Coatings

13 pages, 3005 KiB

Open AccessArticle

Temperature-Dependent Performance of Thermally Oxidized Zr2.5Nb Alloy for Orthopedic Implants: Mechanical Properties, Wear Resistance, and Biocompatibility

by Yunpeng Xiao, Hanke Song, Tangqing Hu, Yong Luo, Hao Xu and Xiaolei Sun

Coatings 2025, 15(8), 940; https://doi.org/10.3390/coatings15080940 - 11 Aug 2025

Abstract

This study investigates the critical influence of oxidation temperature on the intrinsic characteristics and surface properties of thermally oxidized Zr2.5Nb alloy. The resulting oxide layers were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), surface hardness, and nanoindentation. [...] Read more.

This study investigates the critical influence of oxidation temperature on the intrinsic characteristics and surface properties of thermally oxidized Zr2.5Nb alloy. The resulting oxide layers were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), surface hardness, and nanoindentation. The tribological behavior of the untreated and thermally oxidized Zr2.5Nb alloy was evaluated via reciprocating ball-on-disc wear tests under a load of 29.4 N. MC3T3-E1 cells were employed to assess the biocompatibility. The results show that oxide layers primarily composed of m-ZrO₂ formed on the alloy surface, with thickness increasing from 2.43 µm to 13.59 µm as the oxidation temperature rose from 500 °C to 700 °C. However, this thickness increase was accompanied by elevated defect density. Compared to the untreated alloy, thermally oxidized samples exhibited significantly enhanced hardness and wear resistance. Notably, oxidation at 600 °C produced a dense 5.31 µm oxide layer with optimal structural integrity, achieving an 85% reduction in wear rate and a superior MC3T3-E1 cell relative activity of 123.07 ± 6.02%. These findings provide foundational data for developing zirconium-based implants with improved stability. Full article

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16 pages, 6498 KiB

Open AccessArticle

Near-Nozzle Atomization Characteristics in Air-Assisted Spraying: Integrated VOF-DPM Modeling and Experimental Validation

by Shiming Chen, Yu Zhang, Zhaojie Wu, Gang Fang, Yan Chen and Jimiao Duan

Coatings 2025, 15(8), 939; https://doi.org/10.3390/coatings15080939 - 11 Aug 2025

Abstract

Near-nozzle atomization characteristics in air-assisted spraying were investigated through a novel 3D transient model integrating Volume-of-Fluid and Large Eddy Simulation (VOF-DPM) methods, with experimental validation of droplet distributions (Malvern analyzer) and coating thickness profiles. Key findings reveal that (1) the spray field stabilizes [...] Read more.

Near-nozzle atomization characteristics in air-assisted spraying were investigated through a novel 3D transient model integrating Volume-of-Fluid and Large Eddy Simulation (VOF-DPM) methods, with experimental validation of droplet distributions (Malvern analyzer) and coating thickness profiles. Key findings reveal that (1) the spray field stabilizes within 30 mm downstream, achieving 80% atomization efficiency (droplets ≤ 100 μm) at 27.5 mm axial distance; (2) radial momentum originates dually from fan-shaped airflow (max 595 m/s) and transverse motion induced by central atomizing air entrainment—a previously unreported mechanism; (3) paint loading delays flow stabilization to 2.5 ms (vs. 0.7 ms for gas-only flow) while reducing peak axial velocity by 18%–22% due to gas–liquid momentum exchange; (4) auxiliary and fan airflows synergistically constrain dispersion, forming elliptical sprays with characteristic cone angles of 61.7° (short axis) and 99.1° (long axis). Significantly, surface tension plays a dual role in inhibiting droplet atomization while promoting ligament pinch-off at 8.1 mm breakup length. These results provide the first quantitative characterization of gas–liquid interactions in near-nozzle regions, enabling precise parameter control for enhanced coating uniformity on complex surfaces. Full article

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

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22 pages, 8634 KiB

Open AccessArticle

Effect of Tea Tree Essential Oil@Chitosan Microcapsules on Surface Coating Properties of Pine Wood

by Nana Zhang, Ye Zhu and Xiaoxing Yan

Coatings 2025, 15(8), 938; https://doi.org/10.3390/coatings15080938 - 11 Aug 2025

Abstract

Pine wood has a natural, rustic, and environmentally friendly style and is used in a large number of applications in the furniture industry. However, its soft and porous texture makes it susceptible to bacteria, mould, and other micro-organisms. Pine wood was selected as [...] Read more.

Pine wood has a natural, rustic, and environmentally friendly style and is used in a large number of applications in the furniture industry. However, its soft and porous texture makes it susceptible to bacteria, mould, and other micro-organisms. Pine wood was selected as the test substrate, and tea tree essential oil@chitosan (TTO@CS) microcapsules with emulsifier concentrations of 4%, 5%, and 6% were added to the waterborne topcoat at a content of 1%–9% (in 2% intervals) to investigate their effect on the surface coating properties of pine wood. With the increase in microcapsule content, there was an overall increase in colour difference and light loss rate of pine wood surface coating, and the reflectance showed an increase and then decrease. The overall performance of the pine wood surface coatings containing 7% of 13# microcapsules was found to be excellent: the antimicrobial activity of the coatings was 62.58% for Escherichia coli and 61.29% for Staphylococcus aureus after 48 h, and the antimicrobial activity of the coatings was 40.14% for Escherichia coli and 38.89% for Staphylococcus aureus after 4 months. The colour difference in the coating was 2.37, and the light loss was 63.71%. The reflectance value was found to be 0.6860, while the hardness was determined to be 2H and the adhesion class was categorised as one. The impact resistance class was determined to be three, while the roughness was measured at 1.320 μm. The waterborne coating on the surface of pine wood was modified by microencapsulation technology with the objective of enhancing the antimicrobial properties of pine wood and expanding its scope of application. Full article

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

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24 pages, 4598 KiB

Open AccessArticle

Microbial Biosurfactant as Sustainable Inhibitor to Mitigate Biocorrosion in Metallic Structures Used in the Offshore Energy Sector

by Yslla Emanuelly S. Faccioli, Irinan B. França, Kaio Wêdann Oliveira, Bruno Augusto C. Roque, Alexandre Augusto P. Selva Filho, Attilio Converti, Rita de Cássia F. Soares da Silva and Leonie A. Sarubbo

Coatings 2025, 15(8), 937; https://doi.org/10.3390/coatings15080937 - 11 Aug 2025

Abstract

Microbiologically influenced corrosion (MIC) represents a critical challenge to the integrity of pipelines, piping, and metal structures in offshore environments, directly affecting the safety and operational costs of companies in the energy sector. However, conventional control methods, such as the use of chemical [...] Read more.

Microbiologically influenced corrosion (MIC) represents a critical challenge to the integrity of pipelines, piping, and metal structures in offshore environments, directly affecting the safety and operational costs of companies in the energy sector. However, conventional control methods, such as the use of chemical inhibitors, raise environmental and economic concerns. To face this problem, a biosurfactant produced by Pseudomonas cepacia CCT 6659 was tested as a biocorrosion inhibiting agent on carbon steel specimens immersed in seawater. For this purpose, static and dynamic conditions were simulated using different concentrations of the biosurfactant. Furthermore, analyses were performed using Scanning Electron Microscopy paired with Energy Dispersive Spectroscopy (SEM/EDS) to visualize the morphology of the biofilm and its chemical components. Laboratory tests indicated that the biosurfactant formulated in a 1:5 (v/v) ratio reduced the mass loss of test specimens (119.72 ± 2.64 g/m²) by no less than 57.3% compared to the control (280.28 ± 4.58 g/m²). Under dynamic conditions, the 1:2 (v/v) formulation showed greater protection, being able to reduce specimen corrosion (578.87 ± 7.01 g/m²) by 69.6% compared to the control (1901.41 ± 13.53 g/m²). SEM/EDS analyses revealed changes in surface composition and a reduction in corrosive elements associated with sulfur in the formed biofilms, which may be associated with a decrease in sulfate-reducing bacteria (SRB) activity, suggesting microbial inhibition by the biosurfactant. The results obtained in this study highlight the biosurfactant as a viable and ecological alternative to synthetic inhibitors, with potential application in the protection of metal structures exposed to corrosive environments in offshore energy systems, promoting greater durability, sustainability, and less environmental impact. Full article

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

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17 pages, 2677 KiB

Open AccessArticle

Study of Polyhedral Oligomeric Silsesquioxane-Modified Superwetting Transparent Coating for Anti-Fogging, Stain Resistance, Self-Cleaning and Anti-Biological Application

by Weibiao Zhu, Jinxin He and Xia Dong

Coatings 2025, 15(8), 936; https://doi.org/10.3390/coatings15080936 - 11 Aug 2025

Abstract

Transparent coatings with superwetting properties (superhydrophilicity or superhydrophobicity) have broad application prospects. Usually, most studies have been carried out separately on superhydrophobic coatings or superhydrophilic coatings. In our work, superhydrophilic transparent coatings were prepared by the four-mercapto and four-polyethylene glycol monomethyl acrylate modified [...] Read more.

Transparent coatings with superwetting properties (superhydrophilicity or superhydrophobicity) have broad application prospects. Usually, most studies have been carried out separately on superhydrophobic coatings or superhydrophilic coatings. In our work, superhydrophilic transparent coatings were prepared by the four-mercapto and four-polyethylene glycol monomethyl acrylate modified POSS (POSS-(SH)₄-(PEGMA)₄) (designated as I-coating) as well as superhydrophobic transparent coating (designated as O-coating) were prepared with the mercapto and seven-heptyl decafluoroheptyl acrylate modified POSS (POSS-SH-(DFMA)₇). The similarities and differences in anti-fogging, stain resistance, self-cleaning and anti-biological application between superhydrophobic and superhydrophilic coatings were compared systematically. The results show that superhydrophilic coatings performed better at preventing fog and facilitating self-cleaning; nevertheless, superhydrophobic coatings exhibited superior efficacy in the removal of contaminants such as markers and lipsticks. Both superwetting coatings demonstrated proficiency in self-cleaning and in deterring biological adhesion with respect to low-viscosity oil droplets. The relevant research of this paper provided a reference for the subsequent study on the advantages and disadvantages of superhydrophilic and superhydrophobic as well as its specific application. Full article

(This article belongs to the Section Bioactive Coatings and Biointerfaces)

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21 pages, 4980 KiB

Open AccessArticle

Strength Development of Bottom Ash-Based Geopolymer-Stabilized Recycled Concrete Aggregate as a Pavement Base Material

by Menglim Hoy, Chokchai Traiyasut, Suksun Horpibulsuk, Avirut Chinkulkijniwat, Apichat Suddeepong, Apinun Buritatum, Teerasak Yaowarat, Mantana Julvorawong and Thanaset Savetviwat

Coatings 2025, 15(8), 935; https://doi.org/10.3390/coatings15080935 - 11 Aug 2025

Abstract

This study investigated a 100% waste-derived material system, using bottom ash (BA) and recycled concrete aggregate (RCA) for sustainable pavement base applications. This innovative approach diverts both construction and power plant waste from landfills while replacing conventional natural aggregates and cement-based binders. Five [...] Read more.

This study investigated a 100% waste-derived material system, using bottom ash (BA) and recycled concrete aggregate (RCA) for sustainable pavement base applications. This innovative approach diverts both construction and power plant waste from landfills while replacing conventional natural aggregates and cement-based binders. Five RCA:BA replacement ratios (90:10 to 50:50) were evaluated with three Na₂SiO₃:NaOH alkaline activator ratios (1:1, 1:1.5, and 1:2) through unconfined compressive strength (UCS) testing, scanning electron microscopy, energy dispersive X-ray spectroscopy (SEM-EDX), and X-ray diffraction (XRD) analysis. The RCA90BA10 composition with a G/N ratio of 1:2 achieved exceptional performance, reaching 9.14 MPa UCS at 7 days while exceeding the Department of Highways, Thailand, requirement of 2.413 MPa. All geopolymer-stabilized mixtures substantially surpassed minimum specifications, validating the technology for high-traffic pavement applications. Toughness evaluation confirmed superior energy absorption capacity of 107.89 N·m for the optimal formulation. Microstructural characterization revealed that higher G/N ratios promoted extensive sodium aluminosilicate hydrate and calcium silicate hydrate gel formation, creating dense, well-integrated matrices. XRD patterns confirmed successful geopolymerization through pronounced amorphous gel development between 20° and 35° 2θ, correlating directly with mechanical performance improvements. The RCA90BA10 formulation demonstrated optimal balance between reactive aluminosilicate content and structural aggregate framework. This technology offers significant environmental benefits by diverting construction and power plant waste from landfills while achieving mechanical properties superior to conventional materials, providing a scalable solution for sustainable infrastructure development. Full article

(This article belongs to the Section Environmental Aspects in Colloid and Interface Science)

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14 pages, 10162 KiB

Open AccessArticle

Corrosion Behavior of Porcelain Enamels in Water Tank Storage

by Nicolò Mattei, Luca Benedetti and Stefano Rossi

Coatings 2025, 15(8), 934; https://doi.org/10.3390/coatings15080934 - 11 Aug 2025

Abstract

Recent updates to European Union directives on drinking water have extended safety limits to hot water, increasing the need to assess materials commonly used in water storage systems, such as porcelain enamel. This study investigates the interaction between enameled surfaces and aqueous environments, [...] Read more.

Recent updates to European Union directives on drinking water have extended safety limits to hot water, increasing the need to assess materials commonly used in water storage systems, such as porcelain enamel. This study investigates the interaction between enameled surfaces and aqueous environments, focusing on element release and microstructural alterations. The mass loss and chemical stability of the enamel were evaluated through a combination of surface characterization and Inductively Coupled Plasma (ICP) analysis. Time-resolved quantification of selected elements confirmed that all concentrations remained within EU regulatory thresholds. Additionally, the enamel was subjected to acidic and alkaline environments to explore the influence of pH on degradation mechanisms. Scanning electron microscopy (SEM) revealed that while the enamel undergoes surface-level modifications, the bulk structure remains intact. Notably, alkaline exposure had the strongest impact, dissolving needle-like calcium-rich structures and altering the surface more significantly than water or acid alone. These structures appear to facilitate localized corrosion once degraded. The correlation between surface morphology and elemental release dynamics highlights the critical role of microstructural features in determining long-term chemical resistance. Overall, the results underscore the importance of optimizing both the composition and structure of enamel coatings for applications involving prolonged contact with potable water. Full article

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19 pages, 4696 KiB

Open AccessArticle

Ductile–Brittle Mode Classification for Micro-End Milling of Nano-FTO Thin Film Using AE Monitoring and CNN

by Hee-hwan Lee, Hyo-jeong Kim, Jae-hyeon Nam and Seoung-hwan Lee

Coatings 2025, 15(8), 933; https://doi.org/10.3390/coatings15080933 - 10 Aug 2025

Viewed by 54

Abstract

This study introduces a real-time acoustic emission (AE) monitoring system for the micro-milling of fluorine-doped tin oxide (FTO) thin films, a critical transparent conductive oxide (TCO) material. The system uses AE sensors to capture high-frequency elastic waves generated during the micro-milling process. We [...] Read more.

This study introduces a real-time acoustic emission (AE) monitoring system for the micro-milling of fluorine-doped tin oxide (FTO) thin films, a critical transparent conductive oxide (TCO) material. The system uses AE sensors to capture high-frequency elastic waves generated during the micro-milling process. We combine experimental and theoretical analyses to investigate how various milling parameters influence the AE signals. To address the crucial challenge of ensuring ductile mode cutting in brittle materials like FTO, we employed a convolutional neural network (CNN) to identify the transition between ductile and brittle machining modes. A CNN was trained on energy-based features extracted from the AE signals, achieving a classification accuracy of 97.37%. This high accuracy demonstrates the effectiveness of integrating AE sensing with deep learning for interpreting complex micro-machining data. The results confirm that this combined approach offers a powerful, non-destructive, and intelligent monitoring solution for improving process control and understanding in the micro-milling of fragile conductive thin films. Full article

(This article belongs to the Special Issue Advances in Coating Tribology: Smart, Sustainable and High-Performance Coatings for Next-Generation Applications)

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12 pages, 14320 KiB

Open AccessArticle

Effect of Scanning Speed on Microstructure and Properties of Ni/B₄C/TiC Coating

by Yan Tong, Bo Cui, Yu Liu, You Lv, Qimeng Liu and Dongdong Zhang

Coatings 2025, 15(8), 932; https://doi.org/10.3390/coatings15080932 - 9 Aug 2025

Viewed by 157

Abstract

Ni/B₄C/TiC coating was prepared using laser cladding technology with 45 steel as substrate material. The effects of different scanning speeds on phase composition, microstructure, microhardness, and tribological properties were investigated. It was found that the coating is primarily composed of Fe [...] Read more.

Ni/B₄C/TiC coating was prepared using laser cladding technology with 45 steel as substrate material. The effects of different scanning speeds on phase composition, microstructure, microhardness, and tribological properties were investigated. It was found that the coating is primarily composed of Fe₃B, Fe₃C, B₂Fe₃Ni₃, TiC, and solid solution of [Fe, Ni]. TiC particles are not completely dissolved, which promotes grain refinement. The microhardness increases with the increase in scanning speed and reaches the maximum value at 240 mm/min. The wear resistance test revealed that the coating exhibited the best wear resistance at 240 mm/min. The main wear mechanisms were fatigue wear, abrasive wear, and a small amount of oxidative wear. Full article

(This article belongs to the Special Issue Additive Manufacturing of Metallic Components for Hard Coatings, 2nd Edition)

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21 pages, 745 KiB

Open AccessReview

Sustainable Marine Coatings: Comparing the Costs, Benefits, and Impacts of Biocidal and Biocide-Free Paints

by Oskar Kontus and Jonne Kotta

Coatings 2025, 15(8), 931; https://doi.org/10.3390/coatings15080931 - 9 Aug 2025

Viewed by 80

Abstract

Biofouling presents a major challenge for maritime industries, leading to the widespread use of copper-based biocidal coatings that, while effective, release harmful substances into marine environments. Biocide-free alternatives, such as silicone-based, hydrogel, and natural product-derived coatings, offer more sustainable solutions. This systematic review [...] Read more.

Biofouling presents a major challenge for maritime industries, leading to the widespread use of copper-based biocidal coatings that, while effective, release harmful substances into marine environments. Biocide-free alternatives, such as silicone-based, hydrogel, and natural product-derived coatings, offer more sustainable solutions. This systematic review and meta-analysis assesses the functional, economic, and environmental performance of both coating types using PRISMA guidelines and literature from Scopus and ISI Web of Knowledge (2003–2025). Data from experimental, field, and modeling studies were synthesized, covering fouling intensity, coating durability, toxicity, cost-effectiveness, and regulatory compliance. Biocidal coatings generally performed better short-term, but biocide-free options showed comparable efficacy in some cases and clear environmental benefits. Although initial costs for biocide-free coatings are higher, they may yield savings over time. The meta-analysis found no significant differences in fouling or hydrodynamic performance, though quantitative evidence is limited. Research gaps remain, particularly in long-term studies, highlighting the need for standardized testing and lifecycle assessments to guide sustainable antifouling practices. The outcome of the review also showed that some evidence was excluded due to being in non-indexed sources. This highlights the importance of combining systematic and traditional review methods to ensure a more comprehensive assessment. Full article

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15 pages, 11927 KiB

Open AccessArticle

Investigation of the Microstructure and Properties of Cage-Shaped Hollow Cathode Bias Voltage Modulated Si-Doped DLC Thick Film

by Ming Gong, Haitao Li, Mingzhong Wu and Peng Lv

Coatings 2025, 15(8), 930; https://doi.org/10.3390/coatings15080930 - 8 Aug 2025

Viewed by 189

Abstract

To mitigate the high residual stress inherent in single-layer diamond-like carbon (DLC) films, we fabricate alternating soft/hard multilayer DLC thick films using a cage-type hollow cathode plasma-enhanced chemical vapor deposition (PECVD) system. The microstructure, mechanical properties, and corrosion resistance of these films were [...] Read more.

To mitigate the high residual stress inherent in single-layer diamond-like carbon (DLC) films, we fabricate alternating soft/hard multilayer DLC thick films using a cage-type hollow cathode plasma-enhanced chemical vapor deposition (PECVD) system. The microstructure, mechanical properties, and corrosion resistance of these films were systematically investigated. Periodic film structures were characterized via scanning electron microscopy (SEM), Raman spectroscopy, atomic force microscopy (AFM), and X-Ray photoelectron spectroscopy (XPS). Adhesion and hardness were evaluated using a scratch tester and a nanoindentation tester, respectively, while corrosion resistance was assessed by dynamic potential polarization tests in a 3.5 wt% NaCl solution. Findings indicate that as the modulation period of the Si-DLC films increases, a greater proportion of high-energy carbon particles penetrate the non-biased layer under workpiece bias, ultimately disrupting the layered structure in the 90-layer film. This results in densification, reflected in three key improvements: (1) an increase in sp³-bonded carbon content and enhanced smoothness, (2) enhanced adhesion (from 34 N to 46 N) and nanohardness (from 4.94 GPa to 8.41 GPa), and (3) a tenfold reduction in corrosion current density (i_corr) compared to single-layer Si-DLC films. Full article

(This article belongs to the Section Thin Films)

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22 pages, 6960 KiB

Open AccessArticle

Synergistic Effect of Hetero Interstitial Atoms (C/N/O) on the Thermodynamic Stability in BCC Fe: A DFT Study

by Fang Wang, Tengge Mi, Pinghu Chen, Hongmei Zhu, Yong Chen, Pengbo Zhang, Ruiqing Li and Changjun Qiu

Coatings 2025, 15(8), 929; https://doi.org/10.3390/coatings15080929 - 8 Aug 2025

Viewed by 94

Abstract

Laser cladding rapid solidification technique is an effective strategy for manufacturing ultra-high-strength martensitic stainless steels (UHS-MSS). Due to super-saturation solution strengthening of interstitial atoms (IAs), martensitic stainless steels containing IAs exhibit excellent ultra-high strength and toughness and have high tolerance for oxygen impurities. [...] Read more.

Laser cladding rapid solidification technique is an effective strategy for manufacturing ultra-high-strength martensitic stainless steels (UHS-MSS). Due to super-saturation solution strengthening of interstitial atoms (IAs), martensitic stainless steels containing IAs exhibit excellent ultra-high strength and toughness and have high tolerance for oxygen impurities. Hence, studying the specific speciation and structural characteristics of IAs is of great significance for guiding laser cladding of ultra-high-strength steels. Herein, we use density functional theory (DFT) computations to analyze the stable occupancies of IAs and their interactions in body-centered cubic iron (BCC Fe). The findings show that single IAs prefer to occupy octahedral sites over tetrahedral sites. Therefore, octahedral sites are selected as the optimal sites for the following double IAs study. For homo IAs, C-C and N-N configurations exhibit greater stability at long-range distances, whereas O-O demonstrate optimal stability at intermediate distances. Crucially, hetero IAs configurations are more stable compared to single IAs and homo IAs, exhibiting a synergistic effect. Especially, the C-O combination shows the highest stability and strongest bonding character. Meanwhile, the dissociation behavior of O indicates that C-O and N-O have higher dissociation temperatures than single O, further verifying the synergistic effect of hetero IAs. This provides a theoretical basis for understanding the interstitial solution strengthening of laser cladding UHS-MSS. Full article

(This article belongs to the Special Issue Multi-Principal Element Alloy Design and Surface Modification Technology)

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14 pages, 3326 KiB

Open AccessArticle

Effects of Oxygen Gas Flow During Deposition on the Thermal Shock Life of YSZ Thermal Barrier Coatings Prepared by Electron Beam Physical Vapor Deposition

by Keli Huo, Chunhui Xu, Zhenwu Huang, Jie Xia, Ling Zhang, Xiaoshan Zhang and Tiansheng Li

Coatings 2025, 15(8), 928; https://doi.org/10.3390/coatings15080928 - 8 Aug 2025

Viewed by 146

Abstract

Electron beam physical vapor deposited (EB-PVD) thermal barrier coatings (TBCs) are widely used to protect the hot section parts of aircraft engine turbines due to its uniform columnar microstructure and high strain tolerance. The microstructure and thermal shock life of 7 wt% Y [...] Read more.

Electron beam physical vapor deposited (EB-PVD) thermal barrier coatings (TBCs) are widely used to protect the hot section parts of aircraft engine turbines due to its uniform columnar microstructure and high strain tolerance. The microstructure and thermal shock life of 7 wt% Y₂O₃ stabilized zirconia (YSZ) coatings produced by EB-PVD were investigated as a function of oxygen gas flow during deposition. The surface and cross-section microstructure of EB-PVD YSZ coatings were highly influenced by the oxygen gas flow. When the oxygen gas flow is less than 60 sccm, a sandwich is formed between the bond coat (BC) layer and the YSZ layer, which significantly reduces the thermal shock life of the coating. Full article

(This article belongs to the Special Issue Characterization and Industrial Applications of PVD Coatings)

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16 pages, 3412 KiB

Open AccessArticle

A Study on the Process of Electroplating a Ni Coating on a Carbon Fiber Surface Under the Condition of an Electroplating Solution Without Additives

by Wenjun Huo, Yubo Jia, Riping Zang, Xi Xia and Zhaozhao Lv

Coatings 2025, 15(8), 927; https://doi.org/10.3390/coatings15080927 - 8 Aug 2025

Viewed by 149

Abstract

To achieve superior interfacial bonding between carbon fibers and an Al matrix, this study employed a simplified electroplating system to deposit Ni coatings on carbon fibers using an additive-free electrolyte. The investigation first optimized the carbon fiber heat treatment process, followed by systematic [...] Read more.

To achieve superior interfacial bonding between carbon fibers and an Al matrix, this study employed a simplified electroplating system to deposit Ni coatings on carbon fibers using an additive-free electrolyte. The investigation first optimized the carbon fiber heat treatment process, followed by systematic examination of electroplating parameters affecting the Ni coating microstructure. Key findings demonstrate that (1) thermal treatment of carbon fibers significantly enhances their wettability with the electroplating solution; (2) controlled deposition of smooth, uniform, and continuous Ni coatings requires precise optimization of nickel sulfate concentration, applied voltage, and pH value. This work establishes a cost-effective technical foundation for producing high-quality Ni-coated carbon fibers. Full article

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

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1 pages, 121 KiB

Open AccessRetraction

RETRACTED: Atta et al. Functionalization of Silica with Triazine Hydrazide to Improve Corrosion Protection and Interfacial Adhesion Properties of Epoxy Coating and Steel Substrate. Coatings 2020, 10, 351

by Ayman M. Atta, Mona A. Ahmed, Ahmed M. Tawfek and Ayman El-Faham

Coatings 2025, 15(8), 926; https://doi.org/10.3390/coatings15080926 - 8 Aug 2025

Viewed by 88

Abstract

The journal retracts the article titled “Functionalization of Silica with Triazine Hydrazide to Improve Corrosion Protection and Interfacial Adhesion Properties of Epoxy Coating and Steel Substrate” [...] Full article

21 pages, 4066 KiB

Open AccessReview

Plasma Electrolytic Oxidation (PEO) Coatings for Biomedical Implants: A Review on Enhancing Antibacterial Efficacy Through Controlled Antibiotic Release

by Maryam Molaei, Masoud Atapour and Ehsan Mohammadi Zahrani

Coatings 2025, 15(8), 925; https://doi.org/10.3390/coatings15080925 - 8 Aug 2025

Viewed by 277

Abstract

The use of biomedical implants has significantly enhanced patient survival rates and overall quality of life. However, bacterial infections caused by bacterial adhesion and the subsequent formation of biofilm on the surface of the implants are challenging clinical issues, leading to implant failure [...] Read more.

The use of biomedical implants has significantly enhanced patient survival rates and overall quality of life. However, bacterial infections caused by bacterial adhesion and the subsequent formation of biofilm on the surface of the implants are challenging clinical issues, leading to implant failure and high social and economic costs. Modification of the surface of the implants with antibacterial coatings is a promising technique to address implant-associated bacterial infection problems. One strategy to fabricate bactericidal antibacterial coatings is to load antibacterial agents, like antibiotics—the most important type of antibacterial drug for killing or inhibiting the growth of bacteria—at therapeutic doses into the coatings and subsequently release them, ideally in a controlled way. Plasma electrolytic oxidation (PEO) is a simple, affordable, and eco-friendly method to produce high-performance, multifunctional coatings with desired antibacterial properties. This review examines the antibacterial activity of antibiotic-loaded PEO coatings, offering valuable insights for the development of novel, high-performance antibacterial coatings that meet clinical requirements. Full article

(This article belongs to the Special Issue Advanced Plasma Surface Treatments and Their Applications in Coating Technologies)

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25 pages, 7359 KiB

Open AccessArticle

Street Art in the Rain: Evaluating the Durability of Protective Coatings for Contemporary Muralism Through Accelerated Rain Ageing

by Laura Pagnin, Sara Goidanich, Nicolò Guarnieri, Francesca Caterina Izzo, Jaime Jorge Hormida Henriquez and Lucia Toniolo

Coatings 2025, 15(8), 924; https://doi.org/10.3390/coatings15080924 - 7 Aug 2025

Viewed by 208

Abstract

Contemporary muralism has gained increasing cultural and social relevance in recent years, becoming a prominent form of urban artistic expression. However, its outdoor exposure makes it highly vulnerable to environmental degradation, raising significant challenges for long-term preservation. While solar radiation is widely recognized [...] Read more.

Contemporary muralism has gained increasing cultural and social relevance in recent years, becoming a prominent form of urban artistic expression. However, its outdoor exposure makes it highly vulnerable to environmental degradation, raising significant challenges for long-term preservation. While solar radiation is widely recognized as a main agent of deterioration, the impact of rainfall has received comparatively little attention. This study addresses this gap by evaluating the durability of commercial protective coatings applied to modern paints (alkyd, acrylic, and styrene-acrylic) under simulated rain exposure. The ageing protocol replicates approximately 10 years of cumulative rainfall in Central-Southern Europe. A key innovation of this research is the use of a custom-built rain chamber, uniquely designed to expose a large number of samples simultaneously under highly uniform and controlled rain conditions. The system ensures reproducible exposure through a precision-controlled moving platform and programmable rain delivery. A comprehensive set of analytical techniques was employed to assess morphological, chemical, and functional changes in the coatings and paints before and after ageing. Results highlight the limited performance of current protective materials and the need for more effective solutions for the conservation of contemporary outdoor artworks. Full article

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

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26 pages, 8951 KiB

Open AccessArticle

Optimization of Welding Sequence and Improvement of Welding Process for Large-Diameter Curved Penetrations of Thick Plates

by Haipeng Miao, Yi Shen, Wenbo Xue, Sheng Zhang and Mingxin Yuan

Coatings 2025, 15(8), 923; https://doi.org/10.3390/coatings15080923 - 7 Aug 2025

Viewed by 204

Abstract

To reduce welding deformation during the automated welding of intersection seams on thick plate curved penetrations and thereby improve welding quality and efficiency, an optimized method for segmented and multi-layer multi-pass welding sequences, along with welding process improvement strategies, is proposed. First, based [...] Read more.

To reduce welding deformation during the automated welding of intersection seams on thick plate curved penetrations and thereby improve welding quality and efficiency, an optimized method for segmented and multi-layer multi-pass welding sequences, along with welding process improvement strategies, is proposed. First, based on the welding model of the curved penetrations, a multi-layer multi-pass welding trajectory equation is designed. Next, a Gaussian heat source model is selected, and numerical simulation theories for welding temperature and stress fields are established using finite-element theory. Then, for the intersection seams of curved components with three different thicknesses, four numerical tests of segmented welding sequence optimization are carried out using welding finite-element simulation theory. Finally, the optimal welding process for the welding sequence is improved using orthogonal experimental methods, and the optimal welding process parameters for curved components with different thicknesses are determined. The optimization of welding sequences for intersection seams on three types of thick plates shows that the optimal sequence for segmented welding is first to perform upper–lower diagonal symmetry, followed by left–right symmetry. Compared to other welding sequences, the proposed method reduces welding deformation by an average of 9.24% and welding stress by an average of 7.40%, which verifies the effectiveness of the welding sequence optimization presented in the paper. Full article

(This article belongs to the Special Issue Advances in Metal Additive Manufacturing Technique: Processes and Novel Materials)

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29 pages, 980 KiB

Open AccessReview

Recent Advances in Magnetron Sputtering: From Fundamentals to Industrial Applications

by Przemyslaw Borowski and Jaroslaw Myśliwiec

Coatings 2025, 15(8), 922; https://doi.org/10.3390/coatings15080922 - 7 Aug 2025

Viewed by 292

Abstract

Magnetron Sputter Vacuum Deposition (MSVD) has undergone significant advancements since its inception. This review explores the evolution of MSVD, encompassing its fundamental principles, various techniques (including reactive sputtering, pulsed magnetron sputtering, and high-power impulse magnetron sputtering), and its wide-ranging industrial applications. While detailing [...] Read more.

Magnetron Sputter Vacuum Deposition (MSVD) has undergone significant advancements since its inception. This review explores the evolution of MSVD, encompassing its fundamental principles, various techniques (including reactive sputtering, pulsed magnetron sputtering, and high-power impulse magnetron sputtering), and its wide-ranging industrial applications. While detailing the advantages of high deposition rates, versatility in material selection, and precise control over film properties, the review also addresses inherent challenges such as low target utilization and plasma instability. A significant portion focuses on the crucial role of MSVD in the automotive industry, highlighting its use in creating durable, high-quality coatings for both aesthetic and functional purposes. The transition from traditional electroplating methods to more environmentally friendly MSVD techniques is also discussed, emphasizing the growing demand for sustainable manufacturing processes. This review concludes by summarizing the key advancements, remaining challenges, and potential future trends in magnetron sputtering technologies. Full article

(This article belongs to the Special Issue Magnetron Sputtering Coatings: From Materials to Applications)

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10 pages, 1801 KiB

Open AccessArticle

Strong Radiative Cooling Coating Containing In Situ Grown TiO₂/CNT Hybrids and Polyacrylic Acid Matrix

by Jiaziyi Wang, Yong Liu, Dapeng Liu, Yong Mu and Xilai Jia

Coatings 2025, 15(8), 921; https://doi.org/10.3390/coatings15080921 - 7 Aug 2025

Viewed by 255

Abstract

Traditional forced-air cooling systems suffer from excessive energy consumption and noise pollution. This study proposes an innovative passive cooling strategy through developing aqueous radiative cooling coatings made from a combination of TiO₂-decorated carbon nanotube (TiO₂-CNT) hybrids and polyacrylic acid [...] Read more.

Traditional forced-air cooling systems suffer from excessive energy consumption and noise pollution. This study proposes an innovative passive cooling strategy through developing aqueous radiative cooling coatings made from a combination of TiO₂-decorated carbon nanotube (TiO₂-CNT) hybrids and polyacrylic acid (PAA), designed to simultaneously enhance the heat dissipation and improve the mechanical strength of the coating films. Based on CNTs’ exceptional thermal conductivity and record-high infrared emissivity, bead-like TiO₂-CNT architectures have been prepared as the filler in PAA. The TiO₂ nanoparticles were in situ grown on CNTs, forming a rough surface that can produce asperity contacts and enhance the strength of the TiO₂-CNT/PAA composite. Moreover, this composite enhanced heat dissipation and achieved remarkable cooling efficiency at a small fraction of the filler (0.1 wt%). The optimized coating demonstrated a temperature reduction of 23.8 °C at an operation temperature of 180.7 °C, coupled with obvious mechanical reinforcement (tensile strength from 13.7 MPa of pure PAA to 17.1 MPa). This work achieves the combination of CNT and TiO₂ nanoparticles for strong radiative cooling coating, important for energy-efficient thermal management. Full article

(This article belongs to the Special Issue Advanced Functional Nanostructured Films and Coatings for Energy Applications, 2nd Edition)

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20 pages, 5152 KiB

Open AccessArticle

Grain Boundary Regulation in Aggregated States of MnO_x Nanofibres and the Photoelectric Properties of Their Nanocomposites Across a Broadband Light Spectrum

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

Coatings 2025, 15(8), 920; https://doi.org/10.3390/coatings15080920 - 6 Aug 2025

Viewed by 159

Abstract

Improving charge transport in the aggregated state of nanocomposites is challenging due to the large number of defects present at grain boundaries. To enhance the charge transfer and photogenerated carrier extraction of MnO_x nanofibers, a MnO_x/GO (graphene oxide) nanocomposite was [...] Read more.

Improving charge transport in the aggregated state of nanocomposites is challenging due to the large number of defects present at grain boundaries. To enhance the charge transfer and photogenerated carrier extraction of MnO_x nanofibers, a MnO_x/GO (graphene oxide) nanocomposite was prepared. The effects of GO content and bias on the optoelectronic properties were studied. Representative light sources at 405, 650, 780, 808, 980, and 1064 nm were used to examine the photoelectric signals. The results indicate that the MnO_x/GO nanocomposites have photocurrent switching behaviours from the visible region to the NIR (near-infrared) when the amount of GO added is optimised. It was also found that even with zero bias and storage of the nanocomposite sample at room temperature for over 8 years, a good photoelectric signal could still be extracted. This demonstrates that the MnO_x/GO nanocomposites present a strong built-in electric field that drives the directional motion of photogenerated carriers, avoids the photogenerated carrier recombination, and reflect a good photophysical stability. The strength of the built-in electric field is strongly affected by the component ratios of the resulting nanocomposite. The formation of the built-in electric field results from interfacial charge transfer in the nanocomposite. Modulating the charge behaviour of nanocomposites can significantly improve the physicochemical properties of materials when excited by light with different wavelengths and can be used in multidisciplinary applications. Since the recombination of photogenerated electron–hole pairs is the key bottleneck in multidisciplinary fields, this study provides a simple, low-cost method of tailoring defects at grain boundaries in the aggregated state of nanocomposites. These results can be used as a reference for multidisciplinary fields with low energy consumption. Full article

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

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14 pages, 4458 KiB

Open AccessArticle

The Effect of Crevice Structure on Corrosion Behavior of P110 Carbon Steel in a Carbonated Simulated Concrete Environment

by Fanghai Ling, Chen Li, Hailin Guo and Yong Xiang

Coatings 2025, 15(8), 919; https://doi.org/10.3390/coatings15080919 - 6 Aug 2025

Viewed by 205

Abstract

This study systematically investigated the corrosion behavior of P110 pipeline steel in simulated carbonated concrete environments through a combination of electrochemical testing and multiphysics simulation, with particular focus on revealing the evolution mechanisms of corrosion product deposition and ion concentration distribution under half [...] Read more.

This study systematically investigated the corrosion behavior of P110 pipeline steel in simulated carbonated concrete environments through a combination of electrochemical testing and multiphysics simulation, with particular focus on revealing the evolution mechanisms of corrosion product deposition and ion concentration distribution under half crevice structures, providing new insights into localized corrosion in concealed areas. Experimental results showed that no significant corrosion occurred on the P110 steel surface in uncarbonated simulated pore solution. Conversely, the half crevice structure significantly promoted the development of localized corrosion in carbonated simulated pore solution, with the most severe corrosion and substantial accumulation of corrosion products observed at the crevice mouth region. COMSOL Multiphysics simulations demonstrated that this phenomenon was primarily attributed to local enrichment of Cl⁻ and H⁺ ions, leading to peak corrosion current density, and directional migration of Fe²⁺ ions toward the crevice mouth, causing preferential deposition of corrosion products at this location. This “electrochemical acceleration-corrosion product deposition” multiphysics coupling analysis of corrosion product deposition patterns within crevices represents a new perspective not captured by traditional crevice corrosion models. The established ion migration-corrosion product deposition model provides new theoretical foundations for understanding crevice corrosion mechanisms and predicting the service life of buried concrete pipelines. Full article

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

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17 pages, 2801 KiB

Open AccessArticle

The Influence of Substrate Preparation on the Performance of Two Alkyd Coatings After 7 Years of Exposure in Outdoor Conditions

by Emanuela Carmen Beldean, Maria Cristina Timar and Emilia-Adela Salca Manea

Coatings 2025, 15(8), 918; https://doi.org/10.3390/coatings15080918 - 6 Aug 2025

Viewed by 224

Abstract

Alkyd resins are among the most common coatings used for exterior wood joinery. In Romania, solvent-borne alkyd coatings are widely used to finish wood. The study aims to compare the performance after 7 years of outdoor exposure of two types of alkyd coatings, [...] Read more.

Alkyd resins are among the most common coatings used for exterior wood joinery. In Romania, solvent-borne alkyd coatings are widely used to finish wood. The study aims to compare the performance after 7 years of outdoor exposure of two types of alkyd coatings, a semi-transparent brown stain with micronized pigments (Alk1) and an opaque white enamel (Alk2), applied directly on wood or wood pre-treated with three types of resins: acryl-polyurethane (R1), epoxy (R2), and alkyd-polyurethane (R3). Fir (Abies alba) wood served as the substrate. Cracking, coating adhesion, and biological degradation were periodically assessed through visual inspection and microscopy. Additionally, a cross-cut test was performed, and the loss of coating on the directly exposed upper faces was measured using ImageJ. The results indicated that resin pretreatments somewhat reduced cracking but negatively affected coating adhesion after long-term exposure. All samples pretreated with resins and coated with Alk1 lost more than 50% (up to 78%) of the original finishing film by the end of the test. In comparison, coated control samples lost less than 50%. The Alk2 coating exhibited a film loss between 2% and 12%, compared to an average loss of 9% for the coated control. Overall, samples pretreated with alkyd-polyurethane resin (R3) and coated with alkyd enamel (Alk2) demonstrated the best performance in terms of cracking, adhesion, and discoloration. Full article

(This article belongs to the Collection Wood: Modifications, Coatings, Surfaces, and Interfaces)

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21 pages, 4264 KiB

Open AccessArticle

Study on the Performance Restoration of Aged Asphalt Binder with Vegetable Oil Rejuvenators: Colloidal Stability, Rheological Properties, and Solubility Parameter Analysis

by Heng Yan, Xinxin Cao, Wei Wei, Yongjie Ding and Jukun Guo

Coatings 2025, 15(8), 917; https://doi.org/10.3390/coatings15080917 - 6 Aug 2025

Viewed by 217

Abstract

This study evaluates the effectiveness of various rejuvenating oils, including soybean oil (N-oil), waste frying oil (F-oil), byproduct oil (W-oil), and aromatic hydrocarbon oil (A-oil), in restoring aged asphalt coatings by reducing asphaltene flocculation and improving colloidal stability. The rejuvenators were incorporated into [...] Read more.

This study evaluates the effectiveness of various rejuvenating oils, including soybean oil (N-oil), waste frying oil (F-oil), byproduct oil (W-oil), and aromatic hydrocarbon oil (A-oil), in restoring aged asphalt coatings by reducing asphaltene flocculation and improving colloidal stability. The rejuvenators were incorporated into aged asphalt binder via direct mixing at controlled dosages. Their effects were assessed using microscopy, droplet diffusion analysis, rheological testing (DSR and BBR), and molecular dynamics simulations. The aim is to compare the compatibility, solubility behavior, and rejuvenation potential of plant-based and mineral-based oils. The results indicate that N-oil and F-oil promote asphaltene aggregation, which supports structural rebuilding. In contrast, A-oil and W-oil act as solvents that disperse asphaltenes. Among the tested oils, N-oil exhibited the best overall performance in enhancing flowability, low-temperature flexibility, and chemical compatibility. This study presents a novel method to evaluate rejuvenator effectiveness by quantifying colloidal stability through grayscale analysis of droplet diffusion patterns. This integrated approach offers both mechanistic insights and practical guidance for selecting bio-based rejuvenators in asphalt recycling. Full article

(This article belongs to the Section Environmental Aspects in Colloid and Interface Science)

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14 pages, 5840 KiB

Open AccessArticle

Paint Removal Performance and Sub-Surface Microstructural Evolution of Ti6Al4V Alloy Using Different Process Parameters of Continuous Laser Cleaning

by Haoye Zeng, Biwen Li, Liangbin Hu, Yun Zhang, Ruiqing Li, Chaochao Zhou and Pinghu Chen

Coatings 2025, 15(8), 916; https://doi.org/10.3390/coatings15080916 - 6 Aug 2025

Viewed by 270

Abstract

Laser cleaning technology has been increasingly applied in the removal of damaged protective coatings from aircraft components due to its environmental friendliness and high efficiency. Appropriate laser cleaning process parameters improve cleaning efficiency while preventing substrate damage. In this study, a Gaussian continuous-wave [...] Read more.

Laser cleaning technology has been increasingly applied in the removal of damaged protective coatings from aircraft components due to its environmental friendliness and high efficiency. Appropriate laser cleaning process parameters improve cleaning efficiency while preventing substrate damage. In this study, a Gaussian continuous-wave laser was used to remove the 120 μm coating on the surface of Ti6Al4V alloy. The influence of laser power (100 W to 200 W) and scanning speed (520 mm/min to 610 mm/min) on the paint removal effect was explored based on paint removal rate, surface roughness, microstructural evolution, and the hardness’ change in the direction of heat transfer. The results reveal that optimal paint removal parameters are achieved at a laser power of 100 W with a scanning speed of 550 mm/min. The surface roughness of the sample after paint removal (55 nm) is similar to that of the original substrate (56 nm). Through EBSD analysis, the influence of laser thermal accumulation on the microstructure of the substrate is relatively small. The average hardness of the cross-section after cleaning was 347 HV, which was only 3.41% higher than that of the original substrate. This confirms that parameter-controlled laser cleaning can effectively remove ~120 μm thick paint layers without inflicting damage on the substrate. Full article

(This article belongs to the Special Issue Multi-Principal Element Alloy Design and Surface Modification Technology)

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17 pages, 3870 KiB

Open AccessReview

Eco-Friendly, Biomass-Derived Materials for Electrochemical Energy Storage Devices

by Yeong-Seok Oh, Seung Woo Seo, Jeong-jin Yang, Moongook Jeong and Seongki Ahn

Coatings 2025, 15(8), 915; https://doi.org/10.3390/coatings15080915 - 5 Aug 2025

Viewed by 346

Abstract

This mini-review emphasizes the potential of biomass-derived materials as sustainable components for next-generation electrochemical energy storage systems. Biomass obtained from abundant and renewable natural resources can be transformed into carbonaceous materials. These materials typically possess hierarchical porosities, adjustable surface functionalities, and inherent heteroatom [...] Read more.

This mini-review emphasizes the potential of biomass-derived materials as sustainable components for next-generation electrochemical energy storage systems. Biomass obtained from abundant and renewable natural resources can be transformed into carbonaceous materials. These materials typically possess hierarchical porosities, adjustable surface functionalities, and inherent heteroatom doping. These physical and chemical characteristics provide the structural and chemical flexibility needed for various electrochemical applications. Additionally, biomass-derived materials offer a cost-effective and eco-friendly alternative to traditional components, promoting green chemistry and circular resource utilization. This review provides a systematic overview of synthesis methods, structural design strategies, and material engineering approaches for their use in lithium-ion batteries (LIBs), lithium–sulfur batteries (LSBs), and supercapacitors (SCs). It also highlights key challenges in these systems, such as the severe volume expansion of anode materials in LIBs and the shuttle effect in LSBs and discusses how biomass-derived carbon can help address these issues. Full article

(This article belongs to the Special Issue Surface Engineering for Advanced Applications in Electronics and Energy)

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14 pages, 2180 KiB

Open AccessArticle

Study on Preparation of Nano-CeO₂ Modified Aluminized Coating by Low Temperature Pack Aluminizing on γ-TiAl Intermetallic Compound

by Jiahui Song, Yunmei Long, Yifan He, Yichen Li, Dianqi Huang, Yan Gu, Xingyao Wang, Jinlong Wang and Minghui Chen

Coatings 2025, 15(8), 914; https://doi.org/10.3390/coatings15080914 - 5 Aug 2025

Viewed by 322

Abstract

TiAl alloy offers advantages including low density, high specific strength and stiffness, and excellent high-temperature creep resistance. It is widely used in the aerospace, automotive, and chemical sectors, as well as in other fields. However, at temperatures of 800 °C and above, it [...] Read more.

TiAl alloy offers advantages including low density, high specific strength and stiffness, and excellent high-temperature creep resistance. It is widely used in the aerospace, automotive, and chemical sectors, as well as in other fields. However, at temperatures of 800 °C and above, it forms a porous oxide film predominantly composed of TiO₂, which fails to provide adequate protection. Applying high-temperature protective coatings is therefore essential. Oxides demonstrating protective efficacy at elevated temperatures include Al₂O₃, Cr₂O₃, and SiO₂. The Pilling–Bedworth Ratio (PBR)—defined as the ratio of the volume of the oxide formed to the volume of the metal consumed—serves as a critical criterion for assessing oxide film integrity. A PBR value greater than 1 but less than 2 indicates superior film integrity and enhanced oxidation resistance. Among common oxides, Al₂O₃ exhibits a PBR value within this optimal range (1−2), rendering aluminum-based compound coatings the most extensively utilized. Aluminum coatings can be applied via methods such as pack cementation, thermal spraying, and hot-dip aluminizing. Pack cementation, being the simplest to operate, is widely employed. In this study, a powder mixture with the composition Al:Al₂O₃:NH₄Cl:CeO₂ = 30:66:3:1 was used to aluminize γ-TiAl intermetallic compound specimens via pack cementation at 600 °C for 5 h. Subsequent isothermal oxidation at 900 °C for 20 h yielded an oxidation kinetic curve adhering to the parabolic rate law. This treatment significantly enhanced the high-temperature oxidation resistance of the γ-TiAl intermetallic compound, thereby broadening its potential application scenarios. Full article

(This article belongs to the Special Issue High-Temperature Protective Coatings)

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9 pages, 1868 KiB

Open AccessCommunication

Research on the Temperature Dependence of Deformation and Residual Stress via Image Relative Method

by Haiyan Li, Lei Zhang, Yudi Mao, Jinlun Zhang, Detian Wan and Yiwang Bao

Coatings 2025, 15(8), 913; https://doi.org/10.3390/coatings15080913 - 5 Aug 2025

Viewed by 179

Abstract

Temperature dependence of the deformation behavior and the residual stress in 304 stainless steel beams with single-sided Al₂O₃ coatings of varying thicknesses are analyzed using the image relative method. The results demonstrate that, due to the mismatch of thermal expansion [...] Read more.

Temperature dependence of the deformation behavior and the residual stress in 304 stainless steel beams with single-sided Al₂O₃ coatings of varying thicknesses are analyzed using the image relative method. The results demonstrate that, due to the mismatch of thermal expansion coefficient between the coating and substrate, residual stresses were produced, which caused the bending deformation of the single-side coated specimens. Moreover, coating thickness significantly influences the deformation behavior of specimens. Within the elastic deformation regime, the single-side coated specimens would exhibit alternating bending and flattening deformations in response to the fluctuations of temperature. The higher ratio of the coating thickness to the substrate thickness is, the smaller bending curvature of specimens becomes, and the lower residual compressive stresses in the coating are. For the specimens undergoing elastic deformation, residual stresses can be effectively calculated through the Stoney’s formula. However, as the thickness of coating is close to that of substrate (the corresponding specimens would be regarded as the laminated composites), plastic deformation occurs. And the residual stresses in those specimens vary along the direction of the thickness and the length. In addition, the residual stress decreased with increasing temperature because of the stress relaxation. Full article

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

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15 pages, 3705 KiB

Open AccessArticle

Mechanical Properties and Modification Mechanism of Thermosetting Polyurethane-Modified Asphalt

by Wei Zhuang, Tingting Ding, Chuanqin Pang, Xuwang Jiao, Litao Geng and Min Sun

Coatings 2025, 15(8), 912; https://doi.org/10.3390/coatings15080912 - 4 Aug 2025

Viewed by 288

Abstract

To study the mechanical properties and modification mechanism of thermosetting polyurethane (PU)-modified asphalt, the effects of polyurethane dosage on the workability of polyurethane-modified asphalt were analyzed by means of rotational viscosity tests. The mechanical properties of polyurethane-modified asphalt with different polyurethane dosages were [...] Read more.

To study the mechanical properties and modification mechanism of thermosetting polyurethane (PU)-modified asphalt, the effects of polyurethane dosage on the workability of polyurethane-modified asphalt were analyzed by means of rotational viscosity tests. The mechanical properties of polyurethane-modified asphalt with different polyurethane dosages were explored using tensile tests and dynamic mechanical analysis (DMA). In addition, the thermodynamic behavior and micromorphology of polyurethane-modified asphalt were also thoroughly investigated using the test results of differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). The results showed that PU obtained the optimum workability when the polyurethane dose was 50%: at 120 min, its rotational viscosity was 1005 cp, which was lower than 2800 cp (40% PU) and 760 cp (60% PU). Additionally, the results of fracture elongation and fracture strength indicated that the PU-modified asphalt had good flexibility and strength. Compared with base asphalt, the tensile strength of 50% PU-modified asphalt increased by 509%, which was significantly higher than 157% (40% PU) and more balanced than 897% (60% PU) in terms of strength and flexibility. Added PU can significantly improve the elasticity of asphalt at high temperatures, while increasing the proportion of asphalt adhesive components, enhancing the deformation ability and temperature stability of asphalt. As the dose of PU increases, the interface between asphalt and PU blended more fully, and the surface became smoother. When the dose of PU was 50% or more, the interface between asphalt and PU was well integrated with a smooth and flat surface, forming a more uniform and stable cross-linked network structure. Full article

(This article belongs to the Section Environmental Aspects in Colloid and Interface Science)

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16 pages, 5703 KiB

Open AccessArticle

Optimization of Multi-Objective Process Parameters and Performance Analysis of High-Speed Laser Cladding of TC4/AISI431 Composite Coatings

by Fumin Hong and Tianlu Wei

Coatings 2025, 15(8), 911; https://doi.org/10.3390/coatings15080911 - 4 Aug 2025

Viewed by 273

Abstract

The authors of this paper investigated the process parameters of high-speed laser cladding of TC4/AISI431 composite coatings on the surface of C45 steel, choosing laser power, scanning speed, and TC4 addition as the experimental factors, and porosity, microhardness, and corrosion resistance as the [...] Read more.

The authors of this paper investigated the process parameters of high-speed laser cladding of TC4/AISI431 composite coatings on the surface of C45 steel, choosing laser power, scanning speed, and TC4 addition as the experimental factors, and porosity, microhardness, and corrosion resistance as the target indices. A regression model was established based on the response surface methodology BBD, and the reliability of the model was analyzed using an ANOVA. Then, the WOA was used for multi-objective optimization. The optimal parameter set was determined as follows: a laser power of 5315 W, a scanning speed of 378 mm/s, and a TC4 addition of 3.6%. The microstructure and surface elemental composition of the coating were analyzed. The results showed that the porosity reduced by 60% and that the corrosion resistance improved by 79.98%, while the microhardness remained essentially unchanged. Full article

(This article belongs to the Section Laser Coatings)

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