Interstitial alloys are characterized by the presence of small atoms that occupy the spaces between larger atoms in the crystal lattice.

In these alloys, small atoms such as carbon, nitrogen, and hydrogen fit into the interstitial sites—gaps that exist between the larger atoms in the crystal structure. These small atoms do not replace the larger atoms; instead, they create a distortion within the crystal lattice. This distortion enhances the hardness and strength of the alloy compared to the pure metal. A well-known example of an interstitial alloy is steel, which is produced by adding carbon to iron.

In contrast, substitutional alloys involve the replacement of some of the original metal’s atoms with atoms of a different element. This substitution alters the alloy’s properties, including its melting point, density, and electrical conductivity. A classic example of a substitutional alloy is brass, which is created by adding zinc to copper.

In summary, the key distinction between interstitial and substitutional alloys lies in their atomic arrangements. In interstitial alloys, small atoms occupy the interstitial sites without displacing the larger atoms, resulting in a distortion of the crystal lattice that increases the alloy’s strength and hardness. Conversely, in substitutional alloys, the replacement of atoms leads to significant changes in the alloy’s overall properties.