metal matrix сomposites (rus. композиты с металлической матрицей abbr., КММ) — composites, whose matrix is formed of metal or metal alloy.

Description

Metal matrix composites are divided into composites reinforced by fibres (fibrous composites) and composites filled with fine particles insoluble in the base metal (dispersion-strengthened composites).

Fibre composites with metal matrix have two major advantages over the more common composites with polymer matrix: they can be used at much higher temperatures and have higher performance in relatively small heavily loaded structural elements. The latter is determined by the possibility of significant mass reduction of coupling elements due to the greater strength of the metal matrix, as compared, for example, to the polymer matrix, and the processability of composites having such a matrix (possibility of using threaded connections, etc.).

The fibres in MMCs carry the main load, and the length of load transfer in this type of composites is much smaller than the corresponding length in polymer matrix composites because of the high possible shear stresses in them, provided the fibre-matrix interface is sufficiently strong. This yields a positive effect on the strength properties of the composite because of scale dependence of the fibre strength. In some situations the fibre-matrix interaction can significantly increase the effective fibre strength, and as a result the real strength of the composite is higher than the value obtained using the test results of individual fibres. Such effects make fibrous MMCs promising materials. Another important feature of MMCs with a ductile metal matrix is the possibility of designing structures with brittle fibres, whose crack resistance would exceed the crack resistance of the unreinforced matrix.

Typical composites with metal matrix include boron-aluminium (boron fibre and aluminium alloy-based matrix), carbon-aluminium (carbon fibre in aluminium matrix), composites with silicon carbide fibres in a titanium or titanium aluminide matrix, as well as with oxide fibres in a nickel-based matrix. The latter allows a significant increase (up to 1,200°C) to the use temperature of heat-resistant materials.

In contrast to fibre composites, in dispersion-strengthened materials the matrix is the main load-bearing component and the dispersed particles inhibit dislocation motion, thus increasing the yield point and strength of the material. High strength is achieved at particle sizes from 10 to 500 nm with an average distance between the particles from 100 to 500 nm and given their uniform distribution in the matrix. Dispersion-strengthened composites can be obtained on the basis of most engineering metals and alloys.

Today MMCs are mainly used in aerospace structures; in the future they could replace metal alloys in many terrestrial applications, including automotive.

Author

  • Mileiko Sergey T.

Sources

  1. Concise Encyclopedia of Composite Materials / Ed. by A. Kelly. — Elsevier Science, 1994. — 378 p.
  2. Handbook of Composites. V. 4 / Ed. by A. Kelly, S. T. Mileiko. — NorthHolland, Amsterdam, 1983.
  3. Composite materials. Handbook / Ed. by V.V. Vasil'ev, Ju. M. Tarnopol'skij. — Moscow.: Mashinostroenie, 1990. — 510pp.
  4. Mileiko S. T. Metal and Ceramic Based Composites. — Elsevier Science, 1997. — 704 p.

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