Showing papers on "Ceramic matrix composite published in 1992"

Gas separation system

Abstract: A solid state electrolytic cell for separating oxygen or nitrogen from the air which employs a flexible, ductile ceramic composite as the solid electrolyte is provided. The ductile ceramic composite solid electrolyte comprises a continuous, ordered, repeating, interconnected ductile metallic array substantially surrounded by and intimately integrated within a ceramic matrix. The cell is connected to a power supply so when current is passed through the cell, oxygen or nitrogen is separated from the air passing through the cell.

Damage and Failure in Unidirectional Ceramic–Matrix Composites

Abstract: A study of the mechanical characteristics of a unidirectional fiber–reinforced calcium aluminosilicate matrix composite has been conducted. The properties have been related to the individual properties of the matrix, the fibers, and the interfaces, as well as the residual stress, using available models of matrix cracking and fiber fracture. Comparisons have been made with lithium aluminosilicate matrix composites. Predictions of initial matrix cracking and of ultimate strength using the models are found to correlate well with the measured values. However, deficiencies have been noted in the ability of the models to predict the evolution of matrix cracks, plus associated changes in the modulus.

Behaviour of unidirectional and crossply ceramic matrix composites under quasi-static tensile loading

Abstract: Experimental results are presented for the quasi-static tensile behaviour of unidirectional, (0/90)s, (02/904)s and (0/90)3s silicon carbide fibre (Nicalon) reinforced calcium aluminosilicate glass-ceramic matrix laminates. The stress-strain behaviour and associated damage development is described in detail for each laminate. The damage development is quantified by counts of crack density (in both the longitudinal and transverse plies) and stiffness reduction as functions of applied strain. The damage initiation and growth (and its effect on residual properties) are discussed with reference to the Aveston-Cooper-Kelly (ACK) theory for unidirectional ply cracking and crossply laminate shear-lag (originally developed for polymer matrix composites) to describe the transverse ply cracking behaviour.

Damage Mechanisms and the Mechanical Properties of a Laminated 0/90 Ceramic/Matrix Composite

Abstract: The tensile properties of a 0/90 laminated CAS matrix composite reinforced with Nicalon fibers have been measured. Some effects of notches have also been explored. Changes in modulus and permanent strain caused by matrix cracking have been measured and compared with available models. For this comparison, independent measurements have been made of the constituent properties and the residual stress. The ultimate tensile strength has also been measured and compared with a global load-sharing model. It is concluded that lower-bound matrix cracking models provide good predictability of the stresses at which various matrix cracking mechanisms first operate. Also, the ultimate tensile strength is found to be consistent with a global load-sharing model, based on the in situ strength properties of the fibers. Conversely, the evolution of matrix cracks at stresses above the lower bound has yet to be adequately modeled. In addition, a need is identified for improved models relating elastic properties and permanent strains to matrix crack spacing.

Thermal spray powders for abradable coatings, abradable coatings containing solid lubricants and methods of fabricating abradable coatings

Abstract: Thermal spray powders are characterized by the presence of a matrix-forming component, a solid lubricant component and a plastic component. Abradable coatings formed by thermal spraying the powders abrade readily to form abradable seals. The abradable coatings have a metal, metal alloy, or ceramic matrix with discrete inclusions of solid lubricant and plastic. The thermal spray powders may be prepared as mechanically fused agglomerates.

Corrosion of High-Performance Ceramics

Abstract: 1 Introduction- 2 Oxidation in Oxygen and Air- 21 Silicon Nitride Ceramics- 211 Thermodynamics of Si3N4 Oxidation- 212 Composition of Oxide Layer- 213 Effect of Phase and Chemical Composition of Ceramics- 214 Oxidation of Porous Ceramics- 215 Oxidation of Dense Ceramics- 216 Peculiarities of Oxidation Kinetics- 22 Silicon Carbide Ceramics- 221 Thermodynamics of SiC Oxidation- 222 Composition of Oxide Layer- 223 Hot-Pressed and Sintered SiC- 224 Self-Bonded and Recrystallized SiC- 23 Aluminium Nitride Ceramics- 24 Boron Carbide Ceramics- 25 Boron Nitride Ceramics- 26 Ceramic Matrix Composites- 261 Nonoxide Matrix Composites- 262 Oxide Matrix Composites- 3 Gaseous Corrosion of Ceramics- 31 Hot Corrosion- 311 Silicon Nitride Ceramics- 312 Silicon Carbide Ceramics- 313 Oxide Ceramics- 32 Water Vapour Corrosion- 321 Nonoxide Ceramics- 322 Zirconia Ceramics- 33 Corrosion in Carbon Oxide Environments- 34 Corrosion in Halogen- and Chalcogen-Containing Environments- 4 Corrosion in Liquid Media- 41 Corrosion in Solutions- 411 Silicon Nitride Ceramics- 412 Silicon Carbide Ceramics- 413 Aluminium Nitride Ceramics- 414 Boron Carbide Ceramics- 415 Boron Nitride Ceramics- 416 Oxide Ceramics- 42 Molten Salt and Alkali Corrosion- 5 Corrosion Effect on Ceramic Properties- 51 Preoxidation of Ceramics- 511 Silicon Nitride Ceramics- 512 Silicon Carbide Ceramics- 513 Aluminium Nitride Ceramics- 514 Zirconia Ceramics- 52 Effect of Corrosion in Different Environments- 521 Hot Corrosion- 522 Molten Salt Corrosion- 523 Corrosion in Solutions- 6 Mechanical Properties and Corrosion- 61 Effect of Oxidation on Results of High-Temperature Mechanical Tests- 611 Silicon Nitride Ceramics- 612 Silicon Carbide Ceramics- 613 Boron Carbide Ceramics- 62 Effect of Salts on High-Temperature Strength- 63 Failure of Ceramics Affected by Long-Term Mechanical Loading in Corrosive Environment- 631 Silicon Nitride Ceramics- 632 Silicon Carbide Ceramics- 633 Alumina Ceramics- 634 Zirconia Ceramics- 635 Salt-Assisted Strength Degradation- 636 Triboxidation- 64 Lifetime Prediction in View of Environmental Effects- 7 Corrosion Protection and Development of Corrosion-Resistant Ceramics- 71 Chemical-Vapour Deposited Coatings- 72 Sprayed and Sputtered Coatings- 73 Impregnation and Other Methods of Protection- 74 Choice of Optimum Ceramic Composition- References

Advanced aerospace materials

Abstract: 1. Situation and Perspectives.- 2. Metallic Materials and Metal Matrix Composites.- 2.1 Metallic Materials.- 2.1.1 Aluminium Alloys.- 2.1.1.1 High-Strength Aluminium Alloys.- 2.1.1.2 Aluminium-Lithium Alloys.- 2.1.1.3 Powder Metallurgy of Aluminium Alloys.- 2.1.2 Titanium Alloys and Aluminides.- 2.1.2.1 Titanium Alloys.- 2.1.2.2 Titanium Aluminides.- 2.1.3 Superalloys and Coatings.- 2.1.3.1 Superalloys.- 2.1.3.2 High Temperature Corrosion.- 2.1.3.3 Coatings.- 2.2 Metal-Matrix Composites.- 2.2.1 Metal-Matrix Composites with Aluminium Matrix.- 2.2.2 Fibre Reinforced Aluminium Laminates.- 2.2.3 Titanium Matrix Composites.- 2.2.4 Interfaces in Metal Matrix Composites.- 3. Ceramic Materials and Ceramic Matrix Composites.- 3.1 Non-Oxide Materials (Silicon Nitride).- 3.1.1 Fabrication and Microstructural Development of Non-Oxide Ceramics (Silicon Nitride).- 3.1.2 Silicon Nitride Matrix Composites.- 3.1.3 Fracture and Fatigue of Non-Oxide Ceramics.- 3.2 Oxide Materials (Mullite).- 3.3 Imaging Microstructures of Monolithic Carbons and Carbon/Carbon Composites in the TEM.- 4. Polymer Matrix Composites.- 4.1 Quasi-Static Strength of Polymer Matrix Composites.- 4.2 Fatigue Strength of Polymer Matrix Composites.- 5. Materials Characterization and Life Prediction.- 5.1 Microstructural and Microanalytic Methods.- 5.2 Fatigue and Fracture of Metallic Materials.- 5.2.1 Random Load Fatigue and Life Prediction.- 5.2.2 Physical Reasons for the Existence of ?Keff.- 5.2.3 Crack Growth Life Prediction.- 5.3 Special Testing Techniques.- 5.3.1 Stress Corrosion Testing.- 5.3.2 Biaxial Testing.- 5.3.3 Chevron Notched Specimen Testing.- Abbreviations.- Laudatio.

Determination of macro‐ and micromechanical and interfacial elastic properties of composites from ultrasonic data

Abstract: A self‐reference ultrasonic bulk wave method for nondestructive measurement of elastic properties of ceramic matrix composites has been developed. The method has the advantage of minimizing the effect of geometrical imperfection of the sample. The experiment has been done on silicon carbide (SiC) fiber‐reinforced reaction‐bonded silicon nitride (Si3N4) matrix composites. The composite elastic constants are extracted from the experimental phase velocities using a nonlinear optimization procedure to find the best fit between experimental data and the solutions of the Christoffel equation. The effect of individual constituents on the overall composite properties has been investigated. The effects of porosity on the matrix properties and water saturation of pores on the immersion ultrasonic measurements are taken into account using a micromechanical model for two‐phase particulate composites. This model is validated by experimental data. A microstructural model for analysis of elastic properties of ceramic ma...

The hertzian stress field and formation of cone cracks. II : Determination of fracture toughness

Abstract: A method for determining the fracture toughness by Hertzian indentation has been developed. Three materials, a ceramic matrix composite, a fine grained Al2O3 and glass, were indented by a spherical WC/Co indenter at various loads. The samples were then sectioned and polished and the length of the Hertzian cone cracks were measured. The fracture toughness was found to be independent of cone crack length and indentation load. Values of fracture toughness for the ceramic composite, the fine grained Al2O3 and soda-lime glass were 6.7, 3.77 and 0.8 MPa m 1 2 respectively.

Crystal growth of SiC whisker from the SiO(g)-CO system

Abstract: The growth of SiC whisker is carried out and the effects of th partial pressure of SiO(g) and CO(g) and deposition temperature on the morphology of SiC deposits were investigated

Role of Interfacial Carbon layer in the Thermal Diffusivity/Conductivity of Silicon Carbide Fiber-Reinforced Reaction-Bonded Silicon Nitride Matrix Composites

Abstract: Experiments were carried out on samples of reaction-bonded silicon nitride uniaxially reinforced by SiC monofilaments with and without a 3-micron-thick carbon-rich coating. It is found that a combination of a carbon coatings on the fibers and an interfacial gap due to the thermal expansion mismatch in the composite can significantly (by a factor of 2) lower the effective thermal diffusivity in the direction transverse to the fiber. At atmospheric pressure, gaseous conduction across the interfacial gap makes a significant contribution to the heat transfer across the interface, indicated by significantly lower values of the effective thermal diffusivity under vacuum than in nitrogen or helium at atmospheric pressure.

Effect of HIPing on the effective thermal conductivity/diffusivity and the interfacial thermal conductance of uniaxial SiC fibrereinforced RBSN

Abstract: Hot isostatic pressing (HIPing) was found to increase the thermal diffusivity/conductivity of uniaxial silicon carbide fibre-reinforced reaction-bonded silicon nitride (RBSN) matrix composites, as the result of the densification of the matrix, the increase in the grain size of the silicon carbide and the improved thermal contact between the fibres and the matrix Transverse to the fibre direction the thermal diffusivity/conductivity was found to be a function of the surrounding gaseous atmosphere due to the access of the gas phase to the fibre-matrix interface, which was facilitated by the existence of an interfacial gap due to the thermal expansion mismatch between the fibres and the matrix The interfacial conductance was found to exhibit a strong positive temperature dependence as the result of the closure of the interfacial gap with increasing temperature

Oxidation Effects on the Mechanical Properties of a SiC-Fiber-Reinforced Reaction-Bonded Si3N4 Matrix Composite

Abstract: The room-temperature mechanical properties of SiC fiber reinforced reaction bonded silicon nitride composites were measured after 100 hrs exposure at temperatures to 1400 C in nitrogen and oxygen environments. The composites consisted of approx. 30 vol percent uniaxially aligned 142 micron diameter SiC fibers in a reaction bonded Si3N4 matrix. The results indicate that composites heat treated in a nitrogen environment at temperatures to 1400 C showed deformation and fracture behavior equivalent to that of the as-fabricated composites. Also, the composites heat treated in an oxidizing environment beyond 400 C yielded significantly lower tensile strength values. Specifically in the temperature range from 600 to 1000 C, composites retained approx. 40 percent of their as-fabricated strength, and those heat treated in the temperatures from 1200 to 1400 C retained 70 percent. Nonetheless, for all oxygen heat treatment conditions, composite specimens displayed strain capability beyond the matrix fracture stress; a typical behavior of a tough composite.

Composite reaction texturing of superconducting ceramic composites

Abstract: Textured composite Bi2Sr2Ca1Cu2O8+a (2212) conductors have been fabricated by a novel method termed composite reaction texturing (CRT) that makes use of inert whiskers or fibers to align superconducting grains and control their morphology. The process has two stages, the initial alignment of fibre material in a precursor followed by a composite reaction stage to develop a textured microstructure. In this work, disk‐shaped pellets with whisker alignment in the pellet plane were reacted to produce CRT material with a transport critical‐current density in excess of 4×103 A cm−2 at 77 K (B=0). At 4.5 K, the critical‐current density was ∼105 A cm−2 in zero field and 2.104 A cm−2 at 12 T. The method clearly has promise for the production by a wind‐and‐react technique of high critical‐current conductors with large cross sections.

Combustion synthesis of ceramic-metal

Abstract: One of the main disadvantages of combustion synthesis of ceramic and composite materials is the relatively high levels of porosity,e.g., ≥50 pct, present in the product. This article discusses a novel application of combustion synthesis for producing ceramic-metal composites with reduced levels of porosity by allowing an excess amount of liquid metal, generated by the exothermic reaction, to infiltrate the pores. This application of combustion synthesis of ceramic-metal composite materials is discussed with respect to a model reaction system that utilizes an inexpensive oxide,i.e., TiO2, reacted with carbon and an excess stoichiometric amount of alu-minum. The aluminum is in the liquid state at the ignition temperature and is intentionally allowed to infiltrate the porous ceramic matrix,i.e., TiC-Al2O3, produced from the combustion synthesis reaction. Thisin situ process for producing ceramic-metal composites by the simul-taneous liquid metal infiltration of the pores in a ceramic matrix using the combustion synthesis approach provides considerable advantages over conventional processes which involve two stages,i.e., sintering followed by liquid metal infiltration. However, there are also certain limitations with respect to total penetration of the liquid metal into the porous ceramic matrix and main-taining a stable propagation of the combustion reaction.

Carbon fiber-reinforced composite material having a gradient carbide coating

Abstract: A coated carbon fiber-reinforced composite material comprising a substrate material which comprises a carbon or ceramic matrix and reinforcing carbon fibers and a coating layer which comprises silicon carbide and at least one material selected from the group consisting of titanium carbide, zirconium carbide and hafnium carbide, wherein a part of the coating layer contacting to the substrate consists of at least one material selected from the group consisting of titanium carbide, zirconium carbide and hafnium carbide, a surface part of the coating layer consists of silicon carbide and a composition in an intermediate part between the part contacting to the substrate and the surface part continuously or stepwise changes from at least one material selected from the group consisting of titanium carbide, zirconium carbide and hafnium carbide to silicon carbide, and a carbon fiber-reinforced composite material comprising a matrix which comprises carbon and oxidation resistant ceramic and reinforcing carbon fiber contained in the matrix and optionally a coating layer which comprises hafnium carbide, wherein both surface parts of the matrix consists of the oxidation resistant ceramic, a center part of the matrix consists of carbon and a composition in each of intermediate parts between each surface and the center part continuously or stepwise changes from the oxidation resistant ceramic to carbon, which have improved oxidation resistance and thermal shock resistance.

Strength, toughness and R-curve behaviour of SiC whisker-reinforced composite Si3N4 with reference to monolithic Si3N4

Abstract: The flexural strength and fracture toughness of 30 vol% SiC whisker-reinforced Si3N4 material were determined as a function of temperature from 25 to 1400°C in an air environment. It was found that both strength and toughness of the composite material were almost the same as those of the monolithic counterpart. The room-temperature strength was retained up to 1100°C; however, appreciable strength degradation started at 1200°C and reached a maximum at 1400°C due to stable crack growth. In contrast, the fracture toughness of the two materials was independent of temperature with an average value of 5.66 MPam1/2. It was also observed that the composite material exhibited no rising R-curve behaviour at room temperature, as was the case for the monolithic material. These results indicate that SiC whisker addition to the Si3N4 matrix did not provide any favourable effects on strength, toughness and R-curve behaviour.

Fiber pullout processes and mechanisms of a carbon fiber reinforced silicon nitride ceramic composite

Abstract: Details of fiber pullout processes and mechanisms are addressed for a carbon fiber reinforced silicon nitride ceramic composite. The energy for fiber pullout, γpo, is experimentally measured by the work-of-fracture technique using test specimens with a circumferential notch. A precise determination of the distribution of pullout fibers combined with the experimental results of the pullout energy provides an important insight into the micromechanical processes and mechanisms of the composite fracture. Various energy dissipation processes associated with the composite fracture, the frictional interface shear stress, the Weibull modulus of the reinforcing fibers, and composite designs for improved toughening are discussed.

Ultrahigh Temperature Assessment Study: Ceramic Matrix Composites

Abstract: : As part of the US Air Force initiative to develop high temperature materials for use in future gas turbine engines, a literature survey coupled with an assessment of recently completed experimental programs sponsored by the Air Force was made to evaluate prospective materials capable of operating at 1650 deg C or above in oxidizing environments The assessment reviews fundamental considerations associated with the use of ceramics and ceramic matrix composites in representative environments and includes discussions on potential performance requirements Key material categories (eg, borides, carbides, nitrides, silicides, beryllides, and oxides) are evaluated with respect to their strengths and weaknesses The reinforcements available for high temperature composite applications are reviewed and several prospective composite systems considered A principal conclusion relative to possible uses for long-term man-rated gas turbine engines is that oxide/oxide composites-have the best potential for functional use in oxidizing environments above 1650 deg C provided adequate single-crystal reinforcement fibers can be developed Several nonoxide materials and composites were identified for possible uses in short- duty cycle non-man-rated applications In addition to materials development, there will be critical need for high-temperature test facilities that can be operated in representative oxidizing environments Ceramics, Composites, Ultrahigh temperature, Matrix, Fiber reinforcement, Oxidation, Fracture toughness, Strength, Creep, Fatigue

Cyclic deformation, fracture, and nondestructive evaluation of advanced materials

Abstract: Papers are presented on cyclic fatigue of alumnia, fatigue crack growth in ceramics and ceramic-matrix composites, fatigue test methodology and results for ceramic matrix composites at room and elevated temperatures, and modeling crack growth resistance in ceramics and ceramic-matrix composites Attention is also given to thermomechanical cyclic deformation of metal-matrix composites, the effect of tensile mean stress on the fatigue behavior of single-crystal and directionally solidified superalloys, the influence of constituent properties on the compression behavior of aluminates with discontinuities, and cyclic creep effects in single-overlap bonded joints under constant-amplitude testing Other papers discuss an ultrasonic wave technique to assess cyclic-load fatigue damage in silicon-carbide whisker-reinforced 2124 aluminum alloy composites, nondestructive characterization for metal-matrix composite fabrication, NDE of a ceramic matrix composite material, and split spectrum processing of backscattered Rayleigh wave signals to improve detectability of fatigue microcracks

Method of forming coatings by plasma spraying magnetic-cerment dielectric composite particles

Abstract: A method of forming high temperature resistant coatings from a quantity of composite particles, each comprising very small magnetic particles in a ceramic matrix by plasma spraying the composite particles onto a surface. Typically, the surface to be coated is pre-treated by a combination of solvent cleaning and abrasion, such as by grit blasting. In some cases the surface is coated with a thin electrically conductive transition layer having a coefficient of thermal expansion intermediate those of the surface and the composite coating. A quantity of finely divided composite particles are then prepared, each of the particles comprising a ceramic matrix containing plural spaced very small magnetic metal particles. In some cases, a small quantity of smaller pure matrix particles or lower melting particles are mixed with the composite particles to improve bonding. The composite particles are plasma sprayed onto the surface to be coated at temperatures such that only the surfaces of the composite particles are melted, thereby permitting higher magnetic material loadings without forming an excessively electrically conductive coating. The resulting coating is durable, has high temperature resistance and absorbs incident microwave energy.

Disc brake for vehicles

Abstract: A disc brake for vehicles according to this invention is directed to enhancing the coefficient of friction and wear resistance in the friction members, and to reducing the size and weight of the disc brake, in turn, the unspring weight so as to improve operation stability in driving a vehicle. In the disc brake according to the constitution of this invention, either the disc or the brake pads are made of a carbon fiber reinforced ceramic composite consisting of a ceramic matrix reinforced by a carbon fiber.

Fiber-Matrix interactions in brittle matrix composites

Abstract: Brittle matrix composites, including carbon-carbon (C-C) and ceramic matrix, offer a new dimension in the area of high-temperature structural materials. Fiber-matrix interactions determine the mechanism of the load transfer between the fiber and matrix and resulting mechanical properties. Composites studied in this work include a C-C composite densified with a chemical vapor infiltration (CVI) pyrolytic carbon, silicon carbide fiber-silicon carbide matrix composite, and carbon fiber-silicon carbide matrix composites densified by the CVI technique. The type of the interfacial carbon in C-C composites was found to control their mechanical properties. The presence of the compressive stress exerted by the matrix on the carbon fibers was attributed to an increase in flexural strength. The transverse matrix cracking in C/SiC composites was believed to cause a lowering in the flexural strength value. Brittle fracture behavior of SiC/SiC composites was correlated with the presence of an amorphous silica layer at the fiber-matrix interface.