Lattice dislocations

Solid metals obtained upon solidification of the molten metal exhibit grain structure. They consist of fine crystallites randomly oriented in space. The size of the individual crystallites (grains) is between 10 m (fine-grained structure) and 10 m (coarse-grained structure). The crystal stracture of the individual grains as a rule is not ideal. It contains various types of defects vacant sites, interstitial atoms or ions, and dislocations (lattice shearing or bending). Microcracks sometimes evolve in the zones between crystallites. 

Fig. 8.2 Lattice matching, a concept borrowed from the semiconductor industry, matches lattice symmetry and lattice constants of metals and ceramics at the atomic level to minimize interfacial stress and minimize formation of dislocations. Lattice matching allows production of more stable cermets and allows better deposition of metal films atop porous ceramics...

The lattice misfit at moving phase boundaries is accommodated by misfit dislocations, lattice rotations, etc. An important consideration will be the role of size in determining these effects neither misfit dislocations nor lattice rotations may be necessary when the new phase is very small. The chemical abrupmess of the interface is particularly interesting when the oxygen sublattice is almost common to the two materials as we saw in Section 15.6 for the Ni0/NiFe204 interface. This interface can then move by only the cations moving. However, if misfit dislocations are present, as in Figure 15.3, then the anions must also move. 

Tab. 2 Dominant type of dislocation, lattice mismatch, and growth modes...

FIGURE 8.1 A schematic illustration showing an edge dislocation in a lattice. The partition of the dislocated lattice into a linear elastic region and a nonhnear atomistic region allows a multiscale treatment of the problem. 

In addition to the investigated materials, dislocation lattices may also occur in other systems, e.g. ... 

All of these two dimensional bubble raft demonstrations simulate the arrangement of atoms in crystalline materials. Dislocations, lattice defects, grain boundaries and recrystallization are all phenomena that occur in three dimensional crystalline materials. 

Obviously all the additions are not swelling inhibitors and there are indeed additive elements for which the role is not very marked, such as V, a potential partner of a tristabilization. The rather deleterious influence of V has been pointed out by C. Delalande who demonstrated in his thesis [42] that vanadium stabilizes a high density of cavities without having any particular influence on the dislocations lattice as is the case for titanium and niobium. It is also the case of tin, antimony, and to a lesser extent germanium [43]. Considering Co, this element must be limited due to problems with neutron activation. 

Figure 7.17 (a) Representation of tensile lattice strains imposed on host atoms by a smaller substitutional impurity atom, b) Possible locations of smaller impurity atoms relative to an edge dislocation such that there is partial cancellation of impurity-dislocation lattice strains. 

Dislocation, lattice (crystallography) A line of displacement of atoms in a lattice. Often formed during mechanical stress to relieve some of the stress. 

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