| An alloy is a combination, either in | | | | Classification |
| solution or compound, of two or more | | | | Alloys can be classified by the number |
| elements, at least one of which is a | | | | of their constituents. An alloy with two |
| metal, and where the resulting material | | | | components is called a binary alloy; one |
| has metallic properties. The resulting | | | | with three is a ternary alloy, and so |
| metallic substance usually has different | | | | forth. Alloys can be further classified |
| properties (sometimes significantly | | | | as either substitution alloys or |
| different) from those of its components. | | | | interstitial alloys, depending on their |
| Properties | | | | method of formation. In substitution |
| Alloys are usually prepared to improve | | | | alloys, the atoms of the components are |
| on the properties of their components. | | | | approximately the same size and the |
| For instance, Steel, is stronger than | | | | various atoms are simply substituted for |
| iron, its primary component. The | | | | one another in the crystal structure. An |
| physical properties of an alloy, such as | | | | example of a (binary) substitution alloy |
| density, reactivity and electrical and | | | | is brass, made up of copper and zinc. |
| thermal conductivity may not differ | | | | Interstitial alloys occur when the atoms |
| greatly from the alloy's elements, but | | | | of one component are substantially |
| engineering properties, such as tensile | | | | smaller than the other and the smaller |
| strength, shear strength and Young's | | | | atoms fit into the spaces (interstices) |
| modulus, can be substantially different | | | | between the larger atoms. |
| from those of the constituent materials. | | | | Terminology |
| This is sometimes due to the differing | | | | In practice, some alloys are used so |
| sizes of the atoms in the alloy—larger | | | | predominantly with respect to their base |
| atoms exert a compressive force on | | | | metals that the name of the primary |
| neighbouring atoms, and smaller atoms | | | | constituent is also used as the name of |
| exert a tensile force on their | | | | the alloy. For example, 14 karat gold is |
| neighbours. This helps the alloy resist | | | | an alloy of gold with other elements. |
| deformation, unlike a pure metal where | | | | Similarly, the silver used in jewelry |
| the atoms move more freely. | | | | and the aluminium used as a structural |
| Unlike pure metals, most alloys do not | | | | building material are also alloys. |
| have a single melting point. Instead, | | | | The term "alloy" is sometime used in |
| they have a melting range in which the | | | | everyday speech as a synonym for a |
| material is a mixture of solid and | | | | particular alloy. For example, |
| liquid phases. The temperature at which | | | | automobile wheels made of "aluminium |
| melting begins is called the solidus, | | | | alloy" are commonly referred to as |
| and that at which melting is complete is | | | | simply "alloy wheels". The usage is |
| called the liquidus. However, for most | | | | obviously indefinite, since steels and |
| pairs of elements, there is a particular | | | | most other metals in practical use are |
| ratio which has a single melting point; | | | | also alloys. |
| this is called the eutectic mixture. | | | | |