陶瓷干法成型过程分析与建模

针对陶瓷千法成型过程机理复杂、影响因素众多的特点,从系统辨识和过程控制的角度,首先采用Hammerstein-Wiener(H-W)模型来描述一个完整的陶瓷干法压制成型过程,其次利用关键项分离技术和广义递推最小二乘法(RGIA)来估计模型参数。最后对陶瓷粉末压制成型过程进行仿真研究,建模结果验证了所提出建模方案的有效性。     

Superplasticity and superplastic forming of aluminum metal-matrix composites

Superplasticity hos been observed in many aluminum metal-matrix composites at extremely high strain rates (approximately 0.1–1 S^?1). These materials generally exhibited a strain-rate sensitivity value of about 0.3 and a maximum elongation of about 300%. It is believed thot the presence ofa liquid phose, or in some cases a low-melting-point region, at the reinforcement/matrix interfaces is responsible for the phenomenon. This phenomenon is not observed in all reinforced composites, despite the fact thot they contain fine grain sizes. Thus, a fine matrix grain size is a necessary but insufficient condition for the high-strain-rate superplasticity.     

Plasma spray forming metals,intermetallics, and composites

Plasma spray processing is a droplet deposition method that combines the steps of melting, rapid solidification, and consolidation into a single step. The versatility of the technology enables the processing of free-standing bulk, near-net shapes of a wide range of alloys, intermetallics, ceramics, and composites, while still retaining the benefits of rapid solidification processing. In particular, it is possible to produce dense forms through vacuum plasma spraying.     

Plasma spray forming of intermetallics and their composites\

Extracted from the Symposium on Spray Forming held at the Na-tional Thermal Spray Conference (Anaheim), June 1993     

铝基复合材料凝固与成形一体化技术

针对铝基复合材料塑性成形困难、增强相与基体金属界面相容性差的问题,提出铝基复合材料凝固与成形一体化技术,实现了铝基复合材料管材、线材和型材的连续近终形成形,并改善粒子相与铝界面相容性和强化作用,达到短流程,低能耗成形的目的.研究了铝基复合材料连续凝固与成形过程的组织演化规律和制品性能,优化了凝固成形条件.     

Height-related magnetoelectric performance of PZT/Ni layered composites

The effect of height on performance of the PZT/Ni cylindrical bilayered magnetoelectric(ME) composites was studied in situ in this paper.Multiple resonant peaks appear between 1 and 300 kHz frequency for cylinders of different heights.The first resonance frequency does not change with the cylinder height decreasing,but the second and the third resonant frequencies increase.The first three resonant modes are attributed to the cylinder radial,first-order height resonance,and second-order height resonance,respectively.The appropriate size and resonance frequency were chosen to obtain the highest ME voltage coefficient when designing cylindrical bilayered magnetoelectric devices.This article provides reference to design cylindrical magnetoelectric devices.     

陶瓷及陶瓷基复合材料连接的研究进展

综述了近年来陶瓷及陶瓷基复合材料连接的研究进展。包括陶瓷及陶瓷基复合材料润湿机理的研究、润湿性的改善、连接界面组织结构的演变及与接头力学性能的关系、接头连接机理及连接应力的缓解方法。同时,对连接中间层的选择,包括玻璃陶瓷中间层、复合中间层、复合钎料及梯度中间层的研究也进行了归纳总结。分析了目前研究已经取得的突破进展及仍然存在的问题,并对未来陶瓷及陶瓷基复合材料连接的研究方向进行了展望。     

The thermal plasma near-net-shape spray forming of Al composites

The vacuum-plasma-spraying technique presented in this article is suited to produce aluminum-matrix composites with a low coefficient of thermal expansion reinforced with fine ceramic particles, resulting in a uniform particle dispersion and bulk porosity of less than 1.5% in the as-sprayed condition. Plastic deformation of the plates followed by annealing resulted in significant increases in ultimate tensile strength, hardness, and elongation.     

Actuation behaviour of layered composites of polyaniline,carbon nanotubes and polypyrrole

Layered composites of polyaniline (PAn), single-walled carbon nanotubes (CNTs) and polypyrrole (PPy) were produced by coating PAn or PAn/CNT on a PPy hollow fibre containing a platinum (Pt) helix. The actuation behaviour of PAn/PPy and PAn/CNT/PPy composites was compared with that of neat PPy. The Pt helix reduces the IR drop along the fibre, thus enhancing the actuation strain. Components of the composite with low actuation strain such as PAn and/or CNT restrict the actuation displacement of the PPy substrate causing a reduced strain in the composite. In particular, a minimal quantity of CNT (1.3 wt.%) in the composite leads to a discernible decrease in actuation strain but also increases the Young's modulus and tensile strength of the composite. Sodium nitrate (1 M) aqueous solution used as an electrolyte gives good actuation stability where the actuation strain is almost independent of applied stress (5–12 MPa). This can be explained by the unchanged Young's modulus at the reduced (contracted) and oxidized (expanded) states during the actuation process. The polyaniline/polypyrrole composite produced the highest work-per-cycle reported to date under isotonic conditions.     

Substrate stiffness determination in curved layered composites using bending methods

Bending tests are conveniently used to determine mechanically the elastic modulus of materials. However, in the case of asymmetrical, coated specimens that exhibit warping due to mismatch in thermal or isothermal expansion of the individual layers, non-linear deformation behaviour is present and the stiffness evaluation becomes difficult with this method. A bending test procedure is outlined which uses a flat composite specimen obtained by joining two spherically curved layered specimen along their coating surfaces. The elastic behaviour of the joint specimen essentially reflects the stiffness of the substrate since the thin coatings and the thin adhesive layer are located close to the neutral specimen axis of the bending test. The method is illustrated using warped anode-substrate/electrolyte sheets of solid oxide fuel cells. The results of ring-on-ring tests with anode substrate or electrolyte under tension and with the joint specimen are presented and discussed.     

金属陶瓷复合材料陶瓷粉的制备

介绍了金属陶瓷复合材料用陶瓷粉的制备方法。陶瓷粉体通过凝胶溶胶形式制备。     

Using rapid infrared forming to control interfaces in titanium-matrix composites

Control of the fiber-matrix reaction during composite fabrication is commonly achieved by shortening the processing time, coating the reinforcement with relatively inert materials, or adding alloying elements to retard the reaction. To minimize the processing time, a rapid infrared forming (RIF) technique for metal-matrix composite fabrication has been developed. Experiments have shown that the RIF technique is a quick, simple, and low-cost process to fabricate titanium-alloy matrix composites reinforced with either silicon carbide or carbon fibers. Due to short processing times, typically on the order of 1–2 minutes in an inert atmosphere for composites with up to eight-ply reinforcements, the interfacial reaction is limited and well controlled. Composites fabricated by this technique have mechanical properties that are either comparable to or, in several cases, superior to those made with conventional diffusion-bonding techniques.     

绝缘性陶瓷电火花加工中生成导电膜的特性分析

采用辅助电极法，在设定加工条件下对绝缘性陶瓷材料Si3N4进行了电火花加工实验，分析了加工中生成导电膜的原因，研究了加工条件、加工深度与生成导电膜的厚度、电阻等特性的关系，指出了加工深度对生成导电膜的影响较大，且加工深度越深，生成导电膜厚度越厚、电阻越小。     

Study on surface roughness model and surface forming mechanism of ceramics in quick point grinding

The quick-point grinding experiment of fluorophlogopite was conducted by using a MK9025A profile grinder which considered the simple single factor, such as the grinding wheel and table feed speed, grinding depth, inclining angle and deflection angle. The experimental results indicated that the surface roughness was mainly influenced on inclining angle and deflecting angle. Moreover, the modified model of the quick-point grinding process was proposed in the paper, which based on Malkin kinematics model, Snoeys empirical model and grinding thickness empirical model. The inclining angle and deflecting angle was introduced in the modified model. Comparison of the predicted results of these models and experimental ones indicated that the modified model was in well agreement with the experimental data. Further, standard deviation of these models and experiment was studied in the paper, it is found that the modified model was the more ideal. In order to study the effect of various technology factors on the sensitivity of surface roughness, “Relative extremum error” concept was first proposed in the paper. It was found that simple single factor in the modified model were relatively sensitive to surface roughness than other models.     

An investigation on kerf characteristics in abrasive waterjet cutting of layered composites

Layered composites are “difficult-to-machine” materials as it is inhomogeneous due to the matrix properties, fibre orientation, and relative volume fraction of matrix. Abrasive waterjet cutting has proven to be a viable technique to machine such materials compared to conventional machining. This paper presents an investigation on the kerf taper angle, an important cutting performance measure, generated by abrasive waterjet (AWJ) technique to machine two types of composites: epoxy pre-impregnated graphite woven fabric and glass epoxy. Comprehensive factorial design of experiments was carried out in varying the traverse speed, abrasive flow rate, standoff distance and water pressure. Using the dimensional technique and adopting the energy conservation approach, the kerf taper angle has been related to the operating parameters in a form of a predictive model. Verification of the model for using it as a practical guideline has been found to agree with the experiments.     

陶瓷及陶瓷基复合材料高温钎料的研究现状与进展

为充分发挥高温结构陶瓷材料的高温件能优势,针对陶瓷及陶瓷基复合材料的高温钎料的研究一直足陶瓷连接领域的发展方向.文章综述了SigN4、SiC陶瓷和C/C复合材料对应的高温钎料的研究难点和研究现状.虽然高温钎料的研究获得一些进展,但仍缺乏对陶瓷具有连接强度岛而且耐高温性能好的实用高温钎料.指出对于Si3N4陶瓷,以V为活性元素的高温钎料值得深入研究;而在设计和研制SiC连接用的高温新钎料时.应该允分考虑钎料与SiC之间的界面反应并予以控制.并对C/SiC陶瓷基复合材料用高温钎料的研究进行了简要的探讨.     

三维网络陶瓷增强铝基复合材料的干摩擦磨损性能

设计和制备了一种新型的三维网络陶瓷(骨架)增强铝合金复合材料.研究了铝合金及不同成分复合材料在不同温度及载荷下的摩擦系数和磨损率;用扫描电镜(SEM)观察其磨损表面,并分析了三维网络陶瓷(骨架)对铝合金磨损机制的影响.结果表明:复合材料的耐磨性远优于铝合金,而且随着三维网络陶瓷体积分数、温度及载荷的增加,复合材料的抗磨损性能明显提高;这种新型复合材料的摩擦系数随载荷变化保持稳定;在很宽的温度范围内,摩擦系数的稳定性均优于铝合金.这是由于三维网络陶瓷在磨损表面形成硬的微凸体起承载作用,其独特的结构制约了基体合金的塑性变形和高温软化,有利于磨损表面氧化膜的留存.     

Thermal spraying of billets and fiber prepregs for semi-solid forming of metal matrix composites

The use of thermal spray processes with subsequent material densification by semi-solid forming can yield advantages for manufacturing of metal matrix composites (MMC) compared to well-established manufacturing methods like spray forming or diffusion bonding. The main challenges of this method lie in well defined process temperatures during material deposition and forming, handling of the material during the processes, microstructure of the semi-finished matrix, and economical efficiency of the process chain.Particulate reinforcement of light metal matrix material is mainly aimed on improvement of mechanical properties at elevated temperatures, e.g. wear behavior, creep resistance, yield and tensile strength. Composite formation for particle reinforced metals (PRM) by thermal spraying with the arc wire system is achieved by simultaneous deposition of matrix and reinforcement by means of cored wires. Unidirectional (UD) fiber reinforced MMC yield highest specific mechanical properties and can be processed by winding of a continuous fiber strand and coating of the fiber layer by arc wire spraying with wires from light alloy matrix material or by plasma spraying with mixed powders. The coating process can be simultaneous to the winding process or in a separate step for prepreg manufacturing with shape and fiber content adapted to the final component geometry and load case.