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Impurity
atoms may be attracted to a dislocation line because of the local stress
field around the line. An aggregate of such impurities, an impurity cluster,
will make it more difficult to move the dislocation away from their location
in the lattice and the dislocation is said to be pinned by the cluster.
The photograph shows a dislocation in MgO that is pinned by impurities.
One cluster is at the junction of three dislocations (a node) and other
clusters are on the individual dislocation lines. The magnification of
the electron micrograph is circa 90,000 x. |
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