Coatings

12 pages, 580 KiB

Open AccessArticle

B2 NiAl Coatings Alloyed with Rare Earth Element Y: A First-Principles Study

by Junqi He, Ligang Yu and Jinfeng Zhang

Coatings 2025, 15(6), 671; https://doi.org/10.3390/coatings15060671 (registering DOI) - 31 May 2025

NiAl coatings are critical for protecting components in high-temperature environments. In order to improve the mechanical properties of NiAl coatings, in this study, the elastic and electronic properties of NiAl coatings alloyed with different contents of rare earth element (REE) Y were investigated [...] Read more.

NiAl coatings are critical for protecting components in high-temperature environments. In order to improve the mechanical properties of NiAl coatings, in this study, the elastic and electronic properties of NiAl coatings alloyed with different contents of rare earth element (REE) Y were investigated by using the density functional theory (DFT). It was found that NiAl alloys with 3.125 at.% of Y exhibited higher hardness, while those with 6.25 at.% of Y showed better ductility. This phenomenon is explained by population analysis, which reveals that the covalency of Ni-Ni and Al-Al bonds is stronger in Ni₁₅YAl₁₆ than in Ni₇YA₈, whereas Ni-Al bonds exhibit stronger covalency in Ni₇YAl₈. Additionally, the ionicity of Y-Al bonds is higher in Ni₇YAl₈ than in Ni₁₅YAl₁₆. These results deepen our understanding of how rare earth elements modify the mechanical properties of NiAl alloys, thereby providing a theoretical basis for further exploration of their strengthening mechanisms. Full article

(This article belongs to the Special Issue Theoretical and Experimental Analysis of Material Surface Friction and Corrosion)

12 pages, 5568 KiB

Open AccessArticle

Preparation of WC + NbC Particle-Reinforced Ni60-Based Composite Coating by Laser Cladding on Q235 Steel

by Aishan Aliye, Zhixuan Xiao, Chao Gao, Wenqing Shi and Jiang Huang

Coatings 2025, 15(6), 670; https://doi.org/10.3390/coatings15060670 (registering DOI) - 31 May 2025

Abstract

In this paper, the preparation of Ni60 + WC/NbC composite coating by laser cladding technology was studied. The coating properties were analyzed by a scanning electron microscope (SEM), an energy dispersion spectroscope (EDS), X-ray diffraction (XRD), a hardness tester, and a friction and [...] Read more.

In this paper, the preparation of Ni60 + WC/NbC composite coating by laser cladding technology was studied. The coating properties were analyzed by a scanning electron microscope (SEM), an energy dispersion spectroscope (EDS), X-ray diffraction (XRD), a hardness tester, and a friction and wear tester. The results show that WC and NbC, as two typical ceramic reinforcing phases, play a positive role in improving the wear resistance and hardness of the coating. Under the action of a high-temperature (about 2500 °C) laser beam, some complex compounds, such as Ni₃Fe and M₂₃C₆ (M=Fe, Cr) are formed in the coating, which leads to the left deviation of XRD peak position. With the decrease in WC and the increase in Nb particles, the wear mechanism of the coating changes from abrasive wear to adhesive wear. When adding 10% WC, the microhardness of the coating reaches 809.5 HV, the coefficient of friction is 0.496, and the wear rate is 1.1804 × 10⁻⁷ mm³ N⁻¹ • m⁻¹, which shows the best wear resistance. Full article

(This article belongs to the Special Issue Surface Modification of Materials by Laser Processing)

13 pages, 1995 KiB

Open AccessArticle

Tuning Electrical and Optical Properties of SnO₂ Thin Films by Dual-Doping Al and Sb

by Yuxin Wang, Hongyu Zhang, Xinyi Zhang, Zhengkai Zhou and Lu Wang

Coatings 2025, 15(6), 669; https://doi.org/10.3390/coatings15060669 (registering DOI) - 30 May 2025

Abstract

The Al-Sb co-doped SnO₂ composite thin films were prepared by the sol–gel spin-coating method. The structure, morphology, optical and electrical properties of the samples were investigated using XRD, XPS, SEM, UV-Vis spectroscopy, and Hall effect tester, respectively. It was found that when [...] Read more.

The Al-Sb co-doped SnO₂ composite thin films were prepared by the sol–gel spin-coating method. The structure, morphology, optical and electrical properties of the samples were investigated using XRD, XPS, SEM, UV-Vis spectroscopy, and Hall effect tester, respectively. It was found that when the aluminum doping amount was 15 at%, the resistivity of the sample was the lowest, and the overall optoelectronic performance was the best. Moreover, the Al-SnO₂ composite thin film transformed from an n-type semiconductor to a p-type semiconductor. When Al and Sb were co-doped, the carrier concentration increased significantly from 4.234 × 10¹⁹ to 6.455 × 10²⁰. Finally, the conduction type of the Al-Sb-SnO₂ composite thin film changed from p-type to n-type. In terms of optical performance, the transmittance of the Al-Sb co-doped SnO₂ composite thin films in the visible light region was significantly improved, reaching up to 80% on average, which is favorable for applications in transparent optoelectronic devices. Additionally, the absorption edge of the thin films exhibited a blue-shift after co-doping, indicating an increase in the bandgap energy, which can be exploited to tune the light-absorption properties of the thin films for specific photonic applications. Full article

(This article belongs to the Special Issue Research Progress and Prospect of Functional Thin Films & Hard Protective Coatings)

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24 pages, 1036 KiB

Open AccessReview

Comprehensive Review of Thermally Induced Self-Healing Behavior in Asphalt Mixtures and the Role of Steel Slag

by Yihong Yan, Wenbo Li, Chaochao Liu and Boyang Pan

Coatings 2025, 15(6), 668; https://doi.org/10.3390/coatings15060668 (registering DOI) - 30 May 2025

Abstract

Asphalt pavements face escalating challenges from traffic loading, climate change, and material degradation, necessitating innovative maintenance solutions. Thermally induced self-healing technologies, leveraging the viscoelastic properties of asphalt binders, can autonomously repair microcracks through targeted thermal activation. This review explored thermally induced self-healing in [...] Read more.

Asphalt pavements face escalating challenges from traffic loading, climate change, and material degradation, necessitating innovative maintenance solutions. Thermally induced self-healing technologies, leveraging the viscoelastic properties of asphalt binders, can autonomously repair microcracks through targeted thermal activation. This review explored thermally induced self-healing in asphalt mixtures, with a focus on leveraging steel slag as a functional aggregate to enhance sustainability and durability. Two thermal-activation methods, electromagnetic induction and microwave heating, were critically analyzed, highlighting their distinct advantages in heating efficiency, depth, and uniformity. Steel slag offers dual benefits: improving mechanical interlock and skid resistance in mixtures while facilitating efficient heat generation via electromagnetic induction or microwave heating. However, challenges such as hydration-induced expansion, heterogeneous slag composition, and energy-intensive heating processes impede widespread adoption. Pretreatment methods, including natural aging, carbonation, and surface modifications, are essential to mitigate volumetric instability and optimize slag performance. Key factors influencing healing efficacy, including binder properties, operational parameters (e.g., microwave power, frequency), and environmental trade-offs, were systematically evaluated. Future research directions emphasized standardized pretreatment protocols, hybrid heating technologies for uniform temperature distribution, and smart-infrastructure integration for predictive maintenance. Full article

(This article belongs to the Special Issue Novel Cleaner Materials for Pavements)

13 pages, 1623 KiB

Open AccessArticle

Effect of Nb on Laves Phase Formation and Wear Resistance in Laser-Cladding CrFeNi Medium-Entropy Alloy Coatings

by Zehuan Chen, Fangyan Luo, Hongtao Jin, Zhen Peng, Wenqing Shi and Jiang Huang

Coatings 2025, 15(6), 667; https://doi.org/10.3390/coatings15060667 (registering DOI) - 30 May 2025

Abstract

In this study, 20 wt.% of Nb was incorporated into a CrFeNi medium-entropy alloy (MEA) powder system to prepare CrFeNi-Nb composite coatings on a Q235B mild steel substrate by laser cladding technology. The effects of Nb addition on the phase composition, microstructure, and [...] Read more.

In this study, 20 wt.% of Nb was incorporated into a CrFeNi medium-entropy alloy (MEA) powder system to prepare CrFeNi-Nb composite coatings on a Q235B mild steel substrate by laser cladding technology. The effects of Nb addition on the phase composition, microstructure, and wear resistance of CrFeNi coatings were systematically investigated. Microstructural characterization revealed that the CrFeNi coating exhibited a single face-centered cubic (FCC) phase structure, while the CrFeNi-Nb composite coating demonstrated a dual-phase structure comprising FCC phase and Laves phase. The Laves phase significantly enhanced the microhardness and wear resistance of the coating. The average microhardness of the CrFeNi-Nb coating increased by 259.62% compared to the substrate and 190.58% compared to the Nb-free CrFeNi coating. The average coefficient of friction (COF) of the coating decreased from 0.74 to 0.68; the wear rate reduced from 5.77 × 10⁻⁴ mm³ N⁻¹ m⁻¹ to 2.26 × 10⁻⁴ mm³ N⁻¹ m⁻¹; and the weight loss decreased from 10.77 mg to 4.3 mg. The experimental results demonstrated that the addition of Nb promoted the formation of the Laves phase in the CrFeNi MEA, which effectively improved the wear resistance of the coating. Full article

(This article belongs to the Special Issue Effects of Laser Treatment on Surface Characterization and Mechanical Properties of Alloys, 2nd Edition)

15 pages, 3531 KiB

Open AccessArticle

Formation and Bioactivity of Composite Structure with Sr-HA Phase and H₂Ti₅O₁₁·H₂O Nanorods on Ti Surface via Ultrasonic-Assisted Micro-Arc Oxidation and Heat Treatment

by Qing Du, Qiang Zhai, Su Cheng, Yudong Lin, Daqing Wei, Yaming Wang and Yu Zhou

Coatings 2025, 15(6), 666; https://doi.org/10.3390/coatings15060666 (registering DOI) - 30 May 2025

Abstract

To address the biological inertness of pure titanium implants, a composite coating with a strontium-doped hydroxyapatite (Sr-HA) phase and H₂Ti₅O₁₁·H₂O nanorods was engineered via ultrasonic-assisted micro-arc oxidation (UMAO) with hydrothermal treatment (HT). The ultrasonic field [...] Read more.

To address the biological inertness of pure titanium implants, a composite coating with a strontium-doped hydroxyapatite (Sr-HA) phase and H₂Ti₅O₁₁·H₂O nanorods was engineered via ultrasonic-assisted micro-arc oxidation (UMAO) with hydrothermal treatment (HT). The ultrasonic field was applied to modulate the MAO discharge behavior, enhancing ion transport and coating formation. Structural characterization revealed that UMAO-HT coatings exhibited a lower anatase/rutile ratio and higher Sr-HA crystallinity, as compared to MAO-HT. In vitro simulated body immersion studies showed that UMAO-HT induced rapid apatite formation within 24 h, with a better apatite-inducing ability than the conventional MAO-HT. Density functional theory (DFT) simulations demonstrated that Sr substitution in HA lowered the (001) surface work function, enhancing Ca²⁺ adsorption energy and promoting apatite phase nucleation. This work reported the synergistic effects of ultrasonic-induced microstructure optimization and Sr-HA higher bioactivity, providing a mechanistic framework for designing next-generation bioactive coatings with enhanced osseointegration potential. Full article

(This article belongs to the Collection Feature Paper Collection for Topic Editors and Invited Scholars in Coatings)

22 pages, 1631 KiB

Open AccessReview

A Vegetable-Oil-Based Polyurethane Coating for Controlled Nutrient Release: A Review

by Lyu Yao, Azizah Baharum, Lih Jiun Yu, Zibo Yan and Khairiah Haji Badri

Coatings 2025, 15(6), 665; https://doi.org/10.3390/coatings15060665 - 30 May 2025

Abstract

Bio-based polyurethane (PU) is synthesized either via the prepolymerization or addition polymerization of bio-based polyols and isocyanates. PU synthesized from vegetable-oil-based polyols has excellent properties for various application needs. Bio-based PU coatings from renewable vegetable oil show good degradability in soil while controlling [...] Read more.

Bio-based polyurethane (PU) is synthesized either via the prepolymerization or addition polymerization of bio-based polyols and isocyanates. PU synthesized from vegetable-oil-based polyols has excellent properties for various application needs. Bio-based PU coatings from renewable vegetable oil show good degradability in soil while controlling the nutrient release process. Castor oil, soybean oil, palm oil, olive oil, linseed oil, rapeseed oil, cottonseed oil, and recycled oil have been explored in the study of bio-based PU coatings for controlled nutrient release. Castor oil as a natural polyol has been widely studied. Generally, the epoxidation ring opening method is preferred to prepare bio-based polyols. Almost all of these studies used a drum coating machine to complete the coating process. To obtain better controlled release performance, a vegetable-oil-based PU (VPU) coating was modified by increasing the degrees of crosslinking and hydrophobicity and improving the coating uniformity. The nutrient release duration of the modified castor-oil-based PU-coated fertilizer reached 200 days. VPU-coated fertilizers, in contrast to traditional fertilizers, effectively reduce the detrimental impact on the environment. Although the preparation of VPU-coated fertilizers is still at the laboratory scale, application research has been carried out in field crops. Full article

(This article belongs to the Special Issue Preparation and Applications of Bio-Based Polymer Coatings)

22 pages, 16082 KiB

Open AccessArticle

Investigation of Superhydrophobic, Drag-Reducing and Anti-Icing Properties of Swimming Goggles

by Junyi Ding, Haiqi Lin, Xubin Guo, Guangfei Wang, Yangyang Jia and Lu Tang

Coatings 2025, 15(6), 664; https://doi.org/10.3390/coatings15060664 - 30 May 2025

Abstract

Swimming goggles still face numerous challenges in practical use, including deterioration and failure of anti-fog coatings, residual water marks on lens surfaces, and relatively short service life in complex environments. When swimming outdoors during winter, goggles also present an icing problem. To address [...] Read more.

Swimming goggles still face numerous challenges in practical use, including deterioration and failure of anti-fog coatings, residual water marks on lens surfaces, and relatively short service life in complex environments. When swimming outdoors during winter, goggles also present an icing problem. To address these problems and enhance the performance of swimming goggles, this study employs a combination of plasma cleaning and mechanical spraying methods, utilizing HB-139 SiO₂ to modify the surface of goggle lenses, thereby fabricating lenses with superhydrophobic properties. The changes in lens surfaces before and after friction and immersion treatments were characterized using three-dimensional profilometry and scanning electron microscopy, further investigating the hydrophobic, drag-reducing, wear-resistant, and anti-icing properties of the lenses. Experimental results demonstrate that SiO₂ can enhance the hydrophobic, drag-reducing, durability, and anti-icing performance of the lenses. Under standard conditions, the contact angle of modified samples reached 162.33 ± 3.15°, representing a 48.77 ± 2.15% improvement over original samples. Under friction conditions, modified samples exhibited a 45.86 ± 2.53% increase in contact angle compared to original samples, with Sa values decreasing by 58.64 ± 3.21%. Under immersion conditions, modified samples showed a 54.37 ± 2.44% increase in contact angle relative to original samples. The modified samples demonstrated excellent droplet bouncing performance at temperatures of −10 °C, 10 °C, and 30 °C. De-icing efficiency improved by 14.94 ± 2.37%. Throughout the experimental process, SiO₂ demonstrated exceptional hydrophobic, drag-reducing, durability, and anti-icing capabilities. This establishes a robust foundation for the exemplary performance of swimming goggles in both training and competitive contexts. Full article

(This article belongs to the Special Issue Research Progress and Application of Super-hydrophobic Anti-icing Surface)

21 pages, 3077 KiB

Open AccessArticle

Development of Iron-Modified Cotton Material: Surface Characterization, Biochemical Activity, and Cytotoxicity Assessment

by Marcin H. Kudzin, Zdzisława Mrozińska, Anna Kaczmarek, Jerzy J. Chruściel, Anna Pinar, Edyta Sulak, Syed Ali Raza Shah, Michał Juszczak, Katarzyna Woźniak and Michał B. Ponczek

Coatings 2025, 15(6), 663; https://doi.org/10.3390/coatings15060663 - 30 May 2025

Abstract

Cotton, commonly used in wound care, has limitations such as quick saturation and wound adhesion, prompting surface modifications. In our studies, iron, which promotes platelet aggregation and coagulation, was deposited onto cotton via direct current (DC) magnetron sputtering. Thus, the biochemical properties of [...] Read more.

Cotton, commonly used in wound care, has limitations such as quick saturation and wound adhesion, prompting surface modifications. In our studies, iron, which promotes platelet aggregation and coagulation, was deposited onto cotton via direct current (DC) magnetron sputtering. Thus, the biochemical properties of cotton fabrics were enhanced. Microscopic analyses revealed uniform iron coating on the fibers, and biochemical tests, such as activated partial thromboplastin time (aPTT) and prothrombin time (PT), showed that the modification did not affect the material’s coagulation activity. Measurements with the thiobarbituric acid (TBA) method (TBARS) showed that iron-modified cotton had antioxidant activity by lowering lipid peroxidation, which can be beneficial for better wound healing and lower infection risk. Moreover, our analysis showed the absence of cyto- and genotoxic properties against normal peripheral blood mononuclear cells (PBM cells). It was found that tested fabrics did not directly interact with DNA. Full article

17 pages, 5593 KiB

Open AccessArticle

Machining-Induced Surface Integrity Enhancement of Ti-6Al-4V Titanium Alloy via Ultrasonic Vibration Side Milling Under High-Speed Machining and Dry Conditions

by Dong Wang, Aowei Han, Jinyong Han, Mingliang Zhang, Xiaodong Yan, Fuquan Nie and Zhenlong Peng

Coatings 2025, 15(6), 662; https://doi.org/10.3390/coatings15060662 - 30 May 2025

Abstract

Ti-6Al-4V titanium alloy is widely used in aerospace and other fields due to its excellent performance, but conventional machining has problems such as high cutting force, high temperature, and tool wear, which leads to the difficulty of balancing surface quality and efficiency. Ultrasonic [...] Read more.

Ti-6Al-4V titanium alloy is widely used in aerospace and other fields due to its excellent performance, but conventional machining has problems such as high cutting force, high temperature, and tool wear, which leads to the difficulty of balancing surface quality and efficiency. Ultrasonic vibration-assisted machining can effectively improve machining performance. Although the cutting force and heat of ultrasonic vibration-assisted machining have been researched widely in the past, the selection of process parameters and the mechanism of surface integrity improvement under dry high-speed milling still need to be investigated in depth. In this research, we compare the surface topography, roughness, hardness, and residual stress of conventional milling (CM) and ultrasonic vibration side milling (UVSM) at four cutting speeds (40, 60, 80, and 100 m/min) and two feeds (0.01 and 0.02 mm/z) and reveal the mechanism of improving the surface integrity of Ti-6Al-4V under dry high-speed conditions. The results show that compared to CM, UVSM leads to a reduction in surface roughness, maintains a good surface profile at high feed, increases the residual compressive stress by up to 79%, and increases the surface hardness by 9.88%–14.06%. Its discontinuous cutting characteristics reduce cutting forces and heat accumulations, effectively improving surface integrity. However, higher cutting parameters lead to increased roughness and lower residual compressive stresses, requiring a balance between efficiency and quality. The research results provide process guidance for ultrasonic dry high-speed machining of Ti-6Al-4V, which is important for precision manufacturing. Full article

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13 pages, 2809 KiB

Open AccessArticle

Initial Stages of Al-AM60-Modified Surface of Magnesium Alloy Activity Exposed to Simulated Marine Environment

by Gerardo Sánchez, Lucien Veleva and Eduardo Flores

Coatings 2025, 15(6), 661; https://doi.org/10.3390/coatings15060661 - 30 May 2025

Abstract

The surface of AM60 magnesium alloy was modified with Al-nanocoating ~65.62 nm, using DC magnetron sputtering to enhance its resistance to degradation under aggressive marine ambience. The sputtered Al film showed adhesion to the α-Mg matrix, covering the dispersed particles of the β [...] Read more.

The surface of AM60 magnesium alloy was modified with Al-nanocoating ~65.62 nm, using DC magnetron sputtering to enhance its resistance to degradation under aggressive marine ambience. The sputtered Al film showed adhesion to the α-Mg matrix, covering the dispersed particles of the β-Mg₁₇Al₁₂ secondary phase. The aluminum nanofilm was composed of (111) and (200) crystal planes of metallic aluminum (Al⁰) and Al₂O₃ (Al³⁺). After 30 days of immersion in a simulated marine environment (SME, pH 7.8), the Al-AM60 maintained a lower alkaline value (pH~8.13) of SME than that of uncoated AM60, attributed to α-Mg electrochemical oxidation to Al₂O₃ and its posterior dissolution, consuming OH⁻ ions. Consequently, the concentration of the released Mg²⁺ ions from the Al-AM60 surface was reduced ~2.3 times (~15 mg L⁻¹). The Rp (polarization resistance), as inversely proportional to the corrosion current, was extracted from the EIS impedance data fitted to an equivalent electrical circuit. After 30 days in SME solution, the Rp value of the Al-AM60 modified surface was ~3.5 times higher than that of AM60 (~15.46 kΩ cm²), confirming that the sputtered aluminum nano-deposit layer can hinder the corrosion process. These reported findings indicated that sputtered Al nano-coatings can mitigate the surface degradation of Mg-Al alloys in saline aggressive marine environments. Full article

(This article belongs to the Special Issue Effects of Surface Layer Modification on Fatigue, Corrosion and Wear Behavior of Metallic Materials)

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33 pages, 9219 KiB

Open AccessReview

Multiscale Modeling and Data-Driven Life Prediction of Kinematic Interface Behaviors in Mechanical Drive Systems

by Yue Liu, Qiang Wei, Wenkui Wang, Libin Zhao and Ning Hu

Coatings 2025, 15(6), 660; https://doi.org/10.3390/coatings15060660 - 30 May 2025

Abstract

The multiscale coupling characteristics of the kinematic interface behavior of mechanical transmission systems are the core factors affecting system accuracy and lifetime. In this paper, we propose an innovative framework to achieve multiscale modeling from surface topographic parameters to system-level dynamics response through [...] Read more.

The multiscale coupling characteristics of the kinematic interface behavior of mechanical transmission systems are the core factors affecting system accuracy and lifetime. In this paper, we propose an innovative framework to achieve multiscale modeling from surface topographic parameters to system-level dynamics response through four stages: microscopic topographic regulation, mesoscopic wear modeling, macroscopic gap evolution, and system vibration prediction. Through the active design of laser-textured surfaces and gradient coatings, the contact stress distribution can be regulated to keep the wear extension; combined with the multiscale physical model and joint simulation technology, the dynamic feedback mechanism of wear–gap–vibration is revealed. Aiming at the challenges of data scarcity and mechanism complexity, we integrate data enhancement and migration learning techniques to construct a hybrid mechanism–data-driven life prediction model. This paper breaks through the limitations of traditional isolated analysis and provides theoretical support for the design optimization and intelligent operation and maintenance of high-precision transmission systems. Full article

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21 pages, 5864 KiB

Open AccessArticle

Study on Abrasion Resistance of Granite Manufactured Sand Concrete Based on Indoor Abrasion Tester

by Zhitang Li, Yuankuo Wang, Xiaolong Yang, Junlin Liang, Yuanfeng Chen and Minqiang Pan

Coatings 2025, 15(6), 659; https://doi.org/10.3390/coatings15060659 - 30 May 2025

Abstract

The long-term wear resistance of granite manufactured sand (HGY) concrete has not been sufficiently investigated. This deficiency makes it difficult to accurately predict and evaluate the service life and durability of such concrete pavements in practical engineering applications. Consequently, this study employed a [...] Read more.

The long-term wear resistance of granite manufactured sand (HGY) concrete has not been sufficiently investigated. This deficiency makes it difficult to accurately predict and evaluate the service life and durability of such concrete pavements in practical engineering applications. Consequently, this study employed a self-developed indoor abrasion test device and combined it with scanning electron microscope (SEM) and X-ray diffraction (XRD) technologies. From the two dimensions of macroscopic performance and microscopic structure, the mechanisms’ influence of the effective sand ratio, stone powder content, and fine aggregate lithology on the wear resistance of HGY concrete were systematically investigated. The optimal content of the effective sand and stone powder content were determined, and the long-term evolution law of the wear resistance of HGY concrete was revealed. The results demonstrate that increasing the effective sand content will reduce the mass loss of concrete. When the stone powder content is 9%, the wear resistance of the concrete is optimal. The order of mass loss of different fine aggregate lithologies is river sand (HS) > limestone mechanism sand (SHY) > HGY, and the wear resistance of HGY is better than that of other fine aggregates. Increasing the effective sand content can enhance the bonding strength between the aggregate and the cement matrix and reduce the porosity, which is conducive to improving the wear resistance of the concrete. Under a relatively small stone powder content, as the amount of stone powder added increases, the pore structure becomes tighter, and the wear resistance of the concrete becomes better. Compared to HS, the manufactured sand (MS) containing stone powder can optimize the pore structure and hydration products of concrete, improve the pore structure of concrete, and improve the wear resistance. Full article

(This article belongs to the Special Issue Synthesis and Application of Functional Polymer Coatings)

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19 pages, 8829 KiB

Open AccessArticle

Erosive Wear of Stainless Steel-Based Hardfacings with Ex-Situ and In-Situ Synthesized TiC

by Sibel Yöyler, Andrei Surženkov, Marek Tarraste, Mart Kolnes and Kristjan Juhani

Coatings 2025, 15(6), 658; https://doi.org/10.3390/coatings15060658 - 29 May 2025

Abstract

The resistance to erosion of stainless steel-based plasma transferred arc (PTA)-cladded hardfacings reinforced with ex-situ-synthesized TiC is compared to those reinforced using in-situ-synthesized TiC (formed from TiO₂ and graphite). The PTA cladding was performed under an optimized torch linear velocity of 0.7 [...] Read more.

The resistance to erosion of stainless steel-based plasma transferred arc (PTA)-cladded hardfacings reinforced with ex-situ-synthesized TiC is compared to those reinforced using in-situ-synthesized TiC (formed from TiO₂ and graphite). The PTA cladding was performed under an optimized torch linear velocity of 0.7 m/s and cladding current of 115 A. The microstructure of the cladded overlay was analyzed using scanning electron microscopy (SEM), and the phase composition was determined using X-ray diffraction (XRD). Vickers macrohardness measurements were made at representative areas at the surface of the overlays. An erosive wear test was conducted with impact angles of 30° and 90° and impact velocities of 20, 50, and 80 m/s. The formation of TiC from TiO₂ and graphite started during ball milling and ended during the cladding stage. The final TiC content in the hardfacings was below nominal, which is likely due to carbide segregation occurring during the cladding process. The highest hardness was 2.4 times that of stainless steel, which was observed in the deposit containing 60 vol.% ex-situ-synthesized TiC. Both ex-situ and in-situ TiC reinforcement improved resistance to erosion, providing up to 1.5 times better resistance under the 30° impact angle and up to 6.3 times under the 90° impact angle than that of stainless steel. However, ex-situ TiC showed a slightly larger improvement. At the 30° impact angle, the primary wear mechanism is micro-ploughing, but at the 90° impact angle it is surface fatigue. Both mechanisms appeared at both angles under 80 m/s impact velocity. Full article

12 pages, 1878 KiB

Open AccessArticle

Photocatalytic Properties of ZnO/WO₃ Coatings Formed by Plasma Electrolytic Oxidation of a Zinc Substrate in a Tungsten-Containing Electrolyte

by Stevan Stojadinović, Dejan Pjević and Nenad Radić

Coatings 2025, 15(6), 657; https://doi.org/10.3390/coatings15060657 - 29 May 2025

Abstract

ZnO/WO₃ coatings were synthesized by the plasma electrolytic oxidation of zinc in an alkaline phosphate electrolyte (supporting electrolyte, SE) with the addition of WO₃ particles or tungstosilicic acid (WSiA, H₄SiW₁₂O₄₀) at concentrations of up to [...] Read more.

ZnO/WO₃ coatings were synthesized by the plasma electrolytic oxidation of zinc in an alkaline phosphate electrolyte (supporting electrolyte, SE) with the addition of WO₃ particles or tungstosilicic acid (WSiA, H₄SiW₁₂O₄₀) at concentrations of up to 1.0 g/L. These coatings were intended for the decomposition of methyl orange (MO) through photocatalysis. The morphology, chemical composition, crystal structure and absorption properties of the coatings were investigated using scanning electron microscopy, energy dispersive X-ray spectroscopy, wavelength-dispersive X-ray spectroscopy, X-ray diffraction, photoelectron spectroscopy and diffuse reflectance spectroscopy. Under artificial sunlight, the PA of the coatings was investigated using MO decomposition. The photocatalytic activity (PA) of the ZnO/WO₃ coatings was higher than that of the ZnO obtained in SE. The decrease in the recombination rate of photo-generated electron/hole pairs due to the coupling of ZnO and WO₃ is related to the increased PA. The PA for ZnO and the most photocatalytically active ZnO/WO₃ was around 72% and 96%, respectively, after 8 h of irradiation. A mechanism for MO photo-degradation by the ZnO/WO₃ photocatalyst was also proposed. Full article

(This article belongs to the Special Issue Recent Advances in Functional Transparent Semiconductor Films and Coatings; 2nd Edition)

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19 pages, 5085 KiB

Open AccessArticle

Multiscale Simulation of Graphene Growth on Cu(111): Insights from DFT, MD, KMC, and Thermodynamic Analyses

by Yadian Xie, Xu Tang, Yujia Zhang, Guangxu Yang, Hanqing Yu, Bo Yang and Gang Xie

Coatings 2025, 15(6), 656; https://doi.org/10.3390/coatings15060656 - 29 May 2025

Abstract

In chemical vapor deposition (CVD)-mediated graphene growth, copper foil serves as both a catalyst for methane decomposition and as a substrate for graphene nucleation and growth. Due to the low solubility of carbon in copper and the ease of transferring graphene from its [...] Read more.

In chemical vapor deposition (CVD)-mediated graphene growth, copper foil serves as both a catalyst for methane decomposition and as a substrate for graphene nucleation and growth. Due to the low solubility of carbon in copper and the ease of transferring graphene from its surface, copper—particularly the Cu(111) facet—is widely favored for high-quality, monolayer graphene synthesis. In this article, the thermodynamic processes involved in methane dissociation and graphene nucleation on the Cu(111) surface were investigated using density functional theory (DFT). Molecular dynamics simulations were performed for structural optimization and to evaluate the reaction energies. Additionally, the average adsorption energies (ΔEad) of carbon clusters with varying atomic numbers on the Cu(111) surface were calculated. The graphene growth process was further modeled using the kinetic Monte Carlo (KMC) method to simulate carbon atom migration and nucleation dynamics. Thermodynamic analysis based on equilibrium component data was conducted to examine the influence of key operational parameters—temperature, pressure, and the CH₄/H₂ partial pressure ratio—on the graphene deposition rate. Full article

(This article belongs to the Special Issue Recent Progress in Thin Films and Surfaces: Deposition, Characterization and Various Applications)

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14 pages, 3237 KiB

Open AccessArticle

Effect of Si and HA on the Mechanical Characteristics of Spark-Plasma-Sintered Mg–Zn–Mn–(Si–HA) Composites

by Abdulaziz Kurdi, Doaa Almalki, Sayan Sarkar, Alaa Aldurihem, Ahmed Degnah and Animesh Kumar Basak

Coatings 2025, 15(6), 655; https://doi.org/10.3390/coatings15060655 - 29 May 2025

Abstract

Mg–Zn–Mn-based biocomposites hold prospects as potential orthopedic material. The composition of these composites can be modulated, based on applications, by selective elemental alloying. Towards that, the addition of silicon (Si), hydroxyapatite (HA), or both is considered, followed by the consolidation method, such as [...] Read more.

Mg–Zn–Mn-based biocomposites hold prospects as potential orthopedic material. The composition of these composites can be modulated, based on applications, by selective elemental alloying. Towards that, the addition of silicon (Si), hydroxyapatite (HA), or both is considered, followed by the consolidation method, such as spark plasma sintering (SPS). In this study, the micro-mechanical properties of Mg–Zn–Mn–(Si–HA) composites were investigated through the micro-pillar compression method. The effect of Si and HA incorporation on the mechanical characteristics and deformation mechanism was also elucidated. The microstructure of the composite presents porosity, together with different bioactive phases, such as Mg–Zn, CaMg, Mn–P, MgSi₂, Mn–Si, Mn–CaO, CaMgSi, and Ca–Mn–O. Such porous structures were determined to facilitate cell growth when used as an implant, particularly for musculoskeletal-related disabilities. The yield stress (YS) and compressive stress of the Mg–Zn–Mn–Si–HA were about 1543 ± 99 MPa and 1825 ± 102 MPa, respectively. These values were about 5.8 and 4.8 times higher, respectively, than those of Mg–Zn–Mn–HA composites (266 ± 42 MPa and 380 ± 10 MPa, respectively), and the same was observed for the elastic modulus. Besides that, alloying with HA and Si alters the deformation mechanism from brittle (for Mg–Zn–Mn–Si composites) or ductile (for Mg–Zn–Mn–HA composites) to predominant ductile failure without compromising the attained mechanical properties. Full article

(This article belongs to the Collection Feature Paper Collection in Plasma Coatings, Surfaces & Interfaces)

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15 pages, 10012 KiB

Open AccessArticle

Preparation and Optimization of NiFe₂O₄/GAC Composite Catalyst and Its Application in PEM Electrolytic Ozonation for Sulfamethoxazole Degradation

by Xiaohong Xu, Bo Wen, Yu Yan, Xinrui Ren and Bo Zhang

Coatings 2025, 15(6), 654; https://doi.org/10.3390/coatings15060654 - 29 May 2025

Abstract

With the increasing detection of antibiotics such as sulfamethoxazole (SMX) in water bodies, developing efficient and eco-friendly treatment technologies is critical. This study employs a hydrothermal impregnation method to prepare a NiFe₂O₄/granular activated carbon (GAC) composite catalyst, optimized for [...] Read more.

With the increasing detection of antibiotics such as sulfamethoxazole (SMX) in water bodies, developing efficient and eco-friendly treatment technologies is critical. This study employs a hydrothermal impregnation method to prepare a NiFe₂O₄/granular activated carbon (GAC) composite catalyst, optimized for use in a proton exchange membrane (PEM) electrolytic ozonation system to degrade SMX. Single-factor experiments optimized preparation conditions with a Fe:Ni molar ratio of 3:1, a GAC:Fe + Ni mass ratio of 2:1, and calcination at 500 °C for 3 h. The catalyst was characterized using XRD, SEM, TEM, XPS, and FT-IR, confirming a spinel NiFe₂O₄ structure (crystal size ~15.2 nm) uniformly dispersed on GAC, with an Fe:Ni atomic ratio of ~2.1:1. In the PEM system, the optimized catalyst achieved a 99.15% ± 0.3% SMX degradation rate (50 mg/L) within 25 min, compared to 95.06% ± 0.6% in 30 min without a catalyst. The catalyst maintained 98.45% ± 0.5% efficiency after three cycles, demonstrating excellent stability. The synergy between GAC adsorption and NiFe₂O₄ catalysis, driven by Fe³⁺/Fe²⁺ redox cycling, enhances ·OH generation from ozone decomposition, boosting SMX degradation. This work provides a robust catalyst for antibiotic wastewater treatment and a foundation for scaling up catalytic ozonation. Full article

(This article belongs to the Special Issue Functional Coatings in Electrochemistry and Electrocatalysis)

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21 pages, 4658 KiB

Open AccessArticle

Potentiostatic Plasma Electrolytic Oxidation (PEO) of Aluminum Alloy AA6082: Effect of Electrical Input on Coating Microstructure and Corrosion Resistance

by Alberto Berardi, Matteo Gamba, Luca Paterlini, Federica Ceriani and Marco Ormellese

Coatings 2025, 15(6), 653; https://doi.org/10.3390/coatings15060653 - 29 May 2025

Abstract

Aluminum alloy AA6082 (Al-Si-Mg) is a lightweight alloy that requires thick barrier coatings to be protected from localized corrosion. Plasma Electrolytic Oxidation (PEO) coating is a common anodic surface treatment used for growing protective oxides; the main process variables of PEO are the [...] Read more.

Aluminum alloy AA6082 (Al-Si-Mg) is a lightweight alloy that requires thick barrier coatings to be protected from localized corrosion. Plasma Electrolytic Oxidation (PEO) coating is a common anodic surface treatment used for growing protective oxides; the main process variables of PEO are the composition of the electrolytic solution and the electrical input. This work focuses on the optimization of the electrical input by comparing different coatings produced by potentiostatic PEO at the effective potential of 350 V, applied by different combinations of voltage ramps with various slopes and maintenance times at the fixed potential. All processes lasted five minutes. The innovative character of this research work is the evaluation of the combined effect of the anodizing voltage and its different trends with time on the coating structure and morphology. The corrosion resistance of coated AA6082 is assessed in contact with chlorides, reproducing seawater. The resulting anodic coatings were compared in terms of structure, composition (thickness, XRD, SEM-EDS) and corrosion resistance (potentiodynamic polarization and electrochemical impedance spectroscopy), finding that longer maintenance at high anodizing potentials promotes localized high-energy plasma discharges, producing larger pores and thicker, but less protective coatings. Results show that the coating thickness increases with the maintenance time (maximum thickness value~17.6 μm). Shorter maintenance periods and longer voltage ramps lead to a lower surface porosity and enhanced corrosion performances of the oxide. The thinnest and least porous coating exhibits the best corrosion behavior (CR~1.1 μm/year). Full article

(This article belongs to the Special Issue Tribomechanical and Corrosion Tests for Advanced Surface Characterization)

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