Showing papers on "Ceramic matrix composite published in 2003"

Ceramic Matrix Composites

Abstract: Ceramic materials in general have a very attractive package of properties: high strength and high stiffness at very high temperatures, chemical inertness, low density, and so on. This attractive package is marred by one deadly flaw, namely, an utter lack of toughness. They are prone to catastrophic failures in the presence of flaws (surface or internal). They are extremely susceptible to thermal shock and are easily damaged during fabrication and/or service. It is therefore understandable that an overriding consideration in ceramic matrix composites (CMCs) is to toughen the ceramics by incorporating fibers in them and thus exploit the attractive high-temperature strength and environmental resistance of ceramic materials without risking a catastrophic failure. It is worth pointing out at the very outset that there are certain basic differences between CMCs and other composites. The general philosophy in nonceramic matrix composites is to have the fiber bear a greater proportion of the applied load. This load partitioning depends on the ratio of fiber and matrix elastic moduli, Ef/Em. In nonceramic matrix composites, this ratio can be very high, while in CMCs, it is rather low and can be as low as unity; think of alumina fiber reinforced alumina matrix composite. Another distinctive point regarding CMCs is that because of limited matrix ductility and generally high fabrication temperature, thermal mismatch between components has a very important bearing on CMC performance. The problem of chemical compatibility between components in CMCs has ramifications similar to those in, say, MMCs. We first describe some of the processing techniques for CMCs, followed by a description of some salient characteristics of CMCs regarding interface and mechanical properties and, in particular, the various possible toughness mechanisms, and finally a description of some applications of CMCs.

Characterization and High-Temperature Mechanical Behavior of an Oxide/Oxide Composite

Abstract: An oxide/oxide ceramic fiber-matrix composite (CMC) has been extensively characterized for high-temperature aerospace structural applications. This CMC is called GEN-IV™, and it has a porous and cracked aluminosilicate matrix reinforced by 3M Nextel 610™ alumina fibers woven in a balanced eight harness weave (8HSW). This CMC has been specifically designed without an interphase between the fiber and matrix, and it relies on the porous matrix for flaw tolerance. Stress-strain response is nearly linear to failure and without a well-defined proportional limit in tension and compression. In-plane shear and interlaminar strength increases with increasing temperature. The 1000°C fatigue limit in air at 105 cycles is 160 MPa, and the residual tensile strength of run-out specimens is not affected by the fatigue loading. The creep-rupture resistance above 1000°C is relatively poor, but it can be improved with a more-creep-resistant fiber.

Microwave dielectric properties of glass-ceramic composites for low temperature co-firable ceramics

Abstract: Ba–B–Si glass was added to Ba–Nd–Sm–Bi–Ti–O (BRT114) microwave dielectric material for LTCC applications. Conventional one-step processing method for preparing glass-BRT114 composite materials yields low dielectric constant, since the glass was easy to react with BRT114 and forms a low dielectric constant phase, Ba3B6Si2O16. A large proportion of pores appeared. The nature of glass, whether it is sol-gel derived or fused, shows marked influence on the microstructure and microwave dielectric properties of the composites. A two-step process containing precoating the BRT114 powders with a thin layer of glass, followed by conventional samples preparation process, tremendously improved the densification behaviour of the material. The formation of pores and interactions between glass and BRT114 was greatly suppressed such that materials with high dielectric constant (er=40) were achieved by sintering 9 wt.% glass-containing composite at 950 °C for 2.5 h.

Boron carbide based ceramic matrix composites

Abstract: The present invention is a composite material, a process and a product formed by the process. The composite is formed by a process that includes forming a fibrous structure comprising fibers into a preform, coating the fibers of the fibrous structure preform with elemental carbon to impregnate that preform, infiltrating the preform with boron carbide to form an impregnated green body. The impregnated green body is infiltrated with liquid naphthalene or other carbon precursor, which is thereafter pyrolyzed to form a carbon char. Then, the char infiltrated green body is infiltrated with molten silicon to form a continuous matrix throughout the composite. The silicon in the continuous matrix is reacted with the carbon char to form silicon carbide.

Metal and ceramic matrix composites

Abstract: SECTION 1: INDUSTRIAL PERSPECTIVE Introduction Metal matrix composites for aeroengines Metal matrix composites in high performance internal combustion engines High modulus steel composites for automobiles Metal matrix composites for aerospace structures Ceramic matrix composites for industrial gas turbines Composite superconductors SECTION 2: MANUFACTURING AND PROCESSING Introduction Fabrication and recycling of aluminium metal matrix composites Aluminium metal matrix composites by reactive and semi-solid squeeze casting Deformation processing of particle reinforced metal matrix composites Processing of titanium-silicon carbide fibre composites Manufacture of ceramic fibre-metal matrix composites SECTION 3: MECHANICAL BEHAVIOUR Introduction Deformation and damage in metal matrix composites Fatigue of discontinuous metal matrix composites Mechanical behaviour of intermetallics and intermetallic matrix composites Fracture of titanium aluminide-silicon carbide fibre composites Structure-property relationships in ceramic matrix composites Microstructure and performance limits of ceramic matrix composites SECTION 4: NEW FIBRES AND COMPOSITES Introduction Silicon carbide based and oxide fibre reinforcements High-strength high-conductivity copper composites Porous particle composites Active composites Ceramic nanocomposites Oxide eutectic ceramic matrix composites

Effect of SiC particle dispersion on microstructure and mechanical properties of polymer-derived SiC/SiC composite

Abstract: To improve the performance of SiC fiber-reinforced SiC matrix composite (SiC/SiC composite), a polymer impregnation and pyrolysis process (PIP process) has been developed by incorporating an inert filler with polyvinylsilane. Composites consolidated with slurries of various filler contents were thoroughly examined at each repetition of the PIP process. The fiber volume fraction and matrix microstructure in the composites were determined during consolidation as a function of the filler content. Densification behavior during multiple PIP processing was much dependent on the microstructure formed in consolidation. Transmission electron microscopy revealed the effect of filler content on the microstructure of the matrix and of the fiber/matrix interface. In addition, the relationships between the microstructure and the mechanical properties were evaluated from a fundamental viewpoint.

Mechanical properties of several advanced Tyranno-SA fiber-reinforced CVI-SiC matrix composites

Abstract: A recently developed SiC fiber, Tyranno-SA (2D plain-woven), was used as the reinforcement in several SiC/SiC composites. The composites were fabricated by chemical vapor infiltration (CVI) process. The mechanical properties and fracture behaviors were investigated using three-point bending test. The Tyranno-SA fiber possesses rough fiber surface with pure SiC surface chemistry, which may result in strong fiber/matrix bonding and fiber sliding resistance. Various pyrolytic carbon (PyC) and SiC/PyC interlayer coatings were applied in the composites to modify the mechanical properties of the interface. The interlayers were deposited by isothermal CVI process. The test results revealed a close PyC layer dependence of the strength of the composites. The ultimate flexural strength (UFS) increased with the increasing of the PyC layer thickness up to 100 nm, and then, kept at similar level till 200 nm. The Tyranno-SA/SiC composites exhibited relatively high proportional limit stresses due mainly to the large Young's modulus of the fiber. Fiber pullouts were observed at the fracture surfaces of all the interlayered composites. Attractive promising was exhibited on further improvement of the mechanical properties of the composites through further improvement of the interfacial properties and the matrix densification process.

Processing and Properties of a Porous Oxide Matrix Composite Reinforced with Continuous Oxide Fibers

Abstract: A process to manufacture porous oxide matrix/polycrystalline oxide fiber composites was developed and evaluated. The method uses infiltration of fiber cloths with an aqueous slurry of mullite/alumina powders to make prepregs. By careful manipulation of the interparticle pair potential in the slurry, a consolidated slurry with a high particle density is produced with a sufficiently low viscosity to allow efficient infiltration of the fiber tows. Vibration-assisted infiltration of stacked, cloth prepregs in combination with a simple vacuum bag technique produced composites with homogeneous microstructures. The method has the additional advantage of allowing complex shapes to be made. Subsequent infiltration of the powder mixture with an alumina precursor was made to strengthen the matrix. The porous matrix, without fibers, possessed good thermal stability and showed linear shrinkage of 0.9% on heat treatment at 1200°C. Mechanical properties were evaluated in flexural testing in a manner that precluded interlaminar shear failure before failure via the tensile stresses. It was shown that the composite produced by this method was comparable to porous oxide matrix composites manufactured by other processes using the same fibers (N610 and N720). The ratio of notch strength to unnotch strength for a crack to width ratio of 0.5 was 0.7–0.9, indicating moderate notch sensitivity. Interlaminar shear strength, which is dominated by matrix strength, changed from 7 to 12 MPa for matrix porosity ranging from 38% to 43%, respectively. The porous microstructure did not change after aging at 1200°C for 100 h. Heat treatment at 1300°C for 100 h reduced the strength for the N610 and N720 composites by 35% and 20%, respectively, and increased their brittle nature.

Ceramic fiber composite and method for making the same

Abstract: A ceramic fiber composite comprises ceramic fibers bonded together by an at least partially ceramic binder formed from a nanoclay and at least one of a ceramic precursor material or a ceramic material. The present invention also concerns methods of forming ceramic fiber composites and burners containing them.

Numerical analysis of the transverse thermal conductivity of composites with imperfect interfaces

Abstract: Estimation of the transverse thermal conductivity of continuous fiber reinforced composites containing a random fiber distribution with imperfect interfaces was performed using finite element analysis. FEA results were compared with the classical solution of Hasselman and Johnson to determine limits of applicability. The Hasselman and Johnson model predicts the effective thermal conductivity within 3 percent of the numerical estimates for interfacial conductance values of 1 × 10 -2 - 1 × 10 3 W/m 2 K, fiber-matrix conductivity ratios between 1 and 100, and fiber volume fractions up to 50 percent which are properties typical of ceramic composites

Processing and characterisation of a fine nickel oxide/zirconia/composite prepared by polymeric complex solution synthesis

Abstract: A homogeneous dispersion of nickel in a YSZ ceramic matrix by the polymeric organic complex solution method was achieved. A YSZ powder was added to the polymeric gel containing Ni 2+ cations leading to an organic resin in which the YSZ particles were embedded. By further heat treatment a composite of ultrafine nickel oxide dispersed in the YSZ matrix was attained. After sintering and reducing treatment of nanocrystalline NiO/YSZ composite, the microstructure of the Ni/YSZ cermet showed a uniform distribution of the porous metallic Ni particles of about 1–2 μm surrounded by a microporous space. The electrical properties of NiO/YSZ (55/45 wt.%) composites were studied using impedance spectroscopy in the temperature range from 100 to about 700 °C. Variations in activation energy were in agreement to the NiO electrical behaviour with increasing temperatures for polymer complex solution NiO/YSZ prepared composite, which indicates a uniform and fine-grained microstructure, in which the YSZ–YSZ and/or the NiO–NiO particle contacts were predominant.

Creep behaviour of a SiC/Si-B-C composite with a self-healing multilayered matrix

Abstract: The creep behaviour of a SiC/Si-B-C composite at 1200 °C in argon is investigated under static and cyclic loading conditions. The SiC/Si-B-C composite consists of a multilayered self healing matrix reinforced with Nicalon fibers. It was produced via chemical vapor infiltration (CVI). The creep behaviour is examined with respect to the extent of damage created during an initial step of monotonic loading and controlled through the applied strain. The creep rate is shown to be dictated mainly by creep of fibers and interfacial debonding, whereas no significant creep induced matrix cracking was detected.

Bond enhancement for thermally insulated ceramic matrix composite materials

Abstract: A composite structure ( 62 ) having a bond enhancement member ( 76 ) extending across a bond joint ( 86 ) between a ceramic matrix composite (CMC) material ( 80 ) and a ceramic insulation material ( 82 ), and a method of fabricating such a structure. The bond enhancement member may extend completely through the CMC material to be partially embedded in a core material ( 84 ) bonded to the CMC material on an opposed side from the insulation material. A mold ( 26 ) formed of a fugitive material having particles ( 18 ) of a bond enhancement material may be used to form the CMC material. A two-piece mold ( 38, 46 ) may be used to drive a bond enhancement member partially into the CMC material. A compressible material ( 56 ) containing the bond enhancement member may be compressed between a hard tool ( 60 ) and the CMC material to drive a bond enhancement member partially into the CMC material. A surface ( 98 ) of a ceramic insulation material ( 92 ) having a bond enhancement member ( 96 ) extending therefrom may be used as a mold for laying up a CMC material.

Effect of Silver Addition on the Dielectric Properties of Barium Titanate‐Based X7R Ceramics

Abstract: Different amounts of silver (0.5–10 wt%) have been mixed with EIA X7R-type ceramic powders based on barium titanate. The XRD analysis indicated that no phases other than BaTiO3 and silver were present in the doped ceramics; it further suggested that no reaction took place between BaTiO3 and silver during calcination and sintering. SEM observation showed that the silver particles presented island distribution in the BaTiO3 ceramic matrix. The densification and dielectric properties of the silver-doped ceramics in disk form were investigated. A large amount of silver addition (>1 wt%) was found to improve the sintered density and dielectric properties. The temperature coefficient of capacitors of the ceramics doped with 10 wt% silver still met the X7R characteristics, and the dielectric constant of the ceramics at room temperature was >6000, which is the highest dielectric constant in the BaTiO3-based X7R system.

Synthesis of BaAl2Si2O8 glass-ceramic by a sol-gel method and the fabrication of SiCpl/BaAl2Si2O8 composites

Abstract: BaAl2Si2O8 glass ceramics were synthesized by sol-gel using partial alkoxides. The crystallization behavior of BaAl2Si2O8 gel was characterized by XRD, DTA and TGA techniques. Barium aluminosilicate glass ceramic matrix composites reinforced with SiC platelets were fabricated by hot pressing method. The microstructure, mechanical properties and fracture behavior of the composites were investigated by X-ray diffraction, scanning and transimision electron microcopies, and three point bending tests. The results show that the flexural strength and the fracture toughness of the SiCpl/BAS composites increases with increasing SiC platelet content. By incorporation of 30 vol.% SiCpl, the flexural strength and the fracture toughness of the composites increase 80% and 114% compared to the pure BAS matrix, respectively. The main toughening mechanism is crack deflection.

Mesostructure of WHIPOX all oxide CMCs

Abstract: Wound highly porous oxide matrix (WHIPOX) ceramic matrix composites consist of oxide fibers (mullite- or alumina-type) which are embedded in mullite- or alumina-rich matrices, respectively. In the ideal case the fiber distribution is homogeneous; in reality, however, fabrication (winding)-induced matrix agglomerations do occur. As knowledge on the homogeneity of the material is crucial for the prediction of the mechanical behavior a technique to describe the mesostructure of WHIPOX quantitatively has been developed by means of optical microscopy (transmitted light). The technique makes use of light conductivity and opacity of fibers and matrix, respectively. Three-dimensional plots of the matrix agglomerations were obtained by tomographic methods using ≈25 individual slices of 1.5 mm thickness for each sample. Samples from different sites of a WHIPOX plate, and samples which have been differently pressed prior to sintering were examined mesostructurally. The study showed that delamination-induced failure of WHIPOX is essentially controlled by localized interlaminate matrix agglomerations. Compression of WHIPOX plates in the pre-sintering moist stage helps to achieve a better homogeneity and thus improved shear strength of WHIPOX components.

Combined Spectroscopic and Thermodynamic Investigation of Nextel‐720 Fiber/Alumina Ceramic‐Matrix Composite in Air and Water Vapor at 1100°C

Abstract: The high-temperature performance of a Nextel-720 fiber/ Al 2 O 3 composite in air and water vapor at 1100°C was investigated using X-ray photoelectron spectroscopy (XPS) and thermodynamic calculations. In the presence of water vapor, the formation of volatile Si(OH) 4 was responsible for the loss of mullite phase in the fiber of the ceramic-matrix composite (CMC). XPS analysis revealed the formation of surface aluminosilicates for the water-vapor-exposed CMC for 1000 h.