Alloy
If a metal is combined with other chemical elements (metallic or nonmetallic) to form a solution or compound, and if the combination has metallic properties, the resulting material is called an alloy. Generally, the properties of the alloy are significantly different from those of its components. An alloy with two components is called a binary alloy; one with three is a ternary alloy; one with four is a quaternary alloy.
Alloys are usually designed to have properties that are more desirable than those of their constituents. For instance, steel is stronger than iron, its main element. The alloy "inherits" some of the characteristics of the elements it was made from—usually properties such as density, reactivity, and electrical and thermal conductivity. By contrast, properties such as tensile strength, Young's modulus, and shear strength can differ vastly from those of its constituent materials. These differences are caused by various factors, including the packing of atoms of differing sizes within the alloy. Larger atoms exert a compressive force on neighboring atoms, and smaller atoms exert a tensile force on their neighbors. Consequently, an alloy tends to resist deformation more than a pure metal, in which the atoms are freer to move.
Unlike pure metals, most alloys do not have a single melting point. Instead, they have a melting range in which the material is a mixture of solid and liquid phases. The temperature at which melting begins is called the solidus, and that at which melting is complete is called the liquidus. However, for most pairs of elements, there is a particular ratio which has a single melting point, and this is called a eutectic mixture.
In practice, some alloys are used so predominantly with respect to their base metals that the name of the primary constituent is also used as the name of the alloy. For example, 14 carat (58%) gold is an alloy of gold with other elements. Similarly, the silver used in jewellery and the aluminium used as a structural building material are also alloys.
The term "alloy" is sometimes used in everyday speech as a synonym for "aluminium alloy"; one example of such usage is the "alloy wheels" which might be fitted to an automobile. (This usage is obviously indefinite, since all steels and most other metals in practical use are also alloys.)
See also
- List of alloys
- Intermetallics
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