What is alloys

If a metal contains one or more foreign substances (the proportion of which exceeds a certain minimum level), we speak of an alloy - also called mixed crystal. Metals that contain such small amounts of impurities that we can call them pure in materials engineering are rarely used in mechanical engineering.
In addition to other metals, non-metals can also be part of an alloy. These alloy components and their proportional amount have - as already described in the previous material technology scripts - a great influence on the properties of the respective metal or alloy.

1) Single phase alloy

The base metal of an alloy can form a solid solution with the alloying element or elements; this is referred to as atomic mixtures. In the single-phase alloy, the base metal and alloy element form a common lattice structure. The properties of the resulting alloy are essentially determined by the chemical composition.
The alloys were also described in a previous materials engineering script as lattice defects (which in principle they are).

A further distinction is made between single-phase alloys:

1a) Substitution solid solution / exchange solid solution

In the case of substitution solid solution, a regular atom of the base metal is replaced by an atom of the alloying element, i.e. substituted. This type of alloy is formed when the base metal and alloy element have the same lattice type and the lattice constant and atomic radii are similar. In addition, the substitution crystal only forms when metals are mixed.
In the picture below you can see a schematic representation of a substitution solid solution. The atoms shown in black represent the foreign atoms here.

1b) interstitial solid solution

In the case of the mixed crystal, a foreign atom is intercalated between the atoms of the base metal. This means that the foreign atom - it can be a different metal or a non-metal - sits on an interstitial space. The formation of an intercalation solid solution as an alloy occurs primarily with spatially small atoms such as hydrogen, carbon and nitrogen.
In the picture below you can see a schematic representation of an embedded solid solution. The black atoms that lie in the spaces between the main lattice represent the foreign atoms here.

2) Multi-phase alloy

If the base metal and alloy element have poor solubility or miscibility with one another, several phases are formed. The properties of the resulting alloy are essentially influenced by the distribution of the phases (structure).
The picture below shows a multiphase alloy.