Page 311 - Carrahers_Polymer_Chemistry,_Eighth_Edition

274 Carraher’s Polymer Chemistry

TABLE 8.6
Typical Metal-Composite Matches
Discontinuous Phase
Matrix Material Form Material
Aluminum Fibers Boron
Alumina
Graphite
Alumina-silica
Silicon carbide
Whiskers Silicon carbide
Particulates Silicon carbide
Boron carbide
Titanium Fibers Boron (coated)
Silicon carbide
Particulates Titanium carbide
Copper Fibers Graphite
Silicon carbide
Particulates Boron carbide
Silicon carbide
Titanium carbide
Wires Niobium-titanium
Niobium-tin
Magnesium Fibers Alumina
Graphite
Particulates Boron carbide
Silicon carbide
Whiskers Silicon carbide
Superalloys Wires Tungsten

but there are a number of other materials whose fibers and whiskers are employed, including
silicon carbide, boron carbide, coated boron, and wire materials such as niobium-titanium and
niobium-tin and tungsten. By volume, the amount of whiskers, wires, and particulates is greater
for the MMCs.
As in the case with polymer-intense composites, the matrix and fiber must be matched for decent

properties. Table 8.6 contains a listing of typical matrix/fi ber mixes.
In some cases, alloy formation is possible. The term MMC is restricted to materials where such
alloy formation does not occur so that there is a phase separation between the matrix and reinforc-
ing material.
In comparison to single-metal materials such as aluminum, copper, and iron, MMCs generally
have

A higher strength-to-density ratio
A better fatigue and wear resistance
A better high-temperature strength
A lower creep related to lower coefficients of thermal expansion and they are stiffer

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