定向多孔陶瓷的制备与应用进展

定向多孔陶瓷因具有良好的流体渗透性及力学性能越来越引起人们的广泛重视。综述了定向多孔陶瓷常见的制备工艺,分别介绍了阳极氧化工艺、生物模板工艺、添加造孔剂工艺、冷冻干燥工艺以及其他常见工艺的原理以及国内外发展现状,总结了各种工艺的特点,其中阳极氧化工艺主要用于制备高度定向周期排列的介孔结构,此法存在基体与多孔材料分离时产生环境污染问题;生物模板工艺主要利用天然木材为模板,通过渗透、热解、反应等工艺步骤直接复型其生物形态的定向孔结构,此法制备的定向多孔陶瓷气孔率较低、力学性能较差且其制备步骤较为繁琐等问题;添加造孔剂工艺是利用高长径比的造孔剂通过挤压或者施加磁场等方式使其定向排列从而得到定向孔,此法生产大型陶瓷产品时具有一定的优势;冷冻干燥工艺主要是冷冻凝固陶瓷浆料,使浆料中的溶剂定向生长为"冰晶"随后减压干燥以去除凝固相溶剂,从而制备出多孔陶瓷,此法制备的成品孔隙率易于控制且定向孔连通性良好。综述了定向多孔陶瓷作为陶瓷过滤器和交叉复合材料预制体的应用,并对其制备工艺进行了总结与展望。     

外磁场在定向凝固过程中的应用研究

以磁场对合金凝固组织的影响为基础,综述了近年来交变磁场和稳恒磁场在定向凝固过程中的应用和发展,总结了外磁场对定向凝固过程中合金微观组织的作用机制,并展望了今后的研究方向。     

影响凹印铜金粉印金光泽度的主要因素

在研究国内外铜金粉的微观形貌、厚度、水面遮盖率、定向排列、光泽度和粒度分布的基础上，分析了影响凹印铜金粉印金光泽度的主要因素。结果表明，国产铜金粉颗粒级差大、细小颗粒所占比例过多、金属片太厚、水面遮盖率小、定向排列不好等是影响国产铜金粉印金光泽度的主要因素。     

抽拉速率对高温合金叶片定向凝固组织的影响

采用以液态金属锡作为冷却介质的定向凝固设备,研究了五种不同的抽拉速率对叶片定向结晶组织的影响。结果表明抽拉速率对高温合金叶片的定向结晶组织具有重要的影响,抽拉速率为6mm/min时,可保证叶片的良好成形,定向柱晶挺直,晶粒沿竖直方向排列整齐,晶粒大小均匀。抽拉速率增大,合金组织细化,枝晶间距变小。     

粉末热挤压法制备Mg2B2O5w/6061Al复合材料的组织和力学性能研究

采用粉末冶金法制备了含量分别为5%、10%、15%、20%(体积分数,下同)的硼酸镁(Mg2B2O5)晶须增强6061铝基复合材料,利用SEM和EPMA研究了复合材料的微观组织,并测定了其力学性能。结果表明:在复合材料制备过程中Mg2B2O5晶须发生了破碎和折断,Mg2B2O5多以晶须团聚体的形式存在,出现尺寸为10~25μm的颗粒状增强体;Mg2B2O5晶须沿挤压方向定向排列,并且定向排列性随晶须含量的增加而减弱;复合材料的抗拉强度随着晶须含量的增加先升高后降低,并在晶须含量为15%时达到最大值191MPa,较基体合金增加16.5%;复合材料的伸长率随晶须含量的增加逐渐下降,当晶须含量为20%时降至最低值6.3%。     

0.1%C低碳钢连铸坯表层微观组织演变过程热模拟

连铸坯表层微观组织直接影响其表面质量，研究微观组织演变过程与工艺条件的关系对认识机制并优化连铸工艺具有重要意义。根据连铸坯传热特点，利用凝固过程热模拟方法再现铸坯表层传热过程，通过液淬实验观察了连铸坯表层微观组织的演变过程，并比较了热模拟铸坯和实际铸坯在传热、枝晶生长速度和微观组织方面的相似性。结果表明，热模拟实验可以很好地反映连铸条件下的传热及微观组织演变过程，为研究工艺条件对铸坯表层微观组织的影响提供了可行的途径。在所选模拟连铸条件下，0.1%C低碳钢的连铸坯表层奥氏体晶粒尺寸(D)与凝固时间(t)符合关系式：D=80.74×ln(t+2.95)-90.49。     

3004铝合金中间退火的织构变化与显微结构研究

本文采用 X 射线衍射技术研究了3004铝合金板材在中间退火过程中织构的变化及立方织构的形成规律,并用高压透射电镜原位动态观察、内耗测定和金相方法探讨了退火过程微观组织结构的变化。研究结果表明:中间退火可大量地形成立方织构;热轧工艺及第二相粒子的种类、数量、大小与分布等对退火再结晶织构的生长有显著的影响。此外,由 X 射线织构分析和高压透射电镜动态观察,论证了立方织构形成的机理符合定向形核与定向生长的综合机制的理论。     

高温轧制工艺微观机理研究

改变材料中微合金元素的组成和含量是高温轧制工艺(HTP)的基础,高温轧制工艺改善了材料的组织结构和力学性能并降低了生产成本,同时,轧制时变形抗力的减小也降低了轧机的负荷并有利于板形的控制。为了使高温轧制工艺广泛应用于轧制工程领域,从微观机理角度对该工艺进行研究就显得很有必要。本文以低碳、高铌和低钼成分的X80管线钢为研究对象,分析了试轧钢板的微观组织和力学性能并利用透射电镜重点研究了析出粒子的大小、形貌、成分及其析出行为。研究结果表明,高温轧制工艺生产的高铌针状铁素体钢的微观组织和力学性能满足了工程要求,析出物大部分为圆形Nb(C,N)附着在热稳定性较高的方形TiN粒子上形成的不规则复合析出。     

铼对定向合金组织和性能的影响

以一种定向合金为基础成分，加入不同含量的Re，采用定向凝固工艺浇注性能试棒，通过SEM研究了含Re合金的微观组织特征及Re在不同相中的分布情况，比较了不同Re含量的室温拉伸和高温持久性能。研究结果表明：通过加入Re可以有效提高合金的室温拉伸屈服强度和高温持久寿命，但室温和高温塑性有所降低。加入Re后合金的铸态组织变化不大：γ γ′共晶相数量随Re含量的增加而略有增多，并且尺寸变小。Re主要分布于γ基体中，在强化相γ′中的分布很少，并通过在γ基体中阻碍位错运动有效提高合金的高温强度。     

Ti8LC钛合金热处理工艺对硬度和组织的影响

钛合金Ti8LC是一种新型低成本近а型的钛合金,为了研究该合金热处理对其组织结构的影响规律,对其进行不同温度固溶处理,随后在不同温度进行时效热处理.用金相显微镜和扫描电镜观察了不同热处理工艺下的微观组织形貌,并通过能谱分析了不同工艺下元素的含量变化.采用洛氏硬度计测试了试样的平均硬度,分析了固溶温度和时效温度对其微观组织形态的变化影响,以及硬度大小、微观组织结构中相的形态和组织组成的相关性.结果表明:固溶处理温度对Ti8LC固溶后的显微组织及随后的时效组织都有极大的影响,随固溶温度的升高,由片状逐渐转为块状.经相同时效工艺处理的合金其显微组织受固溶后组织的遗传影响,合金的硬度随着固溶温度的升高.先降低后升高;通过微观组织和硬度的良好配合,可以确定Ti8LC合金固溶时效的最佳工艺.     

Directional solidification of eutectics: New prospects for refractory oxide cermaics (review)

Conclusions The directional solidification of the eutectic in the refractory oxide systems results in the formation of a plate-shaped or fibrous oriented composite structure. The theoretical fundamentals of the method of directionally solidified eutectics, developed on the basis of the metallic systems, can also be applied extensively to refractory oxide DSEs so that their structure and composition can be controlled in the required direction.The orientation relations between the phases of the refractory oxide DSEs and the construction of the interphase boundaries result in the formation of semicoherent interphase boundaries. This is one of the conditions for the higher and thermal stability of the materials.The mechanical properties of the materials based on refractory oxide DSEs are controlled by the structure of the oriented eutectic. Disruption of flat frontal growth in solidification leads to the formation of a cellular structure. The cell boundaries are the weakest area of the material and control its behavior during failure.The materials based on the direction solidified refractory oxide eutectics have unique set of the applied properties and are highly promising for use as structural materials at elevated (up to 1500°C) temperatures.The materials made of the refractory oxide DSEs can be used in practice after developing high-productivity methods of their growth which would make it possible to produce components of the required shape.Translated from Poroshkovaya Metallurgiya, No. 8(320), pp. 58–69, August, 1989.     

Application of atomized copper powder in obtaining copper-graphite contacts

Conclusions The method of decomposing salts makes it possible to obtain materials which, by their tribotechnical and electrocontact properties, are not inferior to the standard materials for electric brushes brands MG, MGSOA. The oriented laminated structure of fine-grained copper in graphite causes the formation of surface layers that are characteristic of normal mechanochemical wear. This improves the wear resistance of the material and stabilizes its electrocontact characteristics.Translated from Poroshkovaya Metallurgiya, No. 2(278), pp. 63–68, February, 1986.     

Certain regularities in the strength of soft-fiber reinforced plastics with two-component warps

Summary Formulas are derived for the ultimate strength of fiber-reinforced plastics on an oriented two-component warp. on a crossed two-component warp, and on an oriented cotton—Kapron warp.The formulas make possible an analytical calculation of the strength of these materials, proceeding from the properties of the fibers, and thus selection of the optimal composition of the material ensuring the given properties.     

Effects of symmetry,texture and topology on triple junction character distribution in polycrystalline materials

Studies of triple junctions in f.c.c. polycrystalline material were carried out analytically and by computer modelling. An analysis of triple junction symmetry identified a group of triple junctions having at least a common axis, along with a subgroup of triple junctions having symmetry axes as common axes. Frequencies of occurrence of Coincident Axial Direction and Coincident Site Lattice triple junctions are assessed in both randomly oriented and fibre textured materials. Distributions of I- and U-line triple junctions are evaluated in randomly oriented and fibre textured materials, and in polycrystalline materials composed of CSL grain boundaries. Finally, and optimal three-dimensional polycrystalline material is proposed from a topological point of view.     

Marketing your product: The psychologist as communicator.

A questionnaire on the importance of different types of communication materials was sent to 60 persons who had requested from Boys Town material concerning the psychologically oriented teaching-family model of residential treatment. Ss, divided into 4 groups on the basis of their familiarity with the program, generally ranked how-to books and videotapes as more important than more traditional means of communication such as journal articles and textbook chapters. Results are discussed in terms of the need for nonacademic psychologists to learn new communication approaches. (6 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Rolling and recrystallization textures in directionally solidified aluminium

From directionally solidified aluminium with a 〈100〉 fibre texture specimens of different orientations were cut and the textures after rolling (95% reduction) and recrystallization were determined. The results are discussed on the basis of the current concepts on deformation and recrystallization in single and polycrystalline materials. Due to the strong influence of the different starting textures, characteristic differences in the rolling textures are obtained. For the first time, a case is reported for which an experimental rolling texture is completely explicable in terms of the Taylor theory under full constraints condition. Further, the recrystallization textures, although appearing more uniform, exhibit clear differences which yield new evidence with respect to the mechanisms of formation of the cube texture. It shows that in the present case for obtaining a pronounced cube texture, both the conditions of oriented growth (in the sense of 40° 〈111〉 rotations) and oriented nucleation (in the sense of properly oriented transition bands) must occur.     

Anisotropy Influence on Hysteresis and Additional Loss in Silicon Steel Sheets

Non‐ and grain‐oriented electrical steels were tested in an Epstein frame. The materials were magnetised under sinusoidal flux waveform at 20, 50 and 150 Hz. Loss was separated into hysteresis, eddy current and excess loss components. The relationship between the hysteresis angle, additional loss factor and the magnetocrystalline anisotropy was shown. It was found that both hysteresis and additional losses are strongly dependent on the texture showing opposite trends as the flux density increases. The aim of the present paper is to provide a contribution to the understanding of magnetic losses in soft metallic ferromagnetic materials.     

Microstructure and toughness in high speed tool steels: the influence of hot reduction and austenitization temperature

Measurements of transverse rupture strength are reported for AISI M2, AISI M 35, AISI T 15 and ASP 30 produced by conventional ingot metallurgy, sintering of cold pressed powders, and hot rolling of HIP billets. Also reported are the size distributions of undissolved carbides and the effects of hot reduction and austenitization temperature on these and on the transverse rupture strength of test bars from the centre and the periphery of the bar stock, and of test bars oriented longitudinally and transversally to the rolling direction. Fracture initiating defects were identified and their size measured by SEM fractography. The results are discussed in terms of a fracture mechanical model for transverse rupture strength. It is inferred that in ingot-derived materials, fracture is initiated by micro-cracks formed by subcritical crack growth within the carbide stringers. In powder metallurgy materials, large carbides or carbide clusters initiate fracture. The model explains the dependence of transverse rupture strength on carbide distribution, degree of hot working, austenitization temperature, and specimen orientation. It is emphasized that transverse rupture strength is suitable for characterizing the defect population of a tool steel, but not the fracture resistance of small stressed volumes such as the cutting edge of a tool bit.     

Structural aspect of the problem of designing superconducting materials based on Bi-2212 ion-plasma coatings for operation in strong magnetic fields

The Bi-2212 crystal structure parameters and the structural states of the material of thick ion-plasma coatings are analyzed during their production. These structural states include the amorphization of the coating material; changes in the modulated structure of Bi-2212; the formation of a basal texture, which characterizes oriented grain growth during heat treatment; and the improvement of integrain contacts. Problems related to the creation of high-current superconducting Bi-2212-based composites and those related to Chevrel phases, which began to be studied a decade earlier, are considered to be common. The differences in the changes of the critical currents of these materials in an applied magnetic field are associated with the difference in the superconducting fragments in their crystal structures. The development of studies dealing with the creation of superconducting composites containing ion-plasma coatings and intended for operation in strong magnetic fields is considered.     

电机用取向电工钢设计与应用技术研究

针对高性能电机日益严苛的转矩密度、效率等指标问题,传统软磁材料的性能已发挥到极致,探索和应用新型软磁材料是提高电机性能的重要途径。本文提出将沿轧制方向上具有高磁感、低铁损的取向电工钢应用到永磁同步电机的定子齿部的设计,并与传统的无取向电工钢电机进行了对比分析。相比传统材料电机,取向电工钢电机转矩可提升3.4%,铁损可降低18%,且电机整体效率有所提升。为取向电工钢软磁材料在高性能电机中的应用奠定了基础。