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      20 November 2021, Volume 49 Issue 11 Previous Issue    Next Issue
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    Review
    Research progress in graphene based thermal conductivity materials
    Yue LI, Jiong-li LI, Qiao-si ZHU, Jia-feng LIANG, Jian-qiang GUO, Xu-dong WANG
    2021, 49 (11): 1-13.   DOI: 10.11868/j.issn.1001-4381.2020.000935
    Abstract ( 540 ( PDF (7901KB)( 866 Citation

    As a two-dimensional(2D) building block of new materials, graphene has received widespread attention due to its exceptional thermal properties. The thermal properties and recent advances on graphene-based material were reviewed. The intrinsic thermal conductivity of graphene and the effect of layers, defects and edge were briefly introduced. The resent research progress in graphene fiber as thermal conductivity material was analyzed and discussed. A variety of graphene films (graphene film, graphene hybrid film, graphene/polymer composite film) were grouped by category and the influencing factors of the thermal conductivity were reviewed. The structure, thermal conductivity property and current researches of 3D graphene (graphene with random orientation in the polymer matrix, graphene with specific orientation in the polymer matrix) were summarized. Finally, the challenges and prospects of graphene-based materials were also pointed out, especially inhigh power, highly integrated systems such as LED lighting and smart phones, graphene based thermal conductivity materials have a good development prospect.

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    Research progress in graphene-based aerogel microspheres
    Tian LI, Dan-dan ZHI, Zi-hao GUO, Wei-lin GUO, Mei-ling ZHANG, Fan-bin MENG
    2021, 49 (11): 14-29.   DOI: 10.11868/j.issn.1001-4381.2021.000030
    Abstract ( 292 ( PDF (23594KB)( 425 Citation

    In recent years, graphene-based aerogels (GAs) have been extensively studied owing to the excellent characteristics of low density, high specific surface area and porous structure, which show great potential in many applications. The disadvantages of traditional bulk graphene-based aerogels, for instance, strong device-dependence, large size and poor scalable production, limit their practical application and development. Meanwhile, conventional preparation techniques ignore the requirements of materials shape and size for specific application scenarios. As a new aerogels display form with novel structure, graphene-based aerogel microspheres (GAMs) not only have various advantages of GAs but possess properties of flexible and controllable size and scalable production, which tremendously enrich the application scenarios of GAMs.The fabrication methods and structure of GAMs, as well as the application fields of water pollution treatment, electromagnetic wave absorption and electrocatalysis were elaborated in this review.Meanwhile, the internal mechanism of GAS during molding assembly process was also pointed out.

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    Progress in transparent bulletproof armor based on ceramics
    Jia-xi LIU, Xiao-dong SHI, Liang-bao JIANG, Xiao-yu LI, Min-bo WANG, Yue YAN
    2021, 49 (11): 30-40.   DOI: 10.11868/j.issn.1001-4381.2020.001117
    Abstract ( 320 ( PDF (8647KB)( 224 Citation

    Requirements for the cockpit of military vehicles are constantly increasing as a result of escalating threats. The traditional transparent bulletproof armor based on glass have been unsatisfactory to relevant application requirements, and lighter and thinner transparent armor based on ceramics is becoming main option. Similar to other bulletproof armor, the main research fields of transparent bulletproof armor include: seek materials with higher performance for armor components; guide the structure design and ballistic test by experiment or computer simulation; understand the main performance of armor materials, the holistic performance of the armor system and the interaction between the components of the whole system more deeply. Based on this notion, the advantages and disadvantages, preparation technology, development, and application situation of the three kinds of ceramic materials commonly used in transparent armor were summarized. Among the three kinds of ceramics, sapphire has the best static parameters. As for the actual effect of bulletproof, the polycrystalline ceramics are better. The main reason for this phenomenon is that the different fragmentation modes of the two kinds of ceramics lead to the difference of projectile-target interaction effect. After that, the crack growth under high strain rate and bullet-proof property of single crystal, polycrystalline ceramics and glass were discussed. Under uniaxial, high strain rate compression, the crack propagation characteristics of materials are sensitive to impact energy/velocity. Polycrystalline ceramics has a composite failure mode of intergranular fracture and intragranular fracture. Under high energy impact, the damage zone of sapphire is similar to polycrystalline ceramics. Lower than critical energy, some sapphire plate orientations damage would be dominated. Finally, the material selection standards and structural design principles of each functional layer were summarized and prospected. Fine grain polycrystalline ceramic materials with high Young's modulus and high hardness are preferred for the strike-layer. Materials with good fracture toughness, high bending stiffness and the ability to localization of the damage within a narrow region should be selected for the intermediate layer. The materials of backing layer require ductility and low density. The bulletproof efficiency of the transparent-armor systems depends on the type and the degree of interaction/integration of different functional layers.

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    Demand for high performance materials in development of China's aerospace science and technology
    Yi-ren ZHOU, Zi-cai SHEN, Zhen-yi QI, Yu-xiong XUE, Hong-bo HE, Yan-zhi WANG
    2021, 49 (11): 41-50.   DOI: 10.11868/j.issn.1001-4381.2021.000129
    Abstract ( 332 ( PDF (4129KB)( 436 Citation

    With the success of bringing back lunar samples, Mars exploration and space station construction, new requirements for high performance materials were put forward with the devel-opment of China's new space missions. Based on the analysis of the current situation and trend of China's aerospace development, some demands for high performance materials such as lightweight high performance structural materials, lightweight high efficiency thermal protection materials, structural & functional integration materials, new multifunctional composite protective materials, extreme temperature resistant functional materials, intelligent materials, high performance spacesuit materials, functional gradient materials, meta-materials, 3D printing materials and 4D printing materials were analyzed. Finally, nanotechnology, material genetic engineering and other new technologies were put forward to incorporate the space environment into the whole process of aerospace materials development and to further carry out the research and development of aerospace materials.

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    Micro-alloying influence in microstructure evolution and mechanical properties of TiB2 particle reinforced aluminum matrix composites: a review
    Yan-qing XUE, Bo LI, Xin-liang WANG, Han ZHANG, Qi-tang HAO
    2021, 49 (11): 51-61.   DOI: 10.11868/j.issn.1001-4381.2021.000078
    Abstract ( 249 ( PDF (16712KB)( 132 Citation

    Micro-addition of alloying elements is not only an effective method to improve the overall performance of aluminum matrix composites but also a proven workable low-cost technology in improving the reinforced phase/matrix interface structure and regulating the mechanical property of strength-toughness other than the physical processes such as electromagnetic stirring and ultrasonic vibration, as well as preparation technologies like bimodal structure and biomimetic layered materials, etc. In recent years, the research of alloying elements in TiB2 particles reinforced aluminum matrix composites has attracted much attention and achieved remarkable results which lay a good foundation for better understanding of its mechanism on the nano-level or even the atomic level. A series of latest developments on the properties of TiB2/Al composites by adding alloying elements at home and abroad were summarized, i.e. TiB2 particle morphology, microstructure and mechanical properties.The mechanism of micro-alloying and its prospect on regulating crack initiation and propagation, exerting intrinsic mechanical properties of micro and nano scale, along with coordinating the dilemma of strength-ductility trade-off were also forecasted, aimed at providing reference for the preparation of high-performance aluminum matrix composites.

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    Research Article
    Experimental study on compressive properties of CFRP laminates at high temperatures via digital image correlation
    Yang YANG, Xin-wen CHEN, Wei SUN, Li-ting MA, Xiang WANG, Guang-ping GUO
    2021, 49 (11): 62-72.   DOI: 10.11868/j.issn.1001-4381.2020.000793
    Abstract ( 147 ( PDF (22391KB)( 301 Citation

    The high-temperature compressive properties are indispensable mechanical performance parameters for the structural design of composites, but it is difficult to be measured effectively by traditional techniques. In this study, the high temperature compressive experiment of carbon fiber reinforced plastics (CFRP) laminates was conducted in high-temperature experimental system based on digital image correlation (DIC) method. And the compressive properties, stress-strain curves and the evolution of axial full-field strain of CCF300/5228A with 0° and 90° ply-ups at 130℃ were obtained. Moreover, they were compared with those obtained at room temperature. Furthermore, the fracture analysis of the compressed specimens was carried out through scanning electron microscopy (SEM), meanwhile the effects of high temperature and lay-up on the compressive properties were discussed combining with the experimental results. Finally, an experimental verification was carried out and the results obtained demonstrated the feasibility and reliability of the experimental system and relevant experimental methods. The results show that the retention rate of 0° and 90° compressive strength at 130℃ are 70.5% and 62.6%, respectively, while the retention rate of compressive modulus are 88.0% and 75.4%, respectively, indicating that the strength and modulus of the laminates which are controlled by the matrix are more sensitive to high temperature.

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    Anti-high speed impact properties of carbon fiber/bismaleimide resin composites
    Shan-qun GU, Dai-jun ZHANG, Shan-long FU, Yan-feng LIU, Jun LI, Qi ZOU, Xiang-bao CHEN
    2021, 49 (11): 73-82.   DOI: 10.11868/j.issn.1001-4381.2019.001234
    Abstract ( 193 ( PDF (29842KB)( 124 Citation

    The carbon fiber/bismaleimide resin composites were prepared by the autoclave molding process. Effects of carbon fiber type and volume fraction of carbon fiber on the high speed impact properties were investigated by air cannon impact testing machine, ultrasonic C-scanner and electronic universal material testing machine. The results demonstrate that the anti-high speed impact property of TZ1000G carbon fiber reinforced composites is superior to that of the CCF300 carbon fiber, CCF700S carbon fiber and CCF800H carbon fiber reinforced composites. Also, the volume fraction of carbon fiber can improve the anti-high speed impact property of the composites. Meanwhile, the results also indicate that failure modes are highly dependent on the impact velocity. Specifically, when the impact velocity is low, a circular pit with fiber delamination appears around on the impact surface of the composites while delamination appears on the back surface 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 the tearing fracture is observed on the back surface.

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    Effect of ultraviolet accelerated aging on mechanical and optical properties of polycarbonate
    Qi-wei SUN, Tao WANG, Yu-hong CHEN, Yong GE, Jian-lin LANG, Bo-lun WANG, Yue YAN
    2021, 49 (11): 83-89.   DOI: 10.11868/j.issn.1001-4381.2020.001006
    Abstract ( 116 ( PDF (12470KB)( 85 Citation

    In order to explore the effect of accelerated UV aging on the mechanical and optical properties of polycarbonate, the changes of polycarbonate's transmittance, yellow index, tensile properties and flexural properties with aging time and radiation intensity were studied by using the method of exposure to laboratory fluorescent ultraviolet lamps source. The results show that the light transmittance of polycarbonate is decreased with the increase of UV aging time and radiation intensity. According to FT-IR, several colored groups are created in polycarbonate because of prolonging the aging time and increasing the radiation intensity, which affects the optical property of polycarbonate. The tensile strength and elongation at break of polycarbonate are decreasd with the increase of UV aging time and irradiation intensity. The microcracks and holes on surface of polycarbonate are produced by longer aging time and higher radiation energy, which expand under tensile load and cause fracture. The flexural strength of polycarbonate is increased with the increase of UV aging time and irradiation intensity if the testing surface is irradiated. The degradation layer formed on the surface of the material increases the stiffness of polycarbonate, which leads to the increase of strength. The tensile modulus and bending modulus of polycarbonate are less affected by aging time and irradiation strength because UV accelerated aging has little effect on molecular weight.

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    Effects of temperature and storage period on polarization of poly(vinylidene fluoride-trifluoroethylene) ultrathin films
    Zhi SHI, Xing-jia LI, Xiu-li ZHANG, Xiang-jian MENG, Zhi-qiang HUANG, Dan-dan ZHANG, Hong-xia XU
    2021, 49 (11): 90-97.   DOI: 10.11868/j.issn.1001-4381.2020.000964
    Abstract ( 132 ( PDF (7037KB)( 78 Citation

    The polarization switching properties of P(VDF-TrFE) ultrathin films with different storage periods were measured. The dependence of polarization properties on temperature and storage period was investigated. The experimental results suggest that the relative remanent polarization (Pr/Pr0) remains on a relatively high level of 0.70 at 60℃, 106 polarzation swiching test, even to the ultrathin film capacitors stored in atmosphere for five months. The time stability model of polarization switching is predicted by the evolution of polarization switching with the number of electric field cycles. Moreover, when the changes of the molecular chain are simulated by different storage periods and testing temperatures, an inhibited hydrogen fluoride (HF) gas formation scheme in the capacitors was proposed. This work further validated the time stability model and microscopic dynamics associated with trapped charge. These results provide an effective method for designing an optimum protocol for flexible electronic devices based on P(VDF-TrFE) copolymer ultrathin films.

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    Structure and transparent conductive properties of F-doped ZnO(FZO) thin films prepared by reactive magnetron sputtering
    Bai-lin ZHU, Si-long ZHENG, Ting XIE, Jun WU
    2021, 49 (11): 98-104.   DOI: 10.11868/j.issn.1001-4381.2021.000132
    Abstract ( 120 ( PDF (4981KB)( 108 Citation

    F-doped ZnO (FZO) films were prepared by reactive sputtering using Zn/ZnO/ZnF2 mixture as the target at substrate temperature (Ts) of 150℃ and 300℃ and sputtering atmosphere of Ar+O2 and Ar+H2. The effect of gas flux, Ts, and sputtering atmosphere on the structure and transparent conductive properties of the thin film was investigated. The results show that for FZO films prepared under Ar+O2, Ts=300℃ is conductive to the preparation of films with (002) preferred orientation, high crystallinity, low compressive stress and good transparent conductive properties. For the films prepared under Ar+H2, with the increase of Ts to 300℃, the crystallinity and transmittance of the films improve and the compressive stress reduces, but the film thickness significantly reduces and leads to the deterioration of the conductive properties of the films. The FZO films prepared in the two atmospheres are compared, and it is found that the films prepared in Ar+H2 can obtain better transparent conductive properties (the resistivity of 3.5×10-3 Ω·cm and the average transmittance in visible range of 87%) at 150℃ and in H2 flux range of 0.8-3.2 mL·min-1. The etching effect of H plasma and H doping in the Ar+H2 atmosphere, the bombardment of O ions and the change of oxygen defects of the films in the Ar+O2 atmosphere, the enhancement in reaction activity and mobility of deposited atoms with increasing Ts, and the relationship between Eg and carrier concentration are discussed in detail.

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    Microstructure and tribological properties of Co-Ti3SiC2 self-lubricating composite coatings on 304 stainless steel by laser cladding
    Gang WANG, Xiu-bo LIU, Yi-fan LIU, Yang ZHU, Chun-sheng OUYANG, Yuan MENG, Ying-she LUO
    2021, 49 (11): 105-115.   DOI: 10.11868/j.issn.1001-4381.2021.000329
    Abstract ( 153 ( PDF (23037KB)( 83 Citation

    The self lubricating wear-resistant coatings were prepared on the surface of 304 stainless steel successfully using laser cladding synchronous powder feeding method, the ratio of cladding powder was pure Co, Co-2%Ti3SiC2(mass fraction, the same below) and Co-8%Ti3SiC2. The microstructure of the cladding coating was characterized by scanning electron microscope(SEM), energy spectrum analyzer(EDS) and X-ray diffractometer(XRD). The tribological performance and related mechanisms of 304 substrate and coatings at RT/600℃ were systematically investigated. The results show that the average microhardness of the N1, N2 and N3 coatings are 285.7HV0.5, 356.3HV0.5 and 463.8HV0.5, which are all much higher than that of the matrix(240.3HV0.5). Co-Ti3SiC2 composite coatings are composed of continuous matrix γ-Co solid solution, hard phase (Fe2C, Cr7C3 and TiC) and lubricating phase Ti3SiC2. At room temperature, the friction coefficients of the matrix and the N1, N2 and N3 coatings are 0.56, 0.62, 0.68 and 0.42, the wear rates of the N1, N2, N3 coatings are 9.15×10-5, 7.81×10-5, 4.66×10-5 mm3/(N·m), which are lower than that of the matrix (66.42×10-5 mm3/(N·m)); at high temperature, the friction coefficients of the matrix and the N1, N2 and N3 coatings are 0.66, 0.54, 0.52 and 0.46, the wear rates of the N1, N2, N3 coatings are 37.79×10-5, 35.6×10-5, 18.83×10-5 mm3/(N·m), which are lower than that of the matrix (41.3×10-5 mm3/(N·m)).At room temperature and 600℃, compared with the 304 stainless substrate, the coatings have the obvious higher microhardness, and the Co-8%Ti3SiC2 coating exhibits the best self-lubricating wear resistance.

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    Densification method of air-plasma-sprayed environmental barrier coatings achieved by pre-heat treatment
    Bo YANG, Guang-rong LI, Tong XU, Guan-jun YANG
    2021, 49 (11): 116-124.   DOI: 10.11868/j.issn.1001-4381.2020.001156
    Abstract ( 136 ( PDF (21593KB)( 109 Citation

    High density of the top coat of environmental barrier coatings (EBC) is important for ensuring its performance in water vapor environment, which is also significant for prolonging service lifetime of SiCf/SiC aero-engine hot components. In this work, densification of the top coat of EBC was achieved by pre-heat treatment. In detail, the as-sprayed porous Yb2SiO5 coatings were heat-treated at the high temperature of 1250℃ to 1450℃, which improve the density significantly. Changes in microstructure and mechanical properties during the pre-heat treatment were studied by classifying defects into different types. The processes of defects-healing were observed, and the mechanism responsible for coating densification was revealed. Results show that the porosity of as-sprayed Yb2SiO5 coating is high due to the existence of three types of micro-defects, including two-dimensional (2D) inter-splat pores, 2D intra-splat cracks and three-dimensional (3D) spherical pores. During the pre-heat treatment process, 2D defects are healed to be reduced in a large amount in a short duration, while the 3D spherical pores seem unchanged. The mechanism of defects-healing in the heat treatment process is that grain growth inside the coating makes surface of the pores rough, which leads to multiple bridge-connection of 2D pores. As a result, the original continuous defects are divided into several sections and are further spheroidized. The method of pre-heat treatment for APS-EBC would make a fundamental contribution to its further engineering application.

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    Effect of ceramic particles on corrosion resistance of thermal sprayed stainless steel coating
    Quan TANG, Suo-de ZHANG, Min XU, Jian-qiang WANG
    2021, 49 (11): 125-135.   DOI: 10.11868/j.issn.1001-4381.2020.001177
    Abstract ( 140 ( PDF (33487KB)( 81 Citation

    The ceramic particles of different types and sizes reinforced stainless steel composite coatings were successfully prepared by high-velocity air fuel (HVAF) spraying technique. The effects of the types and sizes of ceramic particles on the hardness, porosity and corrosion resistance of the composite coating were systematically studied. The microstructure, hardness and corrosion behavior of stainless steel/ceramic particle composite coating were systematically characterized and analyzed by scanning electron microscope, automatic hardness tester, Image Pro Plus software and electrochemical workstation. The results show that the larger brown alumina (Al2O3) particles reinforced stainless steel composite coating has low porosity (0.7863%), high hardness (637HV0.1) and excellent corrosion resistance, and its self-corrosion potential is -454.14 mV and self-corrosion current density is 22.208 mA·cm-2. The fine silicon carbide (SiC) particles reinforced stainless steel composite coating also has a relatively high hardness (600HV0.1) and good corrosion resistance, and its self-corrosion potential is -463.68 mV and self-corrosion current density is 23.738 mA·cm-2.

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    Analysis of hot deformation behavior and processing map of extruded AZ40 alloy
    Sheng-xing ZHI, Xing-gang LI, Jia-wei YUAN, Yong-jun LI, Ming-long MA, Guo-liang SHI, Kui ZHANG
    2021, 49 (11): 136-146.   DOI: 10.11868/j.issn.1001-4381.2021.000136
    Abstract ( 122 ( PDF (18760KB)( 95 Citation

    The Gleeble-3500 thermal simulation tester was used to perform hot deformation behavior on the extruded AZ40 Mg alloy to analyze the trend of the true stress-strain curve after compression and to obtain the influence of the flow stress on the deformation temperature and strain rate. Subsequently, the constitutive equation was constructed for extruded AZ40 alloy based on the hyperbolic-sine relationship, and the thermal processing map of extruded AZ40 alloy was established based on the dynamic material model (DMM), thereby estimating the processing range of extruded AZ40 alloy. The results show that the rheological curve of extruded AZ40 alloy is characterized by obvious dynamic recrystallization. Furthermore, during the compression process, the peak stress of extruded AZ40 alloy decreases with the increase of deformation temperature, while increases with the increase of strain rate. Moreover, the proportion of dynamic recrystallized grains (DRGs) decreases with the increase of the strain rate under the same deformation temperature condition; while the DRGs size increases with the increase of the deformation temperature under the same strain rate condition. The coarse uncrystallized grains show obvious crystallographic orientations of 〈10${\rm{\bar 1}}$0〉‖ND and 〈2${\rm{\bar 1}}$${\rm{\bar 1}}$0〉‖ND, while crystallographic orientation of DRGs is random distributed. Finally, through thermal processing map and tissue analysis, the optimal processing window was identified as T=573 K, $\dot \varepsilon $=0.1 s-1.

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    Applicability analysis of cyclic plasticity constitutive model for superalloy foils
    Yan-ju WANG, Shen-long LI, Wei-lin HE, Ai-xue SHA, Chong-lin JIA, Bao MENG, Min WAN
    2021, 49 (11): 147-155.   DOI: 10.11868/j.issn.1001-4381.2021.000372
    Abstract ( 119 ( PDF (7737KB)( 101 Citation

    Superalloy has excellent comprehensive properties and is the preferred material for high performance components of aeroengine. Due to its high yield strength and obvious springback, it is difficult to control the forming precision of superalloy component. Therefore, it is crucial to study the applicability of cyclic constitutive models in the deformation simulation of superalloy foils. Based on the cyclic shearing test, the characterization effects of different cyclic plastic constitutive models on the cyclic plastic deformation response of superalloy were studied. By comparing the results of U-bending test with the simulation results of finite element software, the accuracy of springback prediction of different yield criteria combined with different cyclic plastic constitutive models was analyzed. The results show that Y-U (Yoshida-Uemori) model has the best characterizing effect on the response of cyclic plastic deformation, while A-F (Armstrong-Frederick) model and ANK (the anisotropic nonlinear kinematic) model have close characterizing effect. For the prediction accuracy of springback, the fitting accuracy of Y-U model is higher than that of isotropic model and A-F model. However, the yield criterion has little influence on the prediction accuracy of springback. The prediction deviation of Y-U model based on Hill48 yield criterion and YLD-2000 yield criterion can be controlled within 5%.

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    Effect of minor boron on mechanical properties of Ti-Fe-Cu-Sn-Nb alloys
    Zhi-cong GAN, Shuo WANG, Sheng-feng SHAN, Bing ZHANG, Yuan-zhi JIA, Ming-zhen MA
    2021, 49 (11): 156-162.   DOI: 10.11868/j.issn.1001-4381.2019.001222
    Abstract ( 112 ( PDF (8972KB)( 66 Citation

    Based on grain refinement and secondary phase strengthening, minor boron (B) was added to near β-Ti alloy to strengthen the alloys. Ti85Fe6Cu5Sn2Nb2 alloys with various B contents were designed, prepared by using a non-consumable vacuum arc melting furnace, and hot rolled at 800℃followed by quenching. The effects of minor B addition on the microstructure and mechanical properties of Ti85Fe6Cu5Sn2Nb2 alloy were investigated through microstructure observation, tensile mechanical test, fracture observation and transmit electron microscopy. The results reveal that minor B addition can refine the grains, improve the strength whereas the plasticity of the alloy is decreased. The alloy containing 0.15% (mass fraction)B possesses the better comprehensive mechanical properties(σ0.2=1105 MPa, δb=4.5%).With the increase of B content, the strength of the alloy is increased and reaches up to 1156 MPa. Orthorhombic TiB compounds are formed in the alloy, distributed in the β-Tialloy matrix. Upon deformation, the fracture of TiB phases, cutting and debonding of TiB phases to the alloy matrix, formed the fracture source, resulted in the decrease of the alloy plasticity.

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    Effect of nano-Cr particles on solder joint properties of Sn-Zn-Bi-In/Cu brazing
    Guang-zhu LIU, Di YUE, Yu KANG, Hong-yu XIE, Ding-jin HE
    2021, 49 (11): 163-170.   DOI: 10.11868/j.issn.1001-4381.2021.000247
    Abstract ( 135 ( PDF (13837KB)( 89 Citation

    The new composite solder Sn-5Zn-10Bi-10In-xCr (x=0%, 0.1%, 0.3%, 0.5%, mass fraction) was made by adding different contents of nano-Cr particles to the Sn-Zn-Bi-In solder. The effect of nano-Cr particles on the microstructure, element distribution, phase composition and mechanical properties of brazing joints before and after aging was studied. The results show that the addition of nano-Cr particles can inhibit the growth of intermetallic compounds (IMCs) in the solder joints. With the increase of the content of nano-Cr particles, the thickness of the IMCs diffusion layer is gradually decreased; the IMCs diffusion layer at the interface near the base material Cu is Cu5Zn8 phase, and the side close to the solder zone is the Cu6Sn5 phase; as the aging time increases, the Cu5Zn8 compound on the solder side grows and is decomposed, and the Cu3Sn phase is formed; the nano-Cr particles inhibit the further growth of the IMCs diffusion layer during the aging process; as the content of Cr particles increases, the shear strength and microhardness of the solder joints increase first and then decrease. The shear strength and hardness of the Sn-5Zn-10Bi-10In-0.3Cr/Cu solder joints are the highest; the shear strength is lower than before aging, but the addition of nano-Cr particles keeps the solder joints with good shear strength. After aging, the microhardness of the solder area of the solder joints increases compared with that before aging, but it has always been maintained at below 30HV0.1.

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    GO enhanced visible-light response of g-C3N4 aerogel and degradation of unsymmetrical dimethylhydrazine in wastewater
    Feng ZHOU, Xiang-hong REN, Hong-fu QIANG, Yi-zhi ZENG, Miao-miao FAN
    2021, 49 (11): 171-178.   DOI: 10.11868/j.issn.1001-4381.2020.001089
    Abstract ( 180 ( PDF (10998KB)( 135 Citation

    A series of GO/g-C3N4 aerogel materials were prepared by the methods of ultrasonic peeling, solution cross-linking and freeze-drying, and the proportion of raw materials were optimized. The materials were characterized by SEM, XRD, and UV-vis absorption spectrum. The photocatalytic activity was evaluated by the degradation of unsymmetrical dimethylhydrazine (UDMH) wastewater. The pure g-C3N4 aerogel was dominated by mesoporous structure. As the graphene oxide (GO) ratio increases, the layered structure and macroporous structure of the material gradually increase, and all show strong adsorption performance. When the mass fraction of GO is 25%, the photocatalytic degradation of UDMH wastewater is the best and the performance is stable after 5 cycles, the photocatalytic activity is only reduced by 7.15%. Through the study on the energy band structure, characterization of photoelectric effect and PL spectrum, the results show that the g-C3N4 molecular orbital energy level and band gap (Eg) were impacted by the cross-linking between the π-π bond of GO layers and the aromatic ring of g-C3N4, which improve the response performance to visible light. The metallic properties of GO facilitate the rapid separation of photogenerated electron-hole pairs and improve the photocatalytic activity. According to the band gap calculation and the intrinsic molecular orbital of the material, the main active species for GOCN photocatalytic degradation of UDMH wastewater are ·O2- and h+.

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