Metal matrix composite

A metal matrix composite (MMC) is composite material with at least two constituent parts, one being a metal necessarily, the other material may be a different metal or another material, such as a ceramic or organic compound. When at least three materials are present, it is called a hybrid composite. An MMC is complementary to a cermet.

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 Al4C3 on the surface of the fibre. To prevent this reaction, the carbon fibres are coated with nickel or titanium boride.

Matrix

The matrix is the 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 compliant 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 polycrystaline diamond tooling (PCD).

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.[1]

Manufacturing and forming methods

MMC manufacturing can be broken into three types—solid, liquid, and vapor.

Solid state methods

Liquid state methods

Semi-solid state methods

Vapor deposition

In-situ fabrication technique

Applications

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 damage, 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

References

  1. Materials science and Engineering, an introduction. William D. Callister Jr, 7th Ed, Wiley and sons publishing
  2. Yufeng Wu, Gap Yong Kim, Carbon nanotube reinforced aluminum composite fabricated by semi-solid powder processing ,Journal of Materials Processing Technology, Volume 211, Issue 8, August 2011, Pages 1341–1347, http://www.sciencedirect.com/science/article/pii/S0924013611000707
  3. Yufeng Wu, Gap Yong Kim, et alFabrication of Al6061 composite with high SiC particle loading by semi-solid powder processing, Acta Materialia, Volume 58, Issue 13, August 2010, Pages 4398–4405, http://www.sciencedirect.com/science/article/pii/S0924013611000707
  4. Yufeng Wu, Gap Yong Kim, et alCompaction behavior of Al6061 and SiC binary powder mixture in the mushy state, Journal of Materials Processing Technology, Volume 216, February 2015, Pages 484-491, http://www.sciencedirect.com/science/article/pii/S0924013614003707
  5. University of Virginia's Directed Vapor Deposition (DVD) technology
  6. Aluminium matrix composite (AMC) inserts for reinforced brake calipers (Archived)
  7. Industry Solutions - Metal Matrix Composites - High performance, high strength, metal matrix composite material (Archived)
  8. Ratti, A.; R. Gough; M. Hoff; R. Keller; K. Kennedy; R MacGill; J. Staples (1999). "The SNS RFQ Prototype Module" (PDF). Particle Accelerator Conference, 1999. 2 (1): 884–886. doi:10.1109/PAC.1999.795388. ISBN 0-7803-5573-3.
  9. Mochizuki, T.; Y. Sakurai; D. Shu; T. M. Kuzay; H. Kitamura (1998). "Design of Compact Absorbers for High-Heat-Load X-ray Undulator Beamlines at SPring-8" (PDF). Journal of Synchrotron Radiation 5 (4): 1199–1201. doi:10.1107/S0909049598000387. PMID 16687820.

External links

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