Coatings

20 pages, 1408 KiB

Open AccessArticle

An Integrated Model for Mass Transport, Corrosion Propagation, and Cracking in Offshore Reinforced Concrete Structures

by Wenchao Li, Huaikuan Wang, Jiangshun Wu, Bo Zhang, Yuming Lai, Feifei Huang and Ying Jin

Coatings 2025, 15(2), 172; https://doi.org/10.3390/coatings15020172 - 3 Feb 2025

The corrosion of steel reinforcements substantially degrades the longevity of reinforced concrete structures, particularly in marine settings. This investigation introduces a comprehensive model that simulates the processes involved in moisture and chloride ion transport, rebar corrosion, and the consequent cracking of concrete. The [...] Read more.

The corrosion of steel reinforcements substantially degrades the longevity of reinforced concrete structures, particularly in marine settings. This investigation introduces a comprehensive model that simulates the processes involved in moisture and chloride ion transport, rebar corrosion, and the consequent cracking of concrete. The model reveals that the transport dynamics of chloride ions are primarily dictated by their penetration rates through the solution. The sensitivity of the steel to corrosion is a function of the concentrations of water and chloride ions, whereas the rate of corrosion predominantly depends on the availability of oxygen at the corrosive site. Oxygen diffusion is the rate-limiting step in the entire process of the electrochemical reactions of the rebar. And the peak corrosion rates are observed at the interface between the solution and the gas phase. The model calculates the stress and strain in the concrete resulting from volumetric expansion due to oxidization of the steel bars. By accurately reproducing the progression of corrosion-related damage, this model provides crucial insights for predicting the service life of offshore concrete structures and enhancing durability against aggressive environmental conditions. Full article

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

19 pages, 18115 KiB

Open AccessArticle

Research on Laser Cladding Inconel 625 Coating Process for TRT Blades

by Jian-Tao Yao, Guo-Dong Zhang, Ze-Lin Chen, Yu-Hu Qu, Li-Shuang Wang and Hui Dong

Coatings 2025, 15(2), 171; https://doi.org/10.3390/coatings15020171 - 3 Feb 2025

Abstract

In this study, Inconel 625 coatings were deposited onto the surface of 2Cr13 stainless steel via laser cladding technology to ensure their corrosion resistance and mechanical properties. The microstructure and characteristics of coatings were adjusted by varying laser power (1200, 1500, and 1800 [...] Read more.

In this study, Inconel 625 coatings were deposited onto the surface of 2Cr13 stainless steel via laser cladding technology to ensure their corrosion resistance and mechanical properties. The microstructure and characteristics of coatings were adjusted by varying laser power (1200, 1500, and 1800 W), scanning speed (10, 15, and 25 mm/s), and overlap rate (40%, 50%, and 70%). The results showed that the impact resistance of blades was improved by 23% to 30% compared to the substrate, whereas the self-corrosion current density was reduced by 94%–98%, which indicated the outstanding resistance of specimens to damage and corrosion. At the same time, the appropriate processing parameters enabled the surface hardness of the 2Cr13 substrate to be improved. This study provides practical technical guidance for the repair of 2Cr13 blades and a comprehensive enhancement of their corrosion resistance and mechanical properties through parameter optimization. Full article

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

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13 pages, 3704 KiB

Open AccessArticle

Physical Properties and Rheological Characteristics of Cigarette Butt-Modified Asphalt Binders

by Xinhe Hu, Xianglong Chen, Jie Yu, Gang Cheng, Yunxiao Yuan and Lizhou Zhang

Coatings 2025, 15(2), 170; https://doi.org/10.3390/coatings15020170 - 3 Feb 2025

Abstract

Cigarette butt (CB) waste is abundant and difficult to biodegrade, which is dangerous for both the environment and human health. The key reason CBs are littered is that people do not know much about the harm CBs pose to the environment. Recycling CBs [...] Read more.

Cigarette butt (CB) waste is abundant and difficult to biodegrade, which is dangerous for both the environment and human health. The key reason CBs are littered is that people do not know much about the harm CBs pose to the environment. Recycling CBs in infrastructure construction can help raise people’s awareness. To promote the recycling of CB waste, this paper aimed to determine the feasibility of using CBs as a modifier for asphalt binders. In this research, CBs were preprocessed and mixed with virgin asphalt binder as a fiber modifier. Comprehensive laboratory investigations, including a softening point test, viscosity test, storage stability test, and temperature sweep test, were performed, along with a frequency sweep test, to evaluate the performance of the modified samples. During this investigation, samples were prepared with 1%, 2%, 3%, and 4% CBs. The results of the CB-modified samples were compared with the sample consisting of fresh bitumen (0% fiber). The results show that the physical and rheological properties of bitumen with incorporated CBs improved significantly, and CBs could be used instead of virgin cellulose fiber as a fiber modifier. However, CB-modified asphalt reduced the storage stability and low-temperature performance of the samples. Further research should focus on improving the storage stability and low-temperature performance of CB-modified asphalt binders to facilitate their application in asphalt pavements. Full article

(This article belongs to the Special Issue Surface and Interface Characteristics of Pavements: New Perspectives and Applications)

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15 pages, 4169 KiB

Open AccessArticle

Mechanism of Free Silver Formation While Preparing Silver-Coated Copper Powder by Chemical Plating and Its Control

by Junquan Chen, Xiaoyun Zhu, Nan Yang, Xiang Li and Bingzhe Yang

Coatings 2025, 15(2), 169; https://doi.org/10.3390/coatings15020169 - 3 Feb 2025

Abstract

When silver-coated copper powder is produced through chemical plating, free silver is often formed, which not only lowers coating quality but also increases the consumption of silver salt. Therefore, understanding the mechanism of free silver formation during the chemical plating process is essential [...] Read more.

When silver-coated copper powder is produced through chemical plating, free silver is often formed, which not only lowers coating quality but also increases the consumption of silver salt. Therefore, understanding the mechanism of free silver formation during the chemical plating process is essential for improving this process and enhancing the quality of silver-coated copper powder. This paper investigates the contents of free silver as well as the morphology and properties of the powder under different conditions by varying reaction parameters during the preparation of silver-coated copper powder. The morphology, phase, and properties of the powder samples are characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), and a resistance tester. In addition, the cathodic polarization behavior of the plating solution is analyzed using an electrochemical workstation. The results show that the complexing agent, reaction temperature, main salt drop acceleration rate, and dispersant concentration all affect the generation of free silver, and the complexing agent has the greatest impact. Full article

(This article belongs to the Collection Feature Paper Collection in Surface Characterization, Deposition and Modification)

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10 pages, 1831 KiB

Open AccessArticle

B-10-Based Macrostructured Cathode for Neutron Detectors

by Alexander G. Kolesnikov, Aleksey K. Kurilkin, Viktor I. Bodnarchuk, Alexander S. Ovodov and Marat R. Gafurov

Coatings 2025, 15(2), 168; https://doi.org/10.3390/coatings15020168 - 2 Feb 2025

Abstract

This paper focuses on the search for the desired thickness of the ¹⁰

B_{4}

C thin-film coating, as well as the macrostructuring of the aluminum foil substrate used as a cathode in the production of a multiwire gas detector of thermal neutrons. [...] Read more.

This paper focuses on the search for the desired thickness of the ¹⁰

B_{4}

C thin-film coating, as well as the macrostructuring of the aluminum foil substrate used as a cathode in the production of a multiwire gas detector of thermal neutrons. The impact of the ¹⁰

B_{4}

C film thickness from 1.0 to 2.5

μ

m and of the 0.05 mm thick

Λ

-shaped macrostructured aluminum foil substrate with an angle at the

Λ

-vertex from 10 to 45 degrees, with a height from 0.5 to 4 mm and a distance between the

Λ

-structures from 0.1 to 0.8 relative units on the neutron registration efficiency 1.8Å, was investigated. Numerical modeling of the electrostatic field was carried out using the Elcut software package. The interaction of neutrons with the ¹⁰

B_{4}

C thin-film coating was modeled using the Monte Carlo method in the Geant4 program. The optimal values of the geometrical parameters for the best neutron registration efficiency were determined. Full article

(This article belongs to the Section Bioactive Coatings and Biointerfaces)

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14 pages, 3473 KiB

Open AccessArticle

Phase Field Simulation and Experimental Study of Carbide Precipitation Process in Submerged Arc Welding on Descaling Roll

by Xing Han, Chang Li, Guohua Lv, Xinggang Wang, Hao Zhan, Fanhong Kong, Lei Feng, Han Sun and Fenghua Luo

Coatings 2025, 15(2), 167; https://doi.org/10.3390/coatings15020167 - 2 Feb 2025

Abstract

The mechanical properties of surfacing layers are significantly affected by the precipitation and evolution of carbides in nickel-based alloys. At present, the study of carbide precipitation in a Ni-Cr-B-Si surfacing layer is described by using the phase field method. In this paper, the [...] Read more.

The mechanical properties of surfacing layers are significantly affected by the precipitation and evolution of carbides in nickel-based alloys. At present, the study of carbide precipitation in a Ni-Cr-B-Si surfacing layer is described by using the phase field method. In this paper, the true Gibbs free energy of the M₂₃C₆ carbide phase in Ni-Cr-C ternary alloy was established by the CALPHAD method and thermodynamic database. The growth and coarsening process of M₂₃C₆ carbide was simulated based on phase field method. The microstructure of M₂₃C₆ carbide of Ni-Cr-C alloy at 1373 °C isothermal aging time was observed by scanning electron microscope (SEM). The results show that the growth and coarsening of the precipitated M₂₃C₆ carbide phase are undergone through multiple processes during isothermal aging. First, a single precipitate core is formed, and then the single precipitate continues to coarsen and grow, forming a lamellar structure. Two precipitates contact to form a single rod-like structure, and multiple precipitates form slender rod-like structures. Finally, the contacting elongated rod-like structures grow, forming a typical layered eutectic carbide. The precipitation behavior, growth, and coarsening process of M₂₃C₆-type carbides in Ni-Cr-B-Si series alloys are explored through phase field simulation and experimental research in this paper. A theoretical basis is provided for the rational control and distribution of carbides in surfacing layers. A reference is also offered for optimizing the nickel-based superalloy materials used for surfacing the surface of descaling rolls. Full article

(This article belongs to the Special Issue Advances in Processing and Characterization of Metal-Based Nanocomposites Materials towards Development of Functional Applications)

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20 pages, 7199 KiB

Open AccessArticle

Compatibility and Efficacy Evaluations of Organic Protective Coatings for Contemporary Muralism

by Laura Pagnin, Sara Goidanich, Francesca Caterina Izzo, Yezi Zhang, Dominique Scalarone and Lucia Toniolo

Coatings 2025, 15(2), 166; https://doi.org/10.3390/coatings15020166 - 2 Feb 2025

Abstract

Contemporary muralism is a constantly expanding form of urban art, whose preservation is highly debated and for which no specific preventive conservation measures have been defined. The degradation of painting materials remains a dramatic issue as mural paintings undergo rapid and inevitable chemical–physical [...] Read more.

Contemporary muralism is a constantly expanding form of urban art, whose preservation is highly debated and for which no specific preventive conservation measures have been defined. The degradation of painting materials remains a dramatic issue as mural paintings undergo rapid and inevitable chemical–physical reactions, leading to their aesthetic decay and chemical–mechanical disintegration. This work started with interviews with, and questionnaires given to experts in the field from which various needs emerged, including defining a testing protocol for the study of the compatibility and effectiveness of organic coatings to protect street art painted surfaces. Five protective formulations available on the market were selected and applied on mock-ups realized with three different types of paintings (alkyd, acrylic, and styrenic). The efficacy and affinity of the five protective treatments in relation to the different underlying painting layers were investigated. The adopted testing protocol enabled understanding the protection efficacy and compatibility of the different tested formulations in relation to the type of painting and wall preparation. The typology of the underlying paint mainly influences the final aesthetic result, while the application of the primer may play a relevant role in terms of the protection effectiveness, confirming the importance of pre-treating the substrate before painting. The results clearly show that there is still no specific and effective protection system that is appropriate for all commercial paints used by street artists. Full article

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15 pages, 3877 KiB

Open AccessArticle

UV-Curable Optical-Silicone-Modified Coatings Prepared from CO₂-Based Non-Isocyanate Polyurethane Diol

by Nana Sun, Hongyu Zhu, Shuxin Wang, Junyi Li, Guoqiao Lai and Xiongfa Yang

Coatings 2025, 15(2), 165; https://doi.org/10.3390/coatings15020165 - 2 Feb 2025

Abstract

Though polyurethanes (PUs) are widely used in people’s daily lives, traditional PUs are generally fabricated from toxic (poly)isocyanates. Furthermore, (poly)isocyanates are commonly industrially prepared from a seriously toxic and injurious chemical compound named phosgene, which is a dangerous gas that can cause lung [...] Read more.

Though polyurethanes (PUs) are widely used in people’s daily lives, traditional PUs are generally fabricated from toxic (poly)isocyanates. Furthermore, (poly)isocyanates are commonly industrially prepared from a seriously toxic and injurious chemical compound named phosgene, which is a dangerous gas that can cause lung irritation and eventually death. As is known to all, the consumption of carbon dioxide (CO₂)-based raw materials in chemical reactions and productions will be conducive to reducing the greenhouse effect. In this paper, non-isocyanate polyurethane (NIPU) diol was fabricated through a polyaddition reaction from ethylenediamine and CO₂-based ethylene carbonate, and then NIPU-based silicone-containing thiol hyperbranched polymers (NIPU-SiHPs) were synthesized from the NIPU diol. Finally, UV-curable optical-silicone-modified CO₂-based coatings (UV-NIPUs) were fabricated from NIPU-SiHPs and pentaerythritol triacrylate by a UV-initiated thiol-ene click reaction without a UV initiator. The UV-NIPUs demonstrated high transparency over 90% (400–800 nm), good mechanical performance with tensile strength reaching 3.49 MPa, superior thermal stability with an initial decomposition temperature (T_d₅) in the range of 239.7–265.6 °C, moderate hydrophilicity with a water contact angle in the range of 42.6–62.1°, a high pencil hardness in the range of 5–9H, and good adhesive performance of grade 0. The results indicate that it is a promising green chemical strategy to fabricate CO₂-based high-performance materials. Full article

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24 pages, 4174 KiB

Open AccessReview

Study of Grain Boundary: From Crystallization Engineering to Machine Learning

by Zhengran He, Sheng Bi and Kyeiwaa Asare-Yeboah

Coatings 2025, 15(2), 164; https://doi.org/10.3390/coatings15020164 - 2 Feb 2025

Abstract

Grain boundaries play a vital role in determining the structural, functional, mechanical, and electrical properties of semiconductor materials. Recent studies have yielded great advances in understanding and modulating the grain boundaries via semiconductor crystallization engineering and machine learning. In this article, we first [...] Read more.

Grain boundaries play a vital role in determining the structural, functional, mechanical, and electrical properties of semiconductor materials. Recent studies have yielded great advances in understanding and modulating the grain boundaries via semiconductor crystallization engineering and machine learning. In this article, we first provide a review of the miscellaneous methods and approaches that effectively control the nucleation formation, semiconductor crystallization, and grain boundary of organic semiconductors. Using the benchmark small molecular semiconductor 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS pentacene) as a representative example, the crystallization engineering methods include polymer additive mixing, solvent annealing, gas injection, and substrate temperature control. By studying the grain-width-dependent charge transport, we propose a grain boundary model as a fundamental basis to theoretically understand the intrinsic relation between grain boundary engineering and charge carrier mobility. Furthermore, we discuss the various machine learning algorithms and models used to analyze grain boundaries for the various important traits and properties, such as grain boundary crystallography, energy, mobility, and dislocation density. This work highlights the unique advantages of both crystallization engineering and machine learning methods, demonstrates new insights into discovering the presence of grain boundaries and understanding new properties of materials, and sheds light on the great potential of material application in various fields, such as organic electronics. Full article

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13 pages, 1840 KiB

Open AccessArticle

Crystalline Coating and Its Influence on Chloride Ion Diffusion Resistance of Carbonated Concrete

by Martin Mottl, Jiří Pazderka and Pavel Reiterman

Coatings 2025, 15(2), 163; https://doi.org/10.3390/coatings15020163 - 2 Feb 2025

Abstract

Carbonation and chloride ingress are the most important damaging mechanisms for steel-reinforced concrete. The combination of these two corrosion processes accelerates the destruction of concrete, leads to extensive structural repairs, negatively impacts durability, and significantly reduces the service life of the structure. One [...] Read more.

Carbonation and chloride ingress are the most important damaging mechanisms for steel-reinforced concrete. The combination of these two corrosion processes accelerates the destruction of concrete, leads to extensive structural repairs, negatively impacts durability, and significantly reduces the service life of the structure. One possible and effective way to reduce chloride diffusion through the concrete pore system is through the use of crystalline materials. An experimental study focused on the ability of an applied crystalline coating to increase the chloride resistance of carbonated concrete is presented in this paper. Carbonated concrete specimens treated with a crystalline coating were exposed to a sodium chloride solution for various periods of time, and a water-soluble chloride ion content analysis was performed on powder samples taken from the tested specimens. Chloride profiles presenting the chloride ion concentrations at selected depths are presented for multiple types of concrete at various ages to show the effect of crystalline technology on the chloride resistance of concrete. The results of this study confirm the impact of carbonation on chloride ion ingress through concrete and show that crystalline coatings can improve the chloride resistance of concrete. Using crystalline coatings on carbonated concrete can, from a long-term perspective, significantly reduce the chloride ion content in concrete placed in an aggressive environment. The crystalline coatings were functional even after 28 days, when the concentration of chloride ions was below the critical concentration. The crystalline coating was able to reduce the concentration of chloride ions by 68% under the surface of the concrete and by 65% at depths of 20–25 mm after 180 days of immersion, compared to the untreated concrete. Crystalline coatings reduce the depth of critical chloride ion concentration, effectively protect the concrete reinforcement against corrosion and extend the service life of the structure. Full article

(This article belongs to the Special Issue Green and Low-Carbon Buildings: Materials, Technology and Processes and Techniques)

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17 pages, 4122 KiB

Open AccessArticle

Enhancing Biodegradable Packaging: The Role of Tea Polyphenols in Soybean Oil Body Emulsion Films

by Jie Sun, Luyang Wang, Han Chen and Guoyou Yin

Coatings 2025, 15(2), 162; https://doi.org/10.3390/coatings15020162 - 2 Feb 2025

Abstract

To address the increasingly diverse demands for biodegradable packaging materials, such as for their physical properties and antioxidant properties, this study incorporated tea polyphenols (TPs) into soybean oil body emulsions (SOBs) and added a certain proportion of sodium alginate (SA) and octenyl succinic [...] Read more.

To address the increasingly diverse demands for biodegradable packaging materials, such as for their physical properties and antioxidant properties, this study incorporated tea polyphenols (TPs) into soybean oil body emulsions (SOBs) and added a certain proportion of sodium alginate (SA) and octenyl succinic starch sodium (SSOS) to prepare a biodegradable soybean oil body–tea polyphenol (ST) emulsion film. The study systematically evaluated the effects of different concentrations of TP (0–6 wt.%) on the structure, physicochemical properties, antioxidant activity, and antibacterial activity of ST films. The results showed that the physical properties, such as tensile strength and elongation at break, of the films increased significantly with the addition of TP, and the antioxidant and antibacterial activity also increased with the increase in TP concentration. When TP concentration was 2.5 wt.%, the barrier properties of the film (ST-2.5) significantly improved (p < 0.05), while water content and water solubility decreased. The Fourier transform infrared spectroscopy, scanning electron microscopy, and thermogravimetric analysis results showed that the structure of ST films became tighter at this point. The addition of TP also affected the sensory properties of ST films, such as with an increase in the opacity of the film. Compared with the control, the light transmittance of ST-6.0 decreased by 23.68% at a wavelength of 600 nm, indicating a significant reduction in film transparency. Moreover, the biodegradability test showed that ST films have good degradability. Therefore, the ST film, as a functional edible film, has broad application prospects in the food packaging industry. Full article

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14 pages, 4445 KiB

Open AccessArticle

Effect of Macroscopic Composition on the Performance of Self-Compacting Concrete

by He Liu, Wenxi Li, Haonan Zou, Wei Bian, Jingyi Zhang, Ji Zhang and Peng Zhang

Coatings 2025, 15(2), 161; https://doi.org/10.3390/coatings15020161 - 2 Feb 2025

Abstract

In recent years, there has been significant interest in the development of self-compacting concrete (SCC). This study views SCC as a two-phase composite material and introduces a new aggregate spacing coefficient model based on the concept of Fullman’s mean free path and stereological [...] Read more.

In recent years, there has been significant interest in the development of self-compacting concrete (SCC). This study views SCC as a two-phase composite material and introduces a new aggregate spacing coefficient model based on the concept of Fullman’s mean free path and stereological theory. The validity of the aggregate spacing coefficient model was verified. The relationship between the fine and coarse aggregate coefficients and the properties of SCC are revealed. The results show that the slump and slump flow of SCC increase as the fine and coarse aggregate coefficients increase. The coarse aggregate spacing coefficient has a significant influence on the compressive strength and drying shrinkage of SCC. A significant linear relationship between the coarse aggregate spacing coefficient and SCC dry shrinkage properties is revealed. Compared to the conditional mixing proportion method, which considers the aggregate volume as a control factor, the aggregate spacing coefficient takes into account the aggregate volume and gradation, which can more accurately reflect the characteristics of the aggregate. Meanwhile, this new perspective on the macroscopic composition of SCC provides insights into the controlling factors of its performance. Full article

(This article belongs to the Special Issue Advances in Pavement Materials and Civil Engineering)

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14 pages, 4201 KiB

Open AccessArticle

Effects of Ni-Ti Content on Mechanical Properties of Laser Cladding A100-(Ni-Ti) Coatings

by Tengfei Han, Xinyu Yao, Xusheng Mao, Bo Wen, Penghui Liang, Tangya Yan and Xinghui Zhu

Coatings 2025, 15(2), 160; https://doi.org/10.3390/coatings15020160 - 2 Feb 2025

Abstract

Among many methods to enhance the crack resistance of laser cladding coatings, adjusting the composition of laser cladding material is the most simple, feasible, and effective method. To improve the plastic toughness and crack resistance of A100 laser cladding coating, Ni and Ti [...] Read more.

Among many methods to enhance the crack resistance of laser cladding coatings, adjusting the composition of laser cladding material is the most simple, feasible, and effective method. To improve the plastic toughness and crack resistance of A100 laser cladding coating, Ni and Ti powders of an equal molar ratio were added to A100 powder as laser cladding powder. Laser cladding technology prepared A100-(Ni-Ti) coatings without crack defects. The cladding coatings’ phase composition and microstructure were analyzed using XRD and SEM, respectively. A ring-block friction and wear tester tested the wear resistance of the A100-(Ni-Ti) cladding coatings. A100-(Ni-Ti) cladding coatings mainly contain martensite and austenite. The elements Ni and Ti are distributed primarily in the austenitic phase region. The results show that adding Ni and Ti elements can reduce the microhardness of A100 cladding coatings. The average microhardness of the A100-0%(Ni-Ti) cladding coating is 532.50 HV, and the average microhardness of the A100-10%(Ni-Ti) cladding coating is 430.99 HV, while the average microhardness of the A100-30%(Ni-Ti) cladding coating is only 307.49 HV. The wear surface of the A100-10%(Ni-Ti) cladding mainly shows pits and a small amount of adhesive wear. The A100-20%(Ni-Ti) and A100-30%(Ni-Ti) cladding coatings show severe adhesive wear. The A100-10%(Ni-Ti) cladding with high microhardness and good run-in performance exhibits the best wear resistance. Full article

(This article belongs to the Section Laser Coatings)

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14 pages, 5799 KiB

Open AccessArticle

Tribological Behavior and Mechanism of Plasma-Sprayed High-Entropy Monoboride Coating over a Wide Temperature Range

by Chun Guo, Jinpeng Zhu, Yujing Li, Kaijun Yang, Mingliang Li, Hailong Wang and Jilin He

Coatings 2025, 15(2), 159; https://doi.org/10.3390/coatings15020159 - 1 Feb 2025

Abstract

Due to the extremely high hardness of high-entropy monoborides (HEMB), this study successfully prepared a new type of HEMB-(V_0.2Cr_0.2Ta_0.2Mo_0.2W_0.2)B coating by adjusting the spraying process using atmospheric plasma spraying technology. The high-entropy coating [...] Read more.

Due to the extremely high hardness of high-entropy monoborides (HEMB), this study successfully prepared a new type of HEMB-(V_0.2Cr_0.2Ta_0.2Mo_0.2W_0.2)B coating by adjusting the spraying process using atmospheric plasma spraying technology. The high-entropy coating was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS). The change rule concerning the alteration in the phase composition of the coating surface with power and protective atmosphere was explored, indicating that with the decrease in power and the application of a protective atmosphere, the generation of oxide on the coating surface is successfully inhibited. The wear resistance of the coating in a temperature range from room temperature to 800 °C was evaluated in dry sliding wear test conditions. The results indicated that the wear mechanism of (V_0.2Cr_0.2Ta_0.2Mo_0.2W_0.2)B coating below 400 °C is abrasive wear, and above 400 °C, the wear mechanism is mainly oxidative wear. Full article

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18 pages, 4964 KiB

Open AccessArticle

The Numerical Simulation and Experimental Investigation of the Laser Quenching Process of GCr15 Joint Bearings

by Xiuli Yang, Hao Zhang, Dongliang Jin, Xiqiang Ma and Maolin Cheng

Coatings 2025, 15(2), 158; https://doi.org/10.3390/coatings15020158 - 1 Feb 2025

Abstract

Joint bearings are widely used in modern industry in order to improve the mechanical properties of the outer surface of its inner ring. A laser quenching experiment was carried out in this paper. First of all, an experimental investigation was conducted on GCr15 [...] Read more.

Joint bearings are widely used in modern industry in order to improve the mechanical properties of the outer surface of its inner ring. A laser quenching experiment was carried out in this paper. First of all, an experimental investigation was conducted on GCr15 ball-bearing material utilizing laser quenching, focusing on the effects of laser irradiation angles ranging from 0° to 10° and laser power levels between 600 W and 1100 W on the degree of hardening and microstructural alterations of the bearing material. Additionally, a reliable finite element analysis model was developed to assess the temperature field throughout the process. The findings indicate that an inclined laser enhances the stability of the hardened layer. Specifically, the hardening effect is minimal when the laser power is below 700 W, and optimal hardening is observed at power levels between 800 W and 900 W. During the laser quenching process when the temperature of the bearing material surpasses Ac1, the cooling rate can exceed 1700 °C/s. In regions where the peak temperature exceeds Ac1, the microstructure will undergo refinement, resulting in a reduction in the size of the martensite and a significant decrease in the number of carbides. In addition, the hardness value of these regions can be increased by 6 to 8 HRC, and the thickness of the quenching layer may exceed 0.3 mm. In the temperature range between Ac1 and Ms, the bearing material undergoes tempering, resulting in lower hardness compared to the base material, along with larger martensite and carbide particles. Furthermore, when using the overlap technique during the laser quenching, there will be a tempering zone both inside and on the surface of the bearing; meanwhile, the heat zones generated by different passes of the laser may have partly interacted, and the hardened zone generated by the previous pass may undergo tempering again. Full article

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

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16 pages, 6098 KiB

Open AccessArticle

Modulating Micro-Arc Oxidation Coating Properties on 6061 Aluminum Alloy via OH⁻ to F⁻ Ion Ratio Optimization

by Bing Li, Heping Lei, Xing Yang, Xiuxiang Liao, Zhu Huang, Daichao Hao and Bingchun Jiang

Coatings 2025, 15(2), 157; https://doi.org/10.3390/coatings15020157 - 1 Feb 2025

Abstract

We investigate the influence of the NaOH to KF ratio in a silicate electrolyte on the corrosion resistance and tribological properties of micro-arc oxidation (MAO) coatings on a 6061 aluminum alloy. By optimizing the electrolyte composition, we achieved significant improvements in coating quality. [...] Read more.

We investigate the influence of the NaOH to KF ratio in a silicate electrolyte on the corrosion resistance and tribological properties of micro-arc oxidation (MAO) coatings on a 6061 aluminum alloy. By optimizing the electrolyte composition, we achieved significant improvements in coating quality. The surface morphology and composition of the coatings were characterized using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD). Our findings reveal that the coatings produced at a 2:1 NaOH/KF ratio exhibited superior corrosion resistance, with a corrosion potential of −1.279 V, corrosion current density of 1.85 × 10⁻⁷ A·cm⁻², and protective resistance of 1.50 × 10⁵ Ω·cm². Additionally, the surface roughness and coating thickness were measured at 0.68 μm and 8.04 μm, respectively, providing a robust foundation for enhancing the anticorrosive and wear-resistant properties of 6061 aluminum alloy. Full article

(This article belongs to the Special Issue Mechanical Properties and Tribological Behavior of Alloy/Coatings, 2nd Edition)

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11 pages, 32778 KiB

Open AccessArticle

Biomass-Derived Hard Carbon Materials for High-Performance Sodium-Ion Battery

by Yixing Chen, Jiaming Cui, Sheng Wang, Wentao Xu and Ruoqi Guo

Coatings 2025, 15(2), 156; https://doi.org/10.3390/coatings15020156 - 1 Feb 2025

Abstract

Using biomass-derived hard carbon materials as anode materials for sodium-ion batteries has facilitated resource recycling and brought significant economic benefits. However, the main obstacles to the large-scale application of these materials are the low Coulombic efficiency and high irreversible capacity of hard carbon [...] Read more.

Using biomass-derived hard carbon materials as anode materials for sodium-ion batteries has facilitated resource recycling and brought significant economic benefits. However, the main obstacles to the large-scale application of these materials are the low Coulombic efficiency and high irreversible capacity of hard carbon materials. This study used waste moso bamboo as a carbon source to prepare and pre-oxidize hard carbon through a stepped temperature sintering process. The introduction of oxygen atoms into the carbon layers has been shown to increase the spacing between the carbon layers, which facilitates the insertion of sodium-ions into them. Moreover, the presence of oxygen-containing groups increases the number of edge and vacancy defects in the carbon skeleton, thereby enhancing the actual capacity of the material. Studies have indicated that different pre-oxidation times have varying impacts on the electrochemical properties of hard carbon materials. This study used discarded moso bamboo as the raw material, and the optimal pre-oxidation duration of bamboo-based hard carbon was determined to be 4.5 h through a series of comparative experiments. A high-performance biomass-derived hard carbon material was prepared via a stepwise sintering process. It exhibited a specific capacity of 301.4 mAh·g⁻¹ at 0.1 C and a first-cycle Coulombic efficiency of 87%. Full article

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21 pages, 11288 KiB

Open AccessArticle

Impact of NiTi Shape Memory Alloy Substrate Phase Transitions Induced by Extreme Temperature Variations on the Tribological Properties of TiN Thin Films

by Mingxi Hou, Dong Xie, Xiaoting Wang, Min Guan, Diqi Ren, Yongyao Su, Donglin Ma and Yongxiang Leng

Coatings 2025, 15(2), 155; https://doi.org/10.3390/coatings15020155 - 1 Feb 2025

Abstract

NiTi alloys and thin film/NiTi composites are extensively utilized in frictional environments, particularly those experiencing extreme temperature fluctuations. Current studies mainly focus on preparing wear-resistant films on NiTi alloy surfaces but neglect the potential impact of temperature-induced phase transitions in the NiTi substrate [...] Read more.

NiTi alloys and thin film/NiTi composites are extensively utilized in frictional environments, particularly those experiencing extreme temperature fluctuations. Current studies mainly focus on preparing wear-resistant films on NiTi alloy surfaces but neglect the potential impact of temperature-induced phase transitions in the NiTi substrate on thin films’ performance. This study examines the effect of NiTi alloy phase transitions, induced by extreme temperature variations, on the tribological properties of TiN thin films on NiTi substrates. TiN films (1 μm thick) were deposited on NiTi alloy surfaces using magnetron sputtering technology. The transition of the main phase in the NiTi substrate between the R phase and the B19′ phase was achieved via liquid nitrogen cooling (−196 °C) and water bath heating (90 °C). XRD, EDS, SEM, and tribological tests analyzed the phase structure, elemental composition, micromorphology, and tribological behavior. Fatigue wear was identified as the predominant wear mechanism for the TiN films, with minor contributions from oxidative and abrasive wear. Phase transition from the R phase to the B19′ phase in the NiTi substrate induced by temperature change couls reduce the wear rate of the TiN film by up to 41.97% and decrease the friction coefficient from about 0.45 to about 0.25. Furthermore, the shape memory effect of the NiTi alloy substrate, caused by B19′ → B2 phase transition, resulted in the recovery of the TiN thin film wear track depth from 920 nm to 550 nm, manifesting a “self-healing” phenomenon. The results in this study are important and necessary for the provision of thin film/NiTi composites in frictional environments. Full article

(This article belongs to the Special Issue Mechanical Properties and Tribological Behavior of Alloy/Coatings, 2nd Edition)

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16 pages, 7277 KiB

Open AccessArticle

Surface Morphology Control of Ag-Coated Cu Particles and Its Effect on Oxidation Resistance

by Xianke Lu, Sixiang Kuang, Yuyuan Zhao and Xinyi Zeng

Coatings 2025, 15(2), 154; https://doi.org/10.3390/coatings15020154 - 1 Feb 2025

Abstract

Silver-coated copper (Ag-coated Cu) powder, combining the cost-effectiveness of copper with the oxidation resistance of silver, holds significant application value in photovoltaics and electronic pastes. In this study, Ag-coated Cu powder with a dense, uniform, smooth, and fully covered silver layer, as well [...] Read more.

Silver-coated copper (Ag-coated Cu) powder, combining the cost-effectiveness of copper with the oxidation resistance of silver, holds significant application value in photovoltaics and electronic pastes. In this study, Ag-coated Cu powder with a dense, uniform, smooth, and fully covered silver layer, as well as excellent dispersibility, was successfully prepared using the combined effects of ultrasonic and mechanical stirring. This study systematically analyzed the effects of different stirring conditions (mechanical stirring alone and mechanical stirring with ultrasonic oscillation), reaction rates (silver–ammonia solution supply rates of 1 mL/min to 9 mL/min), and silver contents (18%, 24%, and 28%) on the surface morphology and oxidation resistance of Ag-coated Cu powder. The results show that in the absence of ultrasonic oscillation, the uniformity and coverage of the silver layer were poor, with significant copper particle dissolution leading to hollow silver shells. Ultrasonic oscillation effectively reduced the roughness of the silver layer, improving its uniformity and coverage. Increasing the reaction rate had a minimal impact on the surface morphology but reduced the oxidation resistance of the powder. This study also analyzed the formation mechanisms of Ag-coated Cu with different surface morphologies, providing valuable guidance for producing high-quality Ag-coated Cu powder. Full article

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