Showing papers on "Ceramic matrix composite published in 1998"

The design of the fibre-matrix interfacial zone in ceramic matrix composites

Abstract: Ceramic matrix composites are tough when the fibre-matrix bonding is properly controlled during processing, via the use of an interphase. The interphase is either formed in situ as the result of fibre-matrix interactions or deposited on the fibre surface prior to composite fabrication. It has several key functions, including crack deflection, load transfer, diffusion barrier and residual stress relaxation. Four types of interphase are depicted involving weak interfaces, materials with a layered crystal structure (pyrocarbon, BN, micas and phyllosiloxides, or materials with the β-alumina/magnetoplumbite structures), multilayers such as (PyC-SiC)n or (BN-SiC)n or, finally, porous materials. Achieving high mechanical properties and long lifetimes in severe environments require a subtle design of the fibre-matrix interfacial zone, which is depicted for Nicalon/glass–ceramic and Nicalon/SiC-matrix composites.

High temperature insulation for ceramic matrix composites

Abstract: A ceramic composition is provided to insulate ceramic matrix composites under high temperature, high heat flux environments. The composition comprises a plurality of hollow oxide-based spheres of various dimensions, a phosphate binder, and at least one oxide filler powder, whereby the phosphate binder partially fills gaps between the spheres and the filler powders. The spheres are situated in the phosphate binder and the filler powders such that each sphere is in contact with at least one other sphere. The spheres may be any combination of Mullite spheres, Alumina spheres, or stabilized Zirconia spheres. The filler powder may be any combination of Alumina, Mullite, Ceria, or Hafnia. Preferably, the phosphate binder is Aluminum Ortho-Phosphate. A method of manufacturing the ceramic insulating composition and its application to CMC substrates are also provided.

Dense in situ TiB2/TiN and TiB2/TiC ceramic matrix composites: reactive synthesis and properties

Abstract: In the present research, near-fully dense in situ composites were fabricated from cold sintered B4C–3Ti and 2BN–3Ti powder blends with and without the addition of Ni. Two reactive synthesis techniques were employed: combustion consolidation (pressure-assisted thermal explosion) and reactive hot pressing (displacement reaction under pressure) RHP. In both approaches, the processing or preheating temperature (≤1100°C) was considerably lower than those typical of current methods used for the processing/consolidation of ceramic matrix composites. Microstructure characterization of the materials obtained was performed using X-ray diffraction (XRD) and scanning electron microscopy (SEM) with energy dispersive analysis (EDS). Mechanical properties were evaluated by measuring microhardness, fracture toughness and three-point bending strength. Full conversion of reagents into products was achieved in B4C–3Ti, B4C–3Ti–1.5Ni and 2BN–3Ti–1.5Ni blends during combustion consolidation, and a moderate external pressure of 150 MPa was sufficient to ensure full density of the final products. Unlike this, no thermal explosion occurred in 2BN–3Ti samples at 1100°C under pressure. The entire procedure of thermal explosion under pressure could be performed in open air without noticeable oxidation damage to the final product. The RHP processing route yielded dense materials with finer microstructures, however full conversion of reagents into products has not been achieved. The addition of Ni to the powder blends was shown to enhance densification, as well as improve the fracture toughness of the composites synthesized.

Electric-field induced interfacial cracking in multilayer electrostrictive actuators

Abstract: Electric-field induced interfacial cracking in multilayer electrostrictive actuators is studied for two typical cases : (1) an interface crack lying between an electrode layer and ceramic matrix ; and (2) an interface crack with one tip at an embedded electrode-edge Based on the small-scale saturation solutions, a direct method is proposed to calculate the electric-field induced stress intensity factors that avoids calculating the stress field The effectiveness of the direct method is demonstrated by comparing the results derived with the known numerical solutions For either case, the explicit condition is given that prohibits interfacial crack growth by restricting the thickness of ceramic layers and the intensity of the applied electric field Especially, the maximum stress intensity factor derived for the above case (2) is found to be significantly larger than that obtained in the existing works for the electrode-tip matrix cracks This result agrees with the experimental fact that interfacial cracking is the dominant failure mechanism in electrostrictive multilayer devices Hence, the reliability design should be based on the conditions that prohibit interfacial cracking

Temperature-Dependent Absorptances of Ceramics for Nd:YAG and CO2 Laser Processing Applications

Abstract: The absorptance of material at the laser wavelength and as a junction of temperature, ranging from room temperature to the removal point, significantly affects the efficiency of the laser machining process. A priori predictions of a laser machining process, using either simplistic or sophisticated models, require knowledge of the material's absorptance behavior. An experimental apparatus for such measurements is described. The device consists of a specimen mounted inside an integrating sphere, heated rapidly by a CO 2 or a Nd:YAG laser. Reflectances are measured with a small focused probe laser (Nd:YAG or CO 2 ), while specimen surface temperatures are recorded by a high-speed pyrometer. Experimental results have been obtained for wavelengths of 1.06 μm (Nd:YAG) and 10.6 μm (CO 2 ) for graphite, alumina, hot-pressed silicon nitride, sintered α-silicon carbide, as well as two continous-fiber ceramic matrix composites (SiC-based). Data are presented for temperatures between room temperature and the ablation/decomposition points.

Pinning effect of SiC particles on mechanical properties of Al2O3–SiC ceramic matrix composites

Abstract: The fracture mechanical properties of SiC particle reinforced Al2O3 matrix composites were investigated at room temperature and T=1200°C. The results showed that the fracture strength and toughness of composites are enhanced, compared with those of monolithic Al2O3, especially at elevated temperature, and the strength and toughness of composites increase with the increase in the content of SiC particles. It was found that the improvement in fracture mechanical properties of composites is due to the fracture mode transformation from intergranular in monolithic Al2O3 to transgranular in the composites, and the fracture mode change might result mainly from the pinning effect of SiC particles on the Al2O3 boundaries. The study on flexure creep behavior of monolithic Al2O3 and the composites with 20 vol% SiC particles at T=1260°C indicated that the composites also exhibited some improvement in their creep resistance, compared to the creep behavior of monolithic Al2O3, due to the pinning effect of SiC particles at Al2O3 grain boundaries on grain boundary sliding during creeping.

On the micromechanical failure modes in a class of ideal brittle matrix composites. Part 1. Coated-fiber composites

Abstract: Models are presented for the penetration and debonding modes of failure of ceramic matrix composites. Test data on silicon carbide-glass composites with uniform fiber spacing are used to examine the quality of these models for use in the constituent material design problem. Testing of uncoated-fiber composites has provided more conclusive evidence regarding the applicability of the model.

Design of High Preformance CMC Brake Discs

Abstract: Ceramic matrix composite (CMC) materials based on 2D-carbon fibre preforms show high heat-absorption capacities and good tribological as well as thermomechanical properties. To take advantage of the full lightweight potential of these new materials in high performance automotive brake discs, the thermal conductivity transverse to the friction surface has to be high in order to reduce the surface temperature. Experimental tests showed, that lower surface temperatures prevent overheating of the brake`s periphery and stabilizes the friction behaviour. In this study different design approaches with improved transverse heat conductivity have been investigated by finite element analysis. C/C-SiC bolts as well as SiC coatings and combinations of them have been investigated and compared with an orthotropic brake disc, showing a reduction of temperature of up to 50%. Original sized brake discs with C/C-SiC have been manufactured and tested under real conditions which verified the calculations. Using only low-cost CMC materials and avoiding any additional processing steps, the potential of C/C-SiC brake discs are very attractive under tribological as well as under economical aspects. (orig.) 4 refs.

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

Abstract: 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.

Oxidation resistance of SiC/SiC micro and minicomposites with a highly crystallised BN interphase

Abstract: A three dimensionally ordered hex-BN is deposited by LPCVD from the BF3–NH3 system at relatively low temperature. This coating was studied in term of crystallisation by X-ray diffraction, and transmission electron microscopy. SiC/SiC microcomposites with such a BN interphase were produced in a first step. Their mechanical behaviour was determined under tensile loading at room temperature. They exhibited a wide non-linear stress–strain domain similar to that commonly observed during the damage of a ceramic matrix composite. Further, static fatigue tests at 700°C in air were carried out on a few microcomposites. The long lifetimes provide evidence that such a BN-based interphase brings a real improvement in the oxidation resistance. In a second step, from these latter results, minicomposites were prepared with a complex interphase consisting of a few layers of BN, which included a highly crystallised layer. Similar mechanical tests at room temperature and static fatigue tests at high temperature in air were performed. Despite the change of geometry (single fibre to a tow), damage capability and improved oxidation resistance are observed in comparison with minicomposites with a carbon interphase.

High temperature oxidation of ceramic matrix composites

Abstract: Ceramic matrix composites are developmental high temperature materials. We focus on composites with Sic matrices, Sic fibers, and BN fiber coatings. High temperature oxidatiodcorrosion reactions are discussed for each of these constituents. Sic forms a highly protective SiO, scale in pure oxygen, but problems arise in complex gas mixtures. These include: SiO(g) formation, Si-0-H(g) formation, impurity enhanced SiO, formation, and fluxing of SiO, in molten salts and slags. Refractory oxide coat- ings may minimize these effects. The major issue with these composites is oxidation of the BN fiber coating. The key reactions here are borosilicate glass formation, poten- tial gettering of oxygen by Sic, and volatilization. We conclude with an oxidation study of an actual composite, which illustrates some of these effects.

Microstructure and Stability of Polymer‐Derived Ceramics; the Si–C–N System

Abstract: Monolithic polymer-derived Si-C-N ceramics were processed by blending 70 vol% of both crosslinked and pyrolyzed Si-C-N powder particles with an oligomeric Si-C-N precursor (liquid polysilazane). The respective Si-C-N powder particles were prepared from the same liquid precursor, however, pre-heated at 300 and 1000 °C. Powder compacts were annealed at 300 °C, in order to crosslink the liquid precursor that acts as a binder phase between the powder particles. After crosslinking, an additional heat treatment was performed at 1540 °C to transform both the binder phase and the particles into a homogeneous ceramic matrix. Microstructure development and, in particular, crystallization behavior of the monoliths were characterized by transmission electron microscopy (TEM). In general, the two starting materials, which only differ with respect to the pre-heat treatment of the powder particles, evolved markedly different microstructures. The material prepared with 300 °C polymer powder and oligomeric binder revealed a homogeneous amorphous microstructure with only a small fraction of crystallized spherical inclusions after exposure to 1540 °C. In contrast, blending the powder particles annealed at 1000 °C with the same binder yielded a high degree of SiC crystallization within regions that were formerly filled by the polymeric binder. The Si-C-N powder particles, however, remained amorphous. As will be shown, the observed microstructure variations are closely related to the residual porosity of the system. Moreover, phase separation in the amorphous matrix can also affect the overall stability of such polymer-derived ceramics, when exposed to high temperatures. A distinction between open and closed systems allows to explain the observed microstructure variations and, more importantly, a correlation with the high-temperature stability of the materials.

Tribological properties of self-lubricating CMC/Al2O3 pairs at high temperature in air

Abstract: Three different self-lubricating ceramic matrix composites (CMCs) were fabricated by hot-pressed sintering. They are: Al2O3-50CaF2, Al2O3-20Ag20CaF2, and Al2O3-10Ag20CaF2. Tribological tests were performed at temperatures ranging from 20°C to 800°C in air using a pin-on-disk tester. The experimental results show that the addition of the solid lubricants CaF2 and Ag can evidently reduce the friction coefficients of alumina between 200°C and 650°C but not at room temperature and the wear rate of disks and pins at elevated temperature. The improvements in the friction and wear properties of CMC were due to the formation of a well-covered solid lubricating film. However, breakdown of the lubricating films at 800°C resulted in high friction and wear.

Advanced multilayered and fibre-reinforced composites

Abstract: Preface Part 1: Micromechanics and Local Deformation Effects Use of Composites in Infrastructure D Hui, PK Dutta Principles and Approaches of Advanced Experimental Mechanics in Service of Modern Technology JT Pindera Actual Three-Dimensional Stresses in Composite Structures and in Local Effects in Homogeneous Structures Case Studies JT Pindera Strain Path Effect on Debonding and Non-Linear Constitutive Model for Rigid Particles Reinforced Metal/Ceramic Matrix Composite V Skorohod, et al On the Stochastic Micromechanical Approach to the Response Behaviour of Engineering Materials YM Haddad Higher-order Micro-Macrostructural Theory for the Analysis of Functionally Graded Materials M-J Pindera, et al Indirect Determination of Mechanical Properties of Reinforcement in Fibrous Polymeric Composites AP Wilczynski The Modification of Hydrodynamic Model of Alekseevskii-Tate for Multilayered and Gradient Plates VV Kartuzov, et al The Application of Self-Consistent Approaches to Modelling Mechanical Behaviour of Heterogeneous Two Phase Solids DS Wilkinson, E Maire On the Behaviour of Materials with Binary Microstructures DR Axelrad, YM Haddad Part 2: Ceramic Matrix Composites Titanium-Matrix Composites in Comparison with Ceramic Ones SA Firstov Fracture Characteristics of Layered and Nano-Particle Reinforced Si3N4 J Dusza, P Sajgalik Rising Fracture Resistance of Whisker-Reinforced Alumina and Silicon Nitride P Hvizdos, J Dusza Formation of Carbon Coatings on Carbide Fibers and Particles by Disproportionation Reactions YG Gogotsi Problems of the Determination of the Mechanical Properties of Endless-Fibre Reinforced Ceramic Composites W Lins, et al CeramicMatrix Composites Microstructure and Thermostructural Performance Limits MH Lewis, et al Elastic Modulus in Rigid Al2O3/ZrO2 Ceramic Laminates JS Moya, et al Processing of Multilayered Si3N4-TiN Hot-Pressed Ceramic Composites V Yaroshenko, et al Effect of Residual Stresses on the Mechanical Response of Continuous Fibre Reinforced Ceramic Matrix Composites M Steen Electrically Conductive Ceramic Composites G Van de Goor, et al Chemical Modification of Carbon Materials LV Golovko, et al Novel Oxide Fibres to Reinforce Metal, Intermetallic and Ceramic Matrices ST Mileiko A New Class of 'in-situ' Fiber Reinforced Boride Composite Ceramic Materials YuB Paderno Toughening by Pores AD Vasilev, SA Firstov Threadlike Single Crystals of Transition Metals Borides YuB Paderno Modelling of Thermal Residual Stresses in Ceramic Coatings with a Graded Composite Interlayer V Teixeira, et al Fiber Reinforced Oxide Ceramic Matrix Composites R Janssen Residual Stresses in PVD/Plasma Sprayed Thermal Barrier Multilayered Coatings at High Temperature V Teixeira, et al Review on Advanced Research on Ceramic Materials in Ukraine AD Vasilev, YM Haddad Part 3: Metal Matrix and Polymeric Matrix Composites Metal/Metal Laminates with Controlled Macrostructure: Problems and Prospects O Ercan, et al The Electrodynamic Properties of Fiber Composites VYu Reshetnyak, et al Multiaxial Three-Dimensional (3-D) Circular Weaving and Multiaxial 3-D Circular Woven Preforms for Composite AK Bilisik Analysis of Filament Wound Tubes Against Torsion L Parnas, N Akkas On Non-Linear Response of Polyester Tan

Probabilistic-statistical approach to matrix damage and stress–Strain behavior of 2-D woven SiC/SiC ceramic matrix composites

Abstract: The matrix damage evolution in a 2-D SiC/SiC composite reinforced with fabrics of fiber bundles was predicted from properties of basic constituents using a finite element analysis of failure probabilities. Failure probabilities were computed using a finite element post processor including the multiaxial elemental strength model for handling fracture statistics under multiaxial stress-states. The associated stress–strain behavior of the selected elementary cell was derived from the stress analysis. The predicted matrix damage evolution was found in good agreement with that identified by microscopy on practical 2-D SiC/SiC woven composites under tension. The predicted stress–strain behavior and Young’s moduli compared satisfactorily with the experimental data. The approach was then applied to a cell of fully dense 2-D woven SiC/SiC composite under tension, and then to a cell of conventional 2-D woven SiC/SiC composite subject to a gradient of forces.

Tensile mastercurve of ceramic matrix composites : significance and implications for modelling

Abstract: The concept of a tensile mastercurve which uniquely represents the mechanical response to time-independent tensile loading is presented. It is shown how the mastercurve can be determined from individual tensile tests with unloading–reloading cycles, and how it provides a rationalisation of both the temperature dependence and the scatter in tensile behaviour. Implications for modelling of the mechanical behaviour are outlined.

Silicon carbide fibers with boron nitride coatings

Abstract: A process for forming a uniform, boron nitride coating on a boron-doped, refractory carbide body, and in particular on a sintered, boron-doped, silicon carbide fiber, where the body is exposed to a nitrogen-containing atmosphere at a temperature equal to or greater than the densification or sintering temperature. The coated fibers exhibit no loss in strength properties and show improved creep resistance.

Design, Fabrication and Characterization of High Temperature Joints in Ceramic Composites

Abstract: Ceramic joining has been recognized as one of the enabling technologies for the successful utilization of ceramic components in a number of demanding, high temperature applications. Various joint design philosophies and design issues have been discussed along with an affordable, robust ceramic joining technology (ARCJoinT). A wide variety of silicon carbide-based composite materials, in different shapes and sizes, have been joined using this technology. This technique is capable of producing joints with tailorable thickness and composition. The room and high temperature mechanical properties and fractography of ceramic joints have been reported. These joints maintain their mechanical strength up to 1200 C in air. This technology is suitable for the joining of large and complex shaped ceramic composite components and with certain modifications, can be applied to repair of ceramic components damaged in service.

Combustion chemical vapor deposition (CCVD) of LaPO4 monazite and beta-alumina on alumina fibers for ceramic matrix composites

Abstract: This research used the low cost, open atmosphere combustion chemical vapor deposition (CCVDSM) method to efficiently deposit protective coatings onto alumina fibers (3M Nextel™ 610) for use in ceramic matrix composites (CMCs). La-monazite (LaPO4) and beta-alumina were the primary candidate debonding coating materials investigated. The coated fibers provide thermochemical stability, as well as desired debonding/sliding interface characteristics to the CMC. Dense and uniform La-phosphate coatings were obtained at deposition temperatures as low as 900–1000°C with minimal degradation of fibers. However, all of the β-alumina phases required high deposition temperatures and, thus, could not be applied onto the Nextel™ 610 alumina fibers. The fibers appeared to have complete and relatively uniform coatings around individual filaments when 420 and 1260 filament tows were coated via the CCVD process. Fibers up to 3 feet long were fed through the deposition flame in the laboratory of MicroCoating Technologies (MCT). TEM analyses performed at Wright-Patterson AFB on the CCVD coated fibers showed a 10–30 nm thick La-rich layer at the fiber/coating interface, and a layer of columnar monazite 0.1–1 μm thick covered with sooty carbon of

Micro-Raman study of SiC fibre-oxide matrix reaction

Abstract: Micro-Raman analysis is a non-destructive technique used to provide information on the compressive/tensile strain applied to a fibre embedded in a ceramic matrix composite. Carefull analysis of this information helps to understand the physical-chemical evolution of the fibre. Example of continuous SiC Nicalon® fibres reinforcing various ceramic matrices (mullite, NASICON) shows how the comparison between fibre core and fibre periphery spectra-using wavenumber, bandwidth and intensity—provides independant tools to check the fibre evolution and to distinguish thermally and chemically induced transformations.

Process for the preparation of thick-walled ceramic products

Abstract: A process for the preparation of ceramic articles having a thickness of at least about 2.5 cm, which comprises: a) selecting the ceramic composition from the group consisting of silicate material, metal oxides, nitrides and carbides, and mixtures thereof, optionally adding ceramic fibers, such as boron nitride or silicon carbide fibers, to the ceramic composition, b) autoclaving the ceramic composition to increase its hydrogen form contents, which increases the compositions's microwave absorptivity, c) forming the ceramic composition into the desired shape, and d) subjecting the composition so shaped to microwave energy to internally heat and thereby dry and sinter the composition, optionally with external heat applied by means of electrical resistance or gas fired heating. Novel apparatuses for the extrusion and vibrocompaction of ceramic compositions, the drying of ceramic masses, kilns for microwave-assisted firing of the ceramic articles, cars, and a hydraulic air handling system for tunnel kilns.

Sol–gel synthesis of ceramic matrix composites

Abstract: Sol–gel techniques have been used to produce various high temperature ceramic matrix composites including Ni/α-Al2O3, Fe/α-Al2O3, Ni/ZrO2, SiC(whisker)/α-Al2O3, and SiC(platelet)/α-Al2O3, as well as chemically modified versions of some of these systems. In all cases, the composites have displayed uniform microstructures with a high degree of dispersion between the matrix and reinforcement phases, a goal often not achieved when utilizing conventional powder mixing and processing techniques. The metal–ceramic composites investigated exhibit enhanced toughness and machinability as well as the potential for catalytic applications due to their novel fine-scale microstructure. Likewise, the SiC-reinforced alumina materials have been shown to be lighter, stiffer and tougher than pure alumina, without the use of the extreme hot-pressing temperatures and pressures needed by conventional powder processing approaches to produce the same results.

Ceramic matrix composites

Abstract: This invention pertains to ceramic matrix composites that comprise the coated ceramic fibers wherein the coating comprises at least one binary coating of boron nitride (BN) and silicon nitride (Si 3 N 4 ) within ceramic matrices derived from curable preceramic polymers. The composites can be formed into complex shapes which have good oxidation resistance at high temperature, good resistance to moisture high flexural strength and are resistant to moisture.

Damage modelling for a laminated ceramic composite

Abstract: A general theory of damage mechanics is applied to a fibre-reinforced ceramic matrix composite, SiC/MAS-L, in order to describe its non-linear mechanical behaviour up to failure. This study is limited to the case of quasi-monotonic loading at room temperature. The model, which uses an anisotropic damage theory previously applied to other composites, is a mesoscopic-scale model which has been developed using tension–compression tests on different stacking sequences and applies in the case of multiaxial loading. It includes the marked differences observed between mechanical behaviour in tension and in compression, and is also able to predict the failure values.