纳米复相陶瓷制备技术的研究现状

纳米增强相在陶瓷基体中以纳米尺度稳定地均匀分布,是制备高性能纳米复相陶瓷材料的关键.介绍了纳米复相陶瓷的特性,几种具有广阔应用前景的纳米复相陶瓷材料的制备方法及研究成果.存在的问题主要有纳米增强相的均匀分散,还没有成熟的低成本、高性能且产业化的制备工艺,指出纳米复相陶瓷的研究将围绕这2个问题而进行.     

高性能纳米复相陶瓷日前在上海研制成功

据媒体报道，一种高性能纳米复相陶瓷最近在上海硅酸盐研究所研制成功。这种新型陶瓷的强度，韧性以及电阻率等性能均达到国际水准。由于它是几种陶瓷复合而成，并添加了具有磁性、电性、光性能的其他材料，因而既拥有结构陶瓷的力学性能，又具备功能陶瓷的特殊功能。磁性材料的添加，大大降低了电阻     

纳米复相陶瓷的制备、显微结构和性能

从纳米复相陶瓷的分类、材料的设计和制备以及材料的微观结构和性能等方面对纳米复相陶瓷进行了详细的阐述,并提出通过纳米和微米复合相互结合以及控制调节材料中晶粒形状和大小来改善瓷体性能的设想．     

高性能可加工3Y-TZP/BN纳米复相陶瓷的制备

利用化学包覆和热压烧结制备出3Y-TZP/BN纳米复相陶瓷,BN体积分数分别为10%～30%.XRD和TEM揭示,大长径比的纳米h-BN颗粒均匀分布在ZrO2晶界;与原始尺寸相比,ZrO2晶粒没有明显长大.与对应的微米复相陶瓷相比较,3Y-TZP/BN纳米复相陶瓷的弯曲强度及断裂韧性得到显著提高.当BN的体积分数达到20%时,复相陶瓷可用WC刀具容易地加工.BN的体积分数达到30%时,3Y-TZP/BN纳米复相陶瓷具有最佳的综合性能:弯曲强度为774MPa,断裂韧性为7.85MPa·m1/2,以及优异的可加工性能.     

纳米碳化硅基复相陶瓷的分散和烧结技术研究进展

碳化硅陶瓷是一种高性能的陶瓷,具有高强度、高硬度、耐高温、耐化学腐蚀、高热导率、低热膨胀以及低密度等性能,广泛应用于各个工业领域以及航空航天领域.从纳米复相陶瓷制备过程中的分散方法以及碳化硅基陶瓷的烧结方法与烧结助剂等方面详细论述了目前有关碳化硅基纳米复相陶瓷的研究进展.     

Al2O3/SiC纳米复相陶瓷材料的研究进展

Al2O3/SiC纳米复相陶瓷由于具有优异的室温及高温机械性能而成为结构陶瓷领域研究的热点.本文就Al2O3/SiC纳米复相陶瓷的不同制备加工方式及增强增韧机理进行了详细的阐述.其中粉体的均匀混合是制备过程的关键因素,残余应力及裂纹偏转导致的穿晶断裂以及裂纹尖端SiC颗粒的桥联作用是复相陶瓷强度和韧性增加的主导因素.     

柠檬酸盐聚合物前驱体法制备锆钛酸铅纳米复相陶瓷研究

采用聚合物前驱体法成功制备出PZT/ZrO2纳米复相陶瓷。烧结过程中ZrO2相从固溶体中析出,制备出内晶型纳米复相陶瓷。对物相、组成和微观结构进行了分析和研究。随ZrO2的加入量增加断口从沿晶穿晶混合断裂变为穿晶断裂。     

SHS纳米/微米块体复相陶瓷微观结构与断裂

通过在(CrO3 Al)燃烧体系中添加一定量的ZrO2(2Y)粉末,利用SHS冶金技术直接制备出Al2O3-35vol%ZrO2纳米/微米结构块体复相陶瓷,研究该复相陶瓷的微观结构与断裂行为.研究发现:该复相陶瓷基体主要由纳米/微米相晶内型结构共晶体组织构成;Vickers压痕试验显示引发陶瓷裂纹扩展的压痕压制临界载荷为30 kg;ZrO2相所具有的应力诱发相变增韧机制和微裂纹增韧机制均很微弱;裂纹扩展主要受纳米/微米相晶内型结构共晶体控制,使该复相陶瓷在断裂过程中呈现出强烈的裂纹偏转绕过机制.     

SHS纳米组织Al2O3-ZrO2共晶复相陶瓷断裂力学研究

通过对纳米组织Al2O3-ZrO2共晶复相陶瓷的Vickers压痕测试、SEM观察与XRD分析,发现诱发该复相陶瓷中位裂纹扩展的压痕压制载荷临界值为30kg,复相陶瓷的裂纹扩展主要受晶内型纳米相微观结构所控制,分布于纳米组织Al2O3-ZrO2共晶复相陶瓷中的ZrO2纳米相的结构、含量与分布及ZrO2纳米相与基体相之间的残余应力场决定着该复相陶瓷的断裂力学.     

放电等离子超快速烧结 SiC-Al2O3纳米复相陶瓷

本文介绍用非均相沉淀法制备的纳米SiC-Al2O3复合粉体经放电等离子超快速烧结得到晶内型的纳米复相陶瓷,超快速烧结的升温速率为600℃/min,在烧结温度不保温,迅即在3min内冷却至600℃以下.与热压烧结相比,可降低烧结温度200℃以上.力学性能研究结果表明,在1450℃超快速烧结得到的纳米复相陶瓷的抗弯强度高达1000MPa,维氏硬度为 19GPa,断裂韧性也比Al2O3有所提高.TEM像显示纳米SiC颗粒大多分布在Al2O3母体晶粒内,而断裂表面的SEM像表明,穿晶断裂是其主要的断裂模式,这是所制备的纳米复相陶瓷力学性能大幅提高的主要原因.     

Polishing of ceramic tiles

Grinding and polishing are important steps in the production of decorative vitreous ceramic tiles. Different combinations of finishing wheels and polishing wheels are tested to optimize their selection. The results show that the surface glossiness depends not only on the surface quality before machining, but also on the characteristics of the ceramic tiles as well as the performance of grinding and polishing wheels. The performance of the polishing wheel is the key for a good final surface quality. The surface glossiness after finishing must be above 20° in order to get higher polishing quality because finishing will limit the maximum surface glossiness by polishing. The optimized combination of grinding and polishing wheels for all the steps will achieve shorter machining times and better surface quality. No obvious relationships are found between the hardness of ceramic tiles and surface quality or the wear of grinding wheels; therefore, the hardness of the ceramic tile cannot be used for evaluating its machinability.     

Fabrication of hybrid ceramic matrix composites

The desire to improve the transverse properties and microcracking stress of unidirectional continuous fiber reinforced ceramic matrix composites has led to development of the hybrid ceramic matrix composite (HCMC). This paper discusses the techniques we used in the fabrication of HCMC specimens used for mechanical characterization.     

Freeze-form extrusion fabrication of ceramic parts

A novel, environmentally friendly solid freeform fabrication method called freeze-form extrusion fabrication (FEF) has been developed for the fabrication of ceramic-based components. The method is based on deposition of ceramic pastes using water as the media. The ceramic solids loading can be 50 vol.% or higher and initial studies have focused on the use of aluminum oxide (Al₂O₃). The FEF system components and their interaction are examined, and the main process parameters affecting part geometry defined. Three-dimensional shaped components have been fabricated by extrusion deposition of the ceramic paste in a layer-by-layer fashion. The feasibility of this process has been demonstrated by building components having a simple geometry, such as cylinders and solid or hollow cones. Hollow cones have also been fabricated to demonstrate the ability to build structures with sloped walls.     

On the fracture toughness of ceramic matrix composites

Based on the resistance curve (R-curve) behaviour of ceramic matrix composites (CMCs) determined under either quasi-static or cyclic loading, the crack-face fibre bridging stress field is determined for the compact tension (CT) test specimen geometry. Two different methods have been used for the analysis of the bridging stresses. The first considers a compliance approach. Using the difference in compliance calibration curves with and without bridging and assuming a power-law relation between bridging stress and crack opening displacement, the bridging stress field was calculated. The second approach uses the existence of an invariant stress reversal point in the CT geometry and assuming that the material exhibits linear elastic fracture behaviour, yields a recurrence relation for the bridging stresses resulting in a piece-wise constant stress function. Both models are applied to the experimentally determined fracture behaviour of a 2D carbon/carbon (C/C) composite, and the resulting bridging stress distributions are discussed.     

Freeze-form extrusion fabrication of ceramic parts

A novel, environmentally friendly solid freeform fabrication method called freeze-form extrusion fabrication (FEF) has been developed for the fabrication of ceramic-based components. The method is based on deposition of ceramic pastes using water as the media. The ceramic solids loading can be 50 vol.% or higher and initial studies have focused on the use of aluminum oxide (Al₂O₃). The FEF system components and their interaction are examined, and the main process parameters affecting part geometry defined. Three-dimensional shaped components have been fabricated by extrusion deposition of the ceramic paste in a layer-by-layer fashion. The feasibility of this process has been demonstrated by building components having a simple geometry, such as cylinders and solid or hollow cones. Hollow cones have also been fabricated to demonstrate the ability to build structures with sloped walls.     

Fracture in angle-ply ceramic matrix composites

An analytical/computational fracture mechanics scheme, combined with finite element computations, is presented to explain observed fracture patterns in angle ply fiber-reinforced ceramic composite laminates. Unlike polymeric composites, where microcracks are channeled parallel to the fiber directions, cracks in ceramic composites initiate perpendicularly to the load axis. The results presented herein provide rational explanations for the experimental observations and confirm the advantages bestowed by multi-directional reinforcements. Such reinforcements would still allow the development of multitudes of matrix cracks, bridged by intact fibers, that lead to the desirable gradual and `graceful' failure of the composite. At the same time, multidirectional reinforcement prevents premature failures by constraining the laminate against interfacial fiber/matrix debondings. Such debondings, which may otherwise grow rapidly along the abovementioned weak interfaces, may readily occur in unidirectionally reinforced off-axis laminates, as noted in a preceding article.     

Concrete with ceramic waste aggregate

Use of hazardous industrial wastes in concrete-making will lead to greener environment. In ceramic industry about 30% production goes as waste, which is not recycled at present. In this study an attempt has been made to find the suitability of the ceramic industrial wastes as a possible substitute for conventional crushed stone coarse aggregate. Experiments were carried out to determine the compressive, splitting tensile and flexural strengths and the modulus of elasticity of concrete with ceramic waste coarse aggregate and to compare them with those of conventional concrete made with crushed stone coarse aggregate. The properties of the aggregates were also compared. Test results indicate that the workability of ceramic waste coarse aggregate concrete is good and the strength characteristics are comparable to those of the conventional concrete.     

Conditions for matrix crack deflection at an interface in ceramic matrix composites

This paper describes a numerical approach developed to simulate the mechanism of matrix crack deflection at the fibre/matrix interface in brittle matrix composites. For this purpose, the fracture behaviour of a unit cell (microcomposite) consisting of a single fibre surrounded by a cylindrical tube of matrix was studied with the help of a finite element model. A fracture mechanics approach was used to design a criterion for deflection at the fibre/matrix interface of an annular crack present in the matrix. The analysis of the fracture behaviour of SiC/SiC and SiC/glass ceramics microcomposites shows that the introduction of a low modulus and low toughness interfacial layer at the fibre/matrix interface (e.g. a carbon coating) greatly favours matrix crack deflection at the interphase/fibre interface.     

A novel technique for the preparation of fine ceramic oxides

In this paper, we put forward a novel and simple chemical route for the preparation of fine ceramic oxides i.e. ferrites using triethylammonium carbonate as the precipitating agent. The particles were studied and characterized by X-ray diffraction and scanning electron microscopy. The emphasis is on the superiority of this technique over other chemical and conventional routes.     

A novel ceramic printing technique based on electrostatic atomization of a suspension

A novel computer-controlled method of depositing ceramic droplets, according to a pre-determined architecture is described. A 21 vol% alumina suspension flowing through a nozzle was subjected to electrostatic atomization in the cone-jet mode at different applied voltages. By using a point-like ground electrode the resulting spray was focused and printed on a substrate placed between the nozzle and the ground electrode. The substrate was moved with the aid of a 2-axis computer controlled stepper motor driven system which enabled the forming of different ceramic architectures. As an example, the word CERAMIC was printed. At an applied voltage of 10 kV, droplet relics in the print were in the size range 30–60 μm. Electronic Publication