Editing Metal matrix composite (section)

== 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 [[aluminium]] matrix to synthesize composites showing low density and high strength. However, carbon reacts with aluminium to generate a brittle and water-soluble compound [[aluminium carbide|Al<sub>4</sub>C<sub>3</sub>]] on the surface of the fiber. To prevent this reaction, the carbon fibers are coated with [[nickel]] or [[titanium boride]].

=== Matrix ===
The matrix is the [[Single crystal|monolithic]] material into which the reinforcement is embedded, and is completely continuous. This means that there is a path through the matrix to any point in the material, unlike two materials sandwiched together. In structural applications, the matrix is usually a lighter metal such as [[aluminum]], [[magnesium]], or [[titanium]], and provides a complete support for the reinforcement. In high-temperature applications, [[cobalt]] and cobalt–nickel alloy matrices are common.

=== Reinforcement ===
The reinforcement material is embedded into a 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, such as extrusion, forging, or rolling. In addition, they may be machined using conventional techniques, but commonly would need the use of polycrystalline diamond tooling (PCD).

Continuous reinforcement uses monofilament wires or fibers such as [[carbon (fiber)|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 [[Monocrystalline whisker|"whiskers"]], short fibers, or particles. The most common reinforcing materials in this category are [[alumina]] and [[silicon carbide]].<ref>''Materials science and Engineering, an introduction''. William D. Callister Jr, 7th Ed, Wiley and sons publishing</ref>