23 February 2025, Volume 38 Issue 1
    

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  • Research Progress of Mechanisms and Influencing Factors of Solid Superlubricity in DLC Films
    YU Qingyuan, CHEN Xinchun, ZHANG Chenhui
    China Surface Engineering. 2025, 38(1): 1-22. https://doi.org/10.11933/j.issn.1007-9289.20240105001
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    Macroscopic solid superlubricity (with a friction factor on the order of 0.001) in diamond-like carbon (DLC) films has attracted widespread attention in the academic community in recent years due to its significant potential in the domain of solid lubrication under extreme working conditions, such as vacuum, high contact pressures, and wide temperature ranges. However, the deposition methods and bonding structures of DLC films are diverse, and specific intrinsic compositions and structures, as well as external working conditions, are required to achieve macroscopic superlubricity in DLC films. Thus, this review discusses current research progress on the structural regulation of DLC films, diverse superlubricity behaviors in DLC films, key influencing factors, and their corresponding mechanisms. First, the current structural classification, deposition methods, and recent research on the bonding structure regulation principles of DLC films for solid superlubricity were summarized. An effective strategy for synthesizing DLC films with superior solid superlubricity is to adjust the composition and energy of deposition ions to balance the surface chemisorption and subsurface implantation growth modes, leading to an optimized combination of mechanical stiffness and hydrogen content of DLC films. Subsequently, the research trajectory on superlubricity in DLC films was reviewed, and the latest developments categorized by mechanisms were introduced. The combinations of DLC and environmental media available for superlubricity are diverse, and include hydrogenated amorphous carbon (a-C:H) in dry inert atmospheres, doped a-C:H in humid air or water-based liquids, hydrogen-free DLC in oil-based liquids, and DLC films in nanomaterial-containing environments. Furthermore, the influencing mechanisms of the internal elemental composition and bonding structure of DLC films, as well as external working conditions such as the environment, contact pressure, and temperature on the superlubricity behavior of DLC are discussed in detail. Sufficient hydrogen content is necessary for DLC films to achieve superlubricity in dry inert atmospheres, such as N2, Ar, and vacuum. The self-lubrication properties of DLC films can be significantly affected by O2 and H2O molecules in humid air, due to intensified interfacial chemical bonding, disordered water adsorption layers, enhanced hydrogen bonding forces, and van der Waals forces caused by tribo-chemically generated highly polar groups. Elemental doping with Si, S, and Ti can effectively suppress the moisture sensitivity of DLC films via their participation in the structural evolution of sliding interfaces. Sufficiently high contact pressure is also necessary for solid superlubricity in DLC films, which is mainly due to the self-lubrication effect of contact-pressure-triggered locally short-range-ordered layered-like sp2 nanoclustering structures. Overly high contact pressure deteriorates the superlubricity state of DLC films through hydrogen detachment and microstructural destruction of the counterpart surfaces. Ultralow temperature (<-100 ℃) can increase the friction factor of DLC films due to the suppression of thermal activation and structural evolution of sliding interfaces. On the contrary, high temperature (>300 ℃) facilitates the failure of a-C:H films due to excessively promoted hydrogen detachment, graphitization, and oxidation in air. Additionally, the mechanism behind the solid superlubricity of DLC is discussed from the perspective of interfacial bonding structural evolution. The tribo-generated transfer films on smooth-stiff surfaces, hydrogen passivation of surface dangling bonds, and generation of short-range ordered graphite-like nanostructures are key factors for the establishment of superlubricity in DLC films, which simultaneously suppress the three main contributors of macroscopic friction force: interfacial abrasion, shearing, and adhesion effect. Finally, the unresolved issues and related research trends in the underlying science and engineering applications of DLC are summarized. The connection of deposition parameters with growth theories, the nanostructure of superlubricious sliding surfaces and their evolutionary pathway, the environment and working condition sensitivity, and the influencing mechanisms of multi-element, multilayer, micro-nano textured, and media-synergistic lubrication strategies require further research. These findings can provide technical support for the design and application of superlubricious DLC films for dry-sliding friction pairs under extreme engineering conditions.
  • Research Progress of Biomimetic and Intelligent Marine Anti-fouling Coating Materials
    JIA Bo, LIU Jie, ZHENG Nan, WANG Xiaojun, WANG Guoqing, LI Wenge, LU Jiufu, DANG Lihong
    China Surface Engineering. 2025, 38(1): 23-39. https://doi.org/10.11933/j.issn.1007-9289.20231117001
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    Based on the background of the anticipated Industry 4.0 era, the promotion of “Made in China 2025” and the strategy of maritime power, traditional marine anti-fouling coating materials have gradually withdrawn from the historical stage and been replaced by new biomimetic and intelligent marine anti-fouling coating materials. However, a comprehensive and systematic review of new biomimetic and intelligent marine anti-fouling coating materials is still lacking. Therefore, this study reviews the research progress of biomimetic anti-fouling coating materials constructed by biomimetic anti-fouling strategies, such as micro-nanostructure surface, release of green anti-fouling agent, super-slippery surface, dynamic surface, and self-healing. Meanwhile, the research progress of intelligent anti-fouling coating materials formed by intelligent anti-fouling strategies, such as pH, temperature, and light response control, is reviewed. The research progress of synergistic anti-fouling coating materials constructed by the synergistic anti-fouling strategies, namely the combination of biomimetic and intelligent anti-fouling strategies, is also reviewed. Finally, the preparation methods, anti-fouling mechanisms, effects, advantages and disadvantages, and the development trends of the above coating materials are summarized. The emerging biomimetic and intelligent marine anti-fouling coating technology are currently recognized in marine anti-fouling, and has achieved good research results; however, some problems are yet to be resolved. For example, the toxic components of current coating materials have uncertainties and potential risks to the growth and reproduction of marine organisms and marine ecosystems; the surface structure of biomimetic anti-fouling coating is complex; weak anti-fouling durability, stability, and high cost. The response of intelligent anti-fouling coating to external conditions is singular; the anti-fouling stability is not high, and the intelligent anti-fouling evaluation system and mechanism are unclear. Other issues include multi-strategy combined anti-fouling coatings and limited research on the synergistic anti-fouling mechanism between various strategies. Furthermore, the future development direction of anti-fouling coating materials constructed by biomimetic and intelligent multi-antifouling strategies is suggested. In selecting coating materials, the marine environment affinity components are used to replace the toxic components to reduce the risk of toxic substance release into the marine environment; adhering to the principle of "from the ocean, to the ocean" vigorously tap the marine biological resources, extract or synthesize new and efficient bio-antifouling agents to block the related signals and metabolic pathways of fouling organisms to inhibit the deposition and attachment of fouling organisms, rather than direct poisoning, thereby reducing the genetic risk to marine organisms; strengthening the basic research of bionics and biomimetic technology, and studying the microstructure surface, metabolism, and release law and stress behavior of anti-fouling attached organisms to quickly improve the overall design level of biomimetic anti-fouling coating; an intelligent “on-off” anti-fouling system with multiple conditional response was designed, which meets the requirements of convenient and accessible practical application environment and can quickly start and stop according to the specific environment, promoting the broad application of biomimetic and intelligent marine anti-fouling coating materials; increasing the research of multi-strategy combined anti-fouling method systems, such as expanding various anti-fouling strategies and an in-depth study of the synergistic anti-fouling mechanism between various strategies to solve the problem of a single anti-fouling strategy failing to meet the requirements of long-term, stable anti-fouling in the actual complex marine environment, thus ensuring long-term stable and efficient anti-fouling of coating materials. The multi-strategy combined anti-fouling method system will become an important development trend in marine anti-fouling in the future. This study mainly proposes the guiding viewpoint of the method system of the synergistic effect of biomimetic and intelligent multi-antifouling strategies, addressing the issue of limited review articles in the industry. Given the continuous progress of science and technology, the multi-strategy joint anti-fouling method system is expected to promote new breakthroughs in the marine anti-fouling industry in China. Biomimetic and intelligent marine anti-fouling coating materials will become a major development direction of marine anti-fouling in the future. In addition, they have important reference value for the development of national defense and military, marine engineering, maritime transportation, marine fishery, and other fields.
  • Research Status and Challenges of Space Atomic Oxygen Resistant Coatings
    WANG Hu, HE Yanchun, LI Zhonghua, ZHOU Chao, LI Kun, LI Xuelei, ZUO Huaping, WANG Xiaoyi, WANG Lanxi, YANG Miao, LI Yi, ZHOU Hui, ZHANG Bin
    China Surface Engineering. 2025, 38(1): 40-56. https://doi.org/10.11933/j.issn.1007-9289.20230916001
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    Within the orbital altitude range of 180 km to 650 km, oxygen molecules in the atmosphere tend to decompose into atomic oxygen when exposed to ultraviolet light. Due to its strong oxidizability, atomic oxygen, is capable of causing erosion effects on the surface materials of spacecraft. Complex structural evolutions, such as mass loss, thickness reduction, and changes in surface morphology are involved in this process. So that performance degradation inevitably occurs, highlighting the importance of protecting the surface materials of low-orbit spacecrafts. The adoption of protective coatings is an effective way to improve the atomic oxygen protection performance of materials and ensure the long lifespan and high reliability of low-orbit spacecraft. The research progress of atomic oxygen protective coatings is briefly reviewed, and the factors affecting the performance of atomic oxygen protective coatings are studied. The results show that surface roughness, defects composition and structure of the coating have significant influences on its atomic oxygen protection effect. A rough surface of the coating has advantage in increasing the probability of collisions between atomic oxygen and surface materials, while defects in the coating provide more channels for atomic oxygen and enhance the erosion effects, and the composition and structure of the coating will affect the probability of atomic oxygen reactions. The types of space atomic oxygen protective coatings are investigated, and the characteristics of different types of coatings are analyzed. Atomic oxygen protective coatings can be divided into inorganic coatings, organosilicon coatings, and composite structure coatings. Among them, inorganic coatings are generally solid oxides with a dense structure, and this type of coatings has excellent protective performance but poor flexibility. Organosilicon coatings are mainly composed of elements such as Si, H, C, and O. Good flexibility is achieved through the formation of a polymer-like network structure in organosilicon coatings. When eroded by atomic oxygen, a dense silicon oxide layer appears during the reaction between atomic oxygen and Si atoms located at the surface of coatings, which prevents further erosion. However, under the action of high flux atomic oxygen, the coating surface is prone to shrinkage, resulting in a “tiled” surface and coating cracking. The composite structure atomic oxygen protective coatings can make up for the shortcomings of single-structure coatings and adapt to the needs of different application conditions, however, the performance of this type of coatings is highly correlated with their structure and requires. The coating preparation methods are sorted and summarized, while the advantages / disadvantages and application objects of different preparation techniques are analyzed based on a comprehensive comparison: inorganic coatings with dense morphology can be obtained through magnetron sputtering process, which is mainly suitable for preparing coatings / films on rigid or semi-rigid substrates. Plasma-enhanced chemical vapor deposition in coating preparation corresponds to lower deposition temperature, less thermal damage to substrates. And a wider application range because both inorganic coatings and organic coatings can be achieved in this way. However, due to process limitations, this technology can only be applied to planar substrates and cannot be applied to three-dimensional complex structural parts; ion beam co-deposition can conveniently prepare multi-component composite structure coatings, so it is the main preparation technology for composite atomic oxygen protective coatings; atomic layer deposition has precise coating thickness control, a dense coating structure, no pinholes and other defects, and can form a uniform film on the substrate surface with complex configurations such as steps and grooves. Moreover, it can repair the defects on the substrate surface, therefore having obvious advantages in atomic oxygen protection and achieving good atomic oxygen protection performance at a relatively thin thickness. However, the disadvantage is the low deposition rate, low efficiency, and high stress when preparing thick coatings. Cracks are prone to occur when applied on flexible substrate surfaces. The sol-gel method for preparing coating materials has a low temperature during the process, uniform coating structure, easy control of the reaction process, and low cost. However, in general, the coating thickness is relatively high, requiring tens of microns or more and high quality, which is not conducive to the light weighting of spacecraft. Therefore, it is mainly applied to small structural parts. The precursor photolysis / hydrothermal curing method requires post-treatment such as irradiation and heating when preparing coatings, and the uniformity control is more difficult when implemented on a large area. Therefore, it is suitable for local coating and repair of easily damaged areas on the surface of structural parts. The further development trend of atomic oxygen protective coatings is analyzed and introduced. The research provides the necessary research basis and reference for the atomic oxygen protection of materials for low-orbit spacecraft in China and provides research ideas for the further development of atomic oxygen protective coating technology.
  • Post-treatment Method of Tool Coating: Research Status and Development Trend
    DENG Jiedong, JIANG Feng, ZHA Xuming, XI Linqing, LIN Liangliang, LI Yousheng
    China Surface Engineering. 2025, 38(1): 57-74. https://doi.org/10.11933/j.issn.1007-9289.20230510001
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    The advancement of technology in today’s society has led to higher performance demands for machining tools, and tool coatings have become a primary method for enhancing tool performance. To fully exploit the inherent properties of coated tools, post-treatment is essential. This paper aims to summarize the commonly used post-treatment methods for coated tools, which include sandblasting, polishing, heat treatment, energy field / beam treatments, and others. Sandblasting is the most widely used post-treatment method for coatings. The effectiveness of the post-blasting treatment is determined by three key parameters: grit, pressure, and time. Careful analysis of these variables shows that sandblasting can efficiently remove larger particles from the coated surface while enhancing its overall quality, provided that appropriate conditions are met. Another traditional surface-polishing technique is mechanical polishing, which uses flexible polishing tools, abrasive particles, and other media to modify the workpiece surface. This process effectively removes burrs and larger particles, resulting in a significant reduction in surface roughness. Both sandblasting and mechanical polishing contribute to achieving finer surface finishes on coated materials. Heat treatment is another widely adopted method for both tool treatment and post-treatment of coated tools. During the deposition of tool coatings, the substrate temperature remains low, causing rapid cooling of the coating material. Due to differences in the thermal expansion coefficients between the grains within the coating, thermal stress arises, which can accelerate tool failure. Heat treatment plays a crucial role in relieving some of the strain energy within the coating, adjusting the state of the coating-substrate interface, enhancing microstructural properties, and ultimately improving the performance of coated tools. A recent advancement in post-treatment methods for coatings is the use of energy fields or beam treatments. Energy field treatments include various techniques such as magnetic fields, electron beams, ion beams, lasers, and other similar methods. Compared to mechanical and heat treatments, energy field treatments offer greater controllability and a broader range of action. Research indicates that applying different energy field parameters during post-treatment can enhance not only the surface integrity of the coating but also the bonding strength between the coating and the underlying substrate. This technique involves localized heating of specific areas on the coating using high-density energy, leading to surface remelting and changes in roughness. Additionally, rapid heating and the ensuing energy waves generate thermal stress, which strengthens the coating, substrate, and bonding interfaces. As a result, this process significantly enhances the bonding strength between the coating and the substrate, thereby improving the overall performance of the coating.Although progress has been made in the post-treatment of coated tools, these methods are not yet widely applied in practice, with the exception of polishing. By analyzing the advantages and disadvantages of each post-treatment method, this study clarifies their respective scopes of application, addresses the fragmentation of research in this field, improves understanding of post-treatment methods for tool coatings, and provides a useful reference for the future development of post-treatment technology for coated tools.
  • Effect of Scanning Path on Residual Stress and Tribological Properties of Multi-pass Laser Cladding Layers
    DONG Mohan, JIN Kangning, HUANG Guoshun, ZHAO Hairui, XUAN Lijian, QIAO Xiaoxi, CHEN Ping
    China Surface Engineering. 2025, 38(1): 75-86. https://doi.org/10.11933/j.issn.1007-9289.20230830001
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    Laser cladding technology is widely used in the field of surface protection and remanufacturing because of its advantages, such as metallurgical bonding between the cladding layer and substrate, high processing efficiency, low dilution rate, and high energy input. It improves the wear resistance and corrosion resistance of the substrate, as well as the life of the cladding layer of the parts. However, instantaneous melting and rapid solidification of the melt pool during the laser cladding process lead to uneven stress within the cladding layer. It has been shown that even if the basic parameters are the same, the scanning paths and scanning time intervals of different lasers significantly influence the temperature distribution, and an uneven temperature distribution further leads to an uneven distribution of thermal stresses, which can cause coating quality issues. To analyze the effect of the scanning paths on the residual stress and tribological properties of the multi-pass laser cladding layer, a multi-pass laser cladding layer of Inconel 718 was prepared on 316L stainless steel using different scanning paths, and the distribution of residual stress in the cladding layer was investigated based on the thermoelastic-plastic model and the residual stress analyzer. The microstructure and hardness distribution of the cladding layer were studied using an X-ray diffractometer, a metallurgical microscope, and a hardness testing system. The tribological properties of the cladding were evaluated using a comprehensive material surface property tester and a laser confocal microscope. The results show that, owing to the difference in temperature cycling during the cladding process, the reciprocating scanning path has the shortest interval between each cladding pass and the lowest surface residual stress. The isotropic and dispersive scanning paths exhibit intermediate surface residual stress levels, while the shrinkage scanning path, which has the largest accumulation of heat in the central region of the cladding layer, exhibits the highest surface residual stress. The isotropic scanning path results in the most homogeneous microstructure due to the differences in temperature cycling during the process. In terms of microstructure, the isotropic scanning path exhibits the most uniform microstructure. Due to the consistent time intervals between each fusion cladding pass, the cooling process remains stable, resulting in minimal changes in crystal size from the cladding layer to the fusion zone. The shrinkage path has the largest accumulation of heat in the fusion cladding layer, and the low cooling rate allowed the crystals more time to grow, which resulted in significant changes in the size of the crystals at the bottom. Owing to the differences between the primary arm spacing and the volume fraction of the Laves phase in the fused cladding, the isotropic scanning path has a uniform distribution with a low content of the Laves phase and the lowest abrasion rate of the fused cladding layer. The reciprocating and dispersive scanning paths have intermediate abrasion rates, while the shrinkage-type scanning path has the highest abrasion rate due to its larger number of Laves phases. Therefore, a reciprocating scanning path should be selected for multi-pass cladding to reduce residual stresses in the cladding layer, and an isotropic scanning path should be selected to reduce the wear rate of the cladding layer. The results of the different scanning paths are expected to provide a theoretical basis for the selection of process parameters in the fields of surface protection and remanufacturing.
  • Enhancing Thermal Fatigue Resistance of 160CrNiMo Rollers with Laser-clad Iron-based Coatings Doped with Mo and V
    ZHANG Xulong, ZHANG Yunhua, HU Dengwen, LIU Yan, FANG Qiang, HAN Hui
    China Surface Engineering. 2025, 38(1): 87-98. https://doi.org/10.11933/j.issn.1007-9289.20231020001
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    In the production process of a hundred-meter-long high-speed railway track, the rolling mill serves as a key component, bearing the effects of alternating high-temperature rolling parts and cooling water. It also faces significant extrusion, shear, and thermal stresses on the surface, resulting in problems such as short service life and severe roller surface wear due to failure. As a primary consumable component in the production processes of many industries, the scrapping a large number of rolls results in considerable waste of energy and resources in China. To repair the surface of scrapped rolls and improve their thermal fatigue performance, we developed the powder composition of iron-based powder, leveraging the good compatibility between the iron-based powder and the matrix material and the reduced cracking during the melting process. Considering the actual production conditions of the rolling mill, selecting an appropriate strengthening element is necessary to improve the performance of the repaired surface. Mo exhibits a good solid-solution strengthening effect and forms carbides, thereby enhancing the strength and wear resistance of the substrate. To further improve the wear resistance of the cladding layer while ensuring good thermal fatigue performance, elemental V was added to improve high-temperature stability, allowing the cladding layer material to maintain good performance at elevated temperatures. A laser cladding technique was used to prepare an iron-based coating using T504 as the base powder, with Mo and V added to the surface of a fatigue- failed 160CrNiMo roller material. The crack propagation rate and mechanism in the base material and cladding layer during thermal fatigue were analyzed using optical microscopy, scanning electron microscopy, and thermal fatigue testing machines. The results show that the average hardness of the cladding layer with Mo and V ratios of 1:0.5, 1:1, and 1:1.5 is 59.2 HRC, 59.9 HRC, and 59.1 HRC, respectively, representing an average increase of 33.4% compared to the substrate; The driving force for crack propagation during thermal fatigue tests primarily arises from the thermal stress generated by cold and hot cycles. After 2000 thermal fatigue testing cycles, the crack length in the matrix material sample measured 11.289 mm. Due to its high carbon equivalent, the brittle phase of eutectic M7C3, which contains a higher Cr content than the surrounding material, exhibited a different coefficient of thermal expansion. This mismatch became the main channel for crack propagation during the thermal fatigue testing process, where cracks primarily propagated in a transgranular form. The crack lengths of the samples with added Mo and V mass ratios of 1:0.5, 1:1, and 1:1.5 in the cladding layer were 3.185 mm, 16.596 mm, and 8.401 mm, respectively. The high hardness of the cladding layer, resulting from the addition of Mo and V, increased its brittleness. As the V content increased, the eutectic structure of the cladding layer gradually appeared to break down; the initial boundary became clear and blurred, compromising the integrity of the structure and leading to an increase in the number and length of microcracks. During thermal fatigue testing, the propagation of fatigue cracks was predominantly brittle and transgranular, exhibiting a rapid propagation rate. The sample completed the rapid crack propagation stage after 50-100 cycles. However, appropriate addition of V can improve high-temperature stability and result in shorter cracks. When the mass ratio of Mo to V was 1:0.5, the thermal fatigue performance of the roller material before repair improved by 71.7%. A comparison of the thermal fatigue characteristics of the iron-based coatings with different Mo and V mass ratios provides an experimental basis for selecting iron-based coating systems for roller repair.
  • Preparation and Surface Properties of Cr Coatings in High-power Pulsed Magnetron Sputtering Tubes with External Auxiliary Anode
    WANG Zijia, LI Yuxin, HU Tianshi, TIAN Xiubo, GONG Chunzhi, ZHANG Hui
    China Surface Engineering. 2025, 38(1): 99-106. https://doi.org/10.11933/j.issn.1007-9289.20240109001
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    The working environment of the inner surfaces of tubes in industrial production is harsh, necessitating higher performance against corrosion, friction, and wear. To improve the properties of the inner surfaces of tube and barrel parts, a high-power impulse magnetron sputtering (HiPIMS) coating method with an auxiliary anode is proposed. The auxiliary anode was first placed near the tube tail to attract plasma into the inner part of the tube. Chromium (Cr) coating was then deposited on the inner wall of a carbon steel tube with a diameter of 40 mm and a length of 120 mm. The effects of the auxiliary anode voltage on the discharge characteristics of the Cr target as well as the structure and mechanical properties of the Cr coating deposited on the tube’s inner surface were explored. The accessible depth of Cr deposition inside the tube was established. The plasma distribution inside the tube following the addition of the auxiliary anode was analyzed and a theoretical model was developed. The experiments demonstrated that the substrate current increases with higher auxiliary anode voltages, particularly at the tube tail position. When the auxiliary anode is positioned at the end of the tube, it attracts electrons deeper into the tube, resulting in increased ionization of additional ions and electrons during their movement. The ions generated by ionization are attracted to the inner wall of the tube by the negative charge carried by the tube. This can be inferred by comparing the emission spectral intensity curve between the nozzle and the tube tail. At the port position, when the auxiliary anode voltage is 20 V, the Ar+ feature peak value is the lowest, whereas the corresponding Cr* feature peak value is the highest. We infer that at 20 V, most of the energy is absorbed by the excited particles. However, under the influence of the auxiliary anode, electron escape is accelerated, inhibiting the discharge. The Cr film deposited at the tube port has a columnar structure, as shown by the cross-section morphology of the film deposited at different auxiliary anode voltages. At higher auxiliary anode voltages, the columnar crystal width decreases, and the deposited film becomes denser. As the auxiliary cathode voltage increases, the overall depth of the deposited chromium layer in the tube also increases. However, the deposition rate decreases with an increase in auxiliary anode voltage. This may be due to the higher energy of the particles that derives from the increased auxiliary anode voltage, which leads to the film densification and enhanced etching effects, thereby decreasing the deposition rate. The coating hardness and elastic modulus of the Cr film both increased initially and then decreased with increasing auxiliary anode voltage. At an auxiliary anode voltage of 40 V, the Cr coating achieved the best depth with the highest hardness and elastic modulus. Under HiPIMS discharge conditions, the effects of the auxiliary anode on the plasma can generally be summarized. First, by attracting electrons, the auxiliary anode regulates the direction of plasma’s movement. The plasma concentration can be greatly increased by the additional anode. An additional anode at the tube's end modifies the distribution of electric field lines in the vacuum chamber, reducing the number of escaping electrons. Second, high-density, high-energy plasma preferentially forms along the tube axis towards the auxiliary anode at the tube’s end, promoting further collision ionization of neutral particles inside the tube and delaying the decrease in plasma density caused by the increased distance from the target surface. The Cr coating deposited on the inner surface of the tube can be widely used in harsh environments.
  • Experimental Research on Pulse Magnetic Field Assisted Magnetic Abrasive Finishing
    YAN Yuhang, WANG Huijiang, DING Yunlong, WANG Jie, MA Xiaogang, HAN Bing, JU Dongying
    China Surface Engineering. 2025, 38(1): 107-117. https://doi.org/10.11933/j.issn.1007-9289.20240112005
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    SUS304 stainless steel is a common stainless steel material with good corrosion resistance, heat resistance, and mechanical properties. But various defects may appear on its surface. Therefore, in response to the surface quality problems of SUS304 stainless steel plate, magnetic abrasive finishing method is used to remove the surface defects and original texture of SUS304 stainless steel plate. Traditional magnetic abrasive finishing has a relatively single magnetic field during processing, and the movement trajectory of the abrasive particles is relatively regular, so that the grinding marks are obvious. Moreover, because of overheating of the electromagnet, the working time can not be too long, which leads to lower working efficiency. Based on the traditional magnetic abrasive finishing, a pulse magnetic field has been added and a circuit has been designed. This not only complicates the magnetic field in the processing area and diversifies the processing trajectory, but also solves the serious heating problem of electromagnetic, and working efficiency of the device can be improved. Therefore, a pulsed magnetic field assisted planar magnetic abrasive finishing device was proposed, and the permanent magnet assisted with pulse magnetic field of electromagnetic was simulated using magnetic field simulation software. Firstly, the field domain was set as a transient field, and the materials in the device were set. Furthermore, an air domain was added. Finally, a calculation step was added to analyze the magnetic field under different distribution states. Based on the results of simulation, the influence of magnetic field on the motion of abrasive particles can be observed. In order to explore the influence factors of planar magnetic abrasive finishing assisted with pulse magnetic field, response surface methodology was used to optimize the data of three influencing factors: pulse current amplitude, pulse current frequency, and pulse current duty cycle. Through single factor experiments, the range of the three factors was obtained: pulse current amplitude is 15V, 25V and 35V; pulse current frequency is 1Hz, 3Hz and 5Hz; pulse current duty cycle is 15%, 50%, and 85%. By generating and adjusting the frequency and duty cycle of the pulse current through a signal generator, the pulse magnetic field generated by the electromagnet can be precisely controlled. The grinding effects of different grinding magnetic fields under different parameters on SUS304 stainless steel plate was compared through experiments. When the grinding gap is 2mm, the effects of different voltage amplitudes, current frequencies, and current duty cycles on the surface quality of the workpiece were compared. The surface quality of the workpiece before and after processing was measured and compared using a stylus surface roughness measuring instrument and an ultra depth of field 3D electron microscope, and the simulation results were verified. The experimental results of planar magnetic abrasive finishing assisted with pulse magnetic field show that through response surface data optimization, when the machining parameters are pulse current amplitude of 20V, pulse current frequency of 4.5Hz, and pulse current duty cycle of 50%, the surface roughness Ra of SUS304 stainless steel plate after grinding is reduced to 0.047μm from the original 0.346μm. The design of circuit effectively solves the serious heating problem of electromagnetic. This circuit not only effectively reduces the heat generated during working process of electromagnetic, but also ensure the stable operation of the equipment and increases the service life span of the electromagnetic. By precisely controlling the amplitude, frequency, and duty cycle of pulse current, the motion trajectory of magnetic abrasive particles can be effectively changed. The periodically changing grinding magnetic field can make the abrasive particles move periodically, achieving rolling and updating during the grinding process. This can significantly reduce the surface roughness of workpiece and provide a reliable method for improving the machining quality. This processing method has greatly improved the grinding efficiency and processing effect.
  • Relationship Between the Pore Morphology and Macroscopic Elasticity of Thermal Barrier Coatings Inverted by Ultrasonic Echo Based on Multiple Elastic Parameters
    MA Zhiyuan, YANG Jiwei, SUN Luoming, LIN Li
    China Surface Engineering. 2025, 38(1): 118-126. https://doi.org/10.11933/j.issn.1007-9289.20230905001
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    Thermal barrier coatings (TBCs) have excellent properties, including a high melting point, low thermal conductivity, and high thermal expansion coefficient, which can significantly improve the efficiency and extend the service life of high-temperature components in the aerospace industry. Due to the characteristics of the TBC preparation process, pores are inevitably present inside the coatings and significantly affect the mechanical properties of the TBCs, particularly their elastic properties. Therefore, exploring the relationship between the microstructural characteristics of TBCs and the macroscopic elasticity is crucial for optimizing the parameters of the preparation process and predicting the service life. The internal pores of TBCs exhibit complex morphologies, such as irregular shapes and rough boundaries. However, existing research on TBCs based on elliptical approximations have focused on the relationships among the porosity, size, orientation, and macroscopic elasticity without considering the effects of irregular pore morphology on the macroscopic elasticity. In this study, a water-immersion ultrasonic back-reflection experiment was conducted using test samples with an Al2O3 coating plasma-sprayed onto a stainless steel substrate. The experimental setup consisted of an angle meter, a 10 mm thick acrylic glass flat-bottomed reflector, and an SM-J3B-300 water-immersion ultrasonic testing system, which included a GE USIP 40 ultrasonic generator, Tektronix DPO 4034B digital oscilloscope, nominal 5-MHz water-immersion pulse-focusing probe, three-dimensional stepper device, and self-built rotational angle measurement device used for precise control of the sample’s axial rotation angle. The backscattered signal from the flat-bottomed reflector surface at the vertical incidence was used as a reference signal, and the angle meter displayed the θi values. The coating was continuously rotated in the x1-x3 plane from 0°to 90°in increments of 1°. The ultrasonic backscattered signals corresponding to different incident angles θi were collected as the analysis signals. A simulation was performed based on the water-immersion ultrasonic back-reflection experiment. A newly proposed random sphere model (RSM) and random void model (RVM) were separately used to build TBC simulation models based on the characteristic parameters, namely, porosity (p), aspect ratio (α), and orientation factor (λ), which were obtained from the observation and statistical analysis of multiple (>32) metallographic photos of the plasma-sprayed Al2O3 coating. Ultrasonic testing finite element numerical simulations with the models were then conducted to analyze the effects of different pore morphologies on the wave velocities at multiple incident angles. Combining the Christoffel equation with sensitivity analysis, which can improve the efficiency of ultrasonic signal selection, enables accurate inversion of multiple unknown elastic constants of TBCs. The effects of irregular pore morphology on the elastic constants of TBCs were revealed by comparing the elastic constants obtained through inversion from experiments and two types of models with those calculated using micromechanical theory. The results of ultrasonic measurements, numerical simulations, and theoretical calculations of the elastic constants of the plasma-sprayed Al2O3 coatings showed that the elastic constants exhibited obvious elastic anisotropy. Numerical simulation results based on the RSM model showed good consistency with the theoretical values, with a relative deviation of less than 3.32%. This showed that the theoretical results were more applicable to the analysis of relatively regular morphological pores that can be approximated as spheres or ellipsoids. However, the elastic constants measured based on the RVM model had a higher relative deviation of as much as 12.53%, and the relative deviation of the ultrasonic experimental results was up to 59.91%, indicating that the effects of irregular pore morphology on the macroscopic elasticity of TBCs could not be ignored. Moreover, the inversion results using the irregular RVM model were closer to the experimental results than those based on the RSM model, further illustrating that the irregular pore morphology significantly affected the elastic performance of the coating.
  • Corrosion Resistance of Alkali-etched Hollow Halloysite Microtubes Loaded with 2-Mercaptobenzothiazole and Encapsulated with Chitosan for Self-healing Coatings
    SHI Hao, WANG Zhihao, CHU Guiwen, ZHANG Peiqi, LIU Runyuan, WANG Yixiang, SUN Lei, SONG Liying, JIANG Quantong, MA Fubin
    China Surface Engineering. 2025, 38(1): 127-140. https://doi.org/10.11933/j.issn.1007-9289.20231102002
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    Metal equipment is vulnerable to corrosion when used in harsh marine environments. The speed, fuel consumption, and service life of marine equipment are greatly reduced owing to seawater corrosion, which results in significant economic losses every year, severely impeding the development of the national economy. Therefore, protecting marine equipment from corrosion damage has always been an urgent issue. Currently, coating technology is one of the most effective and commonly used methods for protecting metals from corrosion. Preparing self-healing coatings with better performance by adding micromaterials and nanomaterials to the coatings and further improving the corrosion protection ability of the coatings has recently become an important research direction for metal protective coatings. However, most inorganic microcarriers and nanocarriers have agglomeration problems in organic coatings, which affects the corrosion resistance and service life of self-healing coatings. In this study, the natural halloysite microtube (HMT) was reamed by alkali etching to increase its inner diameter. Secondly, the corrosion inhibitor, 2-mercaptobenzothiazole (MBT), was loaded into alkali-etched halloysite microtubes (HMTs) by vacuum adsorption in a vacuum chamber. Then, chitosan (CS) was coated on the outer surface of HMTs under acidic conditions to prepare micron fillers with a corrosion inhibition function. Finally, micron fillers were added to the PDMS coating at the rate of 15 wt.% and fully stirred to prepare the self-healing coating. Fourier-transform infrared spectroscopy (FTIR) was used to confirm the successful loading of MBT into HMTs, and the corrosion inhibition function of the inhibitor remained effective. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were employed to observe the morphological structures of HMTs, HMTs-MBT, and CS-HMTs-MBT. Through thermal gravimetric analysis (TGA), HMTs were shown to carry approximately 13 wt.% of MBT, and HMTs encapsulated with CS accounted for approximately 61 wt.% by mass. The dispersion of various samples in polydimethylsiloxane (PDMS) coatings was tested, demonstrating that CS encapsulation could enhance the dispersion of microcarriers within the coating. Electrochemical impedance spectroscopy (EIS) was used to assess the self-healing ability of the coating. An analysis of |Z|0.01 Hz indicated that the self-healing ability of the coating reached its maximum on the fourth day. Data from impedance measurements were fitted using ZSimpWin to validate the corrosion resistance of the self-healing coating. After a four-day immersion experiment, energy dispersive spectrometer (EDS) and X-ray photoelectron spectroscopy (XPS) were utilized to confirm that the copper ion content at the scratch site of the self-healing coating had dropped to zero. In addition, scanning Kelvin probe (SKP) tests indicated the disappearance of the potential well at the scratch site, signifying that the coating had been repaired by the corrosion inhibitor. Utilizing the excellent dispersion properties of CS in organic coatings enhances the dispersibility of CS-HMTs-MBT in PDMS coatings. When the coating was scratched, the corrosion inhibitor MBT was released and adsorbed onto the metal surface, forming a tight film that isolates corrosive substances. This study performed etching modification on halloysite micron tubes to increase their corrosion inhibitor loading capacity and verified the feasibility of carrying corrosion inhibitor MBT in the modified tubes. On this basis, CS film was applied to the micron tubes to improve the dispersion of the micron tubes in the coating. The self-healing coating was prepared by loading the corrosion inhibitor and encapsulated with chitosan as a filler in the inner cavity of the HMTs. Controlled and long-term release, protecting metal parts and compensating for performance deficiencies of ordinary coatings, was achieved. This study thus demonstrates the possibility of preparing self-healing coatings suitable for harsh corrosive environments.
  • Corrosion Behavior and Static Load Compression Creep Performance of Metal Rubber under Different Surface Treatment Processes
    LAI Fuqiang, HU Anqiong, HAO Xiangfei, BAI Hongbai, REN Zhiying, WU Yiwan
    China Surface Engineering. 2025, 38(1): 141-151. https://doi.org/10.11933/j.issn.1007-9289.20230831003
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    Metal rubber (MR) is recognized for its exceptional qualities as a vibration and damping structural material, and it exhibits commendable creep resistance under regular work conditions. However, the extent of its creep resistance when subjected to environmental challenges, such as the wet marine environments found aboard ships or the oil-polluted settings that are characteristic of factory processing equipment, remains undetermined. Currently, the literature contains limited investigations into the static compressive creep behavior of MR within marine corrosive environments. This scarcity of research underscores the need for further exploration to ascertain the performance capabilities of MR under these harsh circumstances. Leveraging these insights, this study initiates the fabrication of MR specimens from 304 stainless steel wire via a series of processes including winding, drawing, blank winding, and stamping. Subsequently, the MR specimens undergo distinct surface modification treatments: silanization (S), chemical pickling (P), and a combination of chemical pickling followed by silanization (P-S). These treatments yield three categories of MR specimens that exhibit varied surface attributes. A 5wt.% NaCl solution is employed to emulate a marine environment, and an alternate immersion corrosion creep (AICC) test is conducted on the MR specimens with the aforementioned surface treatments. The post-test analysis involves the examination of the micro-morphology, elemental composition of corrosion products, corrosion resistance, and creep resistance of the three specimens. Characterization techniques, such as tungsten filament scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), and electrochemical comprehensive testing are utilized to facilitate these assessments. The results show that after the AICC test, the corrosion products of the three specimens are mainly O, Fe, and Cr. The corrosion products on the surface of the untreated and S-MR specimens are covered in bulk on the surface of the wire. The P-MR and P-S-MR specimens are adhered to the metal wire in the form of a cell. The electrochemical test results show that the S-MR has the lowest corrosion potential (Ecorr) and the highest corrosion current density (icorr) under the AICC conditions, indicating that it has the worst pitting resistance and is more prone to pitting reactions. However, compared with untreated specimens, the impedance Rp and diffusion coefficient n of S-MR specimens are higher, whereas the Q value is lower, indicating that the passivation film stability is better and the corrosion rate is lower. The Ecorr of P-S-MR specimens is -447.37 mV, which is relatively high, whereas their icorr is relatively low, at 0.91 μA·cm-2. In addition, the overall corrosion rates of S-MR, P-MR, and P-S-MR are 0.024 9, 0.019 2, and 0.013 4 mm / a, respectively, which are lower than those of the untreated specimens (0.044 1 mm / a). The results show that the silane film produced by silanization has a better protective effect on the S-MR specimens, and the comprehensive comparison shows that the P-S-MR specimens show the best corrosion resistance in the 5wt.% NaCl solution. According to the variation amplitude of the mechanical performance of each specimen during the AICC test, the creep phenomena of the four specimens occurs in different degrees in the intermediate immersion corrosion environment. The height variation amplitude h, average stiffness variation amplitude k, energy dissipation variation amplitude e, and loss factor variation amplitude l of the P-S-MR specimens are -2.23%, 19.21%, -15.14%, and -3.79%, respectively, whereas the k and e values of the untreated specimens are 29.45% and -29.31%, respectively, which are close to the failure threshold of ±30%. Moreover, the overall magnitude of the mechanical performance change amplitude maintains the same order: untreated > S-MR > P-MR > P-S-MR. These results show that the changes in mechanical performance of MR specimens are affected by the degree of corrosion. That is, the higher the degree of corrosion, the higher the degree of creep caused to the specimens. These results also indicate that the P-S treatment of MR specimens is an effective technical approach by which to improve their corrosion and creep resistance. Therefore, this research can serve as an important reference for the extension of the engineering applications of metal rubber.
  • Impact of Surface Texture Arrangement on Lubrication Performance of Sliding Friction Pairs
    SUN Haocheng, YAN Zhijun, XU Jiujun, LIU Ze, WU Shibo, SUN Tao
    China Surface Engineering. 2025, 38(1): 152-161. https://doi.org/10.11933/j.issn.1007-9289.20231231001
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    Currently, few studies have addressed three-dimensional numerical models that consider oil film thickness, hydrodynamic pressure, and cavitation effects. Notably, a research gap exists in exploring the influence of texture distribution modes on lubrication performance. Therefore, advancing relevant research is imperative. To investigate the impact of surface texture distribution modes on lubrication performance under fluid lubrication conditions, this study aims to establish a three-dimensional calculation model for non-uniform texture distribution while accounting for oil film thickness. The model will utilize Computational Fluid Dynamics (CFD) methods, along with a User Defined Function (UDF) and dynamic mesh technology, to systematically explore how texture area density and distribution modes affect key parameters, including friction factor, oil film thickness, pressure distribution, and gas phase distribution. The numerical simulation results indicate that, under constant external load conditions, increasing texture area density leads to a decrease in the spacing of uniformly distributed textures. This phenomenon enhances the hydrodynamic lubrication effect while concurrently inhibiting the cavitation effect, resulting in a thinning of the oil film and an increase in the friction factor. In contrast, non-uniformly distributed textures enhance the hydrodynamic lubrication effect and weaken the suppression of the cavitation effect. This leads to an increase in the bearing capacity of the oil film, thickening of the oil film, a decrease in the velocity gradient, a reduction in shear stress, and a lower friction factor. Additionally, non-uniformly distributed textures alter pressure distribution, forming a localized high-pressure zone. The high-pressure zone generated by gradually sparse textures is larger and positioned closer to the symmetry center compared to that created by closely distributed textures. In terms of gas volume, the cavity volume associated for sparser distribution textures is greater than that of more closely arranged textures. Overall, lubrication performance is superior for sparser distribution textures compared to closely arranged ones. When the texture area density is 14.14%, the friction factor for sparser distribution textures is reduced by 26.5% compared to uniformly distributed textures. Simultaneously, the air volume fraction increases by 22.9%, and oil film thickness increases by 53.5%. For closely distributed textures, the friction factor decreases by 24.2%, the air volume fraction increases by 16.7%, and the oil film thickness increases by 32.5%. According to the experimental results, as rotational speed increases, oil film thickness across all three texture distributions demonstrates an upward trend, enhancing lubrication at the friction interface and reducing the friction factor. Notably, the non-uniformly distributed texture exhibits greater oil film thickness and a smaller friction factor than the uniformly distributed texture. This finding suggests that non-uniformly distributed textures can effectively improve lubrication performance. Furthermore, sparser distribution textures outperform closely arranged textures in overall performance, corroborating the simulation results. In this study, a UDF program was employed to control and compute in FLUENT software, considering the influence of changes in oil film thickness under constant load conditions. By analyzing the impact of surface texture distribution modes on lubrication performance, this study provides new insights and theoretical references for optimizing texture distribution design and enhancing research methodologies related to texture performance.
  • Effects of Hydrophilic V-shaped Array Wetting Patterns on Oil Film Thickness in Line Contact with a Limited Lubricant Supply
    LIU Yuting, GUO Feng, LI Ziying, JIN Wei, JING Zhaogang, CHEN Qingsong
    China Surface Engineering. 2025, 38(1): 162-171. https://doi.org/10.11933/j.issn.1007-9289.20240103002
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    Line contact lubrication often suffers from oil starvation due to inadequate lubricant replenishment. Developing new replenishment strategies is essential for enhancing lubrication efficiency and extending the lifespan of components. This study presents an innovative lubrication replenishment technique by establishing oleophilic V-shaped array patterns on the surface using a chemical coating (AF) method. Via a lubricant film interferometry system, experiments were conducted to assess the impact of pattern length, orientation, and angle on oil film thickness under limited oil supply conditions in cylinder roller-glass disc line contact. The results reveal that the non-uniform wetting properties created by the oleophilic V-shaped array patterns facilitate the smooth flow of oil back to the center of the track, thereby improving oil supply at the inlet and increasing the lubricant film thickness. The pattern length influences the smoothness of lubricant flow from the sides to the center, with optimal lubrication achieved when the pattern width matches the track width. At high experimental speeds (u = 640 and 800 mm / s), the oil film thickness enhancement rates for a 1-μL oil supply reach 17.3% and 23.6%, respectively. However, a significant difference between the pattern width and lubrication track results in an increased time for the lubricant to return from the side ridges to the track, leading to insufficient replenishment at the inlet and worsening oil starvation. Fluorescence microscopy observations of oil pools at the inlet during backward and forward pattern movements reveal wave-like formations along the width of the roller. During backward movement, the V-shaped array (with the V opening facing the contact area) effectively reduces oil backflow and side leakage, significantly enhancing oil collection capacity at the inlet and increasing the amount of oil absorbed. By contrast, during forward movement, the V-shaped pattern accelerates oil diffusion to the sides of the track, resulting in lower oil film thickness than the original surface and exacerbating oil starvation. Further investigations using lubricants of varying viscosities show that as viscosity increases, oil starvation during forward movement becomes more pronounced, as higher viscosity hinders backflow. The study also examines the effect of pattern angles on oil film thickness and compares the oil film enhancement rates of the oleophilic V-shaped array pattern with spaced wetting patterns under similar conditions. The results indicate that the V-shaped wetting pattern exhibits higher oil film enhancement rates than spaced wetting patterns across different viscosity lubricants. For example, the oil film growth rates for the 120° V-shaped wetting array surface under PAO4, PAO8, and PAO20 are 109.298%, 187.335%, and 13.84%, respectively, whereas the 180° interlaced wetting surface shows film thickness enhancement rates of 58.79%, -1.74%, and -19.72%, respectively. This phenomenon becomes more evident as lubricant viscosity increases. The different film formation mechanisms between the two patterns likely contribute to these results. During backward movement, more oil accumulates in the geometrically reduced areas of the V-shaped pattern, creating additional pressure in the inlet oil pool and increasing oil absorption. However, during operation, some AF may transfer to adjacent hydrophilic areas on the 180° interlaced wetting surface, reducing surface energy and causing dewetting, which enhances oil film load-carrying capacity. The proposed method of employing chemically coated V-shaped array patterns to enhance lubrication is simpler, more efficient, and cost effective as compared with manufacturing techniques involving physical texturing. It provides a pathway for reducing wear and friction in line contact components and lays a research foundation for designing and applying geometrically patterned wetting surfaces in engineering.
  • Preparation and Electrothermal Properties of FeCrAl / GF / CFRP Laminates
    CAO Zeren, CHEN Lei, WEI Shibo, ZHANG Xiaoqiong, WANG Tao
    China Surface Engineering. 2025, 38(1): 172-181. https://doi.org/10.11933/j.issn.1007-9289.20230822001
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    Icing is a major problem faced by aircraft flying at high altitudes in cold and humid conditions and poses a tremendous threat to the flight safety of aircraft. Research and development of new deicing technology is thus of great importance. Electrothermal deicing is a new type of deicing technology that uses electric heating elements to heat a composite substrate, effectively solving the problem of high energy consumption of current hot-air deicing technology used in aircrafts. In addition, in combination with a fiber metal laminate (FML), which has the characteristics of easy preparation and excellent mechanical properties, a new type of laminated material that utilizes high-resistance stainless steel foil tape and a carbon fiber prepreg composite is proposed. The surface-pretreated FeCrAl is sequentially laminated with glass fiber (GF) and a carbon fiber epoxy resin prepreg (CFRP) and then cured by hot pressing in a vacuum environment. The interfacial bonding condition of the FML is characterized by scanning electron microscopy observation of the cross-sectional morphology of the laminates and by tensile shear tests on the prepared single-layer tensile shear specimens. The metal-fiber interface is well bonded in the FML cross-section at a magnification of ×2000 without delamination. Fewer holes and cracks are present in the resin matrix, and the tensile shear strength of the single-lap tensile shear specimen can reach 7.1 MPa. Results show that the pretreatment of the metal surface can effectively improve the interfacial bonding strength of the FML. Different electrodes and loading methods produce different contact resistances at the current input, and the magnitude of the contact resistance affects the local temperature of the load. Therefore, the effects of three electrode loading methods, namely, double-sided conductive copper foil tape, a copper foil strip, and conductive silver paste combined with a copper foil strip, on the contact resistance are investigated separately. The output voltages of the pulsed power supply fed with a constant 10 A DC current feedback under each of the three methods show that the poor conductivity of the epoxy resin in the conductive silver paste and copper foil tape result in a higher contact resistance of the system than that of the direct contact when using only the copper foil strip. Therefore, using a direct-contact copper foil strip as the electrode loading method in electrothermal testing is appropriate. The electrical and thermal performances of the FML are tested at different power densities. The temperature change curve of the FML is recorded using thermocouples, and the temperature distribution after stabilization is observed using a thermal imager. The tests show that the FML can increase from room temperature to 65 ℃ in 10 min at a power density input of 0.164 W / cm2 at a uniform temperature distribution. The static electrothermal process of the FML is simulated using ABAQUS, and the simulation results are in close agreement with the experimental data. The deicing performance of the FML is tested in a low-temperature environment by applying heat to the plate via a 20 A constant DC to the accumulated ice, and the FML can completely melt the accumulated ice within 260 s. The fatigue performance of the FML is tested by repeated electrified heating followed by cooling. After 30 cycles of electrified heating, the electric heating performance of the FML does not change, and the test shows that the excellent fatigue performance of the FML can solve the problem of performance degradation of deicing coatings under repeated use. The research thus shows that FMLs have excellent electric heating, fatigue, and deicing performance and offer the advantages of easy preparation, high specific strength, and high specific stiffness. FMLs can therefore be used as deicing materials for aircraft wing skins.
  • Numerical Simulation of Cu / Al Composite Plate Rolling Interface Dynamic Composite Process Based on Contact Model of Penalty Method
    SUN Qimei, QIN Zhiwei, ZHAO Chenchen, SUN Yabo, WANG Tao
    China Surface Engineering. 2025, 38(1): 182-194. https://doi.org/10.11933/j.issn.1007-9289.20230305001
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    Numerical simulations are powerful tools for analyzing the rolling process of metal composite plates. However, the current numerical models for simulating the cold-rolling compounding of dissimilar metal-layered plates mostly adopt either interface binding or friction constraints. These approaches fail to accurately judge and simulate dynamic compounding at the interface, making it difficult to achieve precise predictions of the true stress-strain field, macroscopic warping, and thickness ratio of composite plates. Additionally, simulations involving high reduction rates in a single pass often suffer from severe mesh distortion and nonconvergence issues, hindering the integrated development of simulations in the field of rolling compounding. In this paper, we propose a novel numerical model to overcome these limitations. The finite element modeling of the Cu/Al plates in this model employs elongated meshes with an aspect ratio of at least 2. This improvement addresses the shortcomings of previous compounding criteria, which only considered normal forces, by incorporating tangential force constraints. This enhancement allows for a more accurate representation of the actual rolling compounding process, which involves the combined action of normal and tangential forces. The research objectives of this study are multifaceted. First, we aim to develop a robust numerical model that can accurately simulate the rolling compounding process of dissimilar metal-layered plates. Second, we seek to predict the quality of the composite metal plates in terms of their stress-strain field, warping degree, and post-rolling thickness ratio. The study's methodology involves several key steps. Initially, we developed a finite element model using elongated meshes with aspect ratios of at least 2. This choice of mesh design helps reduce mesh distortion and improves the convergence of the simulations. We then incorporated tangential force constraints into the model to address the limitations of previous models that only considered normal forces. This dual consideration of normal and tangential forces allows for a more realistic simulation of the rolling compounding process. The model's performance was evaluated through a series of simulations involving Cu/Al plates with various thickness ratios (2:4, 3:3, and 4:2) and reduction rates ranging from 40% to 60%. The simulation results were analyzed to assess the accuracy of the model in predicting the stress-strain field, degree of warping, and post-rolling thickness ratio of the composite plates. One of the key innovations of this model is its ability to mitigate severe mesh distortion and non-convergence issues that plague high-reduction-rate simulations. Using elongated meshes and incorporating tangential force constraints, the model provides a more realistic simulation of the rolling compounding process. This allows for more accurate predictions of the stress-strain field, warping degree, and post-rolling thickness ratio of the composite plate. The simulation results demonstrated that the proposed model can effectively simulate the rolling compounding process of Cu/Al plates with various thickness ratios and reduction rates. The predictions of the warping degree and post-rolling thickness ratio of the model were accurate, with errors within acceptable limits. Specifically, the error in predicting the degree of warping was less than 7.40%, and the error in predicting the post-rolling thickness ratio was generally less than 10%. This shows that the model can be used to predict the mass of the composite metal plates and has the potential to explore the internal mechanism of the rolling composite. In conclusion, the proposed numerical model addresses the limitations of existing models by incorporating elongated meshes and tangential force constraints. This allows for more accurate simulations of the rolling compounding process, leading to better predictions of the stress-strain field, warping degree, and post-rolling thickness ratio of the composite plate. The model initially solves serious mesh distortion and calculation non-convergence problems in high-pressure rate simulations and provides a reference for the process optimization of composite metal plates.
  • Effect of Sintering Temperature on Microstructure and Electrical Properties of ZnO Varistor Ceramics with Bi / Sb Ratio of 4∶1
    XIE Chenglong, CHEN Zhiqin, CHENG Lihong, LI Wenkui, ZHANG Hao, AI Jianping, YAO Jinliang, ZHENG Qiaoling
    China Surface Engineering. 2025, 38(1): 195-202. https://doi.org/10.11933/j.issn.1007-9289.20240530003
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    As the core component of metal-oxide arresters, ZnO varistors directly affect the insulation level of power equipment and the overvoltage level of the power system. ZnO varistors are crucial in suppressing overvoltage in power transmission and distribution systems. High-performance ZnO varistors are beneficial for improving the protection capability of the arrester, while affording lightweight and miniaturized equipment. Optimizing multivariate regulation technology and improving the sintering process are important for the development of high-performance ZnO varistors. However, the typical high-temperature sintering processes consume a significant amount of energy. To improve the energy-saving effect and comprehensive performance of ZnO varistors, the effects of different sintering temperatures (880, 930, 980, 1 030, 1 080 ℃) on the microstructure, electrical properties, and grain-boundary characteristic parameters of two types of ZnO varistors (ZB4 and ZB6) with a Bi / Sb ratio of 4∶1 are investigated in this study. The results show that the ZnO grains grow gradually as the sintering temperature increases. At the same sintering temperature, the liquid-phase amount of the ZB6-series samples is higher than that of the ZB4-series samples, which is beneficial to the distribution of the second phase around the ZnO grains. This corresponds to an improvement in the uniformity of the microstructure of the samples and an increase in the effective grain boundaries. The breakdown voltages of the ZB4- and ZB6-series samples are 329-1 074 V / mm and 429-1 161 V / mm, respectively. These breakdown voltages first increase and then decrease as the sintering temperature increases. In both the ZB4- and ZB6-series samples, the Bi / Sb ratio is 4∶1. The Bi2O3 contents in the ZB4 and ZB6 samples are 0.40mol.% and 0.60mol.%, respectively. At the same sintering temperature, the amount of Bi-rich phase in the ZB6-series sample increases, which is conducive to the integration of other metal oxides into the liquid phase. This improves the uniformity of the doping distribution and microstructure. By contrast, the formation of more Bi-rich phases, the incorporation of other metal oxides into the liquid phase, and the distribution of the liquid phase to the grain boundaries increase the number of grain boundaries formed and enhance the ability to increase the grain-boundary barrier height. At the same sintering temperature, an increase in the Bi-rich phase in the ZB6 sample improves the uniformity of its microstructure, thus resulting in a higher proportion of grain boundaries in the ZB6 sample than in the ZB4 sample. When the breakdown voltage increases, the corresponding grain-boundary barrier height increases as well. In general, the ZB6-series samples exhibit better nonlinearity and smaller leakage currents than the corresponding ZB4-series samples. At a sintering temperature of 930 ℃, the ZB4 and ZB6 samples achieve the best comprehensive electrical properties. The ZB4-930 sample (ZB4 sintered at 930 ℃) indicates a breakdown voltage of 1 074 V / mm, nonlinear coefficient of 6.58, leakage current of 101 μA, and grain-boundary barrier height of 2.42 eV. The ZB6-930 sample (ZB6 sintered at 930 ℃) demonstrates the best electrical performance, with a breakdown voltage of 1 161 V / mm, nonlinear coefficient of 13.22, leakage current of 24.5 μA, and grain-boundary barrier height of 2.97 eV. An appropriate Bi / Sb ratio is key to achieving low-temperature sintering for preparing ZnO varistor ceramics with excellent comprehensive performance. The results of this study provide an important experimental and theoretical basis for the development of high-performance ZnO varistors and the improvement of their energy-saving effects.
  • Microstructure Transformation of Al-Si Alloy Coatings Induced by Heat Treatment and Its Effect on High Temperature Tribological Properties
    XU Haobo, MA Guozheng, HE Pengfei, LI Guolu, LIU Ming, GUO Weiling, WANG Haidou
    China Surface Engineering. 2025, 38(1): 203-215. https://doi.org/10.11933/j.issn.1007-9289.20230525001
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    Al-Si alloys are ideal materials for the preparation of aluminum alloy engines. However, the wear resistance of Al-Si alloys produced through casting technology is poor, making them unsuitable for use under harsh working conditions inside an engine. They can only be used to make external cylinder blocks. Coatings prepared by supersonic plasma spraying have advantages such as high bonding strength and a dense microstructure. Therefore, using supersonic plasma spraying technology to prepare structurally excellent Al-Si coatings on the surface of Al-Si alloys can improve their high-temperature friction performance, which is expected to facilitate the preparation of all-aluminum engines. In this study, Al-35Si-4Fe powder was used as the raw material, and ultrasonic plasma spraying was used to prepare an Al-Si alloy. Owing to the high heat input in the ultrasonic plasma spraying process, Al is burned out, thus achieving the in-situ preparation of Al-40Si-5Fe coatings. According to the differential scanning calorimetry analysis results of the Al-40Si-5Fe coating, heat treatment of the Al-40Si-5Fe coating was carried out at 330 ℃, which promoted the transformation of the coating structure and ultimately improved the high-temperature friction performance of the coating. The microstructures of the coatings before and after the heat treatment were observed using scanning electron microscopy and transmission electron microscopy. The results indicated that the spray coating structure was dense and presented a typical thermal spray coating structure. Owing to the difference in cooling rate, there was a significant difference in the upper and lower microstructure of a single spread. The upper part of a single spread consisted of a primary Si phase and an Al/Si eutectic phase, while the lower part consisted of an incomplete amorphous structure. The average size of the primary Si phase in the sprayed coating is approximately 200 nm. During the 330 ℃ heat treatment process, thermal activation energy promoted the fusion and growth of the Si phase. The formation of a mesh-like Si-phase skeleton with a smooth surface inside the coating significantly improved the uniformity of the coating structure. The hardness and elastic modulus of the sprayed coating are 460.4 HV0.2 and 98.6 GPa. After heat treatment, owing to grain growth and amorphization, the hardness of the coating gradually decreased, and the elastic modulus gradually increased. The hardness and elastic modulus of the 330 ℃×24 h heat-treated coating are 336.3 HV0.2 and 108.5 GPa, respectively. Under the dry friction test conditions of load 3 N, stroke 4 mm, and frequency 5 Hz at 220 ℃, the average coefficient of friction and wear rate of the 330 ℃×24 h heat-treated coating were 0.38 and 1.35×10-4 mm3/Nm, respectively, which are 19.1% and 5.6% lower than those of the sprayed coating, respectively. Using a scanning electron microscope to observe the worn surface of the coating, it was found that there were obvious furrows, plastic deformation, and adhesive damage on the worn surface of the sprayed coating. Therefore, the wear mechanisms of the sprayed coatings are abrasive and adhesive. A large number of furrows were also found on the surface of the 330 ℃×24 h heat-treated coating, but the degree of plastic deformation was low and adhesion damage was less. Therefore, the wear mechanism of the 330 ℃×24 h heat-treated coating is mainly abrasive wear, accompanied by a small amount of adhesive wear. The network Si phase structure in the 330 ℃×24 h heat-treated coating can maintain the strengthening effect on the substrate in an environment of 220 ℃, effectively reducing the degree of plastic deformation of the coating and the adhesion behavior between friction pairs during the friction process, and significantly improving the high temperature friction performance of the coating.
  • Effect of HiPIMS Sputtered AlCrN Coating Structures on Anti-aluminum Adhesion Properties
    QIN Yadong, GAO Fanyuan, XU Yi, XIA Yuan
    China Surface Engineering. 2025, 38(1): 216-227. https://doi.org/10.11933/j.issn.1007-9289.20240206001
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    Integrated die-casting molds have emerged in response to lightweight, energy-saving, and environmental protection policies in the automotive industry. These molds are subjected to the alternating effects of high-temperature and high-speed aluminum liquid cooling and heating, and traditional surface treatment technologies cannot meet these harsh service conditions. The coating prepared by high-energy pulsed magnetron sputtering (HiPIMS) is dense, smooth, and exhibits good mechanical properties. The preparation of the AlCrN coating using HiPIMS technology is an important measure for improving the aluminum adhesion resistance of integrated die-casting dies. Based on plasma emission spectroscopy (OES), HiPIMS technology was used to prepare high-performance AlCrN coatings with a dense structure at various N2 / Ar flow ratios. The discharge characteristics and time-averaged OES spectra of HiPIMS were examined using a digital oscilloscope, high-voltage probe, current probe, and plasma emission monitor. The crystal phase structure, grain size, and surface cross-sectional morphology of the coating were analyzed using an X-ray diffractometer and scanning electron microscope. The nano-hardness and elastic modulus of the film were measured using a nano-indentation instrument. An anti-adhesion test with liquid aluminum was designed to assess the performance of the coating structure at 700 °C. The results showed that as the N2 / Ar flow ratios increased, the peak current under HiPIMS and peak power density also increased. The deposition rate first increased and then decreased, and the grain size and microstructure of the coating changed significantly. Numerous ionic states appeared in the film-forming environment, and the strength of CrII, AlII, and NII increased significantly. As the strength of CrII / CrI increased, the ionization rate of metal atoms in the target also increased with the N2 / Ar flow ratio during sputtering. With the change in the N2 / Ar flow rate, the coating structure primarily exhibited three states: an amorphous structure, a hcp-AlN and fcc-AlCrN mixed phase, and a single fcc-AlCrN phase. Obvious differences could be observed in the microstructure of each phase. The variation in N2 / Ar flow ratios significantly affected the structure and properties of AlCrN coatings. In the experiment, the nitrogen content of the coating remained high and demonstrated an overall increasing trend with the N2 / Ar flow ratio, ultimately approaching the stoichiometric composition in the fcc-AlCrN structure. The fcc-AlCrN phase coating with a preferred orientation of (220) was prepared at the highest N2 / Ar flow ratio, resulting in the highest hardness and elastic modulus. Simultaneously, it had the highest H / E and H3 / E2 ratios as compared with the other experimental groups. A laboratory-level efficient anti-aluminum adhesion test was next designed. In this test, the structure demonstrated good characteristics without aluminum adhesion, and the phase structure and composition of the coating did not change significantly. The surface integrity of the coating remained intact without obvious damage. The stability of the fcc-AlCrN structure in the liquid aluminum was the key to its excellent anti-aluminum adhesion performance. In this study, high-performance AlCrN coatings were prepared by varying the N2 / Ar flow ratio, which improved the aluminum adhesion resistance of the integrated die-casting die surface.
  • Underwater Repair Technology for Hole Defects in the Wall Face of a Spent Fuel Pool
    ZHAO Youliang, ZHU Jialei, ZHOU Feihong, ZHAO Xiaoxin, ZHAO Zhibo, ZHAO Liang, ZHANG Guangliang, GUO Fangtao, HUANG Yushan
    China Surface Engineering. 2025, 38(1): 228-240. https://doi.org/10.11933/j.issn.1007-9289.20230916002
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    Due to long-term service, the stainless steel cladding on the bottom and wall of a spent fuel pool in a nuclear power plant can cause cracks, holes, and other defects, leading to the leakage of radioactive liquid and negatively affecting the environment. This in turn affects the safe operation of the plant. Traditional manual welding by divers or shutdown maintenance of nuclear power plants cannot meet current maintenance requirements, and local dry automatic underwater welding maintenance is a development trend. Compared with the underwater welding of the bottom cover plate, the pressure difference in the wall position due to drainage and the effects of gravity on the molten pool are more obvious. The welding and drainage process for underwater repair of the wall cover plate is more difficult to implement, significantly increasing repair difficulties. Therefore, this study explores and optimizes the local dry drainage and welding process of a wall cladding. To simulate the underwater repair of a spent fuel pool wall cladding in a nuclear power plant, a local dry underwater tungsten inert gas (TIG) shielded welding repair system was developed that includes a mobile positioning mechanism, TIG power supply, underwater TIG welding drainage device, control system, wire feeder, and experimental pool. The local dry underwater TIG welding drainage device has high adaptability in multiple positions and is suitable for welding repair in underwater environments at wall positions. The study employed a self-built underwater TIG wire filling welding test system and used a square repair plate of 80 mm × 80 mm × 4 mm to address the large area of cracks and hole defects in the weld seam of the spent fuel pool wall cladding. After the repair plate was aligned with the original weld seam of the spent fuel pool wall cladding to be repaired, the welding of the repair plate was decomposed into horizontal and vertical positions for welding. A KEMPPI TIG welding machine and Funis KD7000 wire feeder were used as experimental equipment to conduct TIG wire filling welding process tests in both horizontal and vertical positions in underwater and air environments. The microstructure, chemical composition, and phase composition of welded joints were compared under the two environments. The results show that due to rapid cooling of the molten pool, the cross-sectional size of the underwater environment weld is slightly smaller than that of the air environment. The content of δ ferrit and hardness in the underwater environment is higher than that in the air environment, and the maximum microhardness appears at the aggregation of feathery ferrite. The grain size of the weld seam in the underwater environment is slightly larger than that in the air environment, whereas the corrosion resistance is slightly lower than that in the air environment. However, the difference is not significant. The Cr element is precipitated from the weld seam metal in both environments to improve its corrosion resistance. The quality of the welding repair of the underwater repair plate is essentially comparable to that in the air environment and meets the repair requirements for the wall position of the spent fuel pool cladding plate. The proposed dry underwater TIG shielded welding repair system can be used in the protection and repair of 304 stainless steel claddings in underwater environments. This study presents the following innovations. Defect free stainless steel clad plate repair welds were prepared at the wall position of an underwater environment using the local dry underwater TIG wire filling welding process. A comparative analysis was conducted to assess the effects of the underwater environment on the microstructural evolution, phase composition, and chemical elements of the transverse and vertical positions of the cladding weld seam. The microhardness and corrosion resistance of the stainless steel clad plate weld prepared in the underwater environment are found to be similar to those of the stainless steel clad plate weld prepared in the air environment.
  • Influence of Restraint and Restraint Position on Residual Stress and Welding Deformation of Ultra-high-strength Steel T-joint
    WANG Chongyang, NI Junjie, ZHANG Haiyan, GAO Zhanqi, HUANG Zhiquan, DENG Dean
    China Surface Engineering. 2025, 38(1): 241-254. https://doi.org/10.11933/j.issn.1007-9289.20231123002
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    In recent years, ultra-high-strength steel (UHSS) has been widely utilized in engineering structures, mining machinery, and military equipment. However, the high strengthening of UHSS poses two significant challenges to welding technology. On one hand, it leads to higher peak residual stresses induced by the welding process, which can cause hot cracks, cold cracks, stress corrosion, and fatigue failure. On the other hand, significant welding deformation is inevitably generated when thin-plate UHSS structures are welded. Welding deformation not only affects the appearance quality and dimensional accuracy of the product but also brings difficulties in welding assembly. Currently, research on residual stress and welding deformation by scholars remains very limited. Recent achievements in computational welding mechanics have demonstrated that numerical simulation technology based on the finite element method is a promising approach to determine the residual stresses in welded joints or even large welded structures. This study focuses on 1600 MPa grade UHSS, used for a specific type of vehicle. Tensile tests at room temperature, 200, 400, 600, and 800°C were conducted on a universal tensile testing machine to obtain stress-strain curves under different temperature conditions, and to determine the yield strength of UHSS at each temperature from the curves. The thermal expansion specimen was heated to 1000°C and then cooled to room temperature to obtain the strain-temperature curve and phase transition temperature of UHSS during heating and cooling processes. JMatPro software was used to obtain other thermophysical parameters of UHSS, and to establish a material model and phase transformation model for UHSS. Subsequently, a finite element calculation method was developed using SYSWELD software, which considers the solid-state phase transformation of UHSS and combines multiple fields of thermal metallurgy mechanics. In the numerical simulation, the microstructure calculations of martensite and austenite were considered for the UHSS. During the heating process above the starting temperature of the austenite transformation, martensite begins to transform into austenite. When the temperature reaches the end temperature of the austenite transformation, the austenitization of UHSS is completed; during the cooling process, the undercooled austenite in the heat-affected zone transforms into martensite. The double-ellipsoidal heat source model proposed by Goldak was used as the welding heat source model. In addition to considering material nonlinearity, geometric nonlinearity was also considered in the numerical simulation. The developed numerical simulation method was used to simulate the residual stress and welding deformation of UHSS T-joints under the free state and different restraint positions. In the restrained cases, the calculation of the residual stress and welding deformation was completed in the constrained state. When the joints cooled to room temperature, the structural restraint was released, and a free restraint was used to fully release the residual stress and welding deformation of the T-joint. Finally, the residual stress and welding deformation results for the UHSS T-joints at different structural restraint positions were obtained. Based on the numerical simulation results, the influence of the structural restraints and their positions on the residual stress and welding deformation has been discussed. The numerical simulation results show that structural restraints increase the peak longitudinal tensile and compressive stresses of T-joints and reduce the peak transverse tensile stress, as well as compressive plastic strain, lateral shrinkage, and angular deformation. This effect is more significant when the restraint position is closer to the weld seam. To ensure the safety of welding structures, when applying the structural restraint method in actual welding, the position of the structural restraint should not be too close to the weld seam. The numerical simulation of the study of restraint and restraint positions provides a theoretical basis for controlling the residual stress and welding deformation in UHSS.
  • Hydrogen Damage Behavior in High-strength X100 Pipeline Steel Weldments Induced by Electrochemical Hydrogen Charging
    LAN Liangyun, YIN Jiyao, CHANG Zhiyuan, GUO You, KONG Xiangwei
    China Surface Engineering. 2025, 38(1): 255-264. https://doi.org/10.11933/j.issn.1007-9289.20231118001
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    Blending hydrogen with natural gas is an effective method for improving the energy content per unit volume of natural gas and reducing greenhouse gas emissions, as hydrogen serves as a green and clean energy carrier. However, the presence of hydrogen poses a significant challenge for pipelines: hydrogen embrittlement (HE). Hydrogen can permeate into the metal, deteriorating its mechanical properties, particularly in welded joints, which are particularly vulnerable to HE due to factors such as inhomogeneous microstructures and oxide inclusions. To date, however, the relationship between the microstructure of each subzone of a welded joint and its intrinsic susceptibility to hydrogen embrittlement has not been thoroughly investigated. In this study, electrochemical hydrogen charging was employed to investigate the hydrogen damage behavior of high-strength X100 pipeline steel weldments in the absence of external stress. Combining microstructural characterization techniques—such as optical microscopy, laser scanning confocal microscopy, electron backscattering diffraction (EBSD), and quantitative analyses of hydrogen damage levels at each subzone of the welded joint allowed for a detailed exploration of the intrinsic susceptibility of each subzone's microstructure to HE. The results showed that, after identical hydrogen charging, the hydrogen escape velocity varied among different subzones, decreasing in the following order: base metal, heat-affected zone, and weld metal. According to the surface hydrogen damage modes observed, hydrogen blisters were identified as the primary damage mode for the base metal, exhibiting a height of several micrometers and a diameter of several millimeters. In contrast, hydrogen-induced cracking occurred in the weld metal and heat-affected zone on the sample surface, rather than hydrogen blister damage. With increasing current density, both the size and number of hydrogen blisters notably increased, accompanied by severe hydrogen-induced cracking in the cross-section. Quantitative analyses revealed that the weld metal exhibited excellent resistance to hydrogen damage, whereas the base metal was the most susceptible to hydrogen damage when the current density was insufficiently high. However, when a high current density (e.g., 80 mA / cm2) was applied, multiple hydrogen cracks appeared in the coarse-grained heat-affected zone, making it the most susceptible subzone to hydrogen embrittlement. The high resistance of the weld metal to HE is primarily attributed to the presence of acicular ferrite, which possesses a complex and effective grain structure with an extremely low volume fraction of random boundaries. This configuration allows for a more uniform distribution of diffusible hydrogen atoms in the weld metal, resulting in a hydrogen diffusion coefficient that is generally lower than that in the base metal. In contrast, the hydrogen-induced cracks in the base metal consistently nucleate at the pancaked prior austenite grain boundaries, indicating that these boundaries are preferred sites for crack nucleation due to the abundance of inherited deformation dislocations. Moreover, the parallel bainitic block boundaries create rapid diffusion paths for atomic hydrogen across the pancaked prior austenite grains, facilitating the propagation of hydrogen-induced cracks along the rolling direction. Consequently, closer attention should be given to the base metal under relatively low hydrogen fugacity conditions. When hydrogen fugacity is sufficiently high, the heat-affected zone (HAZ) becomes the most susceptible subzone to HE, particularly in the coarse-grained HAZ. This study provides crucial insights into the weakest links within welded joints and offers predictive tools for assessing structural integrity under varying hydrogen fugacity conditions.
  • Laser Vertical Welding of S32101 Stainless Steel in Air and Underwater Environments: Comparison of Process and Weld Properties
    LI Songzhao, ZHU Jialei, SONG Kuangda, ZHANG Hongtao, LI Guixin, HUANG Yushan, ZHAO Xiaoxin, LI Shougen
    China Surface Engineering. 2025, 38(1): 265-277. https://doi.org/10.11933/j.issn.1007-9289.20240108001
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    The spent fuel pool is a square structure that requires different welding positions to repair crack defects in stainless steel cladding. However, domestic research on the repair of defects in the wall position of the spent fuel pool is limited. Vertical welding is commonly used for large, heavy structural parts, but because of its welding position, it is prone to issues such as unstable transitions of the molten droplet and downward flow of the molten pool, resulting in weld porosity, lack of fusion, and other defects. By contrast, laser welding features low heat input and rapid cooling, which effectively mitigates the downward flow of the molten pool and reduces the impact of the vertical position of the weld caused by the weld. Local dry underwater welding technology combines the advantages of high weld quality of dry underwater welding and the simplicity of wet welding, which is the current preferred method for the underwater repair of nuclear power plants. Therefore, this study examined crack defects on the wall surface of a spent fuel pool by combining local dry underwater welding technology with laser vertical welding. S32101 duplex stainless steel was used as the base material, and bevel filler tests were conducted on a 4-mm U-shape bevel in both air and underwater environments. The organization and properties of the vertical weld in the two environments were analyzed comparatively. The results showed that compared with the air environment, the heat-affected zone of the weld in the underwater environment was smaller, with less austenite precipitation and insufficient growth in the cladding zone. The ferrite content in both the air and underwater environments was ranked as follows: HAZ > covered weld channel > undercut weld channel > filler weld channel. The overall ferrite content in the cladding zone was higher in the underwater environment as compared with that in the air environment. This difference was due to the greater degree of supercooling and faster cooling rate underwater, which prevented sufficient precipitation of austenite, resulting in a lower overall austenite content. XRD test results indicated that the cladding layer in both environments contained of both ferrite and austenite phases. The hardness distribution of the welds in both environments was consistent, following the order of melt-covered zone > heat-affected zone > parent material. The hardness of each area in the melt-coated layer was slightly higher than that of the filler channel, whereas the filler channel was slightly higher than the bottoming channel. Overall, the hardness of the welds in the underwater environment was higher than that of air-environment welds. Compared with the air environment weld, the tensile strength and impact work of the underwater environment weld decreased but still exhibited good mechanical properties. The impedance spectra and polarization curves from electrochemical corrosion experiments demonstrated that the corrosion resistance of underwater environment welds is lower than that of air-environment welds but still better than that of the base material. In summary, the underwater environment affects the organizational composition, mechanical properties, and corrosion resistance of the weld to varying degrees. However, its overall performance still surpasses that of the base material. This indicates that local dry underwater laser welding technology is highly feasible for the repair of spent fuel pool cladding walls in nuclear power plants, and the research results can provide theoretical and experimental foundations for in-service repair of the spent fuel pool walls.
  • Friction Reduction and Wear Resistance of a Composite PTFE Hard Anodized Layer on Aluminum Alloy Actuator Parts
    HU Bo, REN Junhui, SHI Xiaofei, BAI Changning, QIANG Li, ZHANG Junyan
    China Surface Engineering. 2025, 38(1): 278-289. https://doi.org/10.11933/j.issn.1007-9289.20231115001
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    Hydraulic actuators are widely used in aircraft wings, doors, and landing gears. The reciprocating seal is a common seal type. Seal failure can significantly affect aircraft mission execution and flight safety. The surface roughness of the seal pair is a major controllable parameter in engineering and greatly influences sealing performance. Therefore, analyzing the effect of surface roughness on the sealing performance of actuators is both theoretically and practically significant. The Al2O3 oxide film formed on the surface of aluminum alloys after hard anodic oxidation has certain wear resistance, insulation, and corrosion resistance, making it widely used in aviation hydraulic systems. However, the hard anodized film (hard oxygen film) has problems such as high porosity, roughness, and friction coefficient, which can exacerbate wear and tear on the friction mating surfaces, severely limiting its practical service. Hard anodization of aluminum alloy is a dynamic process involving the formation and dissolution of the film layer in a low-temperature sulfuric acid solution. The film layer is generally divided into a compact layer adjacent to the substrate and a looser layer extending outward. Consequently, the surface hardness is low, and the roughness is inadequate. An in-situ synthesis technology is utilized to enhance the surface roughness of the aluminum alloy hard anodized film and improve its friction-reducing performance, thus meeting the service requirements of the new generation of aeronautical actuators for weight reduction and high mobility. First, wed added 15-20 mL / L of PTFE (Polytetrafluoroethylene) concentrated dispersion liquid and a proper amount of composite surfactant into the anodizing bath liquid. We then stirred it for 30 min using a direct current constant current method at a current density at the beginning of hard anodic oxidation of 0.5-1 A / dm2. The current density was increased every 5 min until the desired current density was reached, where the film thickness required by the process was maintained to complete the anodic oxidation. During the hard anodizing of the aluminum alloy composite PTFE, negatively charged PTFE particles were pretreated with a composite surfactant and moved towards the surface of the aluminum alloy substrate under the action of an external electric field. As the oxide film continuously formed, the PTFE particles were absorbed and encapsulated in the film. The pores of the film layer were nearly filled with PTFE, where the PTFE was fully dispersed in the oxide liquid. The particles have a heat absorption function, effectively dissipating Joule heat from the substrate surface. Reducing the dissolution rate of the composite oxide film facilitated the formation of a low porosity and relatively compact film layer. This involved preparing the aluminum alloy composite PTFE hard oxygen film layer and detecting and analyzing its hardness, thickness, cross-sectional morphology, and phase composition. The relationship between the polishing amount and the roughness of the film was analyzed by using a three-dimensional roughness tester. Finally, the wear resistance of the friction pair with different roughness levels was verified through engineering simulation using an abrasion tester. The results showed that the hardness of the aluminum alloy composite PTFE hard oxygen film was higher than that of the hard anodized film, with surface roughness reduced from Ra2.4 μm to Ral.0 μm. Following 10 μm polishing, the surface roughness was less than Ra0.2 μm. Under the same load and time conditions, the friction coefficient of the composite film pair and the wear rate of the friction pair were both lower, at 0.08 and only 2.10 × 10-7 mm3 / Nm, respectively. No peeling was observed in the product’s functional test, and the wear amount was minimal, meeting the product’s performance requirements. In addition, the product (aluminum alloy actuator parts with composite PTFE hard oxygen film) exhibited a self-polishing effect during actual use, which helps shorten the production cycle and significantly reduces costs. The friction and wear behaviors of hard oxygen film layers and composite PTFE hard oxygen film layers were compared and analyzed using the friction and wear pair of a piston (7075)-sealing ring (4FT-32) in an aeronautical hydraulic actuator. This analysis provides data and testing support for the design and treatment of aluminum alloy cylinder-piston pairs and other relevant friction pairs with different application requirements, facilitating the engineering implementation and application of friction pairs in actuating system components.
  • Dynamic Wear Simulation and Optimization of Wind Turbine Yaw Brake Pads
    LI Lixia, WANG Jianmei, HOU Jian, SHAO Xulong
    China Surface Engineering. 2025, 38(1): 290-302. https://doi.org/10.11933/j.issn.1007-9289.20231031002
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    The performance of a wind power yaw braking system determines the accuracy of yaw to wind, yaw movement stability, and the safety and reliability of an entire wind turbine operation. Wind power yaw braking conditions and yaw brake pads selection affects the brake disc and brake pads braking interface wear conditions, because the brake pad material hardness is lower than that of the brake disc. Excessive wear of the caliper steel plate will cause damage to the brake disc, and result in yaw process jitter, the frequent replacement of brake pads, increased repair costs, and the decreased operational efficiency of the unit. Existing brake discs for low-speed and heavy-load applications, such as yaw and low-speed and heavy-duty braking conditions, are rarely studied, and finite element and experimental methods are typically used to measure the wear of braking interfaces. Hence, a three-dimensional simplified model of a yaw brake composed of a Q345E yaw brake disc and composite resin-based brake pad is established to address the wear problem in the yaw braking process, considering the dynamic change in the interface between the brake disc and brake pad. First, the relatively mature Archard wear theory combined with the finite element discretization calculation was adopted to accurately simulate the wear state of the yaw brake pads, and adaptive mesh technology was used to re-divide the mesh when mesh aberrations occurred. Simultaneously, the mesh in the contact area was encrypted to make the calculation results more convergent. In addition, two common shapes of yaw brake discs, namely, straight-edge type and boss-type, were selected to ensure that they had the same nominal contact area to investigate the dynamic changes and distributions of the wear depth and contact pressure of the two types of brake pads during the braking process via three influencing factors: the braking pressure, yaw speed, and friction coefficient. Finally, experimental schemes of the three factors and three levels were designed based on a full factorial simulation and Box-Behnken design response surface method. This was followed by a numerical simulation to obtain experimental results, establish the response surface model, and optimize related parameters. The results show that brake pads under different working conditions wear seriously at the friction inlet, and the wear state exhibits a significant front-end effect that is relatively serious at high contact pressures. Under the same influencing factors, the wear volume and wear depth increase with the increase of the different influencing factors. Moreover, the initial wear stage is faster due to the sudden change of the load applied, and when it reaches the stable wear stage, the contact area increases. Then, the change area becomes slower, and, in general, the straight-edge brake pad is more wear resistant than the boss-type brake pad. The brake pressure and yaw speed have a significant effect on the wear depth and contact pressure, whereas the friction coefficient is less significant for them and increases steadily over a small range. With the aim of reducing wear in practical engineering applications, optimal parameter combinations of a braking pressure of 2.001 MPa, yaw speed of 2 r/min, and friction coefficient of 0.333 were obtained via the optimization of the response surface parameters. Moreover, a simulation of the optimized working conditions was conducted. The error was less than 5%, compared with the predicted values of the response surface model, which verifies the accuracy of the response surface model. Hence, the finite element wear simulation revealed the influence of different shapes of brake pads on yaw brake wear, as well as provided technical and theoretical support for the selection of yaw brake pads.
  • Application of Vacuum Metal Deposition for Development of Latent Fingerprints on Metal Surfaces
    ZHANG Zhenqing, LI Baoming, DENG Xun, WANG Mingchao, SHEN Jin
    China Surface Engineering. 2025, 38(1): 303-313. https://doi.org/10.11933/j.issn.1007-9289.20230302001
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    The number of criminal cases involving metal objects, such as controlled knives, has gradually increased in recent years. Perpetrators frequently leave fingerprints on metal surfaces, such as stainless-steel door handles, tools, and knives, which can provide crucial evidence. Traditional methods for developing latent fingerprints on metal surfaces include powder, laser, multiband light-source, suspension development, smoke, and high-voltage electrostatic methods. When traditional methods are used to reveal fingerprints on metal surfaces, the ridge lines of the fingerprints often visually interfere with scratches on the metal surface, which can affect the clarity of the fingerprint display. Furthermore, these methods require high equipment standards and are challenging to operate onsite, making them difficult to be implemented widely by local public security organizations. The vacuum metal deposition (VMD) exhibits several characteristics that make it highly sensitive and versatile. One of its key advantages is its ability to preserve DNA and other biologically active components in fingerprints, making it suitable for various applications. VMD is widely used to reveal the latent fingerprints of nonpermeable and semipermeable objects, and it also has a significant effect on aged and problematic latent fingerprints. The handprinted lines are clear and coherent, displaying significant contrast and detailed features. The advantage of VMD lies in its strong sensitivity and effective development of potential fingerprints on challenging materials that conventional methods struggle to process, thus playing a crucial role in critical and complex cases. According to the specifications for producing handprinted samples, latent fingerprints were stamped on brass, red copper, 304 stainless steel, and aluminum alloys. First, this study examined how the combination of two sprayed metals, arranged according to their relative atomic masses, affected the appearance of handprints. Based on this premise, the effects of the quantity and sequence of the sprayed metal on the appearance of the handprints was further investigated. Finally, the effect of the remaining time of latent fingerprints on the development of fingermarks on the four metal objects was examined through statistical analysis. This includes the display rate, average score of the developing effect, and number of latent fingermarks corresponding to the grade score of the development effect. In the experiment, silver and zinc were the highest-quality combinations of metals sprayed on brass, red copper, and 304 stainless steel. For the spraying process, 10 mg of silver and 100 mg of zinc were applied in order of silver followed by zinc, which yielded the best results with latent fingerprints. Gold and zinc were the highest-quality combinations of metals sprayed onto aluminum alloys. For the spraying process, 4 mg of gold and 100 mg of zinc were selected in the sequence of gold followed by zinc; this sequence yielded the best-quality latent fingerprints. Differences in the surface structures of metal objects resulted in varying adsorption capabilities for the different sprayed metals. In addition, the contrast in the color background on different metal substrates caused the combination of zinc / silver to have an optimal effect on brass, purple copper, and 304 stainless steel, whereas the combination of zinc / gold yielded superior quality on aluminum alloy substrates. Moreover, the appearance rate of latent fingerprints on the four types of metal objects gradually increased on days 1, 4, and 7. VMD effectively revealed latent fingerprints on metal objects within a retention period of seven days. In addition, the quantity of sprayed metal, combination of different sprayed metals, sequence of sprayed metals, and remaining time of latent fingerprints influenced the display rate and the developing effect of potential handprints on metal objects. VMD has a significant advantage in developing latent fingerprints on metal objects and serves as a valuable alternative to existing development methods.
ISSN 1007-9289　CN 11-3905/TG
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Sponsored by: Chinese Mechanical Engineering Society
Edited and Published by: Editorial Office of China Surface Engineering
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