关键词： SiC/W层状复合材料   显微结构   力学性能  

摘要： 以 Si C陶瓷片为基体层 ,金属 W为夹层 ,热压烧结制成 Si C/W层状复合材料。 X射线衍射分析显示 :夹层中的 W与 Si C反应生成了 W5Si3和 WC,无金属 W存在。断面扫描电镜分析表明 :(1 )夹层由颗粒状晶体 (W5Si3)和片状晶体 (WC)组成 ,片状晶片重叠为二级层状结构。 (2 )基体层 (Si C层 )的断裂方式为裂纹沿晶断裂 :夹层的断裂方式有两种 :一是裂纹沿颗粒状晶体的晶界的沿晶断裂 ,二是裂纹穿过片状晶体的穿晶断裂 ,断口还观察到片状晶片的拨出。材料力学性能呈现的规律为 :夹层厚度在 1 0～ 50 μm内 ,随夹层厚度的增加 ,断裂韧性增加 。

关键词： 电子商务   网络安全   互联网  

摘要： 2 1世纪是电子商务 (ElectronicCommerce ,EC)来临的时代 ,电子商务作为一种先进的交易方式正在风靡全球 ,并对商业贸易领域中传统的观念和行为方式生产着巨大的冲击和影响。在本文中作者提出了在电子商务活动中已经出现的或将来一定会出现的问题 ,阐述了可以解决电子商力中的安全性问题的技术 ;虚拟专用技术、加密技术、证证技术和防火墙技术 ,最后提出了发展我国电子商务的几点建议。

关键词： 磁电阻   Sr2FeMoO6陶瓷   微结构   钙钛矿结构  

摘要： 研究了在钙钛矿结构 Sr2 Fe Mo O6 陶瓷中存在的多种不同的有序晶格结构 .如 Fe- Mo离子在简单钙钛矿结构 ABO3中的 B位无序分布 ;Fe- Mo B位空间排列的 Na Cl型有序分布的钙钛矿结构及在 c轴方向具有 3倍简单钙钛矿结构周期的层状超结构等 .结果表明 ,通过正确选择 Sr2 Fe Mo O6 陶瓷材料的微结构 。

关键词： 赛隆   耐火材料   显微结构   耐火砖  

摘要： 分析了几种赛隆结合碳化硅砖、刚玉砖的显微结构，从显微结构及赛隆相的形成上探讨了适宜的赛隆结合耐火材料工业化生产的途径。

关键词： 显微结构   氧化物   耐火材料   非氧化物   复合材料  

摘要： 利用SEM、TEM及HREM研究了氧化物-非氧化物复合材料的显微结构特征。结果表明 :( 1 )在氧化物基体中引入非氧化物 ,非氧化物颗粒将穿插于氧化物颗粒构成的骨架中 ;在非氧化物基体中引入氧化物 ,氧化物颗粒将弥散于非氧化物颗粒构成的编织状结构的空隙处。 ( 2 )氧化物与非氧化物之间的结合方式可分为 :(a)直接结合 (在没有助烧剂、直接烧结的情况下 ) ;(b)通过晶界非晶质薄膜相结合 (在有助烧剂参与的直接烧结和反应烧结的情况下 )。 ( 3)所研究的试样中普遍存在有微裂纹 ,这些微裂纹将有助于材料抗热震性的改善。

关键词： Polystyrenes   TOUGHNESS   Prediction models   Voids   deformation bands   small size   microtectonics   Strain softening  

摘要： The influence of microstructural properties on the macroscopic mechanical behaviour has been studied by finite element predictions of the response of different microstructures of polystyrene (PS) or polycarbonate (PC) containing voids or rubbery particles, subjected to unidirectional extension. The voids represent a low-modulus non-adhering dispersed phase. The rubbery inclusions, which are assumed to be pre-cavitated and perfectly adhering, idealise core-shell particles with a hard rubber shell and a soft non-adhering or pre-cavitated core. The predictions show that the inclusion properties strongly affect the averaged post-yield response of the heterogeneous systems. Especially the post-yield strain softening can be eliminated by the introduction of voids in PC or rubbery particles in PS. Since macroscopic strain softening is believed to be the main cause of catastrophical stress or strain localisations, the softening elimination is believed to be primarily responsible for toughness enhancement of the polystyrene or polycarbonate systems. The results and experiences are extrapolated in order to explain the influence of the absolute length scale of a sub-micron sized morphology on the macroscopic behaviour, especially toughness. Two potential sources of particle-size effects are presented that may result in a stabilised, and thus tougher, macroscopic mechanical response, i.e. the yield stress reduction near a surface or interface because of a locally enhanced mobility of the polymer segments, and the temporary excessive hardening because of a sufficiently small size of the yield zones which results in a reduced effective entanglement distance. The paper concludes with a discussion on the extension of this knowledge to all other, for the moment amorphous, polymers. (C) 2000 Kluwer Academic Publishers.

关键词： INTERFACIAL DEBONDING   Menopause   Scanning Electron Microscope   impact velocity   Fragments   surface texture   Surface morphology  

摘要： Fracture morphology and texture were observed on the impact generated graphite/epoxy composite fragments. The work identifies and explains changes in the surface texture of the fragments generated at different impact velocities (122 to 610 m/s, 400 to 2000 ft/s) and over a wide range of specimen temperatures (-54 to 24 degrees C, -64 to 75 degrees F). The composite panels were impacted by spherical steel projectiles, acid the entire spall was carefully collected after the impact. The spall was differentiated according to different sizes and shapes. A few fragments representing each shape and size were selected to analyze the surface morphology using scanning electron microscopy (SEM). Change in the surface texture was observed according to the different sizes and shapes, and the change in size and shape of the fragments was credited to the change in impact force. The results following from the close and intense observation of several SEM fractographs revealed that the surface texture of the fragments is strongly dependent on the type of forces acting at the point of impact resulting in four different modes of failure: delamination, transverse matrix cracking, fiber fracture and fiber-matrix interface debonding. Published by Elsevier Science Ltd.

关键词： annealing   grain boundaries   grain boundary network   scanning electron microscopy   electron diffraction  

摘要： Recently, there has been increased attention toward determination of the grain boundary character distribution (GBCD) and manipulation of the relative fractions of "special" and "random" boundaries in the microstructure through thermomechanical processing techniques in order to improve materials properties like corrosion, creep resistance, and weldability. Most of the "optimization" treatments reported in the literature have been performed on f.c.c. metals and alloys with medium to low stacking fault energies, and have resulted in microstructures with high fractions of Sigma 3, Sigma 9, and Sigma 27 boundaries, or Sigma 3(n) boundaries. Experiments to modify the GBCD of oxygen-free electronic Cu and Inconel 600 through sequential thermomechanical processing are presented and the efficacy of these processing routes is assessed in terms of microstructural descriptors like the random grain boundary network and the distribution of triple junctions. This analysis has shown that Sigma 3(n) reactions, which occur as a consequence of multiple twinning, not only improve the GBCD but are also critical for disrupting the connectivity of the random boundary network. Published by Elsevier Science Ltd on behalf of Acta Metallurgica Inc.

关键词： 钛   氧化锆   梯度材料   结构   金属陶瓷   复合材料  

摘要： 采用粉末冶金法热压合成了Ti-ZrO2 系梯度功能材料 .用有限元法模拟了设计材料的残余热应力分布 .利用扫描电镜、电子探针、透射电镜和X射线衍射等手段 ,对Ti-ZrO2 系梯度材料组成相的分布形态、相组成以及组元之间的界面结合状态等进行了详细的研究 .结果表明 :合成的材料具有宏观组织不均匀性与微观组织连续性的特征 ,Ti-ZrO2 系梯度材料由α -Ti、四方相ZrO2 和单斜相ZrO2 组成 .合成条件下组元Ti和ZrO2 之间不发生化学反应 ,具有良好的化学相容性 .

关键词： 绝热材料   硅酸钙   硬硅钙石   水热合成   显微结构  

摘要： 超轻硅酸钙绝热材料的固相含量只占整个体积的 5%以下 ,要使如此之少的固相充满全部体积 ,并成为具有相当强度的刚性体 ,材料必须具有纤维状的显微结构 .超轻硅酸钙材料实际上是由硬硅钙石纤维状晶体组成的多孔球状团聚体构成 .整个材料的气孔率达95%以上 ,气孔半径呈多重分布 .球状团聚体越大材料越轻 .为获得理想的显微结构 ,需要设计合理的硬硅钙石合成工艺和压滤成型工艺 .合成工艺参数包括原料的配比、水热合成反应的温度、压力、时间、搅拌方式以及合成添加剂 ;成型工艺参数包括成型料浆中玻璃纤维的添加量、液体的表面张力、料浆温度和成型压力 .