Ceramic Matrix Composites CMCs

Most fiber-matrix composites (FMCs) are named according to the type of matrix involved. Metal-matrix composites (MMCs), ceramic-matrix composites (CMCs), and polymer-matrix composites (PMCs) have completely different structures and completely different applications. Oftentimes the temperatnre at which the composite mnst operate dictates which type of matrix material is to be nsed. The maximum operating temperatures of the three types of FMCs are listed in Table 1.27. 

Chemical Vapor Infiltration (CVI). Recall from Section 3.4.2 that CVI is primarily nsed to create ceramic matrix composites, CMCs. Fabrication of CMCs by CVI involves a sequence of steps, the first of which is to prepare a preform of the desired shape and fiber architecture. This is commonly accomplished by layup onto a shaped form of layers from multifilament fibers using some of the techniques previously described, such as filament winding. 

The program also addressed the need to develop lough ceramic-matrix composites (CMCs) with much greater resistance to brittle fracture. Early in the program, researchers round that the chemical structure that imparts superior thermal and mechanical properties to ceramics also results in negative altribuies. panicularly of brittleness, which easily can lead 10 catastrophic failure. 

Access to phase pure silicon nitride materials via processable precursors is limited to just three approaches. The first, shown in reaction 6, provides one of the first oligomers exploited as a preceramic polymer24,253. This simple polysilazane, containing only Si, N and H, is known to be relatively unstable and will crosslink on its own to give intractable gels. Furthermore, it does not offer the 3Si I4N stoichiometry required for Si3N4. Nonetheless, it is useful as a binder and for fiber-reinforced ceramic matrix composites (CMCs)31. 

Various researchers have used different techniques for the fabrication of ceramic matrix composite (CMC) by using (a) chemical vapour deposition (CVD), (b) chemical vapour infiltration (CVI) and (c) modelling of CVI [43-54], but it is difficult to fabricate glass/glass-ceramic composite using these techniques. 

The applications of glass/glass-ceramic matrix composites (CMC) can be divided into two specific categories aerospace applications and non-aerospace applications. In aerospace applications, performance is the prime consideration, while in non-aerospace applications cost-effectiveness is paramount. The characteristic properties of materials for aerospace applications should be... 

Whisker-reinforced glass-ceramic matrices are expected to find several applications in automotive components, metal forming, cutting tools, etc., due to their low thermal expansion, high thermal shock resistance, high reliability and low material and processing costs. Some industrial applications for continuous fibre-reinforced ceramic matrix composites (CMCs) are listed below. 

The aim of this chapter is to present an overview of the performance of ceramic matrix composites (CMCs) under conditions of thermal shock, i.e. when they are subjected to sudden changes in temperature during either heating or cooling. 

At DLR, three different classes of ceramic materials have been developed for the use in energy applications Oxide/oxide and non oxide Ceramic Matrix Composites (CMC) as well as monolithic SiSiC materials. 

Typical hot structures are nose cones, wing leading edges, rudders, elevens and flaps refractory carbon/carbon composites and ceramic-matrix composites (CMC) are regarded as candidates for these applications. 

A special ceramic is hydraulic (or water-cured) cement. World production of hydraulic cement is about 1.5 billion tons per year. The top three producers are China, Japan, and the United States. When mixed with sand and gravel, we obtain concrete—the most widely utilized construction material in the industrialized nations. In essence, concrete is a ceramic matrix composite (CMC) in which not just the matrix but also the reinforcing material is ceramic. 

In Table 18.6 we list different toughening mechanisms for ceramic-matrix composites (CMCs). Illustrate each mechanism using a sketch and, where appropriate, indicate the differences between using particles, platelets,... 

Chemical vapor deposition is one of the most important deposition techniques for forming ceramic films and coatings. We described two examples in Chapter 20 in which CVD is used in composites. It is used to form SiC fibers by the reaction between CHsSiCls and H2 on a tungsten wire. It is also used to form the matrix phase in a ceramic matrix composite (CMC) by a process known as chemical-vapor infiltration. In later chapters we describe the CVD technique again, e.g., it is used in the formation of optical fibers. 

H. Wurtinger and A. Miihlratzer, Cost effective manufacturing methods for structural ceramic matrix composite (CMC) components, ASME Paper 96-GT-296, 1996. 

There are three types of composite materials Ceramic matrix composites (CMC) consisting of fibers embedded in a ceramic matrix. 

The ceramic matrix composites (CMCs) contain brittle fibers and a brittle matrix. This combination ends up in a damage tolerant material. CMCs are of interest to thermostmctural applications. They consist of ceramics or carbon reinforced with continuous ceramic or carbon fibers. Their mechanical behavior displays several typical features that differentiate them from the other composites (such as polymer matrix composites, metal matrix composites, etc. .. ) and from the homogeneous (monolithic) materials. 

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. 

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