Fabrication Of Ceramic Composites Research Articles

Fabrication of Ceramic Composites by Microwave Sintering

Fabrication of Ceramic Composites by Microwave Sintering

Application of Carbon Fiber-Reinforced Ceramic Composites in Active Thermal Protection of Advanced Propulsion Systems: A Review.

Thermal protection is one of the crucial issues for the advanced propulsion systems of Reusable Launch Vehicles. New service requirements for materials, such as high strength, low density, low thermal expansion, high thermal stability, etc., are raised for the thermal structure with the increasing demand of flight Mach numbers and thrust-to-weight ratio. Carbon fiber-reinforced ceramic composites, which generally meet the aforementioned requirements, show great potential for various applications and they have been widely applied in the thermal protection for hypersonic vehicles. This paper gives a comprehensive and systematic review of current research status for carbon fiber-reinforced ceramic composites applied in the thermal structure of advanced propulsion systems. Three aspects are presented and discussed: the ceramic composites fabrication and the property characterization, the thermal performance of composite thermal structure used in practical engines, and the numerical methods for predicting mechanical and thermal properties of composites as well as the physicochemical phenomenon in the cooling channels. Firstly, the main manufacturing processes for the carbon-reinforced ceramic composites are presented and the corresponding advantages and disadvantages are analyzed. The high-temperature oxidation and ablation behaviors of composites are demonstrated and the improvement of oxidation and ablation resistance by introducing the ultra-high-temperature ceramics into C/C composites is discussed in detail. Then, several typical applications of carbon fiber-reinforced ceramic composites (mainly C/SiC), including the work of RCI, JAXA and NASA, have been reviewed and analyzed. After that, the current research status of macroscale equivalent and multiscale numerical methods for predicting the mechanical and thermal properties of composites as well as the complex physicochemical phenomenon occurring in hydrocarbon fuels are sorted out. Finally, several potential prospects are pointed out for the future research on the thermal protection of advanced propulsion systems based on the carbon fiber-reinforced ceramic composites.

Synthesis of Porous Biomimetic Composites: A Sea Urchin Skeleton Used as a Template

The paper presents an original method for the template synthesis of biomimetic porous composites using polyferrophenylsiloxane (PFPS) and the skeleton of the sea urchin Strongylocentrotus intermedius as a structuring template. The study aimed to form an organosilicon base of a composite with an inverted structure relative to the original structure of the sea urchin shell with a period of structure movement of about 20 µm and ceramic composites fabrication with the silicate base with an average pore size distribution of about 10 μm obtained by the reaction of PFPS with the inorganic base of the sea urchin test under conditions of calcination at 1000 °C followed by acid etching. The composition and morphology of the obtained composites were investigated by IR, XRD, XPS, EDX, and SEM techniques and by mercury porosimetry; the parameters of the porous structures depend on the selected methods of their synthesis. The proposed method is of fundamental importance for developing methods for the chemical synthesis of new biomimetics with a unique porosity architecture based on environmentally friendly natural raw materials for a vast practical application.

Fabrication and parametric optimization of SiO2-BN gelcast ceramic composites using response surface methodology

Abstract Gelcasting, a novel technique was introduced to fabricate SiO2-BN ceramic composites with controlled porosity and flexural strength. Aqueous SiO2-BN slurries with solids content up to 50% were prepared by varied contents of boron nitride, monomers, and their ratio. The effects of these parameters on the properties of ceramic composites were investigated by developing mathematical models using response surface methodology. In the present work, central composite face-centered design with 6 center points was used. The optimized values obtained for maximum flexural strength is 77.6 MPa and that of porosity is 23.72% respectively. The results show that optimization techniques have a potential in the fabrication of ceramic composites.

Polymeric liquid precursor of multi-component ZrC–SiC ceramic

Polymeric liquid ceramic precursors for the production of multi-component ZrC–SiC ceramics were prepared by reactive blending of polyzirconoxanesal, phenylacetylene-terminated polysilane and bisphenol-A type benzoxazine. The polymeric liquid precursors of ZrC–SiC ceramic have the processing capability of Precursor-Infiltration-and-Pyrolysis technique in ceramic composites fabrication. The thermal cure reactions included by the catalytic polymerisation of ethynyl groups, the ring opening polymerisation of benzoxazine rings, and the condensation of zirconate with phenolic hydroxyl and Si–H at 200–350°C. The monolithic ceramics were formed upon pyrolysis at 1000, 1200 and 1600°C in a yield of 65, 62 and 40%, respectively. X-ray diffraction and SEM–EDS results revealed that almost pure, elemental, uniformly distributed ZrC–SiC multi-component ceramic monolith was obtained through pyrolysis at 1600°C via carbothermal reduction of ZrO2.

Preparation, thermal cure and ceramization of liquid precursors of SiC–ZrC

Liquid PEPSI–PZO, as precursor of SiC–ZrC multi-component ceramic, was prepared by facile reactive blending method, using phenylethynylpolysilane (PEPSI) as silicon and carbon source and polyzirconoxanesal (PZO) as zirconium source. The processing capability of PEPSI–PZO met the demands of Precursor-infiltration–pyrolysis technique (PIP) in ceramic composites fabrication. The thermal cure was realized at 130–330°C by ethynyl polymerization and condensations. The thermal cure of PEPSI–PZO precursor was promoted by catalyst Ni(acac)2, and the curing initiation and curing peak temperatures decreased by 25 and 70°C, respectively. Evidenced by ceramic yields and XRD results, the thermal pyrolysis was catalyzed by Ni(acac)2, (ceramic yield was improved by 5–10%). XRD and SEM-EDS results showed that SiC–ZrC by 1600°C pyrolysis was highly crystalline, due to the occurrence of carbothermal reduction reaction. The liquid precursor of SiC–ZrC is an ideal candidate of low cost precursors for high-temperature ceramics and ceramic matrix composites.

Bulk TiB₂-Based Ceramic Composites with Improved Mechanical Property Using Fe-Ni-Ti-Al as a Sintering Aid.

The densification behavior, microstructure and mechanical properties of bulk TiB2-based ceramic composites, fabricated using the spark plasma sintering (SPS) technique with elements of (Fe–Ni–Ti–Al) sinter-aid were investigated. Comparing the change of shrinkage displacement of pure TiB2 and TiB2–5 wt% (Fe–Ni–Ti–Al), the addition of elements Fe–Ni–Ti–Al into TiB2 can facilitate sintering of the TiB2 ceramics. As the sintering temperature exceeds 1300 °C, the relative density does not significantly change. Alumina particles and austenite (Fe–Ni–Ti) metallic binder distributed homogeneously in the grain boundary of TiB2 can inhibit the growth of the TiB2 grains when the sintering temperature is below 1300 °C. The density and particle size of TiB2 greatly influence the mechanical behavior of TiB2–5 wt% (Fe–Ni–Ti–Al) composites. The specimen sintered at 1300 has the highest microhardness of 21.1 ± 0.1 GPa with an elastic modulus of 461.4 GPa. The content of secondary borides (M2B, being M = Fe, Ni), which are more brittle than TiB2 particles, can also influence the fracture toughness. The specimen sintered at 1500 °C has the highest fracture toughness of 6.16 ± 0.30 MPa·m1/2 with the smallest M2B phase. The results obtained provide insight into fabrication of ceramic composites with improved mechanical property.

Extraordinary thermal stability of SiC particulate-reinforced polymer-derived Si–B–C–N composites

A composite composed of SiC filler and Si–B–C–N matrix retained its properties even after heat treatment at 2000 °C for 10 h in Ar. The weight loss of the composite was less than 2% at 2100 °C. The composite showed excellent resistance to creep at 1400 °C in air and was strongly oxidation resistant at least up to 1450 °C. The material can be used for the fabrication of fiber-reinforced ceramic matrix composites with high thermal stability.

Design of Ceramic Composite Based on the Impact Resistance and its Machining Application

An optimum model for the compositional design of advanced ceramic composites is built based on the impact resistance. The relative impact modulus IM0 is defined as an index for the characterization of impact resistance of brittle ceramics. Computer aided optimum technique is used to get the optimum compositions of the material. Results show that the material can be expected to have the highest impact resistance which is nearly 86% higher than that of the pure alumina when the volume fraction of Al2O3, SiC and Ti(C,N) is 72.3%, 14.8% and 12.9%, respectively. An advanced SiC/Ti(C,N)/Al2O3 ceramic composite is then fabricated according to the optimum results. When used as cutting tools, its impact fracture resistance is approximately 71%-76% higher than that of the pure alumina ceramic in the machining of hardened carbon steel. The increment coincides well with that predicted directly from the optimum model. It suggests that the method is feasible in the design and fabrication of ceramic composites especially for machining application.

Fabrication of ceramic composites by directed metal oxidation

To explain the growth mechanism of Al2O3/Al Lanxide composites, the dynamics of the directed oxidation of Al−Mg−Si alloys are analyzed. The experimental methods to produce Lanxide composites by directed oxidation of metal melts at high temperatures are presented. The effect of the processing factors on the microstructures and properties of Al2O3/Al composites and enforced Al2O3/Al composites is also analyzed. Compared with sintering ceramic composites, the advantages of Lanxide process and Lanxide materials are as following: it is a near net shaped process; the process is very simple; the microstructures and properties of Lanxide materials can be adjusted; and this process can be used to infiltrate ceramic fiber or particle preforms.

Fibrous Filler-Matrix Interaction in Oxide Composites

The interaction between a fibrous alumina filler and a hydrated zirconia matrix during the fabrication of ceramic composites is studied. The influence of the crystal structure and porosity of the filler on the properties of the ZrO2-Al2O3 composite material is investigated. It is found that, as a result of addition of alumina fibers of cubic and monoclinic structures (γ- and θ-phases), the ZrO2 hydrogel interacts with fibers and solid ZrO2 solutions of tetragonal structure are formed. These solutions exist over the range of 600 to 1200°C and, at annealing above 1200°C, due to crystallographic transitions the of γ- and θ-phases, they break down, namely Al2O3 transforms into α-corundum and ZrO2 into a monoclinic modification. However, the material does not fail and a stable porous ceramic composite is formed. To manufacture a composite with improved mechanical characteristics, fibrous alumina fillers with the structure of -corundum must be used.

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.

Continuous fibre reinforced mullite matrix composites by sol–gel processing: Part I Fabrication and microstructures

The fabrication of ceramic composites based on a mullite matrix uniaxially reinforced with either high strength carbon or Nicalon-SiC continuous fibres is described. Sols of high solids contents of up to 40 vol% were prepared using colloidal silica sol with either α-alumina powder or colloidal boehmite as reactants for the preparation of the mullite matrix, 3Al2O3·2SiO2. Single-stage infiltration was used for the preparation of prepregs for laminating into composites. The composites were consolidated by uniaxially hot-pressing at 1300 or 1550°C, depending on the matrix precursors and the final phases in the matrix. Highly densified composites with fibre volume fractions of 32–60% were obtained and the microstructures characterised by mercury porosimetry, X-ray diffraction, scanning electron microscopy and transmission electron microscopy.

Fabrication of ceramic composites: forced CVI

Forced chemical vapor infiltration (FCVI) is being developed as an efficient means for producing thick-wall ceramic matrix components. Recent efforts have focussed on process scale-up, modeling and the properties of the resultant material. Disks 24.6 cm in diameter and 1.27 cm thick have been produced. Composites of Nicalon TM fibers and SiC matrix have exhibited 480 MPa strength in flexure.

Analytical Modeling of Chemical Vapor Infiltration in Fabrication of Ceramic Composites

A model for chemical vapor infiltration is applied to the study of the growth of alumina from the chemical reaction among AlCl3, H2, and CO2 within a SiC‐fiber bundle which is situated in an isothermal hot‐wall reactor. The pore space between the fibers is simulated by cylindrical capillary tubes. The model considers binary diffusion of CO2 and H2, chemical reaction on the inner surface of the tube, and deposition film growth. Furthermore, diffusion‐controiled and chemical‐reaction‐controlled processes are taken into account to determine the dominating process in chemical vapor infiltration. Both molecular diffusion and Knudsen diffusion are considered sequentially in this model during the infiltration process. Based upon this model, the optimum processing conditions required for chemical vapor infiltration to form a SiC/Al2O3 composite can be predicted for different fiber preform systems.

Degradation Mechanisms of Silicon Carbide Fibers

The effects of high temperatures on polymer‐derived Nicalon and chemically vapor‐deposited (CVD) SiC fibers have been investigated by mass‐spectrometric vapor pressure studies and by SEM observations of exposed fibers. Vaporization is kinetically limited for both materials; the predominant species vaporizing from Nicalon is SiO, whereas CO predominates in vaporization of CVD SiC fibers. The inherent instability of Nicalon and other SiC fibers in contact with matrices must be considered in ceramic composite fabrication and use.

The technology of ceramic-fibre ceramic-matrix composites

Recent advances in ceramic fibre technology, ceramic forming processes and ceramic composite fabrication are reviewed. Some of the techniques developed in the Harwell Ceramics Centre are referred to and suggestions made for possible composite fabrication routes