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Alloys and phase diagrams

An alloy is a mixture of a metal with other elements to achieve desired properties, like carbon steel (iron and carbon) or brass (copper and zinc). A phase diagram shows which phases are stable at different temperatures and compositions, and is used to understand and plan heat treatment.

alloy=base metal+alloying element(s)\text{alloy} = \text{base metal} + \text{alloying element(s)}definition of an alloy

Example

The iron–carbon diagram shows that even under 2% carbon in iron dramatically changes the steel's properties, from soft and ductile to hard and brittle.

A phase diagram tells you which phases exist at equilibrium — not how fast they form on cooling.
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Part of Materials Technology: Structure.