Alloy
A metallic material made by combining a metal with one or more other elements.
Unit
Dimensionless
In depth
Alloys may be substitutional, where atoms of similar size replace one another in the lattice, or interstitial, where small atoms fill the gaps. Either way the disrupted lattice resists dislocation movement, so alloys are almost always harder and stronger than their parent metals.
Examples in the real world
Brass (copper and zinc), bronze (copper and tin), stainless steel (iron, chromium and nickel), and duralumin.