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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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    Liquid Oxide Flow During Oxidation of Zirconium Diboride-Silicon Carbide Ultra High Temperature Ceramics

    Sindhura GangireddySigrun N. KarlsdottirJohn W. Halloran
    144-148页
    查看更多>>摘要：Recent ideas on the oxidation of ZrB_2-SiC are presented, emphasizing the behavior of the boria-silica-zirconia liquid (BSZ liquid) which forms during oxidation and flows to transport silica and zirconia to the surface of the scale. Oxide film microstructure is strongly influenced by the boron oxide, which acts as a volatile flux.
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    Nonlinear Elastic Deformation of MAX phases

    Aiguo ZhouM. W. Barsoum
    149-153页
    查看更多>>摘要：MAX phases, include Ti_3SiC_2, Ti_2AlC etc, are machinable ternary carbides or nitrides with excellent properties. These materials, however, have obvious nonlinear elastic deformation due to nano-layered crystal structure. The stress-strain curves of cyclically load-unload test have obvious hysteretic loops. Because of this mechanical hysteresis, the strain of MAX phases at one time is not determined only by the stress applied to the sample at this time. Here the influence of grain size, chemical composition and porosity on the nonlinear elastic strain was introduced. Because of two properties of this hysteresis: wiping out and congruency, the classic hysteretic mathematic model (Preisach-Mayergoyz model, P-M model) can be applied to calculate the strain of MAX phases after any complex deformation history.
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    Finite Element Analysis on Temperature-Stress of Permeable Refractory Ceramic under Working Process in Ladle

    Gu HuazhiHuang AoWang Houzhi
    154-157页
    查看更多>>摘要：According to the practical physical dimension and processing parameters of ladle with bottom gas blowing in a factory, a geometrical model was established and mesh structure was completed, Eulerian multiphase model and porous media model were adopted for the two-phase flow in ladle, which was coupled, the effect of temperature field and thermal stress in course of working process of permeable-gas refractory ceramic was studied by finite element approach. The correlations between processing, structure, and high-temperature mechanical properties were discussed, and the material and structure of permeable-gas ceramic were designed to optimum. The results show that: The steady gas flow rate can avoid wearing of permeable-gas refractory ceramic from cataclysm of temperature-stress; After the material and structure of permeable-gas refractory ceramic are optimized, the effect on ceramic wearing of temperature-stress in condition of oxygen washing is weakened. It is an important guiding for preparation of permeable-gas refractory ceramic with long life, which will make for highly active refining ladle.
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    • NETL
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    Convective Heat Transfer Steady Thermal Stress in a ZrO_2/FGM/Ti-6Al-4V Composite ECBF Plate with Temperature-Dependent Material Properties

    Yangjian XuHaiyang DuDaihui Tu
    158-161页
    查看更多>>摘要：A NFE model is constructed to analyze the convective heat transfer steady thermal stress in a ZrO_2/FGM/Ti-6Al-4V composite ECBF plate with temperature-dependent material properties. From numerical calculation, when h_a=h_b , T_0=300K, T_a=550K and T_b=1800K, the stress distributions in the plate were obtained. The results are as follows. With the increase of the FGM gradient layer thickness, the stress distribution in the composite plate is more reasonable. With the increase of M, the thermal stress change increases obviously in metal and ceramic layers, and the stress on the ceramic surface reduces. With the increase of porosity, the change of stress at the bonding interfaces increases, and the tensile stress on the surface of ceramics reaches the maximum. Compared with h_a=h_b=1, when h_a =h_b = 10, the stress on the metal surface reduces by 25.1%, and the maximum compressive stress on the surface of ceramics increases about 1.2GPa. Compared with the nongraded two-layered ceramic/metal composite plate, the thermal stress of ZrO_2/FGM/Ti-6Al -4V composite ECBF plate is very gentle. When we consider the temperature dependency of the material properties, the thermal stress in graded three-layered composite plate becomes small obviously. The results provide the foundations of theoretical calculation for the design and application of the composite plate.
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    Processing and Characterization of Nano Silicon Carbide Ceramics via Precursor Pyrolysis

    Dong-Lin ZhaoLei ZhangZeng-Min Shen
    162-164页
    查看更多>>摘要：Nano silicon carbide ceramics were prepared via precursor pyrolysis. Polycarbosilane (PCS) and divinylbenzene (DVB) were selected as a precursor to silicon carbide ceramics and a cross-linking reagent for PCS, respectively. The cross-linking properties and pyrolysis of PCS and DVB were investigated by changing the mass ratios of PCS/DVB. The mass ratio of PCS/DVB has a great effect on silicon carbide ceramic yield. The cured PCS/DVB with a mass ratio of 1:0.5 has the highest SiC ceramic yield (63.1%) at the temperature up to 1500℃ and its pyrolyzates consiste of nano silicon carbide with a diameter of 10-40 nm. The microstructures of the nano silicon carbide ceramics were characterized by SEM and XRD. The pyrolysis behavior of the cured PCS/DVB was characterized by thermogravimetry in nitrogen atmosphere.
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    Synthesis, Microstructure and Mechanical Properties of ZrB_2 Ceramic Prepared by Mechanical Alloying and Spark Plasma Sintering

    Chun Feng HuYoshio SakkaTetsuo UchikoshiTohru S. Suzuki...
    165-168页
    查看更多>>摘要：Dense bulk ZrB_2 ceramic was synthesized by mechanical alloying (MA) and followed spark plasma sintering (SPS) using zirconium and boron as initial materials. It was found that MA process was effective to fragment the coarse metal zirconium particles from 45 μm to less than 1 μm within 20 hours. In comparison with the commercial ZrB_2 powder, the as-obtained zirconium and boron mixture powders showed higher sinterability. When the sintering was carried out at 1800℃, the relative density of synthesized ZrB_2 samples using mixture powder was above 95%, higher than that of ZrB_2 sample prepared using commercial powder (73%). Vickers hardness of those ZrB_2 samples was at the same level of 15 GPa. However, the fracture toughness of ZrB_2 samples seemed to depend on the heating rate of the SPS process. Corresponding to the heating rates of 10, 50, and 100℃/min, the fracture toughness of as-prepared ZrB_2 samples were 3.83, 3.19, and 2.74 MPa·m~(1/2), respectively.
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    Detection of Amorphous Silica in Air-Oxidized Ti_3SiC_2 at 500-1000℃ by NMR and SIMS

    W.K. PangI.M. LowlJ. V. Hanna
    169-172页
    查看更多>>摘要：The use of secondary-ion mass spectrometry (SIMS), nuclear magnetic resonance (NMR) and transmission electron microscopy (TEM) to detect the existence of amorphous silica in Ti_3SiC_2 oxidised at 500-1000℃ is described. The formation of an amorphous SiO_2 layer and its growth in thickness with temperature was monitored using dynamic SIMS. Results of NMR and TEM verify for the first time the direct evidence of amorphous silica formation during the oxidation of Ti_3SiC_2 at ≤1000℃.
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    • NETL
    • NSTL
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    Microstructure and Mechanical Properties of Hot Pressed ZrC-SiC-ZrB_2 Composites

    Baoxia MaWenbo HanXinghong Zhang
    173-177页
    查看更多>>摘要：Ternary ZrC-SiC-ZrB_2 ceramic composites were prepared by hot pressing at 1900℃ for 60 min under a pressure of 30 MPa in argon. The influence of ZrB_2 content on the microstructure and mechanical properties of ZrC-SiC-ZrB_2 composites was investigated. Examination of SEM showed that the microstructure of the composites consisted of the equiaxed ZrB_2, ZrC and SiC grains, and there was a slight tendency of reduction for grain size in ZrC with increasing ZrB_2 content. The hardness increased considerably from 23.3 GPa for the ZS material to 26.4 GPa for the ZS20B material. Flexural strength was a strong function of ZrB_2 content, increasing from 407 MPa without ZrB_2 addition to 627 MPa when the ZrB_2 content was 20vol.%. However, the addition of ZrB_2 has little influence on the fracture toughness, ranging between 5.5 and 5.7 MPam~(l/2).
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    Electronic Structures and Chemical Bonding of the Layered Tungsten Borides: an ab initio Calculation

    Xu XuewenLi YangxianZhou WeibingZhu Jiaoqun...
    178-181页
    查看更多>>摘要：We have investigated the electronic structures and chemical bonding of four tungsten borides, including two WB_2 compounds with different crystal structures, α-W_2B_5 and ε-WB_(2.5), by ab initio calculations based on density function theory (DFT). The calculated density of state (DOS) shows that all compounds are metallic. The DOS at Fermi level is mainly contributed from 5d states of W atoms. The strong covalent bonds of boron atoms make these compounds stable. Due to a lack of electrons in boron sublattices, weak ionic bonds are generated. The charge density distributions indicate the solid B layers or B polyhedrons are interleaved by the W layers.
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    Hot-Pressed TiB_2 Ceramics With B_4C and C Additives

    Li WangWei-Ming GuoYao-Gang LiGuo-Jun Zhang...
    182-184页
    查看更多>>摘要：Effects of B_4C and C additives on the densification behavior, phase composition, and microstructure of TiB_2 ceramics were studied. The relative density of pure TiB_2 ceramics by hot pressing at 2000℃ for 1 h was only 77.4%. With the introduction of B_4C and C additives, the relative density increase to 97.4% and 98.1%, respectively. The great improvement on densification was due to the removal of surface oxides of TiB_2 powders by reaction with B_4C and C additives. Microstructure observation showed the addition of B_4C led to some TiB_2 grains abnormal growth (>10 μm), whereas the addition of C produced a uniform and fine-grained microstructure.
      原文链接:
    • NETL
    • NSTL
    • Trans Tech Publications Ltd