Structure of Metals
DOE-HDBK-1017/1-93
IMPERFECTIONS IN METALS
Interstitial impurities called network modifiers act as point defects in
amorphous solids. The presence of point defects can enhance or lessen
the value of a material for engineering construction depending upon the
intended use.
Figure 7 Point Defects
Figure 8 Line Defects (Dislocations)
Line imperfections are called dislocations
and occur in crystalline materials only.
Dislocations can be an edge type, screw
type, or mixed type, depending on how
they distort the lattice, as shown in
Figure 8. It is important to note that
dislocations cannot end inside a crystal.
They must end at a crystal edge or other
dislocation, or they must close back on
themselves.
Edge dislocations consist of an extra row
or plane of atoms in the crystal structure.
The imperfection may extend in a straight
line all the way through the crystal or it
may follow an irregular path. It may
also be short, extending only a small
distance into the crystal causing a slip of
one atomic distance along the glide plane
(direction the edge imperfection is
moving).
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