关键词： 内氧化   Ag-SnO_(2)   显微结构  

摘要： Ag -Sn -M(M =Bi、Cu)合金粉末内氧化后经压制、烧结、挤压、加工制备成Ag-SnO2 接点材料。用光学显微镜 ,X射线衍射和SEM研究其显微结构。结果表明 :在Ag-SnO2 材料中存在Ag、SnO2 、Bi2 SnO7和CuO ,氧化物以极细小的颗粒分布在银基体中。

关键词： F01   J01   V01   W02  

摘要： This paper reports a systematic study which examined the use of a pulsed Nd:YAG laser to weld sheet materials of V-Cr-Ti alloys and to characterize the microstructural and mechanical properties of the resulting joints. Deep penetration, defect-free, and oxygen contamination free welds were achieved under an optimum combination of laser parameters including focal length of lens, pulse energy, pulse repetition rate, beam travel speed, and an innovative shielding gas arrangement. The key for defect-free welds was found to be the stabilization of the keyhole and providing an escape path for the gas trapped in the molten weld pool. Oxygen and nitrogen uptakes were reduced to levels only a few ppm higher than the starting material by design and development of an environmental control box (ECB). Laser-applied post-weld heat treatments showed that five-passes of a diffuse laser beam over the welded region softened the weld material, especially in the root region. (C) 2000 Elsevier Science B.V. All rights reserved.

关键词： Hydrogen   Behavior   F82h  

摘要： Two candidate materials for the blanket components of ITER were studied by the internal friction method. For low-activation martensitic F82H steel measurements of anelasticity were carried out in the temperature range of 80-500 K after preliminary electrolytical hydrogen charging. A broad multicomponent internal friction peak was detected in hydrogen-charged F82H steel in the temperature range of 100-450 K at a frequency of I Hz. The effect of the amount and the type of strengthening particles on the internal friction were clarified for CuAl25, CuAl60 and CuAl25 + TiC GlidCop(TM) dispersion strengthened copper alloys in the temperature range of 300-1000 K. The effect of neutron irradiation on internal friction of CuAl25 alloy is also discussed. (C) 2000 Elsevier Science B.V. All rights reserved.

关键词： Vanadium alloys  

摘要： This study is concerned with the microstructural analysis of vanadium carbide (VC)/steel surface alloyed materials fabricated by high-energy electron-beam irradiation. The mixtures of VC powders and MgO-CaO flux were deposited on a plain carbon steel substrate, and then electron beam was irradiated on these mixtures using an electron-beam accelerator. Microstructures of the irradiated surface regions were examined by optical microscopy, scanning electron microscopy, and transmission electron microscopy. Residual pores were found in the specimen processed without flux, but hardly found in the specimens processed with a considerable addition of flux. As a result of irradiation, vanadium content was homogeneously maintained throughout the melted region, and fine vanadium carbides were formed in the melted region. These microstructural modification including the formation of vanadium carbides greatly improved hardness, especially high-temperature hardness up to 500 degreesC.

关键词： Crystal microstructure  

摘要： Dynamic material modeling (DMM) based on the thermodynamic principles of continuum mechanics was discussed. The method correlates the flow behavior with hot workability and microstructural evolution. Some discrepancies of DMM when applied to microstructural evolution were listed. It was found that the strain rate sensitivity has a direct relationship with the workability. Malvern's concepts of entropy were also discussed.

关键词： 锐钛矿TiO2纳米晶体   微结构   尺寸效应  

摘要： 对制备条件相同、晶粒度不同的锐钛矿TiO2 纳米晶体 (n A TiO2 )样品之晶粒微结构进行了细致的X射线衍射(XRD)研究 ,给出了标明晶面指数 (hkl)和晶面间距 (dhkl)值的系列XRD谱 ,并得到了晶面间距、晶格常数、轴比、晶胞体积等参数数值及其相对常规粗晶的变化情况 ,从而初步揭示出该样品晶粒微结构随粒度的变化情况。发现了锐钛矿TiO2

关键词： 电瓷材料   显微结构   力学性能  

摘要： (上接《电瓷避雷器》2 0 0 0年第 4期第 2 4页 )4.2　晶相含量对电瓷材料力学性能的影响4.2 .1　晶相含量对弹性模量的影响文献 [43]中指出 ,立方形颗粒增强复合材料的弹性模量可以由下式表示 :E0 /Ep=　 Ep+(Em-Ep) (1-Vp) 2 / 3Ep+(Em-Ep) (1-Vp) 2 / 3[1-(1-Vp) 1/ 3](19)式中 ,Ep 为分散颗粒相的弹性模量 ,Em为基体的弹性模量 ,Vp 为分散相的体积分数。玻璃相的弹性模量可由下式求出 [46 ]:Em =0 .93dM∑iTmi Xi (2 0 )式中 ,d为玻璃密度 ,M为玻璃分子量 ,Tmi为 i组分熔点 ,Xi 为 i组分的摩尔分数。上式Em 的单位为 GPa,Tmi的单位为 K,d的单位为 g/cm3,M的单位为 g/mol。对于含多种晶相的电瓷材料 ,可按下述方法求 Ep:Ep =∑iEpi Vpi (2 1)式中 ,Epi为 i晶相的弹性量 ,Vpi是扣除玻璃相后 i晶相的体积分数 (∑iVpi=1)。取各种氧化物的熔点如下 [5 4]:Tm( Si O2 ) =1986 K Tm( Al2 O3) =2 ...

关键词： 微创外科手术   微型电子机械系统   内窥镜  

摘要： 对微机电系统在生物医学工程方面的应用进行了研究 ,探讨了微创外科手术这一研究热点 。

关键词： characterizations   iron-cobalt alloys   microstructure   nanopowders  

摘要： One attempt to improve core loss of electromagnetic machines is to utilize nanocrystalline alloys, which are predicted to have extremely soft magnetic properties. High magnetic saturation values and high Curie temperatures make iron-cobalt alloys attractive for such applications. In this work iron-cobalt-vanadium nanopowders were synthesized and compacted. The coated particles were characterized and examined in both the powder and compacted states. Higher than expected coercivities are reported and may be due to the inhomogeneous microstructure resulting from interactions with the vanadium.

关键词： 俄歇电子全息   电子散射   计算机模拟   材料微结构  

摘要： 原子的芯能级电子吸收能量后被激发 ,经过退激发过程发射出的俄歇电子波在传播过程中被周围的原子散射 ,带有周围原子结构信息的散射波 (物波 )与未被散射的电子波 (参考波 )相干涉形成的衍射图即俄歇电子全息图 ,通过全息图的重现 ,可获得原子级分辨率的三维结构信息。本文在合理的物理模型下 ,以Cu单晶以及高温超导YBCO中的Y原子近邻的一些原子簇为计算实例 ,首次就受激原子周围单层近邻原子散射和多层原子散射产生的俄歇电子全息进行了计算机模拟和数值重现 ,获得了三维晶格结构参量 ,并讨论了不同原子序数的原子在全息图形成及重现中的作用。