Suspension processing was used to prepare Al2O3 /SiC whisker and Al2O3/ZrO2 /SiC whisker compacts with high green density, fine pore sizes, and homogeneous microstructure. Procedures for optimizing particle/whisker co-dispersion and subsequent consolidation by slip casting are reviewed. Compacts prepared by slip casting showed significantly higher sintered densities compared to dry-pressed samples.

A model for the deposition of alumina and titanium carbide within a ceramic fiber bundle from the chemical reactions has been examined in this paper. The model considers vapor diffusion, chemical reaction on the inner surface of the capillary, deposition film growth, porosity, and effects of reactants composition at various reactor temperature and pressure. Binary, multicomponent diffusion and Knudsen diffusion have been taken into account for the different stages of the CVI process. Furthermore, both diffusion controlled and reaction controlled processes have been examined in order to determine the dominating process in chemical vapor infiltration.

Ceramic fibers and grids of controlled geometry and composition were fabricated by electron beam evaporation of Al2O3 onto substrates patterned by optical lithography. The fibers were 4 and 5μm wide by 1μm thick. In addition, mixed metal oxide films from 0 to 10at% Ti, Zr, or Cr were produced by coevaporation with Al2O3. The compositions of the films were determined by Rutherford Backscattering Spectroscopy. TEM and electron diffraction examination showed all the films to be amorphous in structure.

The Al2O3 fibers had tensile strengths between 143 and 168 ksi and the Al2O3 film had a microindentation hardness of 8.4 GPa. Films with ≈ 1at% additions of Zr, Ti, and Cr had hardnesses of 11.0, 9.7, and 8.8 GPa respectively. The hardness then decreased with higher Zr, Ti, and Cr concentrations

Titanium containing fibers have been synthesized via the modification of organic materials. Thermal processing of these chemically modified organic fibers in reactive/inert atmospheres, has produced materials containing Ti (C,O). Materials analysis was performed using SEM-EDS, ESCA and Auger spectroscopy. Novel monomeric titanium materials were synthesized for the above mentioned modification of organic materials. Boron containing monomers and polymers were also synthesized as possible precursors for B-N-C materials.

Ferroelectricity in well-poled polyvinylidene fluoride (PVDF) is a phenomenon which is now well supported. However, the piezo- and pyroelectric responses in this polymer are significantly weaker than those of ceramic oxides. It would be attractive to design composite materials which will have the mechanical properties of polymers with the electro-active properties of ceramics. Such materials will be useful for diverse sensor applications, viz, acoustic emission detection, hydrophones, biomedical applications, thin film capacitors etc. One of the chief requirements of a capacitor is that a large capacitance to volume ratio is desirable. A high ratio requires a thin film, a high dielectric constant and an acceptable electrical breakdown strength. Such a material may be designed by a judicious incorporation of fine grain ceramics in a suitable polymer matrix.

This article evaluates the current understanding of relationships between microstructure and mechanical properties in ceramics reinforced with aligned fibers. Emphasis is placed on definition of the micromechanical properties of the interface that govern the composite toughness. Issues such as the debond and sliding resistance of the interface are discussed based on micromechanics calculations and experiments conducted on both model composites and actual composites.

The frictional resistance to sliding of a SiC fiber in a brittle, ceramic matrix has been measured with two different experimental techniques. Both techniques utilize a load-controlled indentation instrument. In the first technique, the ends of individual fibers are displaced down into the matrix. The frictional resistance to sliding, τ, was calculated using the elastic model of Marshall and Oliver and the load-displacement data. Alternatively, fibers have been displaced along their complete lengths through thin sections of the matrix. The critical force for complete slip and the sample geometry determined τ for a given fiber. For this technique slip over the complete length of a fiber was verified by the protrusion of that fiber from the bottom of the sample. By inverting the sample and loading the protruding fiber, the frictional resistance to reverse sliding was also measured. The results obtained from the two complementary techniques are in general agreement.

Single fiber pull-out tests can be used to directly measure the fiber-matrix interfacial shear stress in glass matrix composites. The system under investigation consisted of a soda-lime-silica glass matrix containing SiC monofilaments with a carbon-rich surface. The presence of the carbon-rich layer on the surface of these fibers makes them non-wetting to most glasses; hence the fibers are held in the matrix only by frictional forces acting at the interface. The mechanical gripping responsible for this force can be changed by manipulating the glass matrix/fiber thermal expansion coefficient mismatch. Frictional stresses (τ) and friction coefficients (μ) obtained for SiC monofilaments in a soda-lime-silica glass matrix were compared with previously obtained data on a borosilicate glass matrix (τ = 2–3 MPa, μ = 0.72 ± 0.36). For the soda-lime-silica system, τ's of 4–20 MPa and μ of 0.10 ± 0.03 were obtained. τ in the soda-lime-silica system is higher due to the larger difference in thermal expansion mismatch between the fiber and matrix. The differences in μ may be due to lubrication effects caused by water at the fiber-matrix interface.

Mullite and zircon ceramic matrix composites uniaxially reinforced with as-supplied and BN-coated silicon carbide filaments were fabricated. The filament-matrix interfacial shear stresses were measured by a modified indentation technique and mechanical properties were determined in flexure mode. Significant improvements in strength and toughness were observed for the composites in comparison to monolithic mullite and zircon ceramics. Lower filament-matrix interfacial shear stresses were measured in composites with BN-coated filaments than in composites containing as-supplied filaments. The influence of filament-matrix interfacial shear stress on the critical stress for first matrix cracking, maximum composite strength, and toughness of the composites were studied.

Creep tests were conducted at temperatures from 1673 to 1823 K on samples of Al2O3 containing 9.3, 18 and 30 vol % SiC whiskers. The results show that the strains to failure tend to decrease and the stress exponents for the steady-state creep rates tend to increase with increasing volume percentages of SiC whiskers.

The addition of SiC whiskers to Al2O3 causes significant improvement in mechanical properties, including fracture toughness, thermal shock resistance, and creep resistance. The creep response of a whisker-reinforced alumina composite has been measured using four-point flexural loading at temperatures of 1200 and 1300C. Composites were fabricated by hot-pressing a blend of alumina powder with 33 volume percent SiC whiskers. The creep data showed a stress-dependent stress exponent equal to 1 at low stress levels and ranging from 4–6 at higher stresses. The applied stress at which the transition occurred was temperature dependent and ranged from 50–125 MPa. Mechanisms of creep deformation were determined from TEM observations of specimens prepared from interrupted creep tests. Voids were observed at grain boundary-interface junctions in tensile regions and whiskers within the composite were sometimes oxidized where voids had formed. TEM observations from specific stages of steady state creep reached under different applied loads are presented, and the relative contributions of different deformation mechanisms are discussed.

The fracture mechanisms involved in the toughening of alumina by whisker reinforcement are studied at room temperature. The fracture toughness of a hot pressed SiC-whisker/alumina composite is measured and good agreement is found between the experimental data and a model that takes into account the effects of crack deflection and whisker pullout mechanisms. From the model, it is seen that the role of whisker pullout is negligible compared to that of crack deflection.

Ceramic matrix composites with continuous fibers in glass matrices were tested with instrumented impact apparatuses. The composite architectures were unidirectional (0°) and crossply (0/90°). For the 0/90° laminates, interlaminar and edge on orientation specimens were tested. An orientation dependence was observed. The CMC material with a weaker fiber/matrix interfacial bond had longer fiber pullout, and hence due to the frictional sliding mechanism higher dynamic work to fracture. In the fracture analysis discussion it is suggested that the use of the LEFM, K, parameter should be qualified in the fracture testing of CMC materials. These qualified toughness K values were found to be in the range of those reported for metal matrix composites.

In this paper, the present state of knowledge is reviewed concerning the structure and chemistry of metal/ceramic interfaces. Experimental observations are described for several model systems and open problems concerning different aspects of structure and properties of heterophase boundaries are discussed.

The interfacial chemistry and phases of SiC-reinforced Si3N4 composites have been evaluated by transmission electron microscopy (TEM) with associated x-ray energy dispersive spectroscopy (EDS) microanalysis, and Auger electron spectroscopy (AES). Hot-pressed Si3N4 (HPSN) composites reinforced with Nicalon™ SiC fibers or Tateho SiC wiskers and reaction-bonded Si3N4 (RBSN) composites reinforced with uncoated or coated VLS SiC whiskers have been evaluated. In the Nicalon™ fiber-reinforced HPSN, an interfacial phase composed of a layer of amorphous carbon and an adjacent layer of graphitic carbon was observed and is believed to assist fiber pullout during fracture of the composite. However, the fracture strength and toughness of these composites were considerably less than those of unreinforced HPSN. HPSN composites reinforced with Tateho SiC whiskers contained an interfacial phase believed to be similar to the intergranular phase found in the HPSN matrix. In RBSN composites fabricated with an Fe2O3 sintering aid, the VLS SiC whiskers were severely faceted by a reactive iron silicide phase despite C, BN, or SiO2 coatings on the whiskers. When no sintering aid was used, the uncoated whiskers were not degraded and appeared to be strongly bonded to the RBSN matrix. The composites reinforced with SiO2-coated whiskers possessed the highest fracture strength and toughness, and the composites reinforced with the BN-coated whiskers possessed the lowest fracture strength and toughness.

It has been shown that SiC whisker-reinforced Al2O3 is susceptible to thermal oxidation because of a series of reactions in which SiC is oxidized and then reacts with Al2O3 to form a whisker-free layer of mullite and silica glass. In this paper, the kinetics of the reaction are analyzed as a function of the composition and whisker content of the composite. The mechanism of the reaction is described in terms of the evolution of phases within the reaction layer on the basis of transmission electron microscope observations and concentration profiles determined by electron microprobe analyses. The reaction is initiated by oxidation of SiC, forming silica glass and graphitic carbon. The silica glass penetrates the Al2O3 matrix along grain boundaries, and reacts to form mullite. As the reaction proceeds, Al2O3 is consumed, leaving residual intragranular Al2O3 islands, and a population of transgranular microcracks in the mullite. It has also been shown that Al2O3-SiC composites are susceptible to crack nucleation and growth under cyclic compressive loads. The presence of the mullite reaction layer on the surface of the composite reduces its resistance to crack initiation under these conditions. The threshold for crack initiation in cyclic compression is measured as a function of reaction layer thickness.

The toughness of ceramic-matrix composites is strongly influenced by fiber pull-out. The extent of the pull-out depends upon the properties of the fiber and the fiber/matrix interface. Samples of a SiC/LAS composite were subjected to different heat treatments in order to systematically vary these properties. The predicted distribution of the fiber pull-out lengths was calculated by combining a shear lag analysis with Weibull statistics for the fiber strengths. Comparison of the analysis with experiments and microstructural observations contribute to an understanding of the role of the fiber/matrix interface upon the mechanical properties.

The nature of ultrasonic propagation at cylindrical interfaces is being explored as a potential method for inferring the modulus of the interface in metal matrix composites. In many metal matrix composite systems leaky interface waves have been found to propagate along the interface. The velocity of these waves depends sensitively upon the local moduli and provides a potential basis for measuring these quantities. The opportunity exists to exploit the leaky character of these waves for microscopic imaging at the interface.

The microstructure of the interfacial zone in a SCS6 filaments/Ti-6A1–4V matrix composite was determined using TEM and HREM. The interfacial zone (e ∼5 μm) consists of microstructurally distinct layers. The fiber/matrix interaction resulted in two layers respectively crystallized in grains of about 20 nm and 100 nm. The reaction zones are mainly made of brittle TiC. They are separated from the SiC reinforcement by five layers which form the coating of the SCS6 filament. These five layers may be described as SiC-C composites with either an equiaxe fine grain structure or a distorted lamellar structure. The structure of these layers can explain the toughning of the alloy by the SCS6 filaments despite of the brittle F/M reaction products formed during the processing.

The Al-SiC system has been used as a model system in an examination of phase stability in the presence of a liquid phase and microstructure development in metal-matrix composites. The Al-Si-C phase diagram has been calculated for temperatures between 500°C and 1500°C. The phases formed between Al(liquid) and SiC at 920°C have been determined experimentally, using analytical electron microscopy, in both fiber and particulate composites and compared with what is predicted from the equilibrium phase diagram. The morphologies and the spatial distributions of phases have also been examined in addition to the phase analysis. The only phases found were Al, Al4C3, SiC, and Si. Although Al4SiC4 is calculated to be stable at 920°C, it was not found. The SiC grain structure was found to influence strongly the morphology of the Al4C3-SiC and Al-SiC interfaces.