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Humans
have used the process of sintering for thousands of years. Some
of the first sintered products were bricks heated in open-pit fires
to add strength. Sintered ceramic structures can be found around
the world — examples include porcelain, a glass-bonded ceramic
formed by sintering; and gold-platinum jewelry sintered by the Incas.
Sintered materials today include powder metallurgy, cermets, polymers,
ceramics, and cemented carbides.
Sintering is associated with engineered materials that are net-shaped
with large production quantities and low production costs. Much
commercial activity relies on net shaping using high-value-material
systems such as cemented carbides, where powder compaction and sintering
are the only viable options. The commercial value of sintered engineering
materials (cermets, ceramics, and metals) is estimated at nearly
$23 billion for 2003 (approaching 3 percent of the U.S. materials
processing market). The annual growth rate in the use of sintered
components ranges from 10 to 40 percent, depending on the industry.
Powders provide a fluid-like medium that can be shaped at low pressures.
They allow a metallurgist to combine different elements to make
an alloy, which can have properties better than any of the elements
individually. Sintering is a thermal process (heat) applied to those
shaped powders to bond them into essentially solid components. After
sintering, a material's mechanical and physical properties often
exceed those available through alternative forming processes.
The modern era of sintering is traced to Coolidge, who used tungsten
powder to develop a durable lamp filament. Subsequently, spark plugs,
cemented carbides, porous bronze bearings, electrical insulators,
and copper-graphite electrical contacts were developed in the 1930s.
In the latter part of the twentieth century there was enormous growth
in sintering practice, especially for the creation of technical
ceramics. Today, sintered materials are widely applied in engineering,
especially for high-temperature systems ranging from light bulbs
to jet engines. Sintered materials are also used in a diverse range
of components that touch most industrial and consumer product areas
— computer heat sinks, medical surgical tools, dental orthodontic
brackets, automotive connection rods, electrical contacts, hand
tools, postage meters, oil-well drilling tools, eyeglasses, wristwatch
cases, golf clubs, and lawnmower transmissions, to name a few. |