碳模板转化法制备管状SiC/Si复合陶瓷

利用纸作为原材料,通过卷曲、树脂浸渍、碳化预制备出具有层状结构的管状碳模板,之后在1550℃通过原位反应液相渗Si0.5-1h,在常压烧结条件下制备出具有层状结构特征的SiC/Si管状陶瓷复合材料.采用XRD、SEM对碳模板反应前后的物相变化和显微结构进行了研究.结果表明了该材料的最终产物为β-SiC和Si,且两者分布表现出明显的交替成层现象,呈现出层状陶瓷的结构特征.     

Fabrication of ceramic composites consisting of powders with different specific gravity by the slip-casting technique

For composites, it is of great importance to fabricate well-dispersed green compacts, in order to improve their mechanical properties and reliability. In the present study, the slip-casting technique was applied to the fabrication of ZrO2-WC-Al2O3 composites. The specific gravity of each composition in this material was very different, that is, 6.07 for ZrO2, 15.6 for WC and 3.94 for Al2O3. The compositions in the green compacts were afraid to separate from each other owing to the difference in their specific gravities, leading to heterogeneity in the microstructure. The relative density of the obtained compacts was approximately 60%. WC and Al2O3 were well-dispersed in the ZrO2 matrix. The separation and/or heterogeneity due to difference could not be recognized by energy-dispersive X-ray analysis. The slip-casting technique was found to be applicable to the fabrication of ceramic composites consisting of raw powders with different specific gravities. This revised version was published online in November 2006 with corrections to the Cover Date.     

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.     

Fabrication and performances of epoxy/multi-walled carbon nanotubes/piezoelectric ceramic composites as rigid piezo-damping materials

Piezo-damping epoxy-based composites containing various amounts of multi-walled carbon nanotubes (CNT) and piezoelectric lead zirconate titanate (PZT) were prepared, and their performances were investigated. The composites exhibited a percolation threshold in the range of 1–1.5 g CNT per 100 g epoxy, in which a continuous electro-conductive network formed. Dynamic mechanical thermal analysis reveals that the loss factors of the composites were improved by incorporation of the PZT and the CNT at above critical electrical percolation loading. Based on this new type rigid piezo-damping material, the PZT contributes to the transformation of mechanical noise and vibration energies into electric energy, while the CNT serve in shorting of the generated electric current to the external circuit. Thermal stability and mechanical properties were also improved by incorporating these two fillers. An optimum formulation for the rigid piezo-damping materials can be designed on the basis of the results of this study.     

Fabrication of porous ceramics with controlled pore size by colloidal processing

Well-defined macroporous ceramics consisting of TiO₂ and ZrO₂ have been fabricated by two methods. One is via a template-assisted colloidal processing technique and the other is via a hetero-coagulation of template/ceramic particle colloidal processing. The former technique is as follows. Close-packed polymer spheres were first prepared as a template using centrifugation or gravitational sedimentation, followed by infiltration with alkoxide precursors. Then the removal of the template beads was achieved by calcination of the organic–inorganic hybrids at appropriate temperatures, yielding well-ordered macroporous ceramics. The latter technique is as follows. Core–shell composites of polymer/ceramic were obtained by mixing the oppositely charged two suspensions via electrostatic attraction following by filtration and calcination to produce macroporous ceramic materials. SEM images revealed that macroporous TiO₂ and ZrO₂ with ordered and uniform macropores have been obtained by both procedures.     

Fabrication and characterization of three dimensional woven carbon fiber/silica ceramic matrix composites

Carbon fiber reinforced fused silica composites exhibit the advantages of excellent mechanical properties, high heat resistance, low thermal expansion and low density, but low impact resistance or toughness. A novel modified slurry impregnation and hot pressing (SIHP) method was adopted to fabricate a new type of three dimensional orthogonal woven structure carbon fiber reinforced silica ceramic matrix composites (3D Cf/SiO₂ CMCs) with higher density and lower porosity. Physical characterization, flexural behavior, impact performance and toughening mechanism of the composites were investigated by three-point bending tests, impact tests, and scanning electron microscopy analysis. The 3D Cf/SiO₂ CMC showed a higher flexural strength in both warp (201.6%) and weft (263.6%) directions than those of pure SiO₂ and failed at a non-brittle mode due to the fiber debonding and pullout, and a delaminated failure of the 3D preform. The maximum impact energy absorption of the 3D Cf/SiO₂ CMC was 96.9 kJ/m², almost 4 times as much as those for typical other carbon fiber reinforced CMCs.     

Fabrication of high-temperature resistant oxide ceramic matrix composites

The main objectives of this work are to develop and apply new ceramic matrix materials by which a relatively high level of densification of the final composite may be achieved by pressureless-sintering at temperatures close to 1200°C. A cost-effective processing method for the production of oxide/oxide CMCs materials and components has been achieved.A range of interphase materials is applied to Nextel™ 720 fibres. These include zirconia, neodymium and lanthanum phosphate. A combination of ZrO₂ and the AKP50 alumina powder have been selected as the successful candidates for the interphase and the matrix material, respectively. Work has been conducted on the preparation of slurry systems consisting of these two materials. The prime target was to establish the possibility of achieving good coating around the bulk of the fibres together with a high level of impregnation with the matrix material. Furthermore, the pressure infiltration technique has been applied and as a result composite samples with fibre volume content of 40%, and remaining porosity of around 20 vol% have been routinely produced. Composite room and high-temperature tensile strengths of around 200 MPa have been accomplished.     

Fabrication of nature-inspired bulk laminar composites by a powder processing

Among many kinds of “nano-laminar” composites inspired by the brick and mortar structure of nacre in mollusk shells, a bulky, dense and ceramics–base composite has been a missing piece despite its importance. Here we report that such a composite with a submicron-order layered structure can be fabricated by a simple method, sintering aligned flake-like inorganic powder coated with ductile matrix material. The composites fabricated by this method had crack extension resistance by interface delamination, crack deflection, and ligament bridging by the ductile matrix. They showed non-brittle fracture behavior in a bending test despite a quite high flake volume fraction of over 80%, and had a work of fracture (WOF) of more than 300 J/m², several hundreds times as large as that of monolithic glass.     

Fabrication and mechanical properties of carbon short fiber reinforced barium aluminosilicate glass–ceramic matrix composites

Dense BaSi₂Al₂O₈ (BAS) and Ba_0.75Sr_0.25Si₂Al₂O₈ (BSAS) glass–ceramic matrix composites reinforced with carbon short fibers (C_sf) were fabricated by hot pressing technique. The microstructure, mechanical properties and fracture behavior of the composites were investigated by X-ray diffraction, scanning and transmission electron microscopies, and three-point bend tests. The carbon fibers had a good chemical compatibility with the glass–ceramic matrices and can effectively reinforce the BAS (or BSAS) glass–ceramic because of associated toughening mechanisms such as crack deflection, fiber bridging and pullout effects. Doping of BAS with 25 mol% SrSi₂Al₂O₈ (SAS) can accelerate the hexacelsian to celsian transformation and result in the formation of pure monoclinic celsian in C_sf/BSAS composites, which can avoid the undesirable reversible hexacelsian to orthorhombic transformation at 300 °C and reduce the thermal expansion mismatch between the fiber and matrix.     

碳纳米管增强陶瓷基复合材料研究进展

从制备方法和力学性能两方面出发,综述了碳纳米管增强陶瓷基复合材料的研究现状,针对研究中存在的问题,提出了相应的解决方法,并预测了其发展趋势.     

Fabrication of fibre composites using an aluminium superplastic alloy as matrix

An aluminium superplastic alloy has been used as the matrix for a variety of fibre reinforcements. It is shown that, by hot pressing in the superplastic regime of the alloy, a number of different reinforcements can be incorporated into the matrix. Tensile tests on composites with up to 25 vol % of reinforcement showed good agreement with the rule of mixtures.     

SiBNC_f/SiBNC陶瓷复合材料抗氧化性能

以聚硼硅氮烷(PBSZ)为前驱体,SiBNC纤维(SiBNCf)为增强纤维,采用前驱体聚合物裂解转化与热压烧结技术相结合的方法制备了SiBNCf/SiBNC陶瓷复合材料。在800~1 500℃空气气氛下非等温氧化1~3h,研究了SiBNCf/SiBNC的氧化演变机制及氧化动力学行为。采用SEM、XRD研究了SiBNCf/SiBNC陶瓷复合材料氧化实验前后的微观形貌、物相,采用阿基米德体积排水法和三点弯曲测试法分析了复合材料的密度、孔隙率及力学性能。结果表明:SiBNCf/SiBNC陶瓷复合材料具有优异的抗氧化性能和高温稳定性,生成的氧化膜能有效阻隔氧气的进入,并且有效填补了SiBNCf/SiBNC复合材料的裂纹及孔洞缺陷,具有高温自愈合行为。SiBNCf/SiBNC复合材料氧化后密度提高,这能大幅度提高其三点弯曲强度,当密度从1.67g/cm3提高到1.86g/cm3时,气孔率下降41%,弯曲强度从7.51 MPa提高到26.54 MPa。     

Thermal shock resistance of laminated ceramic matrix composites

The thermal shock resistance capability of laminated ceramic matrix composites is investigated through the study of three-dimensional transient thermal stresses and laminate failure mechanisms. A (–45°/45°)_s SiC/borosilicate glass laminate is utilized as a reference composite system to demonstrate the analytical results. The maximum allowable temperature change, T _max, has been taken as a measure of the thermal shock resistance capability of composites. The effects of fibre orientation, volume fraction, thermal expansion coefficient. Young's modulus, and thermal conductivity on the thermal shock resistance capability, expressed in terms of the maximum allowable temperature change, T _max, have been assessed. Numerical computations are also performed for six composite systems.     

Fabrication of green films of single- and multi-component ceramic composites by electrophoretic deposition technique

An electrophoretic technique for the formation of ceramic composites is demonstrated in the systems of biomedical hydroxyapatite–yttria-stabilized zirconia and ferroelectric barium titanate–strontium titanate. Ceramic powders show different behaviour depending on the nature of the solvent media chosen. For such purposes, a solvent mixture of acetylacetone and alcohols proved effective for adjusting the composition of deposited films. This revised version was published online in November 2006 with corrections to the Cover Date.     

Influence of processing parameters on the formation of WC-Co nanocomposite powder using a polymer as carbon source

Influences of processing parameters on the formation of WC-Co nanocomposite powder employing polyacrylonitrile as a carbon source have been investigated systematically. The processing parameters investigated include firing time and temperature, addition of a small quantity of cobalt acetate initially as a catalyst, and the sample quantity for a given firing scheme. The investigation provides basic information for optimizing processing parameters to obtain finer WC-Co nanocomposite powders with less unwanted phases. Based on the information obtained from systematic investigation, an improved processing procedure is developed, which can avoid some shortcomings of our previously reported procedure. However, the final product still has some undecomposed polymer or uncombined carbon, which needs to be eliminated before the present synthesis route becomes commercially feasible.     

Fabrication of carbon papers using polyacrylonitrile fibers as a binder

Carbon papers (CPs) have been fabricated using wet-laying carbon fibers (CFs) and polyacrylonitrile (PAN) fibers. Scanning electron microscopy revealed that the PAN fibers tightly interconnected the CF junctions with the pores between the fibers. The tensile strength of the carbon webs (CWs) increased as the fraction of PAN fibers used as the binder increased. The CW fabricated with 0.15 wt% PAN fibers had a tensile strength six times greater than that of the CW without PAN fibers. Moreover, by mixing the CFs with PAN fibers in water, the CFs separated from each other in the webs due to the interruption of hydrophobicity between the CFs. After mixing with PAN fibers, the CWs were carbonized at 1200 °C in the presence of a phenolic resin. The PAN fibers maintained their morphology due to their high carbon content after carbonization. The electrical resistivity of the CPs with high PAN fiber content was significantly lower than that of a CP without PAN fibers due to the interconnection of the CFs by the carbonized PAN fibers.     

Microstructural development of woven mullite fibre-reinforced mullite ceramic matrix composites by infiltration processing

Mullite fibre (Nextel 720?)-reinforced mullite ceramic matrix composites (CMCs) with zirconia weak interface were fabricated from heterocoagulated nano-size boehmite/amorphous silica powder particles dispersed in water, using electrophoretic deposition (EPD) and pressure filtration (PF). The nano-size mullite precursor was first prepared and characterised in terms of short-range particle–particle interactions and particle size distribution. Woven Nextel 720 mullite fibres were first desized and then coated with hydrothermally derived zirconia using dip-coating. EPD was performed under constant voltage conditions with varying deposition times, to infiltrate the dispersed powder suspensions into mullite fibre preforms, enabling the parameters necessary for good deposition of stoichiometric mullite to be established. EPD formed bodies were further consolitated using PF. The EPD/PF prepared green body specimens were dried under controlled atmosphere conditions before being sintered at 1200°C for 2 h in air. Mullite fibre mats were fully infiltrated using EPD parameters of 12 V DC applied voltage with 4 min deposition time, then eight EPD infiltrated fibre mats were further consolidated together using PF. The resulting CMC produced contained 35 vol% fibre loading and showed 81% theoretical density aftersintering at 1200°C for 2 h.     

Thermal conductivities of alumina-based multiwall carbon nanotube ceramic composites

Composites incorporating various vol.% (0.0, 1.1, 6.4, and 10.4) of multiwall carbon nanotubes (MWCNTs) in alumina were consolidated by the spark plasma sintering. Their thermal transport properties were investigated over the temperature range 300–800 K as a function of nanotube contents. It was observed that the temperature-dependent effective thermal conductivity decreases with the addition of MWCNTs in alumina. This behavior was analyzed in terms of phonon mean free path, elastic modulus, average sound speed, and interface thermal resistance. Compared with 1/T behavior for pristine alumina, a subtle decrease in temperature dependence of the thermal conductivity of the composites with the addition of MWCNTs is observed, indicating the presence of extra phonon scattering mechanism beyond the intrinsic phonon–phonon scattering. Simulation of experimental results with theoretical model shows that the large interfacial thermal barrier between MWCNTs and alumina plays a dominant role in controlling thermal transport properties of the composites. In addition to dominant interface thermal resistance other secondary factors such as nanotube agglomeration, processing defects, porosity also contribute for low thermal conductivity at the higher volume fraction of MWCNTs in the composite.