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      20 November 2020, Volume 48 Issue 11 Previous Issue    Next Issue
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    Photocatalysis Column
    Research status of volatile organic compounds treatment technology
    Xue-ping DAI, Yan WANG, Xiao-feng XIE, Jing SUN
    2020, 48 (11): 1-8.   DOI: 10.11868/j.issn.1001-4381.2019.000275
    Abstract ( 583 ( PDF (1336KB)( 451 Citation

    With the increasing emission of volatile organic compounds (VOCs), the environmental problems become serious. The VOCs treatment technology is the research hot point of environmental protection. The research progress of decomposition, recycling and combination methods of VOCs treatment technology was reviewed. The traditional decomposition technology is the main method for the degradation of industrial VOCs due to its low cost, maturity, high yield, and efficiency. The emerging technology will be a research hotspot for its high purification efficiency and no secondary pollution and low powder, especially novel decomposition technology. Finally, the combined technology can break through the limitation of a single technology and purify the multi-component VOCs in the end-of-line by synergistic effect.

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    Research progress in photocatalytic degradation of chemical warfare agents
    He-xi LI, Jing-fei CHEN, Cong LU, Xiu-wen QU, Feng-shun XIANG
    2020, 48 (11): 9-24.   DOI: 10.11868/j.issn.1001-4381.2020.000422
    Abstract ( 654 ( PDF (2828KB)( 365 Citation

    The rapid development of photocatalytic technology has attracted attention in the field of decontamination of chemical agents (CWAs). Owing to high-efficiency, broad-spectrum, and environmentally friendly features, photocatalytic technology can overcome many problems encountered by traditional decontamination technology, such as the problem of soil corrosion, and is suitable for the degradation of CWAs. Researchers have conducted a lot of researches on this, and there are also related reviews to discuss in detail the mechanism and application of photocatalytic degradation of CWAs. However, there are many pieces of literature on traditional photocatalytic materials, and few have summarized the mechanism and application of new photocatalytic materials in the degradation of CWAs. Therefore, in this paper, the mechanism of photocatalytic degradation of CWAs, species of photocatalytic materials, the application of photocatalytic degradation of CWAs, especially the researches of new photocatalytic materials, such as metal-organic frameworks, degradation agents were summarized in detail. Photocatalytic technology has advantages over other technologies in the treatment of low-concentration, refractory CWAs. However, the research is still in the laboratory stage and is mostly simulated agent experiments. There are still obstacles when applied to the degradation of real CWAs. In the future, wearable photocatalytic protective materials may be worthy of further research. At the same time, photocatalytic technology has proved to have certain potential in the large-scale destruction of poisons.

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    Structural and photocatalytic properties of rice granular CaIn2O4/In2O3 fabricated by electrospinning
    Qin-ku ZHANG, Da-wei HU, Fan-liao YAN, An-zhi ZUO, Qiang ZHAO
    2020, 48 (11): 25-31.   DOI: 10.11868/j.issn.1001-4381.2019.000705
    Abstract ( 440 ( PDF (5277KB)( 140 Citation

    The rice granular CaIn2O4/In2O3was successfully synthesized via the electrospinning method using calcium nitrate and indium nitrate as the raw materials, polyvinylpyrrolidone (PVP-K30) as a template and ethanol as a solvent. The samples were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), energy spectrum analysis (EDS), transmission electron microscopy (TEM), UV-vis diffuse reflectance spectroscopy (UV-vis DRS) and N2 adsorption-desorption isotherm. The effect of pH value and the initial concentration of methylene blue(MB) on the photocatalytic performance of CaIn2O4/In2O3 was discussed. The results show that the composites consist of orthorhombic CaIn2O4 and cubic In2O3, with particle size of (650±140) nm, energy gap of 3.48 eV and specific surface area of 17.2 m2·g-1. The degradation rate of MB reaches 92% when it is irradiated by simulated sunlight for 120 min and the photocatalysis degradation process fits the first-order kinetic model. Meanwhile, CaIn2O4/In2O3 has an excellent reusability and stability. The coupling of CaIn2O4 and In2O3 enables the photogenerated carriers to be effectively separated and therefore produces CaIn2O4/In2O3 composites with excellent photocatalytic performance.

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    Preparation and characterization of nitrogen and silver co-doped TiO2 nanocatalyst for visible light photocatalysis
    Yuan BAI, Chao-zhi ZHANG, Hong-qi SUN, Bin CHEN
    2020, 48 (11): 32-38.   DOI: 10.11868/j.issn.1001-4381.2019.000151
    Abstract ( 470 ( PDF (2695KB)( 151 Citation

    Nitrogen and silver co-doped TiO2 photocatalytic material was prepared by improved sol-gel method. Physiochemical properties were characterized by means of X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) and ultraviolet-visible diffuse spectroscopy (UV-Vis). The results show that nitrogen doping is substituted into TiO2 lattice, but catalyst grain growth cannot be inhibited. Due to the addition of Ag element, catalyst grain growth is inhibited. Greatest band-gap narrowing occurs due to nitrogen and silver co-doping. The experiments of photogradation of phenol show that photocatalytic efficiency of catalysts prepared by the improved sol-gel method is significantly higher than that of catalysts prepared by the impregnation method. Under UV-visible irradiation for 120 min, the efficiency of nitrogen and silver co-doped TiO2 is 51.3%, and the efficiency is 51.7% under visible light irradiation for 360 min. Fortunately, visible photocatalytic activity is not realised at the cost of UV activity. Nitrogen and silver co-doping not only reduces band gap of TiO2, but also adjusts its absorption threshold to visible region. Simultaneously, oxygen vacancy concentration of catalysts increases and the response of catalysts to visible light significantly enhances, hence photocatalytic activity of nitrogen and silver co-doped TiO2 enhances.

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    Preparation and photocatalytic activity of carbon black/black TiO2 composites
    Tao LI, Hui-min LI, Song-tao LU, Xiao-hong WU
    2020, 48 (11): 39-45.   DOI: 10.11868/j.issn.1001-4381.2019.000687
    Abstract ( 435 ( PDF (3401KB)( 204 Citation

    Black TiO2 (b-TiO2) was synthesized by hydrothermal and chemical reduction methods. Taking advantage of the adhesion effect of poly-dopamine (PDA), CB/b-TiO2 composite material was prepared by modifying b-TiO2 with carbon black (CB). The crystal structure, chemical composition and micro-morphology of the composites were characterized by XRD, XPS, SEM and TEM. The effect of mass ratio of CB to b-TiO2 on morphology and properties of CB/b-TiO2 was studied. The effect of the amount of CB/b-TiO2on photocatalysis degradation properties was also studied and the amount of CB/b-TiO2 was optimized. The results show that when the mass ratio of CB to b-TiO2 is 1:2, the obtained CB/ b-TiO2 has high light absorption performance in the wide spectrum range, CB/b-TiO2exhibits excellent photocatalytic performance. Besides, when the amount of CB/b-TiO2 is 0.5 g/L, the target pollutant malachite green solution MG (10 mg/L) can be degraded by 99.5% after 3 min. Besides, a high degradation rate of 89.2% can still be maintained after 5 cycles, showing good regeneration and utilization performance.

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    Research progress of glass-formation rule and mechanical properties of Fe-based bulk amorphous alloys
    Tian-hao LIU, Sheng-feng GUO
    2020, 48 (11): 46-57.   DOI: 10.11868/j.issn.1001-4381.2020.000389
    Abstract ( 475 ( PDF (4752KB)( 296 Citation

    Amorphous alloy is a new kind of metastable metallic materials, which exhibits many excellent mechanical, physical and chemical properties due to its disordered structure. Since its birth in the 1960s, amorphous alloy has been attracting much attention from the materials field and the industry. Among the developed alloy systems, Fe-based amorphous alloys have the characteristics of high strength, high hardness, relatively low production cost, strong corrosion resistance and excellent soft magnetic properties, hence have a broad application prospect in the field of structural materials and functional materials. However, the relatively weak glass-forming ability and room temperature brittleness seriously restrict the wide application of Fe-based amorphous alloys. Based on this, the two aspects of the Fe-base amorphous alloy was reviewed in the present article, which covers the glass forming rule (including components types, preparation technology, raw material purity, composition design, etc.) and room-temperature mechanical properties (involving strength, toughness, composition and structure design, etc.). The research status, influencing factors and improved methods of glass-forming ability and room temperature mechanical properties of Fe-based amorphous alloys were emphatically analyzed, especially the latest research results of our group in the field of Fe-base amorphous alloy in nearly a decade were covered.In addition, the current difficulties in research and the future development of Fe-based amorphous alloys were also prospected.

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    Research progress in manufacturing technology of Nb-Si based ultra-high temperature structural materials
    Ming LI, Yong-wang KANG, Feng-wei GUO
    2020, 48 (11): 58-67.   DOI: 10.11868/j.issn.1001-4381.2020.000284
    Abstract ( 555 ( PDF (2425KB)( 292 Citation

    Nb-Si based ultra-high temperature structural material is the potential material to break the service temperature limitation of conventional superalloys.However, due to the much higher melting point and the lower plasticity and ductility of Nb-Si based alloys, it is much more difficult to prepare and manufacture than the existing high temperature metal structural materials. The manufacture processes for the complex part with Nb-Si based alloy were reviewed including the developments of the melting technology, the investment casting and the powder metallurgy, and the problems existing in the forming technology were analyzed.Based on the problem analysis, the developing trend was prospected, it is considered that the manufacture technology for Nb-Si based ultra-high temperature structural materials is still in the stage of laboratory research, and in-depth research needs to be carried out continuously on the melting technology for master alloy with large size, the related auxiliary technologies to ultra-high temperature investment casting and the preparation technology for Nb-Si based alloy powder.

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    Research progress in resin based on dynamic covalent chemistry and its composites
    Liang GAO, Hong-yu HUO, Dian-rui ZHOU, Bao-yan ZHANG, Jun HU
    2020, 48 (11): 68-75.   DOI: 10.11868/j.issn.1001-4381.2019.001138
    Abstract ( 557 ( PDF (1826KB)( 448 Citation

    Resin matrix composites have been widely used in aviation, aerospace and other important frontiers. The application proportion of composites has become an important criterion to measure equipment advancement. Thermoset composite materials are well known difficult to be repeatedly processed and recycled, while thermoplastic composite materials show poor processing performance due to the high melting temperature. Nowadays, the growth of dynamic covalent chemistry has obscured the line between thermosets and thermoplastics, which makes it possible to realize the innovative development of resin matrix composites. In this paper, the fundamental theory of dynamic covalent chemistry and covalent adaptable networks were outlined. The research process of resin matrix composites based on dynamic covalent chemistry was introduced in detail. The resin matrix composites exhibit promising prospect owing to the remoldable, ease to recycle, self-healing and smart actuator applications. Finally, some suggestions were put forward for the development of the composites, such as improving bond exchange reaction mechanism and stress relaxation model, developing high-performance and commercial resin systems, also developing technologies for composites forming, connecting, repairing and recycling based on the characteristics of material.

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    Research Article
    Preparation of photo-crosslinking carboxymethyl chitosan hydrogel for sustained drug release
    Bing-na HOU, Jin LI, Kai NI, Chao-yue HAN, Hui-ling SHEN, Lin-lin ZHAO, Zheng-zheng LI
    2020, 48 (11): 76-84.   DOI: 10.11868/j.issn.1001-4381.2020.000025
    Abstract ( 521 ( PDF (3444KB)( 207 Citation

    Carboxymethyl chitosan is an important chitosan derivative with good biocompatibility and degradability, and has a wide range of biomedical applications. In this study, water-soluble carboxymethyl chitosan derivative that can be photo-crosslinked by UV irradiation was synthesized. Methacrylated carboxymethyl chitosan (M-CMCS) was synthesized by N-methacrylation of carboxymethyl chitosan (CMCS). The chemical structures of M-CMCS were characterized by 1H NMR and FT-IR. The M-CMCS hydrogels with different degrees of crosslinking was prepared by UV-triggered photo-crosslinking. The microscopic morphology, mechanical properties, swelling properties, enzymatic degradation properties and in vitro drug release behaviors of M-CMCS hydrogels were investigated by SEM, rheometer, and UV-Vis spectroscopy, respectively. The results show that the degree of methacrylation is gradually increased as the molar ratio of glycidyl methacrylate to carboxymethyl chitosan increases. M-CMCS hydrogels have the structure of high porosity and interconnected pores with the pore size of 1-20 μm. The swelling ratio of M-CMCS hydrogels is decreased as the degree of crosslinking increases. M-CMCS hydrogel can be slowly degraded by lysozyme, and the degradation rate is decreased by increasing the degree of crosslinking. M-CMCS hydrogels show sustained release behavior for anticancer drug gemcitabine, and the drug release can be extended to 4 days. Photo-crosslinked M-CMCS hydrogels show great promise for drug release and tissue engineering.

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    Preparation of hemicellulose-based magnetic hydrogel and its adsorption properties for dye
    Lu-ting ZHAO, Jian ZHANG, Na LI, Mei-hong NIU, Qing-wei PING
    2020, 48 (11): 85-91.   DOI: 10.11868/j.issn.1001-4381.2019.000076
    Abstract ( 382 ( PDF (1972KB)( 166 Citation

    The hemicellulose-based magnetic hydrogel was prepared by free radical polymerization and in situ co-precipitation from corn cob. The properties of the magnetic hydrogel were characterized by means of ICS, scanning electron microscopy(SEM) and universal tensile testing machine. Moreover the adsorption properties on methylene blue were studied. The results show that the hemicellulose-based magnetic hydrogel has super-paramagnetism, with a maximum saturation magnetization intensity of 21.83 A·m2/kg and a maximum compression strength of 0.119 MPa. The adsorption properties on methylene blue are good as well and the removal rate reaches 97%. The prepared hemicellulose-based magnetic hydrogel has good swelling properties, super-paramagnetism and removal efficiency of methylene blue. Furthermore it has better application prospects.

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    PVP-assisted synthesis and photoresponse property of Bi2S3 microflowers
    Yu TIAN, Zhi-peng MAO, Tao-tao DING, Xiao-long ZHU, Guang ZHENG, Zhi-ming ZHAN
    2020, 48 (11): 92-98.   DOI: 10.11868/j.issn.1001-4381.2019.000620
    Abstract ( 4 ( PDF (0KB)( 1 Citation

    Bi2S3 has attracted wide attention due to its application in photoelectric converter, but its preparation conditions are relatively complicated. The Bi2S3 microflowers, which are self-assembled from nanowires and have high photoelectric responsiveness, were synthesized by using polyvinylpyrrolidone (PVP) as structure guide under ethylene glycol solvent heat condition. The effects of different types of surfactants and different reaction time on the morphology of the products were also studied. In addition, a prototype device with photoconductive structure of visible light detection was assembled by using Bi2S3 microflowers and gold fork finger electrode as substrate. The photoresponse properties show that the photocurrent under simulated sunlight is about two orders of magnitude higher than the dark current, and the response time and decay time are 142 ms and 151 ms, respectively, indicating the photodetector has excellent photoelectric responsiveness; the light current is not attenuated by the periodic opening and closing of the photodetector, indicating that the photodetector has good stability.

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    Effects of silicon doping on phase transformation mechanism of titanium dioxide
    Sheng-cai WU, Xian LUO, Yong-fu LONG, Lu ZHANG, Ben-jun XU, Run HUANG
    2020, 48 (11): 99-107.   DOI: 10.11868/j.issn.1001-4381.2019.000996
    Abstract ( 551 ( PDF (4774KB)( 293 Citation

    Under the physical mixed doping of different amounts of SiO2, high temperature in-situ XRD, TEM, XPS and Rietveld full spectrum fitting were used to analyze the change rule of chemical bond and the influence of silicon on the transformation mechanism of anatase to rutile (A→R) TiO2.The results show that the influence mechanism is controlled by distortion energy and crystal nucleus formation. When the doping amount of SiO2 is less than 7.5% (mass fraction, the same as below), the phase transition is inhibited. At this point, Si4+ replaces Ti4+ ions in the titanium dioxide lattice, resulting in distortion and inhibiting the A→R transformation of titanium dioxide. When the doping amount of SiO2 is greater than 7.5%, it is the promotion effect. At this time, the excess SiO2 acts as the crystal nucleus of rutile, thus promoting the transformation of A→R.

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    Preparation of graphene based on liquid phase exfoliation and its application on LiFePO4 electrode for lithium ion battery
    Wen-zheng NAN, Shao-jiu YAN, Si-kan PENG, Chen WANG, Ji-xian WANG
    2020, 48 (11): 108-115.   DOI: 10.11868/j.issn.1001-4381.2019.001162
    Abstract ( 456 ( PDF (4409KB)( 150 Citation

    High-crystallinity and low-defect graphene nanosheets with nano pores were prepared from natural flake graphite via high-pressure homogenization liquid phase exfoliation method.The morphology and structure of as-prepared samples were investigated with scanning electron microscopy, transmission electron microscopy, atomic force microscope, X-ray diffraction and Raman spectroscopy.The electrochemical performance was performed using coin cells assembled in an argon-filled glovebox.It was found that the wrinkled graphene sheets with nanoholes consisted of 5 layers, which had high crystallinity.As conductive additives for LiFePO4 cathode, graphene constructed fast pathway for electron and ion transport in the bulk electrode, resulting in superior rate performance.Electrochemical tests showed that the electrode achieved a high reversible capacity of 90 mAh/g at 10 C rate; in addition, the discharge capacity achieved 90 mAh/g when charging and discharging at 5 C rate for 200 cycles, maintaining 100% capacity retention.The approach preparing graphene is facile, which can be suitable for industrial scale production of graphene materials.

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    Microstructure and properties of selective laser melting AlSi7MgTi alloy
    Peng-jun TANG, Li-jia FANG, Bin YANG, Bing-qing CHEN, Pei-yong LI, Xue-jun ZHANG
    2020, 48 (11): 116-123.   DOI: 10.11868/j.issn.1001-4381.2020.000152
    Abstract ( 525 ( PDF (5734KB)( 182 Citation

    The testing blocks of AlSi7MgTi alloy were prepared by selective laser melting (SLM) technique and T6 heat treatment using alloy powders fabricated by supersonic gas atomization equipment. The microstructure, phase composition, residual stress, and mechanical properties of as-built and T6 treated alloys were investigated by optical microscope, scanning electron microscope, X-ray diffractometer, Raman spectrometer and tensile tests, respectively. The results indicate that as-built alloy mainly consists of supersaturated α(Al) solid solution and Si phases. The microstructure characterized by layer-by-layer stacking and interlaced of "scale-like" melt pool, shows obvious anisotropy. In addition, Si phase exists in the form of cellular eutectic silicon, which is connected by blocky and fibrous eutectic silicon. The eutectic silicon near melt pool boundary is relatively thick, while it is smaller in interior of melt pool. T6 heat treatment promotes the precipitation of Si phases, and leads to the Ostwald coarsening of eutectic silicon. Meanwhile, the melt pool morphologies and cellular eutectic silicon structure are basically eliminated by T6 heat treatment. Additionally, the residual stress is significantly reduced after heat treatment. The tensile strength and yield strength of as-built alloy reach up to 420-430 MPa and 280-300 MPa respectively, with elongation of 5.1%-11.0%. However, the tensile strength of T6 heat treated alloy is reduced to about 360 MPa, and yield strength is almost equal to that of as-built alloy, while elongation increases to 15.2%-16.5%.

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    Microstructure and properties of high-strength Al-Mg-Sc alloys fabricated by selective laser melting
    Li-qi SONG, Yun-jia SHI, Bin CAI, Da-meng YE, Meng-jia LI, Juan LIAN
    2020, 48 (11): 124-130.   DOI: 10.11868/j.issn.1001-4381.2019.000487
    Abstract ( 445 ( PDF (4624KB)( 170 Citation

    By comprehensive analysis of macroscopic characteristics of hardness, electrical conductivity and tensile properties and features of microcosmic morphology, the influence mechanism of process parameters of laser selective melting and following aging treatment on the microstructure, supersaturated solid solution and second-phase precipitation behavior of Al-3.4Mg-1.08Sc alloy fabricated by SLM was discussed. By utilizing the change rules of density and hardness, finally the optimum SLM process parameters and aging system were obtained.The results show that the microstructure of the Al-Mg-Sc alloy fabricated in this experiment is composed of ultrafine equiaxed grains and relatively coarser columnar grains around. The optimal fabrication parameter of Al-Mg-Sc alloy fabricated at platform temperature of 35 ℃ is conducted with scanning speed of 1600 mm/s, laser power of 370 W. The optimum aging time is 12 h at 300 ℃, the yield strength of studied alloy can reach 479.0 MPa through peak aging treatment. Under rapid cooling rate of SLM process, supersaturated solid solution is formed in Al-Mg-Sc alloy, and a large number of nanometer Al3(Sc, Zr) particles are precipitated during the fabrication and heat treatment process, which makes the Al-Mg-Sc alloy present excellent potential of mechanical properties. The fine grain strengthening and the second phase strengthening are the main factors for exhibiting properties of Al-Mg-Sc alloy fabricated by SLM.

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    Friction and wear property of CNT-SiC hybrid reinforced aluminum matrix composites prepared by powder metallurgy
    Jun ZHANG, Chong-yu LIU
    2020, 48 (11): 131-139.   DOI: 10.11868/j.issn.1001-4381.2019.000333
    Abstract ( 478 ( PDF (5553KB)( 200 Citation

    Silicon carbide (SiC) particles, carbon nanotubes (CNT), SiC and CNT hybrid reinforced 7055Al composites were prepared by powder metallurgy with 7055Al as matrix. The dry sliding friction and wear behavior of the three composites were studied. The results show that the wear mass loss increases and the friction coefficient decreases slightly with the increase of the load.The wear mass loss of the SiC-CNT/7055Al composite is lower than that of the single SiC/7055Al and CNT/7055Al reinforced composites at 0.5 MPa and 1.0 MPa.The wear mass loss of the SiC-CNT/7055Al composite increases rapidly at 2.0 MPa. With the increase of the load, the wear resistance of CNT/7055Al composite increases gradually; under medium and high load, the composite owns better wear resistance.The wear amount of SiC/7055Al composite increases gradually with the increase of the load, and the wear mass loss increases little at load of 2.0 MPa.

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    Work-softening mechanism of Cu-Cr-Ti-Si alloy
    Ji-hui YUAN, Hui-ming CHEN, Wei-bin XIE, Hai-gen WEI, Hang WANG, Bin YANG
    2020, 48 (11): 140-146.   DOI: 10.11868/j.issn.1001-4381.2019.000173
    Abstract ( 431 ( PDF (6708KB)( 90 Citation

    The Cu-Cr-Ti and Cu-Cr-Ti-Si alloy ingots were melted in the atmosphere, and then treated with hot rolling-solid solution-aging-cold rolling process. Microstructure and properties of alloy after cold rolling with different deformation were studied. The microstructure of the alloy after cold rolling was analyzed by using OM, electron backscatter diffraction, X-ray diffraction and transmission electron microscopy. The results show that when the deformation ε is greater than 80%, the hardness of Cu-Cr-Ti-Si alloy is decreased. Such phenomenon does not occur in Cu-Cr-Ti alloy. With the increase of deformation, the proportion of low angle grain boundaries in Cu-Cr-Ti-Si alloy is decreased, and the increase of dislocation cells and sub-grains leads to slight decrease of dislocation density. Since no re-crystallization was observed, recovery is responsible for work softening. By analyzing the microstructure before cold rolling, it is found that Si can refine the alloy grains, resulting in smaller grains of Cu-Cr-Ti-Si alloy than Cu-Cr-Ti before deformation. More grain boundaries per unit area provide more energy storage at nucleation sites for recovery during deformation of the alloy.

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    Microstructure features of 24CrNiMo alloy steel fabricated by laser additive manufacturing
    Yun-hua XU, Chun-hua ZHANG, Song ZHANG, Rui-qing QIAO, Jing-bo ZHANG
    2020, 48 (11): 147-154.   DOI: 10.11868/j.issn.1001-4381.2020.000184
    Abstract ( 638 ( PDF (5981KB)( 200 Citation

    Herein, the single-track and block samples of 24CrNiMo alloy steel were prepared by selective laser melting (SLM) technology and laser melting deposition (LMD) technology. The phase composition, microstructure, texture types and micro-hardness of 24CrNiMo low alloy steel under two laser irradiation conditions were studied. The results show that the main phase compositions of 24CrNiMo alloy samples prepared by two methods are α-Fe phase and a small amount of Fe3C.Furthermore, the grain orientation of SLM single-track deposited sample is random and disordered, and there is no obvious preferred orientation.However, the preferred orientation of LMD single-track deposited sample is the (110)〈101〉 plane texture. The grain of SLM block sample has weak 〈111〉 texture parallel to the deposition direction, LMD block sample has strong texture with the 〈111〉epitaxial growth orientation.Additionally, the main microstructure of as-built SLM sample is lower bainite, and the microstructure of as-deposited LMD sample mainly consists of lathbainite. The average micro-hardness SLM sample with fine grain and lower bainite microstructure is higher than that of LMD sample.

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    Microstructure and thermal conductivity of high thermal conductivity carbon/ carbon composites
    Yu-min YAO, Hong LI, Zheng-qi LIU, Min YANG, Mu-su REN, Jin-liang SUN
    2020, 48 (11): 155-161.   DOI: 10.11868/j.issn.1001-4381.2019.000250
    Abstract ( 692 ( PDF (3731KB)( 348 Citation

    Porous carbon/carbon (C/C) composites prepared by pitch-based carbon fiber and mesophase pitch were densified by chemical vapor infiltration (CVI) and precursor impregnation process (PIP). After different heat temperature treatment (HTT), the unidirectional C/C composites and bidirectional C/C composites were obtained. The microstructure of C/C composites was investigated by SEM, XRD, and the thermal conductivity was analyzed based on the thermal conductivity mechanism. The results show that unidirectional C/C composites and bidirectional C/C composites have dense structures and excellent thermal conductivity along the fiber axis. After 3000 ℃ treatment, the structure of graphite flat layers become more distinct and the graphitization degree is increased by 18.84%, leading to higher thermal conductivity. Furthermore, the thermal conductivity in X direction and Y direction of the bidirectional C/C composites can be calculated from that of unidirectional C/C composites in X direction and Z direction.

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    Failure mechanism of stitched three dimension woven composite/Ti alloy hybrid board joint under shear load
    Yi-rong LU, Hua-yong ZHENG, Xiu-hua CHEN, Hai WANG
    2020, 48 (11): 162-169.   DOI: 10.11868/j.issn.1001-4381.2019.001093
    Abstract ( 517 ( PDF (7072KB)( 131 Citation

    In order to study the effect of stitching density, tow size of the suture and diameter of the stitching hole on the shear property of the stitched three-dimensional woven composite/titanium hybrid board stitching connection structure, seven groups of samples with different stitching densities, tow size of the suture and diameter of the stitching hole were tested. A reference group whose samples were unstitched was also tested to show the effect of stitching on the joint. Different failure modes of the lap zone with different stitching parameters were observed in in-situ meso-experiment, and the damage morphologies of the characteristic points on the load-displacement curve were given. The result shows that increasing tow size of the suture and increasing stitching density can both increase the failure load of the hybrid joint. Increasing the stitching density is proved more effective in improving the failure load. Doubling the stitching density can increase the failure load of the stitched joint about 82.0%. Doubling the tow size of the suture can only increase the failure load of the joint about 24.3%; Whether the diameter of the stitching hole is 2 mm or 4 mm do not influence the bearing capacity of the structure obviously, and when the stitching hole diameter reaches 6 mm, the bearing capacity is reduced due to the low strength of the epoxy resin in the gap between stitching hole and suture. It is dangerous to increase diameter of stitching hole above 4 mm; the shear failure of the stitched three-dimension woven composite/titanium alloy hybrid structure is observed by mesoscopic mechanical test. Composite/titanium alloy interface failure, crack initiation and extension in composite or in lap zone and failure of the lap zone are the three main stages of the structure failure observed in the test; The suture failure in the connect zone includes suture pull out and suture cut off. There are three failure modes of the lap zone observed in test. In suture cut off mode, all sutures in lap zone are cut off. The position at which the suture is cut is related to the diameter of the stitching hole. In suture cut off/pull out mixed mode, some of the interface between suture and three-dimension woven composites fail and the suture is partly or completely pull out. In the group with high stitching density, sutures near the end of the three-dimension woven composite crush the composite and extrude out of the composite. Stitching density is the major factor in the failure mode of the joint.

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    Preparation of cyclodextrin microspheres modified epoxy resin and X-ray penetration mechanism of carbon fiber composites
    Ling-qi ZHENG, Gang LI, Xiao-ping YANG, Qiang LI, Ling-fei SHI
    2020, 48 (11): 170-176.   DOI: 10.11868/j.issn.1001-4381.2019.000646
    Abstract ( 459 ( PDF (4263KB)( 158 Citation

    Cyclodextrin microspheres (CDMS) was synthesized by 4, 4'-dicyclohexylmethane diisocyanate and β-cyclodextrin, and applied to prepare the cyclodextrin microspheres modified epoxy resin(CDEP). The microscopic morphology and dispersibility of CDMS in epoxy resin were characterized. Crosslinking density and dielectric properties of CDMS modified epoxy resin were investigated.The T300 carbon fiber fabric/modified epoxy composite was prepared. The X-ray penetration properties of the composite were investigated and X-ray penetration mechanism was proposed. The results show that the dispersibility of spherical CDMS in epoxy resin is good and its average diameter is about (11.5±2) μm. As mass fraction of CDMS is increased from 0% to 5%, the crosslink density of epoxy resin is reduced from 2.50×10-2 mol·cm-3 to 2.35×10-2 mol·cm-3 and dielectric constant is decreased from 4.10 to 3.43. X-ray penetration of composites is increased from 94.97% to 96.82% at 30 kV tube voltage. The number of collisions of X-rays inside the composite is reduced by the cavity structure of the microspheres, which effectively improves the X-ray penetration performance of composites.

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