Dislocations patterning

By understanding the formation of dislocation line images, the formation of the dislocation pattern in Figure 3.47b can be interpreted by a schematic illustration (Figure 3.49). Figure 3.47b shows a line-up of dislocations. The lined-up dislocations lie in a crystal slip plane that is inclined to the transmitted beam. The slip plane is cut off at the upper and lower surfaces of a... 

DISLOCATION PATTERNING AND DEFORMATION PROCESSES IN ICE SINGLE CRYSTALS DEFORMED BY TORSION... 

Preliminary Dislocation Dynamics (DD) simulations using the model developed by Verdier et al. provide a plausible scenario for the dislocation patterning occuring during the deformation of ice single crystals based on cross-slip mechanism. The simulated dislocation multiplication mechanism is consistent with the scale invariant pattemings observed experimentally. 

Figure 5 represents a typical evolution of the dislocation pattern during the deformation. The simulation was performed in a 20 mm diameter crystal, with 2 initial basal planes activated (one system in each plane) at the beginning of the deformation. It clearly appears that the double cross-slip mechanism propagates the plasticity in many other basal planes. One can also notice the asymmetry in the plane expansion due to the dislocation interactions. 

Schwarz K. W. and LeGoues E. K., Dislocation Patterns in Strained Layers from Sources on Parallel Glide Planes, Phys. Rev. Lett. 79, 1877 (1997). 

In materials with high dislocation mobility such as copper, dislocation patterns proceed through the rapid motion of dislocations in a very small volume of the specimen [36]. Under high strain rate deformation conditions, it is expected that the dislocations move at subsonic speed or even as fast as the shear wave velocity. The random motion of dislocations on their slip planes causes random changes not only in the local dislocation densities, but also in the dislocation velocities. 

For some material-environment combinations it has been shown that accelerated anodic dissolution of yielding metal is the significant mechanism. This is the case for austenitic stainless steels in acidic chloride solutions. In these steels, plastic deformation is characterized by a dislocation pattern giving wide slip steps on the surface. For such systems, Scully [7.50] has proposed a model for initiation and development of stress corrosion cracks, which has been supported by other scientists [7.51]. The model in its simplest form is illustrated in Figure 7.52. A necessary condition is that flie surface from the beginning is covered by a passivating film (A). 

Amelinckx, S. (1958) Dislocation patterns in potassium chloride, Acta Met. 6, 34. Seeing GBs in KCl by decoration. 

Figure 12.14 Reprinted from Delavignette, P. and Amelinckx, S. (1962) Dislocation patterns in graphite, ...

Fig. 3.6 Cellular dislocation patterns in undoped GaAs crystals revealed by (a) KOH etching of a 4-inch wafer [42],...

P. Rudolph, 2005, Dislocation Patterning in Semiconductor Compounds , Cryst. Res. Technol. 40, 7 20. 

Juda, M. Naumann, M. Neubert, 2004, Studies on dislocation patterning and bunching in semiconductor compounds (GaAs) ,/. Cryst. Growth 265, 331-340. 

Ch. Frank-Rotsch, U. Juda, F.-M. Kiessling, P. Rudolph, 2005, Dislocation patterning during crystal growth of semiconductor compounds (GaAs) , Mater. Sci. Technol. 21, 1450-1454. 

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