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== Composition==
MMCs are made by dispersing a reinforcing material into a metal matrix. The reinforcement surface can be coated to prevent a chemical reaction with the matrix. For example, carbon fibers are commonly used in aluminum matrix to synthesize composites containing low density and high strength. However, carbon reacts with aluminum to generate a brittle and water-soluble compound
=== Matrix ===
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The reinforcement material is embedded into the matrix. The reinforcement does not always serve a purely structural task (reinforcing the compound), but is also used to change physical properties such as wear resistance, [[friction]] coefficient, or [[thermal conductivity]]. The reinforcement can be either continuous, or discontinuous. Discontinuous MMCs can be [[isotropic]], and can be worked with standard metalworking techniques.
Continuous reinforcement uses monofilament wires or fibers such as [[carbon fiber]] or [[silicon carbide]]. Because the fibers are embedded into the matrix in a certain direction, the result is an [[anisotropic]] structure in which the alignment of the material affects its strength. One of the first MMCs used [[boron]] filament as reinforcement. Discontinuous reinforcement uses "whiskers", short fibers, or particles. The most common reinforcing materials in this category are [[alumina]] and [[silicon carbide]].
== Manufacturing and forming methods ==
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MMCs are nearly always more expensive than the more conventional materials they are replacing. As a result, they are found where improved properties and performance can justify the added cost. Today these applications are found most often in aircraft components, space systems and high-end or "boutique" sports equipment. The scope of applications will certainly increase as manufacturing costs are reduced.
In comparison with conventional polymer matrix composites, MMCs are resistant to fire, can operate in wider range of temperatures, do not absorb [[moisture]], have better electrical and thermal conductivity, are resistant to radiation, and do not display [[outgassing]]. On the other hand, MMCs tend to be more expensive, the fiber-reinforced materials may be difficult to fabricate, and the available experience in use is limited.
==See also==
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