Coatings doi: 10.3390/coatings16060707

Authors: Xinjie Zhao Lei He Yi Xu Guodong Li

In view of the fact that there are few reports on the preparation of NbC coating by high-power pulsed magnetron sputtering (HiPIMS) technology. In this study, the effects of NbC interlayer thickness on the microstructure, corrosion resistance and electrical conductivity of Nb/NbC/C multilayer coatings for proton exchange membrane fuel cell (PEMFC) bipolar plates were studied by using the high ionization characteristics of HiPIMS technology. A series of Nb/NbC/C multilayer coatings with varying NbC interlayer thicknesses was deposited via HiPIMS by modulating the deposition time (20, 40, and 60 min). The microstructure and properties of the coatings were characterized using scanning electron microscopy (SEM), Raman spectroscopy, interfacial contact resistance (ICR), and corrosion current, among other methods. The results indicate that as the NbC interlayer thickness increases, the total coating thickness increases from 0.43 μm to 1.42 μm. All coatings exhibit a uniform and dense microstructure lacking typical coarse columnar structures. Raman and XPS analyses show that the ID/IG ratio increases from 1.98 to 4.04, indicating an increase in sp2-hybridized bond content and a decrease in sp3 content. At a deposition time of 60 min, the coating achieved optimal performance, yielding a critical load (Lc1) of 31.9 N, the lowest average friction coefficient (0.27), the minimum corrosion current density, and an interfacial contact resistance of 7.5 mΩ·cm2. These results demonstrate that the NbC interlayer thickness significantly governs the structure and properties of the Nb/NbC/C multilayer coatings. Specifically, an appropriate increase in the NbC interlayer thickness optimizes the sp2/sp3 hybrid bond ratio, thereby enhancing the overall coating performance.

Coatings doi: 10.3390/coatings16060706

Authors: Mingjun Ding Wenhui Yu Jiaxing Xiao Zhen Xiao Junhao Sun Dongfeng Qi Lihua Zhu Wuhong Xin Hongyu Zheng

Laser powder bed fusion (LPBF) of high-strength aluminum alloy 7075 (AA7075) is severely limited by hot cracking. However, the underlying mechanisms, particularly the coupling between thermal fields, solidification microstructure, and cracking behavior, remain insufficiently clarified. This study elucidates these mechanisms by integrating experimental characterization with thermal simulation to investigate the temperature field, microstructure, and cracking relationships in both AA7075 and a crack-resistant 7075-Er-Zr alloy. Results show that coarse hot crack morphology is highly dependent on linear energy density EL. In AA7075, EL < 450 J/m promotes laterally inclined cracks (short, narrow cracks extending from the melt pool boundary toward the track center), whereas EL higher than that value leads to the continuous centerline cracks (long, wide cracks along the track center). Fine microcracks are also observed at melt pool boundaries. The 7075-Er-Zr alloy demonstrates superior crack resistance. At EL = 600 J/m, longitudinal centerline cracks still penetrate along the track, but the alloy achieves crack-free tracks at 200 W with scanning speeds above 1000 mm/s, otherwise exhibiting only short discontinuous cracks. Microcracks at melt pool boundaries are markedly suppressed in the modified alloy. The enhanced crack resistance is attributed to Er/Zr-induced grain refinement and a transition to an equiaxed grain structure, which disrupts intergranular gaps. Critically, thermal simulations identify an annular region with a peak temperature gradient. In AA7075, this region develops aligned columnar grains that facilitate both microcracks and centerline cracks. In the 7075-Er-Zr alloy, microcracks are fully eliminated within this region. However, a residual crystallographic texture persists in the annular region, which promotes the continued occurrence of centerline cracks under high energy density (e.g., EL = 600 J/m). The annular region remains a critical weak link, and its microstructural control determines the prevailing crack type. This work provides a fundamental understanding of the thermal-microstructural origins of cracking and offers a theoretical foundation for developing crack-resistant aluminum alloys via LPBF.

Coatings doi: 10.3390/coatings16060705

Authors: Zihong Zheng Qi Yan Cuiling Zhao Daxiang Deng Yuchao Bai Fujun Peng

Poor consolidations and the strength–conductivity trade-off limit the performance of copper alloys fabricated by laser powder bed fusion (LPBF). To address this, this study developed a strategy combining the response surface methodology (RSM) with direct ageing treatment (DAT) to achieve a favorable strength–conductivity synergy. The results showed that under the optimal process parameters, a high relative density of 99.25% (8.95 g/cm3 for theoretical density) was obtained. After direct ageing treatment at 490 °C for 60 min, the CuCrZr exhibited an ultimate tensile strength of 399.31 MPa and a thermal conductivity of 326.53 W/(m·K). To reveal the underlying mechanisms, this study employed a combination of systematic characterization via high-resolution transmission electron microscopy (HRTEM) and quantitative modeling. HRTEM characterized the uniformly dispersed nanoscale body-centered cubic (BCC) Cr precipitates that form semi-coherent interfaces with the face-centered cubic (FCC) Cu matrix, showing a crystallographic misorientation of approximately 10.5° intermediate between the classic Nishiyama–Wassermann and Kurdjumov–Sachs orientation relationships. Quantitative modeling indicates that the high strength arises from a synergistic effect: coherent strain fields exerted by the precipitates effectively pin retained dislocations, coupling Orowan and dislocation strengthening. Meanwhile, solute precipitation reduces lattice distortion, restoring notable thermal conductivity.

Coatings doi: 10.3390/coatings16060704

Authors: Ge Cao Haixian Liang Jiali Xiong Tianhong Huang Min Yang He Zhang Zhenyu Wang

Silver nanowire (AgNW) networks have attracted significant attention as leading candidates for flexible transparent electrodes owing to their unique combination of high electrical conductivity, optical transparency, and mechanical compliance. This review presents an overview of recent developments in AgNW-based transparent electrode technologies, with particular emphasis on strategies to improve network conductivity and long-term reliability, including junction engineering, surface modification, encapsulation approaches, and composite structure design. Representative applications in flexible optoelectronic systems, such as organic light-emitting devices, transparent heating elements, and electrochromic platforms, are also discussed. Finally, current challenges and future research directions toward scalable manufacturing and practical implementation of high-performance AgNW electrodes are outlined.

Coatings doi: 10.3390/coatings16060703

Authors: Yingdong Zhao Jiefen Kang Yanan Guo Yongling Ding Huiling Yu Qinxi Dong Huadong Sun Wenshu Cheng Shuhua Song Hong Yin Kunpeng Zhao

Polyester (PET) fibers are widely used to reinforce asphalt materials; however, their smooth and hydrophobic surfaces limit interfacial bonding and restrict their reinforcing efficiency. This study develops an eco-friendly surface modification method based on the chemical modification of gallic acid (GA) and aminosilane (KH792) to enhance the compatibility between PET fibers and asphalt. Modified fibers with various molar ratios of GA/KH792 were prepared and incorporated into asphalt mastic. Their performance was evaluated using softening point, cone penetration, dynamic shear rheometer (DSR), multiple stress creep recovery (MSCR), linear amplitude sweep (LAS), and bending beam rheometer (BBR) tests, combined with interfacial interaction analysis and scanning electron microscopy (SEM). The results show that surface modification significantly improves the reinforcing effect of PET fibers. In particular, the co-modified fiber with a GA/KH792 ratio of 1:1 exhibits the best performance, with increases of 27% in softening point and 105% in shear strength, as well as notable improvements in rutting resistance, fatigue performance, and temperature stability. Interfacial indices and SEM observations confirm enhanced adhesion, dispersion, and load transfer capacity. However, the improvement in low-temperature performance is limited. Overall, GA/KH792 chemical modification effectively enhances fiber asphalt interfacial interaction and provides a simple and sustainable approach for developing high-performance asphalt materials.

Coatings doi: 10.3390/coatings16060702

Authors: Ivan V. Nikiforov Evgeniya S. Zhukovskaya Olga A. Levandnaya Olga S. Antonova Polina A. Krokhicheva Margarita A. Goldberg Ilde Incarnato Angela De Bonis Katia Barbaro Viktoriya G. Yankova Bogdan I. Lazoryak Dina V. Deyneko Julietta V. Rau

The development of multifunctional biomaterials for bone repair requires precursors that combine bioactivity, moderate antimicrobial growth-inhibitory effect, and imaging. This study demonstrates the multifunctional versatility of a single family of rare-earth-doped β-tricalcium phosphates (β-TCPs), Ca9Eu(PO4)7 and Ca9Dy(PO4)7, across three distinct formats: bioactive thin films (for implant coatings), brushite cements (for injectable bone fillers), and radiopaque PMMA bone composites (for load-bearing applications). This work serves as a proof-of-concept that the same doped phosphate precursors can address different clinical needs while retaining bioactivity, antimicrobial properties, and radiopacity. The phosphate precursors were synthesized via solid-state reaction. Pulsed laser deposition (PLD) was used to form amorphous, dense, and crack-free coatings, which exhibited excellent in vitro bioactivity through the rapid dissolution–reprecipitation of a carbonated apatite layer in simulated body fluid. The brushite-based bone cements were produced from doped β-TCPs. These cements demonstrated high cytocompatibility with mesenchymal stromal cells (>89% viability) and significantly enhanced osteogenic differentiation with antimicrobial activity against common pathogens (S. aureus, E. coli, P. aeruginosa). Furthermore, incorporation of these phosphates as fillers into PMMA bone cement resulted in a homogeneous particle distribution with reduced agglomeration compared to undoped β-TCPs, achieving clinically relevant radiopacity values (913 ± 22.4 HU for Dy-doped sample). Post-mortem studies by the CT method were performed on the vertebrae with PMMA–phosphate composites and brushite cements. It was shown that brushite cement in ovine lumbar vertebrae defects exhibited the highest radiopacity (1450–1550 ± 25 HU). The findings establish rare-earth-doped β-TCP as a unified multifunctional precursor that imparts bioactivity, the ability to support in vitro mineralization, antimicrobial properties, and enhanced radiopacity to thin films, phosphate cements, and polymer composite materials.

Coatings doi: 10.3390/coatings16060701

Authors: Junlin Tao Bingxu Lu Mingjie Zhao Qing Lan Yanqi Liu Rui Wang

Layered Li-rich manganese-based Li1.2Ni0.13Co0.13Mn0.54O2 (LNCMO) is regarded as a promising high-capacity cathode material. However, its commercial application is severely hindered by rapid capacity fading, serious voltage decay and poor cycling stability. Herein, a facile non-sintering electrostatic adsorption strategy employing PDDA is proposed to fabricate a uniform and dense graphene oxide (GO) coating on LNCMO particles. Structural and morphological characterizations confirm the successful decoration of GO on the surface of LNCMO. The optimized 0.5@LNCMO sample delivers a discharge capacity of 330 mAh g−1 at 0.1C, and maintains a capacity retention of 86.5% after 200 cycles at 1C and 83.3% after 400 cycles at 5C, showing much better electrochemical performance than pristine LNCMO. This study proves that the proposed strategy is an effective modification method for constructing high-performance Li-rich cathode materials.

Coatings doi: 10.3390/coatings16060700

Authors: Hua Wen Xiaoyu Tan Xin Wei Xu Lei Shucheng Tan Qiangsheng Fu Ying Liu

Sulfate attack is a major cause of deterioration in tunnel lining concrete under aggressive underground conditions. This study investigates the sulfate resistance of fiber-reinforced ferroaluminate cement concrete incorporating steel slag powder through combined experimental and numerical approaches. Specimens with different fiber contents (0, 0.2%, and 0.4%) were subjected to dry–wet cycles in a 5% sodium sulfate solution. The results show that fiber incorporation significantly enhances sulfate resistance, with the optimal performance achieved at 0.2% fiber content. Compared with ordinary Portland cement concrete, ferroaluminate cement-based concrete exhibits improved durability, including lower mass variation, reduced strength degradation, and more stable dynamic elastic modulus. Microstructural analyses indicate that hydration products refine the pore structure, while fibers effectively inhibit crack propagation and expansion damage. Numerical simulation of tunnel lining structures further demonstrates that the optimized material reduces stress concentration, displacement, and crack development. Overall, the proposed material shows superior performance and promising application potential for tunnel linings in sulfate-rich environments.

Coatings doi: 10.3390/coatings16060698

Authors: Yarong Yang Tian Wang Xiaohu Wu Lili Wang Xiansheng Zhang

This study reports a hierarchically structured quasi-three-dimensional (quasi-3D) hydrogel/feather fabric composite evaporator, with MXene integrated as the photothermal material, fabricated via an in situ freeze–thaw and mechanical interlocking strategy. Benefiting from the rational quasi-3D structural design, the evaporator effectively retains the intrinsic facile weaving and assembly advantages of textile substrates, while addressing the poor mechanical stability and disordered water transport channels inherent to conventional hydrogels. The synergistic coupling between the low-evaporation-enthalpy hydrogel network and vertically oriented feather yarns expands the channels for light reflection and absorption, thereby synergistically enhancing light harvesting, thermal regulation, water transport, and salt rejection. The as-prepared evaporator exhibits a light absorption efficiency of 97.6% and an evaporation rate of 2.13 kg m−2 h−1 under 1 sun illumination, while sustaining stable performance over 15 consecutive days of outdoor operation. The incorporation of a foam support layer further facilitates effective heat localization and self-flotation, effectively mitigating thermal losses. This work demonstrates an efficient, flexible, and scalable solar evaporator with great potential for sustainable freshwater production.

Coatings doi: 10.3390/coatings16060699

Authors: Sertaç Tuhta

This study investigated the dynamic performance of laminated veneer lumber (LVL) shear-walled structures retrofitted with an aluminum oxide (Al2O3) nanocoating through finite element analysis (FEA) using SAP2000 software. Later, the ground motion data from the 1968 Takochi-Oki earthquake was used to conduct linear assessments of the structure. LVL, a sustainable and high-performance timber material, was selected for its favorable strength-to-weight ratio and environmental advantages. Two structural models—a reference uncoated LVL structure and an Al2O3-coated counterpart—were analyzed to evaluate the influence of the nanocoating on modal and structural behavior. The Al2O3 coating, applied as a thin surface layer (0.002 m per side), was modeled to enhance stiffness and damping characteristics. Modal analysis revealed an increase in natural frequencies from 0.75–1.72 Hz to 1.19–2.85 Hz after coating, indicating improved rigidity. The maximum top displacement decreased by approximately 18%, from 77 mm to 65 mm, without significant mass addition. Additionally, von Mises stresses were reduced from 86.65 MPa to 8.03 MPa, confirming stress redistribution and improved structural stability. These results demonstrate that the Al2O3 nanocoating effectively enhances the stiffness, damping, and overall dynamic response of LVL shear walls. The proposed method offers a lightweight, non-invasive, and sustainable alternative to conventional retrofitting techniques, contributing to the development of resilient and eco-efficient timber construction systems.

Coatings doi: 10.3390/coatings16060696

Authors: Lijuan Chen Jigang Ma Boxin Wei Feifan Guo Bo Wei Jialin Li Rui Ma Jingxuan Shuang Jianjiang Wang

Corrosion of pipelines by flue gas desulfurization (FGD) wastewater compromises the normal operation of the desulfurization tower, and corrosion under high-chloride conditions in particular severely damages the tower’s internal structure. To further elucidate the corrosion mechanism at elevated Cl− concentrations, the corrosion behavior of 20 steel exposed to high-chloride FGD wastewater at different Cl− concentrations was investigated through weight-loss measurements, electrochemical tests, immersion corrosion experiments, composition analysis, and microscopic morphology characterization. The results revealed that higher Cl− concentrations corresponded to lower corrosion rates: the corrosion rate reached 0.1964 mm/y in the absence of Cl−, but decreased to 0.1537 mm/y at a Cl− concentration of 100,000 mg/L. XPS analysis showed that as the Cl− concentration increased, the corrosion film gradually transformed from porous FeOOH into dense Fe3O4. Localized pitting analysis indicated a positive correlation between Cl− concentration and pitting susceptibility. At Cl− concentrations of 0 and 100,000 mg/L, the corrosion current density decreased from 32.44 μA/cm2 to 6.43 μA/cm2 after 72 h, decreasing by a factor of approximately 5.05. This behavior is attributed to the fact that Cl− increases solution conductivity in high-chloride environments, thereby promoting the formation rate of the corrosion film. Additionally, high Cl− levels reduce dissolved oxygen in the solution, causing the corrosion film to progressively react and form denser Fe3O4. Nevertheless, the high penetrability of Cl− continues to aggravate pitting corrosion of 20 steel.

Coatings doi: 10.3390/coatings16060697

Authors: María Barros Magdalena Alicia Hueto-Escobar Lidia García-Soriano Camilla Mileto Fernando Vegas

Adobe construction, as part of earthen architecture, is a traditional building technique that is widely used but particularly vulnerable to the effects of water and other climatic factors. This article analyses the physical and mechanical behaviour of three different grain sizes of adobe specimens, classified according to the predominant presence of coarse aggregates (CA), fine aggregates (FA), and fine aggregates with plant fibres (AF). In order to assess their response to climatic scenarios, these specimens are subjected to wetting–drying cycles (3, 5, and 7 cycles) and accelerated weathering tests (E) under controlled laboratory conditions. The main objective is to determine the influence of particle size distribution and the incorporation of plant fibres on the strength, stiffness, durability, and hydraulic behaviour of the material. For this purpose, an experimental programme was developed based on compression, modulus of elasticity, ultrasonic, abrasion, hydraulic erosion, and capillary absorption tests, and carried out at different stages of deterioration. Thus, six specimens were analysed for each of the five time points studied (0, 3, 5, 7, E) and for each proposed particle size distributions, giving a total of 450 samples analysed. The results show that the coarse mix exhibits greater overall mechanical stability, whereas the fine mix is more sensitive to the action of water. Although the addition of fibres improves ductility and resistance to surface erosion, it alters the porous structure of the material. Overall, the results confirm that particle size distribution and fibre reinforcement decisively influence the durability of adobe.

Coatings doi: 10.3390/coatings16060695

Authors: Ferhi Selma Menaceur Fouad Rachid Rouabhi

Chicken feet, an abundant and low-cost poultry by-product rich in collagen, were used to extract gelatin, which was then formulated into active biodegradable films containing food-grade clove essential oil (CEO), glycerol, sorbitol, and Tween 20. Gelatin extraction involved 0.5 M NaOH pretreatment followed by 5% acetic acid extraction at 66 °C, yielding 11.22% gelatin. Eight gelatin–CEO films were prepared by varying the CEO concentration and plasticizer composition. The supplier-declared CEO composition was eugenol-dominant, and antibacterial activity against Escherichia coli, Kluyvera sp., and Enterobacter cloacae was assessed by agar disk diffusion, MIC, and MBC assays, each performed in triplicate. CEO inhibition zones of 22, 14, and 19 mm were recorded against E. coli, Kluyvera sp., and E. cloacae, respectively; the blank 6 mm control disks without oil produced no inhibition halo beyond the disk edge. MIC/MBC values were 5/6, 3/4, and 4/5 mg/mL for the same three strains. All films were continuous, smooth, and peelable; sorbitol-containing formulations were clearer and more flexible than sorbitol-free variants. Water solubility ranged from 37.67% to 48.78%, opacity from 5.26 × 10−3 to 9.20 × 10−3 A500 mm−1, and thickness from 11.75 to 23.75 µm. Water vapor transfer was undetectable under the gravimetric screening protocol for all formulations. All films showed complete visual disappearance in soil within 6–10 days. In the cherry tomato trial, the best-performing coatings extended acceptable storage from about 5 days (uncoated control) to 10 days at 17–20 °C.

Coatings doi: 10.3390/coatings16060694

Authors: Bin Ma Huiru Liu Jinhua Zhou Yuejun Sun Aizhi Sun

In this paper, the magnetic properties of HDDR NdFeB powders were improved by the grain boundary diffusion of Cu28Ce72 alloy. The influence and mechanism of Cu28Ce72 alloy and heating process on the coercivity (Hcj), remanence (Br), and maximum magnetic energy product (BHmax) of magnetic powders were investigated. The grain boundary diffusion of Cu28Ce72 alloy can effectively improve the Hcj, Br and BHmax of bonded magnets, exhibiting a trend of first increasing and then decreasing with the increase in diffusion temperature and Cu28Ce72 addition, and the maximum values of 927 kA/m, 0.625 T and 61 kJ/m3 are obtained at the Cu28Ce72 content of 5.0 wt% and the heating temperature of 380 °C. The demagnetization coupling effect is increased by a continuous grain boundary phase formed by the diffusion of Ce and Cu elements into the grain boundaries, and thus the coercivity of magnetic powder is improved. During the diffusion process, Ce element diffuses along the grain boundaries to repair the defective areas around the grains and form a Ce2Fe14B phase, which improves the Hcj and Br of magnetic powders; on the other hand, Ce element diffuses into Nd2Fe14B grains to replace the Nd crystal sites, reducing the Hcj and Br of magnet; therefore, the Hcj and Br of HDDR NdFeB powders are comprehensively affected by these two aspects.

Coatings doi: 10.3390/coatings16060693

Authors: Yidong Huang Ya Liu Bin Dong Xiangying Zhu Changjun Wu

Zn–Al–Mg coatings are widely used because of their excellent corrosion resistance, in which α-Al dendrites play a crucial role. This study investigated the selective corrosion behavior of α-Al dendrites in a hot-dip Zn–14Al–0.5Mg coating, including the as-received state, after 20 months of indoor exposure, and under salt spray corrosion. The coating consisted of α-Al dendrites, η-Zn phase, and a small amount of eutectic Zn–Al–Mg. Minor black spots were observed on the initial surface. After indoor storage, extensive corrosion occurred in α-Al dendritic regions, while the remaining η-Zn became protruding. Corrosion propagated preferentially along the Al-rich dendritic into the coating, reaching the substrate, rather than progressing layer by layer. Electrochemical testing results indicated spatial heterogeneity in the corrosion resistance of the coating surface after long-term indoor storage. Cl− could more readily penetrate into the corroded dendrites, accelerating corrosion and shifting the mode from lateral propagation to vertical penetration. The selective corrosion was attributed to dendrite segregation and surface oxide film breakdown. Controlling dendrite morphology is essential for improving coating performance.

Coatings doi: 10.3390/coatings16060692

Authors: Daolong Xu Daruo Cao Zihan Shan Liang Fang

Photovoltaic modules require efficient sunlight modulation, including enhanced visible transmittance and conversion of unused ultraviolet light. This study develops a synthetic optical coating that achieves both functions by integrating down-conversion BAM (BaMgAl10O17:Eu2+, Mn2+) nanophosphors into a silica anti-reflection sol. The key novelty lies in a synergistic surface engineering strategy that decouples dispersion stabilization from luminescence protection. Five dispersants are systematically compared under combined ball and sand milling. The polyester-modified acrylic long-chain dispersant (DK062) yields a stable nanodispersion with an average particle size of 228 nm and a Zeta potential of −7.61 mV, effectively suppressing re-agglomeration while retaining high photoluminescence. Subsequent surface modification with KH570 grafts a dense silane passivation layer via Si–O–M covalent bonds, further increasing the photoluminescence intensity by 1.39-fold. The optimized nanophosphors are incorporated into a commercial anti-reflection sol and dip-coated onto photovoltaic glass. At a doping concentration of 2‰ and a withdrawal speed of 8 mm/s, the resulting DCSAR coating exhibits an average transmittance of 91.16%—slightly higher than that of the pure anti-reflection coating (90.96%)—while showing strong green emission at 515 nm. Industrial on-site testing further demonstrates an average transmittance of 94.20%–94.31% with uniform green emission. This work provides a scalable route to fabricate highly transparent, light-converting anti-reflection coatings by combining dispersant-assisted milling and silane passivation.

Coatings doi: 10.3390/coatings16060691

Authors: Chen Lv Xiaoyu Liang Hangyu Zhou Chao Han Bingqing Hu Tong Xu

To enhance flame retardancy of waterborne polyurethane (WPU) coatings, this paper proposes a co-modification method using modified graphene oxide (SiO2@GO) and a phosphorus flame retardant (P-). SiO2@GO refers to graphene oxide (GO) with an attached silicon dioxide (SiO2) layer, while the phosphorus flame retardant (P-) in this work is THPO, a reactive flame retardant used as a chain extender. The influence of component additions on flame retardancy was systematically investigated. Modified WPU coatings (P-SiO2@GO/WPU) were prepared using THPO and SiO2@GO as flame-retardant chain extenders. The morphology, structure, and thermal stability of P-SiO2@GO/WPU were characterized by scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, and thermogravimetric analysis (TGA). At 2% SiO2@GO, coatings showed enhanced hydrophobicity (water repellency) and thermal stability. With 4% phosphorus flame retardant (P-), the limiting oxygen index (LOI, a measure of flame retardancy) reached 32.2%, and the heat release rate was 32.4% lower than before modification. A continuous, dense P/Si-containing carbonaceous ceramic-like barrier layer was formed, effectively blocking the release of combustible gases and the transfer of heat, thereby demonstrating excellent flame retardancy. This synergistic P-SiO2@GO/WPU modification offers theoretical support and practical guidance for optimizing and enhancing the flame-retardant performance of WPU coatings.

Coatings doi: 10.3390/coatings16060690

Authors: Mohamed I. Ahmed Aleksandra Zielińska Monika Paul-Samojedny Anna Nowak Mateusz Dulski Aleksandra Strach Izabela Potocka Krzysztof Matus Daniel Wasilkowski

Rising triple-negative breast cancer (TNBC) cases and Candida infection risks during chemotherapy demand novel therapies, with metal-oxide nanocomposites emerging as a promising solution. In this study, we synthesized Ag-ZnO and Cu-ZnO nanocomposites as established quantitative links between their physicochemical properties, ion release behaviour, and biological activity, evaluating antifungal effects against Candida albicans (ATCC 90028) and Saccharomyces cerevisiae (ATCC 9763), and their anticancer potential against MDA-MB-231 cells (ATCC HTB-26). The results revealed Ag (~13–19 nm) and Cu (~4–8 nm) nanoparticles dispersed in a ZnO matrix, with XPS confirming mixed Ag0/Ag(I)/Ag(III) and Cu(I)/Cu(II) speciation. Ag-ZnO NC exhibited strong antifungal activity (MIC = 25 mg L−1) against both fungi, while Cu-ZnO NC was only effective (MIC = 100 mg L−1) against S. cerevisiae. Aqueous release of Ag+ was ~2.6-fold higher than Cu2+. Ag-ZnO NC induced marked ROS generation (~6-fold higher than S. cerevisiae) and dehydrogenase inhibition (6.6- and ~20-fold, respectively). ATR-FTIR linked species-specific susceptibility to cell-wall architecture. SEM confirmed membrane destabilization and perforation. In MDA-MB-231, necrotic fractions reached ~9% and >40% for Ag-ZnO and Cu-ZnO, respectively. Both metal oxide nanocomposites (MONCs) act through ion release, revealing a selectivity window, especially for Ag-ZnO. Further studies on non-cancerous cells, ion-release kinetics, uptake and in vivo validation are essential to establish a therapeutic index.

Coatings doi: 10.3390/coatings16060689

Authors: Tong Niu Yan Li Zhiyuan Liu Jiaqi Liu

To meet practical needs such as anti-icing for wind turbine blades, carbon nanotube coatings (CNTCs)—known for their excellent mechanical properties, high strength, and high thermal conductivity—have emerged as a research hotspot in the field of coating materials and represent a promising option for such applications. Outlines the key properties and mainstream preparation processes of CNT coatings, and provides an objective evaluation of research on their primary properties based on existing findings. Furthermore, to satisfy the comprehensive performance requirements of coatings in practical application scenarios, this paper proposes a property-balancing method for CNTCs specifically tailored to the anti-icing field of wind turbine blades. This method enables the coatings to fully satisfy the practical performance requirements in terms of strength and hydrophobicity, and avoids cost waste caused by excessive single performance beyond actual demands. It is expected to provide a reference for the application of CNTCs in related fields.

Coatings doi: 10.3390/coatings16060688

Authors: Yixiang Ou Yue Zhang Yi Feng Xiaopan Wu Kesheng Wang Zhiqiang Che Wenping Yuan Haoqi Wang Qili Jiang Li Hou Peng’an Zong Feiqiang Li Hua Liu

Applying functional hard protective coatings with friction-reducing and wear-resistant properties to optimize mechanical surfaces and interfaces can significantly enhance the reliability of operating components under extreme conditions and extend their service life. However, the difference of coating preparation technology often leads to great uncertainty in the improvement of the performance and lifetime of functional hard protective coatings. Hence, in this work, TiAlSiCN coatings were deposited at the substrate temperature of 300 °C by varying the C target power from 0 to 900 W using combined high-power impulse magnetron sputtering and pulsed DC magnetron sputtering. The TiAlSiCN coatings deposited at a C target power of 500 W containing the mixed phase of nc-TiAl(C)N, a-Si3N4 and a-C exhibit a simultaneous superhardness of 43.5 GPa and favorable toughness, benefiting from the fully dense microstructure and high surface integrity. The superhard TiAlSiCN coatings show excellent friction-reducing and wear-resistant properties with a low friction coefficient of about 0.1 and specific wear rate of 2.78 × 10−7 mm3·N−1·m−1 under dry reciprocating friction and wear tests. The improved friction and wear performance of TiAlSiCN coatings are mainly attributed to the increased cracking resistance and oxide-based films covering the superhard surface/interface.

Coatings doi: 10.3390/coatings16060687

Authors: Shoufa Liu Jie Luo Pengfei Huang Yinwei Wang Morteza Taheri Chongyu Shi

Refractory high-entropy alloys (RHEAs) have attracted increasing attention for structural applications under extreme conditions; however, the uniformity and reliability of their mechanical properties remain critical challenges, particularly when processed by additive manufacturing. In this work, the microstructural heterogeneity and mechanical uniformity of a selective laser melting (SLM)-fabricated MoNbZrTaW RHEA were systematically investigated. Microstructural characterization revealed a dual-phase BCC structure with dendritic and interdendritic regions distributed along the build direction. Statistical analyses were employed to quantify variations in microstructure and mechanical properties, including hardness, fracture strength, yield strength, and fracture strain. The effects of strain rate and specimen aspect ratio on mechanical behavior were further examined through compression testing. Weibull statistical analysis demonstrated that strength-related properties exhibit high uniformity despite pronounced microstructural heterogeneity, whereas fracture strain shows comparatively greater scatter. The results indicate that solid-solution strengthening governs the mechanical response and helps mitigate the influence of microstructural non-uniformity. These findings provide important insights into the mechanical reliability of SLM-fabricated RHEAs under room-temperature quasi-static loading, and support their potential for further investigation in advanced structural applications.

Coatings doi: 10.3390/coatings16060686

Authors: Sai Vempati Armando José Yáñez Casal Juan Carlos Becerra Permuy José Manuel Amado Paz María José Tobar Vidal

The influence of internal substrate geometry on thermal stability during Laser Directed Energy Deposition Repair (DED-R) remains insufficiently understood, particularly for components containing internal cavities and cooling channels. This study investigates the thermal response of solid (Alpha), blind-hole (Bravo), and channeled (Charlie) AISI 316L substrates using dual infrared thermography, transient finite element modeling, and Short-Time Fourier Transform (STFT)-frequency-domain analysis. Despite substantial differences in internal heat-dissipation pathways, all substrate configurations exhibited similar peak surface temperatures (~1700–2100 °C), indicating that conventional temperature monitoring alone is insufficient to distinguish geometry-dependent melt-pool behavior. To address this limitation, a Spectral Entropy Index (SEI) derived from STFT analysis was proposed to quantify thermal stability. The channeled substrate exhibited the lowest entropy value (Hs = 0.172), compared with the solid (Hs = 0.181) and blind-hole (Hs = 0.183) configurations, indicating a more ordered and predictable thermal response. Furthermore, distinct variations in the spectral stability shadow revealed geometry-dependent oscillatory behavior that was not observable from thermal histories. Finite element simulations showed good agreement with experimental measurements in conduction-dominated regions (RMSE ≈ 46 °C), whereas deviations were observed within the melt-pool region (~250–310 °C), highlighting the increasing influence of fluid-flow phenomena not captured by the conduction-based model. The results demonstrate that internal substrate architecture primarily influences melt-pool stability through frequency-domain thermodynamics rather than significant changes in peak temperature. The proposed STFT method provides a quantitative approach for monitoring thermal stability and assessing the feasibility of L-DED repair over complex internal geometries.

Coatings doi: 10.3390/coatings16060685

Authors: Magdalena Mikus Jolanta Małajowicz Sabina Galus

This study aimed to analyze the effect of various phenolic acids introduced into pectin films on their ability to inhibit microorganisms. The antimicrobial activity of six phenolic acids—gallic, protocatechuic, caffeic, sinapic, coumaric, and ferulic acids—was verified against Bacillus subtilis bacteria. No inhibitory effect was observed when the acids were introduced into the substrates with the films, as the polysaccharide films served as a breeding ground for microorganisms. Bacterial growth was inhibited when pure acid was introduced to the substrate. Gallic and caffeic acid, at concentrations of 50 and 75 mM/dm3, respectively, completely inhibited bacterial growth. However, studies on pears have shown that such concentrations of phenolic acids are unsuitable for fruit coatings, as they lead to cloudiness and impaired visual appeal. Consequently, the lowest effective concentration was applied to fruit, reducing the total bacterial count from 2.59 ± 0.04 to 1.88 ± 0.22 log CFU/mL and mold and yeast counts from 2.11 ± 0.09 to 1.63 ± 0.10 log CFU/mL. The coating produced with the lowest tested concentration of gallic acid reduced the pears’ respiration rate. The amount of CO2 released by coated fruit was approximately 4 mg/kg·h lower than that of uncoated pears, and the level of ethylene released was approximately 6 ppm lower. The addition of gallic acid at a concentration of 15 mM/dm3 to the coating reduced the growth of bacteria, yeasts, and molds. After 12 days of pear storage, the number of microorganisms in coated fruit was approximately 0.71 log CFU/mL lower for bacterial cells and 0.48 log CFU/mL lower for yeasts and molds.

Coatings doi: 10.3390/coatings16060684

Authors: Zipeng Yin Zhensheng Yang Hansheng Liu Zhiying Wang Zhongyu Duan

The corrosion of metal components leads to substantial economic losses and poses serious safety hazards. While organic coatings are regarded as an effective countermeasure, conventional epoxy resins (EPs) often exhibit high brittleness and insufficient corrosion resistance after curing. To overcome these limitations, this study proposes a novel modification strategy. A multilayer graphene-reinforced epoxy composite coating was fabricated via a layer-by-layer spraying process, employing uniformly dispersed modified aramid nanofibers (ANFs) and low-defect graphene as functional fillers. Polydopamine (PDA) was utilized to improve the dispersion of graphene oxide (GO), mitigate defect-associated permeation pathways, and enhance the interfacial bonding between the graphene layer and the epoxy matrix, thereby ensuring coating integrity. Tannic acid (TA) effectively improves the dispersion of ANF within the epoxy, preventing stress concentration. The corrosion resistance and mechanical properties of the composite coating were systematically evaluated. Results demonstrate that the coating achieves a low-frequency impedance of 1.98 × 1010 Ω·cm2. With the incorporation of 0.05% TA-modified ANFs, the elongation at break increases to 68.79%, and the impact resistance is significantly enhanced, with the impact height reaching 50 cm. The composite coating preparation strategy in this work offers a novel approach for constructing multifunctional composite coatings, demonstrating broad application prospects.

Coatings doi: 10.3390/coatings16060683

Authors: Bauyrzhan Rakhadilov Aibol Mural Dauir Kakimzhanov Zhangabay Turar

This study aims to compare the structural, mechanical, tribological, and corrosion properties of gradient and bilayer Al2O3/Cr2O3 coatings obtained by detonation spraying on 316L stainless steel. The coatings were characterized using X-ray diffraction, scanning electron microscopy, energy-dispersive spectroscopy, instrumental indentation, scratch testing, ball-on-disk tribological testing, and potentiodynamic polarization in a 3.5% NaCl solution. The results showed that the gradient Al2O3/Cr2O3 coating had a denser and more homogeneous structure than the bilayer coating. Quantitative SEM image analysis showed that the apparent porosity decreased from 1.285% for the bilayer coating to 0.934% for the gradient coating. Instrumental indentation revealed an increase in hardness from approximately 401 HV to 462 HV and an increase in elastic modulus from about 173 GPa to 183 GPa. The gradient coating also demonstrated higher critical loads during scratch testing, indicating improved resistance to crack initiation and coating failure. Tribological tests showed a lower and more stable coefficient of friction for the gradient coating, decreasing from approximately 0.58–0.60 to 0.52–0.55. Potentiodynamic polarization measurements showed that the corrosion current density decreased from 0.50540 to 0.24155 µA/cm2, while the corrosion rate decreased from 0.00894 to 0.00428 mm/year. These results demonstrate that the gradient coating architecture improves the performance of Al2O3/Cr2O3 coatings by reducing porosity, increasing structural integrity, and promoting an improved structural integrity and reduced defect-related stress concentration through the coating thickness. Therefore, gradient Al2O3/Cr2O3 coatings obtained by detonation spraying are promising for applications requiring enhanced wear and corrosion resistance.

Coatings doi: 10.3390/coatings16060682

Authors: Yajue He Zhihuang Shen Shicong You Xu Zhang Junfeng Huang Chaoshuai Qi

Cobalt ferrite (CoFe2O4) magnetostrictive ultrasonic elliptical vibration cutting (UEVC) tools have recently emerged as a low-cost, low-eddy-loss alternative to piezoelectric and rare-earth-driven cutting heads. The structural design and resonance characterisation of such a dual-bending CoFe2O4 UEVC tool was reported in our previous work. The present paper builds directly on that platform and addresses a different objective: to determine how the four primary process variables—feed rate, cutting speed, cutting depth, and inter-channel phase difference—should be set to obtain the best surface quality on a representative ductile metal. Using H62 brass as the workpiece and a single-crystal diamond tool with a 0.2 mm nose radius and 60° included angle, single-factor experiments are run on a custom 5-axis precision lathe, and surface roughness is mapped in both the cutting and the feed direction with a Keyence VK-X1000 confocal microscope (Keyence, Osaka, Japan). The speed ratio K = Vc/(2πfA) is computed for every test point so that each result can be classified as belonging to the continuous-contact or to the intermittent-contact UEVC regime. The results show: (i) feed rate has a non-monotonic effect, with an optimum at 1 μm where ductile-mode separation is achieved without secondary tool-trajectory overlap, reducing the cutting direction roughness by up to 45% with respect to conventional cutting (CC); (ii) the UEVC advantage shrinks at high cutting speeds because the speed ratio approaches unity and the intermittent regime collapses, but is still 12.6%–38% over the 50–375 mm/s range tested; (iii) the relative improvement is largest at low depth and decreases as the depth grows, retaining 11.5%–49% gain over CC across 0.5–10 μm; (iv) the inter-channel phase difference, which controls the geometry of the tool-tip ellipse, is the strongest single lever—at 60°, the trajectory becomes an oblique ellipse whose major axis is tilted with respect to the cutting direction, bringing the cutting direction roughness down to 1.21 μm against 2.82 μm for CC, a 57% reduction. A simple kinematic argument links this optimum to a maximum effective separation duration per cycle and offers a design rule for analogous UEVC tools.

Coatings doi: 10.3390/coatings16060681

Authors: Adriano Galvão Souza Azevedo Igor Machado Silva Parente Carlos Alexandre Fioroni Holmer Savastano

This study investigates accelerated carbonation as a low-energy alternative to autoclave curing in the production of fiber cement composites reinforced with lignocellulosic fibers. The effects of both curing routes on physical–mechanical performance, durability, and microstructural evolution were systematically evaluated before and after 25 wetting–drying cycles. Carbonation-cured composites achieved mechanical performance comparable to autoclaved materials, while exhibiting higher bulk density (≈1.37–1.38 g/cm3) and a reduction of approximately 15% in total void volume. Water absorption values were up to 17% lower than those of autoclaved counterparts. After accelerated aging, both systems showed stable mechanical properties, with increases in modulus of elasticity of approximately 21% (autoclaved) and 26% (carbonated), indicating ongoing hydration and densification processes. Thermogravimetric analysis revealed carbonation degrees of approximately 16–17%, corresponding to CO2 uptake values of up to 35.8 kg/m3 of fiber cement. X-ray diffraction confirmed the consumption of portlandite and the formation of calcium carbonate phases, contributing to pore refinement and matrix densification. Microstructural observations indicated improved fiber–matrix interaction in carbonated composites due to the precipitation of carbonation products at the interface, whereas autoclaved materials exhibited signs of fiber degradation associated with hydrothermal curing. These effects were reflected in higher deformation capacity and specific energy retention in carbonated systems. Overall, accelerated carbonation represents a promising alternative to autoclave curing, delivering comparable mechanical performance while enhancing fiber durability, refining pore structure, and enabling CO2 sequestration within the cementitious matrix.

Coatings doi: 10.3390/coatings16060680

Authors: Fang Han Huaixing Wen Junhong Jia Junyan Sun Xuanchao Wang

To achieve accurate prediction of the surface COF (coefficient of friction) of titanium alloys under electrochemical corrosion conditions, this study investigates the tribological behavior of titanium alloys across various solutions, concentrations, voltages, and sliding velocities to construct a systematic dataset. Two machine learning models are developed and optimized: a standard Light Gradient Boosting Machine (LightGBM) and an enhanced LightGBM model incorporating lag and rolling features. These models are employed to predict the friction coefficient and feature importance analysis. The results indicate that solution concentration is the primary factor influencing the friction coefficient of the titanium alloy, followed by test duration, while sliding velocity exerts the least influence. Following experimental validation and iterative optimization, the enhanced LightGBM model, integrated with lag and rolling features, demonstrates superior predictive accuracy, achieving a coefficient of determination (R2) of 0.979 on the training set and 0.951 on the test set. This research establishes a data-driven predictive framework that demonstrates superior accuracy and interpretability compared to models using only raw features, showcasing the potential of feature-engineered machine learning in optimizing electrochemical machining parameters.

Coatings doi: 10.3390/coatings16060679

Authors: Dawid Kutyła Michihisa Fukumoto Hiroki Takahashi Ryuu Takahashi Katarzyna Skibińska Piotr Żabiński

Porous bilayer Ni–Co and sandwiched Ni–Co–Ni electrodes were fabricated by combining aqueous electrodeposition with high-temperature molten-salt Al deposition and subsequent electrochemical dissolution in NaCl–KCl–AlF3 melt at 750 °C. The study aimed to determine how the initial layer architecture controls phase evolution, porous structure formation, and hydrogen evolution performance in alkaline media. SEM/EDS and XRD analyses showed that the two electrode designs followed different reaction pathways during molten-salt treatment. In the Ni–Co system, Al reacted predominantly with Co, leading mainly to Co–Al intermetallic formation and, after dissolution, to a highly open coral-like porous network. In contrast, the Ni–Co–Ni architecture promoted mainly Ni–Al phase formation and produced a more compact porous surface with a Ni-rich outer layer. Despite these morphological differences, both layered porous electrodes outperformed untreated Ni and porous Ni in 1 M NaOH. At −0.6 V vs. RHE, porous Ni–Co and NiCo–Ni reached current densities of −162 and −141 mA·cm−2, respectively, compared with −87 mA·cm for porous Ni and −45 mA·cm for flat Ni. The Ni–Co–Ni sandwiched electrode showed the most favourable HER kinetics and benchmark performance, with the lowest Tafel slope (111 mV·dec) and the lowest potentials at −10 and −100 mA·cm (−0.132 and −0.556 V, respectively). These results demonstrate that the electrocatalytic response of molten-salt-derived porous Ni-based electrodes is governed not only by porosity development but also by the spatial arrangement of metallic layers prior to Al infiltration and dealloying.

Coatings doi: 10.3390/coatings16060678

Authors: Nadjet Begag Linda Toukal Khaoula Douadi Imene Benmahammed Ilhem Selatnia Sabrina Bendouma Hassane Lgaz Malika Foudia Amel Djedouani Han-Seung Lee

This study aims to investigate the performance and mechanism of N′-[(E)-phenylmethylidene] furan-2-carbohydrazide (FNH), a hydrazone Schiff base, as a corrosion inhibitor for carbon steel in 1.0 M HCl. The research was conducted by coupling electrochemical testing (Tafel analysis and Impedance spectroscopy) with surface characterization (SEM and AFM) and advanced computational tools, including quantum-chemical modeling and classical molecular dynamics (MD) simulations. Tafel analysis revealed that FNH acts as a mixed-type inhibitor, concurrently slowing iron oxidation and hydrogen reduction. Impedance data showed that the Faradaic resistance grew monotonically with FNH dosage, reaching 95% protection at 1 × 10−4 M. Fitting the results to the Langmuir model indicated a joint physical–chemical anchoring pathway, further confirmed by SEM/AFM inspection which disclosed a uniform organic deposit. Quantum-chemical modeling revealed that protonated species broaden the molecule’s capacity for bidirectional electron exchange, while MD simulations on the Fe (110) slab confirmed a flat-lying geometry that maximizes heteroatom–metal contact. The consistency between laboratory observables and atomic-scale predictions provides a detailed, mechanism-oriented picture of how this organic protective layer curtails acid corrosion.

Coatings doi: 10.3390/coatings16060677

Authors: Wei Xu Zhichao Chen Guofeng Duan Yuyang Wang Hristo Nenov

Microbial fuel cells (MFCs) are promising bioelectrochemical systems for simultaneous wastewater treatment and energy recovery. However, their practical application is still limited by insufficient power output and weak transient energy-supply capability under fluctuating operational conditions. Herein, a bifunctional CF/MXene/FeS composite anode was fabricated through a one-step hydrothermal strategy to simultaneously enhance electricity generation and capacitive charge storage in MFCs. Unlike conventional bioanode modifications that primarily target conductivity enhancement alone, the constructed hierarchical composite integrates conductive MXene nanosheets and electroactive FeS phases to synergistically improve extracellular electron transfer and interfacial charge-storage behavior. The modified electrode exhibited enhanced surface roughness, abundant electroactive sites, and improved biofilm-supporting interfaces. Benefiting from the integrated conductive and electroactive composite framework, the CF/MXene/FeS anode achieved a maximum power density of 1.69 W/m2, which was 70.7% higher than that of pristine CF, together with an increased open-circuit voltage of 0.711 V. In addition, the composite electrode delivered a high total charge density of 13,192.09 C/m2 under the C900/D900 condition. Microbial community analysis further revealed substantial enrichment of electroactive bacteria, with the relative abundance of Geobacter increasing from 0.0058% to 22.84%. This work provides a promising strategy for integrating electricity generation and transient energy storage in bioelectrochemical systems, offering potential applications for energy-buffered MFCs under fluctuating power-demand conditions.

Coatings doi: 10.3390/coatings16060676

Authors: Xiang Liu Hanxu Liu Ci Lv Bo Liu Dekun Zhang

The dynamic spreading behavior of droplets impacting surfaces with different wettability is a critical hydrodynamic issue in industrial applications such as inkjet printing, spray cooling, and pesticide spraying. The maximum spreading diameter coefficient (βmax) is the key parameter characterizing this process. Existing theoretical models often overlook the gravitational potential energy of droplets, resulting in significant discrepancies between the calculated viscous dissipation times and experimental results, which compromises the prediction accuracy. In this study, we incorporated gravitational potential energy into the energy balance system based on the principle of system energy conservation. We introduced the Bond number (Bo) to characterize the coupling effect of gravity and surface tension. By fitting experimental data, we corrected the viscous dissipation time, obtaining tc = 3.17d0/v0, which improves the reliability of dissipated energy calculation. Using Young’s equation and the Cassie model, we derived a fourth-order βmax prediction model that includes the Weber number (We), Reynolds number (Re), contact angle (θc), and Bo number. The results show that regulating the impact height and droplet diameter will affect the trend of the maximum spreading coefficient model curve: the crossover Weber numbers are 41.519 and 41.530 for different liquid viscosities under the specific experimental and modeling conditions of this study. Below these thresholds, the maximum spreading diameter coefficients are more sensitive to impact height (inertial and kinetic-energy) than to droplet diameter (volume, mass, surface energy, gravitational potential energy, Bond number). Above the critical value, the influence of droplet diameter on the maximum spreading diameter coefficient becomes more pronounced. These intersections reflect the balance between size-dependent effects and impact-inertia-related effects under specific conditions, rather than universal physical thresholds. Compared with selected classical models, the proposed model shows better consistency with experimental data and provides improved prediction for the maximum spreading coefficient of water droplets on surfaces with different wettability. This study supplements the perspective of energy analysis for the modeling of droplet impact dynamics, and can provide a basis for the theoretical optimization of spray systems and interfacial fluid control.

Coatings doi: 10.3390/coatings16060675

Authors: Feng Xi Xinyu Wan Hongsong Shi Xindong Chang Shutong Chen Fadzli Mohamed Nazri Yiheng Wang Zhaoqi Wu

Coastal continuous girder bridges are exposed to coupled environmental and seismic hazards during long-term service, including chloride-induced corrosion, freeze–thaw damage, scour, near-field ground motions, and structural irregularity. These factors can progressively reduce structural capacity, amplify seismic demand, redistribute component responses, and affect post-earthquake functionality and recovery. This paper reviews recent advances in the time-dependent seismic vulnerability and resilience assessment of reinforced concrete and prestressed concrete coastal continuous girder bridges. Based on 229 screened publications, the review first summarizes deterioration mechanisms and modelling approaches for chloride corrosion, freeze–thaw damage, and scour, with emphasis on their effects on material degradation, component capacity, foundation restraint, and seismic fragility. The demand-side effects of near-field vertical excitation and pulse-like ground motions are then discussed, followed by the seismic response characteristics of irregular continuous girder bridges, including curved alignments, unequal pier heights, and skewed supports. Existing studies indicate that environmental deterioration can shift fragility curves toward lower intensity levels, near-field vertical excitation can modify axial force, bearing contact state, girder–bearing separation, and impact response, while structural irregularity may concentrate seismic demand in critical components. Furthermore, the review clarifies the transition from time-dependent fragility analysis to functionality loss, recovery modelling, and lifecycle resilience assessment. The main research gaps include simplified deterioration representation, insufficient coupling of deterioration–hazard–irregularity effects, limited validation of time-dependent fragility models, and weak integration between component damage, bridge functionality, recovery trajectories, and resilience indicators. Future studies should develop more unified, uncertainty-informed, and lifecycle-oriented frameworks for coastal bridge vulnerability and resilience assessment.

Coatings doi: 10.3390/coatings16060674

Authors: Huan Luo Hui Sun Peipei Wang Xing Zhao Pascal Briois Alain Billard

The development of protective coatings with simultaneously enhanced mechanical, tribological, and antioxidant properties remains a major challenge for micro-electro-mechanical systems operating under harsh environments. In this work, HfCx/a-C:H coatings with varying carbon contents were deposited by magnetron sputtering. Increasing the C2H2 flow rate from 12 to 20 sccm drove the coating structure to undergo two-stage evolution, from a composite structure dominated by HfC nanograins with a-C:H distributed at triple junctions of HfCx grain boundaries to a typical nanocomposite structure with ~8 nm HfCx nanograins embedded in a continuous a-C:H matrix. The coating deposited at 18 sccm exhibited the highest hardness (31.3 GPa) and effective Young’s modulus (392.3 GPa), owing to enhanced interface-mediated strengthening effect induced by the optimized nanocomposite structure. The coating prepared at 20 sccm showed the lowest friction coefficient (0.28), the lowest wear rate (6.82 × 10−6 mm3/N·m), and the best oxidation resistance. These improvements were supported by the enhanced mechanical properties and a-C:H fraction, the increased interface density and tortuosity, and the regulation of oxidation kinetics by the a-C:H matrix. This work provides an effective strategy for designing multi-functional protective coatings with balanced mechanical, tribological, and oxidation performance.

Coatings doi: 10.3390/coatings16060673

Authors: Xueping Guo Jianming Zhang Yijia Chen Weihang Liu Jian Liu Zhaoju Peng Zhihai Cai Kaihua Zhang Keyang Chen Binggong Yan

Lightweight high-entropy alloy (HEA) coatings are highly desirable for advanced surface protection. This study presents a novel fabrication method for Al-Mg-Ti-Cu-Ni-Cr lightweight HEA coatings via laser cladding combined with in situ alloying, using a specially designed cable-type composite wire consisting of an Al-Mg core sheathed with Cu, Ti, Ni, and Cr-Ni wires. The fabricated coatings exhibit homogeneous composition, high microhardness, and excellent corrosion resistance. Notably, the Al43.5Mg2Ni28Cu15Ti11.5 coating achieves a microhardness of 627 HV0.1 and a corrosion current density of 5.5 × 10−6 A/cm2, while the Al43.6Mg2.1Cr2.5Ni25.2Cu15.2Ti11.4 coating shows 523 HV0.1 and a lower current density of 2.8 × 10−6 A/cm2. Mechanical analysis reveals that the enhanced hardness stems from synergistic strengthening effects—severe lattice distortion, B2 phase coherent precipitation, and grain refinement. The superior corrosion resistance is primarily attributed to a compact Cr2O3 passive film. This work provides a new strategy for designing and additively manufacturing lightweight HEA coatings.

Coatings doi: 10.3390/coatings16060672

Authors: Anna Pirouni Christina Drosou Sokratis Emmanouil Koskinakis Chrysanthos Stergiopoulos Isabel Rodríguez Amado Pablo Fuciños Lorenzo Pastrana Pulkit Mishra Magdalini Krokida

The present study investigates the development of antimicrobial textile coatings by encapsulating zinc oxide (ZnO) particles within electrospun polylactic acid (PLA) fibers. Electrospinning was used to produce uniform fibrous coatings with effective incorporation of ZnO. ZnO reduced solution viscosity and increased conductivity, resulting in thinner and more homogeneous fibers. Thermogravimetric analysis confirmed high encapsulation efficiency (up to 95%) and a significant loading capacity (47.71 ± 1 mg ZnO/g fiber), while scanning electron microscopy revealed uniform fiber structures with high-contrast regions that are qualitatively consistent with the presence of ZnO-rich domains. The release behavior of ZnO was assessed under simulated washing and perspiration conditions. Results showed limited release under sweat conditions (R < 0.07), indicating strong ZnO retention under perspiration-related exposure, whereas washing increased release from the free-standing coatings (up to 0.32), indicating partial ZnO retention under more aggressive aqueous surfactant conditions. Kinetic modeling using first-order, Higuchi, and Korsmeyer–Peppas models indicated that ZnO release was predominantly diffusion-controlled, with the Higuchi and Korsmeyer–Peppas models showing the best fit to the experimental data. Following thermal bonding onto textile substrates, the coatings achieved successful macroscopic integration; however, washing simulation of the bonded coatings resulted in more pronounced ZnO loss, while sweat exposure caused only limited release. The antimicrobial activity of the coatings was assessed against Staphylococcus aureus and Klebsiella pneumoniae (ISO 20743:2021). The PLA/ZnO (5% w/v) system showed strong broad-spectrum antibacterial activity, with values of 4.71 and 3.37, respectively. Overall, electrospun PLA/ZnO coatings show potential as antimicrobial textile coatings, offering controlled release behavior, strong antibacterial activity, and condition-dependent ZnO retention.

Coatings doi: 10.3390/coatings16060671

Authors: Mingyu Luo Haiyan Yang Wei Zhang

In this study, a functional surface coating composed of Fe-Mn binary oxide (FM) and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS, PP) was applied to a PVDF membrane (PP-FM-PVDF) for efficient arsenate (As(V)) removal. PP acts as a dispersant and hydrophilic modifier, ensuring uniform FM distribution and reducing the water contact angle to 50.1°. The PP-FM-PVDF membrane achieves a maximum As(V) adsorption capacity of 30.43 mg/g, outperforming pristine and singly modified membranes. The batch adsorption data fit the Langmuir isotherm (R2 = 0.999) and pseudo-second-order kinetic model (R2 = 0.99), indicating monolayer chemisorption. The coating increases the specific surface area to 27.33 m2/g and the tensile strength to 6.41 MPa. Dynamic filtration shows that 2.70 L (2149.7 L/m2) of 100 μg/L As(V) solution can be treated before the permeate concentration exceeds the WHO guideline of 10 μg/L. After alkaline regeneration (pH 11), 62.9% of the initial capacity is retained. Complementary surface-sensitive analyses (zeta potential, XPS, and EXAFS) reveal that arsenate adsorption occurs primarily through ligand exchange between arsenate oxyanions and Fe/Mn surface hydroxyl groups on the coating, forming inner-sphere bidentate complexes (Fe–O–As and Mn–O–As), while electrostatic interactions play a secondary, pH-dependent role. This surface engineering strategy—synergistically integrating a conductive hydrophilic polymer with a metal oxide as a functional coating on PVDF—offers a reusable, high-performance platform for arsenate remediation, underscoring the critical role of interface design in environmental membrane applications.

Coatings doi: 10.3390/coatings16060669

Authors: Jimin Xue Xiaorong Jin Mengyue Wang Liubo Yuan Huichun Xie Bin Yan

Conventional strategies to enhance the hydrophobicity of polyurethane (PU) coatings typically rely on fragile micro/nanostructures or irradiation-induced crosslinking, both of which suffer from poor controllability and often compromise mechanical robustness. Herein, we report a UV-triggered crosslinking strategy based on coumarin chemistry that enables precise, controllable network formation, thereby simultaneously enhancing the hydrophobicity, adhesion strength, and thermal stability of polydimethylsiloxane (PDMS)-based PU coatings. A series of coumarin-functionalized PDMS-PU coatings (HNP-PDMS-PUx) was prepared by blending coumarin-grafted PDMS (HNP) with PDMS-PU elastomers. Upon 365 nm UV irradiation, the coumarin moieties dimerize, forming a dense, chemically crosslinked “brush-like” structure on the coating surface. The optimal coating (HNP-PDMS-PU3/1) exhibited a significant increase in water contact angle from 108° to 129° on average, reaching a maximum of 134°. The UV-treated coating also showed enhanced adhesion strength (a 45% increase) and improved thermal stability, while maintaining good flexibility (F7 rating) and abrasion resistance (contact angle remained at 126° after 30 cycles). Moreover, the coating demonstrated excellent easy-cleaning performance against both liquid and solid contaminants. This work provides a photochemical strategy that replaces uncontrollable or irreversible crosslinking methods with a controllable UV-triggered approach, enabling synergistic enhancement of multiple properties.

Coatings doi: 10.3390/coatings16060670

Authors: Man Zhang Wenbo Chen Xusheng Li Gui Li Ying Xiong Yixin Zhang Bo Wang Li Liu Longhui Deng Jianing Jiang Shujuan Dong Xueqiang Cao

In this study, the Ca33Mg9Al13Si45 layer was fabricated on the SiCf/SiC surface by APS to simulate the coexistence of high-velocity impact and molten-state deposition. Subsequently, the corrosion and infiltration behaviors of the molten Ca33Mg9Al13Si45 in air and water-vapor environments (H2O:O2 = 90:10 vol%) at 1300 °C for 300 h were investigated. The results indicated that, during corrosion, the molten Ca33Mg9Al13Si45 infiltrated into the interior of the SiCf/SiC through interconnected pores. Under high-temperature air corrosion, Ca and Mg remained restricted to the upper-part pore-filling region. Compared with high-temperature air corrosion, Ca and Mg infiltrated deeper along the pores into the interior of the SiCf/SiC under high-temperature water-vapor corrosion. Once the molten Ca33Mg9Al13Si45 filled these pores, no obvious elemental diffusion or further infiltration was detected at the interface between the molten Ca33Mg9Al13Si45 and SiCf/SiC, suggesting good interfacial chemical stability. The flexural strength of the original SiCf/SiC was 445 ± 43 MPa, while the SiCf/SiC with the molten Ca33Mg9Al13Si45 after high-temperature air corrosion and water-vapor corrosion exhibited flexural strengths of 409 ± 30 MPa and 440 ± 33 MPa. These results demonstrated that the infiltration behavior of the molten Ca33Mg9Al13Si45 had a relatively minor impact on the mechanical behavior of SiCf/SiC, enabling the materials to retain mechanical performance close to the original level after high-temperature exposure.

Coatings doi: 10.3390/coatings16060668

Authors: Wei Zhao Xinyu Li Sibo Shao Dongxue Ning Na Xie Xiujuan Liu Tifeng Jiao

In this work, monodisperse carbon microspheres with an average diameter of approximately 900 nm were successfully synthesized via a hydrothermal method. To further tailor their surface properties, the layer-by-layer (LbL) self-assembly technique was employed, where the cationic polyelectrolyte poly(diallyldimethylammonium chloride) (PDDA) and the anionic polyelectrolyte poly(styrene sulfonate) (PSS) were alternately deposited on the microsphere surface, forming two and four bilayer assemblies, respectively. The resulting composite microspheres exhibited remarkable adsorption performance toward representative dyes in water solution, such as rhodamine B (RhB) and methylene blue (MB). Experimental results demonstrated that the incorporation of a single bilayer significantly reduced the specific surface area but introduced additional active adsorption sites, thereby enhancing dye removal efficiency. However, when the number of bilayers was further increased to two, partial pore coverage and blockage occurred, leading to a reduced surface area and consequently diminished adsorption capacity. These findings highlight that in LbL surface modification, more layers do not necessarily yield better performance, but rather an optimal assembly thickness exists. This insight provides valuable guidance for the rational design of advanced adsorbent materials for wastewater treatment.

Coatings doi: 10.3390/coatings16060667

Authors: Xiaoguang Sun Pranpreeya Wangjina Piya Khamsuk Chuanying Li Jie Wang Ekkarut Viyanit Wanida Pongsaksawad

Organic coatings are the most widely utilized corrosion protection strategy for metallic materials. Nevertheless, they can degrade over time through the effects of UV, moisture, and corrosive media, compromising their protective performance. In order to monitor the coating performance for predictive maintenance, an electrochemical sensor was fabricated using 6005A aluminum alloy and coated with four coating systems: (1) epoxy primer, (2) epoxy primer/polyurethane topcoat, (3) epoxy primer/polyurethane topcoat/aluminum-powder-containing polyester resin, and (4) epoxy primer/polyurethane topcoat/aluminum-powder-containing polyester resin/acrylic coat. The sensors and corresponding coupon samples were exposed for 24 months at two sites in Thailand: Pathum Thani (PTI, suburban) and Chon Buri (CBI, mild marine). Electrochemical impedance spectroscopy (EIS) measurements were conducted at a fixed frequency of 117 Hz, synchronized with on-site meteorological monitoring. Impedance data were converted into a coating aging index (AI) to quantitatively assess the coating degradation. Coating deterioration was observed in PTI as early as at 6 months of exposure. Machine learning modeling revealed that cumulative rainfall was the dominant environmental factor influencing coating degradation. The single epoxy primer layer exhibited the poorest durability, while the incorporation of polyurethane, aluminum-pigmented polyester, and acrylic layers significantly prolonged the protective service life of the coating system.

Coatings doi: 10.3390/coatings16060665

Authors: Zimeng Li Shulan Yu Xiaoxing Yan

Powder coatings applied to medium-density fiberboard (MDF) substrates have attracted increasing attention due to their low volatile organic compound (VOC) emissions and high material utilization efficiency. The review synthesizes the interdisciplinary literature from coating engineering, CMF design, and furniture design. However, existing studies often focus on individual coating properties and lack a systematic framework integrating color, material, and finish (CMF). Therefore, this review examines the design and application of MDF powder coatings from a CMF perspective, focusing on the relationships between coating engineering parameters and user-oriented perceptual requirements. Within this framework, color performance is associated with pigment dispersion and particle size distribution; the material dimension is governed by low-temperature curing kinetics and substrate properties, and the finish dimension is shaped by surface texturing and functional additives. The review also discusses current limitations, including the trade-off between low-temperature curing reactivity and storage stability, the influence of nano-additives on surface quality, and the recyclability challenges of powder-coated MDF. Future research should focus on industrial scalability, lifecycle sustainability, and long-term durability of MDF powder coating systems. This review provides a CMF-oriented framework for linking user experience requirements with coating engineering strategies, which is of great importance for the development of customized home furnishing.

Coatings doi: 10.3390/coatings16060666

Authors: Zihan Cheng Jingya Qi Dan Li Ting Mei Tianyu Sun Jinjian Zhang Jinming Zhao Tansheng Lu

Vehicle fleet renewal policies promoting NEVs aim to decarbonize transportation but inadvertently alter urban atmospheric corrosivity, threatening the durability of infrastructure coatings. This study investigated the cross-system impacts of vehicle trade-in subsidies on the degradation of protective coatings. We developed a coupled framework integrating a Mixed Logit model for fleet evolution, dynamic Life Cycle Assessment for tracking acidic precursors (SO2, NOx), and an Environmental Corrosion Risk Index. Using established Dose–Response Functions, we quantified the lifespan depletion of a standard epoxy zinc-rich primer and polyurethane topcoat system. Our results indicate that aggressive subsidies induce a transition to heavy NEVs, triggering an “emission inversion” that spikes upstream grid acidic emissions. This localized acidification significantly accelerates chemical degradation, reducing the effective service life of infrastructure coatings by 1.3–2.3 years and necessitating premature, costly recoating. We identify a Pareto-optimal subsidy window (8000–10,500 CNY) that effectively balances decarbonization targets with coating preservation. In conclusion, sustainable urban policies must incorporate surface engineering and material durability metrics to prevent emission shifts from compromising the physical integrity of transportation infrastructure.

Coatings doi: 10.3390/coatings16060664

Authors: Tamara-Rita Ovari Gabriel Katona Gabriella Stefánia Szabó Liana Maria Muresan

The expired drug Detralex (90% diosmin and 10% hesperidin), known as an effective corrosion inhibitor, was adsorbed onto mesoporous silica and incorporated into an epoxy matrix to enhance the coating’s corrosion protection in a highly corrosive 3 wt% NaCl solution. It was found that this treatment, by improving adhesion, modifying the hydrophilic properties, and enabling inhibitor release, increased the coating’s resistance over time. Based on an SEM-EDX analysis, even after 24 h of immersion, the epoxy coating with mesoporous nanosilica adsorbed with diosmin and hesperidin retained the incorporated inhibitors. This resulted in a slight increase in the samples’ polarization resistance during longer exposure.

Coatings doi: 10.3390/coatings16060663

Authors: Yanchao Hou Byungchan Lee

Shear Thickening Fluid (STF), as a typical intelligent material, offers a novel approach for developing adaptive protective equipment due to its unique “shear thickening” effect. This review examines STF-based composite materials, encompassing both surface coatings (where STF is dispersed in a polymer matrix applied as a layer) and impregnated structures (where STF is integrated into porous fabric or foam substrates via saturation). It elaborates on design principles, preparation methods, mechanical property modulation, and applications in adaptive protectors for knees, elbows, wrists, ankles, and sports equipment. The review emphasizes how composite strategies overcome STF encapsulation and processing challenges, facilitating laboratory-to-market transition. The core mechanisms underlying the “flexible under normal conditions, rigid upon impact” behavior are discussed at molecular and rheological levels. Key limitations—including fluid leakage, long-term aging, and temperature sensitivity—are critically examined alongside future development trends toward multifunctional, intelligent protective systems.

Coatings doi: 10.3390/coatings16060662

Authors: Lingxiao Hu Xingfu Wang Chuangzhi Jin Yanxu Li Juhua Liang

High-Mn twinning-induced plasticity (TWIP) steels are renowned for their exceptional strength-ductility synergy. However, their practical applications are severely constrained by inadequate yield strength and poor corrosion resistance. In this study, an N-alloyed TWIP steel (Fe-25Mn-12Cr-0.3C-0.3N, wt.%, designated as TWIP-2) was developed, using an N-free counterpart (Fe-25Mn-12Cr-0.3C, TWIP-1) as a reference. Both steels underwent hot forging (HF) followed by solution treatment (ST). The synergistic effects of N alloying and thermomechanical processing on the microstructural evolution, mechanical properties, and corrosion behavior were systematically investigated. Results indicate that all samples retain a single-phase FCC austenitic structure. N alloying increased the yield strength of the hot-forged TWIP steel from 488.1 MPa to 802.9 MPa while maintaining an elongation after fracture around 40%. Solution treatment markedly improved corrosion resistance, changing the corrosion mode from intergranular attack to pitting. The TWIP-2-ST specimen exhibited the lowest corrosion current density of 2.88 × 10−5 A/cm2 and demonstrated the best overall performance. This comprehensive improvement in mechanical and corrosion performance is primarily attributed to the elevated work-hardening capacity, a higher fraction of low-energy grain boundaries, and the beneficial role of interstitial N in suppressing pitting nucleation and propagation.

Coatings doi: 10.3390/coatings16060661

Authors: Jian Zhou Juntao Wu Di Yu Xiaoyong Tan

Waste plastics have attracted widespread attention in asphalt modification because of their environmental and economic benefits. However, the incorporation of waste plastics may weaken asphalt–aggregate interfacial adhesion, thereby increasing the risk of moisture damage in asphalt pavements. Although liquid anti-stripping agents have been widely used in conventional asphalt systems, their effectiveness and performance evolution in waste plastic-modified asphalt (WPA) remain insufficiently understood. To address this gap, this study systematically investigated the effects of two liquid anti-stripping agents, AJ-1 and AMR-II, on the adhesion, rheological properties, and aging behavior of WPA. Specifically, asphalt–aggregate adhesion was evaluated using water-boiling and binder bond strength tests, rheological properties were characterized by dynamic shear rheometer and bending beam rheometer tests, and aging behavior was analyzed through rolling thin-film oven test, pressurized aging vessel, and Fourier transform infrared spectroscopy. The results show that waste plastics reduce the adhesion performance at the asphalt-aggregate interface, whereas anti-stripping agents compensate for this loss. Compared with AJ-1, AMR-II showed stronger adhesion enhancement, increasing the asphalt residual coating ratio by approximately 1.5%–3.5% and the pull-off tensile strength by 17.4%–28.1%, while the corresponding improvements for AJ-1 were approximately 1.3%–2.7% and 13.0%–25.0%, respectively. As the dosage of both anti-stripping agents increased, the penetration index decreased, the temperature susceptibility increased, the softening point generally decreased, and the ductility increased markedly. Temperature sweep results show that both AJ-1 and AMR-II reduce the high-temperature performance of WPA. According to the bending beam rheometer results, AMR-II also enhances the low-temperature performance of WPA. Aging test results indicate that both anti-stripping agents increase the aging sensitivity of WPA to some extent, but the adverse effect of AMR-II on aging resistance is smaller than that of AJ-1, and AMR-II better preserves the low-temperature ductility and adhesion performance after aging. Overall, this study provides a binder scale evaluation showing that 0.4% AMR-II may offer a more balanced strategy for improving the adhesion and service performance of WPA.

Coatings doi: 10.3390/coatings16060660

Authors: Rongfei Zhang Chao Liu Zhenhua Duan Zhenyuan Lv Wei Zhang Huawei Liu

3D-printed concrete (3DPC) enables formwork-free automated construction with geometric flexibility and improved material efficiency, yet its engineering reliability remains limited by interlayer weakening generated during sequential deposition. This review critically examines the formation, cross-scale consequences, and control of weak interlayer interfaces in 3DPC. In most studies, the 3DPC printing interval ranges from 20 s to 120 min, and the average interfacial bond strength ranges from 0.1 to 16 MPa. Interfacial weakness arises from the asynchronous evolution of adjacent layers in terms of contact quality, rheological recovery, moisture exchange, and early-age hydration. This mismatch promotes pore enrichment, discontinuity of hydration products, reduced phase continuity, and consequent local mechanical softening. These defects govern interlayer bonding, crack propagation, anisotropy, and stress-transfer pathways, and their effects propagate from material properties to member response, structural performance, and durability degradation. Rather than treating the interface as a localized cold joint, this review frames it as a process-induced multiscale variable linking printing history, microstructure, mechanical response, transport behavior, and serviceability. Current research remains constrained by non-comparable testing methods, undefined quantitative thresholds, and models that still rely heavily on empirical calibration. Future work should establish standardized characterization, transferable interface descriptors, multiscale predictive models, real-time quality control, and design methods that explicitly incorporate interfacial variability.

Coatings doi: 10.3390/coatings16060659

Authors: Yi Zheng Xin Luo Sizhe Li Zhengxian Shen Hui Su

Faced with a global energy crisis and ecological degradation, overall water splitting (OWS) is a pivotal approach for renewable energy conversion and storage. However, its industrial application is hindered by the high energy barriers/sluggish kinetics of the anodic oxygen evolution reaction (OER), as well as the scarcity of precious metal catalysts limiting large-scale deployment. Herein, a cobalt-based layered double hydroxide (Co-LDH) was used as the precursor, and a multi-strategy synergistic modification (hydrothermal synthesis, Fe doping, sulfurization, and external magnetic field magnetization) was applied to fabricate the Fe-Co3S4-MS-20 min electrocatalyst. This strategy establishes Fe-Co bimetallic synergistic active centers, and magnetic treatment modulates the electron configuration of Fe 3d orbitals without changing the material’s lattice spacing or morphology. Structural characterizations and electrochemical measurements were used to investigate the effects of combined modifications on the catalyst’s phase structure, morphology, electronic structure, and trifunctional catalytic performance toward the hydrogen evolution reaction (HER), OER, and urea oxidation reaction (UOR). The Fe-Co3S4-MS-20 min catalyst exhibits a larger electrochemical active surface area, lower charge transfer resistance, and smaller Tafel slope in 1 M KOH, it achieves overpotentials of 165 mV for HER (10 mA·cm−2) and 310 mV for OER (100 mA·cm−2), along with superior UOR performance and long-term stability. In situ impedance and Raman spectroscopy confirm that magnetization accelerates charge transfer and promotes in situ reconstruction. Synergistic multi-strategy regulation optimizes the electronic structure of active centers, reducing electrocatalytic energy barriers. This work provides new insights into designing high-performance non-precious metal electrocatalysts and offers experimental support for external magnetic field regulation in electrocatalyst modification.

Coatings doi: 10.3390/coatings16060658

Authors: Wei-Che Huang Hao-Wei Chu

In this study, cathodic arc deposition was employed to synthesize CrAlN/TiSiN nanostructured multilayer coatings on silicon wafer substrates. The effects of the multilayer architecture on the microstructure and corrosion resistance of the coatings were systematically investigated. The structural characteristics and performance of the deposited films were analyzed using scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), X-ray diffraction (XRD), and electrochemical polarization measurements. The experimental results demonstrate that various CrAlN/TiSiN multilayer configurations were successfully deposited, forming dense multilayer coatings with a thickness of approximately 1–2 μm and a dominant FCC β1-NaCl crystalline structure. The presence of nanostructured multilayer interfaces effectively inhibited columnar grain growth and contributed to microstructural refinement. XRD analysis revealed competitive growth between the (111) and (200) crystallographic orientations, indicating that the crystallization behavior is influenced by the interplay between surface energy minimization and strain energy accumulation. Contact angle measurements showed that all the coatings exhibited water contact angles exceeding 90°, indicating hydrophobic characteristics and potential anti-fouling capacity. In particular, the CrAlN outer layer structure presented lower surface free energy, which further enhances the coating system’s anti-fouling capacity. Electrochemical polarization results indicate that the corrosion current density of all the coatings remained in the order of 10−7 A/cm2, demonstrating excellent chemical stability. Overall, the CrAlN/TiSiN nanostructured multilayer coatings exhibit pronounced interface strengthening and densification growth mechanisms, which effectively enhance the chemical stability of silicon-based material surfaces. These results could provide valuable insights for the structural design and optimization of high-performance protective coatings.

Coatings doi: 10.3390/coatings16060657

Authors: Daniela A. Pricop Adina Arvinte Lacramioara Oprica Florica Doroftei Laura Ursu Gabriela Vochita Eliza Olteanu Sebastian Pricop Silviu Gurlui Dorina Creanga

The design and study of gold nanoparticles (AuNPs) with improved catalytic properties is of great interest due to the wide range of applications, so the modification of the surface of nanoparticles by coating with organic functional groups, as well as the treatment of these coatings with a light beam, is investigated as a potential nanotechnological tool in this regard. We obtained fine gold nanoparticles (AuNPs) by the conventional method with pH adjustment and by green light irradiation of pristine gold–citrate nanoparticles. The physicochemical properties of these products were revealed by electron microscopy, dark-field optical microscopy, UV-Vis spectrophotometry, dynamic light scattering and cyclic voltammetry. The phenomena at the interface between pristine colloidal nanoparticles and those exposed to green light with environmental fungi were analyzed at the level of the cellulolytic species of Chaetomium globosum, considering the final fate in the biosphere of gold nanoparticles used in the technical and biomedical fields. Measurements of fungal growth in the presence of 200 to 1000 µL/L of AuNP suspensions (or Au content of 0.098 to 0.49 µg/mL) provided semi-quantitative information on their nanotoxicity, focusing on the comparison between non-irradiated and green-light-exposed gold nanoparticles.

Coatings doi: 10.3390/coatings16060656

Authors: Elli Alysandratou Theodore Ganetsos Antreas Kantaros

Everyday heritage objects are often overlooked despite their cultural significance and vulnerability to surface degradation caused by environmental exposure, material ageing, and human interaction. This review examines how surface characterization, digital documentation, additive manufacturing, and extended reality (XR) technologies can be integrated to support the conservation, replication, and inclusive dissemination of such assets. The study synthesizes recent advances in non-destructive surface analysis methods, including spectroscopic and imaging techniques, alongside 3D scanning approaches capable of capturing both geometry and surface condition. These data are linked to additive manufacturing workflows for producing accurate and durable replicas, with particular attention to surface fidelity and material selection. The review further explores how tactile replicas and multimodal interpretation strategies can enhance accessibility for visually impaired users, addressing limitations of visually dominant heritage practices. XR technologies are discussed as complementary tools for interpretation and remote access. The findings highlight that combining surface-focused conservation with digital and fabrication technologies enables more resilient, accessible, and sustainable heritage management. Future research should focus on standardizing inclusive design approaches and improving the integration of surface data into digital and physical reproduction pipelines.

Coatings doi: 10.3390/coatings16060655

Authors: Marlon H. Guerra-Mutis Raul Arrabal Marta Mohedano María Isabel Barrena Jesus M. Vega Javier Díaz Gutiérrez Endzhe Matykina

The present work compares the corrosion performance of additively manufactured (AM) Ti-6Al-4V ELI (Extra-Low Interstitials) alloy manufactured by Laser-Powder Bed Fusion (L-PBF) using virgin powder (Cycle 1/C1 sample) and reused powder feedstock after up to 34 cycles (Cycle 34/C34 sample) of manufacturing. The effect of powder reuse is also evaluated for anodizing and Flash-PEO-coated specimens in Harrison’s (25 °C) and Hanks’ solutions (37 °C), representing simulated atmospheric precipitation and physiological conditions, respectively. Specimens were characterized using common metallographic techniques, X-ray diffraction, scanning electron microscopy and optical profilometry. Corrosion resistance was evaluated using cyclic potentiodynamic polarization (PDP) tests. The oxygen content in the Ti-6Al-4V reaches 0.14 wt.% after 34 cycles (C34) of powder reuse, enhancing its passivity in both Harrison’s and Hanks’ solutions. Both virgin and reused powder builds are susceptible to localized corrosion in Hanks’ solution at potentials above 1.75 V. Melt pool borders are thought to be the preferential sites for localized corrosion, as indicated by Volta potential measurements (ΔV = 100 mV). The number of cycles does not significantly affect the current–voltage responses for anodizing and flash-Plasma Electrolytic Oxidation (Flash-PEO) treatments, although anodizing is slightly more responsive to variations in surface roughness (i.e., real specimen area). Anodizing and Flash-PEO reduce the passive current density by nearly two orders of magnitude. Even after surface treatment, the alloy printed with reused powder revealed better passivity. Flash-PEO coatings yielded significant protection against localized corrosion. This unlocks Flash-PEO processing as a successful protection approach for AM biomedical components.

Coatings doi: 10.3390/coatings16060654

Authors: Guoqun Wu Rui Wang Mengxia Ji Qiuqiao Jiang Ruoyu Wang Jieren Guan Wei Lin

Titanium alloys exhibit exceptional properties that enable their widespread application. Additive manufacturing (AM) technologies offer significant advantages for titanium alloy components, including rapid prototyping, high forming accuracy, and enhanced performance. Consequently, substantial research and industrial applications have emerged in the field of titanium alloy AM. Nevertheless, a systematic comparison and synthesis of related studies remains lacking. This paper reviews four distinct categories of titanium alloy AM processes classified by energy source (laser, electron beam, electric arc, and compressed air-assisted). Each category is analyzed in detail, with comparative assessments of microstructures, performance, and applications. Secondly, the paper comprehensively discusses current and potential applications of titanium alloy AM across aerospace, medical, and industrial sectors while identifying critical research gaps for future development. Finally, the development of novel titanium alloys for AM, titanium alloy AM assisted by acoustic or magnetic fields, and 4D printing of functional titanium alloys are discussed.

Coatings doi: 10.3390/coatings16060653

Authors: Xirui Gao Yanjing He Xian Zou Lin Zhang

Nickel–aluminum bronze (NAB) propellers can be severely damaged by the synergistic action of chloride corrosion and solid–liquid erosion in marine environments. However, the direct application of micro-arc oxidation (MAO) to NAB is fundamentally hindered because NAB is a non-valve metal. Herein, this limitation is circumvented via a novel hybrid strategy integrating friction stir welding (FSW) and MAO. A defect-free aluminum transition layer is first fabricated onto NAB by FSW and thinned to ~30 μm for MAO. An Al2O3-based composite ceramic coating is synthesized, exhibiting a duplex structure with α/γ-Al2O3 and an amorphous Si-O network. The coating demonstrates a nano-hardness of 16.2 ± 2.0 GPa and an elastic modulus of 251.3 ± 31.1 GPa, underpinned by a robust interfacial tensile strength of 72.7 MPa. In 3.5 wt.% NaCl, the corrosion current density is suppressed to 1.335 ± 0.151 × 10−7 A/cm2, while the charge transfer resistance reaches 3.072 × 105 Ω·cm2. Mass loss after 30-day immersion is reduced to ~1/11 of NAB, and erosion loss at 400 rpm is ~1/8 of that of the substrate. Electrochemical results indicate that the Al transition layer provides an initial beneficial contribution, while the MAO ceramic coating further delivers the dominant barrier protection, together leading to the best overall corrosion resistance of the hybrid-treated sample.

Coatings doi: 10.3390/coatings16060652

Authors: Edwin E. Alferez Fabio F. Vallejo Carlos M. Moreno Jhon J. Olaya Luis C. Ardila

The reuse of WC–Co cutting inserts is a relevant strategy to reduce tooling costs and the consumption of critical raw materials, such as W and Co. Still, the effect of stripping and re-coating cycles on tool performance remains largely unexplored. This work investigates the wear behavior of carbide inserts coated with four PVD nitride systems—CrN, TiAlN, TiAlCrN, and TiAlCrSiN—during CNC turning of AISI 4340 steel. A single cutting edge was subjected to two complete reuse cycles consisting of machining six workpieces, electrolytic stripping of the worn coating, and PVD re-deposition. Tool wear and surface integrity were evaluated by 3D optical profilometry, roughness measurements, and SEM/EDS analysis. CrN exhibited progressive crater and flank wear with large material-loss volumes and increasing roughness. TiAlN exhibited pronounced built-up edge/layer formation, resulting in mixed adhesion–spallation behavior and degradation of roughness in the second cycle. TiAlCrN developed stable adhesive layers with limited coating loss, and after re-coating, its roughness decreased from ~2.7 µm to ~1.0 µm. The most complex coating, TiAlCrSiN, provided the lowest roughness (~1.3–1.6 µm) and the smallest wear volumes in both cycles, associated with a fine Al–Si-induced nanostructure and improved oxidation resistance. The results demonstrate that multicomponent nanostructured coatings, particularly TiAlCrN and TiAlCrSiN, can withstand at least one stripping and re-coating cycle without performance loss, supporting the feasibility of controlled insert reuse in turning AISI 4340 steel.

Coatings doi: 10.3390/coatings16060651

Authors: Yibo Xiong Yun Qin Zeyu Ma Wenwu Wang Xiyao Huang Huimin Liang Zilu Hu Xiaoqiao Liao Junyi Zheng Guobin Zhang Liang He

Ester-based electrolytes in sodium-ion batteries (SIBs) offer high oxidative stability but often suffer from poor stability of the solid electrolyte interphase (SEI) on hard carbon anodes, severely limiting fast-charging capabilities and cycling lifespan. To address this interfacial instability, this work introduces trimethoxysilane (HTOS) as an electrolyte additive into 1 M NaPF6 in EC:DMC electrolyte (denoted as ED). Compared with the rough and inorganic-rich interphase formed in the ED electrolyte, the HTOS additive induces the formation of a smoother, more uniform, and organic-rich SEI. This optimized interfacial structure effectively suppresses continuous interfacial degradation during cycling and significantly reduces the apparent activation energy for Na+ migration. Consequently, the HTOS-modified electrolyte demonstrates markedly superior electrochemical performance, delivering a reversible capacity of 198.76 mAh g−1 at 1C and maintaining 85% of the initial capacity after 200 cycles at 0.5 C. This study demonstrates that utilizing silicon-containing functional additives for SEI regulation is a highly effective strategy to enhance the fast-charging and long-term cycling stability of hard carbon anodes in SIBs.

Coatings doi: 10.3390/coatings16060650

Authors: Tingchen Yan Yaming Jia Ning Liu Hongshui Wang Chunyong Liang

This study aimed to address the clinical challenge of secondary caries prevention in dental restorations. Leveraging the sustained fluoride-releasing capacity of calcium fluoride (CaF2) and the broad-spectrum antibacterial activity of zinc oxide (ZnO), we designed and synthesized a novel core–shell CaF2@ZnO nanoparticle filler to synergistically enhance the functional performance of dental resin composites. The filler was successfully prepared via a co-precipitation-hydrothermal method, and its well-defined core–shell architecture was systematically confirmed using XRD, SEM, and TEM. When incorporated into the resin matrix at 10 wt.% loading, the composite containing CaF2@30ZnO demonstrated optimal overall performance. Notably, this formulation enabled sustained fluoride ion release, potent antibacterial efficacy, and excellent in vitro cytocompatibility. Collectively, these findings demonstrate that the CaF2@ZnO nanofiller confers multifunctional benefits—including improved mechanical integrity, long-term fluoride release stability, and targeted antibacterial action—thereby holding significant promise for clinical application in mitigating secondary caries around resin-based restorations.

Coatings doi: 10.3390/coatings16060649

Authors: Haisheng Zhao Wenbin Gao Peiyu Zhang Chongji Diao Chunhua Su Bokai Liu Hongshan Shang Shijie Ma

Polyurethane (PU) mixtures are a promising high-strength, rapid-curing alternative to conventional asphalt, but their widespread application is hindered by slow curing rates and sensitivity to ambient moisture. To address these limitations, this study systematically evaluated the efficacy of three additives—lignin-based fiber, Glauber’s salt, and green vitriol—in regulating the curing behavior and performance of PU mixtures. Marshall stability, volumetric properties, and moisture resistance were measured under both outdoor and controlled laboratory curing conditions. Lignin fiber uniformly accelerates early-stage curing by enhancing moisture distribution via capillary action. Glauber’s salt releases crystalline water, drastically boosting early-age strength (by 162.4% after 2 days) but at the cost of an increased air void content (up to 8.1%) and reduced long-term water stability (residual stability <80%). Green vitriol acts through Fe2+ catalysis and crystalline water release, with its effectiveness being highly temperature- and delay-time-dependent. Combining fiber with Glauber’s salt yields the highest early strength but the shortest construction window (<1 h) and the most severe volumetric deterioration beyond the optimal delay time. All mixtures achieved high ultimate strength after sufficient curing (7 days), but the improvement varied significantly with additive type—ranging from 52.2% (fiber alone) to 162.4% (Glauber’s salt alone). Moreover, even under ideal curing, incomplete –NCO conversion persisted, indicating intrinsic cross-linking limitations. The residual stability of all mixtures fell below the 80% specification for conventional asphalt, suggesting that this metric alone is insufficient for assessing the moisture resistance of high-strength PU mixtures. This study demonstrates that while additives significantly enhance early-age performance, their application requires carefully optimized dosage, delay time, and temperature control to balance early strength gains with long-term volumetric integrity and durability. The findings provide revised evaluation metrics and practical guidelines for implementing PU mixtures in rapid pavement construction and repair.

Coatings doi: 10.3390/coatings16060648

Authors: Vladimir Syasko Alexey Musikhin Igor Gnivush Maria Stepanova Anna Vinogradova

This study assesses the possibility of identifying non-through defects in dielectric coatings, specifically interfacial defects located at the metal–coating boundary, by means of high-voltage non-destructive testing. It is demonstrated that partial discharges causing characteristic distortions of the applied test-voltage pulse can be used as a reliable diagnostic feature of such defects. Using an equivalent capacitive representation of a defective coating, a relationship is established between the apparent charge and the geometry of the air-filled gap. The proposed approach is supported by COMSOL simulations of the electric-field distribution and by experiments performed on Plexiglas specimens containing blind holes of different depths. In addition, a method is developed for isolating the partial-discharge signal based on a weighted sum of increments in the root-mean-square deviations of the second derivative of the voltage waveform. The resulting relationships enable estimation of the residual coating thickness in the defect region.

Coatings doi: 10.3390/coatings16060647

Authors: Christian Marisol Clemente Mirafuentes Manuela Alejandra Zalapa Garibay Juan Carlos García Castrejón José Omar Daválos Ramírez Lázaro Rico Pérez

Corrosion fatigue is an accelerated failure mechanism in metallic components and coated systems, where the effectiveness of the polymer coating is determined by the structural integrity and adhesion at the coating/substrate interface. This study investigated the corrosion fatigue interaction in AISI 410 steel with and without a poly(3-hexylthiophene)/poly (methyl methacrylate) (P3HT/PMMA) coating exposed to a 3 wt.% NaCl solution under four stress levels ∆σ at room temperature. Electrochemical noise (EN) was recorded during the test, the surface and interface were characterized using scanning electron microscopy (SEM), and the mechanical behavior was quantified using da/dN vs. ∆K and σ vs. N curves. The coated samples exhibited a wider potential range (≈±400 mV) than the uncoated steel (≈±200 mV), indicating localized electrochemical activity under the coating. SEM observations revealed microblisters at low stress levels and coating cracking at high stress levels, with localized substrate exposure, slip bands, and microcracks. Overall, the results showed that the corrosion fatigue is governed by electrochemical activity under the coating and cathodic delamination, which reduces adhesion, locally exposes the steel, and causes the initiation and propagation of cracks.

Coatings doi: 10.3390/coatings16060646

Authors: Muyao He Liyan Tao Yile Chen

Solid amine adsorbents can capture CO2 at indoor-relevant concentrations (~1000 ppm), but many high-capacity adsorbents rely on granular or powdery supports that are difficult to integrate directly into air purification systems. Here, we applied three amination strategies to commercial fibrous substrates: bridge-grafting on viscose (TEPA-AMVF), direct grafting on polyacrylonitrile (TEPA-PAN), and physical impregnation on pore-engineered activated carbon fibre felt (PEI-ACF). These adsorbents were systematically screened under simulated indoor conditions (1000 ppm CO2, 27 °C, 50% RH). A significant capacity difference was observed: TEPA-AMVF (24.8 mg g−1) < TEPA-PAN (35.8 mg g−1) ≪ PEI-ACF (97.0 mg g−1). The superior performance of PEI-ACF was attributed to KOH activation, which produced a mesopore-rich structure (average pore diameter 26.1 nm at an optimal KOH/carbon ratio of 1.25) and enabled high nominal amine utilisation (0.19 mmol CO2 mmol N−1). PEI-ACF maintained high breakthrough-derived CO2 uptake across realistic indoor conditions (64.2–118.6 mg g−1 over 0%–100% RH; 71.6–124.5 mg g−1 over 400–5000 ppm CO2), exhibited rapid kinetics (pseudo-first-order rate constant k = 1.77 h−1; 81.7% of equilibrium uptake within 1 h), and showed stable but partial regeneration over four adsorption–desorption cycles at 60–70 °C under N2. Compared with granular or resin-based amine sorbents, the self-supporting PEI-ACF felt is expected to offer practical advantages for filter-integrated CO2 removal, including mechanical integrity under airflow, reduced risk of particle leakage, and compatibility with HVAC filter slots. Remaining challenges include direct pressure-drop validation, operation in O2-containing indoor air, long-term cycling, and management of CO2 released during regeneration.

Coatings doi: 10.3390/coatings16060645

Authors: Lei Shi Zhongxia Liu Aiyun Jiang Bin Cai Bo Ren

To optimize the overall performance of as-cast 8021 aluminum alloy billets for power battery foil, this study explores how Ce addition (0–0.4 wt.%) regulates microstructure, mechanical properties, and corrosion resistance via second-phase reconstruction. Microstructure characterization, mechanical property testing and electrochemical corrosion tests were performed. The results show that Ce addition first refines, then stabilizes, and finally coarsens α-Al grains. The addition of 0.2 wt.% Ce promotes the formation of tentatively identified dispersed Al–Ce–Fe ternary phases, achieving the optimal combination of ductility (elongation: 42.7%) and strength (tensile strength: 95.0 MPa), as well as superior corrosion resistance (icorr = 2.79 × 10−7 Acm−2). Excessive Ce led to possible precipitation of the Al2Ce phase and grain coarsening, deteriorating alloy properties. In conclusion, 0.2 wt.% Ce is the optimal content to balance the microstructure, mechanical and corrosion properties of 8021 aluminum alloy, providing a theoretical basis for its compositional optimization of as-cast billet for battery foil applications.

Coatings doi: 10.3390/coatings16060644

Authors: Hualin Song Yongzhe Feng Di Wu Qifeng Chen Yaofeng Liu Peng Mo Xinru Ding

To investigate the pitting evolution behavior of carbon steel in industrial–coastal atmospheric environments, a multiphysics numerical model was established by coupling tertiary current distribution, mass transport, and deforming geometry based on electrochemical corrosion mechanisms. Based on this framework, the effects of pH, salt concentration, and relative humidity (RH) on the pitting corrosion rate were systematically analyzed, and a predictive model for the pitting rate was subsequently developed. The results indicate that the pitting morphology gradually evolves from an initial conical shape to a hemispherical morphology and eventually develops into a quasi-cylindrical form. When the pH value increases from 6.0 to 7.0, the pitting rate decreases significantly, with a maximum reduction of 23.96%. Within the salt concentration range of 0.5%–1% (mass fraction), increasing salt concentration markedly accelerates the pitting process, resulting in a maximum increase in the pitting rate of 10%. In addition, the pitting rate exhibits a pronounced peak within the RH range of 72%–77%. The corrosion rates predicted by the proposed model are in good agreement with the experimental results, with relative errors within 5%. These results indicate that the numerical model and prediction formula established in the present study can reasonably predict the pitting evolution behavior and corrosion rate of carbon steel.

Coatings doi: 10.3390/coatings16060643

Authors: Irina Aleksandrova Hristian Mitev

The objective of the grinding process is to obtain a better surface finish (roughness, accuracy, etc.) or a high material removal rate of the workpiece. These grinding process response variables depend largely on both the grinding conditions and the topography of the grinding wheels formed during dressing. In this regard, the paper focuses on determining the optimal dressing conditions for grinding wheels dressed with diamond roller dressers during rough and finish grinding. A new multi-objective optimization approach for determining dressing conditions has been proposed, which leads to Pareto-optimal solutions for increasing the grinding process production rate, reducing roughness, and increasing the accuracy of ground surfaces. To demonstrate the performance of this approach, one process of dressing electrocorundum grinding wheels with novel diamond rollers made of medium- and high-strength synthetic diamonds with mixed grain sizes has been selected. Empirical models have been developed to examine the production rate of the grinding process, the roughness of the ground surfaces, and the accuracy of the machined parts. Multi-objective optimization based on a genetic algorithm has been performed by applying two methods: determining an optimal compromise area for the dressing process conditions, and the weighted utility function method. The novelty of the implementation is due to the process of identifying the precise optimal dressing parameters specifically for the investigated mixed-grit diamond rollers. The optimization results show that rough grinding requires uni-directional dressing with a diamond roller AC32 at a feed rate of 1.4 mm/min, a dressing speed ratio of 0.8, a dress-out time of 1.0 s, and a grit size ratio of 2.56, ensuring a production rate of 875 mm3/min, a surface roughness Ra up to 1.25 µm, and a cylindricity deviation up to 12.5 µm. For fine grinding, optimal counter-directional dressing parameters include a feed rate of 0.26 mm/min, a speed ratio of 0.23, a dress-out time of 5.0 s, and a grit size ratio of 2.2, which guarantee a minimum surface roughness Ra of 0.38 µm, a cylindricity deviation of 8.1 µm, and a production rate of at least 600 mm3/min.

Coatings doi: 10.3390/coatings16060642

Authors: Sema Samatya Yılmaz Melek Demirel Selda Daler Rezzan Kasım Mehmet Ufuk Kasım Ayşe Aytaç

In this study glycerol-plasticized sodium caseinate/polyvinyl alcohol NaC/PVA composite films were prepared by solution casting, and the effects of incorporating caffeic acid powder at different concentrations 0% 2.5% 5% and 15% w/w on structural mechanical barrier and postharvest performance were investigated. Caffeic acid (CA) (3,4-dihydroxycinnamic acid) is a naturally occurring phenolic compound commonly found in plant tissues and food sources such as apples, blueberries, and coffee. FTIR analysis revealed that shifts and broadening in OH bands indicated hydrogen bonding interactions between caffeic acid and the polymer matrix influencing structural organization. The pure NaC/PVA film exhibited high WVTR due to glycerol while maintaining low OTR. Adding 2.5% caffeic acid reduced WVTR but increased OTR through structural disruption. At 5% a continuous hydrogen-bonded network formed, restricting chain mobility and reducing free volume, thus lowering WVTR and OTR while preserving mechanical integrity. SEM micrographs revealed that high CA concentrations, particularly at 15%, led to aggregation-induced partial phase separation and consequent performance loss. Packaging treatments mainly affected physical and color attributes rather than primary metabolites. The NaC/PVA/5CA reduced weight loss and delayed sugar accumulation compared with NaC/PVA. Sugars peaked earlier in NaC/PVA but increased continuously in NaC/PVA/5CA, reaching maximum at the final storage stage. These findings indicate concentration-dependent mechanisms and highlight the potential of caffeic acid-based active packaging to regulate metabolism and extend postharvest quality. Overall results support its application in sustainable packaging systems for improved shelf life management.

Coatings doi: 10.3390/coatings16060641

Authors: Taotao Cheng Peng Chen Jiayouyu Jiang Jianhai Yu Kunying Ding

Ceramic thermal protective coatings during long-term service in high-temperature environments are prone to micropore shrinkage, grain coarsening, and porous structure collapse, leading to severe densification. This consequently degrades the durability and reliability of the ceramic coatings. This paper elucidates the sintering densification mechanism of ceramic coatings, analyzes innovations in material systems and multidimensional structural design strategies, and summarizes the state-of-the-art research progress on anti-sintering densification of ceramic coatings. The limitations of conventional techniques that inhibit high-temperature sintering densification via “passive pore retention” are highlighted. A novel strategy based on phase transformation-induced pore formation for achieving “active in situ pore generation” is explored. On this basis, future research directions for enhancing the anti-sintering densification performance of ceramic thermal protective coatings are proposed.

Coatings doi: 10.3390/coatings16060640

Authors: Aiyi Chen Jionghong Liang Haojie Liu Haixing Feng Xiaolong Tang Ziyin Zheng Xutong Zhou Jiangwen Liu Guie Xie

Thrombosis remains a critical challenge for blood-contacting implants, with early-stage protein adsorption and platelet activation playing decisive roles. In this study, we constructed a TiO2/CuO semiconductor heterojunction on titanium surfaces to generate a stable built-in electric field, creating a self-activated bioelectric microenvironment without external stimulation. We evaluated its cytocompatibility and hemocompatibility through static in vitro assays. To distinguish the contributions of surface chemistry, topography, and bioelectric cues, we include control groups of Ti (untreated), TNW (TiO2 network, topography control), and Ti/CuO (CuO nanoparticles without heterojunction, Cu2+ release control). The heterojunction significantly enhances human umbilical vein endothelial cell (HUVEC) adhesion and proliferation while simultaneously suppressing fibrinogen adsorption, platelet adhesion/activation (as assessed by morphological changes), and whole-blood cell adhesion. Compared with Ti/CuO, the heterojunction (TCH) induces substantially stronger endothelialization and anticoagulant effects despite similar Cu2+ release levels (~0.047 μM, far below the reported pro-angiogenic threshold of ~5.0 μM), indicating a predominant role of the built-in electric field. This study preliminarily demonstrates a previously unrecognized role of bioelectric cues in modulating early blood–material interactions. Following rigorous validation under physiologically relevant dynamic flow conditions and in vivo models, interfacial bioelectric engineering emerges as a promising new strategy for designing anticoagulant biomaterials.

Coatings doi: 10.3390/coatings16060639

Authors: Victor Saciotto Joern Kohlscheen Stephen Veldhuis

Controlling deposition parameters is fundamental to obtaining the desired properties of cathodic arc physical vapor deposition (PVD) coatings. Achieving uniform coatings on tools with complex, sharp geometries remains a significant challenge due to localized ion flux concentration. Pulsing the substrate bias is an effective way of controlling deposition energy. However, while widely used in cathodic arc PVD, the relationship between the actual bias waveform, coating integrity on sharp tool geometries, and resulting machining performance has not been systematically established. This study investigates the effect of pulsed bias duty cycle (20% to 90%) and frequency (1 to 20 kHz) on the microstructural evolution, residual stress state, and machining performance of AlTiN coated tools. Real-time oscilloscope measurements demonstrated that system inductance and capacitance significantly distort the ideal bias waveform. Microstructural analysis via Focused Ion Beam/Scanning Electron Microscopy (FIB/SEM) cross-sectioning confirmed that all bias parameters generated a dense microstructure. While pulse frequency had no significant influence on micromechanical properties or residual stress states, the duty cycle was the dominant variable. High-energy deposition (90% duty cycle) increased hardness to 33.9 GPa but generated severe compressive residual stresses (−5.2 GPa). This extreme compressive stress led to catastrophic edge delamination on sharp solid carbide endmills. Conversely, a low-energy 20% duty cycle generated a coating with lower hardness (29.4 GPa) and a near-neutral stress state (0.5 GPa), effectively preserving the edge integrity. Unlike the endmills, the turning inserts maintained their edge integrity across all deposition conditions. During the high-speed (350 m/min) dry turning of AISI 304 stainless steel, all evaluated coatings exhibited comparable tool life and cutting forces. Wear progression was characterized by rake cratering, combined with abrasion and adhesion-induced attrition on the flank. The results indicate that tool life in this extreme environment is governed primarily by high-temperature thermo-chemical stability rather than initial room-temperature hardness. Lower-energy pulsed bias deposition therefore represents a robust strategy for coating a wide range of tool geometries, delivering equivalent high-speed machining performance while preventing stress-induced delamination on sharp features.

Coatings doi: 10.3390/coatings16060638

Authors: Mengfu Zhao Yiming Wen Changle Xiao Fei Hai Hongyan Wu

Copper busbar inserts are critical components of high-voltage connectors in new energy vehicles. The interfacial contact stress between the insert and the polymer directly affects the sealing reliability and service life of the connector. To address the interfacial stress concentration caused by the mismatch in thermal expansion coefficients between metal and polymer, this study employs COMSOL Multiphysics 6.2 simulations to investigate the regulation laws of arc-shaped and trapezoidal microstructures on the interfacial stress of copper–polyphenylene sulfide (PPS)/polypropylene (PP). The response surface methodology (RSM) is introduced to verify simulation reliability and optimize parameters. The simulation results indicate that both structures can effectively reduce interfacial stress, and the stress exhibits a significant nonlinear relationship with the structural parameters. Due to its high temperature resistance and polar thioether bond, PPS demonstrates better interfacial compatibility than PP. Under the same structural position, the maximum stress reduction exceeds 20% (from 0.689 MPa to 0.539 MPa). Moreover, the arc-shaped structure is more effective in alleviating stress concentration than the trapezoidal structure. At the same position, compared to the trapezoidal surface, the arc-shaped surface reduces the valley contact stress of PPS from 0.527 MPa to 0.5 MPa (a decrease of 5.12%) and that of PP from 0.679 MPa to 0.605 MPa (a decrease of 10.9%). The optimal parameters are as follows: an arc-shaped radius width of 1.0 mm, a depth of 0.8 mm; a trapezoidal bottom base of 2.0 mm, a height of 1.2 mm. This study provides a basis for the interface design of metal–polymer composite components and holds significant engineering value for the reliability optimization of high-voltage connectors.

Coatings doi: 10.3390/coatings16060637

Authors: Xianghua Zhan Changfeng Fan Peng Yi Wenlong Feng Yancong Liu

Combining surface texturing and solid lubricant coating is an effective approach to improve tribological performance and service life in surface engineering. However, few studies have systematically compared texture types and their adaptability to varying working conditions. In this work, a textured composite coating with a three-level gradient structure (interface texture–coating–surface texture) was prepared via plasma spraying and laser texturing. Reciprocating dry friction tests were carried out to compare the tribological properties of dimple, linear, and sinusoidal textures. The effects of normal load and sliding speed on friction and wear behavior were investigated. Results demonstrate that the average friction coefficients follow the order: non-textured coating > dimple-textured coating > linear-textured coating > sinusoidal-textured coating. The sinusoidal texture provides the lowest friction coefficient and superior debris capture and storage capacity, which effectively mitigate abrasive wear, adhesive wear, and fatigue spalling, leading to optimal friction reduction. Increasing the load moderately reduces the friction coefficient, but the coating fails rapidly due to severe plastic flow and adhesive tearing when the load exceeds 100 N. The textured composite coating presents favorable velocity adaptability with a friction coefficient reduced by 23.8%–41.3% relative to the non-textured coating. Yet the texture fails rapidly when the sliding speed exceeds 100 mm/s because of intensified adhesive wear and plastic deformation.

Coatings doi: 10.3390/coatings16060636

Authors: He Lu Yuhou Wu Jinghua Li

To further improve the high-temperature dry sliding performance of Si3N4 ceramics, a CrAlN transition layer was introduced to improve interfacial stability, while Ag was incorporated as a solid lubricant into the CrAlN matrix. The effects of Ag content on the microstructure and mechanical properties of the coatings were systematically examined, and the tribological performance was evaluated from 25 °C to 550 °C under dry sliding conditions. The Ag concentration increased with increasing Ag target power and affected the morphology, nanoparticle distribution, surface roughness, and mechanical properties of the coatings. Among the tested samples, the coating containing 9.6 at.% Ag exhibited a comparatively favorable combination of mechanical properties within the investigated composition range, with a hardness of 11.5 GPa, an H/E ratio of 0.0913, and an H3/E2 value of 0.096 GPa. Tribological tests showed that the average coefficient of friction decreased from 0.32 at 25 °C to 0.12 at 550 °C. This reduction may be associated with temperature-assisted Ag redistribution toward the worn surface and the possible development of Ag-rich surface features at elevated temperatures. However, the wear rate increased with temperature, reaching 3.6 × 10−5 mm3/(N·m) at 550 °C, suggesting that friction reduction was accompanied by increased material removal and possible near-surface weakening. These results indicate that controlling Ag content is important for balancing friction reduction and wear resistance in ceramic-based self-lubricating coatings.

Coatings doi: 10.3390/coatings16060635

Authors: Nanling Deng Zegang Zhang Qing Gao Hongbing Zhang Hongqing Wang Rui Li Wei Gong Zhusheng Yang

Lithium–sulfur (Li–S) batteries hold great promise for next-generation energy storage owing to their ultrahigh theoretical energy density; however, their practical application is severely hampered by the polysulfide shuttle effect and the penetration of lithium dendrites through the separator. In this work, a carboxyl-containing anionic polymer (TPU-DMBA) is synthesized and composited with Ketjen Black (KB), and the resulting mixture is coated onto a commercial polypropylene separator via a simple doctor-blade method. In this design, the porous KB network provides physical adsorption to capture polysulfides, while the dissociated carboxylate groups (–COO−) generate strong electrostatic repulsion against negatively charged polysulfide anions (Sn2−). This dual-mechanism strategy—adding electrostatic repulsion on the basis of physical adsorption—effectively suppresses the shuttle effect. In addition, the flexible polymer backbone increases the tensile strength of the separator by approximately 30%, enhancing its resistance against dendrite penetration. The carbon material also significantly improves electrolyte wettability (the contact angle decreases from 41.6° to 11.7°) and ionic conductivity (from 0.48 × 10−3 to 0.88 × 10−3 S cm−1). The polymer itself acts as a binder, eliminating the need for additional binder addition. Benefiting from the synergy of electrostatic repulsion, physical adsorption, and mechanical reinforcement, the prepared modified separator endows the Li–S battery with an initial specific discharge capacity of 1373.15 mAh g−1 at 0.1 C and an initial discharge capacity of 714.46 mAh g−1 at a high rate of 2 C. After 200 cycles at 2 C, the capacity remains 577.93 mAh g−1, with a capacity retention of 80.89%. This work provides a low-cost, scalable, and binder-free separator modification strategy that simultaneously suppresses the polysulfide shuttle and resists dendrite growth, opening a new and effective pathway toward practical high-performance Li–S batteries.

Coatings doi: 10.3390/coatings16060634

Authors: Kseniia Burkovskaia Michał Strankowski Krzysztof Szafran

Graphene derivatives and nano-silicon dioxide (nano-SiO2) have been widely studied as functional nanofillers for architectural coatings. They have the potential to improve mechanical performance, barrier properties, durability, and versatility. However, despite encouraging results in laboratory settings, their use in commercial coating formulations is still limited. This is mainly due to challenges with dispersing nanoparticles, ensuring compatibility with polymer binders, maintaining long-term durability, and achieving formulation stability. In this work, we conducted a thorough review and meta-analysis of 20 peer-reviewed studies to evaluate the performance and limitations of graphene-based materials and nano-SiO2 in architectural and protective coatings. Our literature search followed PRISMA guidelines and included studies that provided quantitative data on dispersion methods, surface functionalization strategies, nanofiller loading levels, and coating performance metrics. This review highlights key relationships between structure, properties, and processing. It points out ongoing challenges that prevent practical use and suggests future research directions to enhance formulation design, improve dispersion stability, and extend the long-term performance of graphene- and nano-SiO2-modified architectural and protective coatings.

Coatings doi: 10.3390/coatings16060633

Authors: Xiaorui Liang Debiao Zhang Fushun Nian

To realize the real-time structural health and operational safety monitoring of military and industrial devices, such as hypersonic vehicles, aero-engine blades, and thermal power plant boilers, at operating temperatures up to and beyond 1400 °C, this study presents a miniaturised, integrated, high-thermal-stability wireless sensor device. This study investigated the influence of temperature on the interdigital electrodes (IDEs) of surface acoustic wave (SAW) temperature sensors for three configurations: bare electrode, single-layer protective film, and multilayer composite film. While the exposed electrode exhibited thermal stability at 1000 °C, it underwent structural failure at 1250 °C. To achieve health monitoring at temperatures exceeding 1400 °C, an Al2O3/AlN/Al2O3 multilayer protective architecture was developed. The device demonstrated functionality up to 1400 °C with a temperature coefficient of frequency (TCF) of −40.03 ppm/°C, yielding a sensitivity of 12.0 kHz/°C at a center frequency of ~300 MHz. The electrode protection structure elevated the maximum operating temperature. A hybrid heterogeneous integration of high-temperature co-fired ceramic (HTCC) inverted-F antenna and a Langasite (LGS) SAW device with a multilayer composite film was realised. The wireless device maintained functionality from room temperature to 1400 °C and withstood 1400 °C for 2 h, exhibiting a maximum repeatability error of 12.67% (corresponding to a temperature measurement error of ~177.4 °C at 1400 °C). This integrated design enables the miniaturization of high-temperature wireless sensors, making them suitable for harsh environments.

Coatings doi: 10.3390/coatings16060632

Authors: Xiaoyuan Hu Xuejing Yao Pingping Zhao Yan Liu Faguo Li

A Ti-Al-Si composite coating was prepared on Ti65 titanium alloy using a two-step hot-dipping + pre-oxidation method to improve its tribological performance and high-temperature oxidation resistance. The second-step dipping time strongly affected the coating microstructure and wear behavior. The optimal coating, prepared with a dipping time of 5 min in each step, exhibited negligible wear after oxidation at 800 °C for 1000 h and 2500 h, with slight adhesive wear and oxidative wear as the dominant mechanisms. Longer dipping times led to mixed wear modes and reduced wear resistance. Under high-temperature corrosion conditions, the coating showed good long-term stability in water vapor, with its mass gain following a sub-parabolic law, Δm = 0.39·t0.47, because the internal multilayered structure effectively blocked inward oxygen diffusion. However, in environments containing NaCl or 75 wt.% Na2SO4 + 25 wt.% NaCl, catastrophic hot corrosion occurred, regardless of the presence of water vapor, through a chlorine-driven oxidation–chlorination–reoxidation autocatalytic cycle. In the mixed salt environment, Na2SO4 decomposition supplied additional oxygen and alkaline species, accelerating the degradation and spallation of the Al2O3 and TiO2 scales. Water vapor further intensified this cycle by generating HCl, which promoted rapid consumption of Al and Ti in the coating. This study reveals the wear behavior and hot corrosion failure mechanisms of Ti-Al-Si coatings under complex conditions, providing guidance for process optimization and applications in marine atmospheres.

Coatings doi: 10.3390/coatings16060631

Authors: Chunlin Lu Weiming Liu Hailian Wei Hairong Gu Yun Zhang Lei Cui Hongbo Pan Huiting Wang Xiaohui Shen Yonggang Liu Yangyang Xiao

The corrosion behavior and time-dependent mechanism of 22MnB5 steel featuring a thinned Al-Si coating (60 g/m2) were systematically investigated in a chloride ion wet–dry cyclic environment, motivated by the demand for thinning and toughening development of aluminum-silicon coatings. A periodic immersion accelerated corrosion test using 3.5% NaCl solution was conducted, together with macro/microscopic morphology observation (SEM/EDS), phase analysis (XRD, FTIR), and electrochemical measurements (polarization curves, EIS). The Al-Si coated steel was studied over corrosion periods of 1, 8, 10, and 20 days to elucidate its corrosion behavior, interfacial evolution, and failure mechanism. The results indicated that the corrosion process exhibited a three-stage evolution: stable protection, rapid failure, and dynamic equilibrium. At the initial stage (1 day), a dense Al2O3 passive film formed on the coating surface, providing excellent substrate protection, with a corrosion current density of only 1.77 µA/cm2 and a maximum charge-transfer resistance (R2) of 652 Ω·cm2. In the middle stage (8 days), Cl− permeated through the cracked film, triggering selective dissolution of Al, while Si was enriched in situ to form a porous residual layer; the corrosion current density (Icorr) sharply increased to 13.25 µA/cm2, and R2 dropped to its minimum of 156.6 Ω·cm2. Corrosion products at this stage were mainly Al2O3 and SiO2, accompanied by small amounts of iron oxyhydroxides and hydroxides, and local coating failure began to appear. During the later stage (10–20 days), the corrosion products evolved into γ-FeOOH, α-FeOOH, and Fe2O3, which, together with an amorphous SiO2 gel network enriched at the interface, formed a dual-layer composite rust layer. R2 consequently recovered from 156.6 Ω·cm2 at 8 days to 424 Ω·cm2 at 20 days, indicating a reduced corrosion rate and entry into a stable inhibition stage. The critical failure mechanism is that Cl− preferentially penetrates the surface of the Al2O3 passive film, disrupting the metastable state of the coating and thereby creating pathways for corrosive media intrusion. The findings of this study can provide technical support for the safe application of such as-received coatings in non-load-bearing components with heat and corrosion resistance requirements.

Coatings doi: 10.3390/coatings16060630

Authors: Shuling Zhang Xiangdong Yang Guangjun Liu Lingxin Bu Shuaichao Fan Xinghua Ma

CrN/DLC composited coatings were deposited on 431 stainless steel, and their structure was analyzed, with particular emphasis on the influence of CrN content on the coating properties. X-ray photoelectron spectroscopy (XPS), nanoindentation testing, scratch testing, and reciprocating tribometry were employed to characterize the chemical composition, mechanical properties, adhesion strength, and tribological performance of the coatings, respectively. Structural analysis indicates that when the ratio of CrN/Cr2N is relatively low (<1), a high content of chromium dinitride (Cr2N) is formed in the interlayers, resulting in a porous and loose coating structure. When the ratio achieves 1:1, an optimal balance, with the CrN content reaching a maximum of 21.04% and the Cr2N content decreasing to a minimum of 20.68%, the densification degree of the coatings is increased, the coating adhesion strength is improved to 11.87 N. Meanwhile, the enhanced formation of the CrN phase improves the hardness to 12.27 GPa. Tribological test results demonstrate that when the ratio is approximately 1:1, the coating exhibits the lowest friction coefficients under dry sliding, deionized water, and artificial seawater conditions (0.0932, 0.1409, and 0.1021, respectively), as well as the minimum wear rates. With the decrease in CrN content of the coatings, the interfacial mismatch degree of the coatings is aggravated, which leads to not only more interfacial defects but also a relatively loose structure, as well as a decrease in the bonding strength (6.81 N), hardness (5.22 GPa), and deformation resistance. Therefore, an excessive Cr2N phase may degrade the hardness-to-elastic modulus ratio (H/E) of the coatings by increasing interfacial mismatch and reducing structural compactness.

Coatings doi: 10.3390/coatings16060629

Authors: Jiacheng Zou Haonan He Wei Tian Chengyan Zhu Fei Ye Xiaoke Jin

Surface stain contamination poses a critical barrier to the automated, high-precision fiber identification required for industrial-scale waste textile recycling. In this study, a dataset comprising 120 physical specimens (yielding 1200 regions of interest, ROIs) across 12 contamination categories was constructed by contaminating cotton, polyester, and poly-cotton blend textiles with carbon black, protein, and oil stains. The spectral interference effects of stains—including baseline drift and spectral overlapping induced by physical shielding and chemical absorption—were systematically analyzed. To identify the optimal classification pipeline, three mathematical preprocessing methods (First Derivative, FD; Standard Normal Variate, SNV; and Multiplicative Scatter Correction, MSC) were evaluated alongside Support Vector Machine (SVM) and One-Dimensional Convolutional Neural Network (1D-CNN) models. Results show that among the SVM-based pipelines, the FD-SVM model effectively resolves overlapping absorption peaks, achieved an average accuracy of 98.17% ± 1.33%, but remains highly dependent on mathematical preprocessing. In contrast, the 1D-CNN model employing a progressive stacking architecture of multi-scale convolutional kernels attains a highly robust mean accuracy of 99.58% ± 0.56% under a strict specimen-level 10-fold cross-validation. It achieves this by directly utilizing radiometrically calibrated raw spectra, thereby effectively bypassing manual spectral feature engineering. These findings demonstrate that Hyperspectral Imaging coupled with end-to-end deep learning provides a feasible and industrially deployable solution for simultaneous stain detection and fiber identification in waste textile sorting.

Coatings doi: 10.3390/coatings16050628

Authors: Yue Yu Duo Ma Tong Zhang Yufei Wang Yupeng Wei Mingxuan Shi Yuquan Cai Meigui Cai Peisheng Li Yongfeng Xin Jinquan Sun

In this study, C/N-containing Fe3O4 oxide films over an inner nitride layer were fabricated on 45# steel by oxynitriding to improve corrosion resistance in chloride-containing environments. The films exhibited a dense polyhedral structure, with nanoscale Fe3O4 precipitates at grain boundaries. Nitrogen and carbon were uniformly distributed within the oxide grains, inducing lattice expansion and modifying the Fe-O bonding environment. First-principles calculations based on C/N substitution models suggested that C/N incorporation may increase the unit cell volume, strengthen lattice bonding, and enhance the theoretical hardness of Fe3O4. The optimally doped films exhibited outstanding corrosion resistance, with a corrosion potential of 0.115 VSCE, a corrosion current density of 3.16 × 10−10 A/cm2 in 3.5 wt.% NaCl solution, and a corrosion-free lifetime of up to 3600 h in neutral salt spray testing. This superior performance is attributed to the synergistic effects of the compact single-phase magnetite layer, grain boundary precipitates, and modified electronic structure, which collectively inhibit chloride ingress and convert localized electrochemical attack into uniform corrosion. The experimental results are consistent with first-principles predictions, which clarified the mechanism of nitrogen doping in material corrosion protection from a mechanistic perspective.

Coatings doi: 10.3390/coatings16050627

Authors: Tianran Zhang Zexi Gao Penghao Zhang Chengguo Yao Shoulong Dong

Direct current (DC) surface flashover on polystyrene (PS) remains a critical bottleneck that impedes its reliable application in high-voltage insulation apparatus. To circumvent the protracted processing durations and stringent film-forming conditions inherent in conventional surface modification techniques, this study proposes a novel “liquid-film-assisted in situ rapid plasma curing” strategy. By harnessing atmospheric-pressure dielectric barrier discharge (DBD) technology within an argon ambient, the rapid (<6 min) and efficient deposition of a fluorosilane (FAS-13) functional coating onto the substrate was achieved. Microscopic characterizations coupled with isothermal surface potential decay (SPD) measurements reveal that this coating substantially mitigates the detrapping and surface migration of charge carriers. Macroscopic DC flashover testing corroborates that, under the optimal modification ratio, the surface breakdown voltage of PS is elevated to 14.04 kV, yielding an insulation gain of 26.94%. To elucidate the underlying physical mechanisms, density functional theory (DFT) calculations were conducted, revealing that the energy band misalignment between the wide-bandgap fluorinated layer and the substrate facilitates the construction of a high-density deep trap network (with a depth of ~0.8 eV) at the coating–substrate interface. By robustly anchoring primary electrons and inducing the formation of a homopolar space charge shielding layer, these deep traps physically arrest the evolution of the secondary electron emission avalanche (SEEA). Consequently, this work not only establishes a viable engineering framework for the rapid, large-scale surface reinforcement of DC insulation equipment but also provides profound quantum chemical insights into interfacial trap regulation within all-organic dielectrics.

Coatings doi: 10.3390/coatings16050622

Authors: Natalia Makuch Michał Kulka Mourad Keddam Piotr Dziarski Dominika Panfil-Pryka Maciej Tuliński

The unique powder-pack boriding technique using an open retort with boriding medium was applied for the first time in order to produce boride layers on K190 ledeburitic chromium steel manufactured using powder metallurgy. The processes were carried out using the commercial Durborid®G powder mixture at 1173 K, 1223 K, and 1273 K for 3 h, 6 h, and 9 h. As a result of the boriding of the high-carbon and high-chromium substrate, three zones were revealed in the produced surface layers: the outer FeB zone, the inner Fe2B zone, and the transition zone, with increased carbon content. The total thickness of the boride layers (FeB + Fe2B) ranged from 14.13 µm at the lowest temperature and shortest time to 65.49 µm at the highest temperature and longest duration. Increasing the temperature and extending the boriding time resulted in a deeper FeB zone as well as a thicker total layer (FeB + Fe2B). The growth kinetics of the produced layers on the surface of K190 steel were analyzed for the first time using the mean diffusion coefficient model. The thicknesses of the FeB zone and the total layer (FeB + Fe2B) were determined. The activation energies of boron for the FeB and Fe2B phases calculated in this work are comparable with other results for the powder-pack boriding of high-carbon tool steels. As a consequence of the high chromium content in K190 steel, chromium borides were observed in the boride zones, which increased the hardness of the surface layer. The highest temperature used resulted in the formation of vanadium borides. The presence of the transition zone with an increased carbon concentration and a high percentage of carbides resulted from the movement of carbon atoms toward the core by the advancing boron diffusion front. The parameters of boriding (temperature and time) as well as the presence of alloying elements in the substrate material influenced the microhardness of the boride layers.

Coatings doi: 10.3390/coatings16050626

Authors: Linzhao Hao Jinling Zhang Xingrong Zhu Jianyong Zhan Huipeng Li Jicheng Zhou

The acetic acid corrosion resistance of silver electrodes is critical for ensuring photovoltaic (PV) module reliability. Ethylene-vinyl acetate (EVA) is the most widely used encapsulant material in photovoltaic modules. Under exposure to light, heat, and moisture, EVA decomposes to generate acetic acid, which corrodes the silver electrodes, leading to energy conversion efficiency degradation of the module. To address this problem, the lead-free paste was formulated and evaluated in this paper to improve the anti-acetic acid performance. The contact resistivity of the front and the rear side of the solar cells have been measured before and after acetic acid exposure, and greater degradation is shown in the front electrode than in the rear side. Furthermore, the lead-free paste demonstrates lower efficiency degradation compared to the lead-containing paste after acetic acid exposure. In addition, top-view and cross-sectional scanning electron microscopy was performed to analyze the mechanism of the acetic acid corrosion resistance, in which the silver acetate particles were observed. Our experimental results demonstrate that the lead-free paste exhibits superior acetic acid corrosion resistance, which is due to its higher glass acidity and the absence of lead oxide that causes enhanced chemical reactivity with acetic acid. Based on these findings, the acetic acid corrosion model is proposed to attribute the conversion efficiency degradation of reactions between acetic acid and silver, as well as the glass of the silver electrodes.

Coatings doi: 10.3390/coatings16050624

Authors: Haojun Zeng Minjie Fang Qiaoyan Chen Junjie Chen Binbin Wei Junhong Huang Ruoxuan Huang Zhengbing Qi

Yttrium doping has been reported to be an effective approach to enhance the mechanical and protective properties of ZrN coatings by magnetron sputtering. Nitrogen (N2) flow ratio during reactive magnetron sputtering is known to critically influence the stoichiometry, defect structure, and microstructure of nitride coatings. However, its systematic effect on Y-doped ZrN (ZrYN) coatings has remained unexplored. In this work, ZrYN coatings with a fixed Y content were deposited by reactive magnetron sputtering under varying N2 flow ratios (0–10%). Their microstructure, mechanical properties, corrosion resistance in 3.5 wt% NaCl solution, and oxidation behavior at 650 °C were systematically investigated. Below 5% N2 flow ratio, the coatings are metallic ZrY, showing very low hardness, poor corrosion resistance, and catastrophic oxidation failure. At N2 flow ratio ≥ 5%, cubic ZrYN forms, with stoichiometry varying from sub-stoichiometric (5%) to near-stoichiometric (7.5%) to over-stoichiometric (10%). The near-stoichiometric coating at 7.5% exhibits the finest columnar grains and densest microstructure, leading to the highest hardness (32.2 ± 1.4 GPa) and an elastic modulus of (469.6 ± 24.5 GPa), as well as the best corrosion resistance (two orders of magnitude lower than bare 316 stainless steel). Upon oxidation, it forms a thin and dense epitaxial t-ZrO2 scale stabilized by Y2O3, suppressing the destructive tetragonal to monoclinic transformation. Off-stoichiometric coatings at 5% and 10% develop thicker, cracked oxide scales and show inferior properties. Precise control of N2 flow ratio is therefore essential to achieve a near-stoichiometric ZrYN coating with superior mechanical, anti-corrosion, and anti-oxidation performance.

Coatings doi: 10.3390/coatings16050625

Authors: Shidong Yan Bo Liu

TiVZrTaHfx (x = 0, 0.1, 0.2, and 0.3, molar ratio) refractory high entropy alloys were prepared by vacuum arc melting. XRD, SEM and compression tests were employed to characterize the effects of minor Hf doping on microstructure and compressive mechanical properties of the TiVZrTa alloy. The results indicated that TiVZrTaHfx alloys gradually transform from a multiphase BCC structure to a single-phase BCC structure with increasing Hf content. Correspondingly, as-cast microstructure evolves from the coexistence of reticular morphology and dendrites into a relatively uniform dendritic structure, and elemental segregation was weakened. The compression results showed that the yield strength increases from 1139 MPa to 1253 MPa, while the compressive strain increases from 5.2% to 10.4%. In addition, the fracture mode changes from quasi-cleavage-dominated fracture to a brittle-ductile mixed fracture with more evident plastic tearing features. These results indicate that minor Hf addition can simultaneously improve the strength and compressive strain of the TiVZrTa alloy.

Coatings doi: 10.3390/coatings16050623

Authors: Rong Tu Haodong He Jiangxin Yang Qingfang Xu Chitengfei Zhang Tenghua Gao Song Zhang Takashi Goto Lianmeng Zhang

Optical fiber sensors deployed in harsh industrial fields, e.g., high-temperature wet-oxygen, face severe challenges in signal attenuation and mechanical degradation. While amorphous silicon oxycarbide (a-SiOC) coatings offer a promising solution due to their adjustable thermo-mechanical properties, balancing their structural density with environmental stability remains a critical technical bottleneck. In this study, a-SiOC coatings were deposited on optical fibers using hexamethyldisilane (HMDS) and trace oxygen via radio-frequency capacitively coupled plasma-enhanced chemical vapor deposition (PECVD). A systematic investigation was conducted to determine the impact of deposition temperature (70–420 °C) on the precursor dissociation kinetics, microstructural evolution, and corrosion resistance of the coatings. An elevation in temperature promotes the elimination of organic terminal groups (–CH3, –H) and enhances surface diffusion, driving the coating from a loose, carbon-rich “polymer-like” structure (dominated by Si–C bonds) to a dense, inorganic “silica-like” skeleton (dominated by Si–O–Si bonds). High-temperature corrosion tests in a wet-oxygen environment (500–900 °C) demonstrate that the failure mechanism is highly dependent on deposition temperature. Coatings deposited at low temperatures suffer catastrophic cracking due to pronounced oxidative shrinkage and the release of volatile species, whereas coatings deposited at 420 °C exhibit microcracking caused by severe carbon phase separation and stress concentration within the rigid inorganic network. In the present system, 350 °C is identified as the optimal deposition temperature, as it achieves the best balance of network densification and structural flexibility, while exhibiting the best mechanical performance.

Coatings doi: 10.3390/coatings16050621

Authors: Dong-Wook Seo So-Hui Park Seung-Hyo Lee

Hot-press forming (HPF) steel is a promising lightweight material for automotive applications but suffers from oxidation and reduced corrosion due to high-temperature processing. Aluminized coatings, particularly Al-10Si, are widely used to mitigate this issue. However, HPF heat treatment can create brittle alloy layers with cracks, compromising retention and increasing corrosion risk. This study investigated the effects of Sr addition on the microstructure and corrosion resistance of Al-Si-coated HPF steel. Al-Si and Al-Si-Sr coatings were applied to steel substrates and subjected to heat treatment to produce heat-treated (HT) Al-Si and HT Al-Si-Sr samples. Sr addition refined and spheroidized eutectic Si particles, improved coating homogeneity, and mitigated vertical crack formation in the Al-Fe-Si intermetallic layer. The resulting dense, crack-free alloy layer effectively shielded the Fe substrate from corrosion. After heat treatment, Sr facilitated the formation of a fine lamellar microstructure and a dense, continuous oxide film, enhancing coating retention and sustaining barrier protection. These improvements significantly delayed corrosion propagation into the Fe substrate. Corrosion resistance was evaluated using salt-spray tests (ASTM B117), potentiodynamic polarization, and electrochemical impedance spectroscopy in 3.5 wt.% NaCl solutions. Microstructural analyses revealed that even minimal Sr content (0.05%) considerably enhanced the performance of Al-Si coatings, demonstrating industrial applicability. This study highlights the potential of Sr-added Al-Si coatings in addressing the demand for lightweight and corrosion-resistant materials in the automotive industry, offering a viable solution for high-performance and environmentally sustainable applications.

Coatings doi: 10.3390/coatings16050619

Authors: Chenghao Zhou Shuaitao Li Yahao Li Mengting Zhang Zhen Ma

The objective of this study was to further improve the wear and corrosion resistance of biomedical Ti6Al4V alloy micro-arc oxidation coating, so as to improve its comprehensive service performance. In this study, the effects of pulsed laser power (20–100 W) on the structure, composition, tribological properties and corrosion resistance of the composite coating were systematically studied by using pulsed laser remelting pretreatment technology. The results show that when the power is 100 W, the microwave stripe and fine grain structure formed by pulsed laser remelting can improve the discharge uniformity during the micro-arc oxidation process. The porosity of the composite coating decreases from 21.32% to 10.94%, and the thickness increases from 8.14 μm to 19.49 μm, which is beneficial to improve the compactness and uniformity of the micro-arc oxidation coating. In addition, the pulse laser remelting pretreatment increased the surface hardness of the composite coating to 745.5 HV, and the friction coefficient decreased from 0.76 to 0.51, thereby improving the wear resistance of the composite coating. The electrochemical test results show that the corrosion current density of the composite coating is reduced from 7.28 × 10−8 A·cm−2 to 1.91 × 10−8 A·cm−2 due to the optimization of the composite coating structure, and the corrosion resistance is significantly enhanced. This study provides an effective pretreatment strategy for the construction of high-performance MAO composite coatings.

Coatings doi: 10.3390/coatings16050620

Authors: Jin Ji Xuxu Deng Changjun Wu Junxiu Chen Xiangying Zhu Ya Liu

This work investigated the effect of yttrium addition on the pre-oxidation behavior of Fe–25Ni–20Cr–4Al–1Nb–1Mn–1.5Si-based alloys at 1000 °C in a 4% H2 + 0.2% CH4 + Ar + 0.25% H2O atmosphere. The oxidation resistance and oxide scale adhesion were evaluated through cyclic oxidation tests and micro-scratch measurements. Results show that the Y-free alloy formed a discontinuous oxide layer, whereas all Y-containing alloys formed a continuous and dense Al2O3 scale. Incorporating 0.2 wt.% Y increased the work of adhesion by approximately 7 to 9 times relative to the Y-free sample, indicating a pronounced interfacial strengthening effect. The role of yttrium content and oxygen partial pressure in promoting alumina-scale formation was discussed based on thermodynamic considerations and microstructural evidence.

Coatings doi: 10.3390/coatings16050618

Authors: Tengwei Wang Yunxiu Sai Liang Sun Jian Huang Pengyue Han Jin Jia

Corrosion and scaling critically threaten the safety and efficiency of oil–gas gathering stations. Through field inspections, water chemistry analysis, scale characterization, and corrosion simulation in Yanchang oilfield, this study identifies severe localized damage in key components—such as valves, bends, and injection pipelines—with service lives of only 1–2 years. Analysis of over 200 scale samples revealed that CaCO3 (42 wt%) and CaSO4 (23 wt%) were the predominant scale types. High salinity >56,000 mg/L, Cl− >31,000 mg/L, and Ca2+ promote under-deposit pitting, galvanic corrosion (e.g., Cu–steel couples), and erosion-corrosion at high-velocity zones. Simulations based on OLI Analyzer Studio (a professional thermodynamic simulation software for electrolyte solution and high-salinity brine systems) reveal that the carbon steel (the primary material for the process pipelines and water injection pipelines in the studied oil–gas gathering and transportation stations) has a corrosion rate rising from 0.078 mm/year at 25 °C to 1.94 mm/year at 90 °C. Despite common use of coatings and cathodic protection, these measures often fail to address site-specific failure mechanisms. The study advocates a tailored mitigation strategy combining material compatibility, real-time water monitoring, optimized filtration, and component-level design. This integrated approach enhances asset reliability and operational safety in onshore oilfields.

Coatings doi: 10.3390/coatings16050617

Authors: Fang Qian Menghua Li Rui Xue Shuai Ding Xiaofan Deng

Aiming at the problems of high friction coefficient, severe wear, and unsatisfactory service life and operational reliability of brass under complex working conditions such as dry friction, wet friction, and oil-lubricated friction, H62 brass was taken as the research object to improve its friction and wear properties via surface micro-texture technology. This study systematically compares the tribological performance of three typical geometric micro-textures under three coupled working conditions for the first time. Circular, rectangular, and hexagonal micro-dimple textures were fabricated on the brass surface using ultraviolet laser micromachining. The control variable method was adopted to systematically investigate the effects of micro-texture parameters including shape, size, and area density on the friction and wear properties of brass under the three typical working conditions, combined with reciprocating friction and wear tests and ultra-depth-of-field microscope characterization. The results show that the hexagonal micro-dimple texture (200 μm in size, 10% in area density) exhibits the optimal friction-reducing and anti-wear performance. Compared with the smooth surface, the friction coefficient decreases from 0.51 to 0.43, and the wear rate of the GCr15 steel ball is reduced by 2.8% under dry friction; the friction coefficient decreases from 0.43 to 0.12 with an 11.8% reduction in wear rate under wet friction; and the friction coefficient decreases from 0.29 to 0.24 with an 8.3% reduction in wear rate under oil lubrication. Relative to dry friction, the wear rates are further reduced by 16.7% and 8.3% under wet friction and oil lubrication, respectively. Different from most existing studies that only focus on a single texture type or a single friction condition, this paper systematically reveals the coupling regulation mechanism between texture parameters and working conditions, clarifies the optimal micro-texture design strategy for multi-working conditions, verifies that hexagonal micro-textures can significantly improve the wear resistance of brass, and provides technical support for the surface optimization design of brass workpieces under complex working conditions.

Coatings doi: 10.3390/coatings16050616

Authors: Min Zhang

As guest editor of Coatings, it is my great pleasure to introduce this Special Issue focused on “Research Progress and Prospect of Functional Thin Films & Hard Protective Coatings” [...]

Coatings doi: 10.3390/coatings16050615

Authors: Anna Wrzodak Justyna Szwejda-Grzybowska Beata Kowalska Jan Aleksander Zdulski

This study evaluated a post-cut treatment combining sanitization, carboxymethylcellulose (CMC) coating, and chokeberry pomace extract for preserving fresh-cut sweet peppers during 7 days of refrigerated storage. Sliced peppers of two cultivars, Sunny F1 (yellow) and Yecla F1 (red), were assigned to five treatments: water washing (control), BioActiW 2000 Food sanitizer (BAW), BAW followed by CMC coating (BAW + CMC), CMC coating with 3.5% chokeberry extract (CMC + AE), and 3.5% aqueous chokeberry extract (AAE). Samples were stored at 5 ± 1 °C and assessed for physicochemical, microbiological, sensory, and postharvest quality attributes. The response was cultivar-dependent. Coating-based treatments reduced polyphenol and L-ascorbic acid contents, although chokeberry-containing formulations mitigated these losses relative to BAW + CMC. Total sugars and carotenoids were not significantly affected. In both cultivars, BAW and BAW + CMC best limited mesophilic bacteria and yeast growth, reduced softening, and decreased weight loss. AAE applied without prior sanitization increased microbial counts in Sunny F1. Sensory analysis showed cultivar-specific acceptance: Sunny F1 tolerated CMC + AE and BAW + CMC better, whereas Yecla F1 was more sensitive to off-flavors linked to the extract. These results indicate that sanitization is essential for microbiological stability, while CMC can provide an additional barrier effect. Chokeberry pomace extract showed mixed effects and appears to be a formulation component whose usefulness depends on cultivar and treatment conditions.

Coatings doi: 10.3390/coatings16050614

Authors: Zibing Pi Boyu Xing Yilin Ma Bo Mai Ruixi Chen Xinfei Wu Jingni Li Xue Liu Dexing Wang Zhaohui Deng Hongwei Cai Jean-Jacques Gaumet Wen Luo

NASICON-type Na3V2(PO4)3 (NVP) is widely regarded as a promising cathode for sodium-ion batteries owing to its robust three-dimensional framework and high operating voltage (~3.4 V vs. Na+/Na). However, NVP suffers severe capacity degradation under fast-charging conditions due to its intrinsically low electronic conductivity, which critically impedes its practical deployment. Herein, we systematically investigate the fast-charging failure mechanism of NVP and propose a trace Sm3+ doping strategy (x = 0.03) to address this limitation. Undoped NVP retains only 13.5% and 56.62% of its initial capacity after 1000 cycles at 5000 mA g−1 and 1307 cycles at 2000 mA g−1, respectively. Post-cycling scanning electron microscopy (SEM) reveals extensive crack formation and particle pulverization, providing direct morphological evidence for structural failure. To overcome this, Sm3+-doped Na3V1.97Sm0.03(PO4)3/C (NVPSM) is synthesized via a sol–gel method. X-ray diffraction (XRD) confirms that the NASICON phase is preserved. Raman spectroscopy reveals an improved graphitization degree (ID/IG = 0.97 vs. 1.02 for NVP), and X-ray photoelectron spectroscopy (XPS) verifies the V3+ oxidation state and the incorporation of Sm3+. Electrochemically, NVPSM achieves capacity retentions of 60.3% after 2300 cycles at 5000 mA g−1 and 83.89% after 1436 cycles at 2000 mA g−1. Electrochemical impedance spectroscopy confirms reduced charge-transfer resistance, and post-cycling SEM shows markedly improved structural integrity. These results demonstrate that trace rare-earth doping effectively mitigates fast-charging-induced structural failure in NVP-based cathodes.

Coatings doi: 10.3390/coatings16050613

Authors: Xiangyu Liu Hongyou Bian Kai Zhang Weijun Liu Fei Xing

Titanium matrix composites (TMCs) are increasingly vital in aerospace for their high specific strength and wear resistance, with compositional gradient design serving as a key strategy to mitigate thermophysical mismatches between ceramic and metal phases. This study utilized laser-directed energy deposition with concurrent wire-powder feeding (LDED-WP) to fabricate TiC/Ti6Al4V gradient composites, employing a laser power of 2700 W, wire feed rates of 110–150 cm/min, and calibrated powder feed rates ranging from 50.22 to 497.13 g/h. Along the build direction, the TiC content was progressively increased from 10 wt.% to 60 wt.%. Investigations into microstructural evolution revealed that the reinforcement morphology transitions from chain-like eutectic TiC to dendritic primary TiC, while the lamellarα-Ti width refines significantly from 4.07 ± 1.15 μm to 0.45 ± 0.29 μm. EBSD analysis confirmed that higher TiC concentrations weaken the characteristic <001> solidification texture, reducing intensity from 11.24 to 7.64. Furthermore, KAM analysis highlighted that thermal expansion and elastic modulus mismatches trigger substantial geometrically necessary dislocation (GND) accumulation at interfaces. Consequently, Vickers hardness improved by 164% along the gradient, peaking at 950 HV. Although the composite achieved an ultimate tensile strength of 630 MPa, the elongation was limited to 2.4% due to crack nucleation in TiC-rich regions and interfacial instability.

Coatings doi: 10.3390/coatings16050612

Authors: Laura Montserrat Alcantar-Martínez Pablo Alfredo Ruiz-Trabolsi Raúl Tadeo-Rosas José Guadalupe Miranda-Hernández Gerardo Terán-Méndez Julio César Velázquez Enrique Hernández-Sánchez

In the original publication [...]

Coatings doi: 10.3390/coatings16050611

Authors: Peng-Jie Zhou Qi-Sheng Liu En-Ze Liu

In this study, two bulk high-entropy alloys, CoCrFeNiAl0.3 doped with Hf and CoCrFeNiAl0.3 doped with Hf and C, were prepared using the vacuum arc melting method. Both HEAs contain Co2Hf phases in the as-cast alloy. The heat treatment did not modify the main matrix phase, and the FCC structure was unchanged. After 10 h of solution treatment at 1210 °C and after 24 h of aging treatment at 800 °C, intergranular carbide Cr23C6 was found to precipitate in the alloys doped with Hf and C. This carbide has a very remarkable strengthening effect on the high-entropy alloy, reaching up to 224.64 HV under a load of 200 g.

Coatings doi: 10.3390/coatings16050610

Authors: Ayman M. Atta Mona A. Ahmed Hamad A. Al-Lohedan Ayman El-Faham

The journal retracts the article titled “Multi-Functional Cardanol Triazine Schiff Base Polyimine Additives for Self-Healing and Super-Hydrophobic Epoxy of Steel Coating” [...]

Coatings doi: 10.3390/coatings16050609

Authors: Konstantinos Antonopoulos Athanasios Tzanis Dirk Drees Michalis Vardavoulias Emmanuel Georgiou Angelos Koutsomichalis Panagiotis Skarvelis Tom Van der Donck

Thermal spray technologies are widely used in aerospace, gas turbine, and automotive industries, where nickel-based superalloys are valued for their mechanical strength and resistance to oxidation and corrosion at elevated temperatures. This study investigates the microstructure and tribological performance of Ni–5Al/Inconel 625 composite coatings deposited on AISI 1025 steel using wire arc spraying, aiming to provide a cost-effective alternative to bulk superalloys and more advanced thermal spray techniques. Microstructural characterization was performed using optical microscopy, scanning electron microscopy, and energy-dispersive X-ray spectroscopy, while surface roughness, microhardness, and dry sliding wear behavior were evaluated using ball-on-disk tests against Al2O3 counter-bodies. Confocal microscopy and three-dimensional triboscopic imaging were employed to analyze wear-track morphology and friction behavior. X-ray diffraction (XRD) analysis confirmed the presence of a predominantly intermetallic Ni3Al (γ′) phase with secondary NiAl in the bond coat, indicating significant interdiffusion between the NiAl bond coat and the Inconel 625 top coat. The top coat exhibited a face-centered cubic (FCC) γ Ni-based solid solution. The coatings exhibited a typical lamellar structure with low porosity (2%–3%) and oxide content of 12%–15%, primarily chromium and niobium oxides located at splat boundaries. Abrasion, combined with interlamellar decohesion, was identified as the dominant wear mechanism. Post-deposition polishing reduced surface roughness from 11.9 µm to 2.12 µm, leading to a 2.5-fold reduction in wear volume and a significant decrease in debris pile-up. The corresponding specific wear rates were approximately 9.3 × 10−5 mm3/Nm and 3 × 10−5 mm3/Nm for the as-prepared and polished conditions, respectively, which are within the range reported in the literature for similar coatings. These findings demonstrate that wire arc-sprayed Ni–5Al/Inconel 625 coatings, particularly after polishing, offer improved wear resistance while maintaining cost-effectiveness, making them a promising alternative for tribological applications.

Coatings doi: 10.3390/coatings16050608

Authors: Zhongying Liu Linjun Liu Shuai Li Sanming Du

Dissimilar 7075-T6 and 6061-T6 aluminum alloy joints were fabricated using pulsed metal inert gas (P-MIG) welding with ER5356 filler wire. The effects of welding current (224 A, 234 A, and 244 A) on macro-morphology, microstructure, mechanical properties, and corrosion behavior were systematically investigated. As welding current increased, the top and bottom reinforcements first increased and then decreased, reaching maximum values at 234 A, while the front weld width exhibited the opposite trend. The weld zone consisted of equiaxed and dendritic grains, with partial remelting of AlFeMnSi intermetallic compounds observed in the heat-affected zones. The microhardness and tensile strength of the joints followed a similar trend of first decreasing and then increasing with welding current, achieving a maximum tensile strength of 203.9 MPa at 244 A, corresponding to 89.5% of the 6061-T6 base metal strength. Corrosion resistance varied across regions depending on the evaluation method. In intergranular corrosion tests, the 7075-HAZ showed the highest susceptibility due to grain boundary segregation of Mg and Zn. In electrochemical tests, the WZ exhibited the poorest corrosion resistance. For the 7075-HAZ, optimal corrosion resistance was achieved at 234 A, attributed to a stable passive film and uniform precipitate distribution. These findings provide valuable guidance for optimizing P-MIG welding parameters for dissimilar 7075/6061 aluminum alloy joints.