Coatings

24 pages, 6981 KiB

Open AccessArticle

Machine-Learning-Driven Optimization of Cold Spray Process Parameters: Robust Inverse Analysis for Higher Deposition Efficiency

by Abderrachid Hamrani, Aditya Medarametla, Denny John and Arvind Agarwal

Coatings 2025, 15(1), 12; https://doi.org/10.3390/coatings15010012 - 26 Dec 2024

Abstract

Cold spray technology has become essential for industries requiring efficient material deposition, yet achieving optimal deposition efficiency (DE) presents challenges due to complex interactions among process parameters. This study developed a two-stage machine learning (ML) framework incorporating Bayesian optimization to address these challenges. [...] Read more.

Cold spray technology has become essential for industries requiring efficient material deposition, yet achieving optimal deposition efficiency (DE) presents challenges due to complex interactions among process parameters. This study developed a two-stage machine learning (ML) framework incorporating Bayesian optimization to address these challenges. In the first stage, a classification model predicted the occurrence of deposition, while the second stage used a regression model to forecast DE values given deposition presence. The approach was validated on Aluminum 6061 data, demonstrating its capability to accurately predict DE and identify optimal process parameters for target efficiencies. Model interpretability was enhanced with SHAP analysis, which identified gas temperature and gas type as primary factors affecting DE. Scenario-based inverse analysis further validated the framework by comparing model-predicted parameters to literature data, revealing high accuracy in replicating real-world conditions. Notably, substituting hydrogen as the gas carrier reduced the required gas temperature and pressure for high DE values, suggesting economic and operational benefits over helium and nitrogen. This study demonstrates the effectiveness of AI-driven solutions in optimizing cold spray processes, contributing to more efficient and practical approaches in material deposition. Full article

(This article belongs to the Special Issue Functional Coatings: Microstructure, Mechanical Properties, and Wear Behaviour)

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19 pages, 14017 KiB

Open AccessArticle

Multi-Step Simulations of Ionized Metal Physical Vapor Deposition to Enhance the Plasma Formation Uniformity

by Cheongbin Cheon, Min Young Hur, Ho Jun Kim and Hae June Lee

Coatings 2025, 15(1), 11; https://doi.org/10.3390/coatings15010011 - 25 Dec 2024

Abstract

Ionized metal physical vapor deposition (IMPVD), which is operated at a very low pressure to take advantage of the metal sputtering effect on the target surface, has unique properties compared with conventional DC magnetron sputtering. In this study, we investigated the effect of [...] Read more.

Ionized metal physical vapor deposition (IMPVD), which is operated at a very low pressure to take advantage of the metal sputtering effect on the target surface, has unique properties compared with conventional DC magnetron sputtering. In this study, we investigated the effect of the rotating magnetic field on the plasma formation of IMPVD to enhance the deposition uniformity. This was accomplished through a multi-step simulation, which enabled plasma analysis, sputtered particle and chemical reaction analysis, and deposition profile analysis. A two-dimensional particle-in-cell Monte Carlo simulation utilizes the exact cross-section data of the Cu ion collisions and calculates the particle trajectories under specific magnetic field profiles. This new methodology gives guidance for the design of the magnetic field profiles of IMPVD and an understanding of the physical mechanism. Full article

(This article belongs to the Special Issue Advanced Coating Technology by Physical Vapor Deposition and Applications)

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15 pages, 4750 KiB

Open AccessArticle

Characterization and Optimization of Boride Coatings on AISI 1137 Steel: Enhancing Surface Properties and Wear Resistance

by Asım Genç, Levent Urtekin and Merdin Danişmaz

Coatings 2025, 15(1), 10; https://doi.org/10.3390/coatings15010010 - 25 Dec 2024

Abstract

This study investigates the optimization of boron coating parameters for medium-carbon steels, specifically AISI 1137, and their subsequent effects on mechanical properties, which are crucial for industrial applications. Despite extensive research on boronizing processes, an understanding of the optimal conditions that enhance wear [...] Read more.

This study investigates the optimization of boron coating parameters for medium-carbon steels, specifically AISI 1137, and their subsequent effects on mechanical properties, which are crucial for industrial applications. Despite extensive research on boronizing processes, an understanding of the optimal conditions that enhance wear resistance and hardness while maintaining structural integrity is still lacking. To address this gap, we systematically examined the impact of boronizing temperatures (850 °C and 950 °C) and durations (2, 4, and 8 h) on the structural and mechanical properties of AISI 1137 steel. Our findings indicate the need for improved surface properties in medium-carbon steels used in demanding environments, such as automotive and machinery components. The boronizing process was carried out using Ekabor 1 powder, with characterization performed through optical microscopy, pin-on-disk wear tests, and Vickers hardness analysis. Results showed that the thickness of the boronized layer ranged from 50.6 μm to 64.8 μm, with wear resistance increasing by 1.8 to 3.9 times at 950 °C compared to at 850 °C. The measured hardness of the boronized surface layers varied between 1963.7 HV and 219.3 HV, decreasing from the boronized layer toward the base material. The optimal parameters for wear resistance and hardness were found to be a temperature of 950 °C and a duration of 8 h, facilitating the formation of FeB and Fe₂B phases, which significantly enhanced the steel’s mechanical properties. This research provides valuable insights into the boronizing process and establishes a foundation for the optimizing of surface treatments to extend the lifespan and performance of medium-carbon steels in industrial use. Full article

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20 pages, 15044 KiB

Open AccessArticle

The Influence of Load and Ball on the Sliding Wear Characteristics of HVOF-Sprayed WC-12Co Composite Coating

by Ali Avcı

Coatings 2025, 15(1), 9; https://doi.org/10.3390/coatings15010009 - 25 Dec 2024

Abstract

This study examines the impact of various abrasive balls and sliding loads on WC-12Co coatings. For this purpose, 4 N, 8 N, and 12 N loads were applied to the WC-12Co composite coatings with Al₂O₃ and Si₃N₄ [...] Read more.

This study examines the impact of various abrasive balls and sliding loads on WC-12Co coatings. For this purpose, 4 N, 8 N, and 12 N loads were applied to the WC-12Co composite coatings with Al₂O₃ and Si₃N₄ balls. WC-12 Co composite was deposited by the high-velocity oxygen fuel method on the AISI 304 substrate. The wear tests were conducted in accordance with ASTM G99 on a ball-on-disc tribometer at room temperature. In order to study the results of the coating tests, wear volume loss was measured against each counter body. Surface roughness and microstructure changes before and after wear were examined by electron microscopy. The resulting wear tracks were examined with an optical profilometer and the wear amount was calculated. When comparing the Al₂O₃ ball with the Si₃N₄ ball, the Al₂O₃ ball corrodes WC-12Co coatings more and is most susceptible to abrasive grooving, brittle cracking, and spalling. Wear rates rose by 77%, 58%, and 67% when the Si₃N₄ abrasive sample and the samples with Al₂O₃ coating were subjected to 4 N, 8 N, and 12 N loads, respectively. WC-12Co coating layers and powders were subjected to X-ray diffraction analyses, which revealed that coarse WC-12Co powder underwent less decarburization due to HVOF spraying. Full article

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11 pages, 5062 KiB

Open AccessArticle

Effect of Sintering Temperature on Tensile Properties of Ti-6Al-4V Alloy Manufactured Through Metal Injection Molding

by Zhengyang Mai, Haiying Wang, Yongjun Su, Changjiang Zhang, Yigao Miao, Chuancang Zhou and Lili Xu

Coatings 2025, 15(1), 8; https://doi.org/10.3390/coatings15010008 - 25 Dec 2024

Abstract

Titanium and titanium alloys exhibit low density, high strength and excellent corrosion resistance, and have become workhorses in modern aerospace and chemical processing industries. Recently, Ti-6Al-4V alloy has been manufactured through metal injection molding (MIM). MIM is widely utilized in various manufacturing industries [...] Read more.

Titanium and titanium alloys exhibit low density, high strength and excellent corrosion resistance, and have become workhorses in modern aerospace and chemical processing industries. Recently, Ti-6Al-4V alloy has been manufactured through metal injection molding (MIM). MIM is widely utilized in various manufacturing industries due to the near-net-forming process, especially in the preparation of difficult-to-deform high-temperature alloys. Sintering temperature is vital to ensuring good tensile mechanical properties. In this work, Ti-6Al-4V alloy was sintered under various sintering temperatures, from 1150 to 1250 °C. The effect of sintering temperature on the mechanical properties was evaluated. The tensile test results exhibited that a yield strength of 896.35 MPa, an ultimate tensile strength of 980.83 MPa and plastic elongation of 9.61% were produced at 1150 °C for 4 h; a yield strength of 877.23 MPa, an ultimate tensile strength of 981.92 MPa and plastic elongation of 7.74% were produced at 1200 °C for 4 h; and a yield strength of 923.33 MPa, an ultimate tensile strength of 1002.24 MPa and plastic elongation of 6.57% were produced at 1250 °C for 4 h. Full article

(This article belongs to the Special Issue Trends in Spark Plasma Sintering of Advanced Materials)

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22 pages, 6005 KiB

Open AccessArticle

A New Method for Evaluating Liquefaction by Energy-Based Pore Water Pressure Models

by Jianlei Zhang, Qiangong Cheng, Haozhen Fan, Mengjie Dai, Yan Li, Jiujiang Wu and Yufeng Wang

Coatings 2025, 15(1), 7; https://doi.org/10.3390/coatings15010007 - 24 Dec 2024

Abstract

Liquefaction-induced damage can be mitigated through remediation methods, contingent upon a thorough evaluation of liquefaction, which necessitates comprehensive investigation. This paper presents a novel energy-based pore pressure model for the assessment of liquefaction potential, utilizing cyclic triaxial numerical tests. In this model, the [...] Read more.

Liquefaction-induced damage can be mitigated through remediation methods, contingent upon a thorough evaluation of liquefaction, which necessitates comprehensive investigation. This paper presents a novel energy-based pore pressure model for the assessment of liquefaction potential, utilizing cyclic triaxial numerical tests. In this model, the energy of the earthquake is quantified using the Arias intensity. The validity of the energy-based pore pressure model was corroborated by the results of cyclic triaxial tests. Based on the validated model, a new methodology that incorporates permeability and the shear stress reduction coefficient was proposed for the evaluation of liquefaction potential. This new approach was further validated through centrifuge tests and numerical simulations. The findings indicate that the proposed method can accurately predict the generation and accumulation of excess pore pressure, thereby demonstrating its efficacy in evaluating ground liquefaction potential. Full article

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

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15 pages, 8986 KiB

Open AccessArticle

Self-Anchoring Coumarin Oxime Ester Photoinitiators with Low Migration for UV-LED Curable Coatings

by Zhihong Chen, Pin Yang, Huaqiao Lu, Shiyun Xiong, Gaole Dai and Zhiquan Li

Coatings 2025, 15(1), 6; https://doi.org/10.3390/coatings15010006 - 24 Dec 2024

Abstract

Reducing photoinitiator migration from photocured coatings remains a critical challenge, particularly for applications in food packaging and healthcare products. Here, we report a series of novel UV-LED sensitive oxime ester photoinitiators that possess self-anchoring ability through incorporating polymerizable double bonds into the coumarin [...] Read more.

Reducing photoinitiator migration from photocured coatings remains a critical challenge, particularly for applications in food packaging and healthcare products. Here, we report a series of novel UV-LED sensitive oxime ester photoinitiators that possess self-anchoring ability through incorporating polymerizable double bonds into the coumarin chromophore. All photoinitiators exhibit strong absorption around 340 nm and efficient photolysis under 365 nm LED irradiation, showing good initiating efficiency in acrylates and thiol-ene formulations. Migration studies show that the incorporation of polymerizable groups at the oxime ester terminus reduces the migration rate of the residual photoinitiator from 81% to 16.3%, while introducing an allyl group into the coumarin structure further decreases it to 5% and potentially suppresses the migration of low-molecular-weight photolysis products. The dual-functionalized derivative achieves the lowest migration rate of 3%. This molecular design strategy provides an effective approach toward safe UV-LED curable coatings with minimal photoinitiator migration. Full article

(This article belongs to the Section Functional Polymer Coatings and Films)

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13 pages, 4456 KiB

Open AccessArticle

Impact of Surface Grinding on the Performance of Tilting Pad Bearings

by Peiji Yang, Peng Li, Qi Yuan, Quan Sun, Zhenya Xing and Zhiming Zhao

Coatings 2025, 15(1), 5; https://doi.org/10.3390/coatings15010005 - 24 Dec 2024

Abstract

Tilting pad bearings are core components of rotating machinery. Due to factors such as manufacturing, installation and operation, there may be a mismatch between the bearing pad surface and the shaft diameter, leading to issues like high bearing temperature and rotor system vibration. [...] Read more.

Tilting pad bearings are core components of rotating machinery. Due to factors such as manufacturing, installation and operation, there may be a mismatch between the bearing pad surface and the shaft diameter, leading to issues like high bearing temperature and rotor system vibration. In engineering practice, surface grinding is often used to resolve these problems. This paper analyzed the mechanism of surface grinding, systematically studies the impact of individual or combined surface grinding on the static and dynamic characteristics of tilting pad bearings and summarizes reasonable pre-load adjustment schemes. The results show that the principle of pad surface grinding is to change the pre-load coefficient of the bearings. The grinding of the oil inlet and outlet sides of the pad surface changes the clearance of the pad, increases the pre-load coefficient, reduces the working temperature of the bearing, increases the thickness of the oil film, and increases power consumption; the grinding of the middle parting surface of the pad changes the clearance of the bearing, increases the pre-load coefficient, and increases the main stiffness and damping coefficient of the bearing. Using these results, a fault diagnosis was performed on a turbine unit with excessive vibration during an on-site operation, leading to effective control. The research provides technical references for the condition monitoring of turbine tilting pad bearing vibrations and the safe operation of units, offering significant engineering implications. Full article

(This article belongs to the Special Issue Trends and Advances in Anti-Wear Materials and Coatings)

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11 pages, 3456 KiB

Open AccessArticle

Two-Dimensional Crystal Growth of MoS₂ Thin Films from Sodium Dodecyl Sulfate Micellar Solutions and Wettability Between Solution and Substrate

by Zhunda Zhu, Yuanyuan Liu, Yasuyuki Sawada and Nagahiro Saito

Coatings 2025, 15(1), 4; https://doi.org/10.3390/coatings15010004 - 24 Dec 2024

Abstract

In this study, the growth of 2D MoS₂ thin films on SiO₂/Si substrates was investigated using sodium dodecyl sulfate (SDS) micellar solutions, and the effects of SDS concentration and substrate treatment on crystal growth were evaluated. By increasing the SDS [...] Read more.

In this study, the growth of 2D MoS₂ thin films on SiO₂/Si substrates was investigated using sodium dodecyl sulfate (SDS) micellar solutions, and the effects of SDS concentration and substrate treatment on crystal growth were evaluated. By increasing the SDS concentration, the wettability was improved, and uniform MoS₂ crystal growth was promoted by micellar formation. When the SDS concentration exceeded 10⁻⁴ mol/L, the static contact angle sharply decreased, indicating uniform 2D material growth. The optimal conditions that enabled a uniform supply of Mo-based precursors were as follows: SDS concentration of 3.5 × 10⁻⁴ mol/L; Na₂MoO₄·2H₂O concentration of 1.7 × 10⁻² mol/L. The results indicate that solution-based processes using SDS are effective for 2D material growth, and they may be a valuable technique in future thin film device fabrication processes. Full article

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14 pages, 7058 KiB

Open AccessArticle

The Enhanced Electrochemical Properties of Lithium-Rich Manganese-Based Cathode Materials via Mg-Al Co-Doping

by Wanting Lu, Wenhui Deng, Xiyan Zheng, Kunling Lin, Mengyuan Liu, Guozhang Zhu, Jingyi Lin, Yi Wei, Feng Wang and Jiageng Liu

Coatings 2025, 15(1), 3; https://doi.org/10.3390/coatings15010003 - 24 Dec 2024

Abstract

Due to the advantages of high capacity, low working voltage, and low cost, lithium-rich manganese-based material (LMR) is the most promising cathode material for lithium-ion batteries; however, the poor cycling life, poor rate performance, and low initial Coulombic efficiency severely restrict its practical [...] Read more.

Due to the advantages of high capacity, low working voltage, and low cost, lithium-rich manganese-based material (LMR) is the most promising cathode material for lithium-ion batteries; however, the poor cycling life, poor rate performance, and low initial Coulombic efficiency severely restrict its practical utility. In this work, the precursor Mn_2/3Ni_1/6Co_1/6CO₃ was obtained by the continuous co-precipitation method, and on this basis, different doping levels of aluminum–magnesium were applied to modify the electrode materials by high-temperature sintering. The first discharge capacity can reach 295.3 mAh·g⁻¹ for the LMR material of Li_1.40(Mn_0.666Ni_0.162Co_0.162Mg_0.005Al_0.005)O₂. The Coulombic efficiency is 83.8%, and the capacity retention rate remains at 84.4% after 300 cycles at a current density of 1 C for the Mg-Al co-doped LMR material, superior to the unmodified sample. The improved electrochemical performance is attributed to the increased oxygen vacancy and enlarged lithium layer spacing after trace magnesium–aluminum co-doping, enhancing the lithium-ion diffusion and effectively mitigating voltage degradation during cycling. Thus, magnesium–aluminum doping modification emerges as a promising method to improve the electrochemical performance of lithium-rich manganese-based cathode materials. Full article

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

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18 pages, 15693 KiB

Open AccessArticle

Time-Optimal Robotic Arm Trajectory Planning for Coating Machinery Based on a Dynamic Adaptive PSO Algorithm

by Jiaqi Liu, Shanhui Liu, Mei Song, Huiran Ren and Haiyang Ji

Coatings 2025, 15(1), 2; https://doi.org/10.3390/coatings15010002 - 24 Dec 2024

Abstract

To address the issues of low trajectory planning efficiency, high motion impact, and poor operational stability in robotic arms during the automatic loading and unloading of aluminum blocks in coating machinery, a time-optimal trajectory optimization method based on a dynamically adaptive Particle Swarm [...] Read more.

To address the issues of low trajectory planning efficiency, high motion impact, and poor operational stability in robotic arms during the automatic loading and unloading of aluminum blocks in coating machinery, a time-optimal trajectory optimization method based on a dynamically adaptive Particle Swarm Optimization (PSO) algorithm is proposed. First, the loading and unloading process of aluminum block components is described, followed by a kinematic analysis of the robotic arm in joint space. Then, the “3-5-3” hybrid polynomial interpolation method is used to fit the robotic arm’s motion trajectory and simulate the analysis. Finally, with the robotic arm’s operation time as the objective function, the dynamically adaptive PSO algorithm is applied to optimize the trajectory constructed by hybrid polynomial interpolation, achieving time-optimal trajectory planning for aluminum block handling. The results demonstrate that the proposed method successfully reduces the trajectory planning times for condition 1 and condition 2 from 6 s to 3.59 s and 3.14 s, respectively, improving overall efficiency by 40.2% and 47.7%. This confirms the feasibility of the method and significantly enhances the efficiency of automated loading and unloading tasks for aluminum blocks in coating machinery. The proposed method is highly adaptable and well-suited for real-time trajectory optimization of robotic arms. It can also be broadly applied to other robotic systems and manufacturing processes, enhancing operational efficiency and stability. Full article

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16 pages, 5926 KiB

Open AccessArticle

Thermoelastic Vibration of Nickel Film Irradiated by Femtosecond Laser: Molecular Dynamics Study

by Wanrong Zhao, Yucheng Gu, Zenan Yang and Zhen Zhang

Coatings 2025, 15(1), 1; https://doi.org/10.3390/coatings15010001 - 24 Dec 2024

Abstract

A detailed understanding of the physical essence of the interaction between a femtosecond laser and its target material remains an important and challenging goal. In this paper, the thermoelastic vibration behavior of nickel films irradiated by a femtosecond laser is studied by a [...] Read more.

A detailed understanding of the physical essence of the interaction between a femtosecond laser and its target material remains an important and challenging goal. In this paper, the thermoelastic vibration behavior of nickel films irradiated by a femtosecond laser is studied by a molecular dynamics method combined with a two-temperature model. The model fully defines the spatial distribution of laser energy, the photoelectron coupling, and the electron-lattice coupling, and elucidates the temperature and stress evolution within the nickel film under femtosecond laser irradiation. Furthermore, the whole process and the mechanism of thermoelastic vibration is revealed at the atomic level. The thermoelastic vibration is divided into two stages, including continuous expansion during the process of energy relaxation and periodic expansion and contraction after reaching thermal equilibrium. The elastic oscillation of thin films is driven by periodic changes in energy, including the energy of atomic thermal motion and collective atomic motion. The effect of pulse fluence on thermoelastic vibration is also discussed in detail to provide reasonable suggestions for limiting this effect. This study provides the theoretical foundation and a feasible method for a deeper understanding of the interaction mechanisms between femtosecond lasers and materials. Full article

(This article belongs to the Special Issue Laser Surface Treatment Technology—New Perspectives)

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10 pages, 2377 KiB

Open AccessArticle

Could Marginal Adaptation of Composite Resin Restorations Be Influenced by a Different Polymer Using Different Techniques?

by Jefferson Ricardo Pereira, Alef Vermudt, Ageu Raupp Junior, Diego Saccon Bordignon, Henrique Vieira Medeiros, Lucas David Galvani, Ricardo Abreu da Rosa, Marcus Vinicius Reis Só and Milton Carlos Kuga

Coatings 2024, 14(12), 1618; https://doi.org/10.3390/coatings14121618 - 23 Dec 2024

Abstract

Background: Marginal adaptation is one of biggest challenges in restorative dentistry, mainly in restoration of composite resin. Even with development of lower shrinkage materials, like those which use the polymer silorane, it is necessary a faithful clinical protocol in order to obtain better [...] Read more.

Background: Marginal adaptation is one of biggest challenges in restorative dentistry, mainly in restoration of composite resin. Even with development of lower shrinkage materials, like those which use the polymer silorane, it is necessary a faithful clinical protocol in order to obtain better results and more clinical durability of restorative procedure. The purpose of this study was investigated if different polymers can influence on marginal adaptation of different composite resin restorations. Material and methods: Twenty class V cavities were confectioned in twenty human molars in a standardized way. Ten dentists received one tooth each and a questionnaire to describe their own clinical protocol. The other 10 teeth were restored by one researcher as control group. The cavities received the adhesive system than increments of composite resin, and so the restorations were finished with finishing bur (KG Sorensen, São Paulo, SP, Brazil) to remove the excess, followed by sof-lex discs (3M ESPE). After this stage, all of specimens were embedded in 1% Methylene blue (Prolabo, Paris, France) during 48 h. The evaluation of pigment penetration into the interfaces was performed after specimens were washed in distilled water and longitudinally sectioned with steel Diamond disc in low velocity. Results: There was significant statistical difference between the different techniques using compose resin. Conclusions: it was possible conclude that the clinical protocol to perform dental restoration interfere dramatically in the final results of restorative procedure. Full article

(This article belongs to the Special Issue Organic and Polymeric Materials: Synthesis, Properties and Applications)

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18 pages, 22445 KiB

Open AccessArticle

Effect of Oscillating Amplitude on Microstructure and Mechanical Property of Laser Welding of Dissimilar Stainless Steel

by Xianhui Zeng, Chao Lu, Quan Zhu, Xiaoli Cui, Zilin Li, Wenqing Shi, Ruihua Zhang, Xiao Liu and Di Tie

Coatings 2024, 14(12), 1617; https://doi.org/10.3390/coatings14121617 - 23 Dec 2024

Abstract

The development of oscillating laser beam welding (OLBW) provides an opportunity to improve the weld formation of dissimilar stainless steels. In this paper, the influence of oscillating amplitude on the weld formation, microstructure, and mechanical properties of dissimilar 430/5Cr15MoV stainless steel was studied. [...] Read more.

The development of oscillating laser beam welding (OLBW) provides an opportunity to improve the weld formation of dissimilar stainless steels. In this paper, the influence of oscillating amplitude on the weld formation, microstructure, and mechanical properties of dissimilar 430/5Cr15MoV stainless steel was studied. The results showed that the weld morphology became smooth and uniform with an increase in the oscillating amplitude, and there was no obvious defect on the surface. The formation mechanism of weld overflow defects on the weld surface was discussed. The width of the weld metal increased with an increase in oscillation amplitude. The influence of beam oscillation on the microstructure of the weld center was significant, i.e., the proportion of equiaxed grains in the center of the welds increased as the oscillation amplitude increased. The maximum microhardness of the weld was obtained at an amplitude of 1.5 mm. Moreover, the tensile strength of the welds reached 477 MPa, which was comparable to the tensile strength of the 430 stainless steel base material. The fracture modes of all welds were typical ductile fractures, which suggests that the oscillation amplitude had a minor effect on the fracture mechanism of the welds. This study provided a new approach to welding dissimilar stainless steels and offers guidance for the selection of an optimum oscillation amplitude. Full article

(This article belongs to the Special Issue Advanced Surface Technology and Application)

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12 pages, 10570 KiB

Open AccessArticle

Effect of Ion-Assisted Deposition Energy of RF Source on Optical Properties, Microstructure, and Residual Stress of HfO₂ Thin Films

by Bo Wang, Jian Zhang, Hai Liu, Haigui Yang, Yanchao Wang, Haifeng Wang, Jingjie Pan, Zhen Liu, Zhenfeng Shen, Wenkai Gao, Hanwen Hu, Yi Zhao, Haolong Tang, Tongtong Wang and Xiaoyi Wang

Coatings 2024, 14(12), 1616; https://doi.org/10.3390/coatings14121616 - 23 Dec 2024

Abstract

HfO₂ thin films were prepared using radio frequency (RF) ion source-assisted deposition, and the effects of auxiliary ion energy on the microstructure, optical properties, and residual stress of the films were systematically studied. The experimental results showed that when the auxiliary ion [...] Read more.

HfO₂ thin films were prepared using radio frequency (RF) ion source-assisted deposition, and the effects of auxiliary ion energy on the microstructure, optical properties, and residual stress of the films were systematically studied. The experimental results showed that when the auxiliary ion energy increased, the extinction coefficient, compressive stress, and optical band gap were gradually increased. These changes were attributed to increased grain boundary defects, crystal structure disorder, and grain size decrease due to high-energy ion bombardment. The HfO₂ films deposited at a lower ion energy (600 V) exhibited higher surface quality (RMS = 0.78 nm), better optical properties (k = 10⁻⁵), and lower residual stress (1.26 GPa). Full article

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16 pages, 5584 KiB

Open AccessArticle

Analyses of the Properties of the NiO-Doped Ga₂O₃ Wide-Bandgap Semiconductor Thin Films

by Cheng-Fu Yang, En-Chi Tsao, Yi-Wen Wang, Hsin-Pei Lin, Teen-Hang Meen and Shu-Han Liao

Coatings 2024, 14(12), 1615; https://doi.org/10.3390/coatings14121615 - 23 Dec 2024

Abstract

The study began by pre-sintering Ga₂O₃ powder at 950 °C for 1 h, followed by the preparation of a mixture of Ga₂O₃ and 12 at% NiO powders to fabricate a source target material. An electron beam (e-beam) [...] Read more.

The study began by pre-sintering Ga₂O₃ powder at 950 °C for 1 h, followed by the preparation of a mixture of Ga₂O₃ and 12 at% NiO powders to fabricate a source target material. An electron beam (e-beam) system was then used to deposit NiO-doped Ga₂O₃ thin films on Si substrates. X-ray diffraction (XRD) analyses revealed that the pre-sintered Ga₂O₃ at 950 °C exhibited β-phase characteristics, and the deposited NiO-doped Ga₂O₃ thin films exhibited an amorphous phase. After the deposition of the NiO-doped Ga₂O₃ thin films, they were divided into two portions. One portion underwent various analyses directly, while the other was annealed at 500 °C in air before being analyzed. Field-emission scanning electron microscopy (FESEM) was utilized to process the surface observation, and the cross-sectional observation was primarily used to measure the thickness of the NiO-doped Ga₂O₃ thin films. UV-Vis spectroscopy was used to calculate the bandgap by analyzing the transmission spectra, while the Agilent B1500A was employed to measure the I-V characteristics. Hall measurements were also performed to assess the mobility, carrier concentration, and resistivity of both NiO-doped Ga₂O₃ thin films. The first innovation is that the 500 °C-annealed NiO-doped Ga₂O₃ thin films exhibited a larger bandgap and better electrical conductivity. The manuscript provides an explanation for the observed increase in the bandgap. Another important innovation is that the 500 °C-annealed NiO-doped Ga₂O₃ thin films revealed a high-energy bandgap of 4.402 eV. The third innovation is that X-ray photoelectron spectroscopy (XPS) analyses of the Ga_2p3/2, Ga_2p1/2, Ga_3d, Ni_2p3/2, and O_1s peaks were conducted to further investigate the reasons behind the enhanced electrical conductivity of the 500 °C-annealed NiO-doped Ga₂O₃ thin films. Full article

(This article belongs to the Special Issue Coatings for Advanced Devices)

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17 pages, 4105 KiB

Open AccessArticle

Experimental and Simulation Studies on Thermal Shock of Multilayer Thermal Barrier Coatings with an Intermediate Transition Layer at 1500 °C

by Pengpeng Liu, Shilong Yang, Kaibin Li, Weize Wang, Yangguang Liu and Ting Yang

Coatings 2024, 14(12), 1614; https://doi.org/10.3390/coatings14121614 - 23 Dec 2024

Abstract

Strain tolerance is a crucial factor affecting the thermal life of coatings, and a higher strain tolerance can effectively alleviate the thermal stresses on coatings during thermal shock. To improve the strain tolerance, the coating structure was optimized by introducing an intermediate transition [...] Read more.

Strain tolerance is a crucial factor affecting the thermal life of coatings, and a higher strain tolerance can effectively alleviate the thermal stresses on coatings during thermal shock. To improve the strain tolerance, the coating structure was optimized by introducing an intermediate transition layer in this study. The intermediate transition layer material was prepared using a 1:1 volume ratio mixture of 6–8 wt. % Yttria-stabilized zirconia (YSZ) and NiCrAlY powders in the experiments. The coating structure consisted of an Al₂O₃-GdAlO₃ (AGAP) anti-erosion layer, a YSZ layer, an intermediate transition layer, and a bonding layer from top to bottom. After thermal shock experiments at 1500 °C, the coatings with the addition of the intermediate transition layer exhibited different failure modes, with the crack location shifting from between the YSZ and the bonding layer to within the intermediate transition layer, compared to the coatings without the intermediate transition layer. Finite element simulation analysis showed that the intermediate transition layer effectively increased the strain tolerance of the coating and significantly reduced the thermal stress. Furthermore, incorporating an embedded micron agglomerated particle-based (EMAP) thermal barrier coating structure into the intermediate transition layer effectively alleviated thermal stresses and enhanced the coating’s thermal insulation performance. Full article

(This article belongs to the Special Issue Advances in the Preparation and Characterization Techniques for Developing Coating Materials and Applications)

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23 pages, 7659 KiB

Open AccessArticle

Laser Preparation and Underwater Drag-Reduction Performance of Secondary Fractal–V Groove Composite Structures on the Surface of Equal-Diameter Revolution Bodies

by Yan Wang, Zhanpeng Hu, Qian Zhang, Zhisheng Yang, Xueyan Zhao and Yonghua Wang

Coatings 2024, 14(12), 1613; https://doi.org/10.3390/coatings14121613 - 23 Dec 2024

Abstract

The reduction of drag for both aircraft and underwater equipment has the potential to reduce their overall energy consumption. Consequently, research into the drag-reducing performance of metal surfaces has significant practical applications. However, there has been more research on the machining of grooves [...] Read more.

The reduction of drag for both aircraft and underwater equipment has the potential to reduce their overall energy consumption. Consequently, research into the drag-reducing performance of metal surfaces has significant practical applications. However, there has been more research on the machining of grooves on flat surfaces and inside tubes and less research on the structure of drag-reducing grooves on the outside of circular rods. This paper presents a study in which laser etching technology is employed to machine a range of secondary fractal topologies and V-groove composite structures on the surface of equal-diameter stainless-steel bodies of revolution. The influence of different parameters on the surface properties of stainless-steel materials is analysed through the use of auxiliary positioning tools, adjustments to laser processing parameters and scanning path schemes, as well as the characterisation of the surface morphology of the processed stainless steel using super-depth microscopy, scanning electron microscopy, and other techniques. Subsequently, an underwater drag-reduction tester is employed to assess the drag-reduction efficacy of the optimised secondary fractal composite structure on the surface of the stainless-steel equal-diameter body of revolution. Subsequently, particle image velocity (PIV) tracking technology is employed to assess the surface flow field velocity and overall velocity average of the secondary fractal composite structure. The findings indicate that the secondary fractal composite structure exhibited a drag-reduction effect on the surface of the stainless-steel body of revolution only when the primary main groove had a width of 0.1 mm. Furthermore, an increase in the Reynolds number Re within the range of 4000 to 7000 resulted in a notable enhancement in the drag-reduction efficacy of the secondary fractal composite structure on the surface of the stainless-steel body of revolution. At Re values of 5000, 6000, and 7000, the corresponding drag-reduction rates were observed to be 5.15%, 5.28%, and 5.40%, respectively. Full article

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9 pages, 1549 KiB

Open AccessArticle

The Modelling of Light Absorption and Reflection in a SiO_x/Si Structure with Al Nanoparticles for Solar Cells

by Jevgenijs Kaupužs, Arturs Medvids, Pavels Onufrijevs, Leonid Fedorenko and Anatoliy Evtukh

Coatings 2024, 14(12), 1612; https://doi.org/10.3390/coatings14121612 - 23 Dec 2024

Abstract

In this study, the light propagation in a structure consisting of

S i O_{x}

on Si substrate with Al nanoparticles regularly placed in the

S i O_{x}

layer is considered. Numerical modelling is performed by solving the Maxwell equations for the [...] Read more.

In this study, the light propagation in a structure consisting of

S i O_{x}

on Si substrate with Al nanoparticles regularly placed in the

S i O_{x}

layer is considered. Numerical modelling is performed by solving the Maxwell equations for the electromagnetic waves. In distinction from the well-known finite-difference time-domain (FDTD) simulation technique, we do not solve time-dependent wave equations here; rather, we propose a new numerical technique. This technique allows us to determine the stationary amplitudes of the electromagnetic oscillations directly from the linear algebraic equation system. The obtained results apply to silicon solar cells with an

S i O_{x}

+ Al top layer to maximise their efficiency. We found that 26 nm and 39 nm diameters of spherical Al nanoparticles are nearly optimal for a λ = 435.8 nm wavelength of the incident light. In addition, we evaluated the (nearly) optimal parameters of their placement in the

S i O_{x}

layer. The results show the possibility of increasing the efficiency of solar cells by increasing the light absorption inside the active Si layer from ≈60% to ≈80%. Future perspectives on the proposed method and its possible applications are discussed. Full article

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