Coatings

31 pages, 7823 KiB

Open AccessArticle

Influence of Alkaline Activator Properties on Corrosion Mechanisms and Durability of Steel Reinforcement in Geopolymer Binders

by Mihail Chira, Adrian-Victor Lăzărescu, Andreea Hegyi, Horatiu Vermesan, Alexandra Csapai, Bradut Alexandru Ionescu, Tudor Panfil Toader and Carmen Florean

Coatings 2025, 15(6), 734; https://doi.org/10.3390/coatings15060734 (registering DOI) - 19 Jun 2025

Abstract

The durability of steel reinforcement in geopolymer composites is significantly influenced by the chemical characteristics of the alkaline medium in which they are embedded. This research offers detailed insights into the corrosion kinetics and mechanisms of geopolymers derived from various fly ash and [...] Read more.

The durability of steel reinforcement in geopolymer composites is significantly influenced by the chemical characteristics of the alkaline medium in which they are embedded. This research offers detailed insights into the corrosion kinetics and mechanisms of geopolymers derived from various fly ash and alkaline activator formulations, considering their inherent microstructural and chemical heterogeneity. This study investigates the effect of the molarity of sodium hydroxide (NaOH) solution and the ratio of sodium silicate to sodium hydroxide (Na₂SiO₃/NaOH) on the corrosion behavior of steel reinforcement in geopolymer matrix under the action of chloride ions. Corrosion of steel reinforcement embedded in geopolymer binder prepared by alkaline activation of fly ash with alkaline activator prepared with different Na₂SiO₃/NaOH ratios (1:1, 1:2, 2:1) and different molar concentrations of NaOH solution (6 M, 8 M and 10 M) was analyzed in terms of process kinetics using Open Circuit Potential (OCP) and Linear Polarization (LP) and mechanism by Electrochemical Impedance Spectroscopy (EIS). The study demonstrates that a Na₂SiO₃:NaOH ratio of 1:2 and an 8 M NaOH solution yield the most favorable combination of physical and mechanical properties and corrosion resistance, confirmed by the highest apparent density, lowest water absorption, and significantly reduced corrosion current densities (as low as 0.72 μA/cm²), as well as highlighting porosity and pH as key factors influencing steel protection in geopolymer matrices. Full article

(This article belongs to the Special Issue Alloy/Metal/Steel Surface: Fabrication, Structure, Friction and Service Life)

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13 pages, 2792 KiB

Open AccessArticle

Engineering C–S–H Sorbents via Hydrothermal Synthesis of PV Glass and Carbide Sludge for Chromium(III) Removal

by Tran Ngo Quan, Le Phan Hoang Chieu and Pham Trung Kien

Coatings 2025, 15(6), 733; https://doi.org/10.3390/coatings15060733 - 19 Jun 2025

Abstract

This study investigates the hydrothermal synthesis of calcium silicate hydrate (C-S-H) from photovoltaic (PV) waste glass and carbide sludge as a strategy for resource recovery and sustainable chromium removal from wastewater. Waste-derived precursors were co-ground, blended at controlled Ca/Si molar ratios (0.8, 1.0, [...] Read more.

This study investigates the hydrothermal synthesis of calcium silicate hydrate (C-S-H) from photovoltaic (PV) waste glass and carbide sludge as a strategy for resource recovery and sustainable chromium removal from wastewater. Waste-derived precursors were co-ground, blended at controlled Ca/Si molar ratios (0.8, 1.0, 1.2), and hydrothermally treated at 180 °C for 96 h to yield C-S-H with tunable morphology and crystallinity. Comprehensive characterization using XRD, FT-IR, SEM-EDX, and UV-Vis spectroscopy revealed that a Ca/Si ratio of 1.0 produced a well-ordered tobermorite/xonotlite structure with a high surface area and fibrous network, which is optimal for adsorption. Batch adsorption experiments showed that this material achieved rapid and efficient Cr(III) removal, exceeding 90% uptake within 9 h through a combination of surface complexation, ion exchange (Ca²⁺/Na⁺ ↔ Cr³⁺), and precipitation of CaCrO₄ phases. Morphological and structural evolution during adsorption was confirmed by SEM, FT-IR, and XRD, while EDX mapping established the progressive incorporation of Cr into the C-S-H matrix. These findings highlight the viability of upcycling industrial waste into advanced C-S-H sorbents for heavy metal remediation. Further work is recommended to address sorbent regeneration, long-term stability, and application to other contaminants, providing a foundation for circular approaches in advanced wastewater treatment. Full article

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15 pages, 2310 KiB

Open AccessArticle

Fucoidan and Hyaluronic Acid Modified ZE21B Magnesium Alloy for Better Hemocompatibility and Vascular Cell Response

by Haoran Wang, Yunwei Gu, Qi Wang, Lingchuang Bai and Shaokang Guan

Coatings 2025, 15(6), 732; https://doi.org/10.3390/coatings15060732 - 19 Jun 2025

Abstract

Magnesium alloy stents exhibit significant potential in the treatment of cardiovascular and cerebrovascular diseases due to their remarkable mechanical support and biodegradability. However, bare magnesium alloy stents often degrade too quickly and exhibit inadequate biocompatibility, which severely restricts their clinical applicability. Herein, a [...] Read more.

Magnesium alloy stents exhibit significant potential in the treatment of cardiovascular and cerebrovascular diseases due to their remarkable mechanical support and biodegradability. However, bare magnesium alloy stents often degrade too quickly and exhibit inadequate biocompatibility, which severely restricts their clinical applicability. Herein, a composite coating consisting of an MgF₂ conversion layer, a polydopamine (PDA) layer, fucoidan, and hyaluronic acid was prepared to enhance the corrosion resistance and biocompatibility of ZE21B alloy for a vascular stent application. The modified ZE21B alloy exhibited relatively high surface roughness, moderate wettability, and better corrosion resistance. Moreover, the modified ZE21B alloy with a low hemolysis rate and fibrinogen adsorption level confirmed improved hemocompatibility for medical requirements. Furthermore, the ZE21B alloy modified with fucoidan and hyaluronic acid enhanced the adhesion, proliferation, and NO release of endothelial cells (ECs). Simultaneously, it inhibits the adhesion and proliferation of smooth muscle cells (SMCs), promoting a competitive advantage for ECs over SMCs due to the synergistic effects of fucoidan and hyaluronic acid. The incorporation of fucoidan and hyaluronic acid markedly improved the corrosion resistance and biocompatibility of the ZE21B magnesium alloy. This development presents a straightforward and effective strategy for the advancement of biodegradable vascular stents. Full article

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11 pages, 2583 KiB

Open AccessArticle

Annealing Treatment of Al₂CoCrFeNi High-Entropy Alloys: Synergistic Effect of Microstructure Modulation on Mechanical and Thermoelectric Properties

by Jiayi Xu, Lequn Kan, Hao Li, Xiaoke Gao, Wei Zhang, Wei Wei, Xiangkui Liu, Wenfeng Yang, Wenwen Sun and Xulong An

Coatings 2025, 15(6), 731; https://doi.org/10.3390/coatings15060731 - 19 Jun 2025

Abstract

This study synthesized Al₂CoCrFeNi high-entropy alloy (HEA) using spark plasma sintering (SPS) followed by annealing treatment. The effects of heat treatment on the microstructure, mechanical properties, wear resistance, and thermoelectric properties were systematically investigated. The annealed alloy exhibited a microhardness increase [...] Read more.

This study synthesized Al₂CoCrFeNi high-entropy alloy (HEA) using spark plasma sintering (SPS) followed by annealing treatment. The effects of heat treatment on the microstructure, mechanical properties, wear resistance, and thermoelectric properties were systematically investigated. The annealed alloy exhibited a microhardness increase from 538.5 HV to 550.9 HV and a significant improvement in ultimate compressive strength from 1540.74 MPa to 2563.67 MPa, attributed to grain homogenization and reduced dislocation density. Wear resistance tests revealed a decrease in wear rate from 7.15 × 10⁻⁵ mm³/(N·m) to 4.74 × 10⁻⁵ mm³/(N·m), with wear morphology analysis confirming enhanced resistance to plastic deformation. Thermoelectric characterization demonstrated that thermal diffusivity increased from 2.98 mm²/s to 3.11 mm²/s at room temperature, while the absolute Seebeck coefficient reached 8.0 μV/K at 200 °C, indicating improved electron transport efficiency due to lattice ordering. This combination of high hardness, high thermal conductivity, and excellent wear resistance presents unique application value in extreme tribological fields involving thermal management and simultaneous surface wear resistance and heat dissipation. Full article

(This article belongs to the Special Issue Advanced High Entropy Alloy Materials and Films: Properties and Applications)

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19 pages, 4071 KiB

Open AccessArticle

Surface Characteristics of TiO₂ Coatings Formed by Micro-Arc Oxidation in Ti-25Ta-xNb Alloys: The Influence of Microstructure and Applied Voltage

by Fernanda de Freitas Quadros, Diego Rafael Nespeque Corrêa, Marco Fosca, Marco Ortenzi, Olga N. Plakhotnaia, Carlos Roberto Grandini and Julietta V. Rau

Coatings 2025, 15(6), 730; https://doi.org/10.3390/coatings15060730 - 19 Jun 2025

Abstract

Due to their excellent mechanical properties and good biocompatibility, titanium (Ti) and its alloys are widely used as biomaterials. However, when implanted in the body, metallic materials may cause serious complications such as wear and infection, leading to patient discomfort and, in some [...] Read more.

Due to their excellent mechanical properties and good biocompatibility, titanium (Ti) and its alloys are widely used as biomaterials. However, when implanted in the body, metallic materials may cause serious complications such as wear and infection, leading to patient discomfort and, in some cases, the need for revision surgery. Micro-arc oxidation (MAO) is a surface modification technique that offers a promising strategy to overcome these challenges. This study investigated the impact of the microstructure of Ti-25 Ta-xNb alloys (x = 10, 20, and 30 wt%) and the variation in applied voltage during the MAO process on the characteristics of the TiO₂ oxide coatings formed. The alloys were treated by MAO at 200, 250, and 300 V using a bioactive electrolyte containing Ca, P, Mg, and Ag. EDS, SEM, XRD, Raman spectroscopy, and adhesion tests performed characterization. Results indicated that Nb addition stabilized the β phase and anticipated the potentiostatic regime. Increasing the voltage supplied to the system provides greater energy, prolonging the galvanostatic regime and promoting the formation of larger and more uniform pores. The oxide coating thickness ranged from approximately 3 to 10 μm, with a tendency to decrease at higher voltages. The coatings exhibited low c, with anatase and rutile phases predominating, the applied voltage and Nb concentration influencing their relative proportions. Even in small amounts, all electrolyte elements (P, Mg, and Ag) were successfully incorporated into the coatings under all conditions. Raman and XRD analyses confirmed a decrease in anatase and an increase in rutile phases with increasing voltage and Nb content. Mechanical testing revealed good adhesion of the coatings in all samples, with the best results obtained at 200 V. The findings demonstrate that the developed coatings exhibit promising characteristics for future surface engineering strategies aimed at improving the performance of metallic biomaterials. Full article

(This article belongs to the Special Issue Films and Coatings with Biomedical Applications)

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14 pages, 3453 KiB

Open AccessArticle

Enhanced Corrosion Resistance and Cytocompatibility of Magnesium Alloys with Mg(OH)₂/Polydopamine Composite Coatings for Orthopedic Applications

by Chunlin Li, Boqiong Li and Wenxia Yan

Coatings 2025, 15(6), 729; https://doi.org/10.3390/coatings15060729 - 18 Jun 2025

Abstract

A critical barrier to the clinical translation of biodegradable magnesium (Mg)-based materials lies in their rapid degradation rate in physiological environment, which leads to premature structural failure and compromised cytocompatibility. Micro-arc oxidation (MAO) coatings offer preliminary corrosion mitigation for Mg alloys, while their [...] Read more.

A critical barrier to the clinical translation of biodegradable magnesium (Mg)-based materials lies in their rapid degradation rate in physiological environment, which leads to premature structural failure and compromised cytocompatibility. Micro-arc oxidation (MAO) coatings offer preliminary corrosion mitigation for Mg alloys, while their inherent structural porosity compromises long-term durability in physiological environment. To address this limitation, we developed a hierarchical coating system consisting of a dense Mg(OH)₂ interlayer (MAO/HT) superimposed on the MAO-treated substrate, followed by a functional polydopamine (PDA) topcoat to create a MAO/HT/PDA composite architecture. The surface characteristics and crystalline structures of these coatings were systematically characterized using field-emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD). The corrosion resistance and interfacsial stability in physiological environment were quantitatively assessed through electrochemical analyses and long-term immersion tests in simulated body fluid (SBF). The cytocompatibility of the coatings was assessed by directly culturing osteoblast on the coated samples. The results reveal that the Mg(OH)₂ film possesses a bulk-like structure and effectively seals the micro-pores of the MAO coating. The current density of MAO/HT/PDA sample decreases by two orders of magnitude compared to that of MAO sample, indicating excellent corrosion resistance. The PDA layer not only acts as a strong barrier to improve the corrosion performance of the coating but also helps maintain the stability of the coating, thus delaying coating destruction in SBF. Moreover, the osteoblast culture results suggest that the MAO/HT/PDA coating promotes cell spread and proliferation noticeably compared to both the MAO and MAO/HT coatings. This study provides compelling evidence that the Mg(OH)₂/PDA composite coating is biodegradable and offers outstanding protection for micro-arc oxidized magnesium. As a result, it holds great promise for significant applications in the field of orthopedic medicine. Full article

(This article belongs to the Special Issue Deposition-Based Coating Solutions for Enhanced Surface Properties)

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21 pages, 8141 KiB

Open AccessArticle

Octahedral Fe₃O₄ Nanozymes Penetrate and Remove Biofilms on Implants via Photomagnetic Response

by Xingpu Yin, Bo Zhao, Lu Chen, Xuan Di, Baoe Li, Hongshui Wang, Donghui Wang and Chunyong Liang

Coatings 2025, 15(6), 728; https://doi.org/10.3390/coatings15060728 - 18 Jun 2025

Abstract

Dental implant papilla (DIP) is susceptible to bacterial adhesion and biofilm formation, and oral pathogenic biofilms can cause persistent oral infections. Enrichment of bacterial biofilms on implants can lead to soft tissue irritation and adjacent bone resorption, severely compromising dental health and potentially [...] Read more.

Dental implant papilla (DIP) is susceptible to bacterial adhesion and biofilm formation, and oral pathogenic biofilms can cause persistent oral infections. Enrichment of bacterial biofilms on implants can lead to soft tissue irritation and adjacent bone resorption, severely compromising dental health and potentially leading to periodontitis, implant loss and costly follow-up care. Nanozymes (NZs) are recently used in biofilm removal as they can induce the production of reactive oxygen species (ROS), which can kill bacteria. However, the short lifespan of ROS limits their diffusion distance, and affects their therapeutic efficacy. In this study, we prepared Fe₃O₄ nanoparticles (NZs) with different morphologies: flower-like (F-Fe₃O₄), hollow spherical (M-Fe₃O₄), octahedral (O-Fe₃O₄), and conventional nanoparticles (N-Fe₃O₄). The ferromagnetic properties of Fe₃O₄ NZs allow them to move and penetrate the biofilm under the action of a magnetic field. The saturation magnetic intensities of the four samples were as follows: F-Fe₃O₄ (23.1 emu g⁻¹), M-Fe₃O₄ (73.34 emu g⁻¹), O-Fe₃O₄ (96.06 emu g⁻¹), and N-Fe₃O₄ (52.15 emu g⁻¹). The synergistic combination of photothermal action and catalytic sterilization can effectively remove the biofilm. In addition, the prepared Fe₃O₄ nanozymes were able to maintain high biological activity on the implant surface with some osteogenic effect. Full article

(This article belongs to the Special Issue Bioactive Coatings on Elements Used in the Oral Cavity Environment)

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11 pages, 7908 KiB

Open AccessArticle

Poly(Methyl Methacrylate)-Based Core-Shell Electrospun Fibers: Structural and Morphological Analysis

by Ivana Stajcic, Vesna Radojevic, Zorica Lazarevic, Milica Curcic, Branka Hadzic, Aleksandar Kojovic and Aleksandar Stajcic

Coatings 2025, 15(6), 727; https://doi.org/10.3390/coatings15060727 - 18 Jun 2025

Abstract

Dicyclopentadiene (DCPD)–poly(methyl methacrylate) (PMMA) core–shell fibers were fabricated via coaxial electrospinning to develop a self-healing polymer composite. A PMMA shell containing a first-generation Grubbs catalyst was co-spun with a DCPD core at 0.5 mL h⁻¹ and 28 kV, yielding smooth, cylindrical fibers. [...] Read more.

Dicyclopentadiene (DCPD)–poly(methyl methacrylate) (PMMA) core–shell fibers were fabricated via coaxial electrospinning to develop a self-healing polymer composite. A PMMA shell containing a first-generation Grubbs catalyst was co-spun with a DCPD core at 0.5 mL h⁻¹ and 28 kV, yielding smooth, cylindrical fibers. The diameter range of nanofibers was 300–900 nm, with 95% below 800 nm, as confirmed by FESEM image analysis. FTIR spectroscopy monitored shell integrity via the PMMA C=O stretch and core polymerization via the trans-C=C bands. The high presence of the 970 cm⁻¹ band in the healed nanofiber mat and the minor appearance in the uncut core–shell mat demonstrated successful DCPD polymerization mostly where the intended damage was. The optical clarity of PMMA enabled the direct monitoring of healing progress via optical microscopy. The presented findings demonstrate that PMMA can retain a liquid active core and catalyst to form a polymer layer on a damaged site and could be used as a model material for other self-healing systems that require healing monitoring. Full article

(This article belongs to the Special Issue Advances in Optical Coatings and Thin Films)

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14 pages, 1479 KiB

Open AccessArticle

Innovative Preservation of Fresh-Cut Potatoes: Synergistic Effects of Antimicrobial Edible Coatings, Ohmic Heating–Osmotic Dehydration, and MAP on Quality and Shelf Life

by Alexandra Mari, Christina Drosou, Konstantina Theodora Laina, Christoforos Vasileiou and Magdalini Krokida

Coatings 2025, 15(6), 726; https://doi.org/10.3390/coatings15060726 - 18 Jun 2025

Abstract

Fresh-cut potatoes are highly perishable, requiring effective preservation strategies to maintain quality and extend shelf life. This study evaluated the use of edible coatings and the combination of osmotic dehydration and ohmic heating (OH-OD), both integrated with modified atmosphere packaging (MAP), to enhance [...] Read more.

Fresh-cut potatoes are highly perishable, requiring effective preservation strategies to maintain quality and extend shelf life. This study evaluated the use of edible coatings and the combination of osmotic dehydration and ohmic heating (OH-OD), both integrated with modified atmosphere packaging (MAP), to enhance microbial stability and reduce quality deterioration. Key quality parameters—including color stability, browning index, weight loss, microbial activity, and sensory attributes—were assessed. Results showed that coated samples (E-FP) had the lowest browning index (59.71) by day 8, compared to a value of 62.69 in control samples (C-FP). OH-OD-treated samples exhibited the least weight loss (6.73%) versus 17.75% in C-FP. Microbial analysis showed that E-FP samples maintained the lowest total viable count by day 8 (3.98 ± 0.02 log CFU/g), compared to OH-OD-FP (4.43 ± 0.13 log CFU/g) and C-FP (4.79 ± 0.06 log CFU/g), confirming the antimicrobial efficacy of the edible coating enriched with rosemary essential oil and ascorbic acid. Sensory evaluation further confirmed that coated samples retained superior sensory qualities, receiving the highest overall acceptance score of 8.86 ± 0.80, compared to values of 7.80 ± 0.98 for control samples (C-FP) and 2.80 ± 0.69 for OH-OD-FP samples, highlighting their enhanced consumer appeal. These findings highlight that combining advanced preservation techniques with MAP can significantly reduce moisture loss and microbial spoilage while maintaining freshness and sensory appeal. This integrated approach offers a promising solution for extending shelf life, reducing food waste, and supporting sustainability in response to consumer demand for minimally processed, high-quality fresh products. Full article

(This article belongs to the Special Issue Advanced Materials for Safe and Smart Food Packaging)

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23 pages, 5461 KiB

Open AccessArticle

Classification and Prediction of Unknown Thermal Barrier Coating Thickness Based on Hybrid Machine Learning and Terahertz Nondestructive Characterization

by Zhou Xu, Jianfei Xu, Yiwen Wu, Changdong Yin, Suqin Chen, Qiang Liu, Xin Ge, Luanfei Wan and Dongdong Ye

Coatings 2025, 15(6), 725; https://doi.org/10.3390/coatings15060725 - 17 Jun 2025

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Abstract

Thickness inspection of thermal barrier coatings is crucial to safeguard the reliability of high-temperature components of aero-engines, but traditional destructive inspection methods are difficult to meet the demand for rapid assessment in the field. In this study, a new non-destructive testing method integrating [...] Read more.

Thickness inspection of thermal barrier coatings is crucial to safeguard the reliability of high-temperature components of aero-engines, but traditional destructive inspection methods are difficult to meet the demand for rapid assessment in the field. In this study, a new non-destructive testing method integrating terahertz time-domain spectroscopy and machine learning algorithms is proposed to systematically study the thickness inspection of 8YSZ coatings prepared by two processes, namely atmospheric plasma spraying (APS) and electron beam physical vapor deposition (EB-PVD). By optimizing the preparation process parameters, 620 sets of specimens with thicknesses of 100–400 μm are prepared, and three types of characteristic parameters, namely, time delay Δt, frequency shift Δf, and energy decay η, are extracted by combining wavelet threshold denoising and time-frequency joint analysis. A CNN-RF cascade model is constructed to realize coating process classification, and an attention-LSTM and SVR weighted fusion model is developed for thickness regression prediction. The results show that the multimodal feature fusion reduces the root-mean-square error of thickness prediction to 8.9 μm, which further improves the accuracy over the single feature model. The classification accuracy reaches 96.8%, of which the feature importance of time delay Δt accounts for 62%. The hierarchical modeling strategy reduces the detection mean absolute error from 6.2 μm to 4.1 μm. the method provides a high-precision solution for intelligent quality assessment of thermal barrier coatings, which is of great significance in promoting the progress of intelligent manufacturing technology for high-end equipment. Full article

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10 pages, 2683 KiB

Open AccessArticle

Effects of Synthesis Process on the Properties of La_1−xSr_xMnO₃ Materials for Thermal Control Coatings

by Fang Jia, Xin Zhang, Xiaoliang Lu, Haoran Peng, Tianjie Shi, Kang Yuan, Xiaoxiao Pang and Rifei Han

Coatings 2025, 15(6), 724; https://doi.org/10.3390/coatings15060724 - 17 Jun 2025

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Abstract

Lanthanum strontium manganate (La_1−xSr_xMnO₃) is considered a highly promising material for the development of intelligent thermal control coatings due to its exceptional properties. Recent studies on this material have primarily utilized solid-state synthesis as the main preparation [...] Read more.

Lanthanum strontium manganate (La_1−xSr_xMnO₃) is considered a highly promising material for the development of intelligent thermal control coatings due to its exceptional properties. Recent studies on this material have primarily utilized solid-state synthesis as the main preparation method. Research efforts have predominantly focused on investigating the effects of material composition, heat treatment processes, and other factors on the properties of the synthesized material. There has been a limited amount of research investigating the influence of chemical precipitation process parameters on the properties of the synthesized La_1−xSr_xMnO₃ material. In this study, the intelligent thermal control coating material La_0.8Sr_0.2MnO₃ was synthesized using the chemical precipitation method. The effects of varying precipitant concentrations on the properties of the synthesized material were investigated. When the precipitant concentration is 12 wt.% or 15 wt.%, the synthesized powder agglomerates predominantly form three-dimensional blocky structures after sintering. At lower concentrations such as 6 wt.% and 9 wt.%, the powder agglomerates predominantly form two-dimensional sheet-like structures after sintering. At precipitant concentrations of 6 wt.% and 9 wt.%, the strontium content in the synthesized powder becomes significantly lower than the designed theoretical value. When the precipitant concentration is relatively high, localized manganese aggregation occurs in the synthesized lanthanum strontium manganate material. The temperature dependence of the emittance test result indicates that the emissivity variation of La_0.8Sr_0.2MnO₃ material synthesized using 12 wt.% ammonia solution as precipitant reaches 0.428 from 173 K to 373 K, demonstrating excellent emissivity modulation performance. Full article

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20 pages, 14981 KiB

Open AccessArticle

Multi-Scale Modelling of Residual Stress on Arbitrary Substrate Geometry in Atmospheric Plasma Spray Process

by Jose Martínez-García, Venancio Martínez-García and Andreas Killinger

Coatings 2025, 15(6), 723; https://doi.org/10.3390/coatings15060723 - 17 Jun 2025

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Abstract

This work presents an exhaustive parametric study of the multi-scale residual stress analysis on arbitrary substrate geometry based on a one-way-coupled thermo-mechanical model in an Atmospheric Plasma Spray process. It was carried out by modifying key process parameters, such as substrate surface geometry, [...] Read more.

This work presents an exhaustive parametric study of the multi-scale residual stress analysis on arbitrary substrate geometry based on a one-way-coupled thermo-mechanical model in an Atmospheric Plasma Spray process. It was carried out by modifying key process parameters, such as substrate surface geometry, substrate pre-heating temperature, and coating thickness, in an Al₂O₃ coating process on an aluminium substrate. The relationship of these parameters to the generation of quenching stress, thermal stress and residual stress was analysed at three different sub-modelling scales, from the macroscopic dimension of the substrate to the microscopic dimension of the splats. The thermo-mechanical phenomena occurring during the deposition process at the microscopic level were discussed in the proposed cases. Understanding these phenomena helps to optimise the parameters of the coating process by identifying the underlying mechanisms responsible for the generation of residual stresses. The simulated residual stresses of the 200 μm Al₂O₃ outer coated aluminium cylinder were experimental validated using the incremental high-speed micro-hole drilling and milling method. Full article

(This article belongs to the Special Issue Advances in Surface Coatings for Wear and Corrosion Protection)

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15 pages, 4658 KiB

Open AccessArticle

Hydrothermal Preparation of Calcium Aluminum Corrosion-Resistant Coatings on AZ91D Magnesium Alloy

by Qingrong Tan, Ying Zhang, Min Jiang and Jiyuan Zhu

Coatings 2025, 15(6), 722; https://doi.org/10.3390/coatings15060722 - 17 Jun 2025

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Abstract

Magnesium alloys are widely used in all kinds of fields because of their excellent mechanical properties, but their application has been prevented by poor corrosion resistance. In this paper, Mg(OH)₂-Ca(OH)₂/Al(OH)₃/Al₂O₃ composite coatings with long-term [...] Read more.

Magnesium alloys are widely used in all kinds of fields because of their excellent mechanical properties, but their application has been prevented by poor corrosion resistance. In this paper, Mg(OH)₂-Ca(OH)₂/Al(OH)₃/Al₂O₃ composite coatings with long-term corrosion resistance were fabricated on the surface of Mg alloys using the hydrothermal method. Among them, the calcium hydroxide/calcium nitrate–alumina coating successfully filled the cracks in the magnesium hydroxide coating. Meanwhile, we explored the influences of different heating times and temperatures on the coating and analyzed its composition. After immersing the coating in a 3.5% NaCl solution for 168 h, only a small portion of the surface dissolved. Electrochemical test results indicated that the corrosion potential and corrosion current density of the coating increased by three orders of magnitude, significantly improving corrosion resistance in comparison to bare samples. Adhesion tests showed that the coating exhibited good bonding performance to the substrate. This method features a simple, pollution-free preparation process and does not require complex instrumentation, thereby enhancing the longevity of the magnesium alloy. Full article

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26 pages, 4725 KiB

Open AccessReview

Hybrid Surface Treatment Technologies Based on the Electrospark Alloying Method: A Review

by Oksana Haponova, Viacheslav Tarelnyk, Tomasz Mościcki and Nataliia Tarelnyk

Coatings 2025, 15(6), 721; https://doi.org/10.3390/coatings15060721 - 16 Jun 2025

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Abstract

Technologies for functional coatings are evolving rapidly, with electrospark alloying (ESA) emerging as a promising method for surface modification due to its efficiency and localized impact. This review analyzes the fundamental principles of ESA and the effects of process parameters on coating characteristics [...] Read more.

Technologies for functional coatings are evolving rapidly, with electrospark alloying (ESA) emerging as a promising method for surface modification due to its efficiency and localized impact. This review analyzes the fundamental principles of ESA and the effects of process parameters on coating characteristics and highlights its advantages and limitations. Particular attention is given to hybrid ESA-based technologies, including combinations with laser treatment, plastic deformation, vapor deposition, and polymer-metal overlays. These hybrid methods significantly improve coating quality by enhancing hardness, adhesion, and structural integrity and reducing roughness and defects. However, the multi-parameter nature of these processes presents optimization challenges. This review identifies knowledge gaps related to process reproducibility, control of microstructure formation, and long-term performance under service conditions. Recent breakthroughs in combining ESA with high-energy surface treatments are discussed. Future research should focus on systematic parameter optimization, in situ diagnostics, and predictive modeling to enable the design of application-specific hybrid coatings. Full article

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

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13 pages, 4953 KiB

Open AccessArticle

Coated High-Performance Paper from Bacterial Cellulose Residue and Eucalyptus Pulp: Enhanced Mechanical Strength, Water Resistance, and Air Barrier Properties

by Preeyanuch Srichola, Kunat Kongsin, Thanyachol Apipatpapha, Jirachaya Boonyarit, Peeraya Ounu and Rungsima Chollakup

Coatings 2025, 15(6), 720; https://doi.org/10.3390/coatings15060720 - 16 Jun 2025

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Abstract

Cellulose-based paper products derived from agro-industrial waste have attracted considerable interest due to their potential in sustainable material development. In this study, bacterial cellulose (BC) residue from the food and beverage industry was employed as a reinforcing agent to fabricate high-performance paper composites [...] Read more.

Cellulose-based paper products derived from agro-industrial waste have attracted considerable interest due to their potential in sustainable material development. In this study, bacterial cellulose (BC) residue from the food and beverage industry was employed as a reinforcing agent to fabricate high-performance paper composites by blending with eucalyptus pulp (EP) at various ratios and basis weights. These papers were coated with a cationic modified starch solution (MS) using a rod coater, followed by hot pressing. Mechanical strengths (TAPPI Standard), water resistance (Cobb test and water contact angle), and air permeability (ASTM D737) were evaluated to assess material performance. The results showed that incorporating 50 wt% BC produced paper with outstanding mechanical performance, characterized by a high tensile index and excellent tear resistance. The application of the MS coating significantly boosted water resistance and air barrier performance, underscoring the effectiveness of this approach in creating high-performance paper materials. The resulting coated composites demonstrated excellent mechanical strength and barrier properties, positioning them as promising candidates for filtration applications such as personal protective face mask membranes. Full article

(This article belongs to the Special Issue Advanced Polymer Coatings: Materials, Methods, and Applications)

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19 pages, 5722 KiB

Open AccessArticle

Comparing Operational Approaches (Spectrophotometric, Electroanalytic and Chromatographic) to Quantify the Concentration of Emerging Contaminants: The Limit of Detection, the Uncertainty of Measurement, Applicability and Open Problems

by Marconi Sandro Franco de Oliveira, Jorge Leandro Aquino de Queiroz, Danyelle Medeiros de Araújo, Mayra Kerolly Sales Monteiro, Karen Giovanna Duarte Magalhaes, Carlos Alberto Martínez-Huitle and Elisama Vieira dos Santos

Coatings 2025, 15(6), 719; https://doi.org/10.3390/coatings15060719 - 14 Jun 2025

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Abstract

In this study, a boron-doped diamond (BDD) sensor was used to study the electroanalytical behavior of emerging contaminants (ECs), such as caffeine, paracetamol and methyl orange. BDD shows strong resolving power for the superimposed voltammetric response of ECs in well-resolved peaks with increased [...] Read more.

In this study, a boron-doped diamond (BDD) sensor was used to study the electroanalytical behavior of emerging contaminants (ECs), such as caffeine, paracetamol and methyl orange. BDD shows strong resolving power for the superimposed voltammetric response of ECs in well-resolved peaks with increased peak current. Differential pulse voltammetry, which is an electroanalytical technique, was compared with two reference techniques including absorption spectrophotometry in the UV-vis region and high-performance liquid chromatography (HPLC) in the detection and quantification of ECs. The results obtained were satisfactory, as the complete removal of ECs was achieved in all applied processes. The detection limits were 0.69 mg L⁻¹, 0.84 mg L⁻¹ and 0.46 mg L⁻¹ for CAF, PAR and MO, respectively. The comparison of electroanalysis results with those obtained by UV-vis and HPLC established and confirmed the potential applicability of the technique for determining CAF, PAR and MO analytes in synthetic effluents and environmental water samples (tap water, groundwater and lagoon water). The electrochemical approach can therefore be highlighted for its low consumption of reagents, ease of operation, time of analysis and excellent precision and accuracy, because these are characteristics that enable the use of this technique as another means of determining analytes in effluents. Full article

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

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24 pages, 4811 KiB

Open AccessArticle

In₂S₃/C₃N₄ Nanocomposite and Its Photoelectric Properties in the Broadband Light Spectrum Range

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

Coatings 2025, 15(6), 718; https://doi.org/10.3390/coatings15060718 - 14 Jun 2025

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Abstract

To extend the spectral utilisation of In₂S₃, an In₂S₃/C₃N₄ nanocomposite was prepared. The effects of different sulphur sources, electrodes, and bias voltages on the optoelectronic performance were examined. Photoelectric properties in response [...] Read more.

To extend the spectral utilisation of In₂S₃, an In₂S₃/C₃N₄ nanocomposite was prepared. The effects of different sulphur sources, electrodes, and bias voltages on the optoelectronic performance were examined. Photoelectric properties in response to light sources with wavelengths of 405, 532, 650, 780, 808, 980, and 1064 nm were investigated using Au electrodes and the carbon electrodes with 5B pencil drawings. This study shows that the aggregation states of the In₂S₃/C₃N₄ nanocomposite possess photocurrent switching responses in the broadband region of the light spectrum. Combining two types of partially visible light-absorbing material extends utilisation to the near-infrared region. Impurities or defects embody an electron-donating effect. Since the energy levels of defects or impurities with an electron-donating effect are close to the conduction band, low-energy lights (especially NIR) can be utilised. The non-equilibrium carrier concentration (photogenerated electrons) of the nanocomposites increases significantly under NIR photoexcitation conditions. Thus, photoconductive behaviour is manifested. A good photoelectric signal was still measured when zero bias was applied. This demonstrates self-powered photoelectric response characteristics. Different sulphur sources significantly affect the photoelectric performance, suggesting that they create different defects that affect charge transport and base current noise. It is believed that interfacial interactions in the In₂S₃/C₃N₄ nanocomposite create a built-in electric field that enhances the separation and transfer of electrons and holes produced by light stimulation. The presence of the built-in electric field also leads to energy band bending, which facilitates the utilisation of the light with longer wavelengths. This study provides a reference for multidisciplinary applications. Full article

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20 pages, 6684 KiB

Open AccessArticle

Study on Rheological Properties of Nano Titanium Dioxide High-Viscosity Modified Asphalt

by Ruiduo Li, Yanzhao Yuan, Yabing Ma, Zhigang Wang, Shikang Zhou and Liqin Li

Coatings 2025, 15(6), 717; https://doi.org/10.3390/coatings15060717 - 14 Jun 2025

Viewed by 202

Abstract

The research on nano titanium dioxide (nano-TiO₂)-modified asphalt has received increasing attention. However, further studies are required in order to ascertain the influence of the phenomenon under discussion on the rheological characteristics and ability to resist deformation of bitumen. In the [...] Read more.

The research on nano titanium dioxide (nano-TiO₂)-modified asphalt has received increasing attention. However, further studies are required in order to ascertain the influence of the phenomenon under discussion on the rheological characteristics and ability to resist deformation of bitumen. In the present study, modified bitumen was formulated by adding nano titanium dioxide. Physical property tests, temperature scanning tests, frequency scanning tests, repeated creep recovery tests, bending creep stiffness tests, and long-term aging performance experiments were carried out on the specimen of asphalt that had undergone the process of modification in order to assess the rheological characteristics and ability to resist unrecoverable deformation of the modified bitumen at different temperatures, both high and low. The outcomes of the repeated creep recovery experiment were analyzed using Burgers and fractional derivative models. The microstructure of nano-TiO₂ high-viscosity modified asphalt was observed by Scanning Electron Microscope(SEM). In order to ascertain the manner in which base bitumen and nano-TiO₂ interact, Fourier transform infrared spectroscopy (FTIR) was utilized in the study. The results show that the thermal stability and prolonged aging resistant properties of the modified bitumen binder improved, but nano-TiO₂ made the asphalt binder weaker and more likely to crack at lower temperatures. Taking into account the variation in the road performance of the bitumen binder, 6% is recommended as the optimal amount of nano-TiO₂. Nano-TiO₂ was mainly uniformly distributed in asphalt and nano-TiO₂ was physically mixed with asphalt. In comparison with the Burgers model, the present fractional derivative empirical creep model can fit the creep test data of the asphalt binder well with the advantages of high accuracy and few parameters. The research results provide a reference for promoting the implementation of modified bitumen incorporating nano-TiO₂. Full article

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17 pages, 3104 KiB

Open AccessArticle

Investigating the Bond Performance of FRP Bars and Concrete Under Dynamic Loading Conditions

by Wenhui Bao, Yini Tan, Hao Li, Chenglong Liang, Hui Chen and Chuanqing Fu

Coatings 2025, 15(6), 716; https://doi.org/10.3390/coatings15060716 - 13 Jun 2025

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Abstract

With growing emphasis on sustainable construction, fiber-reinforced polymer (FRP) bars are increasingly being used as alternatives to steel rebars due to their high strength-to-weight ratio, corrosion resistance, and environmental benefits. This study has investigated the bond behavior between FRP bars and concrete of [...] Read more.

With growing emphasis on sustainable construction, fiber-reinforced polymer (FRP) bars are increasingly being used as alternatives to steel rebars due to their high strength-to-weight ratio, corrosion resistance, and environmental benefits. This study has investigated the bond behavior between FRP bars and concrete of different strength grades under dynamic loading conditions. To analyze the microscopic properties of FRP bar surfaces, the study employs a variety of techniques, including scanning electron microscopy (SEM), atomic force microscopy (AFM), and non-contact surface profilometry. In addition, X-ray photoelectron spectroscopy (XPS), water contact angle (WCA) measurements, and energy dispersive spectrometry (EDS) are used to further investigate surface characteristics. The results reveal a direct correlation between the resin surface roughness of FRP bars and their wettability characteristics, which in turn influence the cement hydration process. Pull-out tests under different loading rates and concrete strength grades have been conducted to evaluate the bond–slip behavior and failure modes. The results indicate that bond strength increases with increasing concrete strength. Dynamic pull-out tests further reveal that higher loading rates generate heterogeneous stress fields, which limit the deformation of FRP bars and consequently diminish the contribution of mechanical interlock to interfacial bonding. Full article

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

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11 pages, 2562 KiB

Open AccessArticle

Biocompatibility of Titanium Oxide Nanotubes Layer Formed on a Ti-6Al-4V Dental Implant Screw in hFOB Cells In Vitro

by José Luis Castrejón Flores, Ángel Daniel Campos Juarez, Alexis Chino Ulloa, Fernando Nava Palafox, David Cruz Ortiz and Itzel Pamela Torres Avila

Coatings 2025, 15(6), 715; https://doi.org/10.3390/coatings15060715 - 13 Jun 2025

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Abstract

The surface modification of dental implants with nanostructured films enables the development of the next generation of biomaterials that promote osseointegration. In this study, a uniform layer of titanium oxide nanotubes (TNTs) was successfully formed on a Ti-6Al-4V dental implant screw through anodic [...] Read more.

The surface modification of dental implants with nanostructured films enables the development of the next generation of biomaterials that promote osseointegration. In this study, a uniform layer of titanium oxide nanotubes (TNTs) was successfully formed on a Ti-6Al-4V dental implant screw through anodic oxidation. TNTs were morphologically characterized by Scanning Electron Microscopy (SEM), obtaining dimensions of 64.88 ± 10 nm in diameter and 5.34 ± 5 µm in length. Additionally, a crystal size of 23.45 nm was determined by X-ray diffraction (XRD) analysis. The TNT layer on the dental implant screw was evaluated in an in vitro system in direct contact with human osteoblast cells (hFOB) for 24 h and 48 h, finding cell growth near to the screw threads. Further, the biocompatibility of the dental screw coated with TNTs was evaluated using a flow cytometric assay with 7-AAD, demonstrating that cell viability was not affected at 24 h and 48 h. This study opens the perspective of the study of inflammation and osseointegration induced by implants coated with TNTs. Full article

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

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10 pages, 2122 KiB

Open AccessArticle

Effect of Normal Load on the Current-Carrying Friction Performance of Copper–10% Graphite Composites

by Zhenghai Yang, Mengfeng Zhao, Xiaowei Wang, Kaifeng Hu, Xiaojun Tian and Yongzhen Zhang

Coatings 2025, 15(6), 714; https://doi.org/10.3390/coatings15060714 - 13 Jun 2025

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Abstract

A copper-10 wt.% graphite composite was paired with QCr0.5 to investigate the effects of normal load on current-carrying friction behavior. Arc discharges were monitored using a high-speed camera and photodiodes. The results indicate that, under the given experimental conditions, normal load predominantly influences [...] Read more.

A copper-10 wt.% graphite composite was paired with QCr0.5 to investigate the effects of normal load on current-carrying friction behavior. Arc discharges were monitored using a high-speed camera and photodiodes. The results indicate that, under the given experimental conditions, normal load predominantly influences the tribological performance of the material. As the c normal load increases, the wear rate decreases rapidly at first and then increases gradually. The optimal normal load was found to be 70 N, at which the wear rate reached a minimum of 0.46 mg/m. Material degradation was found to consist of mechanical damage—mainly plowing and plastic deformation—as well as arc-induced erosion characterized by melting and spattering. With increasing normal load, arc erosion decreased progressively, and the overall damage was minimized at 70 N. Arc erosion contributed to surface wear non-uniformity. Moreover, particular attention should be paid to high-current, long-duration arcs, which can pose serious localized threats to material integrity. Full article

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19 pages, 8597 KiB

Open AccessArticle

Application of Two-Element Zn-Al Metallic Target for Deposition of Aluminum-Doped Zinc Oxide—Analysis of Sputtering Process and Properties of Obtained Transparent Conducting Films

by Szymon Kiełczawa, Artur Wiatrowski, Michał Mazur, Witold Posadowski and Jarosław Domaradzki

Coatings 2025, 15(6), 713; https://doi.org/10.3390/coatings15060713 - 13 Jun 2025

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Abstract

This article analyzes the reactive magnetron sputtering process, using a two-element Zn-Al target, for depositing aluminum-doped zinc oxide (AZO) layers, aimed at transparent electronics. AZO films were deposited on Corning 7059 glass, flexible Corning Willow^® glass and amorphous silica substrates. To optimize [...] Read more.

This article analyzes the reactive magnetron sputtering process, using a two-element Zn-Al target, for depositing aluminum-doped zinc oxide (AZO) layers, aimed at transparent electronics. AZO films were deposited on Corning 7059 glass, flexible Corning Willow^® glass and amorphous silica substrates. To optimize the process, the study examined the target surface state across varying argon/oxygen ratios. The gas mixture significantly influenced the Al/Zn atomic ratio in the films, affecting their structural, optical and electrical performance. Films deposited at 80/20 argon/oxygen ratio—near the dielectric mode—showed high light transmission (84%) but high resistivity (47.4·10⁻³ Ω·cm). Films deposited at ratio of 84/16—close to metallic mode—exhibited lower resistivity (1.9·10⁻³ Ω·cm) but reduced light transmission (65%). The best balance was achieved with an 82/18 ratio, yielding high light transmission (83%) and low resistivity (1.4·10⁻³ Ω·cm). These findings highlight the critical role of sputtering atmosphere in tailoring AZO layer properties for use in transparent electronics. Full article

(This article belongs to the Section Thin Films)

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18 pages, 9843 KiB

Open AccessArticle

Study on the Surface Coating Techniques of Furniture in the Long’en Hall of Qing Changling Mausoleum

by Qirong Li, Fan Zhang, Wei Jia and Yifan Guo

Coatings 2025, 15(6), 712; https://doi.org/10.3390/coatings15060712 - 13 Jun 2025

Viewed by 261

Abstract

As a core structure within the Qing Changling Mausoleum, a UNESCO World Cultural Heritage site, Long’en Hall preserves a relatively complete set of Qing dynasty imperial lacquered furniture. These furnishings provide critical physical evidence for studying Qing dynasty sacrificial rituals and the craftsmanship [...] Read more.

As a core structure within the Qing Changling Mausoleum, a UNESCO World Cultural Heritage site, Long’en Hall preserves a relatively complete set of Qing dynasty imperial lacquered furniture. These furnishings provide critical physical evidence for studying Qing dynasty sacrificial rituals and the craftsmanship of court lacquerware. However, limited research has been conducted on the surface finishing techniques of such furnishings, posing challenges to their conservation and accurate restoration. This study focuses on representative furnishings from Long’en Hall—including an offering table, an incense pavilion, a throne, and a poke lamp—and employed a multi-method analytical approach comprising fluorescence microscopy (FM), scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS), X-ray photoelectron spectroscopy (XPS), and Fourier-transform infrared (FTIR) spectroscopy. The analysis was conducted on the following two levels: the lacquer layer structure and material composition. The results show that the furnishings in the Long’en Hall adopt the typical structure of “lacquer ash layer–color lacquer layer”, and the color lacquer layer is composed of raw lacquer, tung oil, animal glue, and other natural organic ingredients as film-forming materials, supplemented with inorganic mineral pigments such as red lead (Pb₃O₄) and Au metal, which constitutes a stable organic–inorganic composite structure with the lacquer ash layer. The multi-analysis results show a good complementary and cross-corroboration relationship, providing the necessary technical support and a theoretical reference for Qing dynasty palace lacquer wood furniture as cultural relics worthy of scientific protection and imitation. Full article

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

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19 pages, 9213 KiB

Open AccessArticle

Coating of Cubic Boron Nitride Powder with TiN in a Rotating Drum via Gas Phase Processes

by Louis Maier, Mario Krug, Mandy Höhn, Anne-Kathrin Wolfrum, Björn Matthey, Mathias Herrmann, Sören Höhn and Alexander Michaelis

Coatings 2025, 15(6), 711; https://doi.org/10.3390/coatings15060711 - 13 Jun 2025

Viewed by 223

Abstract

To improve the performance of superhard ceramic composites, this study aims to develop a dense, phase-pure, and uniform TiN coating on cubic boron nitride (cBN) particles with a target thickness of at least 150 nm. TiN coatings were applied using atomic layer deposition [...] Read more.

To improve the performance of superhard ceramic composites, this study aims to develop a dense, phase-pure, and uniform TiN coating on cubic boron nitride (cBN) particles with a target thickness of at least 150 nm. TiN coatings were applied using atomic layer deposition (ALD) alone, as well as a combined ALD/chemical vapor deposition (CVD) process. While ALD produced uniform and dense coatings, the thickness remained below 50 nm. The combined ALD/CVD approach achieved greater thicknesses up to 500 nm, though coating homogeneity remained a challenge. Optimization efforts, including increased ALD cycles and reduced CVD pressure, led to improved coating uniformity, with 25%–30% of particles coated to thicknesses ≥ 80 nm. Structural analysis confirmed dense, pore-free TiN_1−x layers for all synthesized powders. In contrast, the commercial reference powder showed a non-uniform, multiphase coating (α − Ti, Ti₂N, and TiN_0.53) with defects. While the ALD/CVD powders exhibited better phase purity than the commercial sample, further optimization is needed to achieve consistent coatings above 150 nm. These results suggest the ALD/CVD route is promising for producing coatings suitable for use in ceramic matrix composites. Full article

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11 pages, 1391 KiB

Open AccessArticle

Influence of Thickness on the Structure and Properties of TiAl(Si)N Gradient Coatings

by Alexey Kassymbaev, Alexandr Myakinin, Gulzhas Uazyrkhanova, Farida Belisarova, Amangeldi Sagidugumar and Ruslan Kimossov

Coatings 2025, 15(6), 710; https://doi.org/10.3390/coatings15060710 - 13 Jun 2025

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Abstract

Enhanced hard coatings with exceptional mechanical and thermal qualities have prompted substantial study into multicomponent nitride systems. TiAl(Si)N coatings have emerged as viable possibilities owing to their remarkable hardness, thermal stability, and oxidation resistance. This work involved the fabrication of thickness-varied TiAl(Si)N gradient [...] Read more.

Enhanced hard coatings with exceptional mechanical and thermal qualities have prompted substantial study into multicomponent nitride systems. TiAl(Si)N coatings have emerged as viable possibilities owing to their remarkable hardness, thermal stability, and oxidation resistance. This work involved the fabrication of thickness-varied TiAl(Si)N gradient coatings using reactive magnetron sputtering, employing a controlled modulation of aluminum and silicon content across the film thickness. Three samples, with thicknesses of ~400 nm, ~600 nm, and ~800 nm, were deposited under uniform Ar/N₂ gas flow ratios, and their microstructural, mechanical, and tribological characteristics were rigorously examined. SEM investigation demonstrated a significant change across thicknesses. XRD results validated the emergence of a predominant cubic TiAl(Si)N phase alongside a secondary hexagonal AlN phase, signifying partial phase segregation. The nanoindentation results indicated that Sample 2 exhibited the maximum hardness (~38 GPa) and Young’s modulus (~550 GPa) due to an optimized equilibrium between solid solution strengthening and nanocomposite production. Tribological testing revealed that Sample 1 displayed the lowest and most consistent friction coefficient, corresponding to its superior H/E and H3/E2 ratios, which signify improved elasticity and resistance to plastic deformation. The findings emphasize that the implementation of a compositional gradient, especially in the distribution of Si and Al, markedly affects the microstructure and performance of TiAl(Si)N coatings. Gradient structures enhance the microstructure, optimize hardness, and increase the friction coefficient. Ongoing refinement of gradient profiles and deposition parameters may further improve the characteristics of TiAl(Si)N coatings, facilitating their wider industrial use. Full article

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

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27 pages, 7536 KiB

Open AccessArticle

Laser-Patterned and Photodeposition Ag-Functionalized TiO₂ Grids on ITO Glass for Enhanced Photocatalytic Degradation

by Bozhidar I. Stefanov

Coatings 2025, 15(6), 709; https://doi.org/10.3390/coatings15060709 - 12 Jun 2025

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Abstract

Laser patterning of sol–gel-derived TiO₂ coatings offers a promising route for fabricating TiO₂-based devices. Conventional approaches require high-power CO₂ lasers, whereas herein is demonstrated an alternative method using a low-cost, blue laser (λ = 445 nm, 1250 mW) to [...] Read more.

Laser patterning of sol–gel-derived TiO₂ coatings offers a promising route for fabricating TiO₂-based devices. Conventional approaches require high-power CO₂ lasers, whereas herein is demonstrated an alternative method using a low-cost, blue laser (λ = 445 nm, 1250 mW) to pattern TiO₂ layers derived from a visible-light-absorbing titanium salicylate sol. Grid-shaped TiO₂ patterns (~250 μm line, 500 μm pitch) were fabricated on indium tin oxide (ITO)-coated glass substrates via dip-coating, laser patterning, selective solvent removal, and annealing at 450 °C. Photocatalytic performance was enhanced through Ag photodeposition from a 5 mM Ag⁺ aqueous electrolyte under UV doses of 5, 10, and 20 J cm⁻². Structural and compositional analysis (XRD, SEM-EDS, AFM, UV–Vis, Raman) confirmed the formation of crystalline anatase TiO₂ and Ag incorporation proportional to the dose. Methylene blue (MB) photooxidation experiments revealed that Ag-functionalized samples showed up to 20% higher degradation efficiency and improved photocatalytic stability across eight consecutive MB oxidation cycles. Additional photoelectrochemical measurements confirmed the formation of a TiO₂/Ag Schottky junction, while surface-enhanced Raman scattering (SERS) signals observed on Ag/TiO₂ grids enabled the detection of MB adsorbates. Full article

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

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16 pages, 3346 KiB

Open AccessArticle

Optimizing the PECVD Process for Stress-Controlled Silicon Nitride Films: Enhancement of Tensile Stress via UV Curing and Layered Deposition

by Jianping Ning, Chunjie Niu, Zhen Tang, Yue Sun, Hao Yan and Dayu Zhou

Coatings 2025, 15(6), 708; https://doi.org/10.3390/coatings15060708 - 12 Jun 2025

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Abstract

Silicon nitride (SiN) films deposited via plasma-enhanced chemical vapor deposition (PECVD) exhibit tunable tensile stress, which is critical for various microelectronic and optoelectronic applications. In this paper, the effects of silane (SiH₄) flow rate during PECVD deposition, ultraviolet (UV) curing, and [...] Read more.

Silicon nitride (SiN) films deposited via plasma-enhanced chemical vapor deposition (PECVD) exhibit tunable tensile stress, which is critical for various microelectronic and optoelectronic applications. In this paper, the effects of silane (SiH₄) flow rate during PECVD deposition, ultraviolet (UV) curing, and layered deposition on the tensile stress of SiN films are mainly investigated. The results reveal that increasing the SiH₄ concentration raises hydrogen incorporation, which modifies internal stress dynamics. UV curing significantly increases tensile stress by breaking N-H and Si-H bonds, facilitating hydrogen desorption, and promoting Si-N-Si crosslinking. The optimal UV curing duration stabilizes tensile stress at approximately 1570 MPa, while excessive UV power alters hydrogen content dynamics, reducing stress. Additionally, layered deposition further amplifies stress enhancement, with films subjected to multiple deposition cycles exhibiting increased densification and crosslinking. The combined optimization of PECVD deposition parameters, UV curing, and layered deposition provides a robust strategy for tailoring SiN film stress, offering a versatile approach to engineering mechanical properties for advanced applications. Full article

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13 pages, 1703 KiB

Open AccessArticle

Effect of Gas Velocity on Thickness Uniformity of TiN_xO_y Thin Film in Atomic Layer Deposition Process

by Ji Won Jang, Nu Ri Kim and Sang Jeen Hong

Coatings 2025, 15(6), 707; https://doi.org/10.3390/coatings15060707 - 12 Jun 2025

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Abstract

Atomic layer deposition (ALD) has emerged as an essential technique, enabling the deposition of titanium nitride (TiN), which is renowned for its exceptional metal diffusion barrier properties. Improving within-wafer uniformity has become increasingly important to actively transition from lab-scale process development to wafer [...] Read more.

Atomic layer deposition (ALD) has emerged as an essential technique, enabling the deposition of titanium nitride (TiN), which is renowned for its exceptional metal diffusion barrier properties. Improving within-wafer uniformity has become increasingly important to actively transition from lab-scale process development to wafer manufacturing. We considered the effect of gas velocity on thickness uniformity through computational fluid dynamics (CFD) simulations. Gas velocity was controlled by varying equipment design parameters, and it was confirmed that the resulting reduction in velocity improved both velocity and thickness uniformity. To validate the simulation results, an ALD reactor was experimentally performed under the same design and process conditions. The measured thickness of the deposited films confirmed an improvement in thickness uniformity, and the cause of the thickness reduction was further investigated. This study demonstrates that controlling gas velocity prov ides valuable insights into improving thickness uniformity in the ALD reactor. It confirms the effectiveness of simulations in overcoming the limitations associated with considering various process and equipment variables, which can be time-consuming and costly. Furthermore, it emphasizes the importance of integrating flow dynamic simulations with process evaluations to contribute to the advancement of semiconductor manufacturing technologies. Full article

(This article belongs to the Special Issue Semiconductor Thin Films and Coatings)

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12 pages, 4897 KiB

Open AccessArticle

Optimized Control of Hot-Working Parameters in Hot-Forged (CoCrNi)₉₄Al₃Ti₃ Medium-Entropy Alloy

by Ao Li, Jiebo Lu, Wenjie Xin, Tengfei Ma, Xiaohong Wang and Yunting Su

Coatings 2025, 15(6), 706; https://doi.org/10.3390/coatings15060706 - 11 Jun 2025

Viewed by 270

Abstract

It is essential to develop the optimal hot-working process of the (CoCrNi)₉₄Al₃Ti₃ alloy, a recently developed precipitation-hardened medium-entropy alloy with promising mechanical properties, for its industrial application. In this study, the hot workability of the as-forged (CoCrNi)₉₄ [...] Read more.

It is essential to develop the optimal hot-working process of the (CoCrNi)₉₄Al₃Ti₃ alloy, a recently developed precipitation-hardened medium-entropy alloy with promising mechanical properties, for its industrial application. In this study, the hot workability of the as-forged (CoCrNi)₉₄Al₃Ti₃ alloy was investigated over a temperature range of 1000 °C to 1150 °C and a strain rate ranging from 0.001 to 1 s⁻¹ using a Gleeble-1500D thermal simulation machine of Dynamic Systems Inc., USA. As a result, the constitutive relationship was established, and the hot deformation activation energy was calculated as 433.2 kJ/mol, suggesting its well-defined plastic flow behavior under low-energy-input conditions. Hot-processing maps were constructed to identify the stable hot-working regions. Microstructure analysis revealed that the hot-forged (CoCrNi)₉₄Al₃Ti₃ alloy exhibited continuous dynamic recrystallization (CDRX) behavior under optimal hot-working conditions. Considering the hot-processing maps and DRX characteristics, the optimal hot-working window of hot-forged (CoCrNi)₉₄Al₃Ti₃ alloy was identified as 1100 °C with a strain rate of 0.1 s⁻¹. This work offers valuable guidance for developing high-efficiency forming processes for (CoCrNi)₉₄Al₃Ti₃ medium-entropy alloy. Full article

(This article belongs to the Special Issue Surface Treatment and Coating of Additively Manufactured Components)

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17 pages, 7275 KiB

Open AccessArticle

Thermal Analysis of Polyurethane Coatings Modified with Graphene and Modification Influence on Mechanical Properties of Hybrid Textile Materials Dedicated to Personal Protective Equipment

by Emilia Irzmańska, Magdalena Jurczyk-Kowalska, Anna Boczkowska, Kamila Sałasińska, Kamila Strycharz, Olga Olejnik and Witold Sygocki

Coatings 2025, 15(6), 705; https://doi.org/10.3390/coatings15060705 - 11 Jun 2025

Viewed by 280

Abstract

This paper is focused on the modification of polyurethane coating applied to the outer layer of hybrid textile materials dedicated to personal protective equipment. For this purpose, graphene with various weight fractions, i.e., 0.25 and 0.5 wt.%, was introduced into the polyurethane matrix. [...] Read more.

This paper is focused on the modification of polyurethane coating applied to the outer layer of hybrid textile materials dedicated to personal protective equipment. For this purpose, graphene with various weight fractions, i.e., 0.25 and 0.5 wt.%, was introduced into the polyurethane matrix. The prepared pastes were applied to meta-aramid fabric as coating. The results of the thermogravimetric analysis of polymer coating showed a shift in the onset temperature of the polymer coating to higher values after graphene addition, which indicates an improvement in thermal stability. Considering mechanical properties, the implementation of the coating on meta-aramid fabric reduces tear resistance but this may be improved by the addition of 0.5 wt.% of graphene. Such a hybrid textile material meets the tearing force requirements for protective clothing for firefighters according to EN 469:2020. Full article

(This article belongs to the Special Issue Advances in Coated Fabrics and Textiles)

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