Geology Reference
In-Depth Information
(a)
(b)
Fig. 6.8 Schematic representation of glide dissociation of an edge dislocation a, giving rise to
partial dislocations separated by a stacking fault b
dislocations separated by a strip of antiphase boundary and, further, the normal
dislocations can themselves be dissociated into partial dislocations (Amelinckx
1979
).
6.2.6 Dislocation Reactions
The dissociation of a perfect dislocation into partials (
Sect. 6.2.5
) is one example
of a more general class of dislocation reactions which may occur when dislocation
lines are brought together or dissociated into separate dislocations (Weertman and
Weertman
1964
, Chap. 4). In all dislocation reactions, a principle of conservation
applies according to which the vector sum of the Burgers vectors must remain the
same. This rule applies, in particular, at nodes of the three-dimensional network of
dislocations in a real crystal, where it can be expressed in the form that, if the
Burgers vectors are given senses according to a consistent rule (
Sect. 6.2.1
),
the vector sum of the Burgers vectors of all the dislocations issuing from a node
must be zero (Friedel
1964
, Chap. 1).
The potential importance of dislocation reactions can be illustrated with the
frequently discussed reaction in face-centered cubic(f.c.c.) crystals which leads to
the formation of a sessile dislocation known as a Lomer-Cottrell lock. Consider
two perfect dislocations, one of Burgers vector
2
011
½
in the (111) plane and one of
