23 June 2025, Volume 38 Issue 3
    

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  • Advances in Additive Manufacturing of Continuous Fiber-reinforced Resin-based Composites
    LIU Xiaolong, WANG Wenyu, ZHAO Yang, WANG Xiaoming, NIU Zongwei
    China Surface Engineering. 2025, 38(3): 1-18. https://doi.org/10.11933/j.issn.1007-9289.20240802002
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    Continuous-fiber-reinforced resin-based composite materials represent a novel class of high-performance composites that have gained traction in recent years. The use of additive manufacturing technology for fabricating these composite materials offers significant advantages, including enhanced manufacturing flexibility and high forming efficiency, thereby making it a key research focus. Herein, the characteristics of both resin matrix and fiber materials are summarized, followed by an examination of the extrusion and impregnation processes involved in the additive manufacturing of continuous fiber-reinforced resin-based composites. Furthermore, the impact of process parameters such as temperature, printing speed, and printing spacing on the material are discussed. Additionally, the microstructure at the fiber-matrix interface and between layers are discussed, in addition to the mechanical properties of the material, including tensile and bending strengths. Finally, the challenges associated with increasing demand and performance limitations in the additive manufacturing of these composites are highlighted, proposing recommendations for their development, such as enhancing material recyclability and optimizing the additive manufacturing process. Both thermoplastic and thermosetting resins typically serve as matrix materials. Thermoplastic materials, exhibiting relatively low melting temperatures, facilitate processing in additive manufacturing. However, the high viscosity of these materials contributes to the low impregnation between fibers and resin, resulting in relatively lower mechanical properties than those of continuous fiber-reinforced composite materials produced via conventional methods. Conversely, thermosetting materials exhibit low viscosity, thereby enhancing fiber impregnation. However, they present challenges in the formation of composite materials, thereby increasing production costs. Additionally, additive manufacturing of thermosetting composite materials generates waste, contributing to material loss. Therefore, investigating the recyclability of these materials remains a crucial area for future research. The additive manufacturing process for continuous fiber-reinforced composite materials is influenced by factors such as fiber impregnation, material extrusion, fiber volume fraction, fiber orientation, and processing temperature, all of which influence material formation. However, significant challenges persist in additive manufacturing, and further improvements in the manufacturing process are essential. Research indicates that compared with composite materials produced via conventional processes, those fabricated via additive manufacturing exhibit lower mechanical properties. The primary factors influencing the mechanical properties of the final material include the bonding between the fiber-matrix interfaces as well as between layers. Inadequate bonding between the materials results in pore formation, causing stress concentration within the material and reducing its mechanical properties, thereby accelerating material failure. To further enhance the performance of fiber-reinforced composite materials and address existing limitations, future research must prioritize the following aspects. First, different matrix materials exhibit distinct effects on the performance of composite materials. Selecting an appropriate matrix material is crucial, necessitating further research into novel resin matrix materials. Additionally, as the use of composite materials increases, their recyclability has become as a critical constraint for industrial applications. Therefore, future research on material recyclability must be prioritized. Second, in the context of additive manufacturing of composite materials, in addition to the inherent properties of the materials, multiple avenues for process improvement exist. The impregnation process can be optimized via auxiliary techniques, such as plasma and oxidation treatments. Furthermore, controlling process parameters such as printing speed, temperature, and environmental conditions is essential for ensuring consistent material properties. Further investigation into the influence of these parameters on the material properties is necessary. Third, defects such as low interface performance and porosity in composite materials are typically attributed to insufficient compaction during the manufacturing process. Improving the compaction process or performing post-processing on the material can significantly enhance the performance of additive manufacturing.
  • Progress on Cold Spray Additive Manufacturing of Aluminum-based Intermetallic Compounds
    GAN Yuhe, WANG Jun, LUO Xiaotao, LI Changjiu
    China Surface Engineering. 2025, 38(3): 19-30. https://doi.org/10.11933/j.issn.1007-9289.20241018001
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    Aluminum-based intermetallic compounds are recognized for their excellent high-temperature mechanical properties, high resistance to oxidation and corrosion at elevated temperatures, and low density. These characteristics make them suitable for a broad range of applications, including protective coatings and structural components in aerospace and other industries. High-energy-beam additive manufacturing technologies, such as laser and electron beam melting processes, are effective for the rapid fabrication of complex metal structures. However, depositing aluminum-based intermetallic compounds remains challenging due to their complex phase structures and inherent brittleness, which often lead to flaws and defects, particularly cracks. Cold spraying, a process characterized by low processing temperatures and high deposition rates, shows significant potential for the low-heat-input fabrication of aluminum-based intermetallic compounds. This paper summarizes and analyzes recent advancements in the preparation of aluminum-based intermetallic compounds using cold spraying. Effects of powder design and fabrication routes on deposition behavior and deposit properties are discussed. These routes include intermetallic compound powder deposition, mixed elemental metal powder cold spraying followed by heat treatment, and cold spraying of mechanically ball-milled pseudo-alloy powders with subsequent heat treatment. First, the deposition behavior of intermetallic compound powders is reviewed and discussed. In the cold spraying process, successful deposition and bonding of spraying particles rely on plastic deformation induced by particle impact. However, due to the intrinsic brittleness of intermetallic compounds at room temperature, it is difficult to deposit particles directly using intermetallic compound powders as feedstock. In practice, when relatively soft materials are used, only a single layer of intermetallic particles can be mechanically embedded into the substrate layer. Subsequent spraying does not contribute to building up of the deposit because achieving successful bonding between intermetallic particles is highly challenging. Although high gas temperatures, even up to 1 000 ℃, are used to soften intermetallic particles, depositing a thick, high-quality deposit remains elusive. Thus, preparing intermetallic deposits using intermetallic feedstock powders continues to be a challenge. To address this issue, an alternative strategy involving the formation of intermetallic compounds during or after deposition has been extensively investigated. Following this strategy, mechanically mixed powders containing aluminum (Al) and other elemental powders, such as iron (Fe), nickel (Ni), or titanium (Ti), are used as feedstock materials. Due to the excellent plastic deformability of elemental metal powders, deposits containing mixed elemental metal particles can be easily deposited by cold spraying at relatively low gas temperatures and pressures. Post-spray heat treatment or annealing is then performed to activate interdiffusion between the Al and Fe / Ni / Ti phases, facilitating the formation of intermetallic compounds. However, the higher deposition efficiency of Al powder compared to Fe / Ni / Ti powders often results in cold-sprayed composite deposits with a higher Al content than the feedstock powder, complicating precise control of the chemical composition. This challenge is particularly pronounced when the feedstock powder contains more than three elemental metal powders. Additionally, during heat treatment, the long diffusion paths required for intermetallic compound formation frequently lead to the creation of numerous Kirkendall pores, and achieving a single intermetallic phase proves difficult. To overcome these challenges, a method involving the cold spraying of mechanically milled pseudo-alloy powders, followed by heat treatment, is proposed. By controlling the intensity and duration of high-energy ball milling, pseudo-alloy powders with alternating submicron lamellae of various metals can be prepared from mechanically mixed metal powders. The composition of the pseudo-alloy powder can be precisely controlled by adjusting the proportions of the raw materials. Moreover, the pseudo-alloy powder retains the plastic deformation capability of the original elemental metals, ensuring efficient deposition during cold spraying. The fine microstructure of the alternating submicron metal lamellae significantly shortens diffusion paths during heat treatment, effectively mitigating the formation of Kirkendall pores in the deposit. Finally, the effects of post-treatments such as friction stir processing (FSP) and hot isostatic pressing (HIP) on the microstructure and properties of the deposit are summarized. FSP treatment greatly refines the microstructure of deposits sprayed with mechanically mixed elemental metal powders, resulting in structures featuring alternating submicron metal lamellae and partially formed intermetallic compounds. This refinement significantly shortens diffusion paths between phases and prevents the formation of Kirkendall pores. However, it is challenging to process parts with complex shapes using this method. In contrast, HIP applies isostatic pressure during treatment, closing Kirkendall pores and making it suitable for parts with complex geometries. Overall, cold spraying of mechanically mixed elemental metal powders followed by HIP treatment, as well as cold spraying of mechanically milled powders combined with subsequent heat treatment, have been shown to produce aluminum-based intermetallic compounds with low porosity and high hardness. By comparing and analyzing the advantages and limitations of different technological routes, this study aims to provide guidance for the cold-spraying additive manufacturing of aluminum-based intermetallic compounds.
  • Research Progress of Ultrasonic Rolling in Metal Surface Nano-strengthening and Microstructure Performance Improvement
    DU Qin, HAO Jingbin, LIU Hao, YANG Haifeng
    China Surface Engineering. 2025, 38(3): 31-56. https://doi.org/10.11933/j.issn.1007-9289.20241031004
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    In the current era of industrial manufacturing and materials science, continuously enhancing material properties to meet the growing application challenges is an ongoing task. Metal materials play a key role in many industries because of their excellent mechanical properties and wide range of applications. Nevertheless, these metals are often subjected to wear, corrosion, and fatigue damage during practical use, which severely reduces their service life and reliability. Therefore, studying effective surface modification technologies that can improve the surface integrity and properties of metals has become a core issue in materials science research. Ultrasonic surface rolling processing (USRP) is an advanced material surface modification technology that combines ultrasonic energy and high-frequency mechanical vibrations to nano-strengthen the metal surface. This technology can cause plastic deformation on the surface of the material and significantly improve its surface integrity and mechanical properties. USRP can generate residual compressive stress on the surface of a material, effectively preventing the formation and expansion of cracks and reducing the permeability of the corrosive medium. In addition, this technology can form a nanostructured layer with a gradient grain size and orientation, thereby significantly enhancing the surface hardness and wear resistance of the material. This review summarizes the research progress in USRP in the fields of steel, aluminum alloy, titanium alloy, magnesium alloy, nickel alloy, and high-entropy alloy. It is demonstrated that these materials have achieved remarkable results in surface nano-strengthening and microstructural and performance improvement following USRP treatment. USRP technology can not only refine the grain size, reduce the surface roughness, and improve the surface hardness, but also convert the residual tensile stress into residual compressive stress to obtain a deeper nano-gradient hardened layer and residual compressive stress-affected area. This compensates for the low production efficiency of traditional mechanical processing methods as well as the mismatch between the working environment and performance requirements of high-performance materials. Finally, future application prospects and development directions of USRP are discussed. It is expected that focus will be placed on the refinement of theoretical models and the diversification of working methods. This research will further explore the theory of contact mechanics and surface integrity to develop a prediction model that can optimize the process parameters. In addition, USRP technology will be adapted to deal with complex parts and improve the efficiency and performance through multi-field coupling and process integration. The expansion of the application range will include composite materials and high-tech fields, including deep-sea exploration and aerospace satellites.
  • Research Progress of Titanium Dioxide Nanotube Arrays Constructed on Biomedical Titanium Surface to Deliver Antimicrobial Drugs
    LIN Xiaoxia, LIU Zhonghao, CHEN Xianshuai, OUYANG Jianglin, LI Wenjie, JIANG Jing
    China Surface Engineering. 2025, 38(3): 57-87. https://doi.org/10.11933/j.issn.1007-9289.20241209003
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    Titanium dioxide nanotubes (Titanium dioxide nanotubes, TiO2 NTs) have garnered significant attention in recent years owing to their unique nanostructures, high specific surface areas, and exceptional antibacterial and drug-release capabilities. As innovative surface-modification materials, TiO2 NTs show great promise for use in biomedical applications, particularly in infection control and drug delivery. The remarkable properties of TiO2 NTs, including their abilities to interact with biological systems, have made them a focal point of research for the development of new therapeutic strategies, particularly for combating bacterial infections. This review systematically examines the fabrication methods of TiO2 NTs and their applications in the antibacterial field, focusing on their roles in controlling bacterial infections and regulating drug release mechanisms. The methods used to fabricate TiO2 NTs, such as anodization, sol-gel processes, and hydrothermal synthesis, are critical for controlling their size, morphology, and surface properties, all of which directly influence their performance in various biomedical applications. These fabrication techniques allow for precise control over nanotube structures, which optimizes their drug-loading capacity and ensures their effectiveness in both infection prevention and controlled drug release. Moreover, TiO2 NTs are highly effective at preventing bacterial adhesion and biofilm formation, which are key challenges in medical treatments. Further, TiO2 NTs can be functionalized by loading various antibacterial agents, such as antibiotics, silver nanoparticles, and other bioactive compounds, to enhance their therapeutic effects. This review discusses various loading techniques, including physical adsorption, layer-by-layer self-assembly, and solution impregnation, for improving the efficiency of drug delivery. Physical adsorption is a simple and widely used technique for loading antibacterial agents, where the agents are adsorbed onto the surfaces of nanotubes. In contrast, layer-by-layer self-assembly creates a more complex structure with multiple layers, thus allowing for a more controlled and sustained release of drugs. Solution impregnation, which is another important technique, facilitates the incorporation of therapeutic agents into nanotubes and ensures that the drugs are released gradually, thus enhancing their antibacterial effects over an extended period. Additionally, sealing technologies are crucial for enhancing the drug release efficiency. Sealing methods typically involve the use of polymers or composite materials that encapsulate drugs, which prevents their premature release and ensures a more controlled and sustained-release profile. These sealing technologies improve the stability and performance of TiO2 NTs in biological environments and thereby optimize their therapeutic benefits. Despite the promising antibacterial properties and biocompatibility of TiO2 NTs, their practical applications face several challenges. Issues such as the structural stability of TiO2 NTs in biological environments, precision of drug release, and long-term safety must be addressed. The degradation and morphological changes in TiO2 NTs in biological fluids can compromise their functionality and biocompatibility. Moreover, ensuring precise drug release is challenging because the careful design of the nanotube structure and loading methods are required. Long-term safety, particularly the potential toxicity of TiO2 NTs and their degradation products, must be further evaluated to ensure their safe use in medical applications. Future research should focus on optimizing the design of TiO2 NTs by exploring new fabrication techniques and developing multifunctional composite materials that combine TiO2 NTs with other materials, such as polymers, natural biomolecules, or nanoparticles. These composite materials can enhance the stability and drug loading as well as control the release of TiO2 NTs, which thereby expands their applications in a variety of therapeutic contexts. Furthermore, clinical trials are required to validate the long-term safety and efficacy of TiO2 NTs in real-world medical applications. By addressing these challenges and advancing the development of TiO2 NTs, their potential for widespread use in the medical field can be realized to thereby provide innovative solutions for infection prevention, controlled drug delivery, and other biomedical treatments.
  • Process and Properties of CVD SiC Coatings Deposited on Additively Manufactured Ceramic Surfaces
    YANG Chenqian, YANG Wenxuan, SUN Ce, ZHANG Song, CHEN Peng, LIU Kai, TU Rong, YANG Meijun, WANG Chunjin, SHI Yusheng
    China Surface Engineering. 2025, 38(3): 88-98. https://doi.org/10.11933/j.issn.1007-9289.20241224005
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    Additive manufacturing technology can realize the integral molding of complex components of ceramic materials, but defects exist, including the “step effect” multiphase distribution, and porosity on the surface of the components. Moreover, subsequent precision machining struggles to meet the urgent demand for high-performance silicon-carbide ceramic components for space optical detectors and semiconductor manufacturing equipment. Therefore, this study proposes a novel approach by which to repair surface defects in ceramic additive manufacturing using the chemical vapor deposition (CVD) of high-purity, high-density silicon carbide coatings. However, the proposed method still faces problems of interfacial bonding with the additive ceramic substrate and the growth pattern of the coating. Hence, the effects of the deposition temperature on the interfacial bonding, micromorphology, surface hardness, and machinability of chemical vapor-deposited silicon carbide on additive manufacturing ceramic surfaces were systematically investigated. This study used rapid laser prototyping and the silicone infiltration composite method to manufacture silicon carbide ceramic substrates and prepare silicon carbide coatings via chemical vapor deposition. The silicon carbide coatings were deposited at different temperatures of 1 200, 1 300, 1 400, and 1 500 ℃. The coatings were then deposited on the surfaces of ceramic substrates at the same temperature. The effects of the deposition temperature on the hardness, deposition efficiency, interfacial bonding, microstructure, and processability of the SiC surface coatings were systematically investigated using various techniques such as scanning electron microscopy (SEM), X-ray diffraction (XRD), surface roughness measurements, micro-computed tomography (micro-CT), and scratch tests. The results showed that the hardness of the additively fabricated SiC ceramic was only 1 226 HV0.5 before any coating was deposited, and the roughness after polishing was 1 980 nm. Because of the presence of multiple phases, the roughness was too high to achieve a mirror effect. At a deposition temperature of 1 200 ℃, a peak of free silicon (Si) appeared in the coating owing to the high precursor gas concentration. However, the temperature was insufficient to promote uniform surface deposition, which resulted in an apparently homogeneous deposition in which free Si atoms in the gas phase were deposited directly onto the substrate. As the deposition temperature increases, the deposition rate accelerates, and the critical nucleation radius of the new phase gradually increases. The critical nucleation free energy also increases, resulting in the formation of larger SiC grains. The Si-C bonds within these grains remained intact, contributing to the overall hardness. However, at an excessively high deposition temperature, pores begin to form between the grains, resulting in low density and high porosity of the substrate and coating. Despite these problems, the silicon carbide coatings deposited at all temperatures formed good bonds with additively fabricated ceramic substrates. Notably, as the deposition temperature reaches 1 400 ℃, the silicon in the substrate begins to evaporate, and defects and porosity appear on the substrate surface. These defects provide additional nucleation points for the coating, and the morphology of the coating at the interface becomes columnar. As the coating grows to a certain thickness, it transforms into a dense structure. The columnar crystals significantly enhance the bond strength of the coating and improve its surface workability, which reduces its roughness to 9.08 nm. After polishing, the coating exhibited a mirror-like finish at all deposition temperatures. Thus, this study demonstrates that the application of CVD SiC coatings can significantly improve the surface quality of additively manufactured ceramics. This approach provides a theoretical basis for engineering applications of high-performance ceramic components in advanced devices.
  • Preparation and Properties of High-temperature Self-lubricating Wear-resistant Coating on 3D-printed SiC Ceramic Surface
    MA Chuchu, ZHANG Yao, LI Tianyang, WANG Youyuan, ZENG Xian, GONG Xiaolong, ZENG Fei, SUN Huajun, YAN Chunze, SHI Yusheng, LIU Kai
    China Surface Engineering. 2025, 38(3): 99-108. https://doi.org/10.11933/j.issn.1007-9289.20241127002
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    3D-printed silicon carbide (SiC) ceramics have excellent qualities such as high strength and temperature resistance and they permit flexible molding of complex shapes, leading to their wide use in energy processing and advanced aerospace applications in recent years. However, they have poor surface abrasion resistance. Using atmospheric plasma spraying (APS) is an economically feasible method for applying high-temperature abrasion-resistant coating on the surface of parts. Among the common self-lubricating wear-resistant coatings, YSZ coating, with its excellent high-temperature stability and oxidation resistance, is generally used in high-temperature environments. However, to improve the performance of the spraying process and reduce friction, a second phase is often added. This paper proposes (1) doping the coating with both low- and high-temperature lubricants to enable wide-temperature lubrication, (2) adding alumina to reduce the melting point of the powder and improve the coating densification, and (3) using a sol-gel-coated powder to improve the bonding between the base and second phases of the coating. In this study, three composite powders with different compositions of YSZ-Al2O3-CaF2-C were prepared using the sol-gel method and centrifugal atomization drying. The corresponding composite coatings (Ca0C0, Ca5C10, and Ca10C5) were deposited on the surface of 3D-printed SiC ceramics using the APS technique. The microstructures, friction properties, and wear mechanisms of the composite coatings were studied at room temperature and 600 ℃. The results show that the coatings have a typical laminated structure. Both the coatings and abrasion marks were primarily composed of YSZ, Al2O3, and m-ZrO2 phases, with CaF2 and C phases in Ca10C5 and Ca5C10 coatings. No other chemical reactions occurred during the coating application or owing to friction. The Ca0C0 coatings without CaF2 and C lubrication phases had the highest hardness, lowest wear rates, and largest friction factor at room temperature and 600 ℃. The strong bonding of the coating to the friction partner at 600 ℃ led to a friction coefficient of more than 1. The stabilized friction factor of Ca10C5 and Ca5C10 coatings were, respectively, 0.239 and 0.130 at room temperature and 0.175 and 0.288 at 600 ℃. The friction factor of Ca5C10 and Ca10C5 coatings considerably reduced upon the addition of CaF2 and C lubrication phases at both room temperature and 600 ℃, reflecting improved self-lubricating properties. However, the addition of the lubrication phases led to a decrease in the hardness of the coatings and an increase in the porosity defects inside the coatings, accompanied by an increase in wear rate. The Ca5C10 coatings with higher C additions were more prone to abrasive debris generation because of the higher volume fraction of C and lower hardness, resulting in higher wear rates. Based on the abrasion mark morphology, the wear mechanism of the coating was concluded to be primarily adhesive and abrasive. The YSZ-10Al2O3-10CaF2-5C coating had a lower friction factor and wear rate (1.02×10-5 mm3 / (N·m) at room temperature and 0.84×10-5 mm3 / (N·m) at 600 ℃) compared with YSZ-10Al2O3-0CaF2-0C and YSZ-10Al2O3-5CaF2-10C coatings in this study. This implies that YSZ-10Al2O3-10CaF2-5C coating has good self-lubricating and wear-resistant properties and can well improve the surface properties of 3D-printed SiC.
  • Microstructure Evolution and Mechanical Performance of Al-Li Alloy Manufactured via Solid-state Friction Stir Additive Manufacturing
    WANG Bo, CHEN Shaolong, GUAN Yuehui, YANG Yi, GUO Yanbing, SHEN Zhikang, LI Wenya
    China Surface Engineering. 2025, 38(3): 109-120. https://doi.org/10.11933/j.issn.1007-9289.20240918001
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    Aluminum-lithium (Al-Li) alloys are highly competitive and attractive lightweight structural materials commonly utilized in the aerospace industry owing to their combination of low density, high damage tolerance, and excellent formability, which enhance the comprehensive mechanical properties of transportation aircraft. Fusion-based additive manufacturing (AM) techniques often suffer from elemental burn-off in high-strength aluminum alloys and similar materials, which can lead to various defects and structural deformations such as porosity, cracks, shrinkage, and micropores. These defects typically arise during the melting and solidification processes. In contrast, friction stir additive manufacturing (FSAM), which is characterized by low-temperature processing and substantial plastic deformation, encourages the formation of fine grains and results in a narrower heat-affected zone, thereby improving the mechanical properties of the fabricated components. FSAM demonstrates significant advantages in the additive manufacturing of lightweight materials, such as aluminum and magnesium alloys. In this study, single-pass multilayer Al-Li alloy samples were fabricated using FSAM. The macroscopic morphology and microstructure of the cross sections were examined using a Leica optical microscope. The fracture mechanisms of the additive samples were analyzed by observing the tensile fracture surfaces using a ZEISS Gemini 500 scanning electron microscope (SEM). The same SEM equipment was used for electron backscatter diffraction (EBSD) mapping to assess the grain size and recrystallization. Microhardness tests were conducted using an SHV-1000Z microhardness tester to produce hardness distribution curves and contour maps of the sample cross sections. Tensile tests were conducted using a WHVS-1 M-AXYZF universal testing machine at a rate of 1.0 mm / s to record the maximum tensile shear force and displacement of each sample. The average values were calculated as the evaluation criteria. Optical microscopy results indicated that the effective additive region of the FSAM samples exhibited a dense structure without visible defects. The material in the stir zone (SZ) experienced the highest peak temperatures and the most intense plastic deformation, undergoing dynamic recrystallization and transformation into finer equiaxed grains. The EBSD analysis revealed that the SZ was entirely composed of fine equiaxed grains. Statistical analysis of grain size demonstrates a gradual decrease in average grain size from the top to the bottom of the SZ, with values of 3.1, 2.9, 2.2, and 2.1 μm, respectively. These variations were strongly influenced by the thermal cycling, stirring, and cooling conditions in each region. Grain-type analysis within the SZ showed that recrystallized grains accounted for 24.349% in the first layer, and the proportion increased to 45.462% in the second layer. In the third and bottom layers, the recrystallized grains comprised 28.441% and 27.053%, respectively. The degree of recrystallization in different regions corresponded to the statistical data of the high-angle grain boundary percentages and geometrically necessary dislocation densities. Microhardness testing reveals a “W”-shaped or “V”-shaped hardness distribution across the sample cross-section, symmetric to the centerline. Hardness progressively decreased from the base material (BM) to the SZ. The average hardness of the BM was 188 HV, whereas the SZ exhibited a relatively lower hardness, indicating a significant reduction due to thermal cycling. Tensile test results showed that the longitudinal specimen (LS) has an ultimate tensile strength (UTS) of 341 MPa and an elongation at break of 5.7%, whereas the transverse specimen (TS) has a UTS of 280 MPa and an elongation at break of 1.1%. The fracture modes in both longitudinal and transverse tensile specimens exhibited typical ductile fracture characteristics. In conclusion, FSAM effectively prevented the formation of multiple defects, promoted the development of fine and dense microstructures, and significantly enhanced the mechanical properties of the additive samples. The study of single-pass multilayer FSAM samples provides insights into the grain characteristics in different regions and their effects on the microhardness and mechanical properties. These findings offer a theoretical basis for further research on FSAM of lightweight, high-performance materials such as aluminum and magnesium alloys.
  • Improving the Microstructure and Wear Resistance of Additively Manufactured 316L Stainless Steel via Ultrasonic Severe Surface Rolling
    ZHANG Tao, CAO Chao, HUANG Di, ZHAO Jiyun
    China Surface Engineering. 2025, 38(3): 121-129. https://doi.org/10.11933/j.issn.1007-9289.20240908001
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    The additive manufacturing of 316L stainless steel presents numerous advantages, such as high efficiency, the ability to create complex geometries via freeform fabrication, and superior mechanical and corrosion resistance properties. These characteristics establish a strong foundation for the integrated manufacturing of critical components used in diverse fields, including mining machinery, engineering equipment, hydraulic systems, and other applications that require a seamless blend of structural integrity and functional performance. Despite these benefits, the wear resistance of additively manufactured 316L stainless steel remains a significant challenge that hinders the broad applicability of 316L stainless steel in demanding environments. Ultrasonic severe surface rolling (USSR) is a promising nanocrystallization technology. This innovative technique can generate thick and uniform gradient surface layers while producing exceptionally smooth surfaces on metallic materials, including 316L stainless steel. Importantly, USSR is effective not only on flat surfaces but also on components with complex geometries, showing its potential to significantly enhance the wear resistance of additively manufactured parts. In this study, selective laser melting (SLM) was used to fabricate 316L stainless steel. The SLM was followed by USSR to improve the wear resistance of the 316L stainless steel. A comprehensive microstructural analysis was performed using transmission electron microscopy and electron backscatter diffraction to investigate the microstructural evolution induced by the USSR treatment. The results indicate that the USSR process induced a gradient heterogeneous structure within the surface layer of the SLM-fabricated 316L stainless steel. This gradient heterogeneous structure is characterized by a microstructural transformation from a homogeneous nanograined structure at the surface to a heterogeneous structure with increasing depth. The surface nanograined structure was composed of austenitic grains and a few martensitic grains with an average grain size of 87 nm. In contrast, the SLM-fabricated sample exhibited a heterogeneous structure composed of austenitic grains with a large average grain size of 27 μm. Linear reciprocating sliding tribological tests were conducted using a ball-on-flat plate configuration at room temperature to evaluate wear resistance under both dry friction and emulsion lubrication conditions. The findings reveal a substantial reduction in wear volume under dry friction. The wear volume for the SLM-fabricated sample decreases from 3.58×10-2 mm3 to 1.90×10-2 mm3 for the USSR-treated sample, representing a notable reduction of 46.93%. Similarly, under emulsion lubrication, the wear volume decreases from 4.74×10-4 mm3 to 2.39×10-4 mm3, representing a reduction of 49.58%. These results unequivocally demonstrate that the USSR method significantly enhances the wear resistance of SLM-fabricated 316L stainless steel. Additionally, microhardness measurements show a marked improvement in hardness, which increases from 237.83 HV to 442.27 HV, representing an impressive enhancement of 86%. Further characterization of the worn surface morphology was conducted using scanning electron microscopy and energy-dispersive X-ray spectroscopy to elucidate the underlying wear mechanisms. The results indicate that the USSR treatment did not fundamentally alter the wear mechanisms of the SLM-fabricated 316L stainless steel. Under dry friction conditions, the worn surface morphology is characterized by high concentrations of elemental oxygen along with visible grooves and pits, suggesting that oxidative wear, abrasive wear, and delamination are the predominant wear mechanisms. In contrast, under emulsion lubrication, the morphology exhibited grooves and pits, indicating that abrasive wear and delamination took precedence in this environment. The observed enhancement in wear resistance is primarily attributable to the increased hardness and deformation resistance resulting from the heterogeneous gradient structure established by the USSR treatment. These findings provide valuable insights and present a novel methodology for enhancing the wear resistance of additively manufactured 316L stainless steel and its associated components, thereby paving the way for its wider adoption in industrial applications. A typical application is the production of durable and highly reliable water-hydraulic components for use in mining machinery.
  • Effect of Y2O3 Addition in Laser Cladding on the Thermal Fatigue of Stellite6 coated H13 Hot Forging Die Substrate Surface
    ZHOU Hu, LI Ribang, LI Ningbo, LI Tan, LUO Lingjie, WANG Bing, CHENG Zhan, LONG Weimin, GUAN Changyong
    China Surface Engineering. 2025, 38(3): 130-138. https://doi.org/10.11933/j.issn.1007-9289.20241205001
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    Thermal forging die technology is a core process for efficient and cost-effective mass production of critical components in the aerospace, aviation, and automotive industries. As essential tools for shaping hot-forged parts, the performance of thermal forging dies directly affects the quality of the forged components and production costs, playing a dominant role in the entire production chain. However, thermally forged dies often suffer from cracking, deformation, and thermal fatigue because of high temperatures, high pressures, and cyclic thermal stresses during service, resulting in premature failure. Therefore, laser cladding technology is applied to deposit high-performance cladding layers on the surface of thermal forging dies to enhance their thermal fatigue resistance under high-temperature conditions. This is of great significance for extending the service life. In response to the working environment and high-temperature application requirements of thermal forging dies, this study employed laser cladding technology to prepare Stellite6 and Y2O3 / Stellite6 coating on the cavity surface of a bucket tooth forging die. Based on the optimized laser process parameters, thermal fatigue tests were conducted on the Stellite6 clads, Y2O3 / Stellite6 composite clads, and H13 die substrate for 400 and 800 cycles, with some samples pretreated with cracks. The macroscopic crack morphology, microstructure, phase composition, surface microhardness, and bending strength of the thermal fatigue samples were systematically analyzed using ultra-depth microscopy, scanning electron microscopy (SEM), X-ray diffraction (XRD), Vickers microhardness testing, and computer-controlled universal testing machines. The results indicated that after 400 thermal fatigue cycles, the surface crack propagation lengths of these two claddings were significantly shorter than those of the H13 die substrate, demonstrating superior thermal fatigue resistance. The XRD analysis revealed the formation of the M23C6 phase in the cladding layers, which was more stable at high temperatures, effectively inhibiting the initiation and propagation of thermal fatigue cracks. Furthermore, the addition of Y2O3 significantly reduced the tendency of surface crack propagation in the Stellite6 cladding layer, further enhancing its thermal fatigue resistance. After 800 thermal fatigue cycles, the 0.8wt.% Y2O3 / Stellite6 coating exhibited excellent thermal fatigue resistance, thermal stability, and high-temperature oxidation resistance. Three-point bending tests revealed that the bending angle of the Stellite6 cladding layer was 2.11 times that of the substrate, whereas the bending strength of the Y2O3 / Stellite6 layer reached 2 716.9 MPa, which was significantly higher than the 1 820.86 MPa of the H13 substrate and 1 706.26 MPa of the Stellite6 layer. The microstructural analysis revealed that the addition of Y2O3 promoted the transformation of dendritic crystals into equiaxed crystals in the Stellite6 cladding layer, resulting in a uniform, fine-grained structure. This microstructural optimization not only improved the toughness of the material but also enhanced its strength and thermal stability by increasing the number of grain boundaries, which as a barrier to dislocation motion. In addition, Y2O3 facilitated the formation of a stable oxide film on the Stellite6 clads, further improving its oxidation resistance and high-temperature performance. Analysis of microhardness changes before and after thermal fatigue testing showed that the average microhardness of the H13 substrate decreased by 152.1 HV0.2. The hardness of the Stellite6 and Y2O3 / Stellite6 coating was also reduced by 91.39% and 98.16%, respectively. The XRD results indicated the formation of a stable γ-Co solid solution and M23C6 carbides in the Stellite6 cladding layer, which helped to maintain superior hardness and oxidation resistance at temperatures above 800 ℃. The addition of Y2O3 further refined the microstructure of the cladding layer, reduced the coarsening rate, and enhanced the oxidation resistance, high-temperature performance, and softening resistance by forming stable oxides. In conclusion, both the Stellite6 cladding layer and Y2O3 / Stellite6 composite cladding layer significantly improved the thermal fatigue resistance of the H13 die substrate, inhibited crack initiation and propagation, and substantially reduced the rate of microhardness degradation. This study provides theoretical support for extending the service life of H13 thermal forging dies and has significant engineering application value for enhancing the performance of thermal forging dies under extreme operating conditions.
  • High Precision Detection of Porosity and its Control in Laser Cladding of IN718 Nickel-based Alloy Utilizing an Enhanced YOLOv5 Algorithm
    SHENG Jie, WANG Yong, XU Tianyi, LIN Xiangqi, MENG Xiankai, ZHOU Jianzhong, CHEN Feng, LI Guo, HUANG Shu
    China Surface Engineering. 2025, 38(3): 139-151. https://doi.org/10.11933/j.issn.1007-9289.20240827001
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    Laser cladding is widely used in the repair of key components of aircraft engines due to its advantages, such as a small heat-affected zone, low dilution rate, good interface metallurgical bonding, and easy implementation of flexible processing. Stress changes induced by rapid heating and cooling during laser cladding and the complex composition of the cladding powder are important causes of cladding defects. Accurately detecting pores to actively regulate cladding porosity is important for improving the surface quality of cladding parts. To enhance the accuracy of porosity detection within laser cladding repair components and adjust the parameters of the laser cladding process, thereby reducing defects such as porosity and cracking in the cladding layer and improving the quality of the laser cladding layer, laser cladding experiments on IN718 nickel-based alloys with various process parameters were conducted in this study. In addition, an improved SP-YOLOv5 algorithm is developed for porosity detection. Initially, a Coordatt attention mechanism module is integrated between the input and convolutional layers to augment the spatial location information weight within the feature map. Subsequently, the YOLOv5 network structure was restructured to bolster its capability for detecting small targets of the porosity class. Furthermore, soft-NMS was implemented in place of the original Non-Maximum Suppression (NMS) for post-processing the detection results, which further reduced the false negative rate of the network. The porosity detection results yielded by the SP-YOLOv5 algorithm were compared with those of YOLOv5, Faster RCNN, RCNN, and ImageJ software analyses, revealing that the SP-YOLOv5 algorithm model achieved the highest accuracy improvement of 10.57%. Based on these findings, measurements of the laser cladding pool temperature, pool area, porosity rate, melting width, melting height, and melting depth of the cladding layer cross-section were performed. The results showed that the area of the molten pool was positively correlated with the laser power and powder feeding rate. As the laser power increased from 1 000 to 1 400 W, the average area of the molten pool increased from 5.77 to 10.52 mm2. On the contrary, the melt-pool area was negatively correlated with the scanning speed. Similarly, the height, width, and depth of the molten pool were positively correlated with the laser power and powder feeding rate, and negatively correlated with the scanning speed. A regression prediction model correlating the laser cladding process parameters with the porosity rate was established using a stacking algorithm, and an optimal set of laser cladding process parameters was derived using a target optimization algorithm. Finally, laser cladding experiments were conducted using the optimal combination of process parameters (laser power of 1 330 W, scanning speed of 460 mm / min, and powder feeding rate of 13 g / min), and the porosity parameters were measured. The experimental results showed that under these optimized parameters, the consistency between the porosity predicted by the stacking model and the actual measured values reached 97.5%, verifying the effectiveness of the optimization method and significantly improving the quality of the cladding layer. The results of this study provide a theoretical foundation for the effective control of porosity defects in laser cladding layers and expand the application of machine vision in thermal repair processes.
  • Effect of Post-weld Heat Treatment on the Microstructure and Wear Performance of Fe-Cr-Mo-C Wear-resistant Hardfacing Alloys
    LI Erhu, CUI Li, SHAO Wei, HE Dingyong, XU Yi, YU Jinman
    China Surface Engineering. 2025, 38(3): 152-160. https://doi.org/10.11933/j.issn.1007-9289.20241223002
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    When a single-tooth roller is used for crushing sintered mixtures over an extended period, the surface of the roller is subjected to high-temperature frictional wear from the sintered mixtures. This leads to severe wear on the surface of the roller, significantly reducing its crushing efficiency and service life. To enhance the high-temperature wear resistance of a single-tooth roller and prolong its service life, Fe-Cr-Mo-C wear-resistant hardfacing alloys containing M7C3 carbide were prepared using the flux-cored arc welding method. The MLS-225 wet rubber wheel wear tester was used to examine the effects of different Cr contents (14, 18, and 23wt.%) and heat treatment processes (heating rate, 10 ℃ / min; heating temperature, 900 ℃; holding time, 2 h; cooling method, furnace cooling) on the microstructure and wear properties of the Fe-Cr-Mo-C wear-resistant hardfacing alloys. The samples were characterized and analyzed using an optical microscope (OM), a Rockwell hardness tester, an X-ray diffractometer (XRD), a scanning electron microscope (SEM), and an energy-dispersive spectrometer (EDS). The results indicated that the Fe-Cr-Mo-C wear-resistant hardfacing alloys are mainly composed of martensite, retained austenite and M7C3. As the Cr content increases from 14wt.% to 23wt.%, the diffraction peaks corresponding to austenite increase slightly, indicating that the content of austenite in the alloy increases marginally as the Cr content increases. This is because an increase in the Cr content reduces the martensite transformation point (Ms point) of the Fe-Cr-Mo-C alloys. Moreover, the area fraction of M7C3 carbide increases from 48.9% to 57.2%, while its size decreases from 27.9 μm to 23.7 μm, with the Cr content increasing from 14wt.% to 23wt.%. The results of the hardness and wear tests show that increasing the Cr content improves the hardness and wear resistance of Fe-Cr-Mo-C wear-resistant hardfacing alloys. The wear particles mainly exert a micro-cutting effect on the alloys, resulting in the formation of plow grooves on their surfaces. The development of the wear resistance of Fe-Cr-Mo-C wear-resistant hardfacing alloys occurs because as the Cr content increases, the amount of carbide hard phases increases, and the microstructure of the hard phase is refined, which enhances the resistance of Fe-Cr-Mo-C alloys to the cutting action of abrasive particles. The wear mechanism of the as-welded Fe-Cr-Mo-C hardfacing alloys under wear conditions is micro-cutting. After heat treatment at 900 ℃ for 2 h, the phase composition of the hardfacing alloys remains unchanged, still consisting of martensite, retained austenite and M7C3. The area fractions of M7C3 carbide in the three hardfacing alloys decrease to 41.4%, 48.9%, and 50.8%, respectively. The size of the M7C3 carbide increases to 32.1, 27.3, and 26.4 μm for Fe-Cr-Mo-C alloys with Cr content of 14, 18, and 23wt.%. Thus, the post-weld heat treatment at 900 ℃ reduces the area fraction of M₇C₃ carbides and causes their coarsening, thereby reducing the wear resistance of the hardfacing alloys. Meanwhile, the wear mechanism remains the micro-cutting by abrasive particles. The influence of post-weld heat treatment on the microstructure and wear properties of Fe-Cr-Mo-C wear-resistant hardfacing alloys provides a reference for research and application in the repair of single-tooth rollers.
  • Microstructure and Properties of Ni-based Gradient Coating Reinforced with Diamond Particles by Induction Brazing
    WU Qilong, SUN Huawei, LI Yujia, SUN Zhipeng, YUAN Shicheng, ZHANG Lei
    China Surface Engineering. 2025, 38(3): 161-172. https://doi.org/10.11933/j.issn.1007-9289.20241013001
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    Wear-resistant coatings are widely applied to component surfaces to extend the service lives of mechanical components. As major equipment has advanced toward longer lifespans, higher efficiencies, and heavier loads, traditional Ni-based coatings have struggled to meet the increasingly complex and demanding conditions, despite the widespread use of such coatings. To enhance the microhardness and wear resistance of these coatings, researchers have focused on improving Ni-based material systems by adding rare earth elements and second-phase reinforcement particles. Diamond, which is the hardest naturally occurring material, has shown great potential to boost wear resistance as a reinforcing particle in Ni-based coatings. However, significant differences in the physical properties of diamonds, Ni-based coatings, and metal substrates can introduce residual stresses. To address this challenge, gradient coatings offer a promising solution that mitigates the stress caused by these differences in properties. A diamond-reinforced, Ni-based gradient composite coating was fabricated on 45 steel substrates using powder pre-positioning and high-frequency induction heating. The microstructure, phase composition, microhardness, and wear performance of the coating were analyzed using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), microhardness testing, and friction wear testing to reveal insights into the wear loss mechanism. The results indicate that the diamond-Ni base layer primarily consists of γ-(Fe,Ni), FeNi3, Cr7C3, CrB, Cr23C6, and diamond phases. Except for the diamond phase, the remaining material phases were similar to those observed in the Ni alloy layer. The microstructure of the gradient coating exhibited noticeable delamination. Numerous coarse incipient Cr7C3 carbides were observed in the Ni base layer. The growth direction of these carbides is closely related to both the composition of the molten metal in the coating and cooling mechanism used during the fabrication process. These Cr7C3 carbides tended to grow vertically within the coating, and their grain sizes decreased progressively as the coating transitioned toward the diamond-reinforced layer. In the diamond-Ni base layer, the carbides were smaller and diffusely distributed throughout the coating. Additionally, a Cr-C intermetallic compound capping layer formed around the diamond particles, thereby establishing a strong metallurgical bond between the diamond and Ni-based brazing alloy. The microhardness of the diamond-enhanced Ni-based gradient composite coatings exhibited a clear gradient distribution. The average microhardness of the Ni alloy layer was 567.9 HV, whereas the diamond/Ni-based layer exhibited a significantly higher average microhardness of 900.1 HV. The incorporation of the diamond particles effectively enhanced the microhardness of the Ni alloy, making it more resistant to wear. This gradient distribution of microhardness was critical for enhancing the overall wear performance of the coating. In the abrasive wear test, the introduction of diamond particles into the Ni-based coating altered both the load-bearing distribution and abrasive grain movement path within the coating. The diamond particles became the primary load-bearing entities during the wear process and effectively obstructed the path of the abrasive grain movement. This change in wear mechanism resulted in a shift from high-load orderly cutting to low-load disorderly cutting, which reduced the wear rate. Moreover, the diamond particles contributed to a reduction in the coefficient of friction. Owing to the low coefficient of friction inherent to diamond, the diamond-Ni layer exhibited a lower coefficient of friction than did the pure Ni alloy layer. However, during frictional interactions, the high hardness of the diamond-Ni layer reduced the deformation ability of the coating, making it challenging for the coating to conform to the friction surface and resulting in significant fluctuations in the coefficient of friction, which is a key consideration for the overall performance of the coating under real-world conditions. The altered wear mechanism and presence of diamond particles resulted in a wear resistance increase of nearly 1.8 times, compared with pure Ni-based coatings. Additionally, the introduction of diamond particles significantly reduced the coefficient of friction of the coating. Hence, this study demonstrates that diamond-reinforced, Ni-based gradient composite coatings hold considerable promise for enhancing the wear resistance and performance of industrial coatings under challenging service conditions.
  • Effect of Addition of CeO2 on Microstructure and Properties of Laser Cladding JG-3 and Numerical Simulation of Temperature Field
    ZHANG Xifeng, GUO Chen, WANG Dong, ZHANG Shuqiu, LI Xiaohai
    China Surface Engineering. 2025, 38(3): 173-184. https://doi.org/10.11933/j.issn.1007-9289.20240919002
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    In the coal industry, 27SiMn steel is widely used in key components, such as hydraulic support posts and jacks. However, frequent exposure to various stresses and wear in complex working environments render 27SiMn steel vulnerable. Therefore, to improve its surface properties and prolong its service life, the method of laser cladding JG-3 alloy powder was adopted. The temperature fields of 27 groups of laser claddings under different process conditions were studied using the ANSYS finite element analysis software, obtaining the temperature-time curve of a certain period of laser cladding. An increase in laser power, along with a decrease in spot diameter and scanning speed, led to an increase in temperature and range of the heat-affected zone in the laser cladding process. By comparing the melting state between the powders and simulation results with the theory of the cladding-layer radius, five groups of excellent parameters were determined, whereby the two groups with the smallest error were selected for the single-pass cladding test for verification. Comparing the simulation results of the melt pool, theoretical results of the melt pool, and actual results of the melt-pool test, the optimal combination of process parameters was determined to be 1 000 W-8 mm / s-5 mm. In surface engineering, adding an appropriate amount of rare earth CeO2 has been demonstrated to be advantageous, promoting microstructural refinement and improving the microhardness and wear resistance of the material. In this study, laser cladding of JG-3 and CeO2 on a 27SiMn steel surface was tested, and the microstructure, phase composition, microhardness, and wear resistance of the coating were analyzed. The results showed that with an increase in CeO2 content, the uniform density and microhardness of the tissue first increased and then decreased, whereas the content of pores, inclusions, friction and wear coefficient, and wear amount first decreased and then increased. In summary, compared to that without CeO2, the microstructure with 0.5% content was more uniform; formation of pores and inclusions was reduced; microhardness was increased; and friction factor and wear amount were reduced. This indicates that 0.5% CeO2 improves the performance of the cladding layer. The addition of 1.0% CeO2 can significantly improve the uniformity and density of the tissue, effectively reducing the generation of pores and inclusions. Concurrently, it promotes the formation of the Cr23C6 phase and Fe(Cr) solid solutions, which further refine the microstructure of the cladding layer. The hardness distribution of 1.0% CeO2 cladding layer was more uniform and reached a peak value, which was 8% higher than that without CeO2. The friction factor and friction mass loss of the material were minimal, displaying the best wear resistance, and the improvement effect on the wear resistance of the cladding layer was the most significant. The higher the CeO2 content, the better the performance was. When the CeO2 content reached 1.5% and 2.0% with an increase in CeO2 content, the uniformity and density of the structure decreased; the porosity and inclusions increased; the microhardness decreased; and the friction coefficient and wear amount increased, which adversely affected the performance of the cladding layer. Thus, 1.0% CeO2 had the best effect on the JG-3 alloy powder. In this study, laser cladding technology was combined with the addition of rare-earth CeO2 to improve the surface properties of 27SiMn steel. The effects of CeO2 on the microstructure and properties of the cladding layer were studied in detail, thereby providing a reference for the improvement of material properties in surface engineering.
  • Corrosion-friction Behavior of Laser Cladding FeCoCrNiAl0.5Ti0.5 High Entropy Alloy Coating
    GUO Yifan, GUO Xueping, LU Bingwen, YAN Xingchen, LIU Min, YIN Shuo
    China Surface Engineering. 2025, 38(3): 185-198. https://doi.org/10.11933/j.issn.1007-9289.20240906001
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    In recent years, laser cladding for the preparation of high-entropy alloys (HEAs) has attracted widespread attention in aerospace, transportation, and marine applications. FeCoCrNi-series high-entropy alloys are among the most widely studied transition-metal HEAs. Due to their unique properties (i.e., high-entropy effect, lattice distortion effect, slow diffusion effect, and cocktail effect), FeCoCrNi-series entropy alloys can achieve synergistic improvement in strength and toughness. Many studies have confirmed that laser-cladding FeCoCrNiAlTi HEA coatings offer excellent mechanical properties, including high strength, toughness, corrosion resistance, and oxidation resistance at high-temperatures. However, there are currently few studies on the friction and wear mechanism of FeCoCrNiAlTi HEA coatings under corrosion-friction coupling, and the interaction between alloy elements, microstructure, wear, and corrosion resistance remains unclear. In this study, a FeCoCrNiAl0.5Ti0.5 HEA coating was prepared on an AISI 1045 steel substrate using laser-cladding technology. Dry and wet friction tests were performed on the coating and substrate immersed in the solution for different durations. The dry and wet friction was tested using a ball-on-disc wear test. After grinding and polishing, the microstructure of the sample surface was characterized, followed by corrosion in an aqua regia solution (75 mL HCl and 25 mL HNO3 per 100 mL solution) for 30 s. The hardness pits of the sample and the transition from the coating to the substrate were observed via optical microscopy (OM). After the wear test, the depths and widths of the wear scars were measured using a three-dimensional profilometer. The microstructures and wear scar characteristics of the samples were characterized using a scanning electron microscope (SEM) equipped with an energy-dispersive X-ray spectroscope (EDS) and an electron backscatter diffraction (EBSD) detector. The phase compositions of the powder and sample were characterized using X-ray diffraction (XRD). The dry and wet friction behaviors of the coating related to atmospheric and corrosive environments were investigated in combination with the friction and wear test results. The results indicated that the microstructure of the laser-cladded FeCoNiCrAl0.5Ti0.5 HEA coating mainly consisted of a dendrite region (DR) with a body-centered cubic (BCC) phase and an interdendritic region (IR) with a face-centered cubic (FCC) phase. In addition, under spinodal decomposition, a portion of the BCC phase in the lamellar eutectic structure of the coating transformed into the L21 phase. The laser-clad FeCoNiCrAl0.5Ti0.5 HEA coating demonstrated excellent wear resistance. The friction factor of HEA coating and the dry friction factor of AISI steel substrate were 0.69 and 0.75, respectively, with wear rates of 5.04×10-5 mm3 / (N·m) and 1.41×10-4 mm3 / (N·m), respectively. The immersion time in a 3.5wt.% NaCl solution significantly influenced the wet friction and wear properties of the laser-cladded FeCoNiCrAl0.5Ti0.5 HEA coating. The wet friction wear rate of the coating increased with the immersion time. The wet friction wear rate of the unimmersed coating was 1.11×10-5 mm3 / (N·m), while that of the coating immersed for 15 days increased by 1.77 times, reaching 3.08×10-5 mm3 / (N·m). The main forms of dry friction and wear of the laser-clad FeCoNiCrAl0.5Ti0.5 HEA coating were three-body wear and abrasive wear, whereas the wet friction wear process was affected by corrosion, oxidation wear, and three-body wear. The wet friction wear process is lubricated by water and oxide films between the friction pairs; therefore, the wear rate is significantly lower than that in dry friction. However, under wet friction conditions, the oxide film was easily corroded, leading to the formation of microcracks and film delamination, ultimately resulting in three-body wear.
  • Monitoring and Closed-loop Control of Laser-directed Energy-deposition Melt Temperature Based on Fuzzy Incremental PID Control
    SU Lizhi, YANG Jianli, LU Tong, XU Zifa, GUO Wei, QIN Xiangli, WANG Wentao, HE Jianqun, MA Xinqiang, CHENG Wei
    China Surface Engineering. 2025, 38(3): 199-212. https://doi.org/10.11933/j.issn.1007-9289.20240728002
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    Laser-directed energy deposition (LDED) is a prominent technology in laser additive manufacturing and is known for its ability to enable the fabrication of complex, high-performance components layer by layer. The high-energy laser beam melts the substrate material, and the powder feeder simultaneously conveys the metal powder into the melt pool to deposit and solidify materials in a controlled manner into the required components The melt-pool temperature is crucial in determining the quality of the final component because it affects the microstructure, mechanical properties, and overall morphology of the deposition. During LDED, the temperature of the melt pool fluctuates owing to several variables, including changes in heat dissipation from the component, external environmental conditions, and equipment variations. These temperature fluctuations can result in defects such as unsatisfactory bonding, distorted geometry, or inconsistent material properties in the final component. Therefore, precise and real-time monitoring of the melt-pool temperature is essential to ensure that the deposition process remains within the optimal operating conditions, thus guaranteeing high-quality component production. The core challenge with LDED is the precise measurement and control of the melt-pool temperature. Measuring temperature directly is challenging owing to the dynamic and high-temperature nature of the melt pool, and conventional temperature-measurement methods may not be applicable or sufficiently precise in such environments. Hence, a color charge-coupled device coaxial temperature-measurement system is developed. This system allows real-time detection of the temperature distribution in the melt pool and provides important data for regulating the process parameters and maintaining the desired temperature profile during deposition. Several factors can affect the melt-pool temperature during LDED, including the powder feed rate, scanning speed, and laser power. A high laser power results in more melting and increases the melt-pool temperature, whereas lower power levels can lower the temperature and result in incomplete melting. Similarly, fluctuations in the powder feed rate and scanning speed can further affect the thermal conditions of the melt pool, thus resulting in temperature changes that may require real-time adjustments. To manage these temperature fluctuations and maintain a consistent process control, a closed-loop control system is required. In this study, an incremental fuzzy proportional-integral-derivative (PID) control algorithm is proposed to effectively control the melt-pool temperature. Fuzzy logic integrated into the PID control algorithm can address the nonlinear and uncertain aspects of LDED. It allows the control system to adapt to fluctuations and disturbances more effectively than conventional PID control methods. Simulink is used to develop a melt-pool temperature control simulation system that provides a theoretical framework to support the control-system design. The simulation allows various process parameters to be tested and the response of the control system to be evaluated under different operating conditions. The effectiveness of the control algorithm is verified through practical experiments, in which the laser power and powder feed rate are adjusted to simulate potential challenges in actual production scenarios. The results show that the fuzzy incremental PID algorithm performs better than the standard incremental PID algorithm, reduces the overshoot and steady-state errors, and improves the overall response time in a dynamic environment. This study contributes to the advancement of LDED technology by providing a novel approach for controlling the melt-pool temperature. By incorporating fuzzy logic into the PID algorithm, the system can manage the complex and nonlinear nature of LDED more accurately, thus ensuring consistent component quality and reducing the risk of defects. The closed-loop control system developed in this study has significant potential for real-world applications, as well as provides a robust solution for addressing temperature fluctuations and improving the reliability of laser additive-manufacturing processes.
  • Identification Method of Acoustic Emission Signals for States and Defects in Laser Cladding Process Based on Deep Learning
    LIU Lin, YANG Bin, YAO Xinyu, DING Haohao, ZHANG Shuyue, LIN Qiang, WANG Wenjian
    China Surface Engineering. 2025, 38(3): 213-224. https://doi.org/10.11933/j.issn.1007-9289.20240726001
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    Laser cladding (LC) is an advanced material surface-modification technology. Fe313 is a widely used LC material. The addition of WC (hard phase) to the Fe313 powder can enhance and improve the wear resistance of the cladding. However, WC increases the difference in the thermophysical properties inside the cladding and between the cladding and substrate, resulting in cladding defects. Therefore, it is important to monitor the cladding defects and achieve feedback regulation. Acoustic emission (AE) refers to the phenomenon of transient elastic waves emitted due to the rapid release of the local energy of the material. During the LC process, owing to differences in the defect type, size, shape, position, and other factors, each type of defect can generate a unique AE signal. The relationship between the AE signal characteristics and defects was established by extracting the characteristics of the AE signal. Combined with a deep-learning algorithm, an identification method for the LC process state and defects was designed, which can lay a foundation for improving the quality of LC. To conduct the full-cycle monitoring of the LC process, the entire process was divided into five states: powder feeding, melting, cooling, cracking, and porosity. In this study, 45 steel was used as the cladding substrate and 30wt.% WCp/Fe as the cladding powder. A single-layer, single-pass LC experiment was designed to collect AE signals during cladding. The samples were then cut, ground, and polished. The internal defects in the samples were observed using a super-depth microscope. A quantitative correlation between the number of defects and AE signal was determined by comparing the results of super-depth microscopic images and AE signals. A single-layer multipass LC experiment was designed, and the AE signals of the five states during the cladding process were collected. The AE signals of the five states were analyzed in the time, frequency, and energy domains. Appropriate LC process parameters for repeated tests were selected to obtain and create a dataset. To avoid significant differences in the feature values and discrete distributions between the data samples, the dataset was preprocessed using maximum normalization. An LC state recognition network model based on a Residual Network (ResNet) was designed to determine the LC state, and the AE signal samples of each cladding state containing 1024 signal features were input into the model. Then, the processing was carried out sequentially through convolutional layers, pooling layers, residual modules, and linear layers, and the recognized LC state was the output. Finally, using an LC defect number and duration recognition algorithm, the number of defects generated and the duration of each type of defect were identified. The AE signals of the five LC states were collected in a single-layer multipass LC experiment. From the time-domain perspective, the absolute amplitudes of the five LC states were sorted from largest to smallest as follows: crack, porosity, cooling, melting, and powder feeding states. From an energy perspective, the amplitudes of the five cladding states were sorted from largest to smallest as follows: crack, porosity, cooling, powder feeding, and melting states. In the frequency domain, the frequency bands of the five LC state signal samples were concentrated at approximately 150 kHz, and the identification method of AE signals for LC defects and states based on deep learning could effectively distinguish between the current LC state and the occurrence of defects. The identification accuracy was 97.74% for the unfamiliar datasets. The AE technology, as a nondestructive testing method, can monitor and identify defect signals in the LC process in real time. Deep learning methods, characterized by strong adaptability and high recognition accuracy, can handle complex nonlinear signals. By combining these two methods, new ideas and approaches are provided for the intelligent development of LC technology, and technical support is provided for the feedback control of LC.
  • Droplet Impacting Dynamics on Slippery Liquid-infused Porous Surfaces
    JIANG Luohao, CHEN Yixin, QI Shuaidong, WANG Jing
    China Surface Engineering. 2025, 38(3): 225-239. https://doi.org/10.11933/j.issn.1007-9289.20241025003
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    Inspired by Nepenthes pitcher plants, slippery liquid-infused porous surfaces (SLIPS) were first created in 2011 to offer a novel approach to surface engineering. Unlike conventional superhydrophobic surfaces (SHS), which rely on air lubrication, SLIPS utilize liquid lubrication with superior durability and pressure stability. With such advances, SLIPS possess outstanding liquid and ice repellency, self-healing, and enhanced optical transparency, which can be implemented in a wide range of energy applications, such as industrial anti-icing, anti-fouling, anti-frosting, and droplet-based power generation. Because most industrial application scenarios for SLIPS frequently encounter impacts of droplets, a mechanistic understanding of the dynamic interactions between SLIPS and impacting droplets is essential for the effective use of SLIPS under specific application conditions. This review systematically examines droplet impacting dynamics on SLIPS. In section 1, we introduce the thermodynamic conditions required to form effective SLIPS and their fabrication methods. There are two major criteria to achieve stable SLIPS: 1. lubricant spreading on the substrate, characterized by the spreading parameter (S) and 2. stabilization by van der Waals forces, characterized by the disjoining pressure or corresponding Hamaker constant (A). The fabrication of SLIPS involves structural treatments on substrates that are followed by chemical functionalization and the final lubrication selection. Based on the substrate structure, SLIPS can be categorized into 1D-SLIPS, 2D-SLIPS, and 3D-SLIPS based on the structural hierarchies varying from one-dimensional mono-molecule layers to two-dimensional micro- / nano-surface structures to three-dimensional crosslinked polymer matrices, respectively. In section 2, we summarize the dynamic behaviors of droplet impacts on SLIPS, including deposition, complete rebound, partial rebound, jet, and splash behaviors under conditions with different Weber numbers or other related dimensionless numbers. As the Weber number increases, the dynamic behaviors of droplets impacting SLIPS transitions from deposition to rebound and eventually to splash. The higher Weber number of a droplet indicates higher inertia before impacting the surface, which introduces stronger inertial forces to overcome the capillarity of the droplet. Eventually, these properties force the droplet to splash into smaller drops. Compared with many solid surfaces, SLIPS demonstrate a higher probability of droplet rebound, resulting in their advantages in the applications of anti-icing and anti-frosting. In section 3, we analyze the spreading dynamics, retraction dynamics, and contact time of SLIPS. In general, the droplet impacting on SLIPS experiences spreading and retraction processes. During the spreading process, the diameter of the droplet in contact with the surface gradually increases until the droplet spreading diameter reaches its maximum, driven by inertial forces. Subsequently, the droplet enters the retraction process under capillary and viscous resistant forces. The maximum spreading diameter can be scaled as βmax ~ We1/4 in most conditions. Moreover, the retraction dynamics dominated by viscous forces are affected significantly by the lubricant viscosity. With the increase of the contact angle and the decrease of the lubricant viscosity, the retraction velocity tends to be higher. Further, the contact time is mainly affected by the diameter of the droplet and the lubricant viscosity but is independent of the droplet impact velocity. Compared with superhydrophobic surfaces, the contact time on SLIPS is generally longer owing to viscous retention. In section 4, the different application potentials of SLIPS are systematically summarized. The stability and self-healing of SLIPS are advantageous for the applications, including anti-icing, anti-fouling, fog harvesting, and electricity generators. These applications with SLIPS may revolutionize the modern biomedical devices, solar panels, wind turbines, and small-scale energy generators. Finally, the dynamic characteristics of droplets impacting the SLIPS and the research direction are summarized and prospected. This review provides a comprehensive understanding of the key physical principles underlying the phenomena of droplet impacts on SLIPS as well as further application conditions of SLIPS in energy industries, including industrial anti-icing, defrosting, surface-enhanced heat transfer, and electricity generation from droplets.
  • Influencing Factors of the Bonding Strength of PVD Coatings on Rolling Bearing Surfaces and its Research Progress
    WANG Bingxu, CAI Zhaobing, LIN Guangpei, DONG Yinghui, GU Le
    China Surface Engineering. 2025, 38(3): 240-259. https://doi.org/10.11933/j.issn.1007-9289.20240507001
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    Rolling bearing surface failure is a key factor that restricts the development of mechanical devices and their service life when facing the harsh working conditions of high speed and heavy load coupled with multiple factors. In a physical vapor deposition (PVD) hard coating-steel substrate system, the mechanical properties of the coating and substrate steel have differences, leading to the insufficiency of the bond strength of coating and substrate, and then, in the high-speed and heavy-duty conditions are prone to cracking, peeling, and ultimately premature failure. PVD technology can protect rolling parts under the rolling contact and reduce surface friction and wear with its high controllability, low deposition temperature, wide range of plateable substrate materials, good mechanical properties, and excellent tribological properties. Further, rolling bearings with the PVD coating can show a longer service life and higher reliability under the same operating conditions; however, there is a lack of systematic introduction on the factors affecting the bond strength and tribological properties of PVD coatings. This paper reviews the latest research results of PVD coatings and discusses effective approaches to improve the bond strength of PVD coatings from multiple perspectives, including coating structure, process conditions, deposition substrate, post-treatment of coatings, and elemental doping: (1) selecting the reasonable coating structure according to different substrates and coating materials; (2) selecting appropriate process parameters such as current, bias voltage, and temperature, according to different coating systems; (3) selecting appropriate coating types according to the mechanical characteristics of the substrate materials; (4) adopting appropriate post-treatment methods; (5) appropriately enhancing the surface roughness of the substrate; and (6) selecting appropriate elements for doping. According to the material properties of different substrates and coatings, different treatment methods are adopted to maximize the coating bond strength and extend the service life of rolling bearings. In addition, this paper introduces the excellent performance of high entropy alloy coating, providing a new solution for the surface protection of rolling bearings under harsh working conditions and effectively improves the rolling bearing surface wear and coating spalling and other failure problems. Further, it has a very large potential application prospects for rolling bearings under harsh working conditions. In addition, this paper introduces the excellent performance of high entropy alloy coating, which provides a new solution for the surface protection of rolling bearings under harsh working conditions and can effectively improve the rolling bearing surface wear, coating spalling, and other failure problems. It also has a very large potential application prospect for rolling bearings under harsh working conditions. In addition, this paper promotes the application of PVD coating in rolling bearings by employing element doping to enhance the comprehensive performance of PVD coating, and suggests the combination of PVD and post-treatment, surface pretreatment, and other methods to form “PVD with pre-treatment,” “PVD with post-processing,” and other composite surface treatment technologies. Thus, the early failure of rolling bearing surface coating caused by an insufficient bond strength and tribological properties can be solved. However, the research on a variety of PVD composite treatment technology remains lacking, and the research on its mechanism and treatment process is insufficient. In the future, if a standardized treatment process is formed, the PVD composite surface treatment technology can solve the early failure phenomenon of rolling bearing surface coatings because of the insufficient bond strength and tribological properties and promote the wider application of physical vapor deposition coatings in the field of bearings.
  • Effect of Cystine Modified Zinc Phosphate on the Corrosion Resistance of Solvent-free Epoxy Coatings
    CHEN Ao, DUAN Haitao, JIN Yijie, ZHAN Shengpeng, ZHANG Wulin, JIA Dan
    China Surface Engineering. 2025, 38(3): 260-271. https://doi.org/10.11933/j.issn.1007-9289.20240105002
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    Solvent-free epoxy coatings are essential in the coating industry owing to their remarkable comprehensive performance characteristics such as high durability, excellent adhesion, and superior resistance to chemicals and mechanical wear. However, despite these advantages, existing solvent-free epoxy coatings have limitations in terms of their service life, particularly in heavy-duty anticorrosion applications such as in marine vessels. The harsh marine environment, with its continuous exposure to saltwater, UV radiation, and fluctuating temperatures, requires coatings with robust and durable corrosion-resistant properties. The current limitations in the service life of solvent-free epoxy coatings impede the extensive application of these coatings in such conditions. To address these challenges and enhance the performance of solvent-free epoxy coatings, an innovative approach was undertaken to develop a solvent-free epoxy anti-corrosion coating (L / EP) using L-cysteine modified zinc phosphate (LZP) as a novel functional filler. This new development aimed to improve both the corrosion resistance and longevity of the coatings, making them more suitable for applications in harsh environments.
    L-Cysteine, which is an amino acid containing a thiol group, was used to modify zinc phosphate to create a unique functional filler. The modification process was characterized using infrared spectroscopy and scanning electron microscopy. Infrared spectroscopy provided insights into the molecular structure of the modified zinc phosphate, confirming the successful integration of L-cysteine. Scanning electron microscopy revealed the morphology and dispersion characteristics of the modified fillers within the epoxy matrix. The incorporation of LZP into the solvent-free epoxy coatings significantly enhanced their performance. Electrochemical workstation and neutral salt-spray tests were performed to systematically evaluate the corrosion resistance of the coatings. The results were promising, demonstrating a substantial improvement in corrosion resistance. Specifically, the L / EP coating exhibited an increase of two orders of magnitude in the electrochemical low-frequency impedance and a 32.60% increase in the corrosion potential compared to the standard epoxy coating without LZP. These metrics are critical indicators of the ability of the coating to resist corrosive elements and maintain its integrity over time. Further optimization revealed that a mass fraction of 3% LZP in the epoxy coating yielded the best corrosion resistance. Under these conditions, the resistance of the coating to salt spray, which is a crucial test simulating the corrosive marine environment, improved by approximately 50% compared to that of the baseline coating without LZP. This significant enhancement can be attributed to the dual actions of the LZP filler, that is physical shielding and chemical corrosion inhibition. The physical shielding effect is attributed to the well-dispersed LZP particles, which create a barrier that obstructs the penetration of corrosive agents. The chemical corrosion inhibition effect is attributed to the L-cysteine molecules, which can interact with the metallic substrate and form a protective layer, further impeding the corrosion processes. The development of L / EP coatings with LZP not only offers a practical solution to extend the service life of epoxy coatings in harsh environments but also contributes to the broader field of environmentally friendly and efficient anti-corrosion technologies. This advancement is aligned with the increasing demand for sustainable, high-performance materials for various industrial applications.
    In conclusion, the introduction of L-cysteine-modified zinc phosphate as a functional filler in solvent-free epoxy coatings is a significant development in enhancing the corrosion resistance and longevity of solvent-free epoxy coatings. Comprehensive characterization and rigorous testing underscored the efficacy of this innovative approach. The superior performance of the L / EP coating has the potential to revolutionize the field of heavy-duty anticorrosion coatings, providing long-lasting protection in harsh environments, such as marine vessels. This development extends the practical applications of solvent-free epoxy coatings and establishes a theoretical and technical foundation for future advancements in the field of protective coatings.
  • Effect of Nitrogen Content on Tribological Behavior of CNx Films Deposited by HiPIMS
    XING Zhaoyang, WANG Xinfei, YANG Panfeng, ZHANG Bin, WANG Xin
    China Surface Engineering. 2025, 38(3): 272-284. https://doi.org/10.11933/j.issn.1007-9289.20240306002
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    Amorphous carbon film, which mainly comprises a network of sp3 and sp2 carbon atoms, has been widely used in many fields because of its excellent mechanical and tribological properties, corrosion resistance, chemical inertness, and superb biocompatibility. Amorphous carbon nitride (CNx) coating has been demonstrated to be a promising lubricating material because of its excellent tribological performance, such as low friction and high wear resistance, during sliding in inert gas environments. However, the deeper mechanism of superlubricity under inert environments remains unclear, which severely limits its industrial application. Previous studies mainly focused on the formation of the sp2-rich carbon tribo-layer on the mating surface and ignored the physical and chemical changes during the sliding process. The high power pulse magnetron sputtering (HiPIMS) technology developed in recent years can effectively improve the ionization rate of the plasma and produce high density, uniform thickness, smooth-surface, and high-adhesion films. Thus, in this study, HiPIMS was used to deposit four kinds of CNx films. The nitrogen gas flow rates were controlled to deposit different amounts of nitrogen content on the films to obtain CNx-0, CNx-50, CNx-80, CNx-160, respectively, which allowed exploration of the effect of nitrogen content on the microstructure, mechanical structure and tribological properties of CNx films. The morphology of the films showed small roughness (Ra ~4.80 nm, CNx-50, for example) in scanning electron microscopy (SEM) and atomic force microscopy (AFM). In Raman shifts, the sp2-C concentration of CNx films increased from CNx-0 to CNx-80, then suddenly decreased, at a nitrogen gas flow rate of 0.16 L / min. The X-ray photoelectron spectroscopy (XPS) measurements confirmed that the nitrogen concentration gradually increased from 8.99% to 12.37% with the raising of the nitrogen flow rate from 0.05 to 0.16 L / min. In addition to component analysis, the fitted XPS spectra exhibited bond evolution according to different binding energies. The proportion of sp2-C component in the CNx films increased from 45.99% at 0 L / min to 58.28% at 0.08 L / min and then suddenly decreased to 48.62% at 0.16 L / min, which is consistent with the results of Raman shifts and confirmed by the N1s spectra. In terms of mechanical properties, the nanoindentation test generated a series of complex results. The introduction of nitrogen increased film hardness, and the elastic module first increased from 0 L / min to 0.08 L / min, and then decreased at 0.16 L / min. However, the adhesion of CNx films decreased at 0.05 L / min and then increased from 0.08 to 0.16 L / min. All the deposited CNx films had a high degree of graphitization, and they all performed well in the nitrogen gas environment after pre-sliding. Although the effect of the running-in process on friction behavior has not been investigated so far, its effect on reducing wear rates and friction coefficients was verified by our experiments. By introducing 1100 cycles of pre-sliding in relative ambient humidity (RH ~50%), a minimum wear rate (0.60×10-7 mm3·N-1·m-1) was obtained for the CNx-80 film, and superlubricity (coefficient of friction (COF) < 0.01) was observed for CNx-50 film for about 40 mins. Optical microscope, focused ion beam high-resolution transmission electron microscopy (FIB-HRTEM), and three-dimensional time-of-flight secondary ion mass spectrometry (3D TOF-SIMS) were used to provide reliable, visual, and direct contact area images of the sliding interface for the analysis of tribological chemistry during the friction test, which showed that the origin of low frictional performance in a nitrogen gas environment is mainly attributed to the termination of the interface by hydrophilic groups such as -OH, -COOH, and -H and the formation of an sp2-rich carbon nitride network tribo-layer on both the mating and top surfaces of the CNx film. The reconstructed film surface after sliding and the synergy of tribochemical reactions promoted superlubricity. This approach offers a new method for reducing COF and wear of amorphous carbon films and provides a reference for the tribological behavior of carbon nitride films with different nitrogen content.
  • Service Life Prediction and Durability Design of Marine Concrete Structures
    DA Bo, QING Jiajun, LIU Jinwen, TAO Tao, LAN Zhiqiang, HAN Yudong, CHEN Da
    China Surface Engineering. 2025, 38(3): 285-296. https://doi.org/10.11933/j.issn.1007-9289.20240911001
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    In the context of the national strategy for “Maritime power” and the construction of the “Belt and Road”, marine engineering infrastructure construction of China has accelerated. The on-site use of raw materials such as coral and seawater to prepare marine concrete (MC) significantly reduces project costs, ensures the construction period, and reduces carbon emissions due to transportation. However, complex and harsh marine environments have a strong corrosive and destructive effect on structures, seriously affecting the use and safety of marine engineering structures. Therefore, it is of great significance to apply additional anticorrosion measures to MC structures and conduct research on service life prediction and durability design. In marine environments, the corrosion of steel bars inside concrete structures caused by chloride ions in seawater is a main reason for the deterioration in the durability of these structures. In this study, to effectively improve the durability of concrete structures in marine engineering, it was treated with two anti-corrosion measures: internal addition of composite active mineral admixtures (MA) and external application of high-permeability epoxy protective materials (SP). By investigating the diffusion law of Cl- in concrete, the effects of thicknesses of concrete protective layers, concrete types, strength grades, exposed areas, and additional anti-corrosion measures on the service life of coral aggregate concrete (CAC) and ordinary aggregate concrete (OAC) structures were studied. Design suggestions for improving the service life of MC structures were proposed based on the ChaDuraLife life prediction method, which combines the characteristics of the exposed environment of concrete structures in marine engineering. Theoretical and data support are provided for the application of MC in practical engineering. The results showed that under the same marine exposure zone, with an increase in the concrete strength grade and protective layer thickness, the service life of the CAC and OAC structures gradually increased. The service life of the OAC structures exhibited the trend of underwater zone > atmospheric zone > tidal zone in different ocean exposure areas. When the concrete strength grade, protective layer thickness, and exposure zone were the same, the service life of CAC structures was shorter than that of OAC and followed the pattern of atmospheric zone > underwater zone > tidal zone. The use of internally mixed composite mineral admixture MA, externally coated high-permeability epoxy protective material SP, and “internally mixed + externally coated” anti-corrosion measures increased the service life of OAC structures by 1.8/1.7, 2.4/2.4, and 3.4/3.2 times, respectively, compared with no measures. In underwater zone of the ocean, for CAC/OAC structures with a conventional protective layer thickness of 6 cm, even if the concrete strength grade reached C50, the service life remained relatively low. Additional anticorrosion measures, such as internal mixing and external coating, were required to improve the durability of the structure. Considering factors such as engineering costs and structural durability, the adoption of OAC structures for nearshore engineering is recommended. When the concrete strength grade is C50 or higher, the protective layer thickness is greater than 14 cm, and when the high-permeability epoxy protective material SP is applied externally, the service life of the underwater structure can reach up to 100 years. It is recommended that CAC structures be used in offshore engineering applications. When the concrete strength is greater than C65 and the thickness of the protective layer is 10 cm, the combined anti-corrosion measure of mixing MA and coating SP can significantly improve the service life of the engineering structure.
  • Microstructure and Properties of 0Cr13Ni5Mo Stainless Steel Prepared by Wire Arc Additive Manufacturing
    YANG Wei, GAO Zhanqi, ZHANG Haiyan, SUN Chuanbo, HUANG Zhiquan, LIU Shengxin
    China Surface Engineering. 2025, 38(3): 297-305. https://doi.org/10.11933/j.issn.1007-9289.20231122002
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    With the continuous demand for energy in society, hydropower energy, as a high-efficiency, clean, and renewable energy source, has become a key object of attention in the development of energy worldwide. In recent years, China has been constructing and developing several hydropower stations. Hydraulic turbines are the core equipment for hydropower generation in hydropower stations. The manufacturing quality of the bucket—a key component of the impact turbine—directly impacts the efficiency and service life of the hydropower system. The high costs and lengthy manufacturing cycles of traditional stainless steel impact turbine buckets have long hindered hydropower progress. Wire arc additive manufacturing (WAAM), however, provides an innovative alternative to address these challenges. WAAM has the advantages of high deposition efficiency, low cost, and large molding size capacity and has broad applications in workpiece remanufacturing and full-scale component fabrication. A 0Cr13Ni5Mo martensitic stainless steel deposit was fabricated using the CMT-based WAAM technique and its microstructure and properties were investigated using optical microscopy, scanning electron microscopy, and mechanical property tests. The surface of the 0Cr13Ni5Mo stainless steel fabricated by WAAM was covered with a thin smooth gray oxide layer, and no defects such as porosity, cracks, and unfused were observed in the microstructure of the deposition layer. A small amount of undesired sputtering formed and fell onto the substrate during the fabrication process. The results show that the microstructure of the 0Cr13Ni5Mo stainless steel deposit fabricated by WAAM at various locations mainly consisted of non-directional lath martensite, and a small amount of δ-ferrite also existed. The orientation and size of the martensite laths varied at different positions. The yield and tensile strengths of the deposit at different locations in the building direction did not differ significantly, and the average yield and tensile strengths of the three samples were 975.7 MPa and 1 040 MPa, respectively, indicating that the arc additive-fabricated 0Cr13Ni5Mo stainless steel deposit has high yield and tensile strengths, which are higher than the minimum values required for casting and forging. However, there was some variation in their elongation, with the top and middle positions exhibiting 15% and 16% elongation, respectively, whereas the bottom position decreased to 11.5% elongation. Ductile dimples observed on the tensile fracture contributed to the material’s improved toughness. The average impact absorbed energy along the welding horizontal direction (X direction) and vertical welding direction (Y direction) was 32.5 J and 36.8 J, respectively, and there were differences in the impact toughness of various orientations, which suggests that arc additively fabricated stainless steel deposits are anisotropic in terms of impact toughness. The impact fracture was a mixed tough-brittle fracture, and the second-phase particles in the tough nest were Mn-Si oxides. The average microhardness of the top deposit was very close to that of the center, which was slightly lower than that of the bottom, and from top to bottom, the average microhardnesses were 355.18 HV0.2, 351.38 HV0.2, and 363.14 HV0.2, respectively. In this study, the deposition thickness could be larger, better reflecting the effect of the location on the mechanical properties. The innovation point of this experiment is the use of CMT-based WAAM technology to obtain 0Cr13Ni5Mo stainless steel deposits and studying the organization and related mechanical properties at different locations, which provides a technical and theoretical basis for the application of low-cost WAAM of impact turbine buckets.
  • Preparation of Micro- and Nano-scale SiCp / 6061Al Composite Coating via High-pressure Cold Spraying
    ZHOU Changzhuang, YIN Puxin, GONG Chunzhi, LIU Qiming
    China Surface Engineering. 2025, 38(3): 306-315. https://doi.org/10.11933/j.issn.1007-9289.20240313003
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    Research on the preparation of SiC particle reinforced aluminum matrix composite coatings via cold spraying has attracted considerable interest. However, a single-scale reinforcement has a limited strengthening effect on composite properties, restricting the optimization and improvement of its comprehensive properties. The micro + nano dual-scale enhancement phase mode was adopted to improve the mechanical properties of the composite coating, and the respective scale advantages and coupling effects of SiC particles on the composite coating were enhanced by adding nanoparticles to prepare the composite coating with excellent comprehensive properties and satisfy the strength and wear resistance requirements and other properties. Micro+nano SiC / 6061Al composite coatings were designed and prepared using high-pressure cold spraying technology. To this end, changes in the microstructure and properties between micro+nano SiC / 6061Al composite coatings and single micron SiC / 6061Al composite coatings were studied. Subsequently, the effect of gas pressure on the microstructure and mechanical properties of the coating during cold spraying was explored. The microstructure of micro+nano SiC / 6061Al composite coating and micro SiC / 6061Al composite coating were studied using scanning electron microscopy (SEM), and the Vicker’s hardness test, friction wear test, and white light diffraction test were performed to test the mechanical properties of the composite coating. The results indicate that the micro+nano SiC / 6061Al composite powder was prepared by high-speed ball milling and mechanical mixing, and the micro+nano SiC / 6061Al composite coating was prepared by cold spraying. The SEM analysis of the mixed powder showed that the mixed powder was composed of an approximately spherical 6061Al alloy powder and fine particles of SiC powder. There are some fine particles on the surface of the spherical 6061Al alloy powder, and no obvious deformation occurs after ball milling. An elemental analysis of the particle surface using energy dispersive X-ray spectrometry (EDS) showed that the hard nano-SiC particles mechanically combine with the 6061Al alloy powder under the action of the grinding ball, gradually combining on the surface of 6061Al powder with an increase in the ball milling time. The SEM characterization results of the composite coating showed that the micro-nano-particle SiC / 6061Al composite coating is more compact compared to that of the micron-reinforced SiC / 6061Al composite coating, and the porosity of the coating is reduced from 1.72±0.07% to 0.21±0.08%. The EDS characterization results of the micro+nano SiC / 6061Al composite coating show that the composite coating is composed of micron SiC, nano SiC, and 6061Al particles. Micrometer and nanometer SiC particles were uniformly distributed in the composite coating, and no segregation occurred. The measurement and calculation of the micro-hardness of the composite coating indicates that the hardness of the micro-nano SiC / 6061Al composite coating is 14% higher than that of the micron SiC / 6061Al composite coating, and the fracture toughness is also increased. Further, with a gradual increase in gas pressure, the hardness of the micro+nano SiC / 6061Al composite coating increases gradually. The measurement of the friction coefficient of the composite coating, the observation of the wear pattern, and the calculation of the wear rate show that, compared to that of the micron SiC / 6061Al composite coating, the friction coefficient, wear depth reduction, and wear rate of the micro+nano SiC / 6061Al composite coating are reduced. Further, the friction coefficient, wear depth, and wear rate of the micro+nano SiC / 6061Al composite coating decrease with an increase in gas pressure. When the gas pressure reaches 5 MPa, the wear rate decreases to 3.0919 × 10-4 mm3 / N·m. The proposed cold spray preparation of the dual-scale SiC / 6061Al composite coatings can provide data support for the future application of SiC particle reinforced aluminum matrix composite coatings.
  • Effect of Spray Power on the Microstructure and Thermal Shock Resistance of 8YSZ / NiCrAlY Protective Coatings
    SHAN Yu, YANG Jingjing, SUN Huwei, YI Gewen, WAN Shanhong, MA Fei, LIU Haijun, MA Xiaoqiang
    China Surface Engineering. 2025, 38(3): 316-329. https://doi.org/10.11933/j.issn.1007-9289.20240110001
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    ：The use of ceramic materials with low thermal conductivities as thermal barrier coatings (TBCs) on critical components of internal combustion engines, such as piston end faces, has recently become a popular research topic. The objective is to enhance the insulation and thermal efficiency of internal combustion engines. These engines frequently undergo start-stop cycles, subjecting the heated components to rapid thermal fluctuations. Consequently, TBCs on the heated surfaces of internal combustion engines must exhibit excellent resistance to thermal shock. During the preparation of yttria-stabilized zirconia (YSZ) TBCs, the axial velocity and melting state of the sprayed powder are critical factors affecting coating quality. While other spray process parameters (such as carrier gas flow rate, powder feed rate, and spray distance) remain fixed, the voltage and current (i.e., power) play a significant role in determining the coating quality. Although researchers have extensively studied the impact of various parameters on the microstructural properties of YSZ coatings, research on their thermal shock resistance, especially at extreme conditions of 800 °C with up to 800 thermal cycles (which closely resemble the severe start-stop process of internal combustion engines), remains relatively scarce. In this study, NiCrAlY / YSZ bilayer (bond layer + ceramic top layer) thermal barrier coatings were prepared on GH4169 and Inconel718 high-temperature alloy substrates (Φ24mm×8mm) using an atmospheric plasma spraying system (9MC, Sulzer Metco, USA). Before spraying, the surfaces of GH4169 and Inconel718 Ni-base superalloy substrates were polished with 80-mesh coarse sandpaper to remove oil, then sandblasted (corundum sand of 80~120 mesh, pressure of 0.4~0.6MPa), and finally subjected to ultrasonic cleaning with acetone solution applied twice to keep the fresh surface clean. The YSZ coating thickness was approximately 600 μm, with a transition bond coat thickness of approximately 100 μm. The prepared YSZ coating samples were labeled as C1 to C4 based on increasing spray power from 35.75 to 42.0 kW, respectively. The microhardness of the coating surfaces was measured using an MH-5 Vickers hardness tester. Additionally, we evaluated the coating-substrate bond strength according to ASTM C633 using a SANS WDW-200 microcomputer-controlled electronic universal material testing machine. X-ray diffraction (XRD), Raman spectroscopy, and scanning electron microscopy (SEM) were used to characterize the phase composition and microstructure of YSZ powder and coatings. Furthermore, we assessed the thermal fatigue resistance of YSZ coatings through a heating-water quenching process at 800 °C (although a real start-stop thermal cycling in internal combustion engines is less severe, this accelerated fatigue test serves as a preliminary evaluation). We found that as the spray power increased from 35.75 to 42 kW, the YSZ coating phase consisted predominantly of tetragonal zirconia. The unmelted zone in the coating decreased or disappeared, resulting in distinct columnar and equiaxed grain regions. At low spray power, the flat particles were not completely stacked and there were more pores and microcracks in the coating, resulting in a lower coating density and cohesive strength. As the spraying power increased, the number of pores and microcracks decreased, leading to a denser coating. The microhardness initially increased and then decreased, whereas the bond strength gradually improved. Among the prepared coatings, C4 (42 kW) exhibited favorable microhardness (817.15 ± 58.65 HV300g) and bond strength (66.37 ± 4.90 MPa). After 800 thermal cycles at 800 °C, the C4 coating surface showed no significant signs of spallation, cracking, or spalling, demonstrating the best thermal shock resistance. However, microstructural damage to the coating was severe, approaching the thermal fatigue limit of the coating. The C4 (42 kW) spray power condition is suitable for preparing YSZ thermal barrier coatings on the heated surfaces of critical components of internal combustion engines because it exhibits good microstructural properties and performance. All in all, in this study we provide theoretical support and data for the application and further development of thermal barrier coatings in internal combustion engines.
  • Cause Analysis and Treatment of Foaming in Hot-dip Galvanizing of High Titanium Mild Steel
    WU Hao, CHEN Haiyan, LI Zibin, LI Lizhi, HUANG Xingbiao, LIAO Qisheng, YUAN Huarong, CHEN Pimao, TONG Fei
    China Surface Engineering. 2025, 38(3): 330-337. https://doi.org/10.11933/j.issn.1007-9289.20240228001
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    With the development of steelmaking and degassing technology in recent years, ultralow carbon steel with carbon and nitrogen contents of 10-4 or less can be produced industrially at lower costs. Ti is added to such ultralow carbon steels to achieve a better performance. Adding Ti is beneficial for refining the grains and improving the welding and machining performance of the steel. However, such steels cannot overcome the shortcomings of traditional carbon steel, which is easily corroded and still requires surface treatments such as hot-dip galvanizing. Zinc is deposited on the surface of steel by hot-dip galvanizing, which forms a protective coating that isolates the substrate from the external environment. The demand for high-performance steel has driven the development of these technologies. Currently, hot-dip galvanizing technology can ensure a dense and non-porous coating that exhibits excellent resistance to atmospheric corrosion. However, excessive Ti content can cause problems in the pickling process of mild steels, which makes them less resistant to pickling and subject to more severe hydrogen evolution corrosion during the pickling process, thereby leading to the blistering of the coating after hot dip galvanizing, which is a coating defect. In this paper, the causes of blistering during the hot-dip galvanizing of high titanium mild steel are analyzed in depth by combining material microscopy and electrochemical kinetics. Material microscopy shows that the surface of the high titanium mild steel after pickling exhibits more pits compared to that of ordinary mild steel. The electrochemical kinetics indicate that high titanium mild steel has poorer resistance to hydrochloric acid corrosion compared to that of ordinary mild steel. These test results suggest that there are two factors that cause the coating defect of blistering: First, the Ti content is too high. An appropriate amount of Ti can improve the formability of mild steel; however, a considerably higher amount of Ti increases the brittleness of the grain boundary. Meanwhile, in high-temperature hot-dip plating, the Fe and Ti elements form an Fe-Ti crystal, trapping the H atom. When cooled down to room temperature and normal pressure, the H atom detaches from the Fe-Ti crystal and combine to form H2, which is generated and released from the narrow volcanic pores. As the pressure of H2 under the plating increases, it eventually leads to deformation of the plating and coating defects. Second, Ti passivates the surface during the long pickling process, leading to a high pitting sensitivity of the material and producing crater-like pitting holes. These pitting holes retain some HCl because of capillary action, and it is difficult to remove during the water washing process. The residual HCl in the pitting holes easily reacts with the substrate to corrode the iron, forming corrosion products such as FeO, Fe2O3, FeCl2, and FeCl3, which worsens the bonding of the zinc layer with the substrate. Meanwhile, the residual H+ absorbs electrons as a depolarizing agent, prompting the formation of H atoms in the cavities. Through production practice, it has been proved that the pickling time for high-titanium mild steel should be shortened compared to that for conventional mild steel, provided it does not affect specimen pickling descaling. This measure effectively slows down hydrogen precipitation and the corrosion of small holes. The pickling time for hot-dip galvanizing of high-titanium mild steel must be strictly limited to 2-4 min to eliminate cavitation defects in the coating.
  • Prediction of Aluminum Coating Single Dot Profile in Low-pressure Cold Spraying
    CAO Bowen, LI Hongjun
    China Surface Engineering. 2025, 38(3): 338-349. https://doi.org/10.11933/j.issn.1007-9289.20240325003
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    Cold spray technology, as an emerging material surface treatment technique, has been considered by academia and industry because of its ability to prepare coatings under conditions of no oxidation and phase transformation. The demand for high-performance, multifunctional composite materials is constantly increasing because of the continuous advancements in industrial technology. The precise control of the surface profile of low-pressure cold sprayed coatings is of significant scientific importance and application value for meeting diverse product demands and enhancing industrial production efficiency. Currently, there is a relative scarcity of systematic research on the prediction and control of the profile of low-pressure cold-sprayed aluminum coatings. During the coating preparation process, coatings created using low-pressure cold spray technology often rely on subsequent processing techniques to achieve the required coating thickness and improve surface smoothness due to the non-uniformity of the coating surface. In this study, a predictive method was established for depositing coatings and the spraying process was simulated. Subsequently, a computational fluid dynamics (CFD) model of the cold spray process was constructed using FLUENT software considering factors such as gas parameters, nozzle characteristics, powder properties, substrate materials, and spraying distance to assess their effect on particle flow, heat transfer, collision, and deposition processes. Key information such as the position, velocity, and quantity of aluminum particles upon collision with the substrate within the jet was also obtained. The height of the deposition coating was deduced based on particle distribution information and deposition model by introducing the “cold spray efficiency,” which represents the combined effect of particle deposition efficiency and compression ratio and calculating the cold spray efficiency at different locations during the cold spraying process. These height values were extracted as discrete points in three-dimensional space and fitted to a surface using the nonlinear least squares Levenberg-Marquardt algorithm, with a Gaussian function selected as the fitting function, to simulate the single dot profile function of low-pressure cold-sprayed aluminum coatings at 1, 3, and 5 s. Through the analysis, data on the amplitude coefficient A and standard deviation σ of the coating profile simulation function as a function of time were obtained and were treated as a quadratic function of time t. Finally, a predictive function was established for the profile of the single dot aluminum deposition coating that changes over time. Experiments of single dot low-pressure cold spraying of aluminum powder were conducted on the surface of a 316L stainless steel substrate, followed by scanning and measuring the coating profile using a high-precision 3D profiler. The measured profiles of the single dot coating at spraying times of 2 s and 4 s were compared with the predicted profiles to evaluate the effectiveness of the proposed predictive model for the single dot profile of low-pressure cold-sprayed aluminum coatings. Further, the cold spray efficiency of aluminum particles during the cold spraying process was calculated and analyzed, revealing a significant correlation between cold spray efficiency and spraying position. The cold spray efficiency was higher within a smaller radius range along the central axis, while the efficiency in the edge areas was lower. The overall cold spray efficiency showed a declining trend over time. Based on the predictive model established in this study, the appropriate spraying time was determined based on the required coating thickness. This method optimized the experimental scheme, reduced the number of necessary experiments, improved research efficiency, and laid the foundation for predicting the profile of continuous cold-sprayed aluminum coatings and the control of the coating profile morphology.
  • Optimization of Milling and Shot Peening Parameters for Allvac 718Plus Based on the Fatigue Performance of Specimens
    ZHANG Ning, GOU Ruijie, YAO Jun, LI Xun
    China Surface Engineering. 2025, 38(3): 350-360. https://doi.org/10.11933/j.issn.1007-9289.20240128002
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    Nickel-based superalloy Allvac 718Plus is an important material for the manufacture of aero-engine blisks. Milling and shot peening are the finish machining processes of blisks, and the machining parameters and coupling effects of milling and shot peening have a direct influence on the machined surface quality. Fatigue fracture is the main failure form of aero-engine blisks. In this study, we explored the influence mechanism of milling and shot peening on the surface integrity and fatigue performance of superalloy Allvac 718Plus specimens. We aimed to provide a reference for the finish machining process of blisks. Based on real processing conditions of aeroengine blisks, surface integrity tests of milling and shot-peening processes were carried out. Processing parameters were selected to reasonably control the surface roughness, microhardness, and residual compressive stress of the fatigue specimens. Based on the surface morphology of the specimens under different processing parameters, tests were conducted to study the effects of the milling and shot-peening parameters on the integrity of the material surface. The degrees of influence were comparatively analyzed. By studying the fatigue performance of the milled specimens, optimized machining parameters for milling were obtained, achieving a fatigue performance from 1.6 to 3.8 times higher than that resulting from the other machining parameters. The main factor affecting the fatigue performance of milling is the residual compressive stress on the surface of the specimen. After the milling process, the specimens machined with both optimized and control group parameters for the milling process were subjected to shot peening. By studying the influence mechanism of the combined processes and parameters on the fatigue performance of the specimens, we found that the fatigue sources of the specimens after milling were located on the surface, whereas the fatigue sources of the specimens after shot peening were located inside the specimens; the final fatigue performance of the specimens increased by 13.46 and 25.41 times for the optimized and control group parameters, respectively. The parameters of the milling process and surface quality still had an influence on the final fatigue performance of the specimens. The fatigue performance of specimens featuring milling optimization parameters was 30% higher than that of specimens featuring control group parameters when the shot-peening coverage reached 500%. By testing the surface integrity of the specimens after shot peening, we found that although the surface roughness of the specimens increased, shot peening improved the surface microhardness and surface residual compressive stress of the specimens. The increase in roughness was harmful to the fatigue performance of the specimens; however, the increases in surface residual stress and surface microhardness were beneficial to the fatigue performance of the specimens. Within the range of test parameter selection, the distance of the center of the fatigue source from the surface gradually increased with increasing shot-peening coverage, and the fatigue performance of the specimen gradually increased. With an increase in shot-peening coverage, the degree of influence of the milling process on the final fatigue performance of the specimens was enhanced. When the shot-peening coverage rate increased to 500%, the fatigue performance of the optimized-parameter specimen was 30% higher than that of the control-parameter specimen. By analyzing the influencing mechanisms and laws governing combined milling and shot-peening machining, we determined efficient processing parameters based on finishing efficiency. Additionally, we identified optimized processing parameters to enhance the fatigue performance of the specimens after combined processing. The effects of milling and shot-peening parameters on the machined surface integrity of Allvac 718Plus and the fatigue performance of specimens were studied, establishing a reference for the combined milling and shot-peening machining of Allvac 718Plus blisks.
  • Analysis on the Tribological Performance of ta-C Coating under a Heavy-loading-point-contact Elastohydrodynamic Lubrication Condition
    SUN Runyang, MA Tao, XIAO Yangyi
    China Surface Engineering. 2025, 38(3): 361-371. https://doi.org/10.11933/j.issn.1007-9289.20240409002
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    Tetrahedral amorphous carbon (ta-C) films show significant effects in enhancing the tribological performance of contact pairs; however, there is a lack of comprehensive research on their application in heavy-duty transmission systems. Under heavy-duty conditions, the surfaces of mechanical components often fail because of high friction and wear coefficients. Studying ta-C coatings that can reduce friction and minimize wear is essential to achieve low energy consumption, high reliability, and long service life of mechanical components. This paper aims to investigate the tribological performance of ta-C coatings on steel balls under heavy-duty dry sliding / oil lubrication conditions and reveals the structure and mechanical properties of ta-C coatings. An elastohydrodynamic lubrication model is established based on the generalized Reynolds equation and loading balance equation to solve the distribution of oil film pressure and thickness under different conditions. The friction and wear behavior of the ta-C coatings is evaluated using ball-disc friction tests under dry friction and oil lubrication conditions. In addition, vibration tests are conducted to explore the fluctuations of vibration acceleration signals in different directions under various conditions, analyzing the factors affecting the effect of ta-C coatings on sample vibrations. The initial findings from nanoindentation tests reveal that ta-C coatings possess impressive nanohardness (~36.11 GPa) and elastic modulus (~298.29 GPa), with a ratio of hardness to elastic modulus exceeding 0.1, which is significantly higher than that of conventional coatings. This implies a superior toughness and potential durability. Meanwhile, the coating is well bonded to the substrate, showing excellent clarity. The ball-disc friction tests reveal that the uncoated samples exhibit more severe wear behavior compared to that of the coated ones. Under oil lubrication conditions, the higher lubricant viscosity, the thicker is the oil film. This can help better isolate the two contact bodies. Friction and wear tests under dry friction and oil lubrication conditions demonstrate that ta-C coatings consistently reduce friction and wear. Therefore, ta-C coatings possess friction-reducing and wear-resistant properties. Despite the varying lubrication conditions, there is no notable difference in the oil film maximum pressure between samples with and without ta-C coatings. Further, a higher lubricant viscosity results in a thicker oil film, which corresponds to a marginally greater coefficient of friction. The relationship underscores the complex interplay between lubricant viscosity and frictional properties. Assessing the effect of ta-C coatings on vibrational behaviour under different conditions indicates that the coefficient of friction of the coating is an important factor affecting vibration, with vibration intensity increasing with an increase in the coefficient of friction. The stiffness and damping of the lubricant become factors influencing vibration when the coefficient of friction is similar. The vibration intensity of the contact pairs decreases with an increase in the stiffness and damping of the lubricating medium. The current study conclusively shows that the dense structure of the carbon-based coatings can effectively improve the tribological performance of the substrate surface under heavy loading dry friction and oil lubrication conditions and reduce the vibration intensity of the substrate surface contact pairs. This has significant theoretical and practical engineering value for improving the design level of coating pairs serving under heavy loading conditions. Reducing friction and minimizing wear are key to achieving the low energy consumption, high reliability, and long service life of mechanical components. Simultaneously, this research finding provides reference for the application of coatings in the mechanical transmission system.
  • Wear and Damage Behaviors of Locally Laser-cladded Wheel Materials in a Humid Hot Environment Using Stainless Steel Powder
    HE Chenggang, WANG Xinji, YU Ruxin, FU Bin, YE Rongwei, LIU Jihua, ZOU Gang, XU Yixun
    China Surface Engineering. 2025, 38(3): 372-383. https://doi.org/10.11933/j.issn.1007-9289.20240312001
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    Towards the end of 2023, the national railway operating mileage reached 159,000 km, of which the high-speed railway contributed to 45,000 km, thus, railway transport plays in important role in China, which has a vast territory. The southern region of China is affected by subtropical monsoon climate, making it hot and rainy all year round, and the atmospheric environment is a damp-heat type. As a key component of railway transportation, the wheel-rail is subjected to an open-climate environment for a long time, making the surface of the wheel-rail prone to corrosion and damage. Thus far, wheel and rail restoration has been extensively researched. Since the development of laser-cladding technology, most researchers focused on completely cladding the wheel-rail sample to improve its anti-wear and anti-corrosion ability. However, local damage is inevitable for the actual service of the wheel-rail, and the exposure of the damaged wheel-rail to the hot and humid environment can lead to increasing wear, seriously affecting the safety of the train service. Thus, the wear and damage behaviors of local laser-cladding stainless steel powder coating on wheel materials under hot and humid environments need to be investigated. In this paper, based on a large number of references and a variety of pre-experiments, three stainless steel powders (304L, 316L, 420) with good bonding properties with the wheel substrate were selected for local laser-cladding repair on the surface of the wheel sample. The microstructure and hardness of the repaired coating were analyzed. The friction and wear test was conducted using an MMS-2A rolling friction and wear test machine, the test temperature was maintained at 50 °C, and the relative humidity was 90% using a temperature and humidity control system. And the surface hardness of the wheel, rail, and stainless steel cladding area was measured using the Vickers hardness tester before and after the test. Before the test, the portable microscope and scanning electron microscope (SEM) were used to observe the surface area of the sample. After the test, the rail and wheel were etched and observed. The plastic deformation, crack growth, and microstructure of the sample section of the wheel and rail were observed using an optical microscope (OM) and SEM. The element composition of the alloy coating was detected using an energy spectrometer, and the damage was observed and analyzed. The results indicate that the change process of the friction factor of the three coated samples is similar, and it can be roughly divided into running-in and stabilization stages. However, the friction factor of the 420 coating sample fluctuates more seriously at low speeds. The wear rate of the wheel samples after local repair is lower than 2µg / m, which indirectly proves the feasibility of using laser-cladding technology for the local repair of damaged wheels. After the test, the surface and profile areas of the three cladding wheel samples were damaged; however, the degree of damage was different. The coating area and substrate area of the surface of the 316L and 420 cladding wheel samples were more seriously damaged, and there were a large number of spalling holes, grinding chips, and surface cracks. This can be attributed to the water film on the surface of the wheel and rail under the high humidity environment and the grinding chips attached to the surface. The “third dielectric layer” was formed, adhesive wear occurred, and there were more spalling pits and large angle short cracks in the section area, among which the crack angle and length of 420 cladding coating samples were the largest. The performance of the three laser cladding coatings on the local repair of the wheel in the high temperature and high humidity environment was compared. The 304L cladding coating was well combined with the wheel substrate, and only a small amount of spalling existed in the bonding area after the test. A small amount of wear chips existed near the heat affected zone. Further, the crack angle of the coating area and substrate area was small, crack depth was shallow, wear amount was small, and wear resistance was good, making it more suitable for the local repair of the wheel under high temperature and a high humidity environment. The research results provide theoretical and technical guidance for the application and optimization of laser-cladding technology in the local repair of train wheels.
  • Parameter Regulation on Large-gap Radio Frequency Plasma Modification of Fluorosiloxane Acrylate
    XU Pan, DENG Haishun, HUANG Zhixiang, HE Tao
    China Surface Engineering. 2025, 38(3): 384-393. https://doi.org/10.11933/j.issn.1007-9289.20240328001
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    Plasma modification is an emerging technology in the medical field; however, the electrode gap of the existing dielectric discharge is too small to be applied for large-scale production. Therefore, a large-gap radio frequency (RF) dielectric barrier discharge device was proposed and developed in this study. The electric field distribution, potential distribution, electron flow density distribution, and ion flow density distribution of the dielectric barrier discharge device were analyzed by using the graphical three-dimensional spatial distribution method. A plasma experimental device was assembled to study the breakdown voltage of different gas media. The effect of the coupling relationships between the gas volume flow and different powers, treatment times, and gas pressures on the contact angle of fluorosiloxane acrylate (XO) materials was evaluated. The contact angle is an important parameter for evaluating the hydrophilicity-hydrophobicity of a material surface. The smaller the contact angle, the better is the wettability. Fig. 13 shows that the contact angle of the XO material is the smallest and the wettability of the material is the best after Ar plasma treatment at 15 W for 9 min. Fig. 14 shows that, for an XO material under a pressure of 10 Pa, the contact angle is 18.86° and processing time is 12 min. However, with a decrease in pressure, the requirement of the air tightness of the vacuum system increases correspondingly, affecting the accuracy and stability of the experiment or process. For a treatment time of 9 min, the contact angle under a pressure of 20 Pa is 25.86°, which is better than that at other times. The pressure of the vacuum system and treatment time were set to 20 Pa and 9 min, respectively after comprehensively evaluating the treatment effect, device requirements for the mass production system, cost-effectiveness, and optimal contact angle. Figure 15 shows that, when air and argon is used as the medium, the contact angle fluctuates greatly and it is difficult to stabilize the treatment time; when nitrogen is used as the gas medium, the best contact angle is 15.17 ° for a treatment time of 15 min; and when oxygen is used as the gas medium, the best contact angle is 9.44° for a treatment time of 6 min. Further, when using oxygen, the contact angle is 10.64° for a treatment time of 9 min, and the contact angle difference between the two is small. Oxygen is selected as the gas medium considering the stability of the gas and the treatment effect of the contact angle. The results indicate that Ar, N2, O2, and air as the gas medium can realize plasma discharge; however, the breakdown voltage of Ar is lower than that of N2, O2, and air, making it easy to form plasma discharge quickly. The Ar, N2, O2, and air gas media correspond to different breakdown voltage values, and the breakdown voltage values of the same gas medium with different gas volume flow rates are different. The optimum conditions for the plasma modification of XO materials include an RF power of 15 W, modification time of 9 min, gas pressure of 20 Pa, gas medium of O2, and gas volume flow rate of 28 mL / min. The contact angle obtained by plasma modification was the best. The contact angle of the XO material decreased from 86.15° to 10.64°, and the hydrophilicity was the best. In this paper, the parameters of optimal RF power, modification time, gas pressure, and gas volume flow rate are studied in different air media, providing new ideas for plasma modification technology.
ISSN 1007-9289　CN 11-3905/TG
Supervised by: China Association for Science and Technology
Sponsored by: Chinese Mechanical Engineering Society
Edited and Published by: Editorial Office of China Surface Engineering
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