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Key engineering materials
Trans Tech Publications Ltd.
Key engineering materials

Trans Tech Publications Ltd.

半月刊

1013-9826

Key engineering materials/Journal Key engineering materials
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    Effects of Carbon Black on Microstructure and Mechanical Properties of Hot Pressed ZrB_2-SiC Ceramics

    Xin SunXinghong ZhangZhi WangWenbo Han...
    185-188页
    查看更多>>摘要：ZrB_2-SiC ultra-high temperature ceramics (UHTCs) was hot-pressed at a temperature of 1900℃ with the addition of carbon black as a reinforcing phase. Microstructure and mechanical properties were investigated. Analysis revealed that the amount of carbon black had a significant influence on the sinterability and mechanical properties of ZrB_2-SiC ceramics. When a small amount ( < 10 vol.%) of carbon black was introduced, it may react with oxide impurities (i.e. ZrO_2, B_2O_3 and SiO_2) present on the surface of the starting powder, thus promote the densification and grain refining of ZrB_2-SiC ceramics. As a result, the mechanical properties including flexural strength and fracture toughness were improved. However, with the further adoption of carbon black, mechanical properties were not improved much, which could be attributed to the redundant phase at grain boundaries. The results presented here point to a potential method for improving densification, microstructure and mechanical properties of ZrB_2-based ceramic composites.
      原文链接:
    • NETL
    • NSTL
    • Trans Tech Publications Ltd

    Influence of Hot Pressing Temperature and SiC Content on the Microstructure and Mechanical Properties of ZrB_2-SiC

    Yong ZhangPing HuXing-Hong Zhang
    189-192页
    查看更多>>摘要：The influence of hot pressing temperature and SiC content on the microstructure and mechanical properties of ZrB_2-SiC ceramics was investigated. ZrB_2 containing 20 volume percent SiC were prepared by hot pressing at 1850, 1900 and 1950℃ for 60 min. Fully dense ceramic was obtained after hot pressing at temperature of 1950℃. In addition, the materials with SiC content of 0, 10vol.%, 15 vol.%, 20 vol.% and 30 vol.% hot pressed at 1950℃ were also investigated. Results showed that the grain size of the ZrB_2 significantly reduced on adding 10vol.% SiC and then decreased slightly with further increasing SiC content, whereas the grain size of SiC exhibited a opposite trend. The flexural strength of ZrB_2-SiC ceramics remarkedly increased on adding 10vol.% SiC due to the significant decrease of ZrB_2 particle size and then slightly increased with increasing SiC content up to 20vol.%. However, further increasing SiC content led to a reduction of the flexural strength.
      原文链接:
    • NETL
    • NSTL
    • Trans Tech Publications Ltd

    Pressureless Sintering of ZrB_2-SiC Ceramics Incorporating Sol-gel Synthesized Ultra-fine Ceramic Powders

    Hui ZhangYongjie YanZhengren HuangXuejian Liu...
    193-196页
    查看更多>>摘要：Ultra-high temperature ceramic composites of ZrB_2-SiC were densified by pressureless sintering. Ultra-fine ZrB_2-SiC composite powders synthesized by sol-gel method were mixed with commercial ZrB_2 and SiC powders. The sintered body of hybrid powders (combined commercial and synthesized composite powders) showed excellent properties not only in the relative density but also the flexure strength. Dry-pressed compacts using 4wt% Mo as a sintering aid were sintered to nearly full density at 2200℃/2h. The average strength was ～560MPa and the maximum was ～632MPa. SEM and TEM showed that SiC particles were distributed homogenously in the ZrB_2 matrix and the average particle size was ～5μm. From HRTEM observations, the grain boundaries were apparently free of glassy phases and no intermediate phases existed.
      原文链接:
    • NETL
    • NSTL
    • Trans Tech Publications Ltd

    Joining of Advanced Ceramics, Glasses and Composites at Politecnico di Torino, Italy

    Valentina CasalegnoQiuling ChenQiuping ChenMilena Salvo...
    197-201页
    查看更多>>摘要：An overview of the last 16 years of activity on joining of advanced ceramics, glasses and ceramic matrix composites at Politecnico di Torino (Italy) will be presented. Results on thermal assisted direct bonding (TADB) of glasses for lab-on-chip devices, C/C composites to Cu-alloys for nuclear fusion components (ITER), SiC and SiC/SiC joints for nuclear components (fusion and fission), glass joining of foam glass, C/C joints for aerospace applications, ceramics to stainless steels for Solid Oxide Fuel Cells (SOFC), will be shown. Mechanical tests on joined components will be discussed, in particular, the results of an experimental campaign on carbon/carbon and ceramic joints tested in pure and apparent shear by nine different configurations.
      原文链接:
    • NETL
    • NSTL
    • Trans Tech Publications Ltd

    Reaction Layer Microstructure of SiC/SiC Joints Brazed by Ag-Cu-Ti Filler Metal

    Yan LiuZhengren HuangXiujian Liu
    202-204页
    查看更多>>摘要：The reaction layer microstructure of SiC/SiC joints brazed by Ag-Cu-Ti filler metal, including composition, morphology, grain size were investigated by X-ray diffraction, electronic probe microanalysis, transmission electron microscope. An obvious reaction layer composed of TiC and Ti_5Si_3 was observed at the interface of SiC substrate and filler metal. There is a representative structure of SiC substrate/continuous fine TiC layer /discontinuous coarse Ti_5Si_3 layer/filler metal in the reaction layer. The continuous TiC layer, composed of about 10 nm roundish grains, is 350 ～400 nm thick. Ti_5Si_3 layer is composed of only one row of Ti_5Si_3 grains, which disperse with diverse size from 100 ～ 500 nm. Different growth behavior of TiC and Ti_5Si_3 is the main reason to form this microstructure.
      原文链接:
    • NETL
    • NSTL
    • Trans Tech Publications Ltd

    Estimating Energy Dissipation of Ceramics via H-E ratio

    Yiwang BaoDetian WanYan Qiu
    205-208页
    查看更多>>摘要：Mechanical properties of ceramics are important for its engineering application. It would be significant and efficient if some properties could be estimated without tests. Energy dissipation capacity of ceramics is estimated in this work via two common parameters, hardness and elastic modulus, which could be obtained from basic data of commercial ceramics or simple tests. The ratio of hardness to reduced modulus H/E_r is found to be related to recovery resistance and energy dissipation capacity of the materials, and the related equations were induced. The reduced modulus can be expressed by conventional elastic modulus E. Thus, the capacity of energy dissipation and elastic recovery can be estimated simply from the H/E ratio. The calculated results indicate that the value of H/E ratio is in reverse proportion to the energy dissipation. Several ceramics with different H/E ratio are analyzed and their energy dissipation capacities are estimated.
      原文链接:
    • NETL
    • NSTL
    • Trans Tech Publications Ltd

    Comparison and Relative Error of Elastic Modulus in Glass Measured by Three Test Techniques

    Yan QiuYiwang BaoXiaogen LiuXiufang Wang...
    209-213页
    查看更多>>摘要：Elastic modulus of glass was measured using static method, dynamic method and Vickers indentation technique, respectively. The residual indent of Vickers indentation is analyzed to estimate the elastic modulus, using conventional hardness tester without load-depth curve. The modulus and hardness of glass are determined by load, deformation and residual semi-angle of the indent. The result is compared with the modulus obtained by conventional dynamic and static methods. It was shown that the modulus measured by dynamic method provides the highest value and the modulus obtained by indentation technique is between the values of dynamic modulus and static modulus. The result also shows that the modulus measured by dynamic method has very stable value and that measured by bending method has the lowest value. The modulus obtained in indentation tests shows relatively greater scatter.
      原文链接:
    • NETL
    • NSTL
    • Trans Tech Publications Ltd

    Synthesis and Luminescent Properties of Mn~(2+)-Doped Zinc Silicate Phosphors by Sol-Gel Method

    Ji-Ming ZhangDong-Lin ZhaoZeng-Min Shen
    214-216页
    查看更多>>摘要：Green light emitting Mn~(2+)-doped Zn_2SiO_4 (Zn_2SiO_4:Mn~(2+)) phosphor nano-particles were synthesized by sol-gel method combined with a furnace firing from the sol-gel solution made with ZnO, MnCO_3 and tetraethoxysilan. The influences of annealing temperatures on the microstructures and photoluminescent properties of the Zn_2SiO_4:Mn~(2+) phosphors were investigated. The structural details of the phosphors were examined through XRD and SEM. The photoluminescent properties of the Zn_2SiO_4:Mn~(2+) phosphors were characterized by excitation and emission spectra. The results indicate that the XRD patterns of the Zn_2SiO_4:Mn~(2+) phosphors exhibit a willemite structure (α-Zn_2SiO_4). Green photoluminescence whose emission peak is located at 525 nm were observed from the synthesized phosphor particles under UV excitation. The photoluminescent mechanisms of the Zn_2SiO_4:Mn~(2+) phosphors were discussed.
      原文链接:
    • NETL
    • NSTL
    • Trans Tech Publications Ltd

    Microwave Dielectric Properties of RENbO_4 (RE=Y, Yb,Ce) Ceramics

    Zhang ZhiliXu ChunLiu Qiuping
    217-220页
    查看更多>>摘要：In the search of more microwave dielectric materials with high-quality factor (Q×f) and high relative dielectric constant (ε_r), RENbO_4 (where RE = Y, Ce, Yb) niobate ceramics were synthesized from a solid-state ceramic route, their sintering behavior and microwave dielectric properties were investigated. All of the RENbO_4 ceramics formed a single-phase fergusonite-type structure (monoclinic, with space group 12/c), except CeNbO_4. They all have an excellent quality factor and dielectric constant value in range of 20 - 28, and the inherent reasons were analyzed.
      原文链接:
    • NETL
    • NSTL
    • Trans Tech Publications Ltd

    Preparation of ZnNb_2O_6 Nano-powders by Pechini Method

    Yingchun ZhangShuming WangXiangna ZhouBaojian Fu...
    221-223页
    查看更多>>摘要：ZnNb_2O_6 ceramics with a columbite crystal structure, is a promising candidate for application in microwave devices. In this study, ZnNb_2O_6 nano-powders were prepared using Nb_2O_5 and Zn(NO_3)_2 as raw materials by Pechini method. The microstructure and crystal structure of ZnNb_2O_6 powders were investigated systematically using X-ray powder diffraction and SEM techniques. The effect of amount of citric and ethylene on the formation of sol-gel and the particle size of ZnNb_2O_6 powders were also investigated using orthogonal design. Finally, the optimum process parameters for synthesis ZnNb_2O_6 nano-powders were obtained in this study.
      原文链接:
    • NETL
    • NSTL
    • Trans Tech Publications Ltd