Coatings

15 pages, 2326 KiB

Open AccessArticle

An Improved Fabrication Method for Van Der Pauw Mobility Measurement on GaN Epitaxy on Conductive and Non-Conductive Substrates

by Dan Qiao, Xianfeng Ni, Qian Fan and Xing Gu

Coatings 2025, 15(4), 491; https://doi.org/10.3390/coatings15040491 (registering DOI) - 20 Apr 2025

Abstract

A novel empirical method for fabricating Van der Pauw Hall test samples on GaN epitaxy is proposed and tested, which enables rapid preparation of Van der Pauw Hall test samples on both conductive and non-conductive substrates. Compared to traditional Van der Pauw Hall [...] Read more.

A novel empirical method for fabricating Van der Pauw Hall test samples on GaN epitaxy is proposed and tested, which enables rapid preparation of Van der Pauw Hall test samples on both conductive and non-conductive substrates. Compared to traditional Van der Pauw Hall sample preparation, this approach eliminates the need for annealing to form Ohmic contacts, thereby facilitating more accurate measurement of the resistivity, Hall coefficient, majority carrier concentration, and mobility in semiconductor wafers, which may be subject to change after high-temperature annealing. This method is based on the use of specialized plasma dry-etched patterns to form the Ohmic electrodes, which reduces the metal–semiconductor contact barrier, allowing the tunneling current to dominate and thus forming Ohmic contacts. In the validation experiments, three different substrate materials for GaN-epi—silicon, sapphire, and silicon carbide—were selected for the preparation of the Van der Pauw Hall test samples, followed by testing and analysis to confirm the accuracy of the new test method. The measurement results for the electron mobility and carrier concentration on the sapphire and silicon carbide substrate samples were verified via the contactless RF reflectance mapping method, with an average difference only 4.0% and 7.0%, respectively, and a minimum of only 0.53% and 1.8%. The proposed fabrication method features a relatively simple structure, enabling rapid preparation and avoiding the damage and errors caused by high-temperature annealing processes. It shows great potential for industrial application on precise carrier property measurements, especially for GaN-epi on a conductive substrate. Full article

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

► Show Figures

Figure 1

14 pages, 17658 KiB

Open AccessArticle

MOF-Derived Hollow Dodecahedral Carbon Structures with Abundant N Sites and Co Nanoparticle-Modified Cu Foil for Dendrite-Free Lithium Metal Battery

by Fei Wang, Huijie Wei, Xinyuan Ren, Junle Zhang, Aiyun Jiang, Yong Liu and Fengzhang Ren

Coatings 2025, 15(4), 490; https://doi.org/10.3390/coatings15040490 (registering DOI) - 20 Apr 2025

Abstract

In this work, hollow dodecahedral carbon structures with abundant N-doping sites and metal nanoparticles (NC-Co-CNTs) based on MOF-derivative materials were designed and prepared as host materials for lithium metal to ensure uniform lithium deposition on a Cu current collector. NC-Co-CNTs have good electrical [...] Read more.

In this work, hollow dodecahedral carbon structures with abundant N-doping sites and metal nanoparticles (NC-Co-CNTs) based on MOF-derivative materials were designed and prepared as host materials for lithium metal to ensure uniform lithium deposition on a Cu current collector. NC-Co-CNTs have good electrical conductivity, which ensures fast electron transport and Li⁺ transfer. The carbon nanotubes catalytically derived by Co can promote the uniform distribution of Li⁺ along the hollow dodecahedral carbon surface and deposition inside the cavity, and the larger electronegativity of N-doped sites and lithophilic sites such as Co nanoparticles can effectively adsorb lithium, inducing the Li⁺ to be deposited in the form of spherical lithium in a dendrite-free state, inhibiting the growth of dendritic lithium and improving the electrochemical performance of the lithium metal battery. Based on the above advantages, the electrodes of NC-Co-CNT-based symmetric cells present superior cycling performance for more than 1100 h with low overpotential at 1 mAh cm⁻²/1 mAh·cm⁻². Even cycling at high current density of 5 mA cm⁻² and high deposition parameters of 5 mAh cm⁻², it still cycles for up to 800 h at a relatively low overpotential. Full article

(This article belongs to the Special Issue Multilayer Coatings for Nanomaterials: From Synthesis to Applications)

► Show Figures

Figure 1

16 pages, 5061 KiB

Open AccessArticle

Bioactive Hydroxyapatite–Carboplatin–Quercetin Coatings for Enhanced Osteointegration and Antitumoral Protection in Hip Endoprostheses

by Gheorghe Iosub, Dana-Ionela Tudorache (Trifa), Ionuț Marinel Iova, Liviu Duta, Valentina Grumezescu, Alexandra Cătălina Bîrcă, Adelina-Gabriela Niculescu, Paul Cătălin Balaure, Ionela Cristina Voinea, Miruna S. Stan, Dragoș Mihai Rădulescu, Adrian Emilian Bădilă, Bogdan Ștefan Vasile, Alexandru Mihai Grumezescu and Adrian Radu Rădulescu

Coatings 2025, 15(4), 489; https://doi.org/10.3390/coatings15040489 (registering DOI) - 20 Apr 2025

Abstract

The recurrence of bone cancer poses severe complications, particularly after orthopedic surgery, necessitating advanced biomaterials with dual functionality. This study develops nanostructured coatings composed of hydroxyapatite, carboplatin, and quercetin, designed to enhance bone regeneration while delivering localized cancer therapy. These coatings present a [...] Read more.

The recurrence of bone cancer poses severe complications, particularly after orthopedic surgery, necessitating advanced biomaterials with dual functionality. This study develops nanostructured coatings composed of hydroxyapatite, carboplatin, and quercetin, designed to enhance bone regeneration while delivering localized cancer therapy. These coatings present a promising solution for hip endoprostheses, addressing osteointegration and tumor recurrence prevention simultaneously. Hydroxyapatite was synthesized and characterized using XRD, TEM, SAED, FTIR, and SEM to assess crystallinity, surface morphology, and functional groups. The coatings were obtained by MAPLE. In vitro biocompatibility tests showed that HAp@CPT and HAp@CPT/QUE coatings supported osteoblast viability and adhesion while exhibiting selective cytotoxic effects on osteosarcoma cells. The Griess assay indicated that nitric oxide (NO) levels remained unchanged in hFOB osteoblasts, confirming that neither coating induced inflammatory responses in healthy cells. In contrast, MG63 osteosarcoma cells exhibited significantly elevated NO levels (p < 0.05) in response to HAp@CPT/QUE, suggesting increased oxidative stress. MTT assay results showed a 12% and 28% reduction in osteosarcoma cell viability for HAp@CPT and HAp@CPT/QUE, respectively. Phase-contrast microscopy further confirmed strong osteoblast adhesion and reduced osteosarcoma attachment, particularly on HAp@CPT/QUE surfaces. These findings highlight the dual functionality of hydroxyapatite–carboplatin–quercetin coatings, promoting osteointegration while exerting localized anticancer effects. Their bone-regenerative and selective cytotoxic properties make them a promising material for hip endoprostheses in oncological orthopedic applications. Full article

(This article belongs to the Special Issue Synthesis and Applications of Bioactive Coatings)

► Show Figures

Figure 1

18 pages, 6463 KiB

Open AccessArticle

Aluminum Oxide Coatings as Nanoadsorbents for the Treatment of Effluents Colored with Eriochrome Black T

by Gustavo R. Kramer, Florencia A. Bruera, Pedro Darío Zapata and Alicia E. Ares

Coatings 2025, 15(4), 488; https://doi.org/10.3390/coatings15040488 (registering DOI) - 20 Apr 2025

Abstract

The contamination of water bodies with toxic compounds from the agricultural, industrial, and domestic sectors is a serious environmental problem. Adsorption is one of the simplest, most functional, and economical methods for treating large volumes of water and removing its contaminant load. Thanks [...] Read more.

The contamination of water bodies with toxic compounds from the agricultural, industrial, and domestic sectors is a serious environmental problem. Adsorption is one of the simplest, most functional, and economical methods for treating large volumes of water and removing its contaminant load. Thanks to its nanoporous structure, versatility, chemical inertness, and low-cost synthesis, anodic aluminum oxide (AAO) can be used as an adsorbent in a wide range of applications. In this work, nanostructured AAO coatings were successfully synthesized, and their performance as adsorbents was evaluated in decolorization tests of Eriochrome Black T (EBT) solutions. The adsorption process was found to be dependent on the initial dye concentration, agitation, temperature, and contact time. At 25 °C and 16 mg·L⁻¹ initial EBT concentration, a maximum removal efficiency (%R) of 78% was obtained after 4.5 h at 500 rpm and after 5.5 h at 100 rpm, while without agitation, after 8.3 h of treatment, the highest %R was 40%. Furthermore, the adsorption rate increased significantly with temperature, reaching a %R of 99% after 2.25 h at 60 °C and 500 rpm. Additionally, it was demonstrated that the adsorbent can be used up to four times with a removal efficiency greater than 50%. Full article

(This article belongs to the Special Issue Manufacturing and Surface Engineering IV)

► Show Figures

Figure 1

14 pages, 6172 KiB

Open AccessArticle

Microstructure and Properties of Al-Cr-N Ternary Wear-Resistant Coatings on Cr12MoV Alloy Tool Steel by Multiarc Ion Plating

by Yuhui Zhou, Qingmin Huang, Shanming Luo and Rongchuan Lin

Coatings 2025, 15(4), 487; https://doi.org/10.3390/coatings15040487 (registering DOI) - 19 Apr 2025

Abstract

Al-Cr-N ternary coatings were deposited on the surface of Cr12MoV alloy tool steel via multiarc ion plating technology. The microstructure and mechanical and tribological properties of these coatings were systematically characterized, analyzed, and compared with those of the uncoated substrate specimens. The results [...] Read more.

Al-Cr-N ternary coatings were deposited on the surface of Cr12MoV alloy tool steel via multiarc ion plating technology. The microstructure and mechanical and tribological properties of these coatings were systematically characterized, analyzed, and compared with those of the uncoated substrate specimens. The results indicated that under optimal conditions, Al70Cr30 alloy was effectively ionized, leading to the formation of AlN and CrN phases between Al ions, Cr ions, and nitrogen atoms. These phases were uniformly distributed within the coating, forming an ordered lattice structure. At a bias voltage of −60 V, the deposited Al-Cr-N coating exhibited a uniform and smooth morphology. However, because of the inherent characteristics of arc deposition, droplets and craters were observed on the coating surface as a result of sputtering and back-sputtering effects. The average nanohardness of the Al-Cr-N ternary coating reached 23.8 ± 3.1 GPa, while the coefficient of friction stabilized at approximately 0.7 during the wear process, compared with around 0.8 for the uncoated Cr12MoV substrate. Compared with the uncoated Cr12MoV substrate, the Al-Cr-N coating demonstrated significantly enhanced hardness and wear resistance, thereby effectively improving the performance of Cr12MoV alloy tool steel. Full article

► Show Figures

Figure 1

31 pages, 2079 KiB

Open AccessReview

Research Progress of Self-Healing Coatings on Ships Against Biological Pollution: A Review

by Wenxu Niu, Jiejun Qian, Xin Wang, Caiping Liang, Li Cui, Haobin Tian and Peter K. Liaw

Coatings 2025, 15(4), 486; https://doi.org/10.3390/coatings15040486 (registering DOI) - 19 Apr 2025

Viewed by 33

Abstract

Marine biofouling is a well-established and significant challenge for the maritime industry. Self-healing coatings applied to ships have demonstrated superior surface properties, including enhanced corrosion resistance and the ability to mitigate biological contamination. Consequently, numerous studies have been conducted to assess different self-repairing [...] Read more.

Marine biofouling is a well-established and significant challenge for the maritime industry. Self-healing coatings applied to ships have demonstrated superior surface properties, including enhanced corrosion resistance and the ability to mitigate biological contamination. Consequently, numerous studies have been conducted to assess different self-repairing coatings, which incorporate mechanisms such as microcapsules, dynamic covalent bonds, and ion exchange. This review begins with an introduction to the process of biofouling formation. It then provides a comprehensive outline of the self-healing coatings that have been developed to improve wear resistance, summarizing the advancements in this area. Finally, building upon these three coating systems, this paper offers a summary of the fabrication and protection technologies for self-healing coatings, including the preparation of micro/nano containers, corrosion warning mechanisms, and intelligent responsive protection. Furthermore, the review explores the future prospects of self-healing coatings, offering valuable insights for researchers in the field. The potential limitations of their application scenarios are also addressed. Full article

► Show Figures

Figure 1

11 pages, 3920 KiB

Open AccessArticle

Impact of Sewing Needle Coating on Needle Heating

by Adnan Mazari and Funda Buyuk Mazari

Coatings 2025, 15(4), 485; https://doi.org/10.3390/coatings15040485 (registering DOI) - 19 Apr 2025

Viewed by 100

Abstract

Sewing needle heating is a common problem in the sewing of technical and medical textiles. The hot needle causes burnt spots on fabric, the breakage of thread and weak seam strength. The most economical way of reducing needle heat is to use thread [...] Read more.

Sewing needle heating is a common problem in the sewing of technical and medical textiles. The hot needle causes burnt spots on fabric, the breakage of thread and weak seam strength. The most economical way of reducing needle heat is to use thread lubrication, needle coating or air cooling. Multiple coated needles are commercially available on the market, including those coated with Nickel, Chromium, Ceramic or Titanium Nitride, etc. In this research, the needles are coated with Diamond-Like Carbon (DLC) for improved frictional properties. Commercially available needles are compared with the DLC-coated needles for sewing performance and needle heat. The results shows a significant decrease in needle friction as compared to the classic needle but the commercial needles coated with Titanium Nitride still performed better. Also, the coating of DLC peeled off in a shorter time during high-speed sewing; within 15 cycles of continuous sewing, there was a significant loss of coating near the needle eye. The novel DLC technique can be of future benefit to sewing needles, offering an improved technique and more cost-effective approach. The results for the DLC-coated needles showed a 9–12% reduction in the needle temperature and, overall, a 12–14% rise in the tensile strength of the thread after sewing as compared to sewing by classical needles. Full article

(This article belongs to the Special Issue Sustainable Coatings for Functional Textile and Packaging Materials)

► Show Figures

Figure 1

17 pages, 3720 KiB

Open AccessArticle

Parametric Study and Improvement of Anti-Corona Structure in Stator Bar End Based on Finite Element Analysis

by Yujia Cheng and Guang Yu

Coatings 2025, 15(4), 484; https://doi.org/10.3390/coatings15040484 (registering DOI) - 18 Apr 2025

Viewed by 128

Abstract

Voltage withstand tests on stator bars can cause destructive phenomena such as thermal breakdown and flashover discharge on the surface of the anti-corona layer. This study optimizes the anti-corona structure at a stator bar’s end to prevent such failures using a 120 MW [...] Read more.

Voltage withstand tests on stator bars can cause destructive phenomena such as thermal breakdown and flashover discharge on the surface of the anti-corona layer. This study optimizes the anti-corona structure at a stator bar’s end to prevent such failures using a 120 MW water-cooled turbogenerator with a rated voltage of 15.75 kV. For a well-designed anti-corona system, the maximum potential gradient of the stator bar should be lower than the discharge intensity of air corona. In our design, the electric field intensity is maintained below 3.1 kV/cm, and the maximum surface loss in the anti-corona layer is limited to less than 0.6 W/cm². Additionally, the terminal voltage is kept lower than that of flashover voltage at rated conditions. Furthermore, the length of the anti-corona layer should be minimized. The optimization process involves determining the rotation angle of the stator bar, calculating the total length of the anti-corona layer, and analyzing the electric field and loss in the layer at different lengths. The results demonstrate that the optimized anti-corona design effectively reduces the risk of flashover and thermal failure, ensuring stable operation under rated conditions. This manuscript belongs to purely computational experiments. At present, the electrical machinery with 120 MW rated power grade is put into operation steadily. There is a growing requirement for anti-corona. In this manuscript, computing method is used to assist the anti-corona structure design. The electrical machinery insulation is improved by better anti-corona materials. Therefore, the service life of electrical machinery can be prolonged, which is significant in engineering. Full article

(This article belongs to the Special Issue Modification and Optimization of Cable Insulation Surface Materials)

► Show Figures

Figure 1

17 pages, 10913 KiB

Open AccessArticle

Study of Gd₂O₃-Doped La₂(Zr_0.7Ce_0.3)₂O₇ Thermal Barriers for Coating Ceramic Materials for CMAS Resistance

by Xiaowei Song, Min Xie, Xiaofu Qu, Xiwen Song, Yonghe Zhang and Rende Mu

Coatings 2025, 15(4), 483; https://doi.org/10.3390/coatings15040483 - 18 Apr 2025

Viewed by 126

Abstract

The stability of thermal barrier coating (TBC) materials during service is a prerequisite for the normal operation of aircraft engines. The high-temperature corrosion of CaO–MgO–Al₂O₃–SiO₂ (CMAS) is an important factor that affects the stability of TBCs on turbine [...] Read more.

The stability of thermal barrier coating (TBC) materials during service is a prerequisite for the normal operation of aircraft engines. The high-temperature corrosion of CaO–MgO–Al₂O₃–SiO₂ (CMAS) is an important factor that affects the stability of TBCs on turbine blades and causes premature engine failure. For traditional 6-8 YSZ, at temperatures of more than 1200 °C, the thermal insulation performance is significantly reduced, which makes it necessary to find new, alternative materials. La₂Zr₂O₇ has good thermal physical properties; the addition of Ce⁴⁺ improves its mechanical properties, while adding Gd₂O₃ affects its corrosion resistance. Herein, high-temperature corrosion studies of (La_1−xGd_x)₂(Zr_0.7Ce_0.3)₂O₇ (L-GZC) (x = 0, 0.3, 0.5, 0.7) ceramic TBC were conducted using CMAS glass at 1250 °C. The results indicate that CMAS rapidly dissolves L-GZC and separates the (La, Gd)₈Ca₂(SiO₄)₆O₂ apatite phase, ZrO₂, and other crystalline phases. These products form a crystalline layer at the contact boundary, which can inhibit further CMAS reactions. Among the coatings examined, the L-GZC ceramic (x = 0.7) exhibits better corrosion resistance, and the penetration depth is <200 μm after high-temperature corrosion at 1250 °C for 5, 10, and 20 h. The failure mechanism and potential risk of CMAS were also analyzed and discussed. The L-GZC ceramic material has good thermal corrosion resistance and is expected to replace the traditional YSZ to better meet the high-temperature working requirements of gas turbines and aircraft engines. Full article

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

► Show Figures

Graphical abstract

23 pages, 8500 KiB

Open AccessArticle

Experimental Investigation and Optimization of the Electrodeposition Parameters of Ni-Al₂O₃ Composite Coating Using the Taguchi Method

by Ilias Reddah, Laala Ghelani, Sofiane Touati, Farid Lekmine, Pavol Hvizdoš, Susana Devesa and Haithem Boumediri

Coatings 2025, 15(4), 482; https://doi.org/10.3390/coatings15040482 - 18 Apr 2025

Viewed by 150

Abstract

In this work, an experimental investigation is conducted with the aim of optimizing the electrodeposition parameters for Ni-Al₂O₃ composite coatings using the Taguchi method. The presented research is structured into two complementary sections. The first segment investigates the characteristics of [...] Read more.

In this work, an experimental investigation is conducted with the aim of optimizing the electrodeposition parameters for Ni-Al₂O₃ composite coatings using the Taguchi method. The presented research is structured into two complementary sections. The first segment investigates the characteristics of Ni and Ni-Al₂O₃ coatings, specifically Al₂O₃ particle incorporation and crystallinity variations, using X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and hardness evaluation through micro-indentation testing. The second section uses statistical techniques, specifically Analysis of Variance (ANOVA) and signal-to-noise (S/N) ratio analysis, to determine which parameters have the most impact on the experimental results. ANOVA and the Response Surface Methodology (RSM) were used in a modeling technique to forecast and optimize the technical responses. Based on an L16 orthogonal design, sixteen tests were carried out to investigate the effects of several important variables, including agitation rate (200–350 rpm), deposition period (15–60 min), alumina concentration (10–25 g.L⁻¹), and current density (2–5 A.dm⁻²). The conditions for optimizing microhardness (HV) and Al₂O₃ integration while limiting average crystallite size (ACS) were identified using the most suitable function. The obtained results reveal significant improvements in the composite coating’s properties, including a 164% increase in microhardness, a 400% rise in alumina incorporation, and a notable reduction in crystallite size, demonstrating the efficacy of the electrodeposition process and optimization strategy adopted. Full article

(This article belongs to the Special Issue Advances of Ceramic and Alloy Coatings, 2nd Edition)

► Show Figures

Figure 1

18 pages, 22450 KiB

Open AccessArticle

A Mechanism of Argon Arc Remelting of LPBF 18Ni300 Steel Surfaces

by Xiaoping Zeng, Yehui Sun, Hong Zhang, Zhi Jia and Quan Kang

Coatings 2025, 15(4), 481; https://doi.org/10.3390/coatings15040481 - 18 Apr 2025

Viewed by 119

Abstract

This study aims to reduce pores, cracks, and other defects on the surface of laser powder bed fusion (LPBF)-fabricated 18Ni300 steel and improve its surface quality. Remelting was carried out on the surface with an argon arc as the heat source. Then, the [...] Read more.

This study aims to reduce pores, cracks, and other defects on the surface of laser powder bed fusion (LPBF)-fabricated 18Ni300 steel and improve its surface quality. Remelting was carried out on the surface with an argon arc as the heat source. Then, the surface layer was characterized using SEM, EDS, XRD, EBSD, and hardness testing. The results showed the following: When the pulse current

I

increased from 16 A to 20 A, the surface hardness of LPBF 18Ni300 increased due to a decrease in defects and an increase in the martensite phase. The driving forces of convection in the molten pool (such as buoyancy, Lorentz magnetic force, surface tension, and plasma flow force) rose with an increase in current. When the current

I

exceeded 20 A, the convection became more intense, making it easier for gas to be entrained into the melt pool, forming pores and introducing new defects, resulting in a decrease in surface hardness. The primary factors affecting the hardness of LPBF 18Ni300 after surface argon arc remelting were pore (defect) weakening and phase transformation strengthening, while the secondary factors included grain refinement strengthening and texture strengthening. The solidification mode of the remelted layer was: L → A → M + A′. The phase transition mode of the heat-affected zone was: M + A′ → A_reverse → M_temper. Compared with the base material and heat-affected zone, the grains in the remelted layer formed a stronger <001> texture with a larger average size (2.51 μm) and a lower misorientation angle. The content of the residual austenite A′ was relatively high in the remelted layer. It was distributed in the form of strips along grain boundaries, and it always maintained a shear–coherent relationship with martensite. Full article

► Show Figures

Figure 1

9 pages, 14768 KiB

Open AccessCommunication

Hierarchical Porous Nickel Anode with Low Polarization at High Current Density

by Ruiqi Song, Zeyu Ma, Qi Shao, Leixin Wu, Xiaoqiao Liao, Wenwu Wang, Jiangwang Wang, Huimin Liang, Muhammad Tahir, Dan Lu and Liang He

Coatings 2025, 15(4), 480; https://doi.org/10.3390/coatings15040480 - 18 Apr 2025

Viewed by 110

Abstract

Metal anodes have attracted much interest in metal batteries because of their high theoretical capacity and outstanding electrochemical performance. However, practical applications of metal anodes are often limited by polarization effects, leading to limited reaction capacity, lower energy efficiency, and shorter cycle life. [...] Read more.

Metal anodes have attracted much interest in metal batteries because of their high theoretical capacity and outstanding electrochemical performance. However, practical applications of metal anodes are often limited by polarization effects, leading to limited reaction capacity, lower energy efficiency, and shorter cycle life. Herein, a hierarchical porous nickel (Ni) is proposed as a promising anode with extremely low polarization at a high current density and reaction capacity. This Ni anode has a large specific surface area, and fast reaction kinetics can be realized. As a result, this porous Ni anode is capable of achieving an extremely low polarization voltage of ~10 mV at 40 mA cm⁻²@40 mAh cm⁻². In contrast, the polarization voltage of the Ni plate anode is ~100 mV at 40 mA cm⁻²@40 mAh cm⁻². Additionally, symmetrical coin cells made in a unique way can be maintained for 800 h at 40 mA cm⁻²@40 mAh cm⁻² and 400 h at 80 mA cm⁻²@80 mAh cm⁻². This porous Ni anode that can achieve low polarization at a high current density/high capacity provides a new direction for developing high-performance nickel metal batteries. Full article

(This article belongs to the Special Issue Energy Storage and Conversion: From Materials, Devices to Applications)

► Show Figures

Figure 1

30 pages, 12443 KiB

Open AccessReview

Review of Physical and Mechanical Properties, Morphology, and Phase Structure in Cr₃C₂-NiCr Composite Coatings Sprayed by HVOF Method

by Bekbolat Seitov, Sherzod Kurbanbekov, Dilnoza Baltabayeva, Dauir Kakimzhanov, Karakoz Katpayeva, Alisher Temirbekov, Sattar Bekbayev and Nurken Mussakhan

Coatings 2025, 15(4), 479; https://doi.org/10.3390/coatings15040479 - 17 Apr 2025

Viewed by 209

Abstract

This review paper presents a detailed analysis of the influence of high-velocity oxygen–fuel (HVOF) spraying parameters on the microstructure formation and performance characteristics of Cr₃C₂-NiCr coatings. Key HVOF parameters, including the spray distance, oxygen-to-fuel ratio, powder feed rate, and [...] Read more.

This review paper presents a detailed analysis of the influence of high-velocity oxygen–fuel (HVOF) spraying parameters on the microstructure formation and performance characteristics of Cr₃C₂-NiCr coatings. Key HVOF parameters, including the spray distance, oxygen-to-fuel ratio, powder feed rate, and spraying temperature, are examined in relation to their impact on coating properties. Structural parameters such as density, porosity, adhesive strength, and microhardness, which determine the mechanical behavior of the coating, are analyzed. Special attention is paid to wear resistance mechanisms, adhesion to the substrate, and resistance to fatigue failure. Additionally, the thermal stability of the coatings, their coefficient of thermal expansion, and oxidation resistance are investigated. This study also evaluates the morphology and phase composition of the coatings under different HVOF spraying conditions. An overview of modern diagnostic techniques, such as electron microscopy and spectroscopy, is provided. Compared to traditional surface treatment methods, HVOF spraying offers superior coating density, higher adhesion strength, and enhanced wear and corrosion resistance, making it an effective solution for extending the service life of components. Based on the findings, this paper highlights promising applications of Cr₃C₂-NiCr coatings in the aviation, power engineering, and mechanical engineering industries, where high wear resistance and thermal stability are crucial. Full article

► Show Figures

Figure 1

18 pages, 1672 KiB

Open AccessArticle

Zero-Reference Depth Curve Estimation-Based Low-Light Image Enhancement Method for Coating Workshop Inspection

by Jiaqi Liu, Shanhui Liu, Wuyang Zhou, Huiran Ren, Wanqiu Zhao and Zheng Li

Coatings 2025, 15(4), 478; https://doi.org/10.3390/coatings15040478 - 17 Apr 2025

Viewed by 75

Abstract

To address the challenges of poor image quality and low detection accuracy in low-light environments during coating workshop inspections, this paper proposes a low-light image enhancement method based on zero-reference depth curve estimation, termed Zero-PTDCE. A low-light image dataset, PT-LLIE, tailored for coating [...] Read more.

To address the challenges of poor image quality and low detection accuracy in low-light environments during coating workshop inspections, this paper proposes a low-light image enhancement method based on zero-reference depth curve estimation, termed Zero-PTDCE. A low-light image dataset, PT-LLIE, tailored for coating workshop scenarios is constructed, encompassing various industrial inspection conditions under different lighting environments to enhance model adaptability. Furthermore, an enhancement network integrating a lightweight denoising module and depthwise separable dilated convolution is designed to reduce noise interference, expand the receptive field, and improve image detail restoration. The network training process employs a multi-constraint strategy by incorporating perceptual loss (L_p), color loss (L_c), spatial consistency loss (L_s), exposure loss (L_e), and total variation smoothness loss (L_tv) to ensure balanced brightness, natural color reproduction, and structural integrity in the enhanced images. Experimental results demonstrate that, compared to existing low-light image enhancement methods, the proposed approach achieves superior performance in terms of peak signal-to-noise ratio (PSNR), structural similarity index (SSIM), and mean absolute error (MAE), while maintaining high computational efficiency. Beyond general visual enhancement, Zero-PTDCE significantly improves the visibility of fine surface features and defect patterns under low-light conditions, which is crucial for the accurate assessment of coating quality, including defect identification such as uneven thickness, delamination, and surface abrasion. This work provides a reliable image enhancement solution for intelligent inspection systems and supports both the automated operation and material quality evaluation in modern coating workshops, contributing to the broader goals of intelligent manufacturing and material characterization. Full article

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

► Show Figures

Figure 1

15 pages, 9696 KiB

Open AccessArticle

Electron Beam Surface Treatment and Its Impact on the Plasticity of Fe-Based High-Entropy Alloy

by Stefan Valkov, Georgi Kotlarski, Stoyan Parshorov, Maria Ormanova, Fatme Padikova, Borislav Stoyanov and Ivan Parshorov

Coatings 2025, 15(4), 477; https://doi.org/10.3390/coatings15040477 - 17 Apr 2025

Viewed by 127

Abstract

In this work, we present results on the impact of electron beam surface modification on the phase composition, microstructure, chemical composition, and mechanical properties of Fe-Ni-Cr-Mo-W high-entropy alloy. During the experiments, the beam power was 600 and 1200 W. The phase composition was [...] Read more.

In this work, we present results on the impact of electron beam surface modification on the phase composition, microstructure, chemical composition, and mechanical properties of Fe-Ni-Cr-Mo-W high-entropy alloy. During the experiments, the beam power was 600 and 1200 W. The phase composition was studied using XRD measurements. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) were used to analyze the microstructure and chemical composition, respectively. The results showed that at the lower value of the power of the electron beam, a distinguished modified zone cannot be observed. With an increase in the discussed technological parameter, a treated zone with a thickness of about 30 μm can be seen on the top of the sample. The modulus of elasticity on the surface of the unprocessed alloy was measured to be 130 GPa and increased to 156 GPa in the case of both technological regimes of the electron beam surface modification process. The hardness on the top of the untreated alloy was about 4.5 GPa and reduced to about 3 GPa in the case of electron beam treatment on the alloy with a beam power of 600 W. The application of the modification process with a higher value of beam power, 1200 W, led to an even further decrease in the hardness, to about 2.8 GPa. The resistance to plastic deformation of the surface of the considered specimens was also analyzed via the H³/E² ratio, and the results show that the application of the treatment procedure leads to a decrease in the resistance to plastic deformation in both cases. This decrease is more pronounced in the case of the treatment with the higher value of power of the electron beam. Full article

(This article belongs to the Special Issue Research on High Entropy Alloys: Design of Experiment and Machining Parameters)

► Show Figures

Figure 1

12 pages, 14079 KiB

Open AccessArticle

Preparation of High-Entropy Silicide Coating on Tantalum Substrate by Silicon Infiltration Method and Its Antioxidant Performance

by Xinli Liu, Dexiang Tian, Jiali Mao, Gang Zhao and Dezhi Wang

Coatings 2025, 15(4), 476; https://doi.org/10.3390/coatings15040476 - 17 Apr 2025

Viewed by 97

Abstract

High-entropy silicide (MeSi₂) coating was prepared by the slurry method and silicon infiltration method using Mo, Cr, Ta, Nb, W, and Si elemental powders as raw materials. The coating consisted of four layers, including a porous MeSi₂ layer, a (CrTa)Si [...] Read more.

High-entropy silicide (MeSi₂) coating was prepared by the slurry method and silicon infiltration method using Mo, Cr, Ta, Nb, W, and Si elemental powders as raw materials. The coating consisted of four layers, including a porous MeSi₂ layer, a (CrTa)Si layer, a TaSi₂ layer, and a Ta₅Si₃ layer from outside to inside. At 600 °C, Si was preferentially oxidized to form SiO₂ oxide film. The mass gain rate of the coating was 0.2 mg/cm² over a period of 100 h oxidation, eliminating the phenomenon of low-temperature pulverization. At 1200 °C, MeSi₂ coating had a protection time of 20 h. During the oxidation process, the coating generated metal oxides, forming a thin SiO₂ oxide film. TaSi₂ and Ta₅Si₃ gradually transformed into Ta₂O₅, and the coating eventually failed. Full article

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

► Show Figures

Figure 1

21 pages, 1862 KiB

Open AccessArticle

Co- and Sn-Doped YMnO₃ Perovskites for Electrocatalytic Water-Splitting and Photocatalytic Pollutant Degradation

by Paula Sfirloaga, Szabolcs Bognár, Bogdan-Ovidiu Taranu, Paulina Vlazan, Maria Poienar and Daniela Šojić Merkulov

Coatings 2025, 15(4), 475; https://doi.org/10.3390/coatings15040475 - 16 Apr 2025

Viewed by 91

Abstract

The current environmental pollution and energy crises are global concerns that must be addressed. Considering this background, three perovskites (YMnO₃, Co-doped YMnO₃, and Sn-doped YMnO₃) were synthesized via a sol–gel method and characterized by XRD, SEM, and [...] Read more.

The current environmental pollution and energy crises are global concerns that must be addressed. Considering this background, three perovskites (YMnO₃, Co-doped YMnO₃, and Sn-doped YMnO₃) were synthesized via a sol–gel method and characterized by XRD, SEM, and EDX. Their water-splitting electrocatalytic activity was evaluated in a strongly alkaline medium. The highest activity was observed during hydrogen evolution reaction (HER) experiments on a glassy carbon electrode coated with a catalyst ink containing the Co-doped material. Initially, the HER overpotential value at −10 mA/cm² was 0.59 V, and the Tafel slope was 115 mV/dec. Following a chronoamperometric stability test, the overpotential became 0.46 V and the Tafel slope 119 mV/dec. The higher HER activity of the modified electrode is ascribed to a higher number of catalytic sites exposed to the electrolyte solution and the presence of Carbon Black. The photocatalytic activity of the perovskites was investigated as well, using different experimental conditions and simulated solar irradiation. The results show that the photocatalytic activity can be improved by doping, and the highest removal efficiency is achieved in the presence of the Co-doped YMnO₃ when ~60% of 17α-ethynylestradiol is degraded. Furthermore, the initial pH has no favorable effect on the degradation efficiency. The reusability of Co-doped YMnO₃ was also tested and minimal activity loss was found after three photocatalytic cycles. Full article

► Show Figures

Graphical abstract

18 pages, 6707 KiB

Open AccessArticle

The Effects of the Finishing Polish Process on the Tribological Properties of Boride Surfaces of AISI 4140 Steel

by Daniel Misael Flores-Arcos, Noé López-Perrusquia, Marco Antonio Doñu-Ruiz, Martin Flores-Martínez, Stephen Muhl Saunders, David Sánchez Huitron and Ernesto David García Bustos

Coatings 2025, 15(4), 474; https://doi.org/10.3390/coatings15040474 - 16 Apr 2025

Viewed by 184

Abstract

In sealing, sliding, and power transmission operations, surface quality and contact tolerances have high impacts on material system efficiency. Although the boriding process improves the wear resistance of metallic surfaces, it increases surface roughness, affecting the tribological efficiency of material systems. This study [...] Read more.

In sealing, sliding, and power transmission operations, surface quality and contact tolerances have high impacts on material system efficiency. Although the boriding process improves the wear resistance of metallic surfaces, it increases surface roughness, affecting the tribological efficiency of material systems. This study presents the tribological results of AISI 4140 boriding surfaces tested using a dehydrated paste pack boriding method with and without a finishing polish process to reduce the roughness. The duration of the boriding process was 1 h at 1123, 1173, 1223, and 1273 K using boron paste obtained from a commercial source and using a pot-polishing process with Al₂O₃ with a particle size of 0.5 μm for 25 min. The samples with and without the finishing polish process were structurally characterized using X-ray diffraction, and the boride coating adhesion was determined using Rockwell C indentation. The tribological properties of the boride surface with and without the finishing polish process were determined using a reciprocating sliding test, with a ZrO₂ ball as a counter body. The boride surfaces’ crystalline structure changed with polishing, which revealed the FeB phase and reduced the roughness value. These modifications in the surface characteristics altered the adhesion and tribological performance of the coating, resulting in a more stable tribological performance on the polished boride surfaces, with a reduction in the coefficient of friction (Cof) value from 0.75 ± 0.02 for the tribological test on the 1123 K-P sample to 0.59 ± 0.002 for the 1273 K-P sample surface at 20 N of applied load. Full article

(This article belongs to the Special Issue Microstructure, Fatigue and Wear Properties of Steels, 2nd Edition)

► Show Figures

Figure 1

19 pages, 6501 KiB

Open AccessArticle

Polysaccharide Thin Films Regulate Adhesion and Function of Human Neural Stem Cells

by Matthew James, Yang Zhou, Fei-Chien Chang and Miqin Zhang

Coatings 2025, 15(4), 473; https://doi.org/10.3390/coatings15040473 - 16 Apr 2025

Viewed by 185

Abstract

Human neural stem cells (hNSCs) are vital for advancing therapies for neurocognitive disorders. However, standard hNSC culture conditions often lack chemically defined and xeno-free substrates, limiting their clinical applicability. Chitosan, known for its biocompatibility, presents a promising alternative for hNSC culture. Hyaluronic acid [...] Read more.

Human neural stem cells (hNSCs) are vital for advancing therapies for neurocognitive disorders. However, standard hNSC culture conditions often lack chemically defined and xeno-free substrates, limiting their clinical applicability. Chitosan, known for its biocompatibility, presents a promising alternative for hNSC culture. Hyaluronic acid (HA) and alginate, with their negative charges, enable effective interaction with positively charged chitosan to form films with enhanced mechanical properties. Incorporating chitosan into substrates creates chitosan–alginate (CA) and chitosan–hyaluronic acid (CHA) composites that meet chemically defined, mechanically tunable, and xeno-free standards. Despite their potential, the effects of these composites’ composition and mechanical properties on hNSC behavior, particularly in film form, remain unexplored. To bridge this gap, we fabricated films with varying chitosan-to-alginate and chitosan-to-hyaluronic acid ratios to assess their influence on hNSC pluripotency under xeno-free conditions. Our results reveal that films with higher chitosan content promote hNSC attachment and proliferation. Conversely, increasing alginate generally decreased cell attachment, proliferation, and multipotency, while increasing HA had no impact on attachment or proliferation but decreased multipotency. This investigation provides insights into the impact of substrate composition and mechanical properties on hNSC behavior, guiding the design of analogous materials for three-dimensional cultures and optimizing stem cell-based therapies for clinical applications. Full article

► Show Figures

Figure 1

18 pages, 10927 KiB

Open AccessArticle

Study on the Formation and Evolution Mechanism of Pinhole in Aluminum Foil for the Lithium-Ion Battery Soft Packaging

by Kai Zhang, Wei Chen, Zhehang Fan, Xiaohu Chen, Changle Xiao, Yunan Chen, Yinhui Xu, Ruian Ni and Hongyan Wu

Coatings 2025, 15(4), 472; https://doi.org/10.3390/coatings15040472 - 16 Apr 2025

Viewed by 168

Abstract

As the crucial core material in aluminum–plastic-laminated films, aluminum foil serves as a barrier and shaping element for lithium-ion battery soft packaging. However, its thinness, measuring only tens of microns, makes it susceptible to the formation of pinholes during the manufacturing process, which [...] Read more.

As the crucial core material in aluminum–plastic-laminated films, aluminum foil serves as a barrier and shaping element for lithium-ion battery soft packaging. However, its thinness, measuring only tens of microns, makes it susceptible to the formation of pinholes during the manufacturing process, which can significantly impact the barrier performance and properties of the aluminum–plastic-laminated film. The morphology and composition of foreign particles that lead to pinholes were analyzed using scanning electron microscopy (SEM) with energy-dispersive spectroscopy (EDS). Additionally, the formation mechanism and evolution law of pinholes were investigated using a laser scanning confocal microscope (LSCM). The results revealed that foreign particles responsible for pinholes originated from the inclusions in the aluminum alloy melt, filter aid particles from rolling oil, and environmental dust particles. To address this issue, potential strategies for controlling foreign particles were proposed. These included purifying the aluminum alloy melt, filtering the rolling oil, and maintaining a clean production environment. The simulated experiments showed that foreign particles were gradually embedded in the aluminum matrix during plastic deformation, leading to damage in the aluminum matrix. When the cumulative rolling reduction ratio exceeded 38%, the aluminum foil and foreign particles began to separate along the rolling direction, resulting in the formation of pinholes. The mechanism of uncoordinated deformation between foreign particles and aluminum foil was elaborated in detail. In addition, the simulation experiment indicated that once the cumulative reduction ratio surpassed 50%, the aspect ratio of the pinhole increased rapidly. When the cumulative reduction ratio increased to 83%, the pinhole began to gradually heal. Consequently, a quantitative relationship model between the pinhole area and the rolling reduction ratio was constructed. The pinhole evolution model enables a rough prediction of the actual pinhole area change and meets the requirements for engineering applications. This research provides both engineering applications and theoretical prediction approaches that can aid in the production of high-quality aluminum foil for lithium-ion battery soft packaging. Full article

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

► Show Figures

Figure 1

19 pages, 5881 KiB

Open AccessArticle

Feasibility of Polyphosphoric Acid in Emulsified Asphalt Modification: Emulsification Characteristics, Rheological Properties, and Modification Mechanism

by Simiao Pan, Xiang Liu, Xiaolong Li, Jingpeng Jia and Jun Yang

Coatings 2025, 15(4), 471; https://doi.org/10.3390/coatings15040471 - 16 Apr 2025

Viewed by 179

Abstract

Polyphosphoric acid (PPA), a chemical modifier widely used in petroleum asphalt, results in significant performance improvements. However, its effectiveness for modified emulsified asphalt has not yet been thoroughly verified. This study aims to investigate the emulsification properties, rheological characteristics, compatibility, and modification mechanisms [...] Read more.

Polyphosphoric acid (PPA), a chemical modifier widely used in petroleum asphalt, results in significant performance improvements. However, its effectiveness for modified emulsified asphalt has not yet been thoroughly verified. This study aims to investigate the emulsification properties, rheological characteristics, compatibility, and modification mechanisms of PPA-modified emulsified asphalt and validate the feasibility of applying PPA for modification. Initially, PPA-modified emulsified asphalt was prepared at different dosages (0%, 0.5%, 1.0%, 1.5%, and 2.0%), and its emulsification characteristics, including evaporation residue properties and storage stability, were evaluated. Subsequently, the rheological performance and compatibility of PPA-modified emulsified asphalt at various temperatures were evaluated using a dynamic shear rheometer. Finally, Fourier transform infrared spectroscopy (FTIR) and fluorescence microscopy (FM) were utilized to investigate the effects of PPA modification on the chemical composition and microscopic characteristics of emulsified asphalt. The results indicated that, with increasing PPA dosage, the softening point of modified emulsified asphalt initially decreased and then increased, while penetration and ductility first increased and then decreased, accompanied by reduced storage stability. Furthermore, PPA modification can enhance the high-temperature stability, fatigue properties, and low-temperature performance of emulsified asphalt, but the effectiveness depended on the dosage of PPA. Specifically, optimal compatibility of modified emulsified asphalt was achieved at a PPA dosage of 1.0%. Notably, PPA underwent hydrolysis within the emulsified asphalt system, leading to modification mechanisms distinct from those observed in base asphalt modification. At a PPA dosage of 1.0%, asphalt particles within the emulsified asphalt exhibited the most uniform distribution. Conversely, excessive PPA dosage (e.g., 2.0%) caused significant particle aggregation, consequently weakening the modification effect. Full article

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

► Show Figures

Figure 1

19 pages, 10296 KiB

Open AccessArticle

Microstructure and Thermal Analysis Kinetics of Y₂Hf₂O₇/Y₃Al₅O₁₂ Composites Prepared by Solution Combustion Synthesis

by Rui Li, Shengyue Gu, Yimin Guo, Bei Xue, Qian Zhou, Ruimei Yuan, Longkang Cong and Yaming Zhang

Coatings 2025, 15(4), 470; https://doi.org/10.3390/coatings15040470 - 15 Apr 2025

Viewed by 125

Abstract

With the development of high-speed and high-temperature equipment, thermal barrier materials are facing increasingly harsh service environments. The addition of YAG to Y₂Hf₂O₇ has been proposed in order to improve its long-term high-temperature performance. In this work, Y [...] Read more.

With the development of high-speed and high-temperature equipment, thermal barrier materials are facing increasingly harsh service environments. The addition of YAG to Y₂Hf₂O₇ has been proposed in order to improve its long-term high-temperature performance. In this work, Y₂Hf₂O₇/Y₃Al₅O₁₂ composite powders were synthesized by combustion synthesis with urea, glycine, EDTA, citric acid, and glucose as fuels, while hafnium tetrachloride, yttrium nitrate hexahydrate, and aluminum nitrate nonahydrate were used as raw materials. The effects of fuels on the morphology and phase composition of synthetic powders were studied. Chemical reaction kinetic parameters were established by the Kissinger, Augis and Bennett, and Mahadevan methods. Y₂Hf₂O₇ and Y₃Al₅O₁₂ are the main components in the powders synthesized with urea as fuel, while YAlO₃ and Y₂Hf₂O₇ are the main phases with the other fuels. SEM and TEM analysis reveal that the powders prepared by the solution combustion method exhibit a typical porous morphology. When urea is used as fuel, the powders show a uniform elemental distribution, distinct ceramic grain crystallization, clear grain boundaries, and a uniform distribution of alternating grains. Compared to several other fuels, urea is more suitable for the preparation of Y₂Hf₂O₇/Y₃Al₅O₁₂ composite powders. In the process of preparing powders with urea, the activation energies for the combustion reaction calculated using the three methods are 100.579, 104.864, and 109.148 kJ·mol⁻¹, while the activation energies related to crystal formation are 120.397, 125.001, and 129.600 kJ·mol⁻¹, respectively. Full article

(This article belongs to the Special Issue Ceramic and Glass Material Coatings)

► Show Figures

Figure 1

15 pages, 7518 KiB

Open AccessArticle

Microstructure, Mechanical Properties, and Corrosion Resistance of NiAl-CoCrFeMo High-Entropy Alloys by Controlling Mo Co-Doping

by Zhixin Xu, Ao Li, Xiaohong Wang, Yunting Su and Tengfei Ma

Coatings 2025, 15(4), 469; https://doi.org/10.3390/coatings15040469 - 15 Apr 2025

Viewed by 202

Abstract

In this work, two alloys of Ni₃₅Al₃₀(FeCo)₂₅Cr_10-xMo_x (x = 0, 5) were prepared via the vacuum arc melting method, and the effects of Mo on the microstructure, mechanical properties, and friction and [...] Read more.

In this work, two alloys of Ni₃₅Al₃₀(FeCo)₂₅Cr_10-xMo_x (x = 0, 5) were prepared via the vacuum arc melting method, and the effects of Mo on the microstructure, mechanical properties, and friction and wear properties of the alloys were investigated. The addition of Mo improved the mechanical properties, wear resistance, and corrosion resistance of the alloy system. With the addition of trace amounts of Mo, the precipitate phase of the alloys transformed from spherical to acicular and plate-like. The precipitated phases in a co-lattice relationship with the matrix allow for a substantial increase in the strength of the alloy at both room and elevated temperatures without a significant loss of plasticity. Ni₃₅Al₃₀(FeCo)₂₅Cr₅Mo₅ has excellent mechanical properties, with a hardness of 558.2 HV; a yield strength of 1320 MPa at 600 °C; and a yield strength of 537 MPa at 850 °C. As the temperature increased, the wear mechanism changed from abrasive wear to adhesive wear. At 600 °C, Ni₃₅Al₃₀(FeCo)₂₅Cr₅Mo₅ had the lowest wear rate of 1.78 × 10⁻⁵ (mm³/Nm). The precipitated phases, which have high hardness and maintain a conformal interface with the matrix, play an important role in slowing delamination wear, keeping the wear rate of this alloy low at both room and high temperatures. Electrochemical experiments on the two alloys at room temperature revealed that Ni₃₅Al₃₀(FeCo)₂₅Cr₅Mo₅ exhibited excellent resistance to pitting, with a pitting potential of 0.016 V. Full article

► Show Figures

Graphical abstract

19 pages, 23277 KiB

Open AccessArticle

Metal Matrix Composite Coatings Deposited by Laser Cladding: On the Effectiveness of WC Reinforcement for Wear Resistance and Its Synergy with the Matrix Material (Ni Versus Co Alloys)

by Leandro João da Silva, Jeferson Trevizan Pacheco, Edja Iandeyara Freitas Moura, Douglas Bezerra de Araújo, Ruham Pablo Reis and Ana Sofia Clímaco Monteiro D’Oliveira

Coatings 2025, 15(4), 468; https://doi.org/10.3390/coatings15040468 - 15 Apr 2025

Viewed by 216

Abstract

This work investigates the effect of the addition of tungsten carbide (WC) particles as reinforcements to Ni (Inconel 625) versus Co (Stellite 6) alloys during deposition by laser cladding to form wear-resistant metal matrix composite (MMC) coatings. While the related literature often associates [...] Read more.

This work investigates the effect of the addition of tungsten carbide (WC) particles as reinforcements to Ni (Inconel 625) versus Co (Stellite 6) alloys during deposition by laser cladding to form wear-resistant metal matrix composite (MMC) coatings. While the related literature often associates the presence of WC with the enhanced wear performance of MMC coatings, this work shows that such an effect is not universal as it may critically depend on the metallic matrix employed. Thus, to demonstrate whether the reinforcement and matrix act synergically in such a scenario or not, MMC coatings formed by Inconel 625 and Stellite 6, both with WC content ranging from 10% to 40%, were deposited under the same laser cladding setup on AISI 304 stainless steel substrates, being WC-free samples produced together for comparison basis. As expected, the hardness levels increased with more WC presence in both matrices, but the wear resistance was specifically evaluated by means of the metal wheel abrasion test (ASTM B611). The results revealed that the use of WC as a reinforcement indeed affects the matrix materials differently; for Stellite 6, the wear resistance increased with up to 20% of WC (in contrast to the hardness indication), whereas for Inconel 625, the wear resistance progressively decreased with more WC content. It was observed via scanning electron microscopy (SEM) that the WC particles within the Inconel 625 alloy tended to intensive cracking, being in this way more prone to detach from the matrix and hence representing a weakening factor for the effectiveness of the coatings produced. Thus, it is concluded that the addition of WC particles, as potential reinforcements for MMC coatings, is not always effective (synergic with the matrix) in providing wear resistance, hence, opposing the prevailing consensus. This outcome and its reasons will certainly help with insights into proper design of MMC coatings, starting with the importance of matrix material selection. Full article

(This article belongs to the Section Laser Coatings)

► Show Figures

Graphical abstract

20 pages, 6451 KiB

Open AccessArticle

Facile Synthesis of Sponge-like Microstructured CuO Anode Material for Rechargeable Lithium-Ion Batteries

by W. T. R. S. Fernando, T. H. N. G. Amaraweera, K. M. D. C. Jayathilaka, L. S. R. Kumara, O. Seo, K. Osaka, O. Sakata, R. P. Wijesundera and H. W. M. A. C. Wijayasinghe

Coatings 2025, 15(4), 467; https://doi.org/10.3390/coatings15040467 - 15 Apr 2025

Viewed by 351

Abstract

CuO was synthesized by employing the facile chemical precipitation technique to vary the concentrations of Cu(NO₃)₂ in a range from 0.001 to 0.1 M. This was carried out in order to find the concentration of Cu(NO₃)₂ that [...] Read more.

CuO was synthesized by employing the facile chemical precipitation technique to vary the concentrations of Cu(NO₃)₂ in a range from 0.001 to 0.1 M. This was carried out in order to find the concentration of Cu(NO₃)₂ that results in optimal electrochemical performance in CuO as an anode electrode material for lithium-ion batteries. Among the investigated concentrations, the 0.03 M Cu(NO₃)₂ showed the best electrochemical performance. Of the synthesized materials, the scanning electron microscopic (SEM) analysis revealed the existence of a sponge-like morphology. X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), synchrotron X-ray diffraction (SXRD) and Raman spectrum confirmed the formation of a required CuO phase. The electron density distribution on the crystalline structure of the synthesized CuO indicates the existence of the highest distribution of electrons around Cu atoms, with enhanced productivity of the conversion mechanism during the cycling process. Further, this study shows that the electronic interfacial properties of Cu/CuO could be improved by optimizing the amount of acetylene black used for the electrode fabrication, with 20 wt% being the optimum value. The electrodes fabricated with the synthesized sponge-like microstructured CuO as the active material exhibited a high initial specific discharge capacity of 3371.9 mA h g⁻¹ and resulted in a specific discharge capacity of 442.9 mA h g⁻¹ (Coulombic efficiency of 97.4%) after 50 cycles, at a rate of 0.2 C. Moreover, the specific discharge capacity reported at the rate of 1.0 C was 217.6 mA h g⁻¹ with a significantly high Coulombic efficiency of about 98.0% after 50 cycles. Altogether, this study reveals the high potentiality of using sponge-like microstructured CuO as a high-performance anode electrode material for LIBs. Full article

(This article belongs to the Special Issue Electrodes and Coatings for Energy Storage Applications: Batteries and Supercapacitors)

► Show Figures

Figure 1

17 pages, 2705 KiB

Open AccessArticle

Evaluation of Hydrogen Trapping Capability at Interfaces Between Vanadium Carbide and Vanadium Nitride Nanoprecipitates with α-Fe by Density Functional Theory

by Shuaijun Yang, Yucheng Zhu, Chaoming Wang, Ruidong Li, Jun Hu and Zhong Chen

Coatings 2025, 15(4), 466; https://doi.org/10.3390/coatings15040466 - 15 Apr 2025

Viewed by 193

Abstract

The interface between dispersed compound nanoprecipitates and metal substrates can act as effective hydrogen traps, impeding hydrogen diffusion and accumulation, thus mitigating the risk of hydrogen embrittlement and hydrogen-induced coating failure. In this study, we considered the precipitation of vanadium carbide (VC) and [...] Read more.

The interface between dispersed compound nanoprecipitates and metal substrates can act as effective hydrogen traps, impeding hydrogen diffusion and accumulation, thus mitigating the risk of hydrogen embrittlement and hydrogen-induced coating failure. In this study, we considered the precipitation of vanadium carbide (VC) and vanadium nitride (VN) nanoprecipitates on a body-centered cubic Fe (α-Fe) substrate in the Kurdjumov–Sachs (K–S) orientation relationship. To evaluate the stability and hydrogen trapping ability of the interface, we used the first-principles method to calculate the interfacial binding energy and hydrogen solution energy. The results show that the stability of the interface was related to the type and length of bonding between atoms at the interface. The interface zone and the interface-like Fe zone have the best hydrogen trapping effect. We found that hydrogen adsorption strength depends on both the Voronoi volume and the number of coordinating atoms. A larger Voronoi volume and smaller coordination number are beneficial for hydrogen capture. When a single vacancy exists around the interface region, the harder it is to form a vacancy, and the more unstable the interface becomes. In addition to the C vacancy at the Baker–Nutting relationship interface found in previous studies being a deep hydrogen trap, the Fe and V vacancies at the α-Fe/VC interface and the V and N vacancies at the α-Fe/VN interface in the K–S relationship also show deep hydrogen capture ability. Full article

► Show Figures

Graphical abstract

17 pages, 9301 KiB

Open AccessReview

Recent Progress in Copper Nanowire-Based Flexible Transparent Conductors

by Jiaxin Shi, Mingyang Zhang, Su Ding and Ge Cao

Coatings 2025, 15(4), 465; https://doi.org/10.3390/coatings15040465 - 15 Apr 2025

Viewed by 266

Abstract

With the increasing demand for alternatives to traditional indium tin oxide (ITO), copper nanowires (Cu NWs) have gained significant attention due to their excellent conductivity, cost-effectiveness, and ease of synthesis. However, challenges such as wire–wire contact resistance and oxidation susceptibility hinder their practical [...] Read more.

With the increasing demand for alternatives to traditional indium tin oxide (ITO), copper nanowires (Cu NWs) have gained significant attention due to their excellent conductivity, cost-effectiveness, and ease of synthesis. However, challenges such as wire–wire contact resistance and oxidation susceptibility hinder their practical applications. This review discusses the development and challenges associated with Cu NW-based flexible transparent conductors (FTCs). Cu NWs are considered a promising alternative to traditional materials like ITO, thanks to their high electrical conductivity and low cost. This paper explores various synthesis methods for Cu NWs, including template-assisted synthesis, hydrazine reduction, and hydrothermal processes, while highlighting the advantages and limitations of each approach. The key challenges, such as contact resistance, oxidation, and the need for protective coatings, are also addressed. Several strategies to enhance the conductivity and stability of Cu NW-based FTCs are proposed, including thermal sintering, laser sintering, acid treatment, and photonic sintering. Additionally, protective coatings like noble metal core–shell layers, electroplated layers, and conductive polymers like PEDOT:PSS are discussed as effective solutions. The integration of graphene with Cu NWs is explored as a promising method to improve oxidation resistance and overall performance. The review concludes with an outlook on the future of Cu NWs in flexible electronics, emphasizing the need for scalable, cost-effective solutions to overcome current challenges and improve the practical application of Cu NW-based FTCs in advanced technologies such as displays, solar cells, and flexible electronics. Full article

(This article belongs to the Special Issue Design of Nanostructures for Energy and Environmental Applications)

► Show Figures

Figure 1

18 pages, 3709 KiB

Open AccessArticle

Microplasma Sprayed Tantalum Coatings on Ti Grade 5 Extra-Low Interstitials: Investigation of Thickness and Porosity Control

by Kuat Kombayev, Fuad Khoshnaw, Yernat Kozhakhmetov, Gulnur Tleuzhanova, Bagdat Azamatov and Yerkezhan Tabiyeva

Coatings 2025, 15(4), 464; https://doi.org/10.3390/coatings15040464 - 15 Apr 2025

Viewed by 230

Abstract

This study investigates the microplasma deposition of molten tantalum (Ta) onto a rotating Grade 5 Ti Extra-Low Interstitial (ELI) alloy, producing multilayer film coatings with a porous microstructure. Optimal parameters for microplasma spraying Ta were experimentally determined to improve the surface properties of [...] Read more.

This study investigates the microplasma deposition of molten tantalum (Ta) onto a rotating Grade 5 Ti Extra-Low Interstitial (ELI) alloy, producing multilayer film coatings with a porous microstructure. Optimal parameters for microplasma spraying Ta were experimentally determined to improve the surface properties of elbow joint implants. The physical and mechanical properties of the Grade 5 Ti ELI substrate and the Ta-based coating were analyzed. Moreover, mathematical modeling was utilized to determine the optimal parameters for the plasma coating process, including key factors such as spray distance, current, and rotational speed, which were systematically applied across three experimental series. A Ta coating thickness of 250 μm was achieved at 35 A current, 410 mm spray distance, and 7 rpm rotation speed under optimized deposition conditions. The results showed a microhardness increase on the Ta-coated surface, peaking above HV1000 with an average of HV742, while the Ti substrate averaged HV325. Additionally, the XRD patterns revealed the presence of metallic Ta alongside Ta oxides, such as Ta₂O and Ta₂O₅, in the Ta coatings. Full article

► Show Figures

Figure 1

21 pages, 5430 KiB

Open AccessArticle

Initial Research on Ultrasonic Vibration-Assisted EDM for Processing Cylindrical Surfaces

by Van-Thanh Dinh, Thi-Tam Do, Thu-Quy Le, Anh-Tung Luu, Ngoc-Pi Vu and Thi-Phuong-Thao Tran

Coatings 2025, 15(4), 463; https://doi.org/10.3390/coatings15040463 - 14 Apr 2025

Viewed by 160

Abstract

Electrical discharge machining represents a non-conventional machining process, specifically designed for the effective fabrication of materials that are difficult to machine and for components with complex geometries. Many studies have been carried out that combine electrical discharge machining with the ultrasonic vibration of [...] Read more.

Electrical discharge machining represents a non-conventional machining process, specifically designed for the effective fabrication of materials that are difficult to machine and for components with complex geometries. Many studies have been carried out that combine electrical discharge machining with the ultrasonic vibration of electrodes. Nevertheless, most of these investigations have concentrated on the processing of hole or cavity components. This document presents an experimental study focused on the design of an electrode holder for ultrasonic vibration electrical discharge machining, focusing on the machining of cylindrical surfaces. This study involved a two-stage design process for the electrode holder, aimed at determining the optimal length to achieve the maximal material removal rate and to ensure surface roughness. The novel aspect of this study is that it is the first to be published on the use of ultrasonic vibration in the electrical discharge machining process for processing cylindrical surfaces. Furthermore, splitting the electrode holder design process into two stages (theoretical calculation and experimental determination) made it possible to identify an electrode holder design for ultrasonic vibration electrical discharge machining that increased the MRR by 35.5% while maintaining SR values that were similar to those produced during the electrical discharge machining without ultrasonic vibration. Full article

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

► Show Figures

Figure 1

14 pages, 2221 KiB

Open AccessArticle

Antifouling Performance and Long-Term Efficiency of a Zwitterionic Sulfobetaine-Hydroxyethyl-Containing Polymethylmethacrylate Ter-Co-Polymer Coating Against Biomass-Producing Photosynthetic Strains

by Rana Haider Ali, Vincenzo Zammuto, Marco Nicolò, Filomena De Leo, Sandra Lo Schiavo and Clara Urzì

Coatings 2025, 15(4), 462; https://doi.org/10.3390/coatings15040462 - 13 Apr 2025

Viewed by 292

Abstract

The antifouling performance of a zwitterionic sulfobetaine-hydroxyethyl-containing polymethylmethacrylate ter-co-polymer (PSBM) is evaluated against three photosynthetic strains, namely Chlorella sp., Nannochloropsis sp., and Arthrospira maxima. PSBM-coated polymethylmethacrylate (PMMA) surfaces displayed a significantly reduced propensity for biofilm formation compared to rough and untreated controls, [...] Read more.

The antifouling performance of a zwitterionic sulfobetaine-hydroxyethyl-containing polymethylmethacrylate ter-co-polymer (PSBM) is evaluated against three photosynthetic strains, namely Chlorella sp., Nannochloropsis sp., and Arthrospira maxima. PSBM-coated polymethylmethacrylate (PMMA) surfaces displayed a significantly reduced propensity for biofilm formation compared to rough and untreated controls, leaving clean surfaces after 7 days of exposure. A tribological approach was adopted to estimate the long-term durability of the PSBM coating. Repeated cycles of exposure to Chlorella sp., Nannochloropsis sp., and A. maxima biomass subject the coating to stress and continuous biofilm challenges. After several cycles, the PSBM coating maintains a higher antifouling efficacy than the untreated PMMA surface, suggesting stability and high potential in photobioreactor applications. Full article

(This article belongs to the Special Issue Trends in Coatings and Surface Technology, 2nd Edition)

► Show Figures

Figure 1

Journal Menu

Journal Browser

Coatings, Volume 15, Issue 4 (April 2025) – 128 articles

Further Information

Guidelines

MDPI Initiatives

Follow MDPI