Slip dislocations

Some materials have a small lattice mismatch with the substrate, less then 1%, and can adopt the same lattice constants at the interface. This, however, still results in some strain, which builds until released, forming slip dislocations etc.. The thickness at which defects occur is of considerable interest and referred to as the critical thickness [14, 15]. Strain can be minimized by adjusting the lattice constants of the... 

Beside dislocation density, dislocation orientation is the primary factor in determining the critical shear stress required for plastic deformation. Dislocations do not move with the same degree of ease in all crystallographic directions or in all crystallographic planes. There is usually a preferred direction for slip dislocation movement. The combination of slip direction and slip plane is called the slip system, and it depends on the crystal structure of the metal. The slip plane is usually that plane having the most dense atomic packing (cf. Section 1.1.1.2). In face-centered cubic structures, this plane is the (111) plane, and the slip direction is the [110] direction. Each slip plane may contain more than one possible slip direction, so several slip systems may exist for a particular crystal structure. Eor FCC, there are a total of 12 possible slip systems four different (111) planes and three independent [110] directions for each plane. The... 

In fee metals, the normal slip dislocations can dissociate into partial dislocations ... 

The sub-boundaries that have been formed seem to be sources of slipping dislocations. The process of generation of mobile dislocations by sub-boundaries is readily affected by the applied stress. The TEM technique allows one to observe the beginning of a dislocation emission. The creation of dislocations occurs as if the sub-boundary blows the dislocations loops. These loops broaden gradually and... 

The distance between dislocations in sub-botmdaries decreases during the primary stage of deformation and the role of sub-boundaries as obstacles for slipping dislocations increases. 

The irradiation effects on the mechanical properties are significant. The interstitial atoms and vacancies resulting from irradiation-induced atomic displacements give rise to the formation of dislocation loops of interstitial and vacancy type. These dislocation loops act as obstacles to slip dislocations and lead to an increase in yield stress and decrease in elongation upon fracture as a function of dose, as shown in Fig. 3.1-93. The effect saturates at about 10 nm. ... 

Note the possible significance of the slip direction here, i.e., <1120) for both 0001 and lOTO systems for 0001 slip, dislocations will be moving parallel to the indented surface when indenting the basal plane, and for (1010) slip only screw dislocations will be emerging onto the indented plane. On the (lOTo) indented surface, edge dislocations will emerge for 1010 slip but only screw dislocations for basal slip. 

Current theories of brittle failure are based on dislocation models in which crack initiation occurs due to slip dislocation coalescence. The failure process consists of three stages ... 

Fig. 2. Transmission electron micrographs of slip dislocations in quartz (a) All in contrast, (b) some out of contrast (note spotty electron beam damage, typical of ( wet ) quartz after irradiation) [151].

Fig. 13.2 Whole-wafer scan of a 200-mm silicon wafer, showing slip bands and thermal slip dislocations nucleated from BMDs. (220) reflection in transmission mode.

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