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  • Table of Content
      20 December 2021, Volume 49 Issue 12 Previous Issue    Next Issue
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    MAGNESIUM ALLOY CORROSION AND PROTECTION COLUMN
    Research status of graphene oxide composite coatings on magnesium alloys
    CHEN Yan-ning, WU Liang, CHEN Yong-hua, CHENG Ling, YAO Wen-hui, PAN Fu-sheng
    2021, 49 (12): 1-13.   DOI: 10.11868/j.issn.1001-4381.2021.000291
    Abstract ( 228 HTML( PDF (19911KB)( 211 Citation
    Magnesium alloy has the advantages of low density, good damping and noise reduction and good electrical conductivity. It is the lightest metal structural material in applications. However, they are easily corroded due to the low potential of magnesium alloy electrodes, which limits their wide application in industry. At present, surface coating protection technology is one of the most effective methods to improve the corrosion resistance of magnesium alloys. Graphene oxide (GO) has excellent thermal, mechanical and barrier properties, and has broad application prospects in metal protection. GO-based composite coatings can provide a good physical barrier to corrosive media and have become one of the candidate materials for anti-corrosion coatings. In this article, the solutions were proposed for the limitations of single-component GO nanosheets, such as agglomeration and poor compatibility. The preparation methods, types and corrosion protection research progress of GO composite coatings were mainly summarized and its protection mechanism was analyzed in depth. Finally, the future development trend of GO application of magnesium alloy surface corrosion protection coating were prospected. The preparation methods and types of GO composite coatings on magnesium alloys were mainly described. The research progress and corrosion protection mechanism of GO coating on magnesium alloy were summarized.
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    Research progress in corrosion resistance of biomedical magnesium alloys
    WANG Rong-xiang, HONG Li-xin, ZHANG Xiao-bo
    2021, 49 (12): 14-27.   DOI: 10.11868/j.issn.1001-4381.2021.000292
    Abstract ( 159 HTML( PDF (19404KB)( 146 Citation
    Biomedical magnesium alloys exhibit high specific strength, low density, proper elastic modulus, biodegradability,good biocompatibility and biomechanical compatibility,thus show extensive application perspective in bone fixation and cardiovascular stent.However, fast and nonuniform corrosion of magnesium alloys may easily cause the premature loss of mechanical integrity that restricts their clinical application in load bearing. In this paper, the research progress of magnesium alloys was systematically reviewed from the aspects of corrosion modes, the intrinsic and external factors affecting corrosion resistance, improvement of intrinsic corrosion resistance and surface modification, and the future development trend of corrosion resistance of biomedical magnesium alloys was prospected. On the one hand, the corrosion resistance of magnesium alloys can be improved by means such as low alloying, high purification and fine crystallization. On the other hand, reliable coatings are designed from the aspects of corrosion resistance, antibacterial and drug loading. In addition, corrosion media, flow field, stress and other in-body service factors should be considered comprehensively to study the corrosion degradation behavior and mechanism of magnesium alloy implanted devices.
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    Research progress in effect of alloying elements on corrosion resistance of magnesium alloys
    YIN Ming, SUN Jun-li, BAO Tong-yao, LIU Xiao-da, DU Hua-yun, WEI Ying-hui, HOU Li-feng
    2021, 49 (12): 28-39.   DOI: 10.11868/j.issn.1001-4381.2021.000289
    Abstract ( 129 HTML( PDF (17200KB)( 106 Citation
    As the lightest metal structural materials, magnesium and its alloys have great potential to achieve lightweight products in the future. However, magnesium has a high corrosion sensitivity, and the magnesium hydroxide film formed on the surface is loose and porous with little protection, which leads to its application being limited. How to improve the corrosion resistance of magnesium has become a worldwide problem that restricts its application. Alloying is one of the ways to radically improve the corrosion resistance of magnesium alloys. In this paper, the corrosion mechanisms of pure magnesium and the mechanisms of alloying elements on the corrosion performance of magnesium alloys are described in terms of the influence of alloying elements on the corrosion resistance of magnesium and its alloys. In addition, protection mechanisms produced by alloying elements on magnesium alloys were compiled, and the protection mechanisms and corresponding characteristics of beneficial elements on magnesium alloys were summarized. This can provide some reference for the development of new magnesium alloys and the improvement of the corrosion resistance of magnesium alloys. In addition, this paper contributes to a better understanding of the corrosion behavior of magnesium alloys. At present, there is no magnesium alloys can be as good as aluminum alloys or stainless steels corrosion resistance, so the development of corrosion-resistant magnesium alloys needs further research. This paper provides a theoretical basis for the interaction between elements in magnesium alloys, which can provide ideas for the development of new corrosion-resistant magnesium alloys. The synergy between the elements will have a significant impact on the design, process and performance of new corrosion resistant magnesium alloys, and as the research progresses, it is expected that new corrosion-resistant magnesium alloys similar to "stainless steel" will be constructed.
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    Research progress on corrosion resistance of magnesium alloys in aspect of element solid-solution and precipitation
    JIANG Shi-yu, YUAN Yuan, CHEN Tao, GU Da-chong
    2021, 49 (12): 40-47.   DOI: 10.11868/j.issn.1001-4381.2021.000286
    Abstract ( 127 HTML( PDF (751KB)( 88 Citation
    The solid solution and precipitations of alloying elements can change the chemical potential of the primary phase and the species of the second phase, which can significantly affect the micro-galvanic corrosion behaviors of magnesium alloys. The influence of solid solution and precipitation on corrosion resistance of magnesium alloys was reviewed.Based on the thermodynamics and dynamics analysis, the effect of solution and precipitation behavior on corrosion behavior of common magnesium alloys was summarized.The necessary conditions for a good candidate material of magnesium alloy were pointed out, and the design method for improving the intrinsic corrosion resistance of magnesium alloy was proposed.Future research should focus on reducing the corrosion rate of magnesium alloys and expanding the application range of magnesium alloys by regulating the types and quantities of alloying elements in magnesium alloys.
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    Hydrogen evolution, efficiency and exacerbated galvanic corrosion damage of magnesium alloy anode
    HUANG Ju-feng, SONG Guang-ling
    2021, 49 (12): 48-56.   DOI: 10.11868/j.issn.1001-4381.2021.000287
    Abstract ( 109 HTML( PDF (7406KB)( 139 Citation
    To address the galvanic corrosion issue that is critically limiting the practical application of Mg alloys, the negative difference effect (NDE), anodic dissolution efficiency, and anodic hydrogen evolution were investigated by means of the hydrogen collection, Mg wire array electrode, and surface microanalyses based on the model of monovalent Mg+ dissolution at film breaks. The results show that anodic hydrogen evolution is closely associated with the negative difference effect, while the micro-galvanic process of Mg is not responsible for the low anodic current efficiency, and the secondary effect of dissolved zinc ions can to some degree reduce the anodic current efficiency. The protectiveness of the surface film is the most important factor determining the current efficiency, anodic hydrogen evolution, and galvanic corrosion damage.
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    Corrosion resistance of cold sprayed aluminum/micro-arc oxidation composite coating on AZ80 magnesium alloy
    LI Zhong-sheng, WU Hu-lin, DING Xing-xing, HUANG An-wei, SONG Kai-qiang, ZHAN Qing-qing, CONG Da-long
    2021, 49 (12): 57-64.   DOI: 10.11868/j.issn.1001-4381.2021.000294
    Abstract ( 114 HTML( PDF (9803KB)( 91 Citation
    A layer of pure aluminum coating was prepared on AZ80 magnesium alloy by cold spray, and then a pure aluminum/aluminum oxide composite coating was successfully fabricated on the surface of pure aluminum coating by micro-arc oxidation. The surface and cross-section morphology, composition and phase structure of the coatings were analyzed by scanning electron microscope (SEM), energy spectrometer (EDS) and X-ray diffractometer (XRD). The corrosion behavior of the coatings immersed in 3.5%NaCl(mass fraction) solution for different time (30 min and 7 days) was investigated using potentiodynamic polarization curves and electrochemical impedance spectroscopy. The results show that after 30 minutes of immersion, the corrosion current densities of the pure aluminum coating and the pure aluminum/aluminum oxide composite coating are 3.7×10-6 A·cm-2 and 8.0×10-7 A· cm-2, respectively; after 7 days of immersion, the corrosion current densities are 9.0×10-6 A·cm-2 and 1.8×10-6 A·cm-2, respectively. Both the pure aluminum/aluminum oxide composite coating and the cold sprayed aluminum coating can effectively delay the corrosion of the magnesium alloy substrate. Among them, the corrosion resistance of the micro-arc oxidation composite coating is nearly 5 times of the cold sprayed pure aluminum coating. The further improvement in corrosion resistance is attributed to the excellent physical barrier effect of the micro-arc oxidation ceramic layer.
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    Synthesis of different inorganic anions intercalated layered double hydroxides and ion exchange characteristics
    XIE Zhi-hui, SHU Ya, HU Ting
    2021, 49 (12): 65-71.   DOI: 10.11868/j.issn.1001-4381.2021.000481
    Abstract ( 97 HTML( PDF (5038KB)( 69 Citation
    Layered double hydroxide (LDH) is an emerging material for corrosion protection of magnesium alloys. However, it is still controversial whether interlayer inorganic anions with strong affinity to LDH layers will exchange with corrosion anion Cl-. To solve this problem, three different inorganic anion intercalated MgAl-X-LDHs (X=PO43-, CO32-, and SO42-) were intended to synthesize and ion exchange experiments were carried out. The test results such as SEM and XRD show that PO43-, CO32-, and SO42- successfully enter the spaces among LDH layers to form three different anion intercalated MgAl-X-LDHs. The results of ion exchange experiments show that Cl- can exchange with the intercalated PO43- and CO32- anions in the LDHs when 10 g/L MgCl2 are added into the 3.5%NaCl (mass fraction) solutions, while the exchange process is hard when MgCl2 is not added into the solution. In the case of MgAl-SO42--LDH, regardless of whether the Mg2+ exists or not, the intercalated SO42- anions in the LDHs can be exchanged with high concentration Cl-, and cannot be exchanged with low concentration Cl-. These results provide theoretical guidance for the design and preparation of different types of LDH anticorrosive coatings on magnesium alloys.
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    Research progress in corrosion resistance and biocompatibility of strontium-containing coatings on medical metal surface
    SUN Wen-xin, FAN Li-jun, ZHENG Zhong-yin, ZOU Yu-hong, TIAN Jing-rui, ZENG Rong-chang
    2021, 49 (12): 72-82.   DOI: 10.11868/j.issn.1001-4381.2021.000293
    Abstract ( 102 HTML( PDF (3556KB)( 45 Citation
    With the progress of global population aging and the incidence rate of bone and joint diseases, the demand for bone repair medical metal materials is increasing.Bio-metallic materials include non-degradable (i.e. titanium) and degradable metals (i.e. magnesium and iron). However, metals are insufficient in corrosion resistance and osseointegration, so their surface modification needs to be optimized. It is noted that strontium (Sr) has the effect of promoting osteogenesis and inhibiting osteoclasts, and thus the use of Sr as a modified component is of great significance for improving the activity of bone cells on biomedical metal surfaces. In this paper, the corrosion resistance and biocompatibility of strontium doped coatings on titanium, magnesium and iron in recent years were summarized and compared.This article focuses on the research on improving the osseointegration performance of composite coatings prepared by combining strontium and carriers with good degradability and biocompatibility(such as hydroxyapatite, brushite, etc.) on the surface of titanium alloy, magnesium alloy and iron alloy. Finally, it is believed that the application of strontium-containing coatings on the surface of metal materials has a wide range of prospects, and it was proposed that the combination of strontium and zinc make the metal materials have antibacterial properties while promoting bone repair.It was expected to provide reference for promising clinical applications of strontium-doped coating.
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    Research progress and existing problems of photocathodic protection technology
    CHEN Fan-wei, LIU Bin, JIAN Dong-hui, LIU Si-qi, LIU Shu-hui, XU Da-wei
    2021, 49 (12): 83-90.   DOI: 10.11868/j.issn.1001-4381.2021.000469
    Abstract ( 104 HTML( PDF (1652KB)( 59 Citation
    In this paper, the research status of photocathodic protection in broadening light absorption range, enhancing electron-hole separation rate and conduction efficiency of electrons, and realizing protection in the dark were discussed. Six modification methods were summarized, including modification of conductive polymers, construction of heterojunction, composition with two-dimensional conductive materials, adjustment and control of topography, doping with metal or non-metallic elements and coupling with energy storage semiconductors. The problems,such as short duration of protection in the dark and low repeatability of some experiments, were pointed out. The unsolved technical difficulties, such as overcoming insufficient natural light intensity, the harsh conditions of electrolyte solution and the complexity of photocathodic protection system design, were analyzed. Finally, several solutions to above problems were proposed, such as the development of semiconductor materials driven by natural light, the preparation of colloidal electrolyte and capsule material for storing electrolyte, and the design of photocathodic protection coatings.
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    REVIEW
    Research progress in carbon nanotube/paraffin phase change composites
    DAI Yuan-zhe, TANG Bo, ZHANG Zhen-yu, REN Shou-long
    2021, 49 (12): 91-99.   DOI: 10.11868/j.issn.1001-4381.2020.000515
    Abstract ( 118 HTML( PDF (4947KB)( 130 Citation
    Paraffin phase change composite material (PPCCM) has attracted increasing attention and research from scholars at home and abroad because of its excellent latent heat value and high energy storage density. As an important class of medium and low temperature phase change materials, PPCCM is the first choice to prepare room temperature and low-temperature composite phase change materials. However, the risk of low thermal conductivity and some defects are obstacles for the industrialization of PPCCM. Due to the unique structure of carbon nanotubes (CNTs) with complex coils and excellent thermal conductivity, CNTs is considered as one of the important candidate materials that are expected to improve the thermal performance of PPCCM significantly. Therefore, the combination of CNTs and paraffin has become a hot issue. In this review, according to the current research status of CNTs and PPCCM in the past few years, the preparation, microencapsulation and practical application were systematically summarized. The challenges(complex preparation process, poor stability, few actual evaluation, etc.) and possible research priorities(doping ratio, wettability, economy, etc.) were also discussed.
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    High temperature oxidation behavior of refractory high entropy alloys NbMoTaWTi/Zr
    WANG Xin, WAN Yi-xing, ZHANG Ping, SHAN Cai-xia, XIE Ying-ying, LIANG Xiu-bing
    2021, 49 (12): 100-106.   DOI: 10.11868/j.issn.1001-4381.2020.000917
    Abstract ( 139 HTML( PDF (23447KB)( 111 Citation
    Refractory high entropy alloys NbMoTaWTi and NbMoTaWZr were prepared by vacuum arc melting.The microstructure and component distribution characteristics were analyzed, and the dynamic behavior during room temperature to 1500℃,as well as the isothermal oxidation behavior at 1200℃ were studied. Results reveal that NbMoTaWTi mainly consists of single body-centred cubic (BCC) phase, and NbMoTaWZr is composed of BCC and Zr-rich phases.These two alloys are both seriously oxidized above 700℃. Comparatively, NbMoTaWTi alloy is superior to NbMoTaWZr in antioxidation below 1300℃.For both two alloys, the oxygen diffusion inward mainly occurs during isothermal oxidation at 1200℃ and catastrophic oxidation takes place after 3 h. The Ti and Zr addition cannot cause selective oxidation. Although these two elements form a composite oxide layer with other refractory metal oxides, the density and the ability to prevent oxidation is not enough.
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    Friction and high temperature oxidation resistance of laser cladding NiCrCoAlY-Cr3C2 composite coating on TC4 titanium alloy
    QIN Xin, QI Wen-jun, ZUO Xiao-gang
    2021, 49 (12): 107-114.   DOI: 10.11868/j.issn.1001-4381.2020.000989
    Abstract ( 101 HTML( PDF (11682KB)( 58 Citation
    In order to improve the surface friction,wear and high temperature oxidation resistance of TC4 titanium alloy, NiCrCoAlY+20%(mass fraction) Cr3C2 mixed powder was selected as the cladding powder to prepare NiCrCoAlY-Cr3C2 composite coating on the surface of TC4 titanium alloy by using laser cladding technology. The microstructure and phase composition of the coating were analyzed by OM, SEM, XRD, EDS, etc.The microhardness of the coating was measured by HXD-1000TB tester. MMG-500 three-body wear tester and WS-G150 smart muffle furnace were used to test the friction,wear and high temperature oxidation resistance of the coating and substrate. The results show that the laser cladding technology can be used to prepare the good composite coating on the surface of TC4 titanium alloy without cracks and pores. The microstructure of the cladding zone is dense, mostly needle-like crystals and dendrites.The microstructure of the bonding zone is mainly composed of planar crystals, cellular crystals and dendrites, which generates a variety of products including the carbides, oxides and intermetallic compounds that can improve wear resistance and high temperature oxidation resistance. The maximum microhardness of the composite coating is 1344HV, which is about 3.8 times of the 350HV of the titanium alloy substrate.The friction factor of the composite coating is 0.2-0.3, which is significantly lower than the friction factor of the titanium alloy substrate of 0.6-0.7. Under the same conditions, the wear mass loss of the composite coating is 0.00060 g, which is 0.9% of that of 0.06508 g of titanium alloy substrate. After oxidation at 850℃ for 100 h, the oxidation mass gain of the composite coating is 6.01 mg·cm-2, which is about 24% of that of 25.10 mg·cm-2 of titanium alloy substrate. Laser cladding technology effectively improves the friction and wear performance and high temperature oxidation resistance of the TC4 titanium alloy surface.
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    Effect of CO-SCR by CTAB modified vanadosilicate molecular sieve on low temperature catalytic denitrification
    HE Han-bing, FU Guo-you, ZHANG Li, ZENG Jing, WANG Yu-si, LONG Hong-ming, FAN You-qi, ZHENG Ya-jie, MA Ying
    2021, 49 (12): 115-122.   DOI: 10.11868/j.issn.1001-4381.2020.001076
    Abstract ( 102 HTML( PDF (11310KB)( 54 Citation
    To improve the NO-CO low-temperature selective catalytic reduction (SCR) denitration rate, finding new effective denitration catalysts has become the focus of the denitration field. A vanadium-substituted molecular sieve AM-6 was synthesized by hydrothermal method, the performance of AM-6 molecular sieve was improved by surfactant-assisted synthesis. The effect of different amounts of CTAB on the morphology, composition and the catalytic reduction performance was studied. These catalysts were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The results show that the addition of CTAB does not introduce other impurity elements. When the ratio of CTAB to V is 1:4, AM-6(1/4CTAB) has more regular surface morphology, better crystalline formability, well-balanced ratio of V5+/V4+,and the denitrification activity reaches 81.54% at 150℃, which is reduced by 50℃ than the temperature at which the denitrification activity of AM-6 reaches 80%.
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    Multi-scale modification of aerospace silicone rubber damping material with wide temperature range
    MI Zhi-an, LI Xue-kuan, ZHAO Yan
    2021, 49 (12): 123-129.   DOI: 10.11868/j.issn.1001-4381.2021.000856
    Abstract ( 101 HTML( PDF (2609KB)( 52 Citation
    Silicone rubber has stable performance in a wide temperature range. However, as its damping factor in the effective damping temperature range is small and the damping performance is limited, multi-scale modification is required. Firstly, the molecular scale modification was carried out, and the molecular structure was adjusted by changing the vinyl content and the addition amount of alkylhydrosilane. The results show that the growth of the vinyl side chain and the successful grafting of the alkyl hydrogen silane on the vinyl side chain increase the barrier of motion of the molecular chain and enhance the damping performance of the silicone rubber. When the vinyl content is 15%(mass fraction,the same as below) and the molar ratio of hydrosilane to vinyl is 3:1, silicone rubber exhibits the best damping performance. On this basis, the micro-scale modification was continued. The results showed that adding phenyl hydrogen-containing silicone oil improved energy absorption efficiency because of the synergistic effect of forming π-π strong interaction bonds and increasing relaxation time. When the damping agent is added at 2%, silicone rubber exhibits the best damping performance. The effective synergy of molecular scale and micro scale significantly enhances the damping performance of silicone rubber, and the multi-scale modification strategy is suitable for preparing damping silicone materials with wide temperature range.
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    Preparation and property on seawater-degradable Fe3O4@PVA/PLGA composite films
    LI Meng-juan, HAN Rong, ZHANG Jing-ya, XU Yong-zheng, HUANG Meng-yuan, GONG Hao-tian, WU Cai-qin
    2021, 49 (12): 130-138.   DOI: 10.11868/j.issn.1001-4381.2020.001014
    Abstract ( 87 HTML( PDF (6927KB)( 63 Citation
    Fe3O4@PVA microcapsule catalyst with dissolution as trigger condition was synthesized by utilizing nano Fe3O4 catalyst as core material and water-soluble polyvinyl alcohol as shell material. The microcapsule catalyst was loaded in poly(lactic-co-glycolic acid)(PLGA) membrane to prepare the freshwater/seawater degradable Fe3O4@PVA/PLGA composite films.Transmission electron microscopy (TEM) and dynamic light scattering (DLS) particle size distribution were used to test the morphology of Fe3O4@PVA. The shell thickness of Fe3O4@PVA core-shell particles is 2-3 nm. The structural characteristics, magnetic and mechanical properties of Fe3O4@PVA core-shell particles and Fe3O4@PVA/PLGA composite membrane were determined by FTIR, XPS, TG, VSM and electronic universal material tests. The degradation properties of Fe3O4@PVA/PLGA composite films in freshwater, seawater, air, darkness and low temperature environments were discussed. The results show that the maximum degradation ratio of Fe3O4@PVA/PLGA composite films is 97.79% at 120 days in seawater and 99.75% at 120 days in freshwater. Fe3O4@PVA/PLGA composite films are degraded in the seawater and the mass average molecular weight decreases from 28440 to 1396.
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    Preparation and lithium storage properties of poly (Schiff base)/carbon nanotubes composites
    HU Xiu-ying, MAO Chong-chong, HE Chang, CAO Zhi-xiang, DING Yi-ming, BAO Ke-yan
    2021, 49 (12): 139-146.   DOI: 10.11868/j.issn.1001-4381.2021.000275
    Abstract ( 89 HTML( PDF (8438KB)( 30 Citation
    In order to solve the problem of capacity reduction of Schiff base monomer in lithium-ion batteries due to the dissolution of active substances, the Schiff base polymer(PI) with C N bond was prepared by one-step condensation method using p-benzaldehyde and p-phenylenediamine as raw materials. Poly(Schiff base)/carbon nanotubes(PI/CNTs) composites with high conductivity were prepared by doping carbon nanotubes(CNTs). The composition, structure, micro morphology and electrochemical properties of the prepared materials were analyzed by using FT-IR, SEM, XRD, TG, XPS and electrochemical workstation. The results indicate that the PI/CNT material with 5%CNTs(mass fraction) is a three-dimensional frame structure, and shows excellent electrochemical performance. The first specific capacity of PI/CNT-3 material is 209.9 mAh·g-1. After 200 cycles, the cycle retention rate is 60.5%. When the rate of charge and discharge is 0.1 C, 0.2 C, 0.5 C, 1 C and 0.1 C, the specific capacity of PI/CNT-3 electrode materials is 182.4, 150.8, 129.8, 101.3 mAh·g-1 and 156.4 mAh·g-1 respectively, which has good cycle stability and rate performance.
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    Mechanical properties of polycarbonate under intermediate strain rates compression
    WANG Bo-lun, WANG Tao, XIANG Ning, GE Yong, LANG Jian-lin, SUN Qi-wei, CHEN Yu-hong, YAN Yue
    2021, 49 (12): 147-155.   DOI: 10.11868/j.issn.1001-4381.2020.000841
    Abstract ( 78 HTML( PDF (9040KB)( 42 Citation
    A high-speed hydraulic servo testing machine was used to carry out intermediate strain rate compression test of polycarbonate, and comparative experiments of low and high strain rate compression were carried out to verify the validity of the intermediate strain rate compression test. Based on the true stress-strain curves at various strain rates and temperatures, the mechanical properties of polycarbonate under compression at intermediate strain rates were obtained. The results show that polycarbonate undergoes four stages of elastic deformation, yielding, strain softening and strain hardening in intermediate strain rate. The strain rate and temperature dependence of material manifest as:yield strength and yield strain are increased with the enhancement of strain rate or reduction of temperature. On the contrary, when increasing temperature or reducing strain rate, the strain softening of the material are more apparent. Based on the experiments, a ZWT nonlinear viscoelastic constitutive model which can describe the compression process of polycarbonate in intermediate strain rates was constructed. This model can provide strong support for the structure design of transparent parts and the simulation of bird strike.
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    Orientation morphology evolution and mechanical properties of injection molded thermoplastic polyurethane
    XIANG Ning, ZHANG Xiao-wen, GE Yong, DING Yao, ZHENG Meng-yao, YAN Yue
    2021, 49 (12): 156-163.   DOI: 10.11868/j.issn.1001-4381.2021.000121
    Abstract ( 75 HTML( PDF (5095KB)( 36 Citation
    The effects of melt flow on the orientation evolution, residual stress and mechanical properties of thermoplastic polyurethane (TPU) during injection molding were studied by birefringence, small angle X-ray scattering (SAXS) and wide angle X-ray scattering (WAXS). The birefringence results show that the residual stress is decreased along the melt flow direction. The hard segments of TPU molecular chains are oriented along the melt flow direction, while the hard domains are oriented perpendicular to the melt flow direction according to the results of SAXS and WAXS. The tensile properties of TPU parts show obvious differences along the melt flow direction and perpendicular to the melt flow direction. The tensile strength of the middle region of the part is the highest because the orientation degree of hard segment and hard domain is the highest in the middle region of the part, and the orientation of hard segment and hard domain is helpful to improve the tensile strength.
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    Tensile fatigue properties of composite/metal bolted joints with 3-pin and sleeves
    AN Zi-qian, SHU Mao-sheng, CHENG Yu-jia, GUO Xin, CHENG Xiao-quan
    2021, 49 (12): 164-174.   DOI: 10.11868/j.issn.1001-4381.2021.000180
    Abstract ( 96 HTML( PDF (27248KB)( 80 Citation
    Countersunk bolt joints with sleeves have been used in composite connection structures, and their fatigue performances need to be studied. Based on the experimental investigation conducted on the single lap CFRP/titanium alloy bolted joint with 3-countersunk head bolt and sleeves, the fatigue models of composite laminates and metal structures were established to analyze the fatigue performances of the structure, and finite element analysis on joints without sleeves was also carried out to study the influences of the sleeves on fatigue performance of the joint. The results show that the use of sleeves can more effectively improve the fatigue performance of the joint compared to that only using interference fit. The fatigue life of laminate is increased by about 3.6 times, the titanium alloy plate increased by about 2.7 times, and the bolts are increased by about 14 times. Only the titanium alloy plate of the joint fails, but not the fastener. Combined with analysis on the experimental results, it is found that the fatigue failure mode of bolted joints structure will change with different load levels due to the different fatigue properties between composite materials and metal materials; and the metal structure is prone to be damaged under a certain load level.
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