There are more than 50,000
materials available to engineers for the design and manufacturing of products
for various applications. These materials range from ordinary metals(copper,
cast iron, brass) that have been available for several hundred years, to the
more recently developed, advanced materials e.g., composites, ceramics and
other high performance materials. Due to the wide choice of materials,
today's engineers are posed with a big challenge for the right selection
of a material and the right choice of a manufacturing process for an
application. It is difficult to study all of these materials individually;
therefore, a broad classification is necessary for simplification and
characterization. These materials, depending on their major characteristics (stiffness,
strength, density and melting temperature) can be broadly divided into four
main categories: (1) metals, (2) plastics, (3) ceramics and (4) composite .
Each class contains large number of materials with a range of properties which
to some extent results in an overlap of properties with other classes.
A ceramic matrix is usually
brittle. Carbon, ceramic, metal and glass fibers are typically used with
ceramic matrices in areas where extreme environments (high temperatures, etc.)
are anticipated. Glass and glass-ceramic composites usually have elastic
modulus much lower than that of the reinforcement. Carbon and metal oxide
fibers are the most common reinforcements with glass matrix composites. The
best characteristics of glass/ceramic matrix composites are their strength at
high service temperatures. The primary applications of glass matrix composites
are for heat-resistant parts in engines exhaust systems and electrical
components.
Increasing quantities of
metal matrix composites (MMCs) are being used to replace conventional materials
in many applications, especially in the automobile and recreational industries.
The MMCs are aluminum alloys reinforced with ceramic particles and these
low-cost composites provide higher strength, stiffness and fatigue resistance
with a minimal enhancement in density over the base alloy. The major advantages
of Aluminum Matrix Composites (AMCs) include greater strength, improved high
temperature properties, controlled thermal expansion coefficient, thermal/heat
management, enhanced/tailored electrical performance, improved abrasion/wear
resistance,improved damping capabilities, low induced radioactivity under
nuclear environments, low stiffness and weight, saving in materials and energy .
The alloy designation for Al
is based on four digits corresponding to the principal alloying elements. The
most important alloying elements in aluminum alloy systems are copper (2xxx),
manganese (3xxx), silicon (4xxx), magnesium (5xxx) and zinc (7xxx). The
most commonly used route for fabrication of these composites has been through
infiltration of molten metal into preformed and porous ceramic bodies. For
example, Al-alloys have been successfully infliltrated with hydraulic or gas
pressure into fly-ash,SiC, Al2O3, MgO and AlN performs. It is very interesting
to emphasize the influence of volume fraction of reinforcing particle on
the mechanical properties of MMCs .
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