IMPERFECTIONS IN METALS
DOE-HDBK-1017/1-93
Structure of Metals
IMPERFECTIONS IN METALS
The discussion of order in microstructures in the previous chapters assumed
idealized microstructures. In reality, materials are not composed of perfect
crystals, nor are they free of impurities that alter their properties. Even
amorphous solids have imperfections and impurities that change their structure.
EO 1.13
IDENTIFY the three types of microscopic imperfections found
in crystalline structures.
EO 1.14
STATE how slip occurs in crystals.
EO 1.15
IDENTIFY the four types of bulk defects.
Microscopic imperfections are generally classified as either point, line, or interfacial
imperfections.
1.
Point imperfections have atomic dimensions.
2.
Line imperfections or dislocations are generally many atoms in length.
3.
Interfacial imperfections are larger than line defects and occur over a two-
dimensional area.
Point imperfections in crystals can be divided into three main defect categories. They
are illustrated in Figure 7.
1.
Vacancy defects result from a missing atom in a lattice position. The
vacancy type of defect can result from imperfect packing during the
crystallization process, or it may be due to increased thermal vibrations
of the atoms brought about by elevated temperature.
2.
Substitutional defects result from an impurity present at a lattice position.
3.
Interstitial defects result from an impurity located at an interstitial site or
one of the lattice atoms being in an interstitial position instead of being
at its lattice position. Interstitial refers to locations between atoms in a
lattice structure.
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