Coatings

14 pages, 23073 KB

Open AccessArticle

Microstructure Regulation and Strength–Ductility Enhancement of Zn-0.5Mn-0.2Mg Alloy via Equal-Channel Angular Pressing

by Jingjing Lu, Zijun Wang, Yuhan Xiong, Hongzhou Dong, Jun Zhou, Xiaoru Zhuo and Yanxin Qiao

Coatings 2026, 16(10), 1162; https://doi.org/10.3390/coatings16101162 - 30 Sep 2026

Abstract

Zn-Mn-based alloys represent promising material candidates for biodegradable orthopedic implants. Nevertheless, their real-world clinical deployment is severely hampered by unsatisfactory mechanical properties. In this research, a Zn-0.5Mn-0.2Mg (wt.%) alloy was subjected to equal-channel angular pressing (ECAP) with 4, 8 and 12 passes, to [...] Read more.

Zn-Mn-based alloys represent promising material candidates for biodegradable orthopedic implants. Nevertheless, their real-world clinical deployment is severely hampered by unsatisfactory mechanical properties. In this research, a Zn-0.5Mn-0.2Mg (wt.%) alloy was subjected to equal-channel angular pressing (ECAP) with 4, 8 and 12 passes, to systematically explore the influence of ECAP on microstructural evolution and tensile properties. Grain refinement proceeds gradually with additional ECAP passes. The average grain size declines from 1.94 μm (4 passes) to 1.09 μm (8 passes) and further decreases to 0.78 μm (12 passes). While the tilted basal texture remains strong and stable (approximately 15.1–15.2 multiples of uniform distribution, MUD) after 4 and 8 passes, a dramatic drop in texture intensity to 6.7 MUD is detected for the 12-pass sample. Yield strength (YS) and ultimate tensile strength (UTS) increase monotonically with pass number from 279 MPa and 311 MPa (4 passes) to 287 MPa and 323 MPa (8 passes), and further to 298 MPa and 348 MPa (12 passes). Grain boundary strengthening serves as the dominant strengthening mechanism, and dislocation hardening provides supplementary strength contributions. Elongation (EL) also shows a pronounced improvement, increasing from 12% (4 passes) and 17% (8 passes) to a high value of 41% (12 passes). The excellent ductility achieved after 12 passes stems from the combined effects of significant texture weakening and refined second-phase particles. Benefiting from the excellent strength and superior ductility, the 12-pass alloy satisfies the mechanical benchmark for load-bearing orthopedic implantation. Full article

(This article belongs to the Section Metal Surface Process)

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19 pages, 39076 KB

Open AccessArticle

Effects of Simulated Ambient Dust on Current-Carrying Tribological Characteristics of Carbon Brushes/Collector Rings

by Yang Li, Xinze Zhao, Wanting Li, Yunhui Li, Hailin Wu, Xiang Xu, Xiaolong Zhang and Wei Yang

Coatings 2026, 16(10), 1161; https://doi.org/10.3390/coatings16101161 - 30 Sep 2026

Abstract

To elucidate the influence of ring-chamber dust on the current-carrying tribological behavior of the carbon brush/collector ring system in hydro-generators, D172 carbon brushes paired with 45 steel collector rings were employed as the research subjects. Current-carrying sliding friction tests were systematically conducted under [...] Read more.

To elucidate the influence of ring-chamber dust on the current-carrying tribological behavior of the carbon brush/collector ring system in hydro-generators, D172 carbon brushes paired with 45 steel collector rings were employed as the research subjects. Current-carrying sliding friction tests were systematically conducted under varying concentrations of carbon powder, iron powder, and carbon–iron mixed powders. The evolution of friction coefficient, wear loss, wear rate, and contact resistance was analyzed in detail, while the worn carbon brush specimens were characterized using three-dimensional profilometry, scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS). The results demonstrate that different wear debris powders, serving as third-body media, exert significant regulatory effects on both interfacial tribological and electrical conduction behaviors. Under the carbon powder condition, a relatively stable carbonaceous third-body layer readily forms at the interface, maintaining low friction coefficient and wear rate—both reaching their minima at 120 mg/min—thus demonstrating effective friction reduction and wear resistance. In contrast, iron powder conditions promote pronounced abrasive action induced by hard particles, which increases the friction coefficient, accelerates carbon brush wear, and deteriorates the interfacial contact state. For carbon–iron mixed powders, the friction and wear levels lie between those observed for pure carbon and pure iron powders; meanwhile, contact resistance decreases steadily with increasing powder supply rate, indicating relatively superior current-carrying stability. The study reveals that carbon powder primarily contributes positively through lubrication and interfacial protection, whereas iron powder exacerbates damage via particle plowing and contact disruption. The synergistic interaction between the two determines the evolution of the interfacial film layer and the resulting changes in electrical contact performance. These findings provide a theoretical basis for wear control and operational maintenance of carbon brush systems in hydro-generators. Full article

(This article belongs to the Special Issue Tribology of Coatings and Surface Layers)

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21 pages, 9999 KB

Open AccessArticle

Enhanced Interfacial Stability of Mn-Based Cation-Disordered Rocksalt Li_1.2Cr_0.3Ti_0.3Mn_0.3O_1.9F_0.1 Cathodes via an Ion-Conductive LAGP Glass Ceramic Coating

by Jiujie Xu, Fugang Lu, Mengchun Fu, Tiesong Lin, Fei Long, Yongkang Dong, Ce Wang, Panpan Lin and Peng He

Coatings 2026, 16(10), 1160; https://doi.org/10.3390/coatings16101160 - 29 Sep 2026

Abstract

Mn-based disordered rock-salt (DRX) cathode materials offer high theoretical capacities and operating voltages, rendering them promising candidates for high-energy-density lithium-ion batteries. However, severe interfacial reactions between Mn-based DRX cathodes and the electrolyte can induce surface degradation and a pronounced increase in interfacial impedance. [...] Read more.

Mn-based disordered rock-salt (DRX) cathode materials offer high theoretical capacities and operating voltages, rendering them promising candidates for high-energy-density lithium-ion batteries. However, severe interfacial reactions between Mn-based DRX cathodes and the electrolyte can induce surface degradation and a pronounced increase in interfacial impedance. In this study, a LAGP glass ceramic coating layer was introduced onto the surface of Li_1.2Cr_0.3Ti_0.3Mn_0.3O_1.9F_0.1 (LCTMOF) particles to minimize direct contact between the active material and the electrolyte, thereby enhancing the capacity retention over 50 cycles. It delivered an initial discharge capacity of 278.7 mAh g⁻¹ and retained 227.3 mAh g⁻¹ after 50 cycles. Relative to the pristine uncoated cathode, the LAGP glass ceramic coating material achieved a capacity retention of 81.5% together with improved rate performance, retaining a high specific capacity of 184.5 mAh g⁻¹ at a current density of 500 mA g⁻¹. Surface XPS analysis, together with the electrochemical results, suggests that the LAGP glass ceramic coating mitigates cathode interfacial degradation under the investigated cycling conditions. Full article

(This article belongs to the Special Issue Ceramic and Glass Material Coatings, 2nd Edition)

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30 pages, 4721 KB

Open AccessArticle

A Comparison of Coating-Defect Detection Models for Wind Turbine Towers

by Ümit Işıkdağ, Yaren Aydın, Sinan Melih Nigdeli and Gebrail Bekdaş

Coatings 2026, 16(10), 1159; https://doi.org/10.3390/coatings16101159 - 29 Sep 2026

Abstract

Wind energy is becoming increasingly important in meeting energy security, grid reliability, and the growing electricity demand. The rapid increase in the number and prevalence of wind turbines has triggered the need for fast, cost-effective, reliable, and easy-to-implement inspection systems. Automated detection of [...] Read more.

Wind energy is becoming increasingly important in meeting energy security, grid reliability, and the growing electricity demand. The rapid increase in the number and prevalence of wind turbines has triggered the need for fast, cost-effective, reliable, and easy-to-implement inspection systems. Automated detection of coating defects is important for the maintenance and corrosion prevention of the turbines. In this context, this study aimed to compare and evaluate the accuracy and efficiency of deep learning models for detection of coating defects from images. In this context, the study evaluates five object detection models, RT-DETR-L, YOLOv8-M, YOLOv9-C, YOLO11-L, and YOLO26-L, on an open coating-defect dataset, with inclusion, pinhole, and scratch classes. Each model was trained with 3 random seeds for images of 640 × 640 and 1088 × 1088-pixel resolutions. At 1088 × 1088, YOLO26-L achieved the highest mean mAP50–95 (0.1142), while RT-DETR-L achieved the highest recall (0.5591) and F1 score (0.2217) at the operating confidence threshold of 0.25; RT-DETR-L was also the slowest model (59.8 ms/image). YOLOv8-M achieved a mean mAP50–95 of 0.0976 together with the lowest latency (34.2 ms/image) and lowest true batch-size-1 peak GPU-memory allocation (278 MB). Reducing the resolution to 640 × 640 lowered mAP50–95 by 25.4% for YOLOv8-M and 33.6% for RT-DETR-L while reducing latency and memory use. The results revealed a pronounced accuracy-efficiency trade-off rather than universal superiority of one model for coating defect detection for wind turbine towers. The dataset was acquired during the wind-tower painting process under controlled industrial imaging conditions, so the results characterise in-process coating inspection rather than the inspection of weathered, in-service turbines. Because only three random seeds were used, paired comparisons between individual models were not statistically conclusive (8 of 100 pairwise tests reached p < 0.05) and the reported rankings are descriptive. Applying operating thresholds—determined on the validation set for each model—to the independent test set altered the architectural ranking. At 1088 × 1088 resolution, YOLO26-L surpassed RT-DETR-L to achieve the highest mean F1 score, whereas at 640 × 640 resolution, RT-DETR-L’s ranking dropped significantly. The fact that the selected thresholds range from 0.076 to 0.456 indicates that the differences observed at the common threshold of 0.25 are sensitive to the choice of threshold. While the mAP50–95 decreased by approximately half in the 640 × 640 evaluation—where data leakage was eliminated—the 1088 × 1088 results were considered optimistic, as they were obtained based on the previous segmentation. Full article

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21 pages, 2248 KB

Open AccessReview

Street Art as Collective Memory—Materiality and Deterioration Factors

by Andrea Poliszuk and Marta S. Maier

Coatings 2026, 16(10), 1158; https://doi.org/10.3390/coatings16101158 - 29 Sep 2026

Abstract

Street art has expanded across many cities around the world and is now an integral part of everyday life. These painted surfaces have been embraced by citizens as objects associated with neighborhood identity, expressions of political messages, and representations of iconic sport and [...] Read more.

Street art has expanded across many cities around the world and is now an integral part of everyday life. These painted surfaces have been embraced by citizens as objects associated with neighborhood identity, expressions of political messages, and representations of iconic sport and music figures, among other forms of cultural expression. However, these artworks are prone to severe degradation due to exposure to outdoor environmental conditions, which negatively affects their preservation. Therefore, considerable efforts have been devoted to investigating the composition of street art paints and their degradation processes upon outdoor exposure. This review presents an updated overview of the main advances in the characterization of street art materials in commercial paints and outdoor mural paintings, focusing on the multi-analytical approaches that employ non-destructive and micro-destructive techniques. It also examines the effects of environmental conditions, particularly on the chromatic alteration of synthetic organic pigments, as well as recent advances in the development of protective coatings for outdoor mural paintings. Finally, this review aims to contribute to the advancement of research on street art materials and to promote the conservation of this cultural heritage. Full article

(This article belongs to the Special Issue New Insights into Everyday Heritage: Surface Analysis and Conservation)

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22 pages, 9768 KB

Open AccessArticle

Subsurface Evolution and Residual Stress Behavior of 7075 Aluminum Alloy Under Multi-Field Water Jet Impact

by Ping Zhang, Jie Gao, Zhimin Zhao and Xiujie Yue

Coatings 2026, 16(10), 1157; https://doi.org/10.3390/coatings16101157 - 29 Sep 2026

Abstract

This study investigates the compound surface modification of 7075 aluminum alloy through the High-Speed Cutting-Solid Projectile Embedded Water Jet (HSC-SPEWJ) method. The research employed SEM, XRD, TEM, and HRTEM techniques to assess how process parameters such as jet pressure, nozzle distance, and nozzle [...] Read more.

This study investigates the compound surface modification of 7075 aluminum alloy through the High-Speed Cutting-Solid Projectile Embedded Water Jet (HSC-SPEWJ) method. The research employed SEM, XRD, TEM, and HRTEM techniques to assess how process parameters such as jet pressure, nozzle distance, and nozzle traverse speed influence surface properties, including surface quality, roughness, microhardness, residual stress, and microstructural evolution in the alloy. The results indicate that the surface of the alloy treated with the SPEWJ process primarily exhibits features such as “craters,” microcracks, and micropores, with the lowest surface roughness recorded at 0.6214 μm. The modification leads to the formation of a plastic deformation layer with depths varying between 28 and 78 μm, with the maximum depth of 78 μm achieved at a jet pressure of 15 MPa. This treatment results in an 8.8% increase in the maximum microhardness when compared to the untreated sample. The greatest work-hardened layer observed extended to a depth of 100 μm. Furthermore, the surface residual compressive stress reached −210.37 MPa, with the stress field extending to 356 μm below the surface. The HSC-SPEWJ treatment also facilitated the formation of high-density dislocations and grain refinement in the alloy, while the size of the Precipitate-Free Zone (PFZ) was reduced by 5 to 10 nm relative to the untreated sample. Full article

(This article belongs to the Section Metal Surface Process)

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4 pages, 165 KB

Open AccessEditorial

Surface and Interface Analysis in Cultural Heritage

by Claudia Pelosi

Coatings 2026, 16(10), 1156; https://doi.org/10.3390/coatings16101156 - 28 Sep 2026

Abstract

The study and analysis of surfaces and interfaces are highly relevant in cultural heritage (CH) for several reasons: (i) to know the composition and materials used to create the artworks [...] Full article

(This article belongs to the Special Issue Surface and Interface Analysis of Cultural Heritage, 2nd Edition)

24 pages, 7193 KB

Open AccessArticle

Multiphysics Modeling of Stress–Hydrogen Diffusion Interaction in X80 Pipeline Steel Containing Double Notches

by Hongjun Wang, Jin Zhang, Kun Qian, Yunqiang Wang, Kejian Huang and Weichen Liu

Coatings 2026, 16(10), 1155; https://doi.org/10.3390/coatings16101155 - 28 Sep 2026

Abstract

With the increasing deployment of hydrogen pipeline transportation, hydrogen embrittlement (HE) of high-strength pipeline steels such as X80 has become a critical concern for structural integrity. In service, surface defects such as notches formed by manufacturing imperfections or mechanical damage can significantly accelerate [...] Read more.

With the increasing deployment of hydrogen pipeline transportation, hydrogen embrittlement (HE) of high-strength pipeline steels such as X80 has become a critical concern for structural integrity. In service, surface defects such as notches formed by manufacturing imperfections or mechanical damage can significantly accelerate hydrogen ingress under combined mechanical loading and hydrogen exposure. In this study, a coupled multiphysics finite element model integrating solid mechanics and hydrogen diffusion was developed in COMSOL to investigate stress-assisted hydrogen transport in X80 pipeline steel containing double surface notches. The effects of notch geometry (angle, depth, and shape) and spatial configuration (spacing) on stress distribution and hydrogen accumulation were analyzed. The results show that smaller notch angles and sharper defects produce higher stress concentration and stronger hydrogen localization, while increasing notch depth enlarges high-stress and hydrogen-rich regions. Reduced notch spacing causes stress field superposition and multi-center hydrogen accumulation, increasing embrittlement susceptibility. Full article

(This article belongs to the Special Issue Recent Progress on Electrochemical Corrosion of Metallic Materials)

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18 pages, 22246 KB

Open AccessArticle

Ultrasonic Surface Modification of WC-Co-Cr Thermal Spray Coatings: Microstructure, Mechanical Properties and Performance

by Lyaila Bayatanova, Nurtoleu Magazov, Bauyrzhan Rakhadilov, Arystanbek Kussainov, Moldir Kaliaskarova and Dauir Kakimzhanov

Coatings 2026, 16(10), 1154; https://doi.org/10.3390/coatings16101154 - 28 Sep 2026

Abstract

Thermal-sprayed WC–Co–Cr coatings are widely used to improve the wear and corrosion resistance of steel components operating under severe service conditions. This study investigates WC–Co–Cr coatings deposited by detonation spraying (DS), high-velocity oxy-fuel (HVOF), and atmospheric plasma spraying (APS) before and after ultrasonic [...] Read more.

Thermal-sprayed WC–Co–Cr coatings are widely used to improve the wear and corrosion resistance of steel components operating under severe service conditions. This study investigates WC–Co–Cr coatings deposited by detonation spraying (DS), high-velocity oxy-fuel (HVOF), and atmospheric plasma spraying (APS) before and after ultrasonic nanocrystal surface modification (UNSM). The coatings were characterized using scanning electron microscopy and energy-dispersive X-ray spectroscopy (SEM/EDS), together with microhardness, tribological, abrasive, erosive, impact-abrasive, cavitation, corrosion, oxidation, and valve endurance tests. The results demonstrate that the deposition technology strongly affects the coating structure and performance. UNSM produced a pronounced increase in microhardness, reaching 1468 HV for DS + UNSM, 1596 HV for HVOF + UNSM, and 1561 HV for APS + UNSM. Ultrasonic treatment also reduced material loss under abrasive, erosive, impact-abrasive, and cavitation conditions. APS + UNSM demonstrated the best performance in the principal laboratory wear tests, with the lowest abrasive mass loss (0.42–0.45 mg), erosive mass loss (0.55–0.60 mg), impact-abrasive mass loss (0.75–0.85 mg), and cavitation mass-loss rate (0.33–0.38 mg/h). In tribological testing, APS + UNSM exhibited the lowest coefficient of friction (0.28), compared with 0.32 for HVOF + UNSM and 0.36 for DS + UNSM. In valve endurance testing, HVOF + UNSM showed the lowest plunger displacement growth rate (0.050 mm/h) and the longest calculated time to reach the 2 mm displacement criterion (22 h). Overall, the combination of thermal spraying and UNSM improves the mechanical and service performance of WC–Co–Cr coatings, while the optimal coating condition depends on the specific degradation mechanism and operating conditions. Full article

(This article belongs to the Section Composite Coatings)

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28 pages, 5304 KB

Open AccessArticle

The Effects of Three-Dimensional Scratch Geometry and Electrolyte Film Thickness on Galvanic Current Distribution in a Ni–W/SiC Coating–Q345B Steel System

by Wenbo Li and Zhengxu Zhao

Coatings 2026, 16(10), 1153; https://doi.org/10.3390/coatings16101153 - 27 Sep 2026

Abstract

Through-coating scratches expose steel surfaces whose arrangement can alter galvanic current distribution. This study combines cross-sectional microscopy and polarization measurements with a three-dimensional finite element comparison of Ni–W/SiC-coated Q345B steel. Electrolyte properties and measured interfacial inputs both correspond to 3.5 wt.% NaCl. Linear, [...] Read more.

Through-coating scratches expose steel surfaces whose arrangement can alter galvanic current distribution. This study combines cross-sectional microscopy and polarization measurements with a three-dimensional finite element comparison of Ni–W/SiC-coated Q345B steel. Electrolyte properties and measured interfacial inputs both correspond to 3.5 wt.% NaCl. Linear, elliptical and circular grooves have a common prescribed bottom area and 180 µm depth, under surface films of 0.642–6.418 µm. Numerical checks include mesh refinement, charge conservation, interpolation ranges and an independently calculated limiting solution. A conditional reaction reconstruction further couples oxygen diffusion to the measured net response and tests source-condition recovery. In the net curve comparison, the linear groove carries the highest bottom current; its excess over the circular groove decreases from 174.2% to 77.3% as the film thickens. At 3.209 µm, doubling width increases bottom current by 32.4% while lowering mean density by 33.8%. Assigning steel kinetics to the sidewalls lowers bottom current by 62.7% and raises total steel current by 72.7%. Oxygen feedback is evaluated separately through net current, oxygen reduction reaction (ORR) consumption and minimum oxygen concentration. Connected partial filling at 3.209 µm retained the shape order. The results describe how scratch geometry and wetting redistribute the net electrochemical response. Full article

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

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22 pages, 24650 KB

Open AccessArticle

Comparative Study of Microcrack Initiation and Fatigue Failure in C75 Steel Quenched in Oil and Salt Bath

by Iuliana Tudorache (Nistor), Cornel Samoila and Doru Ursutiu

Coatings 2026, 16(10), 1152; https://doi.org/10.3390/coatings16101152 - 27 Sep 2026

Abstract

Mechanical properties and fatigue performance are highly dependent on the microstructure formed during heat treatment. C75 steel is widely used in mechanically loaded components subjected to cyclic stresses, where fatigue resistance plays a critical role in ensuring operational reliability and service life. In [...] Read more.

Mechanical properties and fatigue performance are highly dependent on the microstructure formed during heat treatment. C75 steel is widely used in mechanically loaded components subjected to cyclic stresses, where fatigue resistance plays a critical role in ensuring operational reliability and service life. In this context, the present study investigates the influence of bainitic and martensitic microstructures, obtained through salt-bath quenching and oil quenching, respectively, on the fatigue behaviour of C75 steel. To isolate the effect of microstructure, both heat treatment processes were designed to achieve an identical final hardness of 52 HRC, enabling a direct comparison of the resulting microstructures and their influence on the evolution of dynamic stiffness during cyclic loading. Salt-bath quenching resulted in a fine and homogeneous bainitic microstructure, whereas oil quenching produced a predominantly martensitic structure. The treated samples were characterised using hardness measurements, optical microscopy and scanning electron microscopy (SEM). To evaluate the influence of microstructure on fatigue resistance, Wöhler (S-N) curves were established using high-frequency four-point bending fatigue tests performed in accordance with ISO 22407:2007: Metallic Materials—Fatigue Testing—Axial Plane Bending Method. The progression of fatigue damage was assessed through frequency monitoring during cyclic loading, enabling the identification of the onset of frequency decrease and the subsequent evolution of dynamic stiffness during cyclic loading. The results revealed noticeable differences in fatigue behaviour, expressed as descriptive trends, despite similar hardness levels. The two microstructures exhibited different crack-initiation and propagation characteristics, while the overall fatigue performance remained comparable. Furthermore, the results demonstrated that fatigue life is governed not only by hardness but also by microstructural morphology and phase distribution. These findings highlight the critical role of the quenching medium in controlling fatigue damage mechanisms and provide valuable insights for optimising the fatigue performance of C75 steel components subjected to cyclic loading. Full article

(This article belongs to the Special Issue Fatigue and Wear Mechanisms of Different Surface Coatings for Industrial Application)

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36 pages, 3905 KB

Open AccessArticle

Meso-Structural Validation of a Macro-Equivalent Tribological Model for Predicting the Wear of Modified BA16 Asphalt Mixtures

by Andreea Mihale, Marius Gabriel Petrescu, Aristia-Ioana Popovici and Maria Tănase

Coatings 2026, 16(10), 1151; https://doi.org/10.3390/coatings16101151 - 27 Sep 2026

Abstract

When used to analyze the wear of rough surfaces, Archard’s law implicitly assumes that the surface subjected to wear is homogeneous and that its hardness is equal to that of the bulk material, an assumption that does not apply to asphalt mixtures, where, [...] Read more.

When used to analyze the wear of rough surfaces, Archard’s law implicitly assumes that the surface subjected to wear is homogeneous and that its hardness is equal to that of the bulk material, an assumption that does not apply to asphalt mixtures, where, in the case of road pavements, the wearing surface is a mosaic of aggregate particles and binder (bitumen). This study examines this assumption by comparing two models of the wheel–asphalt pavement contact for four BA16 asphalt mixtures: a reference specimen (M0), a modified specimen (M1, characterized by high porosity), a specimen with aggregate replacement in its composition (M2, containing 3% plastic material in flake form), and a specimen with aggregate replacement in its composition (M3, containing 3% cellulosic material in pellet form). The macro-equivalent model treats the specimens as homogeneous media, whereas the meso-structural model explicitly incorporates 93 polyhedral aggregate particles within a representative volume element of 30 mm × 30 mm × 30 mm, under three loading scenarios: severe dry, wet, and thermal conditions, with extreme temperatures of 5 and 40 °C, respectively. The results were assessed using two independent indicators: a composite tribological degradation indicator and an indicator derived from Archard’s law. The explicit modeling shows that the wearing surface contains 16.2% mineral aggregate, compared with 25.2% in the bulk asphalt mixture, while the effective elastic modulus at the wearing surface is 10.5% lower than that of the bulk asphalt mixture. This ratio remains nearly constant (0.894–0.897) for all mixtures and loading scenarios. Both analyses yield the same ranking of wear susceptibility—M0 < M3 < M2 < M1—in all scenarios, with deviations below 4.3%. Tangential loading at the wearing surface triples the stress in the binder and has a predominant effect on wear compared with the normal tire pressure, while the maximum stress occurs precisely at the aggregate–binder interface. Full article

(This article belongs to the Special Issue Surface Engineering: Tribological Behavior of Materials and Coatings)

21 pages, 29980 KB

Open AccessArticle

Effect of Laser Energy Density on the Microstructure, Wear Resistance, and Corrosion Resistance of AlCoCrFeNi High-Entropy Alloy Coatings Fabricated by Laser Cladding on ATI 718Plus

by Xinrui Wang, Hongyou Bian, Han Yin, Weijun Liu, Chengxiao Qi, Kai Zhang and Yichen Wang

Coatings 2026, 16(10), 1150; https://doi.org/10.3390/coatings16101150 - 26 Sep 2026

Abstract

To investigate the effects of laser energy density on the microstructure, phase constitution and distribution, wear resistance, and corrosion resistance of AlCoCrFeNi high-entropy alloy coatings, three coatings were fabricated on ATI 718Plus substrates by laser cladding at different laser energy densities. Their microstructure, [...] Read more.

To investigate the effects of laser energy density on the microstructure, phase constitution and distribution, wear resistance, and corrosion resistance of AlCoCrFeNi high-entropy alloy coatings, three coatings were fabricated on ATI 718Plus substrates by laser cladding at different laser energy densities. Their microstructure, phase constitution, microhardness, tribological behavior, and electrochemical corrosion properties were systematically characterized. The results showed that all coatings exhibited good metallurgical bonding with the substrate. With increasing laser energy density, the coating microstructure initially became finer and more homogeneous and subsequently coarsened. All coatings were primarily composed of BCC/B2 phases with a small fraction of the FCC phase. The coating produced at the medium laser energy density (MHI) exhibited the most homogeneous phase distribution and the highest average microhardness of 576.1 HV_0.3. It also showed the lowest coefficient of friction and specific wear rate, with values of 0.52 and 6.94 × 10⁻⁴ mm³/(N·m), respectively. The dominant wear mechanism was abrasive wear, accompanied by localized delamination and tribo-oxidation. Furthermore, the MHI coating exhibited the highest charge-transfer resistance of 18,880 Ω·cm² and the lowest corrosion current density of 96.8 μA·cm⁻², indicating superior corrosion resistance. These results demonstrate that an appropriate laser energy density promotes a finer and more homogeneous solidification microstructure and a more favorable phase distribution, thereby achieving a synergistic improvement in the hardness, wear resistance, and corrosion resistance of AlCoCrFeNi high-entropy alloy coatings. Full article

(This article belongs to the Special Issue Mechanical Properties and Surface Engineering for Medium- and High-Entropy Alloys)

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25 pages, 7133 KB

Open AccessArticle

Analysis of Tribological Performance of Functionalized Carbon Nanotube-Reinforced Lubricants in Journal Bearings

by Fatma Nazlı Özsolak, İhsan Akşit, Semiha Köprü, Fatma Kılıç Dokan, Cem Sinanoğlu and Fazıl Canbulut

Coatings 2026, 16(10), 1149; https://doi.org/10.3390/coatings16101149 - 26 Sep 2026

Abstract

Reducing friction in radial journal bearings has a direct effect on energy consumption and component service life. This study examined the tribological behavior of a hydrodynamic journal bearing lubricated with Shell Helix Ultra 5W-40 synthetic motor oil blended with functionalized multi-walled carbon nanotubes [...] Read more.

Reducing friction in radial journal bearings has a direct effect on energy consumption and component service life. This study examined the tribological behavior of a hydrodynamic journal bearing lubricated with Shell Helix Ultra 5W-40 synthetic motor oil blended with functionalized multi-walled carbon nanotubes (FMWCNTs) at mass fractions ranging from 0.01 to 0.5 wt%. The nano-lubricants were prepared through mechanical stirring followed by ultrasonication, using Triton X-100 as a surfactant, and they were subsequently characterized by Field Emission Scanning Electron Microscope, FT-IR Spectrometer, Ultraviolet-Visible spectroscopy spectroscopy, and zeta potential measurements. Tests were carried out at loads of 50–500 N, rotational speeds of 0–1500 rpm, and bearing clearances of 0.12–0.28 mm. Stribeck curves were generated to evaluate how FMWCNT concentration influenced the friction coefficient (μ) and the transitions between lubrication regimes. The results show that the effect of adding FMWCNTs on friction depends on both concentration and operating conditions. At 0.01 wt%, friction performance was comparable to or better than that of the base oil. At concentrations of 0.05 wt% and above, the friction coefficient increased noticeably. These findings indicate that selecting an appropriate FMWCNT concentration and maintaining stable dispersion are the key factors governing the performance of FMWCNT-reinforced lubricants. Full article

(This article belongs to the Special Issue Advanced Composite Solutions for Coatings)

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16 pages, 17569 KB

Open AccessArticle

Study of Polyelectrolyte/Silica Coatings Based on Layer-by-Layer Assembly on Iron Powder for Soft Magnetic Composite Materials

by Emir Pošković, Luca Noro, Lorenza Abbà, Fausto Franchini, Marcello Minervini, Luca Ferraris, Federico Carosio, Marco Actis Grande and Alberto Tenconi

Coatings 2026, 16(10), 1148; https://doi.org/10.3390/coatings16101148 - 26 Sep 2026

Abstract

Soft Magnetic Composites (SMCs)—powdered ferromagnetic materials characterized by high macroscopic electrical resistivity—constitute an excellent resource for electrical machines with non-traditional magnetic flux configurations, such as axial flux machines. Their adoption is currently expanding within the mass production of small components, particularly in the [...] Read more.

Soft Magnetic Composites (SMCs)—powdered ferromagnetic materials characterized by high macroscopic electrical resistivity—constitute an excellent resource for electrical machines with non-traditional magnetic flux configurations, such as axial flux machines. Their adoption is currently expanding within the mass production of small components, particularly in the automotive sector. Consequently, numerous research activities focus on performance optimization to maximize and harmonize the mechanical, energetic, and magnetic properties of SMCs. In this context, the layer-by-layer (LbL) chemical deposition process offers multiple degrees of freedom regarding the types, quantities, and arrangements of materials used to construct insulating and binding layers. This study presents a specific system comprising a polymer and nanometric silica, investigating the influence of several process parameters on the overall performance of the final material. The resulting samples were characterized using a hysteresigraph to determine their magnetization curves, relative magnetic permeability, and specific losses across different frequencies. Additionally, mechanical properties were evaluated through transverse rupture strength tests. Full article

(This article belongs to the Special Issue Mechanical and Corrosion Behavious of Aluminium Alloys and Magnetic Materials for Electric Mobility Applications)

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17 pages, 15157 KB

Open AccessArticle

Oil–Water–Quartz Interfacial Regulation by a Temperature- and Salinity-Responsive Gemini Carboxybetaine in Low-Permeability Sandstone: A Digital-Core-Informed Case Study

by Yukun Du, Gang Zhou, Xingyin Huang, Yirui Yu, Fangfei Li and Runlin Du

Coatings 2026, 16(10), 1147; https://doi.org/10.3390/coatings16101147 - 26 Sep 2026

Abstract

The pore geometry and mineral surfaces of low-permeability sandstone constrain both surfactant transport and oil mobilization. We used micro-computed tomography (micro-CT) and scanning electron microscopy (SEM) of Yanchang Formation sandstone from the Hua 182 block to define formulation-screening targets, then evaluated a temperature- [...] Read more.

The pore geometry and mineral surfaces of low-permeability sandstone constrain both surfactant transport and oil mobilization. We used micro-computed tomography (micro-CT) and scanning electron microscopy (SEM) of Yanchang Formation sandstone from the Hua 182 block to define formulation-screening targets, then evaluated a temperature- and salinity-responsive gemini carboxybetaine (TS-CB) at oil–water and oil-aged quartz interfaces. The core had an average porosity of 12.7%, a network tortuosity of 1.8, an average fracture aperture of 18.5 μm, and a clay content of 7.5%. TS-CB had a critical micelle concentration (CMC) of 2.8 × 10⁻⁴ mol/L and reduced oil–water interfacial tension (IFT) to 1.9 × 10⁻² mN/m at 0.5 wt% and 45 °C. Its apparent viscosity reached 78.5 mPa·s at 50 °C, and the contact angle on oil-aged quartz was 12.5° at 0.5 wt%. In parallel-core flooding, the total recovery increment was 16.0 percentage points, compared with 12.0 and 10.2 percentage points for OPAB and HPAB. The results link the measured interfacial and bulk-flow responses with improved recovery in the tested core system. The position and cause of flow redistribution inside the rock remain to be established by direct diagnostics. Full article

(This article belongs to the Section Architectural and Infrastructure Coatings)

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28 pages, 2364 KB

Open AccessReview

Additive Manufacturing for Functional Coatings and Surface-Engineered Materials: Advances, Strategies, and Applications

by Marijan-Pere Marković and Domagoj Vrsaljko

Coatings 2026, 16(10), 1146; https://doi.org/10.3390/coatings16101146 - 26 Sep 2026

Abstract

Additive manufacturing (AM) enables the fabrication of complex three-dimensional architectures, yet the performance of many printed components is ultimately governed by their surfaces and interfaces. Functional coatings and surface-engineering strategies can introduce tailored chemical, physical, electrical, catalytic, optical, or biological properties while preserving [...] Read more.

Additive manufacturing (AM) enables the fabrication of complex three-dimensional architectures, yet the performance of many printed components is ultimately governed by their surfaces and interfaces. Functional coatings and surface-engineering strategies can introduce tailored chemical, physical, electrical, catalytic, optical, or biological properties while preserving the bulk characteristics of the printed material. This review focuses primarily on polymer-based AM, where surface engineering is particularly important because of limited intrinsic surface functionality, process-dependent morphology, and widespread use in microfluidics, sensing, and other functional devices. Metallic, ceramic, and hybrid systems are also considered to illustrate how substrate morphology, porosity, microstructure, and chemical and thermal stability influence coating formation and performance. The review critically examines functional composite feedstocks, chemical and plasma modification, wet-chemical and sol–gel deposition, vapor-phase processes, metallization, laser processing, and hybrid approaches. Particular emphasis is placed on the relationships among AM processing, surface morphology, coating–substrate interfaces, three-dimensional architecture, and application-level performance. Applications in microfluidics and microreactors, catalytic and environmental processes, energy and electrochemical systems, sensing, biomedical technologies, and industrial surfaces are discussed. Key challenges include functionalization of complex geometries, interfacial durability, reproducibility, standardized evaluation, scale-up, and sustainability. Emerging directions in surface-architecture co-design, flow-assisted functionalization, multiphysics modelling, and data-driven optimization are highlighted. Full article

(This article belongs to the Special Issue Recent Developments in Additive Manufacturing of Functional Coatings)

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15 pages, 13660 KB

Open AccessArticle

Microstructure and Mechanical Properties of MoSi₂ Coatings via Magnetron Sputtering and Pack Siliconizing

by Weining Sun, Hui Dong, Jing Yi, Yong Zhou and Jiantao Yao

Coatings 2026, 16(10), 1145; https://doi.org/10.3390/coatings16101145 - 26 Sep 2026

Abstract

MoSi₂ coatings are promising protective materials for hot-section components in aerospace applications, where long-term durability is an important concern. Increasing the coating thickness has been proposed as an important strategy for improving their long-term durability. To prepare MoSi₂ coatings with different [...] Read more.

MoSi₂ coatings are promising protective materials for hot-section components in aerospace applications, where long-term durability is an important concern. Increasing the coating thickness has been proposed as an important strategy for improving their long-term durability. To prepare MoSi₂ coatings with different thicknesses, a Mo precursor layer with a thickness of 30 μm was deposited by direct-current (DC) magnetron sputtering, followed by pack siliconizing at 1300 °C for 3, 5 and 7 h, respectively. The phase composition, thickness, microstructure and mechanical properties were characterized. The results showed that the Mo coating reached a thickness of approximately 30 μm after 18 h of magnetron sputtering, exhibiting a columnar structure without obvious defects. The thicknesses of MoSi₂ coatings were 86.5 μm, 94.7 μm, and 104.3 μm, respectively, showing an approximately linear increase with pack siliconizing time within the investigated range of 3–7 h. The coatings obtained after 3 and 5 h consisted of three sublayers, including an outer MoSi₂ layer, an intermediate (Mo,Nb)₅Si₃-type layer, and an inner Mo/Nb-rich layer. After 7 h, the intermediate layer was no longer clearly distinguishable, and no distinct residual Mo/Nb-rich inner layer was observed. The coating was therefore predominantly composed of MoSi₂, indicating that 7 h represents a practical threshold for essentially complete silicidation of the 30 μm-thick Mo precursor layer under the present conditions. Within the investigated range of 3–7 h, the mean microhardness, elastic modulus and fracture toughness of the MoSi₂ coating increased approximately linearly with pack siliconizing time, with increases of approximately 31.5 HV_0.3, 24.6 GPa and 0.56 MPa·m^1/2, respectively. The results demonstrate that combining a 30 μm-thick Mo precursor layer with subsequent pack siliconizing provides an effective route for fabricating thick MoSi₂-based coatings exceeding 100 μm, together with controllable microstructural evolution and mechanical properties. The potential benefit of such coating thickening for oxidation resistance remains to be verified in future oxidation tests. Full article

(This article belongs to the Section High-Energy Beam Surface Engineering and Coatings)

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27 pages, 16362 KB

Open AccessArticle

Interaction Regimes and Deposition Mechanisms of Ceramic Particles on Porous Substrates During Cold Spraying

by Olha Aleksieieva, Andrii Toporov and Sergiy Antonyuk

Coatings 2026, 16(10), 1144; https://doi.org/10.3390/coatings16101144 - 25 Sep 2026

Abstract

Refractory materials used in thermal reactors are susceptible to degradation because aggressive media penetrate their porous microstructure, while thermo-mechanical loading accelerates material damage. Cold-sprayed ceramic coatings represent a promising approach for surface protection; however, the deposition mechanisms of brittle ceramic particles on porous [...] Read more.

Refractory materials used in thermal reactors are susceptible to degradation because aggressive media penetrate their porous microstructure, while thermo-mechanical loading accelerates material damage. Cold-sprayed ceramic coatings represent a promising approach for surface protection; however, the deposition mechanisms of brittle ceramic particles on porous substrates remain insufficiently understood. This study combines cold spray experiments, computational fluid dynamics (CFD), and an energy-based analytical framework to investigate particle–substrate interactions during ceramic cold spraying. Gas flow and particle trajectories were simulated within µCT-reconstructed pore geometries using Lagrangian particle tracking, while critical impact conditions were evaluated by considering particle fragmentation and substrate damage. The combined numerical and analytical approach reveals distinct interaction regimes governed by the interplay between particle inertia, impact conditions, and the porous substrate morphology. The integrated experimental observations and theoretical analysis indicate that coating formation is governed by two complementary deposition mechanisms. Fine particles are retained by mechanical interlocking within the pore network, whereas fragmentation of larger particles is proposed to generate additional fine debris that progressively fills the remaining pore space and contributes to coating consolidation. The results further identify processing conditions that promote stable coating formation while suppressing substrate erosion. The proposed framework provides a physics-based understanding of ceramic particle deposition on porous substrates and supports the rational design and optimisation of cold spray processes for refractory surface protection. Full article

(This article belongs to the Section Ceramic Coatings and Engineering Technology)

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