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Annealing, in metallurgy and materials science, is a
heat treatment wherein the microstructure of a material is
altered, causing changes in its properties such as strength and
hardness. There are several phases in the annealing process, with
the first being the recovery phase, which results in softening of
the metal through removal of crystal defects and the internal
stresses which they cause. The second phase is recrystallization,
where new grains nucleate and grow to replace those deformed by
internal stresses. If annealing is allowed to continue once
recrystallization has been completed, grain growth will occur, in
which the microstructure starts to coarsen and may cause the metal
to have less than satisfactory mechanical properties.
In the semiconductor industry, silicon wafers are annealed, so
that dopant atoms, usually boron, phosphorus or arsenic, can be
incorporated into substitutional positions in the crystal lattice,
resulting in drastic changes in the electrical properties of the
semiconducting material.
In the cases of copper, steel, and brass this process is
performed by substantially heating the material (generally until
glowing) for an extended period of time and allowing it to cool
slowly. In this fashion the metal is softened and prepared for
further work such as shaping, stamping, or forming.
