Slip along glide planes

The deformation of a rod of zinc into a ribbon, through slip along glide planes. 

Another important class of three-dimensional dislocation configurations are those associated with the cross slip process in which a screw dislocation passes from one glide plane to another. The most familiar mechanism for such cross slip is probably the Friedel-Escaig mechanism, which is illustrated schematically in fig. 8.37. The basic idea is that an extended dislocation suffers a local constriction at some point along the line. This dislocation segment, which after constriction is a pure screw dislocation, can then glide in a different slip plane than that on which is gliding the parent dislocation. This mechanism, like those considered already, is amenable to treatment from both continuum and atomistic perspectives, and we take them each up in turn. 

The slip along a glide plane does not occur by the simultaneous motion of a whole layer of atoms relative to an adjacent layer. Instead, the atoms move one at a time. There is a flaw in the structure, where an atom is missing. The atom to one side of this flaw (which is called a dislocation)-moves to occupy the space, and leaves a space where it was that is, the dislocation moves in the opposite direction to the atom. When the dislocation has moved all the way across the crystal grain, the whole row of atoms has moved, and the lower part of the lower part of the crystal has slipped one atomic diameter in the direction of the strain. A description of some kinds of dislocations is given below. 

Figure 10.6. Application of a tensile force to a cylindrical single crystal causes a shear stress on some crystal planes. When the shear stress is equal to the critical-resolved shear stress (the yield stress), glide proceeds along the slip direction of the planes.

Fig.17. Illustration of how the ends of two dislocations (5 and 6) of the type (110) <1T0> have moved by cross glide out of the normal slip plane, along the (001) planes. The dislocations 1, 2, 3, and 4 have remained on the (110) plane.

Fig. 6.24. A buried strained quantum wire with a slip plane oriented at an angle a to the x—axis. The glide of a threading dislocation leaves behind a dislocation dipole pair with 4 and lb denoting the positions of the dislocations. I denotes distance along the slip plane.

The temperature dependencies of the yield stresses are similar for samples deformed along the <123> and <100> compression axes [54,55,58]. However, the deformation microstructures look very different. This feature is related to the resolved applied stresses on the active slip planes. These stresses are such that, for dissociated glide dislocations, they increase the dissociation width for the <123> loading axis and decrease it for the < 10 0 > loading axis. 

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