Fiber-reinforced ceramic matrix components

As fiber is a primary component in continuous fiber reinforced ceramic matrix composites, its characteristic is an important factor that confines the thermal conductivity of the composites. The ideal SiC fiber should be highly crystalline, oxygen-free, and stoichiometric. As shows in Table I,... 

As structural materials for high-temperature components in advanced engines forpower and propulsion, fiber-reinforced ceramic matrix composites (CMC) offer a variety ofperfor-mance advantages overthe best metallic alloys with current stractural capability to 1100°C. 

Creep resistance is of primary concern in rotating components of a turbine engine. High creep rates can lead to both excessive deformation and uncontrolled stresses. Creep resistance of fiber-reinforced ceramic matrix composites depend on relative creep rates of, stress-relaxation in, and load transfer between constituents. The tensile creep behavior of SiC/RBSN composites containing 24 vol% SiC monofilaments was studied in nitrogen at 1300 C at stress levels ranging from 90 to 150 MPa. Under the creep stress conditions the steady state creep rate ranged from 1.2 x 10 to 5.1 x 10 At stress levels below... 

One approach for fabricating fiber reinforced ceramic matrix composites is the directed oxidation of metals, a process first introduced by Lanxide Corporation [1, 2] and later used successfully to produce turbine engine and aerospace components. Rights to the DIMOX technology, as it was identified, were ultimately acquired by Power Systems Composites, L.L.C., a subsidiary of the Power Systems business of the General Electric Company. 

Fiber reinforced ceramic matrix composites (CMCs) are under active consideration for large, complex high temperature structural components in aerospace and automotive applications. The Blackglas resin system (a low cost polymer-derived ceramic [PDC] technology) was combined with the Nextel 312 ceramic fiber (with a boron nitride interface layer) to produce a sihcon oxycarbide CMC system that was extensively characterized for mechanical, thermal, and electronic properties and oxidation, creep mpture, and fatigue. A gas turbine tailcone was fabricated and showed excellent performance in a 1500-hour engine test. 

Background At elevated temperatures the rapid application of a sustained creep load to a fiber-reinforced ceramic typically produces an instantaneous elastic strain, followed by time-dependent creep deformation. Because the elastic constants, creep rates and stress-relaxation behavior of the fibers and matrix typically differ, a time-dependent redistribution in stress between the fibers and matrix will occur during creep. Even in the absence of an applied load, stress redistribution can occur if differences in the thermal expansion coefficients of the fibers and matrix generate residual stresses when a component is heated. For temperatures sufficient to cause the creep deformation of either constituent, this mismatch in creep resistance causes a progres-... 

The chemical composition of the composite constituents and the interphase is not limited to any particular material class. There are metal-matrix, ceramic-matrix, and polymer-matrix composites, all of which find industrially relevant applications. Similarly, reinforcements in important commercial composites are made of such materials as steel. E-glass, and Kevlar . Many times a bonding agent is added to the fibers prior to compounding to create an interphase of a specified chemistry. We will describe specific component chemistries in subsequent sections. 

Composites may use ceramics as the matrix phase and/or the reinforcing phase. The purpose of a composite is to display a combination of the preferred characteristics of each of the components. In CMCs one of the principal goals has been to increase fracture toughness through reinforcement with whiskers or fibers. When ceramics are the reinforcement phase in, for example, metal matrix composites the result is usually an increase in strength, enhanced creep resistance, and greater wear resistance. Three issues must be solved ... 

In the last few decades, polymeric materials have found many applications and govern a major part of our day-to-day life. The polymeric materials are strong, lightweight, and easily processable with cost-effective techniques [1]. However, the properties of the pure polymeric materials limit their application in diversified fields. The introduction of filler materials into the polymer matrix generates properties superior to those of individual components. The combination forms a single system the polymer nanocomposites exhibit improved strength, stiffness and dimensional stability with adequate physical properties compared to pure ploymer. These nanocomposites can be of different types such as ceramic-based nanocomposites, fiber-reinforced nanocomposites, polymer-clay nanocomposites, etc. 

The composites can be classified on the basis of the form of their structural components fibrous (composed of fibers in a matrix), laminar (composed of layers of materials), and particulate (composed of particles in a matrix). The particulate class can be further subdivided into flake (flat flakes in a matrix) or skeletal (composed of a continuous skeletal matrix filled by a second material). In general, the reinforcing agent can be either fibrous, powdered, spherical, crystalline, or whiskered and either an organic, inorganic, metallic, or ceramic material. 

Multi-component ceramics allow the optimization of various physical properties. These include ceramics which form multi-component oxides as well as fiher-rein-forced ceramic matrix composites. However, the oxidation behavior of these materials is complex compared with the pure materials. The leading fiber-reinforced composites are silicon-based and contain continuous SiC fibers with coatings of graphitic carbon or hexagonal boron nitride. The oxidation of the fiber coating at intermediate temperatures is a major issue and models of this process are discussed for both carbon and boron nitride coatings. 

Composites are usually classified by the type of material used for the matrix. The four primary categories of composites are polymer matrix composites (PMCs), metal matrix composites (MMCs), ceramic matrix composites (CMCs), and carbon matrix composites (CAMCs). The last category, CAMCs, includes carbon/carbon composites (CCCs), which consist of carbon matrices reinforced with carbon fibers. For decades, CCCs were the only significant type of CAMC. However, there are now other types of composites utilizing a carbon matrix. Notable among these is silicon carbide fiber-reinforced carbon, which is being used in military aircraft gas turbine engine components. 

Recent research has explored a wide variety of filler-matrix combinations for ceramic composites. For example, scientists at the Japan Atomic Energy Research Institute have been studying a composite made of silicon carbide fibers embedded in a silicon carbide matrix for use in high-temperature applications, such as spacecraft components and nuclear fusion facilities. Other composites that have been tested include silicon nitride reinforcements embedded in silicon carbide matrix, carbon fibers in boron nitride matrix, silicon nitride in boron nitride, and silicon nitride in titanium nitride. Researchers are also testing other, less common filler and matrix materials in the development of new composites. These include titanium carbide (TiC), titanium boride (TiB2), chromium boride (CrB), zirconium oxide (Zr02), and lanthanum phosphate (LaP04). 

Lanxide A process for making composites of metals with oxides. A molten metal reacts with an adjacent oxidant and is progressively drawn through its own oxidation product so as to yield a ceramic-metal composite. Fibers or other reinforcing materials can be placed in the path of the oxidation reaction and so be incorporated into the final product. The Lanxide Corporation was founded in 1983 in Newark, DE, to exploit this invention. In 1990 it formed a joint venture with DuPont to make electronic components by this process. Variations are Dimox (directed metal oxidation), for making ceramic metal composites, and Primex (pressureless infiltration by metal), for making metal matrix composites. 

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