20 October 2024, Volume 37 Issue 5
    

Download cover
  • Select all
    |
  • Research and Development of Extreme Condition Lubrication and Wear Resistant Surface Engineering Technology
    CHEN Jianmin, CHEN Lei, LI Hongxuan, ZHOU Huidi
    China Surface Engineering. 2024, 37(5): 1-18. https://doi.org/10.11933/j.issn.1007-9289.20240408001
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    It is often the case that extreme conditions are frequently encountered in high-tech equipment, where conventional materials often prove inadequate inmeeting the requirements of intended application. It is therefore imperative that ultra-high-performance materials and technologies be developed to tackle these challenges. In view of the demand for lubricating and wear-resistant surface technology in the development of national frontier equipment under harsh conditions, this study presents a review of recent advancements in this special materials field, with particular focus on the aerospace and nuclear energy sectors. It takes the adhesive solid lubricant coatings developed by our team as object, emphasizing key common technical challenges and addressing practical engineering issues. Including key technologies such as the modification of tough and strong integrated basic resins, the improvement of atomic oxygen resistance by POSS modified resins, the design and adaptive control of lubrication components over a wide temperature range, the design of surface and interface of coatings resistant to special media, and the control of system compatibility. Additionally, a compilation of representative products developed based on this basis is listed, together with an illustration of their exemplary applications in addressing friction-related challenges under extreme conditions within high-tech equipment domains. The application in key components of aircraft and aviation engines, in key components of rockets and satellites, especially in the docking mechanism of space stations, has solved the lubrication and wear problems of components under many extreme conditions in aerospace. This underscores the indispensable and crucial role played by advanced lubrication and wear-resistant surface engineering technologies in driving forward national advancements in high-tech equipment. Finally, considering future developmental requirements for cutting-edge manufacturing at a national level, potential directions for further advancing extreme condition lubrication and wear-resistant surface engineering technologies are explored. This article provides a comprehensive understanding of the demand for extreme condition lubrication and wear-resistant surface engineering technology in the national high-tech field, promotes the high-tech application of related technologies and products, and develops higher limit performance lubrication and wear-resistant surface engineering technology for future high-tech equipment needs. It offers a valuable reference point and provides guidance significance on these matters.
  • Research Progress on the Surface Damage Mechanism and Protection of Armature for Electromagnetic Rail Launch
    LIN Yongqiang, YAO Pingping, WANG Xing, ZHOU Haibin, KANG Li, YUAN Zaihao, DENG Minwen
    China Surface Engineering. 2024, 37(5): 19-36. https://doi.org/10.11933/j.issn.1007-9289.20231114001
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    Electromagnetic launch technologies can directly convert electromagnetic energy into the instantaneous kinetic energy required for launching a payload within a short period. This technology has the advantages of high speed, high safety performance, and strong controllability, offering broad prospects for applications. Unlike mechanical and chemical energy, electromagnetic rail launch technology harnesses electromagnetic energy, enabling the achievement of ultrahigh launch velocities exceeding 2 km/s. During an electromagnetic launching process, a system is subjected to extreme launching conditions, such as high currents (~MA level), strong magnetic fields (~T level), high heat (~103 K), and strong forces (~106 N). Electrical energy is transformed into kinetic energy through an armature, making it a critical component of the launch system. However, the armature inevitably undergoes a series of damage during its operational lifespan, leading to significant changes in the contact characteristics between the armature and rail current-carrying friction pairs. This significantly affects the efficiency and precision of the electromagnetic rail launch system. This paper summarizes recent research progress on the surface damage mechanism and protection of armatures for electromagnetic rail launches, including typical damage characteristics and their influencing factors, a simulation and trend analysis of typical damage mechanisms, and the optimization of armature damage protection. Three primary forms of armature damage have been identified in various studies: current-carrying friction and wear, thermal melting, and transition erosion. The categories of current-carrying friction and wear encompass mechanical, current, and arc wear, presenting a distinct "three-stage" damage progression, correlating with the changes in current during the launch process. Thermal melting occurs owing to the contact resistance and friction between the armature and rails, which generate Joule and frictional heat, ultimately causing the armature surface to melt. Transition erosion manifests as a change in the contact mode between the armature and rails, leading to phenomena such as contact loss, which exacerbate the erosion on the armature surface and intensify the thermal melting damage. The severity and morphology of armature damage are influenced by service variables, inherent armature parameters, and their interplay. Simulations of armature damage mechanisms, conducted using finite element analysis software such as ANSYS, ABAQUS, and COMSOL, primarily focused on three aspects: the concentration of contact stress, current density, and heat. The optimization of armature damage protection requires considering various factors such as the structural designs of the armature and rail current-carrying friction substructure, material selection, and surface coating. These considerations aim to mitigate or prevent armature damage during launch. Existing studies have highlighted Al-Zn-Mg-Cu alloy as one of the most preferred materials for armatures, particularly when applies as a coating for surface protection. Currently, the preparation process, application conditions, and micro-mechanism of aluminum alloy armature coatings are not mature enough, especially in the extreme service environment of the launch process, which has a variety of coupled fields of physical quantities. Surface coatings with various impact resistances and other physical properties can meet the relevant standards, but systematic guidance is still lacking. Finally, a summary and outlook regarding the armature surface damage and protection are presented. The lack of a systematic and complete spatiotemporal evolution law in the morphological study of armature surface damage is attributed to the extreme harshness and multi-field coupling characteristics of the electromagnetic rail-launching armature surface damage formation. Further research is required for theoretical analysis, experimental validation of simulation reproduction methods, and correlation with rail damage characteristics. Future research should focus on the profound coupling of multiphysical fields, dynamic evolution of contact states between the armature and rail, development of three-dimensional analysis models under harsh operating conditions and material property evolution, and development of novel materials and structures for both the armature and rail. This study aims to enhance armature efficiency by incorporating insights from research on armature surface damage and protection, the development of new armature materials, and structural design improvements.
  • Research Progress on High-speed Rub Mechanisms of Aero-engine Compressor Rotor-stator Systems
    PEI Huiping, YANG Yulei, YAO Lipan, CHENG Bingxue
    China Surface Engineering. 2024, 37(5): 37-56. https://doi.org/10.11933/j.issn.1007-9289.20230921001
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    The high-speed rub between the rotating and stationary parts of compressors plays a crucial role in the safe operation of aero engines. Extensive research has been reported on high-speed friction issues concerning compressor rotors and stators. Nevertheless, systematic reviews of relevant research progress have been lacking. This issue must be examined from the perspective of high-speed friction wear and energy-dissipation mechanisms so as to ensure the safe design of advanced aero engines. The operating conditions of the compressor rotor–stator systems are characterized by small radial clearances, high relative tangential velocities, high airflow pressures, and elevated temperatures, which inevitably result in radial rubbing. This high-speed rubbing can damage both the stator coatings and rotor blades, and in extreme cases, lead to serious safety incidents such as "titanium fires " in aero engines. This paper presents a systematic review of research findings pertaining to high-speed friction and wear in rotor–stator interactions, focusing on the mechanisms of friction-induced wear and the associated heat generation. On one hand, the high-speed friction between compressor rotors and stators is influenced by various operational parameters such as intrusion rate, sliding velocity, and contact depth. On the other hand, factors inherent to the rubbing surfaces, such as blade thickness, coating hardness, and material thermophysical properties, also play a crucial role in determining the rubbing behaviors and mechanisms. The predominant wear mechanisms include adhesive wear, abrasive wear, oxidative wear, and several wear maps have been established. Among the operational parameters, intrusion rate and rubbing velocity have the greatest influence. In addition to the typical stator coatings, several new coatings for both the rotor and the stator have been proposed, and corresponding friction and wear mechanisms have been investigated under laboratory conditions. Accurate prediction of the increase in temperature is critical for addressing the heat generation during high-speed friction. A major challenge lies in determining the heat flow distribution; in this regard, various calculation methods have been developed based on fundamental assumptions. These methods provide a theoretical basis for estimating the increase in temperature. After determining the heat flow distribution, a thermal–structural coupled model can be established using finite element analysis to calculate the temperature increase. Experimental results can be used to refine the model and improve the calculation reliability. Moreover, molecular dynamic simulation provides a novel approach to calculate friction heat distribution and flash temperature, without requiring the use of the currently used heat partition coefficients. The heat generated during high-speed friction significantly affects the wear behaviors and mechanism, which is the focus of current studies. However, variations in wear mechanisms may also influence the friction heat generation and partition, especially when tribo-films or tribo-layers with distinct thermal properties from those of the original materials are formed on the surface. By controlling the operational conditions and designing friction interfaces, the generation, distribution, and dissipation of frictional heat can be altered and controlled, thereby reducing the friction and wear produced and, most importantly, the probability of titanium fires. Previous research has revealed friction wear mechanisms and the influence of friction heat under the action of multiple factors, providing theoretical guidance and a basis for engine structural design and coating development. Further studies should focus on novel coating–metal material combinations and explore the effects of additional operational conditions, as well as the influence of complex high-temperature, high-pressure, and high-velocity flows. Moreover, the effects of heat–solid–flow coupling and flash temperature on the friction, wear mechanism, and energy dissipation mechanism should also be considered to effectively address complex problems such as titanium fires. This review provides meaningful guidance for frictional heat calculation, comprehensive analysis of the friction and wear mechanisms of the rotor–stator systems, and development of novel coatings.
  • Research Progress of Alloys Used in Reprocessing Spent Nuclear Fuel and Their Corrosion Behavior
    SONG Guikang, WANG Yi, ZHA Zhibo, GONG Weijia, WANG Xianzong, LI Jinshan, LI Zhongkui
    China Surface Engineering. 2024, 37(5): 57-76. https://doi.org/10.11933/j.issn.1007-9289.20240522002
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    The expansion of nuclear power necessitates the reprocessing of accumulated spent nuclear fuel urgently. Dissolvers and evaporators are critical for reprocessing spent nuclear fuel, where near-boiling concentrated nitric acid is used to dissolve solid fuel. Severely acidic and oxidative conditions during reprocessing accelerate the corrosion of structural materials, thus threatening their service life and safety. Therefore, a review of the corrosion behavior of alloys used in spent-fuel reprocessing offers high scientific and engineering value, under the background of emphasizing the urgency to develop highly corrosion-resistant alloys to enhance reprocessing capabilities. This comprehensive analysis summarizes the corrosion behaviors, influencing factors, and principal challenges associated with three typical alloys used in spent nuclear-fuel reprocessing: low-carbon stainless steel, titanium alloys, and zirconium alloys. Results indicate that the corrosion rates of low-carbon stainless steel, titanium alloys, and zirconium alloys in a nitric-acid environment decrease sequentially by orders of magnitude, with zirconium alloys exhibiting low corrosion rates in the 10-4 range. The complex conditions encountered by spent-fuel dissolvers and high-level waste evaporators, including variations in the nitric-acid concentration and temperature, and the introduction of oxidative ions from actinides, fission products, and corrosion products generated during spent-fuel dissolution affect the corrosion resistance of these materials. Increased temperature and nitric-acid concentration are detrimental to low-carbon stainless steel and zirconium alloys but are beneficial for enhancing the stability of the oxide film on titanium alloys. Oxidizing ions increase the corrosion rate of low-carbon stainless steel but promote the formation and repair of oxide films on titanium and zirconium alloys, thereby inhibiting their corrosion. Stainless steel maintains good corrosion resistance at nitric-acid concentrations below 8 mol / L; however, at higher concentrations and temperatures or in the presence of oxidizing ions, intergranular corrosion occurs because of the preferential dissolution of the passivation film at the grain boundaries. Titanium alloys exhibit excellent corrosion resistance in high-temperature, high-concentration nitric acid but demonstrate a high corrosion rate in weakly oxidizing nitric-acid vapor and condensate phases owing to insufficient Ti4+ for forming a protective TiO2 oxide film. Among the three materials, zirconium alloys indicate the lowest corrosion rate in nitric acid. However, in fluorinated nitric acid, the corrosion rate of zirconium alloys increase because of the susceptibility of their passivation film to damage. Furthermore, the potential for stress corrosion cracking in zirconium alloys must be considered. The intergranular corrosion mechanism of stainless steel, the tri-phase corrosion mechanism of titanium alloys, and the corrosion mechanism of zirconium alloys in fluorinated nitric acid are elucidated. Finally, an outlook on critical areas that require further investigation for the development of these alloys is provided.
  • Tribological Behavior of Gradient Nanostructured Bearing Steel at Elevated Temperatures
    XU Xiaoxiao, LIANG Fei, ZHANG Yaping, LIN Yan, CHEN Xiang, ZHAO Yonghao
    China Surface Engineering. 2024, 37(5): 77-87. https://doi.org/10.11933/j.issn.1007-9289.20240311002
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    Bearings, as the core components of mechanical equipment, reduce friction and ensure rotational accuracy. Bearing steels, which are critical materials for the realization of advanced bearings, must have a long service life and high reliability. With the rapid development of the aerospace and military fields, the local temperature of bearings in aircraft engines, high-speed-train bogies, and rapid-fire weapon systems can reach 350 ℃ or higher. This exceeds the upper temperature limit of conventional bearing steels such as GCr15 and M50NiL. Thus, third-generation bearing steel, exemplified by CSS-42L high-alloy steel, which exhibits excellent corrosion resistance and fracture toughness, has been developed in recent years. It is known that friction and wear damage on the surface of bearing steel under rolling contact are the main factors causing failure of bearing components at elevated temperatures.Researchers found that gradient nanograined (GNG) materials can effectively reduce friction and wear damage by preventing surface roughening and the formation of brittle tribo-layers. However, there is limited research on the tribological behavior of GNG CSS-42L bearing steel at elevated temperatures. In this study, GNG CSS-42L bearing steel was fabricated using surface mechanical rolling treatment. The effect of the gradient nanostructure on the tribological properties of CSS-42L bearing steel was investigated. By also analyzing wear morphology and subsurface microstructure evolution, the corresponding friction and wear mechanisms were clarified. The average grain size of the topmost layer of the GNG CSS-42L bearing steel was 25 nm, which gradually increased with the depth from the surface. The grain size at a depth of 100 μm reached 500 nm or more. Notably, the entire GNG layer exhibited a martensitic structure. High-temperature friction tests within the temperature range of 25-500 ℃ were conducted on the coarse-grained (CG) and GNG CSS-42L bearing steels. The factor of friction of CG CSS-42L decreased from 0.64 to 0.43 as the temperature increased to 500 ℃, and the wear rate initially increased to 3.5×10?5 mm3 / (N·m) at 350 ℃ and then decreased to 6×10?6 mm3 / (N·m) at 500 ℃. Compared to CG bearing steel, the factor of friction of GNG CSS-42L bearing steel was lower than 0.2 at 25 and 200 ℃, then increased to 0.45 at 500 ℃. The wear rates of GNG CSS-42L at 25 and 200 ℃ were 3.8×10?6 and 3.66×10?5 mm3 / (N·m), respectively, much lower than those of CG CSS-42L bearing steel. As the temperature increased to 500 ℃, the wear rates of both CG CSS-42L and GNG CSS-42L bearing steels tended to be comparable. The surface morphology of wear scars showed that the proportion of the oxidation layer in the wear scars increased with the wear temperature. This indicates a transition in the wear mechanism of the GNG CSS-42L bearing steel from abrasive wear to oxidation wear as the temperature increased from 25 to 500 ℃. Subsurface microstructure evolution results demonstrated that the original surface gradient structure remained stable within the range of 25-350 ℃. It is believed that the excellent synergy of strength and ductility, along with the strain accommodation in the GNG layer, suppresses surface roughening and the formation of wear debris, leading to enhanced wear resistance. At 500 ℃, the original gradient structure was fully replaced by a nanograined oxidation layer with a thickness of 3 μm during the wear process. Under friction pair contact, microcracks nucleated and propagated in the oxidation layer, causing the spalling of oxidation debris and increased surface roughness. Thus, the factor of friction and wear rate sharply increased at 500 ℃. These results provide an experimental basis and theoretical foundation for prolonging the service life of bearing components at elevated temperatures.
  • Effect of Epoxy Resin Modification on the Cavitation Erosion Resistance of Polyamide-imide Coatings
    ZHANG Zixuan, HOU Guoliang, WAN Hongqi, MA Junkai, YE Yinping, ZHOU Huidi, CHEN Jianmin
    China Surface Engineering. 2024, 37(5): 88-101. https://doi.org/10.11933/j.issn.1007-9289.20231113001
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    Cavitation is a phenomenon of material damage under extreme conditions of localized high pressure and heat. It commonly occurs in pumps and other flow-through components and can severely limit the service life of these parts. Polyamideimide (PAI) coatings were originally developed to prevent cavitation erosion damage in steel components. However, because of their lightweight requirements in aerospace, they are now being used as light alloys that can withstand low temperatures. Notably, PAI coatings have high curing temperatures that exceed the withstanding temperatures of most lightweight alloys. Although the addition of epoxy resin (EP) is expected to significantly reduce the curing temperature of PAI, it may also alter its overall properties. The corresponding effect on cavitation erosion performance is currently unknown. To address this issue, we prepared pure PAI coatings (P-280) and EP-modified PAI coatings (P-200 and P-170) with varying PAI contents. Using an ultrasonic vibration-accelerated cavitation erosion test, we then compared the cavitation erosion performances of the samples. Through characterization using X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), and nanoindentation, we also analyzed the mechanical and thermal properties of the samples and their force / heat response behaviors under the effects of cavitation load and cavitation heat. This study investigated the mechanical and thermal properties of the samples and their force-and heat-response behaviors using three-dimensional optical shaping. The results indicated that the addition of EP could significantly reduce the curing temperature of PAI by 80–110 ℃. However, this reduction led to the destruction of the mechanical properties of the material, including its toughness, which decreased to 8.21, 5.50, and 3.18 mJ·m?3 in P-280, P-200, and P-170, respectively. This occurred because of the reduction in rigid molecular chains, such as the imide and benzene rings. In P-280, P-200, P-170, the tensile strength decreased gradually from 114.11 to 75.52 and 70.74 MPa. This reduction in strength led to a decrease in the bearing capacity of the coating and increased fatigue cracking under cavitation load, resulting in the formation of a greater number of larger spalling pits. However, the addition of EP significantly degraded the thermal stability of PAI, making it susceptible to melting and decomposition under cavitation heat. The reductions in temperature corresponding to a 5% weight loss of the P-170, P-200, and P-280 samples after 30 min of cavitation erosion were 15.24%, 14.82%, and 9.05%, respectively. This further accelerated the degradation of the mechanical properties of the coating surface and the damage caused by cavitation erosion. In addition, the heat generated by cavitation erosion promoted pyrolysis and hydrolysis of the molecular chains. XPS results indicated a reduction in the oxygen content after 30 min of cavitation erosion. Specifically, P-280, P-200, and P-170 decreased by 0.67, 1.9, and as much as 3.33at.%, respectively. The breakage of the molecular chains further deteriorated the overall performance of the coatings. The SEM morphology of the P-170 flaking debris showed melting under the heat of cavitation and the subsequent condensation of water into spherical debris particles. After 30 min of accelerated cavitation erosion, the mass losses of P-200 and P-170 were 1.7 and 3.6 mg, respectively. These values were 2.1 and 4.5 times higher than that of P-280, respectively. Considering the curing temperature, overall performance, and cavitation resistance of the coating, P-200 was deemed more suitable for application on the surface of light alloy parts. This study provides guidelines for the research and development of PAI coatings based on its investigation of the relationship between the overall and cavitation performances of PAI coatings under different EP contents.
  • Composite Basalt & Polyurea Fiber as A Reinforced Skeleton to Enhance the Wear-corrosion Performance of Water Epoxy Coating
    FAN Xiaoqiang, CHEN Shipeng, HUANG Yu, CAI Meng
    China Surface Engineering. 2024, 37(5): 102-111. https://doi.org/10.11933/j.issn.1007-9289.20231222001
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    As an important supporting structure in wind power equipment, the tower plays a key role in supporting the continuous work of the motor and blades. However, the security risks, maintenance and renewal costs of the tower surface can increase sharply because of corrosion and wear. Organic coatings have been regarded as the most economical and convenient means by which to protect towers from corrosion. Among various coatings, waterborne epoxy resin coating is widely used because it is inexpensive and environmentally friendly. However, micropores and microcracks are usually generated due to the solvent evaporation process, which presents both a path for corrosion medium diffusion and a source of crack initiation and propagation. To address the above issue, various fillers have been introduced into waterborne epoxy resin coating to enhance its comprehensive properties. Among fibrous materials, basalt fiber has several excellent physical and chemical properties, such as excellent chemical stability, radiation resistance, mechanical properties, and low cost. Moreover, its preparation process is less harmful to the environment, and it is a veritable green material. However, adding basalt fibers into epoxy resin coating could lead to the formation of microdefects at the interface between the fibers and the coating due to their large size. Therefore, it is necessary to regulate the surface state of basalt fiber to resolve the incompatibility between the basalt fiber and coating. Hence, in this work, composite fibers (PU@BF) were prepared via in-situ polymer growth technology on the surface of basalt fibers by utilizing the structural and property advantages of polyurea nanofibers (PU) and basalt fibers (BF). Then, PU@BF was introduced into waterborne epoxy resin coating (EP) to prepare a fiber-based composite coating, and the tribological properties and corrosion resistance performance were investigated in depth. The scanning electron microscope results indicated that basalt fibers were uniformly covered by polyurea. The storage modulus values of all composite coatings showed a decreasing trend with increasing temperature, as increasing temperature leads to the accelerated movement of chemical bond chain segments as well as polymer segments. Hence, the coating gradually transitions from a highly elastic state to a viscous state. The storage moduli of EP, PU, BF, and PU@BF at 40 ℃ were 1 445, 1 460, 1 688, and 1 526 MPa, respectively, indicating that the mechanical performance of the composite coating was improved via the introduction of fibers. The friction factor of PU@BF was kept between 0.1–0.2, whereas that of EP was approximately 0.8, demonstrating that the introduced composite fibers had a great antifriction effect. The wear rate of PU@BF was 1.2×10?5 mm3 / (N·m), which was decreased by about 78% compared with that of EP (5.5×10?5 mm3 / (N·m)). The Rc value of PU@BF was 2.5 MΩ·cm2 , whereas that of EP was 0.08 MΩ·cm2 , indicating that PU@BF displayed better anticorrosion performance. Neutral salt spray test results showed that black-gray corrosive pitting was observed on the surface of an Al substrate only after 1 week of test, and the corrosion degree was increased after 3 weeks. However, the surface of an Al substrate of PU@BF was still bright and clean without corrosion, indicating that PU@BF had excellent protection performance. The enhanced antiwear / corrosion performance of PU@BF could be attributed to two reasons. First, the polyurea on the surface of the basalt fiber could reduce the microdefects between basalt fibers and epoxy resin to enhance the interfacial adhesion with epoxy molecules and thereby delay the diffusion of corrosion media during immersion. Second, the surface composite fiber layer can bear the vertical pressure and radial cutting force of the friction pair when the composite is subjected to a reciprocating force, and the inner composite fibers can reduce the deformation of the epoxy by exerting a pinning effect and thereby restricting the initiation and propagation of microcracks during friction. This research verifies the feasibility of a fiber / epoxy composite system to solve the “wear and corrosion” problem of waterborne epoxy coating. The results lay a foundation for the further optimization of the fiber / epoxy composite coating preparation process by exploring the influence law of the fiber orientation distribution on the comprehensive performance of a composite coating and its strengthening mechanism.
  • Progress and Research Status in Machine Learning for Defect Detection in Laser Cladding Coatings
    CHEN Rusen, JI Xiaochao, ZHANG Mengqing, YU Helong, YIN Yanli, ZHOU Jun, WEI Min, SHI Peijing, ZHANG Wei
    China Surface Engineering. 2024, 37(5): 112-137. https://doi.org/10.11933/j.issn.1007-9289.20231115002
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    The rapid development of artificial intelligence technology has led to significant changes and opportunities across various sectors. Machine learning, an important branch of artificial intelligence, can discover laws and patterns from data to make predictions and decisions. Furthermore, it has been widely used in the field of laser cladding in recent years. Laser cladding technology has emerged as a transformative method with numerous advantages, positioning it as a key player in various industrial applications. Its advantages, including high fusion efficiency, optimal material utilization, robust bonding, and extensive design flexibility, render it indispensable for repairing complex surface defects in metal parts. The occurrence of defects during the cladding process can significantly affect the quality and performance of the cladding layer. Ensuring the reliability and repeatability of cladding quality remains a significant challenge in the field of laser cladding technology. In this study, the application of machine learning algorithms in the field of laser cladding defect assessment is explored. A comprehensive and in-depth analysis of common defects and their formation mechanisms in the laser cladding process is provided. The acoustic, optical, and thermal signals generated during the cladding process are summarized, and the corresponding relationships between these signals and the cladding defects are described. Commonly used methods, sensors, and signal characteristics for monitoring the laser cladding process are summarized. Additionally, the classification and features of machine learning algorithms are organized and their use in signal processing is reviewed during the laser cladding process. The classification and characteristics of machine learning algorithms and their applications in laser cladding signal processing are summarized. Machine learning algorithms have been employed in detecting defects in laser cladding, typically by constructing datasets from features extracted from collected signals, the cladding process, and defect characteristics. These algorithms are used to establish relationships between the signals, defects, and the process. However, most current studies on laser cladding monitoring focus on a single pass or a small area of the cladding layer. The use of such small datasets can lead to model overfitting, thereby reducing the accuracy of defect detection. Nevertheless, the application of these algorithms facilitates the introduction of a dynamic feedback control mechanism that optimizes the cladding process and effectively mitigates defects. The convergence of laser cladding and machine learning has emerged as a vibrant area of research, tackling crucial issues and expanding the limits of quality assurance and process optimization. Researchers, both domestically and internationally, have examined pores, cracks, and other defects at various scales through experiments and simulations. However, the mechanisms behind these defects and their impact on the quality of cladding are not yet fully understood. There is a need for more comprehensive methods to study the laser cladding process. Developing a quantitative evaluation system that links the laser cladding process, signal data, and defect quality is a critical challenge in ensuring the reliability of laser cladding quality. Currently, various sensors, including acoustic, optical, and thermal types, are utilized to monitor the laser cladding process. These sensors aid in examining the relationship between the process signals, defects, and quality. However, the limitations in sensor accuracy and the efficiency of defect feature extraction pose challenges in establishing a precise process-signal-defect relationship. The predominant machine learning algorithms used in current research are supervised learning algorithms. However, unsupervised and semi-supervised learning algorithms, which require less data labeling, are drawing attention in the fields of laser melting and cladding process monitoring, demonstrating significant potential. This review emphasizes the current research hotspots and directions for applying machine learning methods in laser cladding.
  • Tribological Performance of Fluorinated Graphite Modified PFPE Grease in Extreme Environment
    HUO Lixia, HE Ying, GOU Shining, FENG Kai, HE Chengdan, LI Xianqiang, LIANG Lu, ZHOU Hui
    China Surface Engineering. 2024, 37(5): 138-146. https://doi.org/10.11933/j.issn.1007-9289.20231122001
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    Frictional heat generated by mechanisms that take service on celestial bodies such as the moon does not dissipate easily owing to the vacuum environment and the low thermal conductivity of celestial soil. Consequently, the temperature of these mechanisms increases significantly. The wear resistance of liquid lubricants at high temperatures degenerates rapidly because the oil film thins out and the oil decomposes. Polytetrafluoroethylene (PTFE) and the soap fiber thickeners of lubricants are susceptible to phase transitions and agglomeration. The wear resistance and thermal stability of lubricants must be improved for mechanisms operating on celestial bodies. The lubricating properties at high temperatures and the thermal stability of fluorinated graphite are excellent. The wear resistance of liquid lubricants for space mechanisms can be improved using fluorinated graphite. In this study, fluorinated-graphite-modified perfluoropolyether (PFPE) greases are prepared using fluorinated graphite with different fluorine-to-carbon ratios and particle sizes, PTFE powders, and D-type PFPE base oil. The thermal behaviors of the materials are characterized using thermogravimetry and differential scanning calorimetry. Electron spectroscopy and X-ray diffraction are used to determine the fluorine-to-carbon ratios and the structures of three types of fluorinated graphite. The effects of different fluorinated graphites on the rheological and tribological properties of the greases are evaluated at 25 ℃ in atmospheric and vacuum environments, as well as at 200 ℃ in a high-temperature vacuum environment. The results show that the decomposition temperature of the three types of fluorinated graphites are higher than 595 ℃, whereas that of the D-type PFPE base oil is 450 ℃. The fluorine-to-carbon ratios of C2FJ1002, CFT10, and CF500 fluorinated graphites are 0.92, 0.88, and 1.04, respectively. Among them, the fluorine-to-carbon ratio of the nanoscale fluorinated graphite, CFT10, is the lowest. The (001) reflection of this nanofluorinated graphite is higher than the others; therefore, its (CF)n is greater than those of the others. The nanoscale fluorinated graphite exhibits the most significant thickening effect on grease at room temperature under low shear owing to its larger specific surface area. However, under high-shear and high-temperature conditions, the thickening effects of the three types of fluorinated graphites are almost uniform At high temperatures, the increased interlayer spacing of fluorinated graphite results in more PFPE oil molecules being absorbed, thus resulting in an increase in the shear viscosity of the grease at a shear rate of 10-15 s?1 . The wear-scar diameter of the grease modified by the abovementioned three types of fluorinated graphites under a 25 ℃ vacuum environment decreases by 7.7%, 11.7%, and 13.2%, respectively. The CF500 fluorinated graphite with the highest fluorine-to-carbon ratio demonstrates the best wear resistance in grease. Additionally, it exhibits a decreasing worn function under a 200 ℃ vacuum environment. The C 1s core-level spectra of the wear scars lubricated by the PFPE grease suggest the formation of amorphous carbon on the wear scar due to the degradation of PFPE. However, the C 1s core-level spectra of the wear scars lubricated with grease, which are modified by the CF500 fluorinated graphite, do not suggest the formation of amorphous carbon. The CF500 fluorinated graphite can shield the tribological surface and mitigate the degradation of the PFPE base oil. The higher the fluorine content, the more prominent is the reduction in wear of the PFPE grease in both vacuum and high-temperature vacuum environments. This is primarily attributed to its higher thermal stability and adsorption capacity for PFPE oil molecules, which reduces the chain breakage and carbonization of PFPE. However, reducing the particle size does not significantly reduce wear.
  • Effect of Target Current on the Structure and Properties of TiB2 Thin Films Prepared by Magnetron Sputtering
    LENG Xiao, LI Hongxuan, JI Li, ZHANG Dingjun
    China Surface Engineering. 2024, 37(5): 147-157. https://doi.org/10.11933/j.issn.1007-9289.20231114002
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    With the continual advancement of machining processes, cutting tools are facing increasingly demanding requirements. However, traditional tools often exchange hardness for toughness and have poor resistance to high temperatures and oxidation, which presents challenges in meeting high-speed cutting conditions. The deposition of a hard oxidation-resistant film on the tool surface can effectively address these issues. However, conventional protective films such as TiN and TiC fail to meet the demands of high-speed cutting and high-precision machining in terms of tool hardness, high-temperature resistance, and anti-adhesion. TiB2 is an ideal protective film for high-speed cutting tools due to its high hardness, high-temperature resistance, antioxidation properties, and low chemical affinity for intermetallic materials. In this study, a closed-field unbalanced DC magnetron sputtering technique was employed to deposit thin-film materials on P(100)-type silicon wafers and Inconel 718, which is a high-temperature nickel-based alloy. The results revealed a close correlation between the properties of the deposited TiB2 films and the magnitude of the target current during sputtering deposition. Specifically, increasing the TiB2 target current led to a higher target power, resulting in the deposition of thicker films within the given time frame, where the average thickness increased from 1.468 to 2.168 μm. In addition, increasing the frequency of target sputtering particle bombardment and the temperature in the deposition chamber enhanced the crystallinity of the films and increased the grain size, where the half-peak width of the preferred crystal plane decreased from 2.795°to 1.993°. The difference in the thermal expansion coefficients of the film bases resulted in residual stresses in the films after cooling to room temperature. As the target current strength increased, the chamber temperature increased, leading to a greater temperature difference between the chamber and room. Consequently, the residual stress of the film increased with the target current. Specifically, the minimum residual stress of the deposited film under a target current of 3.0 A was 0.109 9 GPa, whereas the maximum residual stress under a target current of 6.0 A was 0.382 9 GPa. Moreover, the hardness of the film initially increased and then decreased with an increase in the target current, reaching a peak of 3.0 A under a hardness of 0.382 9 GPa. The lowest hardness of the film occurred under the condition of 3.0 A, measuring 14.40 GPa, whereas the highest hardness was under the condition of 5.0 A, measuring 18.66 GPa. This hardness was closely associated with the crystallinity of the film and the ratio of boron-rich tissue phases. Enhancing the crystallinity of the film reduced the number of defects and concentrated the boron-rich phases at the grain boundaries, thereby preventing slippage when an external force was applied. This improvement was beneficial in enhancing the mechanical properties of the films. Depositing the film at 4.0 A yielded the highest hardness of 0.382 9 GPa. In addition, films deposited at 4.0 A exhibited the lowest wear rate (W = 6.347×10?6 mm3 / (N·m)) within the system. This study explored the optimal DC magnetron sputtering preparation of TiB2 and elucidated the effects of different current strengths on the crystallinity, hardness, and antiwear properties of TiB2 thin films during sputtering deposition. The deposition of TiB2 thin films on cutting tool surfaces effectively mitigates wear problems caused by frictional wear during high-speed cutting, serving as a protective film that efficiently prevents excessive tool failure resulting from high temperature and oxidation. Additionally, it safeguards against wear caused by high temperature and oxidation, prolonging the tool’s service life and improving machining accuracy. These findings provide valuable insights for the research and development of protective films for high-speed cutting tools.
  • Research Status of Numerical Simulation of Particle Deposition in Cold Spraying
    WANG Huipeng, HU Zeling, GUO Weiling, HUANG Yanfei, ZHU Hefa, ZHOU Longlong, XING Zhiguo, WANG Haidou
    China Surface Engineering. 2024, 37(5): 158-176. https://doi.org/10.11933/j.issn.1007-9289.20231008001
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    In the cold spraying process, the original properties of the material are well preserved. Therefore, cold spraying technology has been widely used in recent years. Metal, ceramic, and composite coatings are the most common in this coating field. While the performance of the coating generally depends on the effective deposition of particles on the surface of the substrate, in the cold spraying process, the collision time between the particles and substrate is very short. Thus, the deformation of the particles after their collision can only be observed as a morphological feature. Therefore, numerical simulation is usually used to model and analyze the deposition mechanism of the particles and the factors affecting the deposition behavior, with the goal of understanding the principles and conditions influencing the coating deposition. In this paper, we summarize the studies on metal, ceramic, and composite particles based on numerical simulations, which have established two-and three-dimensional models; adopted and observed single-, two-and multi-particle deposition processes; and explored the deposition mechanism of particles in greater depth using the results from multiple perspectives. The results show that metal particles collide with the matrix, where they produce plastic deformation, are deposited on the surface of the matrix, and form a mechanical bond with it. However, there are also cases where the collision of the particles with the substrate leads to localized melting and the generation of jets, which results in the metallurgical bonding of the particles with the substrate.
    Ceramic particles are fragmented after collision with the substrate and are thus attached to its surface. However, it is difficult to deposit ceramic particles on the surface of the substrate because this collision fragmentation creates a very shallow pit in the substrate, which makes it difficult for the ceramic fragments to be attached to its surface. This process was analyzed using numerical simulation, and the retention of ceramics was studied in relation to the incidence angle of the particles and roughness of the substrate. The bonding effect of composite particles on the surface of the substrate is better than that of metal and ceramic particles. And in metal-ceramic composites, the fragmentation of the ceramic particles increases the deposition of metal particles and reduces the porosity to some extent.
    In addition, three influencing factors are discussed: the particle velocity, particle incidence angle, and particle size. The effect of temperature on the velocity was explored based on the injection of preheated particles into a preheated substrate. The deposition effect was explored in relation to different angles of incidence, and the effect of the particle size was explored based on particle sizes ranging from single particles of different sizes to mixtures of particles of different sizes. The final results showed that the particle velocity is directly related to whether the particles can be deposited on the substrate surface, whereas the particle size is velocity-dependent, with different critical velocities for the deposition of different sized particles. The angle of incidence is also inextricably linked to the velocity, with the magnitude of the angle of incidence related to the velocity component. Thus, it is shown that there is a relationship between the influencing factors, which affect each other. In addition, the analysis of the application of cold spraying to the aviation, naval, and medical fields showed that our country needs to strengthen the development of practical applications of cold spraying technology.
  • Research Progress in Numerical Simulation of Laser Cladding Process and Crack Regulation
    XIE Xiaoming, LIU Xiubo, CHEN Tao, LIU Zhiyuan, MENG Yuan, ZHANG Shihong
    China Surface Engineering. 2024, 37(5): 177-194. https://doi.org/10.11933/j.issn.1007-9289.20231103003
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    Laser cladding is a three-way dynamic laser–powder–substrate interaction process in which the complex heat and mass transfer and convective behavior of the molten pool are closely related to the coating quality. Presently, it is difficult to visually and accurately observe the effect of the transient evolution of the laser cladding process on the coating quality by relying only on experimental methods, and it is limited by the high requirements of specialized equipment, high experimental costs, long cycle time, and other problems, which make it difficult to track the dynamic changes of multi-physical fields in the laser cladding process in real time. With the remarkable development of computer technology, numerical simulation provides an effective method for the in-depth analysis of the temperature change law, residual stress distribution, and melt pool flow behavior in the cladding process and provides a theoretical basis for process optimization and improvement of the coating quality. However, only a few reviews have addressed this aspect. Based on this, this paper reviews the current research status of the numerical simulation of multi-physical fields of the “temperature field–stress field–flow field” from the heat source models, thermal properties of materials, mechanical models and thermal-force coupling methods, as well as the flow behavior of the molten pool. The temperature and flow field evolution affect heat transfer, convection, and solidification in the molten pool, which directly affects the coating quality. Owing to the strong transient nature of laser cladding, stress is easily generated inside the coating, which affects its morphology, dimensions, and performance. However, current research on the numerical simulation of the laser cladding process is still limited in the accurate reflection of the actual cladding situation. In the future, it will be necessary to comprehensively consider the details of multiple physicochemical changes in the laser cladding process, such as phase transition, heat conduction, and heat convection, and build more reliable and accurate models to predict the properties of the cladding layer by considering heat source models and boundary conditions that are more compatible with laser cladding and by reducing model simplification. For the crack regulation problem, the influencing factors causing cracks are summarized. Cracks are mainly caused by residual stress exceeding the tensile strength of the material, while differences in the material properties, dilution rate, and elemental segregation also have an impact. The intrinsic correlation between multi-physics field-coupled dynamic evolution, process optimization, and crack regulation is also outlined. Numerous influencing factors lead to crack generation, and accurate simulation results are necessary to effectively guide practice. Therefore, the difficulties affecting the accuracy of the simulation are summarized, and an outlook is provided. In the future, we can improve the simulation methods, optimize the process and material systems, and combine them with nondestructive testing technology. Comprehensive simulation, experiments, monitoring, and other measures are used to establish a systematic and comprehensive crack quantitative index. Starting from the dynamic evolution level of multiscale multi-physical field coupling, realizing the integrated regulation of cracks will be the focus of future research. With continuous development and improvement at the industrial level, the realization of industrial intelligence and automation is an inevitable trend for future development, and the use of numerical simulation technology to guide the actual laser cladding process is a reliable method for effectively improving the coating quality. Therefore, a systematic review of the intrinsic connection between the dynamic evolution of multi-physics fields in laser cladding and crack regulation is necessary to provide references for subsequent research or practical work on numerical simulation and crack regulation of the laser cladding process.
  • Research Progress in Plasma Spraying Dense Ceramic Coating Technology
    LIU Fangyuan, WEI Lianfeng, ZHANG Weiwei, ZHENG Yong, SHANG Qiao, WANG Yafeng, ZHANG Ran
    China Surface Engineering. 2024, 37(5): 195-219. https://doi.org/10.11933/j.issn.1007-9289.20230920004
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    Owing to their high melting point, strength, and hardness, ceramic coatings have been widely used as wear-resistant, corrosion-resistant, and thermal barrier coatings in fields such as aerospace, nuclear power generation, and weapon equipment. Plasma spraying is a highly promising surface cladding technology and has the advantages of a high heating temperature, high deposition rate, low substrate temperature, wide range of spraying materials, and low investment cost, making it one of the most widely used methods for preparing high-performance ceramic coatings. However, with the rapid development of the modern industry, critical equipment or components operating in extreme environments have higher requirements for the service performance of ceramic coatings. Therefore, improving the density and mechanical properties of plasma-sprayed ceramic coatings has become a popular research topic in this field. In recent decades, researchers worldwide have produced various high-performance dense ceramic coatings using optimized plasma spraying technology. Thus, summarizing the current research progress in this technology is highly significant owing to its large-scale promotion and application. First, the technical characteristics, microstructural features, and main issues of conventional atmospheric plasma spraying (APS) ceramic coatings are introduced from the aspects of the working principle and coating deposition process. Owing to the rapid energy dissipation and severe arc fluctuations associated with conventional APS technology, typical atmospheric plasma-sprayed ceramic coatings contain a large number of unmelted or semi-melted powder particles, as well as rich defect structures, such as large-scale pores and interlaminar cracks. This makes it difficult for the performance of ceramic coatings deposited by the conventional APS process to meet the requirements of industrial applications that require coatings with low porosity and mechanical properties, such as wear-resistant coatings, electrolytes of solid oxide fuel cells, and environmental barrier coatings. Subsequently, the structural design, working principle, and coating performance of eight plasma torch technologies for preparing dense ceramic coatings are systematically reviewed. By optimizing the electrode structure, powder feeding method, plasma jet protection, and heating method of the plasma torch, the operational stability, plasma jet energy output, powder heating, and acceleration efficiency of the plasma torch can be effectively improved. This is beneficial for preparing dense ceramic coatings with low porosity and excellent mechanical properties. Subsequently, the principles, process characteristics, and coating features of three typical high-efficiency plasma spraying processes for preparing dense ceramic coatings are elaborated in detail. By improving the operating pressure, plasma jet length, and powder injection method of the plasma spraying process, three dense ceramic coating plasma spraying processes, namely, very-low-pressure plasma spraying, long laminar plasma spraying, and suspension or solution precursor plasma spraying, are developed. These technologies effectively enhance the energy input and utilization efficiency of the plasma spraying process, significantly improving the heating and acceleration performance of refractory ceramic particles in the plasma jet, and are successfully applied in the preparation of various types of high-performance dense ceramic coatings. Finally, the development status of plasma-sprayed dense ceramic coating technology is summarized, and future development trends are discussed. This paper systematically summarizes the plasma torch technology and plasma spraying process used for preparing dense ceramic coatings, and is expected to provide a reference and guidance for the widespread application of plasma-sprayed dense ceramic coating technology.
  • Research Progress on Failure Mechanism, Material Selection and Structural Design of Long-life Thermal Barrier Coatings
    LIU Yuwei, LI Chun, FENG Shizhao, WANG Ye, ZHOU Shujun, JIN Shuang
    China Surface Engineering. 2024, 37(5): 220-237. https://doi.org/10.11933/j.issn.1007-9289.20231008002
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    Thermal barrier coatings (TBCs) are efficient functional insulation coatings applied to power equipment such as aircraft engines and gas turbines. They have advantages such as low thermal conductivity, good high-temperature phase stability, and fracture toughness. With the continuous enhancement of power systems, key components must often be used in extremely high temperature environments, which can easily lead to the cracking, delamination, degradation, and premature failure of a coating. Therefore, the development of thermal barrier coatings high insulation values and long lives is very important. This article summarizes several typical failure mechanisms of thermal barrier coatings, including failure induced by stress, failure caused by sintering, and failure caused by the infiltration of calcium-magnesium-aluminum silicate (CMAS) and thermally grown oxide (TGO). In order to reduce the residual stress, it is necessary to gradually improve the failure prediction models of TBCs with different preparation processes and different materials, which will improve the reliability and accuracy of the prediction model results. On the other hand, the coating strain tolerance can be increased to release the residual stress, such as by increasing the porosity of the coating and prefabricating cracks in it, which will alleviate the coating stress concentration. In view of the problem of high-temperature sintering, methods to adjust the internal pore structure of the coating by doping metal oxides in the matrix require further study. The thermal-mechanical-chemical coupling effect can be considered to delay the erosion of CMAS, and an in-situ autogenous method can be used to prepare a dense layer, but there have been few studies on this aspect. In addition, a TGO layer with large grain size can be prepared on the surface of the adhesive layer in advance, which can slow down the grain boundary diffusion and limit the growth of TGO by increasing the grain size. Methods have been proposed to reduce the internal porosity of the coating, reduce the difference in interlayer thermal expansion coefficients, and reduce the surface roughness to suppress coating failure. Therefore, the progress on thermal barrier coating research is summarized from two aspects: material selection and the structural design of top coatings. From the perspective of material selection, the problems with using zirconia and some yttrium-stabilized zirconia (YSZ) in long-term high-temperature environments are summarized. In recent years, some advanced coating materials have been developed, including oxide-stabilized zirconia, A2B2O7 oxide, rare-earth tantalite, and self-healing materials. In order to reduce the residual stress, it is necessary to gradually improve the failure prediction models of TBCs with different preparation processes and materials, which will improve the reliability and accuracy of the prediction model results. On the other hand, the coating strain tolerance can be increased to release the residual stress, such as by increasing the porosity of the coating and prefabricating cracks in it, which will alleviate the coating stress concentration. In view of the problem of high-temperature sintering, methods to adjust the internal pore structure of the coating by doping metal oxides in the matrix require further study. The thermal-mechanical-chemical coupling effect can be considered to delay the erosion of CMAS, and an in-situ autogenous method can be used to prepare a dense layer, but there have been few studies on this aspect. In addition, a TGO layer with large grain size can be prepared on the surface of the adhesive layer in advance, which can slow down the grain boundary diffusion and limit the growth of TGO by increasing the grain size. From the perspective of structural design, preparation methods for different coating structures have been introduced. Layered structures, columnar structures, nanostructures, and functionally graded structures are reviewed from the perspectives of their microstructures and corrosion resistance, internal thermal stress, and thermal cycle life values. Finally, the future development directions for long-life thermal barrier coatings are outlined. This review not only discusses the shortcomings of the existing research and direction of future research, but also provides a theoretical basis for the development of a new generation of TBCs with higher corrosion resistances, better thermal insulation values, and longer lives.
  • Research Progress in Residual Stress Modulation of Diamond-like Carbon Film
    DU Naizhou, FU Zhimin, FENG Cun’ao, GUO Peng, LI Xiaowei
    China Surface Engineering. 2024, 37(5): 238-252. https://doi.org/10.11933/j.issn.1007-9289.20220629002
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    Diamond-like carbon (DLC) films are widely recognized for their outstanding properties and exhibit significant potential in various fields. Nevertheless, the presence of high residual stresses in DLC films weakens their adhesion to the substrate, thus resulting in film cracking or spalling. This limitation severely affects their durability and reliability, which is a significant challenge in DLC film research. Moreover, this issue must be addressed to enable the practical application of DLC films. In this paper, stress-generation sources in DLC films are discussed and research progress pertaining to stress modulation is summarized. In particular, elemental doping, transition layers, and process adjustments are elucidated in addition to the current global research landscape. Elemental doping is classified into single-and multi-element doping, which can be further categorized as strong and weak / non-carbide-forming elements, depending on their bonding strength with carbon atoms. The primary objective is to mitigate residual stress by reducing the proportion of distorted C-C bond lengths and C-C-C bond angles in the film, as well as moderating the extent of distortion in the bond lengths and angles. Notably, weak / non-carbide-forming elements, despite significantly reducing internal stresses, deteriorate the mechanical properties owing to their weaker bonding energies. Multi-element doping leverages the complementary properties of diverse elements, thereby reducing the stresses in DLC films significantly while maintaining robust mechanical properties and satisfying the demands of complex operating conditions more comprehensively. Metal doping primarily reduces residual stresses within the structure of DLC films. Nonetheless, owing to the dissimilar thermal-expansion coefficients between the substrate and film, high stresses can persist at the interface. Hence, a transition layer (monolayer, multilayer, gradient, etc.) is introduced between the DLC film and substrate to effectively mitigate residual stresses by alleviating internal stresses caused by mismatches in thermal-expansion coefficients. Furthermore, various deposition parameters, such as the substrate bias pressure, gas-source flux ratio, deposition temperature, deposition pressure, and carbon-source incidence angle, exert different effects on the intrinsic structure of the film. Different parameter combinations result in distinct residual-stress states. More importantly, these process parameters function synergistically, and their effects on the residual stress of the film varies under different conditions. Consequently, a comprehensive consideration of these parameters and their optimization based on specific application requirements is essential during DLC film deposition. Notably, the relationship between microstructural evolution and stress in the same elemental doping system under different preparation methods or in different elemental systems under the same preparation method varies. Hence, a refined computer-simulation technique at the atomic scale is proposed to investigate the effects of various preparation methods on the intrinsic structures of DLC films and to elucidate their stress-evolution patterns. In the future, the integration of advanced materials science and technology, such as machine learning and artificial intelligence, can be considered to further investigate DLC film preparation and stress-control challenges.
  • Organizational and Tribological Properties of Laser-melted NiCoCrTaAl-TiC Composite Coatings
    XIE Yuying, LIU Sisi, LIU Jingang, YANG Zhenghang, JIANG Shengqiang, YANG Shiping
    China Surface Engineering. 2024, 37(5): 253-262. https://doi.org/10.11933/j.issn.1007-9289.20220420001
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    Ni-based alloys exhibit low density, good plasticity, high strength, and excellent corrosion and wear resistance under high-temperature conditions. Therefore, they are often preferred in high-temperature and harsh environments. They are widely used in various military engines and civil equipment fields such as thermal power generation, petrochemicals, and metallurgical industries. However, they are more prone to fatigue and creep damage in high-temperature environments, which seriously affect the working efficiency, reliability, and durability of equipment utilizing Ni-based alloys. To improve the service life of Ni-based alloys in harsh environments, NiCoCrTaAl-TiC composite powders were prepared via vacuum-mixed ball milling, and metal/ceramic composite coatings were successfully deposited on the surface of K418 nickel-based alloys via laser cladding technology. The phase compositions and microstructures of the coatings were examined using an X-ray diffractometer and metallographic microscope. The effects of different Al contents (0, 5, 10, and 15% ) on the mechanical and tribological properties of the NiCoCrTaAl-TiC composite coatings were examined using a micro-Vickers hardness tester, scanning electron microscope, high-speed reciprocating friction and wear tester, and ultra-depth-of-field microscope. Actual operating environments, such as rainwater environment (pH6.2), seawater immersion (pH8), and lubricating oil were simulated for the coating with the best wear resistance, and the corrosion and wear resistances of the coating in different environments were further examined. The results show that the composite coating is mainly composed of TiC, Cr2Ni3, Al2O3, and AlNi3 phases, and intermetallic compounds such as Al4CrNi15 and Al4Ni15Ta. The internal structure of the coating is dense and composed of dendrites in the middle and equiaxed grains at the top. As the Al content increases, the average hardness of the coating initially decreases and then increases. The strengthening mechanism of the hardness corresponds mainly to the joint strengthening of TiC, Al2O3, and AlNi3 phases. Under dry friction conditions, with increasing Al content, the wear loss of the coating initially increases and then decreases. Furthermore, the main wear form changes from adhesive to abrasive wear. In summary, when the Al content is 15wt.%, the composite coating exhibits the best microhardness, microstructure, and tribological properties, and its wear resistance is approximately 25% higher than that of the coating with 0wt.% Al content. Subsequently, the 15wt.% Al composite coating was immersed in rainwater and seawater for 2 h, and its friction coefficient was: lubricating oil ＜ rainwater ＜ seawater. The depth of the wear scar and amount of wear were essentially the same as those of the coating without corrosion treatment, indicating that the addition of Al can improve the corrosion resistance of the composite coating.
  • Influence of Spraying Parameters on the Uniformity of Bolt Surface Coating
    ZHANG Yunpeng, LI Haitao, BAO Sijie, GUO Dongni, WAN Binghua, LU Wenzhuang
    China Surface Engineering. 2024, 37(5): 263-274. https://doi.org/10.11933/j.issn.1007-9289.20230923001
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    Aluminum coatings are applied to the surface of titanium alloy fasteners to prevent galvanic corrosion when these fasteners are connected to aluminum alloy structural components. However, because of the complex geometries of these bolt surfaces and influences of the spray-operation parameters, such aluminum coatings often have an uneven thickness. This inconsistency can lead to bolt connections with decreased reliability and galvanic corrosion protection. Presently, there is a lack of extensive research on the factors affecting the uniformity of these coatings. This study utilized the Euler-Lagrange method to develop a physical model of the two-phase flow in an atomizing spray field. This innovative model was designed to explore how variables like the spray distance, air intake pressure, and sector control pressure impacted the thickness of the coatings applied to bolt surfaces. To verify the theoretical insights provided by the model, a series of corresponding spray experiments were meticulously conducted, and their outcomes were compared with the simulation results. The findings showed that at shorter spray distances, there was a significant variation in the velocity of droplets as they hit different parts of the bolt, leading to a generally thicker and more uneven coating. A notable issue was the greater deposition of paint at the base of the threads, where the coating thickness sometimes exceeded 30μm. When the spray distance was increased, the droplets spread out more, complicating their interaction with the environment and making their trajectory harder to predict. This often resulted in a thinner and less uniform coating on the bolt surface. The role of the air intake pressure was found to be crucial in determining the degree of paint atomization. At lower intake pressures, the atomization process was incomplete, producing larger droplets with an uneven distribution across the surface, which led to the formation of uneven patches. At higher intake pressures, the droplets became excessively fine, spreading across a larger area but ultimately resulting in a thinner coating layer on each individual bolt. The process of adjusting the sector control pressure was instrumental in changing the trajectory of the paint droplets. This adjustment significantly affected the overall spray pattern and specific placement of droplets on the target surface. At lower sector control pressures, the liquid spray was more concentrated within a smaller angular range, resulting in a thicker coating. In contrast, higher sector pressures broadened the overall spray range but caused droplets in the central area of the spray cone to lose momentum and scatter to the sides, which led to a thinner coating. Simulations indicated that the most uniform coating thickness was achieved with a spray distance of approximately 190 mm, an air intake pressure of approximately 0.4 MPa, and a sector control pressure of approximately 0.1 MPa. To verify the accuracy of the simulation in predicting the characteristics of the bolt coating formation and thickness, corresponding parameter experiments were conducted. These experiments were carried out using an automated spraying device. After the coating application and curing, the bolts were sectioned and encapsulated in epoxy resin. The coating thickness was carefully observed and recorded using a metallurgical microscope at a magnification of 400×. These results were then compared with the simulation results. A good correlation between the experimental and simulation outcomes was observed, confirming the feasibility of using the two-phase flow physical model for studying the spray field and predicting the distribution of the coating thickness. This study adopted the Euler-Lagrange method to simulate the process of spraying a bolt surface. The distribution of the coating thickness was analyzed, and a viable method for optimizing the spray parameters was developed.
  • High-temperature Wear Performance of NiCrCoBSi Multiple Principal Elements Alloy Coating Sprayed by HVOF on the Surface of Crystallizer Copper Plate
    HUANG Dongbao, ZHOU Tingwei, YU Haitao, JIA Xiquan, XU Zhenlin, HE Yizhu, DONG Zhenqi, ZHANG Huiyong
    China Surface Engineering. 2024, 37(5): 275-287. https://doi.org/10.11933/j.issn.1007-9289.20230626001
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    Crystallizers are the core components of continuous casting equipment, and their quality directly impacts billet quality and production efficiency. With the advancement of high-drawing-speed continuous casting technology, higher performance requirements for crystallizers have been proposed, particularly concerning wear, a major cause of crystallizer copper plate failure. Currently, electroplated crystallizer coatings hold approximately 80% of the market share. However, the long deposition cycle, low hardness, tendency for coating peeling, and environmental pollution caused by electroplating technology make it inevitable for this technology to be phased out. Supersonic flame spraying (HVOF) is one of the most widely used thermal spraying technologies, capable of producing highly dense and uniform coatings due to its fast flame flow rate, high powder kinetic energy, and low oxidation levels. In addition, the HVOF technology offers a wide range of material options and can be functionally designed to accommodate different sizes and parts of the crystallizer, meeting continuous casting requirements. A NiCrCoBSi multiple principal element alloy coating has been applied to the surface of crystallizer copper plates using HVOF technology to improve their high-temperature wear performance of copper plates. The microstructure of the NiCrCoBSi coating was studied using X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The wear resistance of the coatings was evaluated using frictional wear equipment and compared with that of the commonly marketed electroplated NiCo coating. Additionally, the wear mechanisms of the coatings were analyzed. The results showed that the NiCo coating had a single-phase face-centered cubic solid solution structure, whereas the NiCrCoBSi coating exhibited an FCC solid solution, with CrB and M23C6 as the main phases. Both coatings had high densities with no observed cracks. A clear delamination was found between the NiCo coating and the copper alloy substrate, with no transition zone, indicating a mechanical bond. In contrast, a diffusion layer between the NiCrCoBSi coating and the copper alloy substrate due to diffusion heat treatment after spraying, resulting in the formation of a metallurgical bond. Compared to NiCo coating, NiCrCoBSi coating exhibited a 95% increase in hardness, whereas the fracture toughness decreased by only 5.4%. The friction factor of the NiCo coating fluctuated significantly, ranging from 0.4 to 1.0, and eventually stabilizing around 0.6. Compared with the NiCo coating (0.67), the friction factor of NiCrCoBSi coating is lower (0.51), with the curve showing good stability, ranging from 0.4 to 0.6, and ultimately stabilizing at around 0.52. After wear, the surface of the NiCo coating exhibited large flakes accompanied by dark gray adhesive marks, cracks, and debris. The worn surface of the NiCrCoBSi coating showed signs of debris, peeling, furrowing, and adhesive wear, with many small peeling pits. The wear mechanisms of both coatings were adhesive and fatigue wear, accompanied by a small amount of abrasive wear. The wear rate of NiCrCoBSi coating was 1.53×10?5 mm·N?1 ·m?1 , which is about five times higher than that of NiCo coating (7.91×10?5 mm·N?1 ·m?1 ). The main reasons for the higher wear resistance of the NiCrCoBSi coating are the better hardness, various wear-resistant phases, and the work hardening of the wear surface layer. This hardening occurs due to the plastic deformation of the coating under cyclic loading, during which the hard phases of the coating were cut and rotated. The carbides and borides are refined and spheroidized, enhancing the hardness of the wear surface layer. This research paves the way for developing coatings with excellent wear resistance for copper and their alloys.
  • Preparation of Sn-doped Micro-arc Oxide Coating on Titanium Alloy and its Protective Properties in Simulated Body Fluid Environment
    DENG Wanrong, YANG Wei, LI Keke, WANG Liqun, YANG Decao, ZHAO Chen
    China Surface Engineering. 2024, 37(5): 288-295. https://doi.org/10.11933/j.issn.1007-9289.20230920002
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    With the dramatic increase in the demand for medical implant materials, the TC4 titanium alloy can be used as a replacement material for bone tissue owing to its excellent biocompatibility and corrosion resistance. However, the TC4 titanium alloy has poor antibacterial properties, and there may be a higher risk of bacterial infection after implantation in the human body. Coatings prepared by micro-arc oxidation technology have excellent binding strength and can reduce the risk of bacterial infection of titanium alloys by doping with antimicrobial elements. To improve the protective properties of the TC4 titanium alloy in simulated body fluids (SBF), a constant-voltage mode was adopted, with a voltage of 450 V, frequency of 800 Hz, duty cycle of 6%, and time of 10 min. An Sn-doped micro-arc oxide coating was prepared on a titanium alloy by varying the concentration of Na2SnO3 in the electrolyte. The microscopic morphology and elemental content distribution of the micro-arc oxide coating were studied using a scanning electron microscope with an attached energy dispersive spectrometer, and the phase compositions and compositions of the micro-arc oxide coatings were characterized by X-ray diffraction and X-ray photoelectron spectroscopy. The wear resistance, corrosion resistance, and antibacterial properties of the micro-arc oxide coating in SBF were studied using friction and wear, electrochemical, and antibacterial tests. The results show that the number of pores on the micro-arc oxide coating surface increases after the addition of Na2SnO3. With an increase in the Na2SnO3 concentration, the number of micropores on the surface of the micro-arc oxide coating decreases until they disappear, small particles appear, and the film becomes increasingly dense and uniform. The main components of the micro-arc oxide coatings are TiO2, SiO2, and SnO2. The friction factor of the micro-arc oxide coating without Na2SnO3 is lower than that of TC4. The friction factor of the Sn-doped micro-arc oxide coating in SBF decreases with an increase in the Na2SnO3 concentration, and the width of the wear mark is narrowed. When the concentration of Na2SnO3 is 10 g / L, the Sn-doped micro-arc oxide coating has the smallest friction factor and the narrowest wear mark width of 198.85 μm, which exhibits the best wear resistance, which may be due to the enrichment of small particles and the lubricating effect. However, the micro-arc oxide coating does not improve the corrosion resistance of the TC4 titanium alloy, which may be caused by the presence of micropores and other defects on the surface of the coating and the lower corrosion resistance of SnO2 than that of TiO2. The antibacterial properties of the micro-arc oxide coating improve after the addition of Na2SnO3; the Sn-doped micro-arc oxide coating prepared at a concentration of Na2SnO3 of 10 g / L and the antibacterial properties of the Sn-doped micro-arc oxide coating are the best in SBF. The optical density value decreases from 0.289 to 0.136 in the Staphylococcus aureus solution and from 0.331 to 0.171 in the Escherichia coli solution, because SnO2 could inhibit the growth of bacteria. These results provide experimental support for the application of titanium alloys in the field of biomedicine.
  • Preparation and Properties of (Yb0.25Lu0.25Tm0.25Y0.25)2Si2O7 Environmental Barrier Coating Materials
    HE Hanwei, GUO Xingye, ZHOU Zheng, WU Xu, WU Yang
    China Surface Engineering. 2024, 37(5): 296-304. https://doi.org/10.11933/j.issn.1007-9289.20230917001
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    Environmental barrier coatings (EBCs) can effectively protect SiC-based ceramic matrix composites (CMC-SiC) from high-temperature water vapor corrosion in aero-engines. Rare-earth pyrosilicates (RE2Si2O7) have become one of the most promising EBC materials owing to their coefficient of thermal expansion (CTE), which is similar to that of CMCs, and their excellent high-temperature performance. However, RE2Si2O7 is prone to cracking during thermal cycling, and its ability to resist high-temperature water vapor corrosion is insufficient. High-entropy silicate materials prepared by mixing multiple rare-earth elements tend to exhibit better thermo-physical properties and high-temperature water vapor corrosion resistance. A new type of high-entropy ceramics (Yb0.25Lu0.25Tm0.25Y0.25)2Si2O7 ((4RE0.25)2Si2O7) is synthesized using four rare-earth elements for a high-entropy design. In terms of element selection, pyrosilicates with the rare-earth elements Yb or Lu have stable single β crystal polymorphs and excellent resistance to high-temperature water vapor corrosion. In addition, pyrosilicates with rare-earth elements Tm or Y have β crystal polymorph at high temperatures, and β-Y2Si2O7 has lower thermal conductivity. Therefore, (4RE0.25)2Si2O7 is likely to crystallize in a single β crystal polymorph. The microstructure, phase composition, thermal properties, and resistance to water vapor corrosion are systematically investigated. The experimental results show that (4RE0.25)2Si2O7 bulks with monoclinic β-phase are successfully prepared by non-pressure sintering. The doped rare-earth elements are uniformly distributed in the matrix, and no obvious component segregation occurs. In addition, the atomic proportion of each element in (4RE0.25)2Si2O7 is close to the theoretical value. The thermal gravimetric (TG) curve remains horizontal without obvious weight changes from room temperature to 1300 °C. There are no obvious absorption / exothermic peaks in the differential scanning calorimetry (DSC) curve, indicating that no phase transition or decomposition occurs during heating. It has a low CTE (2.66×10?6 –3.84×10?6 ℃?1 ). The CTE of (4RE0.25)2Si2O7 increases with increasing temperature but is lower than that of Yb2Si2O7 at all temperatures. It can also be applied to substrates with a lower CTE, such as Si3N4 (3×10?6 –4×10?6 °C?1 ). The thermal diffusion coefficient (0.41–0.92 mm2 / s) is lower than that of Yb2Si2O7. Below 500 °C, the thermal conductivity decreases as the temperature increases. When the temperature is higher than 500 °C, the thermal conductivity increases rapidly with the increase in temperature because of the increased effect of thermal radiation, which causes the thermal conductivity of (4RE0.25)2Si2O7 to exceed that of Yb2Si2O7 above 800 °C. To compare the performance of the synthesized (4RE0.25)2Si2O7 in a high-temperature water vapor environment, Yb2Si2O7, which has been proven to exhibit good water vapor corrosion resistance, is selected as the control group. In the atmosphere of 90%Air-10%H2O at 1300 °C for 200 h, the weight loss of (4RE0.25)2Si2O7 is significantly lower than that of Yb2Si2O7, with negligible weight loss from 180 to 200 h. The weight loss is only 0.625 mg / cm2 , which indicates that the (4RE0.25)2Si2O7 bulk is not liable to react with water vapor. After 200 h of water-vapor corrosion, (4RE0.25)2Si2O7 remains single and stable without any phase transition. It contains a small amount of Y2SiO5 impurities before corrosion, which disappear after water vapor corrosion. The slight reaction between Y2SiO5 and H2O, which generates gaseous Y(OH)3 and Si(OH)4, is the main reason for the weight loss in the high-entropy ceramic bulk. There is no significant difference between the EDS energy spectra before and after corrosion. After corrosion, it can be observed that Yb, Lu, and Tm are evenly distributed, whereas Y, Si, and O are concentrated in the areas without pores, which demonstrates that the formation of pores is related to Y2SiO5. Doping multiple rare-earth elements into the lattice of Yb2Si2O7 reduces the diffusion rate of atoms, resulting in better phase stability in high-entropy ceramics. These excellent properties demonstrate that high-entropy silicate ceramics prepared according to the properties of different rare-earth elements have promising potential in terms of their thermal properties, which lays the foundation for their practical application.
  • Effect of NiRe Layer on Oxidation Resistance of NiAl Coatings
    HE Wenxie, LI Wei, JIANG Sumeng, GONG Jun, SUN Chao
    China Surface Engineering. 2024, 37(5): 305-313. https://doi.org/10.11933/j.issn.1007-9289.20240309001
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    Owing to their excellent high-temperature mechanical properties, nickel-based superalloys have been widely used in aviation, particularly in the hot end-components of aeroengines. Al and Cr contribute significantly to the oxidation resistance and thermal corrosion resistance of superalloys; however, they adversely affect the microstructure stability and plasticity of superalloys. Owing to the continuous development of superalloys, the proportions of these two elements are decreasing, thus resulting in a decline in the corrosion resistance of superalloys. To improve the oxidation resistance and thermal corrosion resistance of superalloys, researchers have adopted high-temperature protective coatings in superalloys, which endow excellent comprehensive mechanical properties to the latter. β-NiAl has a high melting point and its Al content is higher than the critical concentration for the selective oxidation of aluminum; thus, it is the main forming phase of simple aluminide coatings. The addition of modified elements into β-NiAl coatings is being actively investigated, whereas studies regarding the Re modification of β-NiAl coatings are few. The method of electroplating NiRe, arc ion plating Al and vacuum heat treatment is adopted to perform Re modification on β-NiAl. To investigate the effect of the NiRe layer on the oxidation resistance of aluminide coatings, the isothermal oxidation properties of Al-diffusion and 1Re-NiAl coatings at 1 100 ℃ are evaluated. The cross-sectional, surface-morphology, and microstructural evolution of the coatings are analyzed via scanning electron microscope (SEM) and X-ray diffraction (XRD). Both coatings are primarily composed of the β-NiAl phase, whereas Zones 1 and 2 of the Al-diffusion coating and Zone 2 of the 1Re-NiAl coating are composed of β-NiAl and white α-W precipitated phases. Similarly, Zone 1 of the outer layer of the 1Re-NiAl coating is composed of β-NiAl and white γ-Re precipitated phases, thus indicting that the formation of α-W can be avoided by incorporating a NiRe layer. The isothermal oxidation kinetic results show that the total mass gain of the 1Re-NiAl coating is 0.62 mg / cm2 after isothermal oxidation for 300 h, which is lower than that of the Al-diffusion coating (2.77 mg / cm2 ). A significant amount of β-NiAl and slight oxide-scale spallation are indicated for the 1Re-NiAl coating. However, the diffraction peak of the β-NiAl phase cannot be detected and oxide-scale spallation on the surface is particularly severe in the Al-diffusion coating after isothermal oxidation for 150 h. The Al-diffusion coating shows severe internal oxidation and oxide-scale spallation (composed primarily of NiAl2O4 spinel), whereas the surface oxide scale of the 1Re-NiAl coating comprises single Al2O3 and indicates slight spallation after isothermal oxidation for 300 h. In the annealing process of the 1Re-NiAl coating, Al first diffuses into the NiRe layer, thus resulting in a gradual increase in Al content in the NiRe layer and a transformation into the β-NiAl phase. Simultaneously, the Re in the original NiRe layer is precipitated in situ to form a Re-rich precipitated phase in the outer layer of Zone 1 owing to the extremely low solid solubility of Re in β-NiAl. Thus, the incorporation of the electroplated NiRe layer can restrain the formation of α-W precipitates in the outer layer of the 1Re-NiAl coating. Moreover, incorporating Re improves the stability of the β-NiAl phase during oxidation and promotes Al diffusion from the inside to the surface of the coating. Thus, the oxidation resistance is improved significantly by incorporating an electroplated NiRe layer. In this study, Re is successfully introduced via electroplating and arc ion plating, and the effect of the NiRe layer on the oxidation resistance of the coating is investigated, which can facilitate future studies regarding Re and other element-modified β-NiAl coatings. Additionally, the reported method has broad application prospects.
  • Effect of La2O3 on Microstructure and Properties of Ti-BN-G Composite Coatings Prepared by Argon Arc Cladding
    HAO Chenfan, MENG Junsheng, LI Qindong, LI Chengshuo, LI Sijie
    China Surface Engineering. 2024, 37(5): 314-324. https://doi.org/10.11933/j.issn.1007-9289.20231023001
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    TC4 alloy (Ti-6Al-4V) is the titanium alloy with the most industrial applications. It is widely used in the biomedical, petrochemical, aerospace, and military industries because of its advantages, which include a low density, high specific strength (strength / density), good corrosion resistance, and good low-temperature performance. It is especially prominent in the field of offshore equipment. TC4 alloy is in great demand for ship structures, where it is mainly used for engine parts, pressure-resistant shells, propellers, seawater pipelines, and other key components. However, TC4 alloy is susceptible to oxidation and has poor wear resistance, low hardness, and other defects, which limit its further development in these application areas. With the continuous development of China's science and technology, the wear-and-tear failure of part surfaces is becoming increasingly prominent. Therefore, it is urgent to use surface engineering technology to repair failed parts or strengthen the surfaces of critical parts used under harsh service conditions. In the field of surface engineering, the moderate addition of the rare earth La2O3 can increase the hardness and wear resistance of a coating. The addition of too small or an excessive amount of the rare earth La2O3 can prevent the composite coating performance from reaching the optimal level. In order to investigate the effects of different mass percent contents of this rare earth (La2O3) on the compositions and performances of composite coatings, La2O3 / Ti-BN-G composite coatings were prepared on the surface of TC4 specimens using argon arc cladding technology. Ti powder, BN powder, graphene powder, and La2O3 were used as the raw materials. Measured quantities of these powders were placed in an onyx research body and fully milled to obtain a homogeneous mixture. It was then pre-coated on the surface of the TC4 alloy, and Ti-BN-G coatings with different La2O3 contents were prepared using argon arc melting and cladding technology. An X-ray diffractometer, scanning electron microscope, and energy spectrum analyzer were used to analyze the physical phases and microstructures of the coatings, and the microhardness of each coating was tested using a micro-Vickers hardness tester. A friction wear tester was used to test the wear rate and friction factor of each coating to analyze its wear resistance. The results showed that the coating phase consisted of granular and dendritic Ti(C, N), needle and rod TiB, and α-Ti phases. The organization changed with an increase in the La2O3 content. When the mass percentage content of La2O3 was 4 wt%, the composite coating had the best tissue refinement effect and most uniform distribution. A surface scan analysis showed that the rare earth La elements were uniformly distributed in the composite coating, which inhibited the growth of the tissues. Thus, the properties were further optimized, and the microhardness of the composite coating was increased by 3.7 times compared with that of the substrate, and the wear resistance was improved by 9.6 times. The wear mechanism was abrasive grain wear. When the mass percentage of La2O3 was 5 wt%, the composite coating was coarse and unevenly distributed, and the hardness and wear resistance were reduced. Finally, it was concluded that the most significant organizational densification and refinement effect was obtained for the composite coating when the mass percentage content of La2O3 was 4 wt%. This coating exhibited high hardness and excellent wear resistance, with further improvements in the mechanical properties of the TC4 alloy. By optimizing the mass percentage of this rare earth (La2O3) to obtain a high-performance coating, the research results provided an experimental basis and theoretical foundation for solving the problem of wear loss on the surfaces of parts.
  • Surface Texturing of 40Cr Steel by Heat-assisted Ultrasonic Rolling
    WANG Mingyuan, DENG Jianxin, WU Jiaxing, TIAN Runzhou, WANG Junyan, MA Kexin
    China Surface Engineering. 2024, 37(5): 325-336. https://doi.org/10.11933/j.issn.1007-9289.20230822003
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    Ultrasonic rolling texturing has been proven to exhibit distinctive surface enhancement effects. However, the singular application of ultrasonic rolling encounters challenges when processing materials with high hardness. Furthermore, its ability to enhance the surface performance of materials has an inherent limitation that restricts its further application. To overcome the limitations of ultrasonic rolling texturing, in this study, a heat-assisted ultrasonic rolling technique was employed for micro-texturing preparation on the surface of 40Cr steel. The study aimed to achieve better performance on textured surfaces by using the temperature field to evaluate the influence of temperature on the microstructure and mechanical properties of the material. Additionally, the study evaluated the effect of temperature on the morphological and mechanical properties of ultrasonic rolling-textured surfaces. Before conducting ultrasonic rolling tests, the specimens underwent grinding and polishing and were heated to predetermined temperatures (20, 100, 150, and 200 °C). The processing trajectory followed a reciprocating linear path. Additionally, a three-dimensional finite element model was established using ABAQUS software to simulate the ultrasonic rolling process at different temperatures, utilizing the Johnson–Cook model to describe the plastic deformation of the material. The simulation results were compared with the experimental results. The latter revealed that the heat-assisted ultrasonic rolling texturing treatment formed a textured array on the material surface consisting of micro-protrusions and micro-grooves. Heating induced material softening and intensified the degree of plastic deformation on the material surface, resulting in a larger-scale morphology of the ultrasonically rolled textured surface. However, at 200 °C, material surface damage occurred because of the adhesion between the rolling ball and substrate. The numerical simulation results indicated that heating intensified the material surface work hardening and expanded the range of residual stress generation. The residual stress values initially increased with the depth and then decreased, reaching a maximum value at a depth of 0.1 mm. The cross-sectional morphology analysis revealed that heat-assisted ultrasonic rolling formed a deeper plastic deformation layer. The alignment between the experimental textured surface profiles and numerical simulation results confirm the reliability of the finite element model. The hardness of the material surface generally increased after heat-assisted ultrasonic rolling texturing, and the residual stress state manifested as a residual compressive stress. Both the residual stress and micro-hardness exhibited an initial increase, followed by a decrease with an increase in temperature. The micro-textured surface prepared at 150 °C demonstrated optimal comprehensive mechanical performance. The initial increase in the residual stress values with the temperature is attributed to the increased plastic deformation on the material surface due to heating, whereas the subsequent decrease in residual stress is associated with thermal stress relaxation. The initial increase in micro-hardness with temperature was a result of enhanced work hardening on the material surface after heating, whereas the decrease in hardness at 200 °C was due to grain growth and organization coarsening after the temperature increase. The XRD test results confirm that the increase in residual stress and micro-hardness is related to the material surface grain refinement caused by heat-assisted ultrasonic rolling. Heating intensified plastic deformation, thereby promoting grain refinement on the material surface. However, the simultaneous increase in temperature led to grain growth and coarsening. The surface prepared at 150 °C exhibited the smallest average grain size, indicating the best comprehensive performance for ultrasonic rolling texturing. The research results validate that introducing heating into the ultrasonic rolling texturing process can further improve the material surface performance, providing a novel avenue for the research and application of ultrasonic rolling technology.
  • High-speed Laser Cladding Ni-coated c-BN Particles Reinforced Wear-resistant Composite Coating and its Wear Behavior
    LIU Kangcheng, LOU Liyan, CAI Zhihai, XING Zhiguo, WANG Haidou, LI Chengxin
    China Surface Engineering. 2024, 37(5): 337-345. https://doi.org/10.11933/j.issn.1007-9289.20230829001
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    Titanium alloys are widely used in aerospace and marine industry because of their low density and high specific strengths. However, their low hardness and poor wear resistance limit their application under various working conditions. Coating is an effective and rapid surface modification method that can improve the wear resistance of titanium alloys under extreme service conditions. In this study, a complete and dense c-BN (cubic boron nitride) composite wear-resistant coating was successfully applied on the surface of titanium alloy using a novel ultra-high-speed laser cladding method. To enhance the mobility of the c-BN ceramic powder, it was coated with Ni via electroless plating, and the effects of Ni coating on the microstructure and wear performance of the coating were comparatively studied. The microstructure, phase composition, and mechanical properties of the coatings were analyzed using an XRD / SEM / EDS microhardness tester and a friction wear tester. The results showed that the c-BN particles partially decomposed under laser irradiation and reacted with Ti in the molten pool to generate TiN, TiB, and other reinforced phases in-situ. In addition, in c-BN(Ni) coatings, the Ni coating on the c-BN surface melted under laser irradiation and entered the Ti lattice or partially reacted with Ti to generate Ti-Ni intermetallic compounds in the molten pool during solidification. This strengthened the solid solution and dispersion of the coating. Thus, the microhardness of the c-BN(Ni) coatings was significantly improved compared to that of the titanium alloy and c-BN coatings without Ni coating. Furthermore, the average microhardness of this coating was more than 1 200 HV0.3, which is more than three times that of the titanium alloy. After etching, for both the c-BN coatings, the top of the coating was mainly TiN, and the bottom of the coating was fine TiB; furthermore, the middle of the coating contained mix of TiN and TiB. The results of friction wear tests using Si3N4 as a counter-abrasive pair showed that these reinforced phases produced an intense counter-abrasive wear, resulting in a high coefficient of friction for the c-BN(Ni) coating. However, a higher microhardness significantly improves the wear resistance. Under the same conditions, the width and thickness of the wear profile of the c-BN(Ni) coating were significantly reduced, and its wear volume was reduced by 72% and 22% compared with those of the titanium alloy and uncoated Ni c-BN coating, respectively. The SEM morphology of the wear surfaces showed an obvious adhesive wear on the titanium alloy, and the c-BN coating without an Ni coating exhibited abrasive wear; furthermore, the c-BN(Ni) coating showed a large number of fish-scale like wear scars, owing to the large number of debris generated by the intense grinding of Si3N4 and hard phase in the coating. The morphology of the titanium alloy showed mainly small-and large-sized debris, whereas those of the two c-BN coatings showed small-sized debris. In this study, the c-BN particles were coated by Ni electroless plating before cladding; thus, the mobility of the c-BN ceramic powder improved during the deposition process, and the microhardness of the composite coatings increased owing to solid solution strengthening and dispersion strengthening of Ni, which led to composite coatings with an excellent wear resistance.
  • Effect of Supersonic Fine Particle Bombardment on Microstructure and Mechanical Properties of Cold-rolled Fe-28Mn-8Al-1C Low-density Steel
    XIONG Yi, Lü Wei, DU Nan, LI Yong, SHU Kanghao, REN Fengzhang
    China Surface Engineering. 2024, 37(5): 346-360. https://doi.org/10.11933/j.issn.1007-9289.20230913001
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    Fe-Mn-Al-C low-density steel has become a preferred material for energy conservation and emission reduction in the automotive industry owing to its low density, high strength, excellent toughness, and significant potential for weight reduction. However, failures often originate from the material surfaces. Moreover, the surface integrity and microstructure directly determine the service life and safety of the material. Efforts have been made to optimize the properties and surface integrity of low-density steel to achieve a good match between its strength and ductility, along with better surface integrity, in addition to extending its service life in operating environments, thereby enhancing the reliability and safety of vehicle operation. Nanocrystallization can be achieved through plastic deformation as a novel surface strengthening technology that utilizes supersonic airflow to carry hard particles and bombard the surface of materials with extremely high kinetic energy, after SFPB, which has the advantages of a high strengthening efficiency, solid particle reuse, and simple and convenient operation, can be used for metal components with complex shapes and large sizes. In this study, to prevent the premature surface failure of low-density steel during service and improve its service life, the surface of cold-rolled Fe-28Mn-8Al-1C low-density steel was nano-treated using supersonic particle bombardment technology. Scanning electron microscope, transmission electron microscope, X-ray diffractometer, micro-hardness tester, universal material testing machine, and other testing methods were used to systematically study the effects of the SFPB impact time and gas pressure on the surface morphology, microstructure, and mechanical properties of cold-rolled Fe-28Mn-8Al-1C low-density steel. The results are as follows: after SFPB treatment, under the impact of high-energy and high-speed Al2O3 particles, gradient nanostructures consisting of the severe plastic deformation layer, micro-plastic deformation layer, and core matrix formed on the surface of cold-rolled Fe-28Mn-8Al-1C low-density steel. The grain size of the surface layer was refined to the nanometer level by “dislocation segmentation.” With the increase in the impact time and gas pressure, the grain size of the surface layer decreased gradually and was refined to 8.68 nm at 1.0 MPa for 150 s. When the gas pressure was 1.0 MPa and the impact time was 120 s, the corresponding ultimate tensile strength and yield strength reached 1 679 MPa and 1 543 MPa, with increases of 15.7% and 26.4%, respectively. As the impact time and gas pressure increased, the surface micro-hardness and plastic deformation layer depth gradually increased, whereas the surface grain size gradually decreased. When the gas pressure was 1.0 MPa and the impact time was 150 s, the surface grain size was 8.68 nm, and the corresponding surface micro-hardness and plastic deformation layer depth were 569 HV and 16 μm, respectively. However, if the impact time was too long or gas pressure too high, stress concentration occurred on the surface of the cold-rolled Fe-28Mn-8Al-1C low-density steel, leading to the initiation and expansion of cracks and resulting in a decrease in its strength. The elongation of the cold-rolled Fe-28Mn-8Al-1C low-density steel under different SFPB process parameters did not change significantly, ranging between 4% and 5%, and the tensile fracture morphology exhibited a mixed mode of ductile and brittle fractures. SFPB technology could achieve controllable preparation of material microstructures by constructing gradient nanostructures on the surface of materials. Simultaneously, the mechanisms of back-stress strengthening and residual compressive stress inhibiting crack initiation and propagation could effectively improve the comprehensive mechanical properties of low-density steel. A novel surface-strengthening technology for the study of Fe-Mn-Al-C low-density steel with high strength and toughness is presented, offering a reference for its production and application in the automotive field in the future.
  • Splat-deposition Behavior and Coating Properties of Low-pressure plasma-sprayed CoNiCrAlY Powder
    YANG Kun, DENG Ziqian, NIU Shaopeng, XU liping, ZENG Wei, DAI Hongliang, SONG Jinbing
    China Surface Engineering. 2024, 37(5): 361-372. https://doi.org/10.11933/j.issn.1007-9289.20220519001
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    Low-pressure plasma-sprayed MCrAlY coatings exhibit excellent high-temperature oxidation resistance and hot corrosion resistance and can be used as high-temperature sealing coating materials, which are widely used to protect the hot-end components in turbine engines. Meanwhile, thermally sprayed coatings are formed on a substrate by the impingement of fully or partly melted feedstock particles, where the next layer is deposited on top of the previously deposited layer until the desired coating thickness is achieved. Therefore, the flattening nature of the molten particles on the substrate or previously deposited coating during thermal spraying is vital to the coating process. However, the relationship between the flattening behavior of individual molten MCrAlY particles and the stacking behavior of subsequently deposited particles with the coated structure, as well as the performance during low-pressure plasma spraying remain unclear. In this study, commercially available CoNiCrAlY powders manufactured via gas atomization are thermally sprayed onto nickel-based superalloy GH3536 substrates via low-pressure plasma spraying. Individual splat depositions are realized on the mirror-polished superalloy substrate and previously deposited CoNiCrAlY coating specimens. A steel slit featuring a hole with a diameter of approximately 10 mm is installed between the plasma torch and substrate to obtain particles with homogeneous thermal and velocity, as well as to avoid the effects of substrate-temperature increase and the accompanying change in substrate topography induced by the heating flow of the plasma jet. Following splat acquisition, a CoNiCrAlY coating with a thickness of several hundred micrometers is sequentially deposited on a blast-treated superalloy substrate. The top and bottom surface morphologies of individual splats and stacked deposits, as well as the microstructure and properties of the coatings, are evaluated systematically. The results show that when spraying is conducted under a reduced ambient pressure, the individual molten CoNiCrAlY particle spread rapidly on the surface of the substrate and solidify into a disk-shaped splat. During the spreading of the molten droplets, the desorption of the adsorbed gas condensation due to temperature increase at the collision zone between the molten droplet and substrate surface, together with the entrapped gas during the in-flight process of the molten particle, aggregated at the bottom of the flattening droplet. Subsequently, the gathered gas escaped from the edge of the flowing deposition on the substrate surface and formed a few short splashing fingers connected to the central core. Owing to the good wetting performance of the similar materials, the subsequent molten particles spread more extensively on the surface of the previously deposited coating. Numerous fully melted and sufficiently flattened splat deposits combined with each other via mechanical interlocking and stacked layerwise to form a dense coating. The porosity of the coating obtained under reduced ambient pressure can be controlled to less than 1%, the oxygen content of the coating is about 0.32%, the adhesion strength exceeds 75 MPa, and the vacuum-heat-treated coating exhibits favorable antioxidation resistance at 1 050 °C. Vacuum heat treatment can improve the microstructural uniformity and cohesive strength of the coating as well as enable the formation of an interdiffusion layer with a thickness of several tens of micrometers at the interface between the coating and substrate, thus further improving the bonding strength between the coating and substrate. The performance of the coating satisfies the technical requirements of protective coatings used for hot-end components in turbine engines. In summary, the low-pressure plasma-sprayed thick CoNiCrAlY coating exhibits a uniform and dense structure and excellent comprehensive properties, which are closely related to the flattening behavior of single molten particles on the substrate and the stacking process of the previously deposited coating. The results provide a basis for the optimization of coating structures and performances by controlling the flattening and stacking behaviors of thermally sprayed particles.
  • Finite Element Simulation and Test Verification of the Effect of Microgrooved Textures on the Stick-slip Vibration of Brake Friction Blocks in High-speed Trains
    ZHANG Qixiang, MO Jiliang, XIANG Zaiyu, WANG Quan, FENG Shuangxi, ZHAI Caizhou, ZHU Song
    China Surface Engineering. 2024, 37(5): 373-383. https://doi.org/10.11933/j.issn.1007-9289.20231101001
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    High-speed train braking systems experience stick-slip vibrations during low-speed braking, particularly before new brake pads reach a stable wear stage. Stick-slip vibrations lead to the abnormal wear and fracture of the friction blocks, threatening train braking safety. Moreover, they produce significant braking noise, which impacts passenger comfort and the everyday lives of residents along the route as well as leads to numerous complaints. Therefore, an in-depth study of the stick-slip vibration mechanism of high-speed train braking systems and the development of effective suppression strategies are crucial for enhancing train safety and passenger comfort. Stick-slip vibration, a typical friction-induced phenomenon, is significantly influenced by interface contact characteristics. Researchers have focused on studying interface contact characteristics and suggested that controlling these characteristics may suppress stick-slip vibrations. Considering the role of the surface texture in improving tribological performance, a series of parallel microgrooved textures of varying quantities are designed on the surfaces of the friction blocks. Finite element simulations and experimental analyses are combined to assess the effectiveness of microgrooved surface textures in suppressing stick-slip vibrations during high-speed train braking. Initially, finite element simulations reveal the effects of the number of surface microgrooved textures of the friction block on the contact stress, wear depth, interface contact degree, and vibration characteristics. These results indicate that the surface-microgrooved textures extended the primary load-bearing area in the direction of the texture, increase the contact area, and achieve a more uniform distribution of the contact stress. As the number of surface-microgrooved textures increases, the degree of interface contact gradually improves, and the amplitude of the displacement and velocity of the friction blocks decreases, transitioning from complex motion to more regular motion. However, finite element analysis alone struggles to account for the effects of wear debris generation and flow during friction, changes in wear surface morphology, and system vibrations, resulting in an incomplete reflection of the interface control function of the microgrooved surface textures. Therefore, friction tests must be conducted to verify the actual effects of surface-microgrooved textures in suppressing stick-slip vibrations. The experimental results indicate that surface-microgrooved textures effectively suppress high-frequency irregular vibrations and reduce the intensity of stick-slip vibrations. An analysis of the contact behavior reveals that microgrooved surface textures increase the actual contact area between the brake disc and friction block and thus play a role in reducing wear and dispersing interface contact stress, thereby favoring a rapid transition to a stable wear state. In addition, the design of surface-microgrooved textures optimizes the flow of interface wear debris, thereby facilitating their easy detachment and ejection, maintaining stable fluctuations in the friction force, and further weakening the intensity of the stick-slip vibration. Consequently, enhancing the friction interface contact state is the key to diminishing the stick-slip vibration intensity, and the optimal interface contact degree and mild wear characteristics contribute significantly to this improvement. The conclusions drawn from this study underscore the significance of enhancing the friction interface contact state to reduce stick-slip vibration intensity. The optimal degree of interface contact and mild wear characteristics are key contributors to this improvement. This study demonstrates that surface-microgrooved textures on friction blocks hold significant potential for mitigating friction-induced stick-slip vibrations during the bedding-in phase. The innovation of this study lies in its comprehensive approach to addressing the stick-slip vibration problem in high-speed train braking systems. Integrating finite element simulations with experimental validation provides a thorough analysis of the effectiveness of surface microgrooved textures. The mechanism by which these textures suppress stick-slip vibrations is elucidated, and practical insights into the design and optimization of friction blocks for high-speed trains are offered.
  • Microstructure and Properties of 304L Stainless Steel Local Dry Underwater Laser Welding Joint with Filler Wire
    ZHAO Zhibo, ZHU Jialei, LI Guixin, LI Songzhao, ZHAO Youliang, ZHAO Liang
    China Surface Engineering. 2024, 37(5): 384-392. https://doi.org/10.11933/j.issn.1007-9289.20230919001
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    At the 75th United Nations General Assembly, China announced that its carbon dioxide emissions would peak before 2030, and the nation will achieve carbon neutrality before 2060. In this context, nuclear power, as a clean, safe, efficient, and stable green and low-carbon energy source that can be developed on a large scale, can play a significant role in promoting green development and helping to achieve the “dual carbon” goals. During the long-term service of nuclear power plants, the stainless steel cladding of the spent fuel pool experiences aging effects, and its failure mechanisms primarily include mechanical impact, uniform corrosion, stress corrosion cracking, and pitting corrosion. Reliable underwater maintenance technology is crucial to ensure the safe operation and smooth life extension of nuclear power plants. Underwater laser welding, a relatively efficient in-situ repair technology, has the advantages of accurate heat input, low residual stress, high welding quality, and fully automated welding process, in addition to being less affected by water pressure. It has received widespread attention for underwater operations. Currently, there are few reports on the repair of crack defects at the L-shaped corner position at the junction between the bottom and wall of spent fuel pools in nuclear power plants. Therefore, a local dry underwater corner welding drainage cover was independently designed, and a local dry underwater laser wire-filling corner welding test was conducted on the 304 L stainless steel used for second-generation spent fuel pool cladding in nuclear power plants. The microstructures of the multi-layer and multi-pass fillet welds were analyzed using an optical microscope. Penetration testing was performed on the surface and cross-section of the weld using a DPT-5 dye penetrant. The micro-hardness distribution in different areas was tested using a micro-hardness tester. The polarization curves and Nyquist spectra of different regions in a 3.5% NaCl solution were measured using a VersaSTAT 3F electrochemical workstation. The results demonstrate that the forming quality of the fillet weld is high, and the metallurgical bonding is tight, with no obvious defects at both macro and micro levels. Owing to the protection of the pure argon gas environment, the surface of the fillet weld inside the underwater drainage hood presents a silver white fish scale as a delicate ripple. The penetration results revealed no obvious defects on the cross-section and surface of the weld seam. The microstructure is mainly composed of austenite and ferrite, and there is a clear boundary between the layers in the weld seam area. The heat-affected zone is not clearly displayed owing to the rapid cooling effect of water. The center structure of the fillet weld is mainly composed of vermicular ferrite, γ Austenite, and lath ferrite, and the crystal morphology is mainly equiaxed crystal. The fusion zone is mainly composed of vermicular ferrite and γ Austenite, with a small amount of feathery ferrite. The crystalline form is mainly columnar crystals, which grow perpendicular to the fusion line toward the center of the weld seam. The overlapping area is mainly composed of vermicular ferrite and γ Austenite. Owing to multiple heat accumulations in the overlap zone, it is equivalent to solid solution treatment on the surface of the weld, resulting in a decrease in the ferrite content and an increase in the austenite grains. The average micro-hardness values of BM, HAZ, and WM for multi-layer and multi-pass corner welding joints are 209 HV, 226 HV, and 234 HV, respectively, with uneven distribution and an approximate M-shaped distribution. The polarization curve and Nyquist spectrum results indicate that the order of resistance to electrochemical corrosion in different regions is BM＞WM＞HAZ. Underwater laser wire-filling corner welding repair experiments were conducted using a self-designed corner welding drainage cover. A good process performance of the corner welding joints was obtained, which can provide a technical reference for the crack repair of spent fuel pools.
ISSN 1007-9289　CN 11-3905/TG
Supervised by: China Association for Science and Technology
Sponsored by: Chinese Mechanical Engineering Society
Edited and Published by: Editorial Office of China Surface Engineering
Copyright © China Surface Engineering, All Rights Reserved.
Postal Code: 100037　
Tel: (010)88379020/88379056　
E-mail：cse1988@csejournal.com
Visited
Total visitors:　
Visitors of today: 　
Now online:
京ICP备05060958号-2    Powered by Beijing Magtech Co. Ltd,.