step aimed at locating a parameter configuration with minimal friction power loss. The results demonstrated that the optimized texture parameters can significantly reduce friction power loss. The lowest friction power loss of 8.96 W was achieved with a dimple depth of 2 µm, distance of 80 µm, and diameter of 60 µm, which contributed to an 8.3% improvement over the reference surface. The model built to describe the investigated texturing approach exhibited a strong correlation with an R² value of 0.93, and the deviation between predicted and measured values was below 1%. Future work will involve tribometer tests to experimentally validate the optimized parameters and confirm the simulation results. Full article

(This article belongs to the Special Issue Oxidation, Wear, Corrosion Behaviors and Activated Bonding Properties of Coatings Deposited on Metals)

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16 pages, 26634 KiB

Open AccessArticle

The Microstructure and Properties of Laser-Cladded Ni-Based Self-Fluxing Alloy Coatings Reinforced by TiC Particles

by Jacek Górka, Aleksandra Lont and Tomasz Poloczek

Coatings 2025, 15(5), 527; https://doi.org/10.3390/coatings15050527 (registering DOI) - 28 Apr 2025

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Abstract

In this study, NiCrBSi composite coatings reinforced with 5–15 wt.% TiC particles were prepared using laser cladding to investigate the influence of the TiC content and laser beam power on the coatings’ quality, structure, and properties. Penetrant tests revealed the presence of cracks [...] Read more.

In this study, NiCrBSi composite coatings reinforced with 5–15 wt.% TiC particles were prepared using laser cladding to investigate the influence of the TiC content and laser beam power on the coatings’ quality, structure, and properties. Penetrant tests revealed the presence of cracks in the composite coatings, which were reduced with the higher laser power due to a decrease in cooling rate. A macroscopic analysis showed that pure NiCrBSi coatings exhibited a high quality and were free of defects, while the addition of TiC particles led to the formation of large pores, particularly in coatings produced with a lower laser power. Microstructural characterization was conducted using Scanning Electron Microscopy (SEM), Energy-Dispersive Spectroscopy (EDS), and X-ray Diffraction (XRD). The microstructure of the pure NiCrBSi coatings consisted of an austenitic matrix with chromium-based precipitates (carbides and borides). Variations in structural morphology across different regions of the coatings and under varying laser powers were described. When TiC particles were added, partial dissolution occurred in the molten pool, enriching it with titanium and carbon, which subsequently led to the precipitation of titanium carbides. The average microhardness of the composite coatings increased by 28%–40% compared to the pure NiCrBSi coating, while the erosion resistance remained comparable. Solid particle erosion tests in accordance with the ASTM G76-18 standard resulted in average erosion values of the pure NiCrBSi coating of 0.0056 and 0.0025 mm³/g for the 30° and 90° impingement angles, respectively. Full article

(This article belongs to the Special Issue Welding Techniques in Surface Engineering)

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23 pages, 8252 KiB

Open AccessArticle

Analysis of Rammed Earth Wall Erosion in Traditional Village Dwellings in Zhuhai City

by Yanjun Wang, Junxin Song, Jiahao Zhang, Yue Huang and Shuai Yang

Coatings 2025, 15(5), 526; https://doi.org/10.3390/coatings15050526 (registering DOI) - 28 Apr 2025

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Abstract

(1) Background: this article focuses on the durability decline problem of rammed earth buildings in Paishan Village, Zhuhai City under the influence of complex environments. It aims to reveal the erosion mechanisms of rammed earth walls caused by different environmental factors (acid rain, [...] Read more.

(1) Background: this article focuses on the durability decline problem of rammed earth buildings in Paishan Village, Zhuhai City under the influence of complex environments. It aims to reveal the erosion mechanisms of rammed earth walls caused by different environmental factors (acid rain, salt spray, humidity, biological activities, etc.), and provide a scientific basis for formulating targeted remediation strategies. (2) Methods: a technical framework combining macroscopic investigation and microscopic analysis was adopted. Ion chromatography, scanning electron microscopy (SEM), and characterization (XRD) were used to study the damage to buildings in Paishan Village under the influence of different environmental factors. (3) Results: The acid rain and sulfate buildup could cause cracks and peeling on the south wall of the rammed earth wall. Salt spray and high humidity conditions exacerbated surface weathering on the west wall. Vibrant biological activity and high humidity made the north wall’s minerals easily dissolve, leaving the structure loose. The east wall was affected by the changing dynamics of carbonate rocks, which made it more vulnerable to weathering. (4) Conclusion: according to the analysis of different walls, specific steps should be taken during future restoration to improve the durability of rammed-earth buildings. Full article

(This article belongs to the Special Issue New Insights into Earthen Site Conservation: Methods, Techniques, Management, and Key Case Studies)

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26 pages, 3160 KiB

Open AccessArticle

Research on Pavement Performance of Steel Slag Asphalt Mastic and Mixtures

by Jianmin Guo, Jincheng Wei, Feiping Xu, Qinsheng Xu, Liang Kang, Wenjuan Wu, Wencheng Shi and Xiangpeng Yan

Coatings 2025, 15(5), 525; https://doi.org/10.3390/coatings15050525 (registering DOI) - 28 Apr 2025

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Abstract

In order to explore the influence of steel slag on the road performance of asphalt mastic and its mixtures, steel slag powder (SSP) and steel slag aggregate (SSA) were used to replace limestone mineral powder filler (MF) and natural limestone aggregate (LA) respectively [...] Read more.

In order to explore the influence of steel slag on the road performance of asphalt mastic and its mixtures, steel slag powder (SSP) and steel slag aggregate (SSA) were used to replace limestone mineral powder filler (MF) and natural limestone aggregate (LA) respectively to prepare asphalt mastic and mixture. A series of standardized tests including penetration, softening point, ductility, viscosity, pull-off strength, dynamic shear rheometer (DSR), and bending beam rheometer (BBR) were carried out to evaluate the performance of asphalt mastics with SSP. Meanwhile, high- and low-temperature performance, moisture stability, volumetric stability, and fatigue resistance were evaluated by wheel tracking, uniaxial penetration strength, Hamburg, three-point bending, freeze–thaw splitting, immersed Marshall stability, water immersion expansion, and two-point bending trapezoidal beam fatigue tests. The results show that compared to the asphalt mastic with MF, enhanced high-temperature deformation resistance and reduced low-temperature cracking resistance of asphalt mastic with SSP were observed, as well as superior aging resistance. The improvements in high-temperature stability, moisture resistance, and fatigue performance were confirmed for asphalt mixtures with SSP/SSA. Additionally, compromised volumetric stability and low-temperature crack resistance were found when SSP/SSA was used in mixtures. Although asphalt mixtures with SSA exhibited 257.79%–424.60% higher expansion rate after 21-day immersion than those with LA, the 3-day immersion expansion rates complied with specification limits (<1.5% per JTG F40-2004). Critical volume expansion control measures should be adopted for full-component applications of steel slag powder/aggregates due to the hydration potential of free lime (f-CaO) and magnesium oxide (MgO) in steel slag under moisture exposure. Full article

(This article belongs to the Special Issue Surface Treatment and Mechanical Properties of Sustainable Pavement Materials)

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11 pages, 4628 KiB

Open AccessArticle

Research on the Heating of Multi-Power Supply Units for Large-Area and Curved-Surface Transparent Electrothermal Films

by Yinjie Dai, Yuehui Hu, Huiwen Liu, Yichuan Chen, Yefu Hu, Xinyue Xu, Jiashun Chen, Zhenghang Lü and Hao Gao

Coatings 2025, 15(5), 524; https://doi.org/10.3390/coatings15050524 (registering DOI) - 28 Apr 2025

Viewed by 114

Abstract

Using multi-power supply units to power large-area electrothermal films can achieve high electrothermal power under low voltage. However, this method may result in poor contact between the electrodes and the electrothermal film, especially for films with large areas and curved surfaces, as well [...] Read more.

Using multi-power supply units to power large-area electrothermal films can achieve high electrothermal power under low voltage. However, this method may result in poor contact between the electrodes and the electrothermal film, especially for films with large areas and curved surfaces, as well as for power supply units with small electrode spacing. This study found that the relative deviation between the measured value (R_M) and the theoretical value (R_P) of the parallel resistance,

\frac{R_{M} - R_{P}}{R_{P}}

, exceeds 12.8% when powering a planar Indium Tin Oxide (ITO) electrothermal film with an area of 5 cm × 5 cm and electrode spacing of less than 0.5 cm using four or more power supply units. This deviation is significantly higher than that observed for power supply units with electrode spacing ≥0.8 cm, where

\frac{R_{M} - R_{P}}{R_{P}}

is 1.4% and 0.3% for spacings of 0.8 cm and 1.1 cm, respectively. By using fine sand, springs, and airbags as power supply pedestals, close contact between the electrodes and the electrothermal film can be achieved for large-area and curved-surface films due to the deformation of the sand, springs, or airbags under the heater’s weight. When an airbag power supply pedestal with twelve power supply units is used to power the bottom of an electrothermal ceramic teacup with a 20 cm² curved ITO transparent electrothermal film, the

\frac{R_{M} - R_{P}}{R_{P}}

is 13.3% and the heating temperature reaches 83.1 °C. Full article

(This article belongs to the Special Issue Environmentally Friendly Energy Conversion Materials and Thin Films)

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13 pages, 3055 KiB

Open AccessArticle

Phosphotungstic Acid Intercalated MgAlLa Ternary Layered Double Hydroxides as High-Efficiency Additives for Epoxy Resin: Synergistic Enhancement of Flame Retardancy and Smoke Suppression

by Wensheng Zhao, Jiao Jin, Zhengkai Guang, Haosen Chen, Yangu Liu, Xiaoling Cheng, Yuan Liu, Xing Wei, Jiebing He and Wenlin Zhao

Coatings 2025, 15(5), 523; https://doi.org/10.3390/coatings15050523 (registering DOI) - 27 Apr 2025

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Abstract

The inherent flammability and toxic smoke emission of epoxy resins (EPs) pose significant challenges to their advanced engineering applications. To address this limitation, we developed a novel flame-retardant additive through the organic modification of layered double hydroxides (LDHs) using a ternary MgAlLa hydrotalcite [...] Read more.

The inherent flammability and toxic smoke emission of epoxy resins (EPs) pose significant challenges to their advanced engineering applications. To address this limitation, we developed a novel flame-retardant additive through the organic modification of layered double hydroxides (LDHs) using a ternary MgAlLa hydrotalcite structure intercalated with phosphotungstic acid (PWA). This innovative design established a synergistic mechanism by combining the catalytic carbonization effect of lanthanum with the radical scavenging capability of PWA. The optimized MgAlLa-PWA/EP composite demonstrated remarkable flame retardancy and smoke suppression improvements, exhibiting 77.9% and 62.4% reductions in the peak heat release rate (pHRR) and total heat release (THR), respectively, compared to pure EP. Particularly noteworthy was the 72.6% decrease in total smoke release (TSR), accompanied by a significant elevation of the limiting oxygen index (LOI) value to 26.8% and achievement of UL-94 V-0 rating. Microstructural analysis revealed that the modified composite formed a continuous and uniform layer with increased density during combustion, effectively inhibiting oxygen exchange, smoke diffusion, and heat transfer. This study provides a novel strategy for designing multi-element synergistic LDHs additive for high-efficiency flame retardancy and smoke suppression of EP. Full article

(This article belongs to the Special Issue Research Progress and Future Prospects of Thermal Protection Coatings)

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18 pages, 14183 KiB

Open AccessArticle

Integrated Utilization Strategies for Red Mud: Iron Extraction, Sintered Brick Production, and Non-Calcined Cementitious Binder Development for Environmental Sustainability

by Bin Li, Fang Xu, Yan Ding, Fei Zheng and Junpeng Zou

Coatings 2025, 15(5), 522; https://doi.org/10.3390/coatings15050522 (registering DOI) - 27 Apr 2025

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Abstract

Red mud (RM), a highly alkaline waste from alumina production, poses severe environmental threats due to massive stockpiling (>350 million tons in China) and groundwater contamination. This study evaluates three scalable strategies to repurpose RM: iron recovery via magnetic separation, sintered brick production [...] Read more.

Red mud (RM), a highly alkaline waste from alumina production, poses severe environmental threats due to massive stockpiling (>350 million tons in China) and groundwater contamination. This study evaluates three scalable strategies to repurpose RM: iron recovery via magnetic separation, sintered brick production using RM–fly ash–granulated blast furnace slag (6:1:3 ratio), and non-calcined cementitious binders combining RM and phosphogypsum (PG). Industrial-scale iron extraction achieved 23.85% recovery of iron concentrate (58% Fe₂O₃ grade) and consumed 3.6 million tons/year of RM, generating CNY 31 million annual profit. Sintered bricks exhibited 10–15 MPa compressive strength, meeting ASTM C62-23 standard while reducing material costs by 30%. The RM–PG binder achieved 40 MPa compressive strength at 28 days without cement or calcination, leveraging RM’s alkalinity (21.95% Na₂O) and PG’s sulfate activation. Collectively, these approaches reduced landfill reliance by 50% and CO₂ emissions by 35%–40% compared to conventional practices. The results demonstrate RM’s potential as a secondary resource, offering economically viable and environmentally sustainable pathways for the alumina industry. Full article

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16 pages, 9789 KiB

Open AccessArticle

Regulation of Microstructure and Mechanical Properties of DC Electrodeposited Copper Foils by Electrolyte Parameters

by Wenwen Ma, Yuehong Zheng, Chong Luo, Tao Feng, Gang Dong, Haoyang Gao and Peiqing La

Coatings 2025, 15(5), 521; https://doi.org/10.3390/coatings15050521 (registering DOI) - 27 Apr 2025

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Abstract

Introducing nano-twins into electrolytic copper foil is an effective method to enhance strength and toughness. While pulse electrodeposition enables the easier preparation of high-density nano-twin copper, large-scale industrial production mainly relies on direct current electrodeposition. Therefore, systematically studying the effects of electroplating parameters [...] Read more.

Introducing nano-twins into electrolytic copper foil is an effective method to enhance strength and toughness. While pulse electrodeposition enables the easier preparation of high-density nano-twin copper, large-scale industrial production mainly relies on direct current electrodeposition. Therefore, systematically studying the effects of electroplating parameters on the microstructure and mechanical properties of direct current electrodeposited copper foil is crucial. In this paper, we discuss the effects of pH value, C_CuSO4, and J_k on the microstructure and mechanical properties of electroplated copper foils at room temperature. The results show that copper foils exhibit stronger (220)_Cu preferred orientation on the M surface than on the S surface with changes in pH value, C_CuSO4, and J_k. When the pH value is 2.5, the C_CuSO4 is between 70 and 90 g/L, and the J_k is within the range of 70–90 mA/cm², the prepared copper foil has better compactness and no obvious pinhole-like defects. Particularly, the copper foil electroplated with a pH value of 2.5, a C_CuSO4 of 80 g/L, and a J_k of 80 mA/cm² consists of equiaxed and columnar grains, featuring small grain size, uniform distribution, and a dense structure, resulting in excellent mechanical properties. Full article

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11 pages, 9122 KiB

Open AccessArticle

Effect of AlTiN Coating Structure on the Cutting Performance of Cemented Carbide PCB Microdrills

by Xiaofan Yang, Haiyang Lin, Yicong Chen, Yajue He and Zhihuang Shen

Coatings 2025, 15(5), 520; https://doi.org/10.3390/coatings15050520 (registering DOI) - 26 Apr 2025

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Abstract

The preparation of high-performance hard coatings on the surface of cemented carbide PCB (printed circuit board) microdrills can effectively decrease the rapid tool wear that occurs during cutting. In this study, arc ion plating technology was employed to deposit conventional AlTiN columnar crystal [...] Read more.

The preparation of high-performance hard coatings on the surface of cemented carbide PCB (printed circuit board) microdrills can effectively decrease the rapid tool wear that occurs during cutting. In this study, arc ion plating technology was employed to deposit conventional AlTiN columnar crystal single-layer coatings and AlTiN nanocrystalline single-layer coatings on the cemented carbide substrates of PCB microdrills. Additionally, a novel AlTiN composite coating with alternating columnar and nanocrystalline layers was designed and deposited. The mechanical properties and morphological characteristics of the three coating structures were analyzed using an indentation tester and scanning electron microscopy. The above three coated PCB microdrills were tested under the same conditions, and the cutting performance and tool wear mechanisms were compared and analyzed. The results show that the primary wear mechanisms for AlTiN-coated PCB microdrills are abrasive wear and coating flaking, and that the microdrill with the AlTiN columnar/nanocrystalline multilayer composite coating has the longest tool life. The novel AlTiN columnar/nanocrystalline composite coating exhibits superior interfacial adhesion strength, higher toughness, and better surface quality, and, hence, is more suitable for the high-speed drilling of PCB microholes. Full article

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20 pages, 4561 KiB

Open AccessArticle

Unmodified Hemp Biowaste as a Sustainable Biosorbent for Congo Red and Remazol Brilliant Blue R

by Ljiljana Suručić, Deana Andrić, Ivana Jevtić, Milan Momčilović, Relja Suručić and Jelena Penjišević

Coatings 2025, 15(5), 519; https://doi.org/10.3390/coatings15050519 (registering DOI) - 26 Apr 2025

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Abstract

Industrial hemp (Cannabis sativa L.) was investigated as a sustainable biosorbent for removing Congo Red (CR) and Remazol Brilliant Blue R (RBBR) from wastewater. The unmodified hemp biosorbent exhibited moderate but practically relevant sorption capacities (4.47 mg/g for CR; 2.44 mg/g for [...] Read more.

Industrial hemp (Cannabis sativa L.) was investigated as a sustainable biosorbent for removing Congo Red (CR) and Remazol Brilliant Blue R (RBBR) from wastewater. The unmodified hemp biosorbent exhibited moderate but practically relevant sorption capacities (4.47 mg/g for CR; 2.44 mg/g for RBBR), outperforming several agricultural waste materials. Kinetic studies revealed rapid uptake, with CR following pseudo-first-order kinetics (t₁/₂ < 15 min) and RBBR fitting the Elovich model, indicating heterogeneous surface interactions. Equilibrium data showed CR adsorption was best described by the Temkin isotherm (R² = 0.983), while RBBR followed the Langmuir model (R² = 0.998), reflecting their distinct binding mechanisms. Thermodynamic analysis confirmed spontaneous (ΔG° < 0), exothermic (ΔH° ≈ −2 kJ/mol), and entropy-driven processes for both dyes. Molecular docking elucidated the structural basis for performance differences: CR’s stronger binding (−7.5 kcal/mol) involved weak noncovalent interaction arising from partial overlap between the π-electron cloud of an aromatic ring and σ-bonds C-C or C-H (π-σ stacking) and hydrogen bonds with cellulose, whereas RBBR’s weaker affinity (−5.4 kcal/mol) relied on weak intermolecular interaction between a hydrogen atom (from a C-H bond) and the π-electron system of an aromatic ring (C-H∙∙∙π interactions). This work establishes industrial hemp as an eco-friendly alternative for dye removal, combining renewable sourcing with multi-mechanism adsorption capabilities suitable for small-scale water treatment applications. Full article

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14 pages, 3853 KiB

Open AccessArticle

Preparation and Characterization of Composite Hydrogen Barrier Coatings with (Graphene–Epoxy Resin)/(Silicon Carbide–Epoxy Resin)/(Graphene–Epoxy Resin) Sandwich Structures

by Ke Cai and Bailing Jiang

Coatings 2025, 15(5), 518; https://doi.org/10.3390/coatings15050518 - 25 Apr 2025

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Abstract

How to solve hydrogen embrittlement (HE) is a key issue that urgently needs to be addressed in the hydrogen energy industry. The use of hydrogen barrier coatings can effectively reduce the occurrence of HE. In this article, we utilized the epoxy resin (ER) [...] Read more.

How to solve hydrogen embrittlement (HE) is a key issue that urgently needs to be addressed in the hydrogen energy industry. The use of hydrogen barrier coatings can effectively reduce the occurrence of HE. In this article, we utilized the epoxy resin (ER) as the base coating and the graphene (GN) and the silicon carbide (SiC) as the additives to prepare the (GN-ER)/(SiC-ER)/(GN-ER) sandwich structure composite hydrogen barrier coatings by the spin coating method and investigated the effect of coating composite ways on the hydrogen barrier performance. The GN-ER and the SiC-ER are used as the hydrogen barrier layer and the hydrogen capture layer, respectively, in order to improve the hydrogen barrier performances jointly. The XRD and the SEM were used to characterize their phase compositions and microstructures, and the hydrogen barrier performances were analyzed by the electrochemical hydrogen permeation curves. The adhesive strength was characterized through the pull-out method. Compared to the single-layer and the double-layer structures, sandwich structures can effectively enhance the hydrogen barrier performance of the coatings, such as the relatively low electrochemical hydrogen diffusion coefficient (D_t, 3.88 × 10⁻⁸ cm²·s⁻¹), the relatively high permeation reduction factor (PRF, 59) and adhesive strength (10.9 MPa). This research may provide a theoretical basis for improving the hydrogen barrier performance of coatings. The (GN-ER)/(SiC ER)/(GN-ER) sandwich structures composite hydrogen barrier coatings can be expected to be used in the field of safe hydrogen storage and transportation. Full article

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20 pages, 13874 KiB

Open AccessArticle

Development of Chitosan-Coated Tung Oil Microcapsules with Antioxidants from Bamboo Leaves for Enhanced Antimicrobial Waterborne Coatings

by Nana Zhang and Xiaoxing Yan

Coatings 2025, 15(5), 517; https://doi.org/10.3390/coatings15050517 - 25 Apr 2025

Viewed by 76

Abstract

Antibacterial microcapsules were prepared by using a compound of chitosan with an antioxidant of bamboo leaves (AOB) as the wall material and tung oil as the core material. The microcapsules were modified by adding them to waterborne coatings, and the modified waterborne coatings [...] Read more.

Antibacterial microcapsules were prepared by using a compound of chitosan with an antioxidant of bamboo leaves (AOB) as the wall material and tung oil as the core material. The microcapsules were modified by adding them to waterborne coatings, and the modified waterborne coatings were coated onto Basswood samples. The performance of the obtained coatings was then characterised through a comparative analysis. The investigation focused on the effect of varying percentages of chitosan and AOB in microcapsules with a constant core-to-wall ratio on the performance of the waterborne on the surface of Basswood. The core-to-wall ratio of the microcapsules was established at 1:2, with the ratios of chitosan and AOB in the walls fixed at 9:1, 8:2, and 7:3, respectively. The results demonstrated that the gloss, impact resistance, and hardness of the coatings exhibited an increase with increasing ratios of AOB under varying M_chitosan:M_AOB (M_C:M_A) conditions. Conversely, the adhesion exhibited a decrease with an increase in AOB. The colour difference value exhibited minimal change. The self-healing rate of the coating exhibited an initial increase, followed by a subsequent decrease, in response to the increasing AOB concentration. The antimicrobial effect was optimised at a ratio of 9:1 for the combination of chitosan and AOB. The coating of Basswood containing 1.0% microcapsules and 9:1 M_C:M_A demonstrated superior performance, exhibiting a gloss of 9.7 GU, a colour difference ΔE of 31.03, a hardness of HB, an adhesion rating of grade 1, an impact resistance of grade 4, a self-healing rate of 19.09%, and a noteworthy antimicrobial effect against both Escherichia coli and Staphylococcus aureus. Full article

(This article belongs to the Special Issue Innovations in Functional Coatings for Wood Processing)

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16 pages, 5694 KiB

Open AccessArticle

Preparation of New Vanadium Base Composite Conversion Coating on 6061 Aluminum Alloy Surface for Sports Equipment

by Yiqun Wang, Xuzheng Qian, Feng Huang and Yingsong Fang

Coatings 2025, 15(5), 516; https://doi.org/10.3390/coatings15050516 - 25 Apr 2025

Viewed by 98

Abstract

The 6061 aluminum alloy is a commonly used metal material for sports equipment but is vulnerable to the external environment and corrosion. A novel V-Zr-Ti composite conversion coating was successfully prepared on the surface of 6061 aluminum alloy, and a thorough investigation was [...] Read more.

The 6061 aluminum alloy is a commonly used metal material for sports equipment but is vulnerable to the external environment and corrosion. A novel V-Zr-Ti composite conversion coating was successfully prepared on the surface of 6061 aluminum alloy, and a thorough investigation was conducted into the effect of the conversion parameters. Furthermore, the microstructure of the conversion coating, element contents of the coating surface, and dynamic evolution characteristics of the conversion solution were systematically investigated, and furthermore, the relationship among them was established. The results show that the optimal conversion time (CTI) and conversion temperature (CTE) for the VZrCC are 12 min and 45 °C. The VZrTiCC can gradually fill surface scratches during the coating-forming process, resulting in a relatively flat and even surface morphology. The conversion element contents on the VZrTiCC surface demonstrated a gradual increase, and the deposition rate was characterized by high Ti, medium Zr, and low V. The phase of the coating is predominantly constituted by metal oxides derived from conversion compositions, with a minor proportion of fluoride. Furthermore, the VZrTiCC can significantly enhance the corrosion resistance of an Al alloy matrix due to its low i_corr and average corrosion rate (ACR), and its corrosion resistance is about 5 times higher than that of the Al alloy matrix. Eventually, the formation process of the VZrTiCC with three key stages was proposed. In subsequent studies, to further establish a composition design framework for the conversion coating, a silane aqueous solution will be added to the existing V-Zr-Ti conversion solution, and a systematic study will be conducted on the V–organic composite conversion coating using computational molecular dynamics simulation combined with experimental characterization. Full article

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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 - 25 Apr 2025

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Abstract

In the original publication [...] Full article

13 pages, 5825 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

Viewed by 98

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)

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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

Viewed by 161

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

Viewed by 187

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

Viewed by 205

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

Viewed by 155

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

Viewed by 190

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

Viewed by 141

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

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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

Viewed by 71

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

Viewed by 155

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

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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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