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      20 January 2021, Volume 49 Issue 1 Previous Issue    Next Issue
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    New Energy Materials Column
    Research progress of self-repairing polymers in electrochemical energy storage devices
    Zi-yang LIU, Yang LI, Xing-jiang LIU, Qiang XU
    2021, 49 (1): 1-10.   DOI: 10.11868/j.issn.1001-4381.2020.000194
    Abstract ( 623 ( PDF (10554KB)( 246 Citation

    Self-healing polymer materials are able to self-repair damage and recover themselves after cracks generating to maintain their structural and functional integrity. According to whether additional repair agent is added, self-healing polymers are mainly divided into two categories, namely extrinsic- and intrinsic-based polymers.The key materials of electrochemical energy storage devices will experience irreversible mechanical damage in extreme condition applications, for example, the energy storage device more prone to physical damage inwearable devices during the multiple bending and deformation processes. These problems severely reduce the stability of energy storage and delivery, and shorten the life of the devices. Therefore, the application of self-healing polymers in electrochemical energy storage devices to improve the stability and life of devices has become one of the research hotspots in recent years. Herein, this article summarizes the repair mechanism of self-healing polymer materials (capsule-based, vascular-based, and intrinsic polymers), with main focus on intrinsic self-healing polymer and its research progress in the field of electrochemical energy storage, which based on molecular interactions to achieve multi-time reversible healing without any additional repair agent.The self-healing electrode and electrolyte system were reviewed respectively, and then the self-healing mechanism and its influence on the electrochemical performance of energy storage devices were described. The research progress of self-healing functional polymer as high specific energy electrode binder, interface modification layer and self-healing electrolyte were summarized in detail. Finally, the future perspectives regarding the future development of self-healing polymer materials were also discussed.

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    Research progress of organic electrolyte for sodium ion battery
    Fu-ming ZHANG, Jing WANG, Peng ZHANG, Zhi-qiang SHI
    2021, 49 (1): 11-22.   DOI: 10.11868/j.issn.1001-4381.2019.001121
    Abstract ( 622 ( PDF (6500KB)( 385 Citation

    As the demand for large-scale batteries for electrical energy storage is increasing, sodium-ion batteries have attracted a lot of attention due to the abundance, cost-effectiveness of sodium resources and resemblance with lithium. In the key material selection of sodium ion battery, electrochemical performance and safety of a sodium-ion battery were affected by the electrolyte, which not only decides the electrochemical window and energy density, but also controls the electrode/electrolyte interfaces. In this paper, the basic requirements and classification of electrolyte of sodium ion battery were reviewed. The selective requirements of electrolyte in sodium ion batteries, the physicochemical properties of different sodium salts and the effects on solid electrolyte interface were discussed. Based on the compatibility of different solvents and materials as well as the energy storage mechanism of materials in different solvent systems, the solid electrolyte interface, rate and cycling performance obtained by materials in ether and ester based electrolytes were analyzed. Finally, the future development of sodium ion battery electrolyte in terms of matching with materials and key characterization methods were prospected.

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    Research progress of high temperature proton exchange membranes applied in fuel cells
    Peng SUN, Zhong-fang LI, Chuan-gang WANG, Yan WANG, Wei-hui CUI, Hong-chang PEI, Xiao-yan YIN
    2021, 49 (1): 23-34.   DOI: 10.11868/j.issn.1001-4381.2019.001097
    Abstract ( 515 ( PDF (8075KB)( 357 Citation

    The fuel cell technology is a highly-efficient clean energy technology which can alleviate the power and environmental problems. Proton exchange membrane fuel cell (PEMFC) is an important type of fuel cell, of which proton exchange membrane is the key component which is proton-conductive and electron-insulating. Elevation of the working temperature of PEMFCs can solve the intractable issues for low-temperature PEMFCs. Therefore, proton exchange membrane materials which can work under high temperature and low relative humidity are required. The main types, preparation and modification methods, and proton exchange mechanisms of high temperature proton exchange membranes were summarized in this review. Proton conductor doped polybenzimidazole (PBI) based membrane materials are potential candidates for high temperature low humidity proton exchange membranes. The preparation, types of proton conductors and performance enhancement methods of PBI based high temperature proton exchange membranes were discussed. The challenges and research trends of high temperature proton exchange membranes were pointed out such as synthesis of new types of proton conductor, improvement of PBI anti-oxidation stability, regulation of membrane microstructure to improve the performance and develop novel polymer electrolytes.

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    Effect of interaction in allophane/PEO/LiClO4 composite solid polymer electrolyte on crystallization of PEO
    Hao WU, Jin QIU, Wei-xing CHEN, Jing-jing YANG, Ai-jie MA, Li-fan CAI
    2021, 49 (1): 35-43.   DOI: 10.11868/j.issn.1001-4381.2020.000174
    Abstract ( 574 ( PDF (12937KB)( 211 Citation

    In order to solve the safety problems in the lithium ion batteries used nowadays, the researchers were increasingly attracted by the solid electrolytes. Allophane was prepared from Na2SiO3 and AlCl3·6H2O by sol-gel method. By mixing the allophane and the polyethylene oxide/lithium perchlorate(PEO/LiClO4)with the solution blending method, the composite solid polymer electrolyte was obtained. X-ray diffraction(XRD), fourier transform infrared spectroscopy(FTIR), differential scanning calorimetry(DSC), transmission electron microscope(TEM), scanning electron microscope(SEM)and optical microscopy(OM)were used to characterize the microstructure and morphology of the samples. The results show that the noncovalent bonding interactions(complexation, hydrogen bonding, and Lewis acid-base interaction)among allophane, LiClO4 and PEO significantly inhibit the crystallization of PEO. The crystallinity of PEO decreases and then increases with the increase of allophone content. Moreover, the crystallinity of PEO decrease with the increase of LiClO4 content. When EO/Li+ molar ratio is 10:1 and the content of allophane is 5%(mass fraction), the crystallinity of PEO in the solid polymer electrolyte is only 4.12%.

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    Research progress in corrosion resistance of high-entropy metallic glasses
    Shu-yan ZHANG, Yang-yang GAO, Zhi-bin ZHANG, Xiu-bing LIANG, Li-zhong WANG
    2021, 49 (1): 44-54.   DOI: 10.11868/j.issn.1001-4381.2020.000254
    Abstract ( 732 ( PDF (2343KB)( 347 Citation

    The high-entropy metallic glasses, as a new kind of alloyed materials, have attracted considerable attention due to its excellent mechanical, anti-corrosion and magnetic properties and so forth, which combines the advantages of high-entropy alloys and metallic glasses. Herein, a comprehensive understanding of the concepts and features of high-entropy metallic glasses was provided as well as its preparation methods, distinguished structure and performance characteristics. The recent developments in the corrosion resistance mechanism and anti-corrosion properties were summarized. A new paradigm of using machine learning to design high-entropy metallic glasses was prospected. It was also pointed out that the precondition to the extensive use of this sort of materials is to explore the corrosion failure mechanism under the working conditions, and to achieve the micro-corrosion resistance mechanism perfection and its preparation process optimization. At present, the applied basic research on the development of high-entropy metallic glasses and its corrosion resistance will provide advanced technical support and material guarantee for the "Marching into the deep ocean" of China's marine industry.

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    Advances in antibacterial research based on two-dimensional nano-materials
    Xuan ZHOU, Yun-fei ZHENG, Qi-lin JIA, Fei-ran ZHANG
    2021, 49 (1): 55-64.   DOI: 10.11868/j.issn.1001-4381.2020.000360
    Abstract ( 632 ( PDF (6129KB)( 205 Citation

    In recent years, antibiotic-resistant bacterial strains have spread rapidly and widely around the world. New antibacterial drugs have emerged to develop. With the development of biological nanotechnology, two-dimensional nanomaterials have become a very promising alternative for the treatment of antibiotic-resistant bacteria. Based on the recent literature, the structural features and antibacterial applications of graphene materials (GMs), transition-metal dichalcogedes (TMDs), layered double hydroxides (LDHs) and MXenes were elaborated, the antibacterial mechanisms of those materials were discussed, such as physical/mechanical damage, lipid extraction, oxidative stress, and photothermal/photodynamic effects, etc. Finally, the antibacterial research progress and challenges of two-dimensional nanomaterials were prospected:(1) 2D materials has a unique space structure and excellent biocompatibility, so it can be used as an ideal carrier for antibacterial drugs; (2) the material has photodynamic and photothermal bactericidal effects, so it has a strong potential to cure local skin infections; (3) it can be made into antibacterial coatings to achieve simple in-situ disinfection applying to sterile medical equipment in the future.

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    Research on application of hot isostatic pressing technology in the field of nickel-based cast superalloys
    Fu-yang SONG, Jian ZHANG, Hui-ming GUO, Mai ZHANG, Yun-song ZHAO, Jiang-bo SHA
    2021, 49 (1): 65-74.   DOI: 10.11868/j.issn.1001-4381.2020.000396
    Abstract ( 451 ( PDF (5689KB)( 184 Citation

    Nickel-based cast superalloy is one of the main materials applied in the manufacture of aeroengine and gas turbine, and it is widely applied in aerospace, energy industry and shipbuilding industries etc.The rapid development of modern aviation industry is inseparable from the rapid improvement of the comprehensive performance of superalloys, and the application of hot isostatic pressing technology in the field of nickel-based casting superalloys plays a pivotal role in improving the comprehensive performance of nickel-based casting superalloys. In this paper, the working principle and application history of hot isostatic pressing technology were introduced. The research and application status of hot isostatic pressing technology in the field of nickel-based casting superalloys was summarized. The research on the effect of hot isostatic pressing on the densification mechanism and microstructure properties of cast superalloys, research on hot isostatic pressing on the microstructure repair of nickel-based cast superalloys in long-term service, and research on the realization of the diffusion bonding of two nickel-based superalloys progress are highlighted and elaborated. At the same time, some problems in the research of hot isostatic pressing technology and the development trend of domestic hot isostatic pressing technology in the field of nickel-based cast superalloys were pointed out.

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    Research Article
    Hot deformation behavior and constitutive equation of TB8 titanium alloy with a lamellar structure of α phase
    Ya-li ZHOU, Qiu-yue YANG, Wen-wei ZHANG, Tian-wen LIU, Wei HE, Zhen WU, Ming WU, Yuan-biao TAN
    2021, 49 (1): 75-81.   DOI: 10.11868/j.issn.1001-4381.2020.000307
    Abstract ( 500 ( PDF (4803KB)( 177 Citation

    The hot deformation behavior of TB8 titanium alloy with a lamellar α structure in the α+β dulex phase region was investigated. The results show that at the strain rate of 1 s-1, a continuous flow softening phenomenon is observed in the curve of the samples deformed at 650 ℃, while a discontinuous yield phenomenon is visual in the curve of the samples when the deformation temperature is higher than 650 ℃. The discontinuous yield phenomenon is gradually disappeared with increasing deformation temperature and strain rate. When the strain rate is 0.001 s-1 and the deformation temperature is 750 ℃ as well as 800 ℃, typical characteristics of dynamic recrystallization is presented in the curve of the samples. The relationship among peak stress σp temperature T and strain rate and is characterized by Arrhenius-type constitutive equation. The equation between the material constants (α, Q, n and lnA) and strain is constructed. The effect of strain on the material constants (α, Q, n and lnA) of the Arrhenius-type constitutive equation is analyzed. The value of α is increased with true strain, while the values of Q, n and lnA are gradually decreased. The correlation coefficient (R2) and the AARE value between the experimental and the predicted stress are 0.945 and 9.08%, respectively. This indicates that the strain-compensates Arrhenius type constitutive equation can better predict the flow stress value under different deformation conditions for the TB8 titanium alloy with a lamellar α structure deformed in the α+β dulex phase region.

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    Effect of minor Ag on microstructure and mechanical properties of ZL114A aluminum alloy
    Zhen WU, Zheng LU, Shan-guang LIU, Chuan-biao LUO
    2021, 49 (1): 82-88.   DOI: 10.11868/j.issn.1001-4381.2019.000531
    Abstract ( 419 ( PDF (17491KB)( 316 Citation

    The effects of trace element Ag on the mechanical properties and microstructure of ZL114A aluminum alloy were investigated by the universal electron tensile testing machine, optical microscopy, scanning electron microscopy and spherical aberration correction field emission transmission electron microscopy. The results show that the tensile strength and yield strength of the alloy are enhanced with the increase of Ag content. However, no significant impact on the elongation is observed with the addition of Ag. When the Ag content reaches 0.55%(mass fraction), the peak aging tensile strength, yield strength, and elongation of ZL114A aluminum alloy increase from 351 MPa to 369 MPa, 309 MPa to 328 MPa, and 2.36% to 2.93%, respectively. There is no evidence of properties of α-Al dendrite and eutectic Si changing under the same condition. The increase of the Ag content promotes the amount of nucleation particles in GP zones, leading to the denser density of β". Ag atoms are observed in the β" phase under high-angle annular dark-field scanning transmission electron microscope (HAADF-STEM) mode, indicating that Ag atoms inhibit the diffusion of Mg atoms as well as Si atoms in the β" phase and the size of β" phase is reduced as a result.

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    Effect of vacuum annealing on performances of in-situ Al2O3 reinforced Fe-Cr-Ni composites
    Chang CHEN, Ru-yi ZHANG, Si-tao SHI, Fen-tian MA
    2021, 49 (1): 89-94.   DOI: 10.11868/j.issn.1001-4381.2019.000998
    Abstract ( 326 ( PDF (3451KB)( 95 Citation

    Fe-Cr-Ni alloys were widely applied to produce aero-engine, industrial gas turbine and other equipments because of their high temperature strength and toughness and creep resistance. In-situ Al2O3/Fe-Cr-Ni composites were prepared by hot pressing sintering process and in-situ synthesis method. In order to reduce the effect of brittle phase on the properties of composites, the prepared samples were kept in vacuum for 2 h at 1000 ℃. Effect of heat treatment on microstructures and mechanical properties of Al2O3/Fe-Cr-Ni composites at room temperature was investigated by XRD and SEM. The results show that Al2O3/Fe-Cr-Ni composites are mainly composed of Fe-Cr-Ni alloy phase, Fe-Cr phase and Al2O3 ceramic reinforcement phase. The Vickers hardness, bending strength and fracture toughness of the hot pressed sintered samples are 4.16 GPa, 298.31 MPa and 8.04 MPa·m1/2, respectively. Austenitic transformation of Fe-Cr phase in composites results in the reduction of hardness to 2.98 GPa through high-heat treatment at 1000 ℃. The values of bending strength and fracture toughness increase obviously with the increasing of the ductile phase contents in the alloy matrix, which are 459.33 MPa and 12.81 MPa·m1/2, respectively.

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    Solid phase diffusion bonding of Ti2AlNb alloy and titanium matrix composites at low temperature
    Xun-ye ZHANG, Qiu-guang ZHANG, Pan-pan LIN, Chun-yue WANG, Peng HE, Tie-song LIN, Wei-min LONG
    2021, 49 (1): 95-103.   DOI: 10.11868/j.issn.1001-4381.2019.001132
    Abstract ( 435 ( PDF (16028KB)( 134 Citation

    The Ti2AlNb alloy and the titanium matrix composites can be joined by direct solid phase diffusion, but the high diffusion temperature causes the base metal to undergo a phase transition, even the joint properties were therefore deteriorated. A method for optimizing the properties of solid phase diffusion joints of Ti2AlNb alloy and Ti matrix composites was proposed by using Ti foil intermediate layer. The results show that after adding 30 μm Ti foil intermediate layer, the diffusion bonding temperature reduces from 950 ℃ to 850 ℃, the deformation rate reduces from 5% to 1.7%, and the decreasing of diffusion bonding temperature can effectively change the structure of the joint interface. The typical interface is Ti2AlNb/B2 phase/α+β dual phase structure/Ti matrix composite, in which the strength of the joint increases by the formation of α+β dual phase structure at the joint interface.When the optimum diffusion bonding parameter is 850 ℃/60 min/5 MPa, the shear strength reaches a maximum value of 399 MPa. The diffusion bonding of Ti2AlNb and Ti based composite at low temperature is realized.

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    Microstructure and densification of 3D weaving preform
    Cheng-jie HUANG, Min YANG, Hong LI, Mu-su REN, Jin-liang SUN
    2021, 49 (1): 104-111.   DOI: 10.11868/j.issn.1001-4381.2020.000348
    Abstract ( 465 ( PDF (13510KB)( 150 Citation

    The carbon fiber preform is the skeleton of the carbon/carbon material. During the densification process, the pores of the preform is filled by the matrix carbon to form a carbon/carbon composite material. In order to explore the relationship between the microstructure of carbon fiber preform and densification, three kinds of three-dimensional woven preforms were used as the research objects. The microstructure of the preform was observed through a metallurgical microscope, and digital models of the theoretical structure of the preforms were established to calculate the volume content of different types of pores in the body, and to study the effect of pore structure on the densification efficiency of chemical vapor deposition. The results show that the pores in the three-dimensional woven preform are periodically and repeatedly arranged. The fiber volume fraction in the preform is related to the XY fiber layer spacing and the Z direction fiber spacing, the smaller the XY fiber layer spacing and the Z direction fiber spacing are, the higher the fiber volume content of the preform is; the preform is mainly composed of the pores in the fiber bundle and the inter-bundle pores surrounded by the X, Y, Z fiber bundles; the pore size and structure of the preform affect the densification efficiency, and the densification rate of the preform with high porosity is higher in the early stage of densification, and the preform with uniform pore structure gains weight quickly in the later stage of densification.

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    Effect of PAN pre-oxidized fibers radial structure distribution characteristics on graphite fibers
    Yi-wei WANG, Yun-feng WANG, Yu WANG, Ai-jun GAO, Liang-hua XU
    2021, 49 (1): 112-118.   DOI: 10.11868/j.issn.1001-4381.2020.000240
    Abstract ( 410 ( PDF (6207KB)( 134 Citation

    The radial structure of PAN-based graphite fibers is one of the important influencing factors to achieve high strength and high modulus. Effectively regulating and optimizing the radial structure distribution characteristics of graphite fibers has important guiding significance for the preparation of high-performance graphite fibers. The effects of PAN pre-oxidized fibers radial structure distribution characteristics on graphite fibers radial structure distribution characteristics and mechanical properties were studied by carbonizing and graphitizing pre-oxidized fibers with different radial distribution characteristics. The results show that the radial structure of graphite fibers is inherited from the radial structure of PAN pre-oxidized fibers. After carbonization and graphitization, the pre-oxidized fibers with more conjugated structures have a higher degree of graphitization, which are conducive to improving the mechanical properties of the fibers. However, the excessively high pre-oxidation temperature not only increases the oxygen-containing structure in the fibers, but also makes the radial structure of the graphite fibers too different, resulting in a decrease in the compactness of the graphite fibers structure and shear stress between the sheath and core, which reduces the fibers carrying capacity and impairs mechanical properties.

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    Research article
    Anti-high speed impact properties of polyimide fiber/bismaleimide resin composites
    Shan-qun GU, Dai-jun ZHANG, Yan-feng LIU, Qi ZOU, Xiang-bao CHEN, Jun LI, Shan-long FU
    2021, 49 (1): 119-125.   DOI: 10.11868/j.issn.1001-4381.2020.000034
    Abstract ( 445 ( PDF (17148KB)( 179 Citation

    The polyimide fiber/ bismaleimide resin composites were prepared by the autoclave molding process. Effects of volume fraction of polyimide fiber and ambient temperature on the high speed impact properties were investigated using the air cannon impact test. The results demonstrate that the anti-high speed impact property of S35 polyimide fiber reinforced composites is superior to that of TC4 titanium alloy under equal area mass.And polyimide fiber composites have excellent high temperature anti-high speed impact property. Meanwhile, the results also indicate that the volume fraction of polyimide fiber can improve the anti-high speed impact property of the composites. Also, the ballistic energy absorption of polyimide fiber reinforced composites with 73% volume fraction at room temperature can reach 227.0 J, which is 240% higher than that of TC4 titanium alloy under equal area mass. Furthermore, when the impact velocity is low, the composites appear a circular pit with fiber delamination around on the impact surface, while the back surface appears delamination along the fiber direction. Also, when the impact velocity is high, a circular hole with fiber delamination around is formed on the impact surface of composites, and large area fiber delamination along the fiber direction is observed on the back surface.

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    Influence of vacuum annealing temperature on the structure and properties of AlCrSiN/Mo self-lubricating coatings
    De-qiang MENG, Tie-gang WANG, Yong PENG, Pei-ling KE, Qiang ZHU, Ren-ren XU, Qian LIU
    2021, 49 (1): 126-132.   DOI: 10.11868/j.issn.1001-4381.2019.001174
    Abstract ( 469 ( PDF (12700KB)( 114 Citation

    The AlCrSiN/Mo self-lubricating coating was prepared by hybrid technology of high power impulse magnetron sputtering and pulsed DC magnetron sputtering, and the structure and properties were modified by vacuum annealing. The influence of vacuum annealing temperature on composition, microstructure, mechanical and tribological properties of AlCrSiN/Mo coatings was systematically investigated by scanning electron microscope, X-ray diffractometer, electron probe analyzer, nano-indentation tester, scratch tester and friction and wear tester. The results show that all the AlCrSiN/Mo coatings possess the nanocomposite structure, namely the nc-(Al, Cr, Mo)N is surrounded by a-Si3N4 amorphous phase. After vacuum annealing, the particle size on the coating surface is increased significantly, whereas the nanohardness and critical load of the coatings are decreased correspondingly, and the wear resistance and antifriction performance are improved significantly. After being annealed at a temperature of 700 ℃, the coating presents the optimum properties with a nanohardness of 18.3 GPa, a friction coefficient of 0.51 and a wear rate of 3.4×10-4 μm3·(N·μm)-1. In this case, the characteristic values of H/E and H3/E*2 keep the highest.

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    Wide temperature range tribological performance of laser in-situ synthesized self-lubricating coating on 304 stainless steel
    Mian WANG, Xiu-bo LIU, Chun-sheng OUYANG, Ying-she LUO, De-qiang CHEN
    2021, 49 (1): 133-143.   DOI: 10.11868/j.issn.1001-4381.2020.000167
    Abstract ( 430 ( PDF (20892KB)( 121 Citation

    304 stainless steel has poor tribological properties at medium and high temperatures, severely limiting its application to the important frictional motion auxiliary parts. In order to improve the tribological properties of 304 stainless steel, Ni60 powder was used as toughening phase, WS2 acted as precursor for synthetic lubricating phase, TiC used as high-hardness and wear-resistant phase, and high-energy laser beam was used to in-situ synthesize a self-lubricating and anti-wear composite coating on its surface. The phase compositions, microstructure, microhardness and surface topogr-aphies of the coating and substrate were characterized by XRD, SEM, microhardness tester, friction and wear tester and the probe-type surface profilometer, and the tribological properties as well as the corresponding wear mechanisms of the coating and substrate at 20, 300, 600, 800 ℃ were systematically studied. Results indicate that the coating is mainly composed of Cr0.19Fe0.7Ni0.11, Ti2SC, Fe2C, Cr7C3, CrS and WS2. Although the average microhardness of the coating (302.0HV0.5) is slightly higher than that of the substrate (257.2HV0.5), the hardness of the upper region of the coating (425.4HV0.5) is about 1.65 times that of the substrate. The friction coefficients and wear rates of coating are lower than that of the substrate at all the isothermal tribological experiments. The coating possesses the best lubrication effect at 300 ℃ with friction coefficient of 0.3031, and the best wear resistance at 600 ℃ with a wear rate of 9.699×10-5 mm3·N-1·m-1.

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    Performance and mechanism analysis of MnOx/HZSM-5 catalytic oxidation of formaldehyde at room temperature
    Xiao-yun HE, Xiao GE, Liu-ming SONG, Ting-ting YANG, Yuan-ke LI, Jin-sheng GOU
    2021, 49 (1): 144-152.   DOI: 10.11868/j.issn.1001-4381.2020.000461
    Abstract ( 357 ( PDF (8062KB)( 106 Citation

    Using HZSM-5 zeolite, potassium permanganate and methanol as raw materials, MnOx/HZSM-5 catalyst was prepared to oxidize formaldehyde at room temperature. X-ray diffraction (XRD), Raman spectroscopy (Raman), scanning electron microscopy (SEM), transmission electron microscopy (TEM), photoelectron spectroscopy (XPS) and other characterization methods were used to analyze the morphology, structure and chemical composition of the catalyst. The catalytic activity and regeneration performance of MnOx/HZSM-5 on formaldehyde were studied, and the mechanism of formaldehyde catalytic oxidation was discussed. The results show that the formaldehyde removal rate of MnOx/HZSM-5 remains at 90% after 1020 minutes of dynamic testing. After five regeneration tests, the removal rate of formaldehyde by MnOx/HZSM-5 remains at 91%. In the static test, the formaldehyde removal rate reaches 97% and the conversion rate of formaldehyde reaches 92%. After analyzing the mechanism of oxidizing formaldehyde with MnOx/HZSM-5, it is found that formaldehyde is first adsorbed by the catalyst to the active site of MnOx. Then it is preliminarily oxidized to intermediate products such as formates or carbonates. Finally, it is deeply oxidized with carbon dioxide and water.

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    Fatigue properties and fracture mechanism of Stellite12 cobalt-based alloy
    Wen-juan MIAO, Rui CAO, Hong-yan CHE, Hao DONG, Jian-hong CHEN
    2021, 49 (1): 153-159.   DOI: 10.11868/j.issn.1001-4381.2020.000076
    Abstract ( 421 ( PDF (17798KB)( 94 Citation

    The three-point bending fatigue method was used to determine the S-N fatigue curves of smooth specimens and straight-notched specimens to study the fatigue properties of Stellite12 cobalt-based alloy, and the fatigue fracture processes of the cobalt-based alloy were investigated by the observation of fracture morphology.The results show that the fatigue limit of the smooth specimen is 545 MPa, which is about 25.4% of the original bending strength of 1552 MPa. The fatigue limit of the straight-notched specimen is about 101 MPa, which is about 19.1% of static bending strength of 517.6 MPa. The fatigue sensitivity of smooth specimens and straight-notched specimens is 397 and 31, respectively. In addition, it is found that the fatigue cracks can initiate in the carbides aggregated regions in the near surface. Surface defects can also induce the initiation of fatigue cracks. The transgranular fracture of the carbides dominates in the crack propagation. The cobalt base metal presents a lot of tearing ridges under the condition of stress ratio R=0.1, but it also shows a certain degree brittle fracture mode, so the fatigue crack propagation mode is a mixed mode of true fatigue and static fatigue.

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    Interface shear strength test and finite element analysis of SiCf/TC17 composites
    Hu LI, Wang-teng-fei FAN, Min-juan WANG, Xu HUANG, Hao HUANG
    2021, 49 (1): 160-167.   DOI: 10.11868/j.issn.1001-4381.2020.000384
    Abstract ( 414 ( PDF (6063KB)( 107 Citation

    The property of continuous SiC fiber reinforced titanium matrix composites is strongly affected by the interface strength.The interface shear strength of SiCf/TC17 was tested by fiber push-out test and then the microstructure of the sample was observed by SEM. The process of cooling from the composite consolidation temperature, specimen preparation for the push-out test, and the actual testing were simulated by using the finite element method. The initial temperature when residual stress begun to exist was identified through regarding the friction force when the fiber was completely separated from the matrix as the starting point.And the distribution of residual stress was analyzed before and after the sample preparation.The influence of the sample thickness and the fiber fraction volume on the distribution of the residual stress was studied.Cohesive zone model was used to analyze the interface chemical bonding strength.The results indicate that the initial temperature below which the residual stress starts to be generated is about 775 ℃.The residual shear stress is introduced at the interface after sample preparation.The difference between the test results of the interface shear strength and the interface chemical bonding strength is due to the existence of the interface residual shear stress.And the interface chemical bonding strength of SiCf/TC17 composites is about 450 MPa at room temperature.

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    Multiaxial fatigue behavior of aluminum alloy thin-walled notched specimens based on DIC
    Ya-jun CHEN, Peng-da XU, Fu-sheng WANG, Chen-chen LIU
    2021, 49 (1): 168-176.   DOI: 10.11868/j.issn.1001-4381.2019.001158
    Abstract ( 381 ( PDF (28728KB)( 243 Citation

    Focusing on the influence of notch on the multiaxial fatigue performance of material, the proportional multiaxial fatigue test was carried out on 7075-T651 aluminum alloy thin-walled notched specimens with variable equivalent stress amplitude. The digital image correlation technique was used to characterize and analyze the critical plane angle. The results show that with the increase of the equivalent stress amplitude, the multiaxial fatigue life of the specimen decreases, and the maximum axial, torsional and shear engineering strains near the notch increase. Under different loading conditions, the strain concentration near the notch increases with the increase of loading cycles. The process of strain change near the notch can be divided into crack initiation, crack growth and instantaneous fracture stages. By introducing the critical plane angle and the maximum positive strain on it, a modified SWT model is proposed. Fine life prediction results are obtained by the modified model with all predicted data in the two scatter bands.

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