Metal Matrix Composites
Metal Matrix Composites (MMCs) are composed of
a metal matrix and a reinforcement, or filler material, which confers
excellent mechanical performance, and can be classified according
to whether the reinforcement is continuous (monofilament or multifilament)
or discontinuous (particle, whisker, short fibre or other). The
principal matrix materials for MMCs are aluminium and its alloys.
To a lesser extent, magnesium and titanium are also used, and for
several specialised applications a copper, zinc or lead matrix may
be employed. MMCs with discontinuous reinforcements are usually
less expensive to produce than continuous fibre reinforced MMCs,
although this benefit is normally offset by their inferior mechanical
properties. Consequently, continuous fibre reinforced MMCs are generally
accepted as offering the ultimate in terms of mechanical properties
and commercial potential.
The UK’s Advisory Council on Science &
Technology in 1992 stated that MMCs can be viewed either as a replacement
for existing materials, but with superior properties, or as a means
of enabling radical changes in system or product design. Moreover,
by utilising near-net shape forming and selective reinforcement
techniques MMCs can offer economically viable solutions for a wide
variety of commercial applications.
In general, the major advantages of Aluminium
Matrix Composites (AMCs) compared to unreinforced materials,
such as steel and other common metals, are as follows:
- Increased specific strength
- Increased specific stiffness
- Increased elevated temperature strength
- Improved wear resistance
- Lower density
- Improved damping capabilities
- Tailorable thermal expansion coefficients
- Good corrosion resistance
These advantages can be quantified in terms of
percentages. For instance, AMCs can offer potential mass savings
of up to 60%, and increases in stiffness and strength of up to 200%
when compared with, for example, conventional aluminium alloys.
Furthermore, AMCs can be produced with near-zero coefficients of
thermal expansion.
Properties of AMCs versus conventional alloys
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