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Alloys
Alloy
structures are formed at the atomic level by introducing more than
one element into a material. The diagram illustrates two ways in which the
solid solution can accommodate the added alloying element or elements. Crystals
are characterized by a regular array of atoms (a) and a "repeat unit,"
the unit cell, contains information about the crystallography of the
material. Alloying elements can be added to this structure in normally occupied
sites to form a substitutional solid solution (b). Brass, the alloy between
copper and zinc, is an example of this type of alloy. In other alloys the
added alloying element is located at sites that are normally empty in the
pure crystal structure. These "interstitial" sites are used in forming
interstitial solid solutions (c). An important example of this type of
alloy is a carbon steel.
More than one element may be added to a matrix
material to achieve desired mechanical or corrosion properties. Stainless
steels contain additions of nickel and chromium in addition to carbon. These
larger alloying atoms use substitutional sites and the carbon the interstitial
sites. |
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