20 April 2024, Volume 37 Issue 2
    

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  • Adaptability Calibration of Big Data Acquisition Sensors for Monitoring Carbon Steel Corrosion in Urban Atmospheric Environment
    ZHANG Fan, XU Di, YANG Xiaojia, WANG Yipin, CHEN Hao, PENG Feifan, AN Jiangfeng, CHENG Xuequn, LI Xiaogang
    China Surface Engineering. 2024, 37(2): 1-15. https://doi.org/10.11933/j.issn.1007-9289.20230625001
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    Traditional methods for monitoring and evaluating corrosion are affected by the extended experimental period and slow pace; thus, they fail to satisfy the demands for data quantity and data continuity. Techniques for online monitoring of atmospheric corrosion require large amounts of continuous and real-time data, and the obtained big data can be effectively simulated, calculated and modeled using computer software to clarify the metal corrosion process and achieve data sharing. Various techniques for detecting atmospheric corrosion have been widely used. However, the accuracy and validation of the data require further experimental verification. In this study, the corrosion rate of Q235 carbon steel in the urban atmosphere was monitored using an outdoor hanging plate, a resistance sensor, and a galvanic sensor. Subsequently, the response surface model was established, and its validity was confirmed via coupled temperature-humidity experiments and alternate drying-wetting simulation experiments. Confocal laser scanning microscope (CLSM), X-ray diffraction (XRD), scanning electron microscopy (SEM), and electrochemical testing were performed to investigate the effects of outdoor exposure and indoor simulation experiment on the surface rust layer of Q235 carbon steel. The results show that the corrosion rates of the resistance and galvanic sensors are 1.295 and 1.084 times the corrosion rate of the hanging plate, respectively. The variation trends of the corrosion rate of the sensor in the coupled temperature-humidity experiments and alternate drying-wetting simulation experiments are consistent with those of the outdoor hanging and response surface model. In the coupled temperature-humidity experiments, the corrosion rates recorded by the resistance and galvanic sensors are 1.136 and 1.018 times that of the hanging plate, respectively. In the low-temperature low-humidity environment, the corrosion rate of the galvanic sensor is similar to that of the hanging plate method. However, in the high-temperature high-humidity environment, the corrosion rate of the sensor is higher than that of the hanging plate. In the alternate drying-wetting simulation experiment, the corrosion rates of the resistance and galvanic sensors are 1.242 and 0.978 times that of the hanging plate sensor, respectively. The corrosion rate of the galvanic sensor initially increases and subsequently decreases because the salt deposited onto the surface participates during the reaction, whereas that of the resistance sensor first increases and then decreases in an alternate period. X-ray photoelectron spectroscopy analysis show that the main components of the rust layer are α-FeOOH, Fe3O4 and γ-FeOOH, with α-FeOOH being the most abundant. Indoor simulation experiments show that with an increase in temperature, the corrosion products on the carbon steel surface change from granular to massive. This is because oxygen solubility in the thin-film liquid decreases, coupled with an increase in the rate of oxygen diffusion through the thin-film liquid to the carbon steel matrix. These factors facilitate the migration rates of Fe2+ and OH? in thin-film liquids and accelerates the electrode process and chemical reaction of the anode and cathode under the thin-film liquid. With the prolongation of corrosion time, the color of the carbon steel surface darkens gradually, transitioning from light yellow to reddish-brown and brown, and the corrosion products become dense and evenly distributed on the surface of the sample, relatively protecting the matrix. Because of the appearance of cracks and pits on rust layer surface, the corrosion rate determined using the sensor are higher than those obtained using the outdoor hanging plate. However, the corrosion rate of the galvanic sensor is closer to that of the hanging plate, indicating that the galvanic sensor is more suitable for use than the hanging plate in urban atmospheric environments.
  • Preparation and Performance Research of Composite Coating on the Surface of Titanium for Space Fuel Cells
    MA Wenbin, ZHANG Hui, YAO Wei, JIANG Zhao
    China Surface Engineering. 2024, 37(2): 16-26. https://doi.org/10.11933/j.issn.1007-9289.20230908002
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    Proton-exchange membrane fuel cells (PEMFCs) are currently widely investigated for the development of space power systems for future deep-space exploration and lunar research stations in China. Key technological research pertaining to PEMFCs for space applications must be conducted urgently. The bipolar plate, which is the core component of PEMFCs, significantly affects the weight and cost of the battery stack. Titanium is the preferred metal-plate material for lightweight space fuel-cells owing to its low density (only 0.6 times that of stainless steel) and high specific strength. However, they are susceptible to corrosion when used in weak acidic environments for long durations. To improve the corrosion resistance of titanium bipolar plates, a Ti / TiN composite coating composed of a Ti transition layer and a TiN surface layer is prepared on the surface of titanium via multi-arc ion plating technology, which is a physical vapor deposition technique. The effects of preparation process parameters such as the substrate temperature and arc current on the microstructure and mechanical / electrochemical properties of the Ti / TiN composite coating are investigated. The cathode sputtering target material is imported titanium metal (purity=99.995%), the sputtering gas is high-purity argon (purity=99.99%), and the reaction gas is high-purity nitrogen (purity=99.99%). The sheet of titanium was sequentially sonicated in acetone, anhydrous ethanol, and deionized water for 15 minutes to remove oil stains and attachments on the surface of the sample. Then, nitrogen flow was used to blow dry the surface moisture of the sample to ensure that there were no residual water stains on the surface. After that, the sample was placed in a drying dish for later use. When the vacuum degree of the equipment is better than 5.0 mPa, perform ion source cleaning to remove the oxide layer on the surface of the Ti substrate and activate the surface of the Ti substrate. When preparing the Ti transition layer on the titanium metal substrate, the target substrate distance is set to 23 cm, the arc current is 70 A, the substrate temperature is 150 ℃, and the deposition time is 10 min. When preparing TiN layers on the Ti transition layer, two different substrate temperatures (150, 230 ℃) and arc currents (50, 120 A) are selected. A field-emission scanning electron microscope (Carl Zeiss AG Corporation) is used to analyze the micromorphology of the Ti / TiN composite coating. An X-ray diffractometer (Rigaku Corporation) is used to analyze the phase composition of the coating. A nanoindentation instrument (Anton Paar) is used to evaluate the mechanical properties of the coating. The indentation depth is controlled to be less than 10% of the thickness of the Ti / TiN composite coating. During testing, the maximum load is increased linearly to 5 mN at a loading and unloading rate of 10 mN / min. A TalySurf CCI Lite optical interferometric surface profilometer (Taylor Hobson) is used to test the surface roughness and thickness of the Ti / TiN composite coating. An electrochemical workstation is used to evaluate the corrosion resistance of the coating under a simulated operating environment of a PEMFC cathode. The results show that the Ti / TiN composite coating prepared under a substrate temperature of 150 ℃ and an arc current of 50 A offers the best surface quality, the lowest surface roughness, and the lowest corrosion current density. The Ti / TiN composite coating with optimized preparation process parameters exhibits excellent surface quality and high corrosion resistance, with a corrosion current density of 6.383 μA / cm2 (i.e., 0.6 times the corrosion current density of titanium). Furthermore, the Ti / TiN composite coating significantly improves the corrosion resistance of titanium. This study provides technical support for the surface modification of metal bipolar plates used in space fuel-cells.
  • Effects of Cu and Ni on Corrosion Behavior of Corrosion-resistant High-manganese Damping Steel in Atmospheric Environment
    SUN Meihui, LI Jiangwen, LIU Wenyue, GUO Chengyu, LI Tianyi, XU Xuexu
    China Surface Engineering. 2024, 37(2): 27-40. https://doi.org/10.11933/j.issn.1007-9289.20230531002
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    High-manganese damping steel has shown broad application prospects in fields such as bridges, rail transit, and military industry that withstand large vibrations and impacts owing to its high strength, ultralow yield ratio, good damping performance, and excellent economic performance. However, the poor corrosion resistance of high-manganese steel has always been a key factor limiting its rapid development. To address this problem, three corrosion-resistant high-manganese damping steels with different Cu and Ni contents were prepared using vacuum induction melting and two-stage rolling processes. The electrochemical properties, corrosion rate, corrosion morphology, corrosion product phase, and structure of the test materials were characterized and analyzed through atmospheric exposure tests and electrochemical testing and by using scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) methods. The research results show that compared to the high-manganese damping steel added with Cu only, the one added with Cu and Ni exhibited better electrochemical stability. The addition of 1.2 wt.% Cu and 1.0 wt.% Ni to steel resulted in a positive shift in the corrosion potential of approximately 200 mV and a decrease in the corrosion current density by approximately 50%. After the exposure experiment, the high-manganese damping steel added with Cu and Ni also exhibited better corrosion resistance. Compared to the 8Cu and 8Cu5Ni steels, the corrosion rate of 12Cu10Ni decreased by approximately 70%. Based on the distribution of elements in the three types of steel, Fe, O, Mn, Cu, and Ni were uniformly distributed in the corrosion product layer without noticeable enrichment. The main corrosion products of the three types of steel were composed of γ-FeOOH, α-FeOOH, Fe3O4, Mn3O4, and manganese iron oxide (MnFe2O4). In the corrosion product layer, Cu and Ni affected the generation of the main corrosion products, on the one hand, and existed in the form of corrosion-resistant products, such as CuO, NiOOH, and NiO, on the other hand. When Cu was added separately to the steel, the ions had sufficient diffusion channels owing to the rapid corrosion of high-manganese steel and the porous corrosion product layer. Therefore, there were fewer Cu products in the corrosion-product layer, and the steel matrix exhibited apparent local corrosion characteristics. The addition of Ni enhanced the formation of corrosion product α-FeOOH, thereby improving the stability and density of the corrosion product layer. The addition of Ni also inhibited the doping of Mn into Fe3O4, resulting in the disappearance of iron-manganese oxides and an overall improvement in the electrochemical stability of the corrosion product layer. As the density of the corrosion-product layer increased, the diffusion of various ions in the steel became difficult, and the Cu oxide content in the corrosion-product layer increased, resulting in uniform corrosion characteristics on the overall surface of the steel. The synergistic addition of higher amounts of Cu and Ni further increased the α-FeOOH content. Notably, corrosion resistant products such as NiOOH and CuO within the corrosion products showed a significant enhancement, whereas the contents of MnFe2O4 and Mn2O3, known for their higher activity, experienced a decrease. The particles of the corrosion product were uniform and small. The overall product layer was dense and smooth, which effectively isolated the erosion of corrosive media and demonstrated excellent protection. The optimization of the synergistic addition of Cu and Ni effectively suppresses the insufficient corrosion resistance of high-manganese steel, providing support data for the design and in-depth research on more corrosion-resistant high-manganese damping steel in the future and a design basis for achieving safe service of high-manganese steel in the atmospheric environment.
  • Corrosion Inhibition Mechanism of S355J0W Steel Against Desulfovibrio vulgaris and Pseudomonas aeruginosa
    LU Shihang, ZHANG Xue, DOU Wenwen, CHEN Shiqiang, LIU Guangzhou
    China Surface Engineering. 2024, 37(2): 41-57. https://doi.org/10.11933/j.issn.1007-9289.20230711002
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    Marine environments are extremely harsh and corrosive. Marine corrosion is mostly associated with the metabolic activity of microorganisms. Microbiologically influenced corrosion (MIC) seriously threatens the reliability and safety of marine engineering facilities and restricts the development of the marine economy. Many methods have been applied to prevent MIC in steels, such as coatings, biocides, cathodic protection, and MIC-resistant alloy steels. The development of MIC-resistant alloy steels by adding alloying elements is an important strategy for marine MIC prevention. Exploring MIC mechanisms can provide a theoretical basis for MIC prevention. Therefore, the inhibition mechanism of S355J0W steel, composed of multiple alloying elements (Cr, Ni, Nb, and Cu), on the MIC caused by typical marine corrosive microorganisms (Desulfovibrio vulgaris and Pseudomonas aeruginosa) is investigated using surface analysis, weight loss, and electrochemical tests, with EH36 steel as a control. The results show that D. vulgaris and P. aeruginosa can acquire electrons from the Fe(0) surface and promote steel corrosion through the biocatalytic reduction of sulfate and nitrate reactions by transferring the electrons harvested from steel to intracellular, respectively. Notably, in both the anaerobic medium containing D. vulgaris and the aerobic medium containing P. aeruginosa, S355J0W steel had a much lower MIC rate than EH36 steel. In the D. vulgaris medium, the weight loss and maximum pitting depth of S355J0W steel were 2.9 mg·cm?2 and 50.4 μm, respectively, whereas these values for EH36 steel were 5.2 mg·cm?2 and 71.5 μm, respectively: the weight loss and maximum pitting depth of S355J0W steel were 56% and 70% of those of EH36 steel, respectively. Meanwhile, in the enriched seawater with P. aeruginosa, the weight loss and maximum pitting depth of S355J0W steel were 2.5 mg·cm?2 and 26.3 μm, respectively, and those of EH36 steel were 4.6 mg·cm?2 and 56.2 μm, respectively: the weight loss and maximum pitting depth of S355J0W steel were 54% and 47% of those of EH36 steel, respectively. In addition, S355J0W steel exhibited higher Rp and Rct values. The weight loss, pitting depth, and electrochemical data confirmed that S355J0W steel has better MIC resistance. Compared to EH36 steel, S355J0W steel contains Cr, Ni, Nb, and additional Cu. On the one hand, the alloy elements in S355J0W steel make the corrosion product film on its surface more protective, with a higher membrane resistance value. In addition, the combined effect of alloying elements on grain refinement can improve the anti-corrosion properties of steels. This can also explain why the corrosion resistance of S355J0W steel is better than that of EH36 steel. By contrast, the sessile D. vulgaris and P. aeruginosa cell counts on the S355J0W steel surface were only 22% and 24%, respectively, of those on the EH36 steel surface, owing to the combined effect of the alloying elements. The extracellular electron transfer (EET) rate is usually the controlling step for corrosion rates; fewer sessile cells lead to a lower EET rate, which reduces the MIC rate of S355J0W steel. Notably, the planktonic cell counts of the two steels did not significantly differ, suggesting that the planktonic D. vulgaris and P. aeruginosa cell counts are not critical in contributing to the difference in corrosion rates. At present, the MIC-resistant properties of metal materials are mainly improved through the addition of Cu, and research is mainly focused on stainless steels. Few studies have been conducted on the effects of the joint action of multiple alloying elements on the MIC-resistant properties of marine structural steels. Therefore, the results of this study are expected to provide new insights into the design and development of MIC prevention strategies for marine structural steels.
  • Marine Atmospheric Corrosion Behavior of Carbon Steel Based on Corrosion Big Data
    XIA Xiaojian, YANG Guowei, LIN Deyuan, LI Qing, ZHU Renzheng, YANG Xiaojia, CHEN Yiyang, WAN Xinyuan, YAN Kanghua, HAN Jiceng, CHEN Yunxiang, HONG Yicheng, CHEN Tianpeng
    China Surface Engineering. 2024, 37(2): 58-71. https://doi.org/10.11933/j.issn.1007-9289.20230710002
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    The “Belt and Road” initiative and the aspiration to evolve into a “Maritime Powerhouse” have highlighted the challenges of marine atmospheric corrosion affecting coastal regions and key maritime infrastructure. This phenomenon presents a critical challenge for the global maritime sector, emphasizing the need for in-depth understanding and effective mitigation strategies to preserve the integrity and operational safety of maritime facilities, thereby preventing significant safety incidents and economic losses. This study focuses on Q235 carbon steel, a material extensively used in maritime constructions, by applying advanced corrosion big data technology. The research methodology incorporates cyclic immersion acceleration tests, enabling the collection of continuous real-time corrosion data. This approach is vital for a comprehensive analysis of the effects of environmental factors such as Cl ? , HSO3 ? , and pH levels on the corrosion behavior of carbon steel in marine atmospheres. The findings of this study indicate a clear correlation between increased concentrations of Cl? and HSO3 ? or a decrease in pH levels and the acceleration of the corrosion process. The gathered data aligns with the observed physical corrosion morphology and rust layer analysis of the steel samples, demonstrating the robustness and reliability of the data-driven approach. This study highlights that at lower Cl? concentrations, the rust layer tends toward greater stability whereas higher concentrations result in decreased stability. With different HSO3 ? concentrations, the corrosion behavior varies: at 0.05%, corrosion proceeds at a steady low rate; at 0.1%, a protective rust layer forms, slowing the corrosion rate; and at 0.2%, the rate increases in the later stages, challenging the stability of the rust layer. In environments with pH values of 5 or 3, the overall trend is a decline in the corrosion rates, in contrast to a pH of 1, where the rate consistently increases. A significant aspect of this study is the integration of traditional corrosion research methodologies with modern big data analytics. This innovative approach represents a substantial advancement in corrosion research, combining the proven reliability of traditional methods with the extensive analytical capabilities of modern data science. The consistency of the big data findings with traditional coupon methods validates this approach, highlighting its effectiveness in providing deep and comprehensive insights into environmental corrosion processes. Furthermore, this research utilizes a range of advanced experimental techniques, such as scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), confocal laser scanning microscopy, and various electrochemical tests. These methods have been instrumental in characterizing the morphological and chemical properties of the rust layer, thereby enriching the overall findings of this study. This extensive study provides a detailed examination of marine atmospheric corrosion, contributing significantly to the field by offering new perspectives and robust methodologies. These contributions are crucial for effectively assessing and mitigating corrosion in maritime environments, aligning with international maritime strategies and infrastructure safety objectives. In summary, this study marks a paradigm shift in corrosion research, blending traditional experimental methods with the advanced analytical capabilities of big data. This integration opens new avenues for future investigations and innovations in the field, underscoring the importance of data-driven approaches in understanding and addressing complex environmental challenges. With its comprehensive analysis, innovative methodology, and significant findings, this research not only deepens the understanding of marine atmospheric corrosion but also establishes a solid foundation for future data-driven studies and solutions in maritime engineering and environmental protection. This study is a testament to the power of integrating traditional research methods with modern data analytics to address complex environmental issues, paving the way for further advancements in the field. Additionally, this study underscores the significance of the ongoing technological advancements in corrosion research. As environmental conditions continue to evolve, adapting and refining research methodologies to keep pace with them is becoming increasingly important. The use of big data and advanced analytical techniques in this study not only demonstrates a progressive approach to understanding marine atmospheric corrosion but also serves as a model for future studies in similar fields. This approach highlights the necessity of continuous innovation and adaptation in scientific research, particularly in areas with significant practical implications such as maritime infrastructure and environmental protection. Embracing these innovative methodologies ensures that research remains relevant, effective, and capable of addressing the complex challenges posed by a dynamically changing environment.
  • Research Progress on the Mechanism of Oxidative Carburization Corrosion and Coating Protection of Steels Served at High-temperature CO2 Environment
    LI Wei, SUN Tao, BO Guowei, ZHANG Chipeng, LI Cong, PENG Zhuoyin
    China Surface Engineering. 2024, 37(2): 72-90. https://doi.org/10.11933/j.issn.1007-9289.20230831004
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    Steel is widely used as various structural components owing to its excellent properties, such as high strength and heat resistance; however, it usually faces severe corrosion problems during service. CO2 corrosion is a common cause of corrosion failure in steel applications. However, a systematic summary of the corrosion behavior of steel in high-temperature CO2 environments is lacking. Therefore, in this study, the current oxidation and carburization mechanisms of steel in high-temperature CO2 environments are summarized, and the effects of temperature, pressure, and other gas impurities in the service environment on the corrosion mode and mechanisms are reviewed. Typically, the CO2 corrosion behavior of steel manifests as carbonation corrosion generated after it is dissolved in water. However, in high-temperature environments, CO2 can directly oxidize the steel surface, which is generally accompanied by carburization, significantly decreasing the mechanical and corrosion resistance of steel. In this case, the composition and structure of the oxide layer are strongly affected by the Cr content in the steel; thus, the corrosion resistance of steel is generally determined by the Cr content. Naturally, Cr2O3 oxide layers are formed in steels with a Cr content higher than 12 wt.% during oxidation, resulting in better resistance to oxidation and carburizing. Increased temperature and pressure can generally aggravate the CO2 corrosion of steel. Therefore, an increased temperature can increase the thickness of the Cr2O3 layer, and the increased pressure mainly affects the carburizing behavior of steels. However, the influence of gas impurities, such as O2, H2O, and SO2, on the CO2 corrosion of steel changes with the type of steel and the service environment. Meanwhile, the development of existing CO2 corrosion models, types of coatings resistant to CO2 corrosion, and their protective effects are discussed. Most models were developed based on experimental results in which the oxidation or carburizing kinetics showed a parabolic trend. Although these models can predict the thickness of the oxide layer and the depth of carburizing, they fail to accurately predict the corrosion life of steel subjected to simultaneous oxidation and carburizing. In addition, CO2 in a flowing state under actual working conditions accelerates the corrosion rate of the steel and causes the oxidation layer to fall off. Therefore, developing models that simultaneously cover the interaction of oxidation and carburizing or consider the erosion caused by the CO2 flow, especially the CO2 flow containing oxide particles, is necessary in the future. To improve the service life of steel in high-temperature CO2 environments, Al, Cr, and other coatings are often prepared to improve the oxidation and carburizing resistance of steel. However, the mechanical properties of coated steels and coatings in a corrosive environment also significantly impact their corrosion behavior, and further study is required. In addition, Ni-based coatings often exhibit better corrosion resistance than other coatings. Therefore, Ni-based alloys are generally used as the main component of steel coatings. However, the high cost of Ni-based coatings limits their widespread applications. For this purpose, the introduction of nanoparticles and effective control of the coating composition and structure based on simulation calculations to improve the mechanical properties and corrosion resistance of coatings hold great promise in coating composition selection. Moreover, improving the adhesion strength and interface stability between the coating and the steel matrix is important to ensure the protective effect of the coatings. This requires the exploration of preparation techniques to improve the uniformity and density of the coating effectively. In such case, this study can not only point out the shortcomings of existing studies and the development direction of future studies, but also provide a comprehensive theoretical basis for the selection of anti-CO2 corrosion protection techniques in high temperature environment and the evaluation of long-term safety service life for steel.
  • Corrosion Behavior of 2507 Duplex Stainless Steel in Acidic and High Chlorine Environments
    LI Yu, LIU Guangming, LI Futian, LIU Chenhui, YANG Shuli, DONG Meng
    China Surface Engineering. 2024, 37(2): 91-100. https://doi.org/10.11933/j.issn.1007-9289.20230928002
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    Thermal evaporation technology is widely used in wastewater treatment. With the continuous evaporation and concentration of wastewater, the Cl? content in the solution increases exponentially, resulting in rapid corrosion and failure of the materials used for evaporation equipment. 2507 duplex stainless steel is often utilized due to its high content of Cr and Mo elements. This material combines the advantages of both ferrite and austenitic stainless steels, resulting in excellent resistance to pitting corrosion.To investigate the corrosion of 2507 duplex stainless steel in acidic and highly chlorinated environments, dynamic potential polarization, electrochemical impedance, Mott-Schottky curves, and dynamic immersion experiments were used. The electrochemical tests were performed in an acidic solution (pH 3) containing fluorine (F? 300 mg / L) and varying concentrations of Cl? (20, 60, 90, 120, 150 g / L) at a temperature of 60 ℃. The stainless steel was subjected to an immersion test in a corrosive solution with 120 g / L of Cl? , 300 mg / L of F? , and pH 3 at 80 ℃ for 35 d. Dynamic stirring was employed at a linear velocity of 2 m / s, and the solution was renewed every 7 d. Three parallel samples were taken, and the properties of the specimens were characterized using metallographic microscopy, scanning electron microscopy (SEM), energy spectrometry (EDS), and 3D microscopy. The study investigated the corrosive effect of chloride ion concentration on 2507 duplex stainless steel through electrochemical tests, and immersion corrosion tests were conducted to examine the corrosion conditions of stainless steel in a highly chlorinated environment.The results indicate that in various electrochemical tests, the corrosion potential Ecorr in the polarization curve shifts towards the negative direction, and the corrosion current density Icorr gradually increases with the rise in chloride ion solubility. Thermodynamically, the more negative the corrosion potential Ecorr, the higher the tendency of the material to corrode; kinetically, the larger the corrosion current density Icorr, the poorer the corrosion resistance of the material. The higher the pitting potential Eb, the stronger the corrosion resistance of the material. The test results indicate that an increase in the chloride ion concentration accelerates the corrosion of the material. In addition, the impedance spectrum shows a decrease in the capacitive arc radius as the concentration of chloride ions increases. A larger capacitive arc radius indicates greater resistance to charge transfer at the interface between the metal and solution, which in turn suggests stronger corrosion resistance of the material. The polarization resistance Rp reflects the state of the surface passivation film and is crucial in evaluating the corrosion resistance. The Rp value decreases as the concentration of chloride ions increases. The Mott-Schottky curve shows an increase in both donor density ND and acceptor density NA with an increase in Cl? concentration, indicating an increase in point defects within the passivation film and a reduction in the corrosion resistance of the material. The metallographic analysis of stainless steel after 35 d of immersion in the corrosive solution revealed that pitting corrosion primarily occurs in the boundary region of the α-phase and γ-phase or in the γ-phase zone. This suggests that in the duplex stainless steel, the α-phase is more corrosion-resistant than the γ-phase. The average corrosion rate of the material was 2.51 μm / a, as measured by the weightlessness method. The SEM morphology revealed a small number of etching holes on the surface of the specimen, with an outer diameter of approximately 70–100 μm. The average pitting depth of the alloy after corrosion was 20.493 μm, and the maximum pitting rate was 0.275 mm / a as measured by 3D microscope. These results indicate mild corrosion and reflect the good corrosion resistance of stainless steel in acidic and highly chlorinated environments. Due to the lack of corrosion data on the materials used in perchlorinated wastewater evaporation equipment, the corrosion of 2507 duplex stainless steel can provide data support for material selection.
  • Progress of Gas-solid Interaction Behavior and Spray System of High Velocity Low Temperature Spray
    MA Shiyue, LIU Meijun, YANG Guanjun, LI Changjiu
    China Surface Engineering. 2024, 37(2): 101-114. https://doi.org/10.11933/j.issn.1007-9289.20230327002
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    High-velocity low-temperature spray is a spray method that utilizes a solid-phase powder or a low-temperature powder containing a non-solid phase to deposit on a substrate surface through collision at high velocity and kinetic energy. Compared to the traditional thermal spray that relies on melting particles for coating deposition, this spray method exhibits potential advantages, such as low oxidation of the material, high bonding strength with the substrate, dense microstructure, and excellent comprehensive mechanical properties. Therefore, it has attracted extensive attention domestically and internationally in the fields of metal or metal matrix composite coatings, additive manufacturing, and the rapid repair of damaged components. First, as typical high-velocity low-temperature spray methods, cold spray, and low-temperature high-velocity oxygen-fuel spray share common characteristics: powder particles interact with the gas in the nozzle, experiencing heating and acceleration through heat transfer and the drag force of the gas. The elevated kinetic and internal energies of the particles may induce certain behaviors that have the potential to enhance interface bonding. These behaviors include fragmentation of the oxidation films, structural changes, and even localized melting upon collision with the material surface. The analysis of some studies indicates a significant influence of velocity and temperature on the material deposition behavior and the final coating performance. Subsequently, spray strategy planning and coating performance modulation can be performed, guided by the deposition window constrained by the particle velocity and temperature. The particle temperature determines the ductility during collision, thereby influencing the deformation behavior, surface morphology, flatness, material jetting behavior, and bonding quality, whereas the velocity determines the kinetic energy during collision, thereby influencing the stress and strain inside the material. The subsequent section of this paper discusses the composition of high-velocity low-temperature spray equipment systems, including the spray gun system (comprising a nozzle and gas heater), powder feeder, gas / fuel sources, spray scanning component, and control system. The structural design strategies of each major component and their influence on the gas-solid flow behavior are discussed in detail. The spray gun is the core component of the spray system, which comprises a nozzle that supplies initial kinetic energy to the gas and a gas heater that supplies initial internal energy to the gas. Under specific process conditions, the particle velocity demonstrates an initial increase followed by a decrease with the expansion length or expansion ratio of the nozzle, whereas the trend of the particle temperature is reversed. Gas heaters are primarily categorized as electric and combustion flame heaters. This serves as a crucial basis for distinguishing between cold spray and high-velocity oxygen-fuel spray. Electric heaters operate at a maximum temperature of approximately 1 300 K and are designed with intricate and convoluted airflow paths within limited volumes to maximize heating efficiency. The maximum temperature of the combustion flame can reach 3 400 K. Adjusting the type and proportion of combustion reactants, along with implementing rational cooling flow control strategies, allows for the continuous regulation of the flame temperature across a wide range. Therefore, a comprehensive approach involving the adjustment of the process parameters and spray gun structure achieves on-demand control of the particle temperature and velocity. Finally, some key issues in the high-velocity low-temperature spray process, and equipment systems are discussed. The main emphasis of this paper is to summarize the methods by which control over coating performance can be attained through the design of the spraying parameters and apparatus. This study contributes to an in-depth understanding of the deposition mechanisms in high-velocity low-temperature sprays and provides a valuable reference for the development of high-performance spray equipment systems.
  • Thermal Stress Analysis Methods of Protective Coating on Polymer Surface for Space: A Review
    XU Mengyun, ZHANG Jinlin, MA Jiayu, TANG Denghang, XU Wenbin, WANG Liang, GU Hongyu, ZHANG Yuzhi, SONG Lixin
    China Surface Engineering. 2024, 37(2): 115-136. https://doi.org/10.11933/j.issn.1007-9289.20230411001
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    Flexible polymer materials, which are key materials for spacecraft surfaces, are exposed to the synergistic erosion of ultraviolet(UV) irradiation, ionizing irradiation, and atomic oxygen in the space environment, resulting in material loss and functional failure. Therefore, to achieve long-term service, it is often necessary to prepare protective coatings on surfaces. For most coating materials, during processing, manufacturing, and use, owing to their brittleness, the coating often exhibits a local stress concentration due to temperature changes. With the continuous increase in thermal stress, cracking and spalling occur after exceeding the tensile strength limit, which has become a significant factor affecting performance. Therefore, the analysis of the thermal stress distribution is significant in the design and optimization of coatings. The analysis methods of thermal stress in coatings can be divided into two categories: experimental measurements and finite element analysis based on numerical simulations. Owing to the limitations of a single stress-testing method, limitations in the process of material stress analysis have not been addressed. Therefore, an increasing number of researchers have combined finite element simulations with experimental characterization. Finite element simulations can be used to analyze the theoretical stress distribution of materials under idealized conditions and further optimize the calculation parameters according to environmental conditions, gradually approaching the coating condition under real conditions. Moreover, measuring the actual stress distribution of a material through experiments and matching it with the calculated results effectively solves the problem of calculation reliability. The key factors influencing the material stress can also be effectively understood by analyzing the gap between the simulation and measured results. The combination of finite element simulations and experimental measurements has gradually become the most widely used method for analyzing the stress of coating materials. Owing to the mutual restrictions of the flexibility and protection ability of space-protective coatings on polymer surfaces, improving the flexibility of materials while maintaining good protection performance has become a key problem. Therefore, the stress analysis of the coating has become an important direction for improving the coating design. Space-protective coatings, especially inorganic coatings with good protective properties, face complex temperature-cycling environments in the actual space environment, and changes in the temperature field cause different degrees of deformation, cracking, and other failures of coating materials. In addition, the protective coating needs to be processed at a certain temperature during the preparation process, and a change in these temperature fields causes stress problems in the protective coating. However, it is difficult for traditional stress testing methods to effectively characterize the process of stress generation and accumulation without failure. Finite element simulation is limited in that it is difficult to establish environmental and material models in the actual application process. Therefore, by summarizing the current common thermal stress analysis methods, this study aims to analyze the relevant factors affecting the service life of the coating, which will help adjust the composition, structure, microstructure, and other parameters of the material, predict the failure form of the coating and optimize the preparation process of the coating material. By analyzing the advantages and limitations of destructive test methods and non-destructive test methods based on experimental measurements, as well as finite element simulations, this paper further summarizes the improvement of the current commonly used stress analysis methods by combining the two to guide the coating design and develop coating materials with a low-stress structure. This study provides technical support for the lightweight development and long-term reliable service of key coating materials for polymer surfaces.
  • Progress on Cutting Performance of Micro-nano Texture Coated Tools
    TIAN Chuchun, JIANG Hongwan, YUAN Sen, DENG Jing, YUE Xi
    China Surface Engineering. 2024, 37(2): 137-160. https://doi.org/10.11933/j.issn.1007-9289.20230412001
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    Tool wear is a serious problem, and a short service life is a challenge in cutting-processing. Following the development of the modern manufacturing industry, titanium alloys, high-temperature alloys, and other difficult-to-machine materials have been adopted widely. However, these materials exhibit low thermal conductivity and small deformation coefficients among other characteristics, resulting in a high cutting force and cutting temperature, tool wear, and serious problems in cutting, thus considerably shortening the service life of the tool and affecting the machining surface quality. Following the advancement of science and technology, green cutting technology is widely used in the modern manufacturing industry, thereby increasing demand in the cutting tools field. Therefore, the use of cutting fluid in the cutting process, which not only improves the lubrication effect of the cutting process, but also reduces tool wear and improves the machining surface quality and performance has been considered. However, the large amount of cutting waste fluids causes environmental pollution and has a serious impact on the operator's health. Therefore, to better respond to green manufacturing and achieve sustainable development, surface coating technology is applied to tool surface coatings with high hardness, high abrasion resistance, and other properties of hard coating materials and solid lubricating materials with a low coefficient of friction (soft coatings). These act as a chemical and thermal barrier to avoid direct contact between the tool and workpiece, reducing the friction and interaction between the tool and workpiece to enhance the tool's oxidation resistance, anti-adhesion properties, and resistance to abrasive wear, thereby extending the tool life and improving the cutting tool performance. In addition, through the principle of friction biomimicry, surface texturing technology is used to place micro-textures on the rake or flank face of the tool, similar to the surface texture of certain natural living creatures, which can improve the friction behavior of the tool-chip contact surface and the tool-workpiece contact surface, enhance the cutting ability of the tool, and improve the suitability of the tool for green cutting. Therefore, this review summarizes research related to the simultaneous placement of micro–nanotextures and coatings on tool surfaces during cutting operations. First, the preparation technology related to the simultaneous placement of the texture and coating on the tool surface is introduced. Second, the mechanism underlying tool action after the simultaneous placement of the texture and coating on the tool surface is analyzed and summarized, which primarily encompasses three aspects in the current study: (1) the texture on the tool surface can improve the adhesion performance of the coating on the tool substrate surface, (2) the texture and coating influence lubrication performance, and (3) the placement of the texture reduces the length of the tool-chip contact. The review focuses on summarizing the wear resistance, bond resistance, and service life of the tool in the cutting process, as well as the changes in cutting force, cutting temperature, and friction coefficient of the tool-chip contact interface in the cutting process after texture and coating are simultaneously performed on the tool surface, and assessing the related influencing mechanisms. The simultaneous placement of textures and coatings on tool surfaces was found to be widely used in green cutting technology, machining of difficult-to-machine materials, and high-speed cutting technology. Based on this, the direction of future development and application prospects of micro-nano texture coated tools are discussed. This review can be used as a basis for more in-depth research on the mechanism underlying micro-nano texture coated tools and their properties, as well as to inspire subsequent research on the simultaneous placement of other shapes of micro-nano textures on the tool surface and the superior performance of multi-composite coatings, gradient coatings, multi-composite nano-coatings, super-hard coatings, and soft-hard composite coatings.
  • In Situ XPS Analysis of Fretting-induced Tribo-chemical Behavior in a Pure Iron
    XIAO Ziyue, SHENG Liangliang, WEI Xuejiao, WEI Huaizheng, XU Xiaojun, ZHU Minhao
    China Surface Engineering. 2024, 37(2): 161-169. https://doi.org/10.11933/j.issn.1007-9289.20230329002
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    Fretting causes severe damage to the material surfaces which leads to the failure of the mechanical components in the fields of railways, mining, and aerospace industries. Many researches have shown that in addition to the fretting parameters such as load, frequency and displacement amplitude, the service environment also has an important impact on fretting. Pure iron has the advantage of high magnetic permeability, high saturated magnetization, low coercivity, low hardness, and high plasticity. It is widely used for manufacturing highly precise electronic devices. Especially in the aerospace industry, fretting damage is more severe under certain conditions such as a vacuum environment and high temperature. The tribochemical reaction occurring on the contact surface during the fretting wear process has a significant influence on determining the associated wear mechanism and fretting wear resistance. To study the tribochemical state and its effect on the fretting wear behavior of pure iron, systematical fretting wear experiments at different displacement amplitudes have been conducted under the vacuum (p=4 mPa) and air atmosphere (p=100 kPa) by using an in-situ XPS analysis test combined with a self-designed high precision fretting wear device. 3D white light interferometer and scanning electron microscope were utilized for quantitative characterization of wear volume and morphological observations of the worn surface, respectively. The results show that pure iron presents significantly different fretting wear characteristics between the vacuum and air atmosphere. With the increase of displacement in the air atmosphere, the fretting regime enters into slip regime (SR) directly from partial slip regime (PSR) without mixed fretting regime (MFR). Under vacuum, it is relatively hard to enter into SR due to the strong interface adhesion, hence resulting in a relatively wide mixed fretting region. Furthermore, in general the contact interface displays a higher friction factor in vacuum than that in air atmosphere at the same displacements. XPS results show that with the increase of the displacement, in vacuum atmosphere there is more exposure of Fe on the worn scar, and the formation of FeO is dominant while no Fe2O3 is produced. In contrast, for the air atmosphere, the tribochemical production of worn scars mainly consists of FeO and Fe2O3, and in SR the formation of Fe2O3 is dominant. The fretting wear volume increases with the increase of displacement amplitude for both vacuum and air atmosphere, but the magnitude of the increase is significantly different. In PSR (D=1 μm), the initial oxide (FeO and Fe2O3) is still observed on the worn surface, thus representing a very slight amount of wear. When the displacement increases to 5μm, in vacuum, the disappearance of Fe2O3 and the exposure of Fe enhance the interface adhesion, which leads to a significant increase in wear volume. In contrast, for the air atmosphere, the production of Fe2O3 and FeO on the worn surface has better lubrication protection, resulting in relatively low wear volume. In SR (D=20 μm), the wear volume in vacuum rises rapidly and the worn surface consists of more Fe and less FeO, which makes the interface adhesion even stronger and hence leads to more serious wear. However, in the air atmosphere the worn surface is almost covered by Fe2O3 and FeO, and lower wear volume can be observed than that in vacuum, which indicates that the FeO and Fe2O3 have good protection with a lubricant role against fretting wear, especially for the Fe2O3. The in-situ XPS technique can characterize the real tribochemical state of the contact surface and reveal more accurately the effect of the tribochemical reaction on the fretting wear behavior, which is of great scientific significance to enrich and develop the basic theory of fretting wear.
  • Effect of Number of Remelting Times on Surface Quality and Wear Performance of 316L Produced by Selective Laser Melting
    LI Qiang, LIU Songyong, WANG Qingyang
    China Surface Engineering. 2024, 37(2): 170-181. https://doi.org/10.11933/j.issn.1007-9289.20230616001
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    The number of remelting times (NRM) significantly influences the surface roughness and wear resistance of components used in selective laser-melting (SLM) additive manufacturing. Therefore, the investigation of its influencing mechanism and the determination of an economical NRM are crucial for applications of SLM additive manufacturing technology. In this paper, 316 L specimens were prepared using an SLM additive manufacturing device, during which they were grouped and remelted by a laser 0–3 times. Subsequently, the surfaces of the remelted specimens were characterized using a three-dimensional profile scanner and a scanning electron microscope. Furthermore, friction and wear experiments were conducted on the specimens using a high-speed reciprocating friction and wear testing machine, and the masses before and after wearing were measured using an electronic analytical balance. The following beneficial findings were observed. The surface roughness of the components in SLM additive manufacturing decreased with an increase in NRM. Specifically, the values of average surface roughness Sa, Sq, Sv, and Sz decreased from 8.437, 11.88, 82.68, and 252.2 μm (normal printing without remelting) to 6.18, 7.735, 37.597, and 104.36 μm (after remelting for three times) by 26.75%, 34.89%, 54.53%, and 58.62%, respectively. The average friction coefficient increased gradually, whereas the mass wear decreased with an increase in NRM. For the specimens remelted two and three times, the instantaneous maximum friction coefficient was greater than 1 in the later stage of the wear experiment. This is attributed to the fact that after multiple remelting times, the surface of each sample becomes very clean, resulting in very close contact between the friction pairs. Moreover, “contact growth” occurs prior to significant sliding, and the frictional force exceeds the positive pressure because of the constantly increasing contact area. These changes in surface roughness and wear performance can be explained as follows. Each remelting process further melts and sinks the welding marks and particles adsorbed on the surface until they disappear. Consequently, the “peak-valley” phenomenon at the overlap of adjacent melt channels is suppressed, and defects such as pores and balls are gradually repaired. Eventually, the surface flattens. Furthermore, different NRMs resulted in varying degrees of variation in surface roughness and wear. Accordingly, this study innovatively proposes the concept of an economical NRM. The comprehensive change rates of the surface roughness and wear performance after one, two, and three remelting cycles were 26.61%, 43.60%, and 23.68%, respectively, and the economical NRM was 2. Finally, application examples of the mining machinery of economical NRM based on the research results are presented. This study is expected to provide new clues for improving the surface quality and wear resistance of components in SLM additive manufacturing while reducing processing costs. Based on different requirements, NRM can be used for SLM additive manufacturing of parts on the surface or layer-by-layer inside. NRM can be used to improve the mechanical, metallurgical, and physical properties of additive manufacturing parts, thereby improving the properties of parts, such as wear resistance, corrosion resistance, and fatigue resistance.
  • Processing Mechanism and Experiment of Ultrasonic Vibration Assisted Cutting of SiCp / Al Composites
    LIN Jieqiong, WU Minglei, LIU Siyang, ZHOU Yan, GU Yan, ZHOU Xiaoqin
    China Surface Engineering. 2024, 37(2): 182-198. https://doi.org/10.11933/j.issn.1007-9289.20230417001
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    SiCp / Al composites contain high hardness SiC particles and are unevenly distributed in the Al matrix, causing the two-phase material to exhibit non-cooperative deformation during processing, thus resulting in problems in conventional cutting force mutation, such as severe tool wear, low processing efficiency, and poor machining surface quality. The introduction of ultrasonic vibration-assisted cutting (UVAC) is an effective way of improving machining quality. The study of the form of particle damage and the material removal mechanism in UVAC is important. To reveal the machining mechanism underlying a 20%SiCp / Al composite material under UVAC conditions and to study the influence law of different process parameters on the cutting force and machining surface quality, a simulation model based on two-dimensional polygon random distribution particles was established using the finite element simulation software Abaqus. The microstructure, deformation, and failure of the SiCp / Al composites were simulated by considering the cohesive elements of particle fracture, matrix deformation, and tensile force between the particles and matrix. The dynamic cutting process of SiCp / Al composites was simulated for conventional cutting (CC) and UVAC, and the influence of different relative positions between the tool and particles on the particle removal behavior was analyzed. The experimental and simulated cutting forces obtained using CC and UVAC were compared using the same parameters, and the accuracy of the finite element simulation was verified. Through the design of a single-factor experiment, the effects of the two machining methods and different machining parameters on the cutting force and surface roughness were compared, the optimal combination of machining parameters was obtained, and the surface topography under the optimal machining parameters was analyzed. The simulation and experimental results show that SiC particle fracture, particle plowing, particle pulling out, and Al matrix tearing are the main factors affecting the processing quality of SiCp / Al composites. Under both CC and UVAC processing conditions, the cutting force initially decreases and then increases as workpiece speed increases; the cutting force gradually increases with increasing feed rate, and then increases with increasing cutting depth. Different relative positions of the tool and particles produce different forms of damage. When the tool path passes through the middle of the SiC particle, the SiC particle is mainly removed in the form of particle fracture. When the tool path passes through the upper part of the SiC particles, the SiC particles are partially unstuck and deflected, and the particles are more easily pressed into the Al matrix. When the tool path passes through the lower half of the SiC particle, the SiC particle integrates with the tool, thereby changing its front angle. The application of ultrasonic vibrations can effectively inhibit the failure of SiC particles and matrix damage, reduce the fracture damage of particles during cutting, reduce the desticking phenomenon of particles, and stabilize the fractured particles in the matrix. Compared to CC, the average cutting force (main cutting force) in machining was reduced by 33%, and the maximum reduction in the machined surface roughness was 531 nm, which significantly improved the quality of the machined surface. The established two-dimensional microscopic multiphase finite element model can effectively simulate the processing defects and crack damage of aluminum matrix composites, reflect the real particle failure behavior during processing, and identify the mechanism underlying the effect of different relative positions between the tool and the particle on the particle removal behavior. The removal mechanism, surface morphology, and cutting force of the UVAC SiCp / Al composites were investigated by combining experiments and simulations. These results provide significant reference for improving the high-quality surface preparation of difficult-to-machine materials.
  • Molecular Dynamics of the Grinding and Polishing Collaborative-processing on Monocrystalline Silicon
    GUO Lei, GUO Pengju, LIU Tiangang, GUO Wanjin, Lü Jingxiang, JIN Qichao
    China Surface Engineering. 2024, 37(2): 199-210. https://doi.org/10.11933/j.issn.1007-9289.20230315001
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    Monocrystalline silicon, a crystalline material widely employed in semiconductor chips, optical components, photovoltaic devices, and other high-end manufacturing applications, possesses exceptional attributes, such as high hardness, strength, thermal stability, and corrosion resistance. Nevertheless, the remarkable mechanical properties and chemical stability of monocrystalline silicon pose significant challenges in machining. Rigid contact between machining tools and materials frequently causes structural and surface quality defects, including cracks and pits, significantly impairing product performance. Currently, the primary method for achieving ultraprecision surface manufacturing of monocrystalline silicon materials is grinding and polishing. The dynamics of abrasive movements during these processes, governing the two-body and three-body wear mechanisms, have a profound impact on the material removal efficiency and surface finish quality. Despite their critical importance, there is a notable research gap in understanding the material-removal mechanisms and surface-morphology evolution during grinding and polishing. To address this gap, our study introduces a molecular dynamics simulation model for the ultraprecision grinding and polishing of single-crystal silicon surfaces, encompassing both fixed and loose abrasives. Our model scrutinizes several pivotal parameters: the depth of cut of the abrasives, the lateral and longitudinal spacing, and their respective effects on the grinding force, material phase transformation, temperature, surface damage, and material removal behavior. The aim was to unveil the underlying principles governing the evolution of surface morphology during the ultra-precision grinding and polishing of single-crystal silicon. Our findings indicate that an increase in the depth of cut for both fixed and loose abrasives results in a higher number of damaged surface atoms in single-crystal silicon materials. The depth of cut significantly influences material removal, crack propagation, and workpiece damage. Notably, both the normal and tangential grinding forces increased with the depth of cut, with the normal grinding force displaying a more pronounced increment for equivalent changes in the depth of cut. Conversely, the tangential force exhibited greater sensitivity to alterations in lateral and longitudinal spacing. However, the tangential grinding force decreased with increasing lateral spacing, followed by an initial decline and then an increase with increasing longitudinal spacing. Our study indicates that the temperature of the workpiece is primarily affected by the depth of cut of the abrasives, whereas the influence of the lateral and longitudinal spacing on the temperature is negligible. An analysis of the diamond structure of single-crystal silicon revealed that a greater longitudinal spacing between abrasives resulted in reduced interference on the workpiece, a decrease in the hexagonal diamond crystal structure, deeper workpiece damage caused by loose abrasives, and an increase in transient defect atoms. A deeper cut depth led to a broader damaged area on the workpiece, a more frequent appearance of the hexagonal diamond crystal structure, and an increased depth of the damaged layer. Regarding the surface morphology, an increasing depth of cut causes a substantial accumulation of atoms from both fixed and loose abrasives during grinding and polishing, resulting in enhanced material removal. A larger lateral spacing enables loose abrasives to polish a larger area, remove more atoms, and consequently increase the atom accumulation. The Wigner-Seitz defect analysis revealed that during the fixed and free abrasive grinding and polishing processes, the grain gap area on the surface of the interference region increased with an increase in lateral spacing. As the cutting depth increases, more atoms are removed from the interference region after grinding and polishing. In the cross-section of the interference region, material removal decreased with an increase in lateral spacing, whereas longitudinal spacing had no significant effect on material removal. However, increasing the cutting depth of the abrasives led to a notable increase in material removal, resulting in larger gap areas and smaller gap sizes, indicating more pronounced atom extrusion. Therefore, this study establishes a robust theoretical foundation for achieving high material removal efficiency and superior surface quality during ultraprecision grinding and polishing processes.
  • Antibacterial Activity and Biocompatibility of Magnesium Oxide Coating Prepared on Micro-arc Oxidized Titanium by Electrophoretic Deposition
    FAN Xinli, DU Jiaheng, XIAO Dongqin, LI Yaohua, HU Liqun, HE Kui, WENG Jie, DUAN Ke, LIU Gangli
    China Surface Engineering. 2024, 37(2): 211-219. https://doi.org/10.11933/j.issn.1007-9289.20230425001
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    Owing to their mechanical properties and biosafety, titanium (Ti) implants are widely used to replace missing teeth; however, their non-antimicrobial properties can lead to infection. The main reasons underlying the failure of oral implant repair are the biofilms and surrounding inflammation caused by bacterial adhesion to the surface of the implants. Implant-related infections considerably influence the effect of surgery and increase the pain and cost incurred by patients; the main pathogen is Porphyromonas gingivalis (P.g). Therefore, endowing the surface of implants with antibacterial ability to reduce the adhesion and colonization of bacteria on the surface of implants, thus reducing the incidence of infection, is necessary. Microarc oxidation (MAO) is currently one of the primary technologies used for implant surface modification. It can form porous titanium dioxide coatings on Ti with strong adhesion under high voltages. Moreover, the introduction of elements (such as calcium and phosphorus.) can promote bone healing and improve the osseointegration properties of the implant. However, owing to the rough and porous surface of micro-arc oxidation Ti (MAO-Ti), bacteria can easily attach and reproduce; therefore, infection will still occur. Magnesium and its compound [magnesium oxide (MgO)] have been found to have excellent antibacterial ability and biocompatibility. Therefore, in this study, MAO and electrophoretic deposition (EPD) were combined to deposit nano-magnesium oxide (nano-MgO) coatings on MAO-Ti for 0, 15, 30, 45, or 60 s, while maintaining its biosafety. The MAO-Ti surface was endowed with antibacterial properties to reduce the incidence of infection. In this study, the in vitro antibacterial properties and biocompatibility of the samples were evaluated, the surface morphology and element composition of the samples were observed by scanning electron microscope (SEM), X-ray diffractometer (XRD), and energy dispersive spectrometer (EDS), the in vitro antibacterial properties of the samples against P.g were evaluated by dilution plate counting, bacterial live / dead staining, and SEM observation, and the in vitro biocompatibilities of human gingival fibroblasts (HGF) were evaluated using the CCK-8 method, cell live / dead staining, and cytoskeleton staining after co-culture with the samples. The results showed that the nano-MgO particles were uniformly agglomerated on the MAO-Ti porous surface, and the coverage rates increased with EPD time. The in vitro antibacterial activity of each sample against P.g was 5%, 26%, 31%, and 54% at 24 h, 39%, 69%, 72%, and 79% at 72 h, and microscopic observation (live / dead staining and SEM) showed that the proportion of live bacterial cells on the surface of the samples decreased with increasing deposition time. After co-culture with HGF cells for 1 d, the relative survival rate of cells was 79%, 76%, 72%, 70%,and 67%, 93%, 92%, 90%, 87%, and 85% after co-culture with HGF cells for 5 d. Only the samples deposited for 60 s had low cytotoxicity on the day 1 (relative cell survival rate = 67%), while, on days 3 and 5, no samples had cell cytotoxicity (all cell relative survival rates ≥70%). Fluorescence microscopy showed that there were almost no dead cells on the surface of MAO-Ti samples, and the proportion of dead cells on the surface of the other four groups increased with EPD time. The morphology of cells on the surface of each group was intact and there was no significant difference among the groups. Therefore, the EPD nano-MgO coatings on the surface of MAO-Ti have excellent in vitro antibacterial properties and biocompatibility, providing a new method for reducing the incidence of infection and pain suffered by patients as well as the cost of operation.
  • Diffusion Reaction Barrier Between UO2 and Zr Shell
    HUANG Jie, ZENG Qiang, LIU Zhe, CHEN Jiangshan, LI Haopeng, LIAO Bin
    China Surface Engineering. 2024, 37(2): 220-226. https://doi.org/10.11933/j.issn.1007-9289.20230427002
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    UO2 ceramic nuclear fuel is characterized by high hardness, a high melting point, and radiation resistance. Consequently, UO2 fuel has been widely used in pressurized water reactors and various research and experimental reactors. UO2 ceramic nuclear fuel pellets are encapsulated in a Zr cladding material to produce fuel elements that are now the mainstream fuel elements for pressurized water reactors owing due to their high strength, plasticity, and thermal conductivity. However, under reactor operating conditions, the UO2 fuel and Zr shell are thermodynamically unstable, and the O atoms in UO2 can diffuse into Zr, forming ZrO2 and other brittle phases that affect the safety and service life of nuclear fuel assemblies. Following the Fukushima accident, higher standards for reactor safety and longevity are demanded worldwide. Fuel assembly safety studies have shown that the formation of an oxygen diffusion barrier layer between the UO2 fuel phase and Zr shell to prevent the diffusion of oxygen atoms from the UO2 phase into the Zr shell is a method for improving the safety and service life of nuclear fuel assemblies. The calculations indicated that Nb and Cr are potential materials for diffusive barrier layers. To investigate the ability of Nb and Cr as diffusive barrier materials for preventing the diffusion of oxygen atoms, Nb, Cr, and Nb / Cr coatings were fabricated on Zr plates via arc-ion plating. Subsequently, the Zr plates with different coatings were tightly bonded to the UO2 plates to form a sandwich diffuser. The diffusing couple was placed in a mold, filled and packed with Zr powder, and placed in a sintering furnace to prepare for the diffusion reaction. Vacuum thermal pressing was used to accelerate diffusion. The experimental conditions of diffusion reaction were as follows: pressure of 50 MPa, reaction temperature of 800 °C, hold temperature time of 4 hours, and furnace cooling were employed. After hot-press sintering, the diffusing couple was cut in the middle to observe and analyze the cross section. Scanning electron microscopy and energy dispersive spectroscopy were used to observe the morphology and analyze the elements. The results showed that the metallic coating effectively prevented diffusion between UO2 and Zr. Comparative studies have found that Nb coatings have more optimized oxygen resistance; however, Nb and Zr diffuse and form a two-phase structure under experimental conditions. The mutual diffusion of Nb and Zr atoms results in a large number of Zr atoms in the Nb coating and a large number of Nb atoms in the Zr shell. Cr was compatible with UO2 and Zr, and no diffusion reactions were observed between UO2 and Zr under the experimental conditions. However, Cr atoms have a greater affinity for O atoms than for Nb atoms, and the concentration of O atoms in the Cr coatings is higher than that in the Nb coatings. If the Cr coating is thin, O atoms can pass through the Cr coating, enter the Zr shell, and affect its properties. In summary, at this limit, a metallic coating can effectively prevent the diffusive reaction between UO2 and Zr. However, a single Nb or Cr coating does not completely solve the problem of diffusion between UO2 and Zr. Based on these results, a Nb / Cr composite layer to solve the diffusion problem between the UO2 fuel and the Zr shell may be a better approach. The side near the UO2 fuel was coated with Nb and that near the Zr shell was coated with Cr. The study of the diffusive reaction barrier layer between the UO2 fuel and Zr shell provides reference for improving the safety and service time of nuclear fuel assemblies.
  • Laser-chemical Composite Polishing and Surface Morphology Evolution of Medical TC4 Titanium Alloy
    SHAO Yong, SUN Shufeng, WANG Pingping, MONKA Peter Pavol, CHEN Bowen, ZHANG Fengyun, WANG Xi, SUN Weili
    China Surface Engineering. 2024, 37(2): 227-237. https://doi.org/10.11933/j.issn.1007-9289.20230227001
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    Surface finish is a crucial quality characteristic of medical device components. However, existing surface polishing technologies have some shortcomings, such as difficulty in controlling the polishing effect, poor precision, and inability to manage components with complex shapes. In this study, a laser-chemical composite polishing system was designed and built for the precision polishing of medical-grade TC4 titanium alloy. The material removal mechanism of laser-chemical composite machining was analyzed. The evolution process of the material surface morphology and surface roughness changes at different polishing stages was investigated by conducting laser chemical composite polishing experiments on medical TC4 titanium alloys; thus, clarifying the mechanism of laser chemical composite polishing. The results show that material removal by laser-chemical composite polishing is based on the combined influence of laser thermal-mechanical effects and laser-induced chemical corrosion. Moreover, these two factors have a synergistic effect under certain conditions, which can mutually promote and enhance material removal efficiency and processing quality. Within an appropriate process window, chemical dissolution can completely remove the residues and remelts generated by laser ablation. Laser irradiation causes temperature differences between the peak and valley regions of the material surface, leading to different chemical dissolution rates. By exploiting the difference in the dissolution rates between the peaks and valleys on the surface of the workpiece, improvements in the surface roughness of the laser-irradiated region were achieved. Moreover, the chemical polishing mechanism is based on the atomic-scale dissolution of materials, which results in higher polishing precision compared with laser thermo-mechanical etching. The ratio of the laser etching material removal to the chemical dissolution material removal determines the ultimate roughness limit of the titanium alloy surface. A higher proportion of chemical dissolution resulted in better surface smoothness but a lower polishing efficiency. Therefore, during the final polishing stage, reducing the energy of laser irradiation on the workpiece surface can decrease the laser etching ratio and improve the final polishing effect. Additionally, the uneven distribution of the alloying elements on the surface of the TC4 titanium alloy affected the final surface smoothness. This is because Al and Fe in TC4 titanium alloys exhibit better chemical activity in acidic environments than V and Ti. During the chemical corrosion process, micro-galvanic cell phenomena occur, leading to preferential dissolution of the anode. Therefore, based on the chemical polishing mechanism, it can be understood that the ultimate polishing limit is influenced by the purity and microstructure of the material. The purer the material composition and smaller the microstructure, the better the final polishing effect. The selective removal of laser-chemical composite polishing is based on laser etching and thermo dissolution induced by laser activation. During laser-chemical composite polishing, laser irradiation acts as a local and selective heat source, inducing appropriate thermal shock and activating a non-uniform chemical reaction between the chemical solution and metal surface, resulting in temperature-induced chemical corrosion. In the laser irradiation area, the passivation film on the metal surface was stripped and dissolved under the dual action of physics and chemistry, whereas other parts of the workpiece material were protected by the passivation film, and almost no corrosion occurred. Under the continuous action of laser etching and chemical dissolution, the etching rates in the laser-irradiated and non-irradiated areas were significantly different, thereby achieving selective etching of the metallic material. The presence of bubbles during processing significantly affects the laser-chemical composite polishing. The causes of bubble generation were analyzed, and several methods were proposed to overcome bubble disturbances. It was demonstrated through experiments that, after taking appropriate measures, the bubble disturbance during the polishing process can be effectively reduced. Finally, the selective precision polishing of the medical TC4 titanium alloy was achieved using suitable process parameters. The surface roughness of laser irradiation area Ra decreased from 5.230 μm to 0.225 μm, and Sa decreased from 8.630 μm to 0.571 μm, which is a decrease of 95.7% and 93.4%, respectively. These research findings provide a reference for the precision polishing of titanium alloys or other self-passivating metals.
  • Preparation of Durable Superhydrophobic Coating and Its Anti-icing, Anti-corrosion, and Self-cleaning Properties
    WANG Bo, XIN Lei, ZHANG Kai, GAO Jian, LI Hao, WU Lianfeng
    China Surface Engineering. 2024, 37(2): 238-247. https://doi.org/10.11933/j.issn.1007-9289.20230310002
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    Aluminum alloys are widely used in ships and offshore platforms owing to their high fatigue strength, excellent corrosion resistance, welding performance and cold workability. Although the surface of the aluminum alloy usually forms an oxide film in natural environments, the film is thin and can easily be damaged during application, resulting in damaging the substrate. Therefore, preparing anti-icing, anti-corrosion and self-cleaning superhydrophobic coatings on aluminum alloy substrates is important for improving their performance and expanding their application fields. Superhydrophobic surfaces are with a water contact angle exceeding 150° and a roll-off angle below 10°. Inspired by superhydrophobic surfaces of nature, researchers have successfully prepared and developed various artificial superhydrophobic coatings that can be applied in various fields, such as self-cleaning, anti-corrosion, and anti-icing. To date, many methods for preparing superhydrophobic coatings with micro-nano structures and low-surface-energy, such as spraying and electrodeposition, have been proposed. However, currently prepared superhydrophobic coatings are highly susceptible to damage because their rough surface morphology is easily damaged by mechanical wear, weak adhesion to the substrate, and poor resistance to harsh conditions, which seriously affects their large-scale application. Therefore, improving the wear resistance of superhydrophobic coatings is an urgent issue. For the micro-nanocomposite structures on superhydrophobic surfaces, the single micron-scale structure protects fragile and functional nanoscale structures because of its ability to withstand more frictional loads than nanoscale structures. Epoxy is a thermosetting resin, and its highly cross-linked three-dimensional network structure endows it with excellent bonding and adhesion performance. The use of sturdy adhesives, such as epoxy resin, to improve the adhesion between the coating and substrate. Moreover, spraying modified micro-nanocomposite particles to create micro-nanostructures is an effective strategy for the large-scale preparation of wear-resistant superhydrophobic coatings. Therefore, in this study, a simple and cost-effective method to prepare a dual-scale durable superhydrophobic coating on an aluminum alloy substrate by one-step spraying of micro / nano mixed particles is proposed. First, an epoxy resin adhesive layer was applied to the surface of the aluminum alloy substrate, after it reached a semi-cured state, a mixed suspension of stearic acid-modified micro SiO2 and nano TiO2 particles was sprayed. After curing, the contact angle between the coating and water was ~155.4° and the roll-off angle was ~3°, indicating excellent superhydrophobicity. The prepared coating surface shows an obvious micro-nanostructures, also modified by low-energy substances, which indicates microstructure and composition conditions for constructing superhydrophobic surfaces. The prepared superhydrophobic coating exhibited strong adhesion on substrate, excellent wear resistance and durability, also with good superhydrophobicity under various tests, including 19 times of tape peeling, 20 cm of sandpaper wear, long-term exposure to ultraviolet light, and droplet testing at different pH. The prepared superhydrophobic coating significantly delayed the freezing time of water in extremely cold weather by approximately eight times that of the substrate. Simultaneously, the synergistic anti-corrosion effect of the epoxy resin and superhydrophobic property caused the prepared coating to exhibit excellent anti-corrosion performance in seawater. In addition, the prepared superhydrophobic coating shows excellent self-cleaning performance, and can be used for the photodegradation of pollutants and purification of water because of the photodegradation performance of TiO2 particles. This simple and environmentally friendly superhydrophobic coating is promised to apply in anti-icing, anti-corrosion and other aspects, and provides a solution for improving the durability of traditional superhydrophobic surfaces.
  • Lubrication Mechanism of MoDDP / CaB Lubricant Additive under Heavy Load, Variable Speed, and Impact Conditions
    WANG Xiaoyong, ZHANG Huifeng, GUO Jiahao, JIANG Yu, JIANG Yuchen
    China Surface Engineering. 2024, 37(2): 248-259. https://doi.org/10.11933/j.issn.1007-9289.20230320001
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    To solve the problem of equipment failure and even safety production accidents caused by lubrication failure under adverse working conditions, and to further enhance the stability and safety of mechanical equipment operation, the anti-wear and friction reduction effect of single and composite lubricant additives of calcium borate (CaB) and molybdenum dialkyl dithiophosphate (MoDDP) under heavy load, variable speed, and impact conditions were investigated. The results show that the organic molybdenum additives can effectively reduce the friction factor and wear spot diameter compared with the base oil. The 1.5 wt.% MoDDP additive exhibited the best friction reduction and anti-wear performance, reducing the friction factor by 41.0% and the wear spot diameter by 48.9% compared to the base oil. Among the four oil samples, the 1.5 wt.% MoDDP / 3.0 wt.% CaB composite lubricant additive showed the best friction and anti-wear effects, reducing the friction factor by 55.0%, 62.7%, and 65.1% and the wear spot depth by 75.8%, 78.8%, and 80.0%, respectively, compared with the base oil at different rotation speeds. With the increase of rotation speed, the friction factor curves of base oil, 2.0 wt.% CaB, and 1.5 wt.% MoDDP fluctuated and the maximum wear spot depth of base oil, 2.0 wt.% CaB, and 1.5 wt.% MoDDP also tended to increase with the rotation speed, while the friction factor curves of 1.5 wt.% MoDDP / 3.0 wt.% CaB composite lubricant were always the most stable. The surface wear spots of the specimens lubricated by 1.5 wt.% MoDDP / 3.0 wt.% CaB composite lubricant at different rotation speeds were uniform, and no significant changes in the wear spot depth were observed, indicating that the rotation speed under heavy load has a slight effect on the friction reduction performance of 1.5 wt.% MoDDP / 3.0 wt.% CaB composite lubricant. The composite lubricant additives exhibited stable and excellent friction reduction and anti-wear performance under heavy loads and variable-speed operating conditions. Under a 50 N impact load, the 1.5 wt.% MoDDP / 3.0 wt.% CaB additive showed the best friction reduction effect, reducing the friction factor by 66.7%. The typical friction factor curves of 1.5 wt.% MoDDP / 3.0 wt.% CaB composite lubricant exhibited the least fluctuation. The 1.5 wt.% MoDDP / 3.0 wt.% CaB composite lubricant additive exhibited the smallest wear spot depth and the smallest increase in depth of wear spot under a 50 N impact load, which can reduce the wear spot depth by 76.5% compared to the base oil. The comparisons of wear spot depth and morphology show that the 1.5 wt.% MoDDP / 3.0 wt.% CaB composite lubricant can play an excellent anti-wear effect under low speed, heavy load, and impact conditions. The MoDDP / CaB composite lubricant additives can generate a metal composite layer containing C-C, Fe2O3, FeB, and MoS2 during the lubrication process. The CaB and MoDDP in the composite lubricant additive can promote each other's reactions and increase the generation of FeB / MoS2 lubricating films. Compared to a single additive and base oil, the composite lubricant additives showed better self-healing performance and synergistic efficacy, forming a lubricating film with a high load-bearing capacity and improving the anti-wear and friction reduction performance of the composite lubricant. The preparation of MoDDP / CaB composite lubricant additives can fully synthesize the stable and excellent lubricating properties of antioxidants, extreme pressure, and wear agents, and the results can provide data and theoretical support for the wide application of composite lubricant additives.
  • Improvement of the Overall Performance of Magnetic Powder Cores by Optimising the Coupling Agent Content
    YU Hongya, YUAN Han, LI Jingzhou, LIU Zhongwu, GUO Baochun, YANG Jianmin, CHEN Rongyin
    China Surface Engineering. 2024, 37(2): 260-268. https://doi.org/10.11933/j.issn.1007-9289.20230420001
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    Magnetic powder cores, also known as soft magnetic composite materials (SMCs), consist of metal magnetic powders coated with an insulating layer formed through a specific pressing process. In engineering applications, magnetic powder cores may be subjected to issues such as cracking, reduced magnetic permeability, and diminished mechanical strength. The insulation coating of the magnetic powder core includes inorganic and organic coatings. Coupling agents, a type of polymer composite additive, have both inorganic and organophilic molecular groups, allowing them to modify the surface of the magnetic powder and serve as a “bridge” between the inorganic and organic coating layers. The gap between academic and industrial research on the cracking and expansion coefficients of magnetic powder cores leads to a poor understanding of the underlying mechanisms. The moldability, magnetic properties, and mechanical properties of carbonyl iron powder (CIP) magnetic powder cores (including magnetic rings, magnetic discs, and molding inductors) with different contents of the KH550 silane coupling agent were investigated in this study. Scanning electron microscopy (SEM), thermomechanical analysis (TMA), and LCR techniques were used for analysis. The SEM images of the magnetic powder core sections indicate that increasing the amount of coupling agent reduces powder agglomeration, which increases the area percentage of the nonmagnetic phase and porosity. With an increase in the coupling agent content, the area percentage of the nonmagnetic phase increased from 18.4% to 31.4%. Notably, the magnetic disc experimental outcomes, influenced by the coupling agent content, thickness, molding pressure, and curing rate, revealed that a higher curing rate, increased thickness, and higher molding pressure made the magnetic discs more susceptible to cracking. However, coupling agents can reduce the cracking tendency of the molding inductors and magnetic rings, thereby enhancing their moldability. The density of the magnetic discs is influenced by both the molding pressure and coupling agent content. When the coupling agent content remains constant, an increase in the molding pressure results in increased density. However, for discs subjected to identical molding pressures, a higher coupling agent content corresponded to a reduced density. Density of the magnetic discs with 0.1 wt.% coupling agent content are abnormal. The TMA showed that the coupling agent can stabilize the resin on the magnetic powder surface and facilitate powder particle rearrangement during curing, thereby increasing the core expansion coefficient. Magnetic powder cores with 0 wt.% and 0.1 wt.% coupling agents have negative expansion coefficients, leading to potential shrinkage and cracking. In contrast, the cores with 0.3 wt. %, 0.5 wt.%, and 0.7 wt.% coupling agents yielded an increased expansion coefficient during resin curing, thereby effectively reducing the core's cracking tendency. However, increasing the coupling agent content can affect the magnetic properties of the core. As the non-magnetic phase and porosity change, the density and magnetic permeability of the magnetic powder core initially increase and subsequently decrease. Similarly, the core loss and quality factors exhibit opposite trends. As the porosity increases, it induces additional coercivity proportional to the square root of the specific pore surface area, consequently leading to increased core loss. The core loss first decreases and then increases, and the quality factor increases before eventually decreasing. This paper also demonstrates that the meshing capability of magnetic powders directly affects their mechanical properties. As the coupling agent content increases, the mechanical strength of the magnetic powder core improves and then declines. Given the moldability of the core and other characteristics, the ideal coupling agent content is 0.3 wt.%. This study explored the effect of the coupling agent on the expansion coefficient of magnetic powder core during curing and unveiled its influence on other properties, laying a robust theoretical foundation for the application of high-performance magnetic powder cores.
ISSN 1007-9289　CN 11-3905/TG
Supervised by: China Association for Science and Technology
Sponsored by: Chinese Mechanical Engineering Society
Edited and Published by: Editorial Office of China Surface Engineering
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