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15 June 2024, Volume 57 Issue 6
  
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  • XIONG Fanqi, JIE Xiaohua, LU Jing, SUN Chengchuan, DENG Bixin
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    In order to improve the wear and corrosion resistances of magnesium alloys and broaden their application areas, a layer of Al-20%(mass fraction) Al2O3(abbreviated as Al-Al2O3) coating was firstly deposited on the surface of the magnesium alloy substrate by cold spraying method as the transition layer of the composite coating, and then an Al2O3-13%(mass fraction) TiO2(abbreviated as AT13) surface layer was prepared on its surface by atmospheric plasma spraying method, thereby obtaining an Al-Al2O3/AT13 composite coating. Subsequently, the surface and cross-sectional morphology of the transition layer and surface layer were analyzed by scanning electron microscopy, and the microhardness and bonding strength of the composite coating were measured using a microhardness tester and a universal testing machine. Moreover, the friction coefficient and wear rate of the composite coating were measured by a friction and wear tester, and the corrosion behavior of the composite coating in a 3.5%(mass fraction) NaCl solution was investigated through dynamic potential scanning technology. Results showed that the microhardness of the Al-Al2O3 transition layer and the AT13 surface layer were(42.3±13.7) HV0.1 and(838.8±87.6) HV0.1, respectively, and the bonding strength of the Al-Al2O3/AT13 composite coating was 31.2 MPa. Additionally, the stable friction coefficient and wear rate of the composite coating were 0.74 and 5.94×10-5 mm3/(N·m) under a load of 40 N and a wear condition of 10 min, and compared with the magnesium alloy substrate [1.89×10-4 mm3/(N·m)], the wear rate was reduced by 68.6%. After being immersed in a 3.5% NaCl solution for 30 min, the corrosion potential of the composite coating was-927 mV, and the corrosion current density was 1.81×10-5 A/cm2. Compared to the magnesium alloy substrate, the corrosion potential increased by 742 mV, and the corrosion current density decreased by an order of magnitude.
  • ZHANG Pu, CAO Silong
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    To address the issue of wear failure in Inconel 718 nickel-based alloy under wide temperature conditions, two different contents of Al2O3+TiO2 particles(10%, 20%, mass fraction) were selected as ceramic reinforcement phases. Two types of Inconel 718-MoS2-Al2O3-TiO2 high-temperature wear-resistant lubricating composite coatings were prepared using laser cladding technology. The microstructure, mechanical properties and tribological behavior of the composite coatings were systematically investigated to provide data support for their application in the field of tribology. Results showed that the composite coatings were primarily composed of γ-Ni solid solution, γ'-Ni3(Ti, Al) intermetallic compounds, Ti3O5 and Al2O3 ceramic reinforcement phases, as well as MoS2 lubricating phase. When the content of TiO2 and Al2O3 reached 20%, higher levels of Ti3O5 and Al2O3 contributed to increased hardness and elastic modulus of the coatings, with a maximum microhardness of up to 455 HV0.3. However, this led to coarser grains of Ti3O5 and Al2O3 phases, which were unfavorable for enhancing the elastic modulus and resistance to plastic deformation. At friction temperatures ranging from room temperature to 200 ℃, the friction coefficient and wear rate of the composite coatings with 10% TiO2 and Al2O3 content significantly increased, reaching maximum values. Wear mechanisms were mainly attributed to abrasive wear and delamination. As the temperature increased to 400 ℃, the formation of a continuous oxide film on the coating abrasion surface led to a significant reduction in wear rate. When the temperature reached 600~800 ℃, both types of composite coatings formed continuous smooth oxide films on the friction surfaces, exhibiting lubricating effects and significantly improving tribological performance, especially with a reduction in wear rate by one order of magnitude compared to Inconel 718 alloy coatings. When the content of TiO2 and Al2O3 reached 20%, the composite coatings demonstrated superior tribological performance at intermediate to high temperatures. A comparative analysis revealed that the Inconel 718-MoS2-Al2O3-TiO2 composite coatings exhibited better tribological performance than Inconel 718 alloy coatings across temperatures ranging from room temperature to 800 ℃.
  • ZHANG Peng, BAI Guangya, NI Xiangping, LI Yuhuan, CHEN Jingyuan, PENG Zheng, YANG Chenggang, LIU Kang, ZHANG Lin, YAN Han, LIN Xiuzhou
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    The superhydrophobic coating can effectively prevent the intrusion, adhesion and condensation of water-containing corrosive media on the surface. However, the poor mechanical and chemical stability of traditional superhydrophobic coatings significantly limits their application in complex and harsh environments. In this study, a superhydrophobic PDMS-EP@SiO2-GO coating was formed on the surface of Q345 steel sheets by using a composite substrate of graphene oxide(GO) and nano silicon dioxide(SiO2) with polydimethylsiloxane(PDMS) and epoxy resin(EP), combined with spraying technology. The superhydrophobic, self-cleaning, anti-fouling, mechanical wear resistance, chemical corrosion resistance and anti-corrosion properties of the coating were studied. Results showed that the water contact angle of PDMS-EP@SiO2-GO was 166.57°, and the sliding angle was less than 3°. Due to the strengthening effect of GO on the coating substrate, the coating maintained a contact angle of more than 155° for liquids with water temperatures ranging from 20 ℃ to 100 ℃ and a contact angle of more than 160° for acidic/alkaline solutions. The sliding angle was less than 4° under the above conditions. After sandpaper friction(total friction length of 40 m) and 30 cycles of tape-peeling tests, the coating still exhibited good superhydrophobic ability, with the contact angle remaining above 152°. In addition, PDMS-EP@SiO2-GO, with excellent water resistance, demonstrated good anti-fouling and self-cleaning properties. In terms of corrosion protection, the lowest frequency impedance of PDMS-EP@SiO2-GO increased by an order of magnitude, and the charge transfer resistance increased by two orders of magnitude, showing excellent corrosion resistance. PDMS-EP@SiO2-GO addressed the problem of weak mechanical and chemical stability in traditional superhydrophobic coatings and enabled the persistent protection of the metal substrate. The as-prepared superhydrophobic coating, with good practicability, contributes to the safe and reliable service of mechanical equipment throughout its life cycle.
  • PANG Sheng, HE Xin, SHANG Ting, LIU Chao, CHENG Xuequn
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    The low-aluminum and low-magnesium Zn1.5Al1.1Mg hot-based Zn-Al-Mg alloy coated plate was employed as research object, the initial corrosion mechanism of the cut edges of low aluminum, low magnesium Zn-Al-Mg alloy coated plates was clarified by SEM, EDS, XRD and other methods. Moreover, through SEM and XRD method, the types and morphology of corrosion products at the cut edges of the specimens after immersion and cyclic corrosion experiments were analyzed for evaluating the protective performance of Zn-Al-Mg alloy coatings on their cut edges. Results showed that the cut edge of the Zn-Al-Mg alloy coating was composed of three microstructures: pure Zn phase, Zn-MgZn2 binary eutectic and Zn-MgZn2-Al ternary eutectic. In general, the ternary eutectic and binary eutectic containing MgZn2 phase served as corrosion initiation points during the initial corrosion stage of Zn-Al-Mg alloy cut edges, and then extended to the entire coating. During the long-term corrosion process of cutting edges in Zn-Al-Mg alloy coatings, the Zn element played a major protective role. Specifically, free Zn2+ accumulated at the cutting edge of the coating by forming basic zinc carbonate [Zn5(OH)6(CO3)2] and basic zinc chloride [Zn5(OH)8Cl2·H2O], hindering the longitudinal expansion of the corrosive medium. Nevertheless, when these precipitates transformed into porous ZnO, the protective capabilities of the coating failed, and the cut edge was damaged.
  • WANG Liyuan, ZHANG Jingchun, SUN Erju, LYU Xiaohui, WEI Enze, WENG Hengzhi, WANG Zhiyi, LU Yi
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    In order to improve the corrosion resistance of welded joints of Titanium(Ti) alloy, using TA2 welded joints as the substrate, a combination of micro-arc oxidation and low-energy modification methods was used to prepare superhydrophobic coatings in the base metal zone, weld zone and heat affected zone, respectively. The microstructure, morphologies and chemical composition of the sample were characterized by metallographic microscopy, scanning electron microscopy(SEM), X-ray diffraction(XRD) and Fourier transform infrared spectroscopy(FTIR). Moreover, the corrosion resistance of the sample in a 3.5%(mass fraction) NaCl solution was tested by electrochemical impedance spectroscopy(EIS). Results showed that the substrate treated by micro-arc oxidation obtained a brain shaped micron groove structure, and its phase composition became anatase type TiO2. After low-energy modification, the water contact angles of the three regions were 154.5°, 152.3° and 153.6°, and the rolling angles were 2.9°, 4.4° and 3.2°, respectively, which exhibited good superhydrophobicity. In EIS testing, the capacitance arc radius of superhydrophobic coatings was the largest, followed by micro-arc oxidation coatings. Both types of which improved the corrosion resistance of the substrate. Among them, the charge transfer resistance of the superhydrophobic sample in the heat affected zone increased by nearly 7 times compared to the substrate, exhibiting the optimal corrosion inhibition performance.
  • MA Changshuai, RAN Changrong, FU Jiangkang, WANG Yunhou, GUO Taixiong, ZHANG Qianfeng
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    For exploring the effect of thiourea on the corrosion resistance of waterborne acrylic resin organic silane composite passivation film on Zn-Al-Mg coating, an aqueous acrylic resin-organosilane was used as the main film-forming material, and different contents of thiourea were added to formulate a chromium-free passivate solution for the composite passivation of Zn-Al-Mg coatings. The particle size of thiourea was measured by Nano ZS90 nanoparticle size analyzer, and the structure of thiourea was tested by Nicolet 6700 Fourier transform infrared spectrometer(FTIR). In addition, the corrosion resistance of the composite passivation film was analyzed through full immersion test, electrochemical test and neutral salt spray test, and the effect of thiourea content on the corrosion rate of the composite passivation film was explored. Results showed that thiourea possessed an inhibitory effect on the corrosion resistance of Zn-Al-Mg coatings, but too much thiourea could lead to a decrease in the corrosion inhibition of the passivation film. Compared with three different addition amounts of thiourea, the corrosion resistance of the Zn-Al-Mg coating was optimal when the mass fraction of thiourea in the passivation solution was 0.5%. Furthermore, thiourea and waterborne acrylic resin organic silane underwent cross-linking, and after corrosion, they formed a complex with metals, forming a dense network structure, which improved the density of the film layer and reduced the corrosion rate of the film layer.
  • WANG Xiu, LI Qiankun, WANG Jihu, LI Hui, WU Yuandong, WEN Shaoguo, MEI Dajiang
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    In order to investigate the effect of filling different masses of inorganic filler CeO2-ZrO2-Al2O3(CZA) powder on the anticorrosive and mechanical properties of acrylic coatings, CZA powder samples were synthesized by drying and calcination using the co-precipitation method. The obtained CZA powder was fully dispersed in acrylic resin with commonly used dispersants, defoamers and other additives available in the market, and the acrylic anticorrosive coatings with different mass fractions were prepared on treated iron plates by the scraping method. Meanwhile, the XRD, SEM and EDS methods were used to analyze the physical phase of the CZA powder samples, and the mechanical property tests and electrochemical anticorrosion property tests were utilized to evaluate the characteristics of the coatings, such as adhesion, hardness, roughness, bending performance, wear resistance, tensile strength, elongation at break and anticorrosion performance. Results showed that the as-prepared CZA powders were solid solutions and showed a tetrahedral structure. After adding CZA powder, the hardness of the coating increased from HB to 1H, the bending properties were all 1T, wear resistance was improved, and adhesion was all grade 1. CZA increased the anticorrosive properties of the coatings compared to acrylic anticorrosive coatings without CZA addition, and the best anticorrosive properties of the coatings were obtained when the mass fraction of filler addition was 10%. Overall, the acrylic anticorrosive coating had certain anticorrosive properties and could effectively prevent the corrosion of corrosive media on the material, which presented certain application prospects in the field of anti-corrosion in the future.
  • WU Mengting, ZHU Zhiping, CAO Jie, TANG Tian, SHI Xiyao
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    For investigating the microbial corrosion behavior of water supply pipelines in thermal power plants using regenerated water as the water source, a circular biofilm hanging plate reactor was used to dynamically simulate the operation status of the regenerated water pipeline. The influence process and mechanism of iron bacteria(IOB), sulfate reducing bacteria(SRB) and their mixture on the corrosion of Q235 steel were studied by measuring the pH value and conductivity of the solution, weight loss of the specimen, electrochemical parameters(such as redox potential, polarization curve, AC impedance), bacterial count, and combining SEM, EDS, XRD and other methods. Results showed that the number of two types of bacteria increased over time, and the pH value of the regenerated water first decreased and then increased, while the conductivity steadily increased. Furthermore, the number of bacteria in the environment was positively correlated with the corrosion rate of pipes at this time, and SRB were the main bacterial species that affected microbial corrosion. Through EDS and XRD analysis, it was found that the main components of corrosion products varied in different environments: the corrosion products during IOB process were mainly FeOOH, with a small amount of Fe2O3 and Fe3O4; the main corrosion products during SRB process were iron oxide and iron sulfide; When SRB+IOB coexisted, the main corrosion products were Fe2O3, Fe3O4 and FeS. Besides, the microbial film and corrosion products generated on the surface of the pipeline in the early stage would inhibit the corrosion of Q235. In the later stage, the deactivation of the microbial film and the detachment of the covered corrosion products would accelerate the corrosion.
  • LI Yizhi, LIU Jingzhou, DIN Zishan, JIANG Xiaohui, GUO Weicheng, JU Pengfei
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    In order to investigate the effect of different substrate surface roughness on the friction and wear properties of amorphous carbon films, and improve the tribological properties of the 2Cr13 sample surface under 601EF lubricating grease lubrication, the methods such as machining, polishing and other techniques were employed to prepare different surface roughness on the surface of 2Cr13 samples. Subsequently, amorphous carbon thin films were prepared on the surface of samples with different roughness by magnetron sputtering. The friction and wear properties of amorphous carbon films and silicon nitride balls under 601EF lubricating grease lubrication were investigated through ball-disc contact friction and wear tests, and the wear places were analyzed by optical microscopy. Results showed that the Si3N4 balls that rubbed against the substrate surface all presented a clear platform, while the substrate surface did not display any obvious grinding marks. The samples with the Ra range of 0.20~0.75 μm on the coupling ball had the smaller wear amount, the wear spot area range was 0.152~0.165 mm2, and the wear form was adhesive wear. By contrast, the samples with the Ra range of 0.95~3.19 μm had more wear amount on the coupling ball, the wear spot area ranging from 0.228~0.275 mm2, and there were furrow-like wear marks, which indicated more serious wear. Under the same operating conditions, as the surface roughness of the substrate increased, the starting and average friction coefficients between the two friction pairs, as well as the wear amount of Si3N4 balls, all showed a trend of first decreasing, then increasing, and then decreasing. When the Ra was 0.56 μm, the tribological performance of the amorphous carbon film was the best, and the friction curve was relatively stable, with an average friction coefficient of 0.162, and the wear amount of its coupling ball was the smallest, 0.152 mm2. In general, the surface roughness of the substrate affected the tribological performance of amorphous carbon films, and the surface with good anti friction properties could be obtained by preparing appropriate roughness on the substrate surface via the means of machining, polishing, etc.
  • YUAN Chaoxin, WANG Xiangqian, LIU Bin, QIANG Jin, XIE Mingling
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    Power components under corrosive environmental conditions are subjected to the double damage of corrosion and wear, and the reciprocating action of the load makes the passivation layer on the metal surface fail and accelerates the damage. Amorphous carbon-based films show the excellent protection in the areas of corrosion and friction. For studying the effect of load on the corrosion and wear properties of amorphous carbon-based thin films, and clarifying the relationship of the each loss component with the change of the load, thin films of a-C, a-C:Cr and a-C:Si were prepared on the surface of 304 stainless steel by magnetron sputtering. Meanwhile, the static corrosion behavior of three films under 5.0 mol/L HNO3 was tested by kinetic potential polarization, and the effect of load on each component of the corrosion friction process was also analyzed and studied by combining the wear amounts of the three films under different loads in deionized water and 5.0 mol/L HNO3 environments. Results showed that Si doping reduced the corrosion current density of a-C films from 1.11×10-6 A/cm2 to 3.96×10-7 A/cm2, while Cr doping slightly decreased the corrosion current density. As the load increased, the corrosion damage component of the three films decreased and the mechanical wear component increased accordingly, corresponding to a weakening of the damage effect on the films due to the corrosion-wear interaction.
  • ZHAO Hengrui, HOU Zhengyu, YANG Haiyan, LIANG Shoucai, CHENG Longsheng, WANG Dan, XIE Fei
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    In order to reduce the harm caused by corrosion to the normal operation of offshore oil and gas pipelines, the effects of the synergistic effect of Cl- and SO42- on the corrosion behavior of 316L stainless steel in the simulated South China Sea marine environment were investigated through the AC impedance technique and the cyclic polarization technique in electrochemical tests, and the corrosion morphology of 316L stainless steel surface was characterized by scanning electron microscopy(SEM). Results showed that when the SO42- content was constant, an increase in Cl- content could reduce the capacitive arc radius, polarization resistance Rp and pitting potential Eb. As the Cl- content increased from 0 to 50 g/L, significant corrosion was observed on the surface of 316L stainless steel. When the Cl- content was constant, an increase in SO42- content reduced the capacitive arc radius, Rp and Eb values. At the same time, the diameter of the corrosion pit on the surface of the specimen expanded, and the depth gradually deepened.
  • HU Zongwu, XING Rui, LU Lifeng
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    Erosion wear is a kind of material wear phenomenon caused by the interaction between solid surface and fluid containing solid particles with a certain velocity, which exists widely in industrial production and is an important reason for failure and damage to many mechanical devices. Especially under gas-solid two-phase flow conditions, bent pipes suffer from severe erosion wear, greatly reducing their service life and even causing major safety accidents. In order to provide reference for the study of erosion wear and anti-erosion wear of equipment under multiphase flow conditions, this article reviewed the current research status and progress on erosion wear of bent pipes under gas-solid two-phase flow conditions in recent years. Moreover, the main methods currently used to study the erosion wear of gas-solid two-phase flow bends were described, the advantages and disadvantages of commonly used experimental research equipment and numerical simulation methods were summarized emphatically. At last, the prospects for future research on erosion wear of bent pipes under gas-solid two-phase flow conditions were presented.
  • HE Tianyi, WANG Haining, LIANG Haozhe, SONG Junfei, ZOU Hongli, WANG Enze, QIAN Youyu, DONG Wenqiang, XIA Qixing
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    The protection of bronze cultural relics is a difficult point in the protection of metal cultural relics. This paper introduced the mechanism of rust layer and typical bronze diseases of bronze cultural relics under different influence factors, and summarized the research progress of harmful rust prevention strategies of bronze cultural relics by taking powdery rust as the example. On this basis, the development direction of bronze cultural relics protection in the future was put forward.
  • FENG Huanzhi, LIU Zixuan, WU Guangai, YANG Zhile, XING Xijin, WANG Zhu
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    The corrosion environment of offshore carbon capture, utilization and storage(CCUS) is harsher compared to onshore conditions, with pipelines and facilities exposed to marine environments externally and containing supercritical CO2 and corrosive impurities internally. In this paper, the corrosion risks and material selection for offshore facilities in CCUS were reviewed. The corrosion risks of metals included those induced by CO2-H2O phases, gas-phase impurities and Cl-. Material selection for metals mainly involved carbon steel, low-alloy steel and corrosion-resistant alloys, which were chosen according to different CCUS conditions. Additionally, non-metallic materials underwent chemical corrosion and physical degradation in supercritical CO2 environments. Increased permeability and expansion rates, and decreased mechanical properties were observed after supercritical CO2 testing. There was a risk of aging in non-metallic pipelines after long-term service. At present, further improvement was needed in understanding the corrosion failure mechanisms of materials in supercritical CO2 systems. Material selection for CCUS offshore facilities was still immature, especially under complex conditions involving multiple impurity gases, requiring more research to refine the selection system of CCUS offshore facility materials and support the large-scale application of CCUS offshore technology.
  • ZHANG Chao, WANG Cheng, WANG Wei, DANG Lei, JIANG Lihong
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    To improve the wear resistance of the inner wall of hydraulic support columns, Fe-based coatings X1, X2 and X3 were prepared on the inner wall of a hydraulic support column using laser cladding technology with three different Ni-content Fe-based alloy powders. The microstructure, mechanical properties and tribological performance of these coatings were analyzed using metallographic microscope, 3D confocal surface topography instrument, universal testing machine and high-speed reciprocating friction and wear testing machine. Results showed that three coatings were homogeneous and compact, and had good metallurgical bonding with the substrate. The cladding layers were mainly composed of α-Fe with a BCC structure and a(Fe-Cr) solid solution, with the formation of a(Fe-Cr-Ni) phase in the X2 and X3 cladding layers. Among the three coatings, the tensile strengthes of X1, X2 and X3 were 563, 597 and 470 MPa, respectively, with X2 having the highest tensile strength. The wear rates of the three coatings were all lower than that of the substrate, with the wear rate of the substrate being approximately eight times that of the X2 coating. The wear mechanism of the substrate was primarily dominated by adhesive wear and abrasive wear, while the wear mechanism of the coatings was mainly abrasive wear.
  • MA Chuang, WANG Zhen, WANG Xinyu, FENG Zenghui, WANG Xingli, LIU Lanxuan
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    In order to obtain coatings with low emissivity, most studies focus on the screening of resin and filler components. However, the influence of process parameters on emissivity during the coating preparation process was rarely studied, and the interaction between various preparation processes was not analyzed. In this study, aluminum powder was selected as the metal filler and fluorocarbon resin was selected as the adhesive to prepare a low-infrared emissivity coating. Initially, single-factor experiments were conducted to regulate the viscosity of the coating(achieved by varying the amount of diluent added to the coating), the wet film thickness of the coating and the curing temperature. The combined effects of these three process parameters on the distribution of aluminum powder in the coating and the infrared emissivity of the coating were analyzed and studied. The response surface methodology was used to further analyze the interactions between the process parameters, and the optimal combination of process parameters were determined to guide the actual coating preparation process. Results showed that the influence of the three process parameters on the emissivity of the coating decreased in the order of coating viscosity > curing temperature > wet film thickness. When the addition amount of diluent was 78 g, the film thickness was 60 μm, and the curing temperature was 73 ℃, the infrared emissivity of the coating was 0.141 in the band of 3~5 μm and 0.177 in the band of 8~12 μm.
  • WANG Jun, FENG Jun, JIN Fanya, ZHAO Yingchao, YANG Xudong, YUAN Shaohua, QI Huarong
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    For obtaining a thick ceramic coating with good film-forming and wear resistance, a new type of composite electrolyte was composed of sodium phosphate and sodium hexametaphosphate as the basic electrolytes, while sodium tungstate and sodium tetraborate were added as additives. In this composite electrolyte system, micro-arc oxidation treatment was performed on 1060 aluminum alloy. Using the coating thickness and surface porosity as optimization indicators, the electrolyte formula was optimized using the L9(34) orthogonal test. Meanwhile, the microstructure, surface porosity, phase composition, thickness, microhardness and wear resistance of ceramic coatings prepared under this electrolyte formula were studied systematically. Results showed that the ceramic coating prepared with a formula of Na3PO4 concentration of 32.0 g/L, Na2B4O7 concentration of 16.0 g/L, Na2WO4 concentration of 4.5 g/L and(NaPO3)6 concentration of 30.0 g/L had the structure with uniform micropores and dense film layer, the thickness of 22.8 μm, the porosity of 3.86%, and the microhardness of 475 HV. Furthermore, the wear resistance of the coating was significantly improved compared to the substrate, and the ceramic coating were mainly composed of γ-Al2O3 and a small amount of α-Al2O3 composition.
  • LI Shuangyue, CHANG Hui, WANG Junzhe, CUI Fengjing, JIA Bowen, LUAN Shengjia, ZHANG Jia, XU Na, GAO Minghao, CHANG Xinchun
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    In order to prepare metallographic samples that accurately characterize the true state of the analyzed samples and evaluate the microstructure of the coating precisely, taking nano-zirconia coating as the research object, metallographic samples were prepared by using different inlaying methods. The influence of different grinding and polishing process parameters on the microstructure evaluation of the coatings based on orthogonal tests was investigated, and the results were verified by measuring the porosity of coatings through the nano-CT method. Results showed that the method of vacuum cold inlay could significantly reduce the phenomenon of coating particle detachment. The factors affecting the porosity of the coating in order of magnitude were the number of revolutions of the grinding disc during rough grinding, the number of fixture revolutions during rough grinding, the polishing time during rough polishing and the pressure during grinding and rough polishing. The optimized parameters for the grinding and polishing process were 15 N pressure for grinding and rough polishing, 200 r/min for the grinding disc during rough grinding, 50 r/min for the fixture during rough grinding, and 9 min for rough polishing. The porosity of the coating under this process was 4.26%, which significantly reduced the phenomenon of shedding of coating particles and allowed the preparation of metallographic samples that reflected the true microstructure of the coating, thereby achieving the goal of accurately evaluating the performance of the coating. The results obtained by the nano-CT method were consistent with the present method.
  • ZHOU Baiyu, HUANG Renchao
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    In order to improve the surface quality and properties of nickel-phosphorus(Ni-P) coatings, a small quantity of copper sulfate(CuSO4·5H2O) was added to the electroless Ni-P plating solution to prepare Ni-P coatings. The surface morphology, composition and structure of the coatings were analyzed using scanning electron microscopy, energy-dispersive spectroscopy and X-ray diffractometer. The effects of CuSO4·5H2O concentration on the microstructure, surface roughness, glossiness, hardness, wear resistance and corrosion resistance of the coatings were investigated. Results showed that when the concentration of CuSO4·5H2O was 0.1 g/L, the coating exhibited a dense, amorphous nodular structure with the best corrosion resistance. At a concentration of 0.2 g/L, the coating had the best surface quality, high hardness and excellent wear resistance, but a small amount of microcrystalline Ni-Cu solid solution appeared in the coating, leading to decreased corrosion resistance. When the concentration of CuSO4·5H2O exceeded 0.2 g/L, the coating formed a mixed crystalline cauliflower-like structure, and both the surface quality and corrosion resistance of the coating deteriorated with increasing CuSO4·5H2O concentration.
  • ZHANG Jiarui, YE Jun, CHEN Yuhuan, SUN Ming, XU He, LI Maosheng, XU Lishu, YU Lin
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    To replace mineral based lubricants and prepare vegetable oil-based lubricants with good stability, easy degradation and environmental friendliness, trimethylolpropane palmitoleate(TMPTO) was synthesized using natural product palmitoleic acid and trimethylolpropane as raw materials, and acidic cation resin Amberlyst as a heterogeneous catalyst. The effects of preparation conditions on the esterification rate of TMPTO were studied, and the optimal synthesis parameters were determined. The physical properties of TMPTO, including kinematic viscosity, viscosity index and flash point were tested. The structure and thermal oxidative stability of TMPTO were characterized using nuclear magnetic resonance(NMR), fourier transform infrared spectroscopy(FTIR), differential scanning calorimetry(DSC) and thermogravimetric analysis(TG). The anti-wear performance, wettability and anti-aluminum corrosion properties of TMPTO were evaluated using a four-ball testing machine, contact angle goniometer and X-ray fluorescence spectrometer(XRF), respectively. Results showed that under the conditions of a reaction temperature of 180 ℃, a vacuum degree of 0.09 MPa, an alcohol-to-acid molar ratio of 1.0∶3.1, a reaction time of 5 h, and a catalyst amount of 0.2%(mass fraction), the esterification rate of palmitic acid reached 81.53%. After four uses of the catalyst, the esterification rate remained at 81.15%. The synthesized trimethylolpropane palmitoleate had an acid value of only 1.87 mg KOH/g, a high flash point(238 ℃), and exhibited excellent anti-aluminum corrosion performance, wettability, thermal oxidative stability and extreme pressure anti-wear properties: the maximum non-seizure load(PB) was ≤88 kg, and the maximum sintering load(PD) was ≤620 kg.
  • LI Changqi, LIU Lie, HAN Lianghua
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    To investigate the effects of ultra-high power continuous laser cleaning on Q355B steel, an ultra-high power fiber laser was used to clean contaminants such as rust from the surface of Q355B steel. The influence of laser scanning speed and power on the cleaning quality was studied under ultra-high power conditions, and the cleaning efficiency was calculated. Results showed that significant damage was caused to the substrate by the laser when the cleaning speed was below 110 mm/s, and there was still some rust on the surface of the substrate when the speed was above 140 mm/s. At speeds of 120~130 mm/s, the substrate was not damaged, and the rust layer was effectively removed. When the speed was kept constant at 120 mm/s, rust was not completely removed at power levels below 7 500 W, and substrate damage occurred at power levels above 8 500 W. Scanning electron microscopy(SEM) was used to analyze the microstructure of the steel surface before and after cleaning. X-ray diffraction(XRD) and energy-dispersive spectroscopy(EDS) were used to characterize the surface of the workpiece. As the scanning speed increased from 100 mm/s to 150 mm/s and the power increased from 7 000 W to 9 000 W, the iron content on the steel surface after cleaning showed a trend of first increasing and then decreasing, while the oxygen content first decreased and then increased. When the laser power was 8 000 W and the scanning speed was 120 mm/s, the mass fraction of iron on the surface of the cleaned workpiece reached its peak, about 79.25%, and the mass fraction of oxygen reached its valley, about 20.75%. The calculation showed that the highest laser cleaning efficiency could reach 43.2 m2/h. By adjusting the laser power and scanning speed, it was possible to safely and effectively remove surface pollutants from Q355B steel while improving the microhardness of the material surface, thereby achieving ideal and efficient laser cleaning effects.
  • CHEN Shuai, LI Hongfu, LUO Xiaowu, XIAO Huihui, SHI Yanjie, LUO Taixing, LIU Yanming, WANG Chen, LYU Xianghong, CUI Guanglei
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    In order to clarify the mutual interference law and interference protection measures of the cathodic protection system of double-pipe pipelines laid in the same trench, a double-pipe same trench laying pipelines(D219 and D457) in Xinjiang oilfield was taken as a model, the coating breakage rate of D219 pipeline was set to 0.1%, and the coating breakage rates of D457 pipelines were set to 0.1%, 0.5%, 1.0%. Numerical simulation methods were used to evaluate the effectiveness and applicability of different cathodic protection designs and cathodic protection interference protection measures. Results showed that mutual interference of cathodic protection systems existed in the pipeline laying in the same trench with shallow buried anode separate cathodic protection. The interference degree of parallel D219 pipelines was enhanced as the breakage rate of the D457 anti-corrosion layer of the interfering pipeline increased, and equalizing line measures could be applied to reduce the interference effectively. The joint cathodic protection measures with shallow buried anode and equalizing line could eliminate the mutual interference of cathodic protection systems for the same trench laying pipelines. The improvement of cathodic protection effect was more significant when the difference in the breakage rate of the anti-corrosion layer of the same trench double-pipe pipelines was large(0.1% of D219 and 1.0% of D457). For the same trench pipelines under joint cathodic protection measures with deep well anode, the cathodic protection effect was poor when the breakage rate of the D457 anti-corrosion layer was large(1.0%) and the soil resistivity was high(50 Ω·m). The improvement of cathodic protection effect was not significant by equalizing line and sacrificial anode measures. Increasing the output current of the deep well anode combined with equalizing line measures could significantly improve the cathodic protection effect of pipelines laid in the same trench.
  • ZHOU Jun, PENG Sizhou, LIU Shitao, HAN Jielin, XIONG Zihao, LIANG Guangchuan
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    To clarify the corrosion problem of a certain gathering and transportation pipeline in the Daniudi gas field, corrosion rate tests, micro-morphology observations and corrosion product analyses were conducted on the corrosion coupons and corroded pipe sections on-site. The corrosion mechanism of the gathering pipeline in an H2S/CO2 coexistence environment was studied to provide a basis for formulating corresponding corrosion protection measures. Results showed that the average corrosion rate of the corrosion coupon was 0.092 3 mm/a, which was higher than the 0.076 0 mm/a required by the industry standard. The local corrosion rate was 0.157 0 mm/a, the pitting corrosion coefficient was 2.7, and the maximum depth of the corrosion pit on the test piece of the corroded pipe section was 88 μm. The corrosion product film had a loose structure and poor protection performance. The corrosion products mainly contained C, O and S elements, which were much higher than the chemical composition of 20 carbon steel. The corrosion products were mainly composed of FeCO3, FeS and Fe2O3, indicating that the corrosion of the gathering pipeline was mainly caused by CO2 and H2S when encountering humid environments.
  • WANG Chuanping, LYU Xiaoming, ZHANG Hongjie, LIU Junlin, PENG Wanli, LIU Mingming, ZHONG Xiaolin, TONG Xubo
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    The corrosion and perforation failure of the flash evaporation heat exchanger tube bundle in a certain treatment station occurred frequently. Therefore, a composition test was conducted on the external media and corrosion products on the surface of the tube bundle. Results showed that the condensate oil medium in the shell side contained a small amount of water, and there were the high concentrations of Cl-, Ca2+ and HCO3- in the water quality components. A black scale layer was formed on the surface of the tube bundle, with patches of corrosion pits under the scale, indicating severe local corrosion. Based on the analysis of the morphology, elements and compounds of the corrosion products, it was found that the corrosion products were mainly composed of FeCO3, and a chlorine-rich layer was formed on the surface of the tube bundle. Therefore, a corrosion mechanism of synergistic HCO3- and Cl- under scale was established. Finally, an integrity management process for flash evaporation heat exchangers with failure control as the core was established, and targeted risk assessment methods and failure control measures were formed to provide assurance for the safe production of the treatment station.
  • XU Wenfang, HUANG Chaopeng, ZHANG Tao, CHEN Jianhua
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    After 5 a of service, severe cracking occurred at the T-type weld seam between the tube sheet and shell of a low-pressure heater in a certain power plant. The causes of the weld cracking were analyzed by macroscopic inspection, fracture morphology analysis, metallographic structure analysis, energy-dispersive spectroscopy(EDS), chemical composition analysis and hardness testing. Results showed that due to the existence of a hardened martensite structure in the heat-affected zone(HAZ) of the welding, which was sensitive to alkali stress corrosion cracking, and the lack of stress reduction heat treatment of the welded joint, alkali embrittlement occurred in the welding heat affected zone of tube plate, and crack branches propagated and penetrated through the weld, causing equipment failure. The analysis of the failure causes of T-type welded joints is of great significance for the design, manufacture, operation of heat exchangers in similar situations under the same working conditions.