MATSE 81
Materials in Today's World

What Are Metal Alloys?

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An alloy is a mixture of a metal with another element, either metal or nonmetal. If we start with a base metal and we add impurity atoms there are two possible outcomes if the two mix. The two different cases are highlighted in the figure below. In the substitutional solid case, the impurity atoms replace the host atoms in the lattice. In the interstitial situation, impurity atoms squeeze between the host atoms.

Substitutional solid solution (e.g., Cu in Ni) or Interstitial solid solution (e.g., C in Fe)
Solid solution of orange atoms in grey atoms
Credit: Callister

In addition to mixing, it is possible for regions of a new phase to form. An illustration of the formation of a second phase in a solid solution is shown below. The second phase can have a different composition and often a different structure.

Second phase particle: different composition and often different structure.
Solid solution of orange atoms in grey atoms with a second phase particle
Credit: Callister

To Watch

Now watch the following video on alloys and how dislocations harden alloys: Properties of Matter: Alloys and Their Properties.

After watching the video, please proceed to the next section on the development of iron smelting.