Dislocation cells

In this study, the appearance and evolution sequence of planar slip bands, in addition to a dislocation cell structure with increasing e,, is identical to that observed in quasi-static studies of the effects of stress path changes on dislocation substructure development [27]. The substructure evolution in copper deformed quasi-statically is known to be influenced by changes in stress path [27]. Deforming a sample in tension at 90° orthogonal to the... 

Appleton and Waddington [40] present experimental evidence that pulse duration also affects residual strength in OFHC copper. Samples shock loaded to 5 GPa for 1.2 ps pulse duration exhibit poorly developed dislocation cell structure with easily resolvable individual dislocations. When the pulse duration is increased to 2.2 ps (still at 5 GPa peak stress) recovered samples show an increase in Vickers hardness [41] and postshock electron micrographs show a well-developed cell structure more like samples shock loaded to 10 GPa (1.2 ps). In the following paragraphs we give several additional examples of how pulse duration affects material hardness. 

Figure 3.47 Bright-field images of dislocations (a) in a Al-Zn-Mg alloys with 3% tension strain (b) lining up in a Ni-Mo alloy and (c) dislocation cell structure in pure Ni. (Reproduced with permission from M. von Heimandahl, Electron Microscopy of Materials, Academic Press, New York. 1980 Elsevier B. V.)...

Fig. 23. Section of reeler mutant mouse cerebellum stained with monoclonal antibody 4C11 against the P400 protein. Note stained Purkinje cells in the cortex (CX) and in the central mass of dislocated cells (DP). Bar = 200 jum. Maeda et al. (1989).

Formation of a dislocation cell structure by static and dynamic recovery processes... 

Whether or not a material becomes aystallographically textured, heavy deformation will produce aligned arrays of dislocation-cell walls (Fig. 6.4). Our present understanding of the eftects of heavy deformation on the microstructures of metals can be traced back to an important series of papers by Hirsch and coworkers... 

With respect to the formulation given by Eq. (13.27) in which a characteristic time was considered tf, now a constant charge density 2 is fixed and the time tf depends on Q that, in turn, varies with environmental conditions. As a proof of this hypothesis, it has been observed [34] that L is of the order of 0.5-1 pm that represents just the typical diameter of dislocation cells. Once 2 is fixed. Ford [35] introduces an apparently contradictory concepts stating that now g is also function of the stress field ahead of the crack tip whose amplitude is defined by the stress intensity factor Kj — a Ja fia), according to a relationship of the type... 

Fig. 3.8 Measured dislocation cell size d vs. calculated normalized resolved shear stress xjCb along the [110] direction of a 6-inch VCz GaAs wafer (empty squares) [77[ and estimated from von Mises stress modeling in VCz GaAs crystals (gray squares) [75] in...

R. J. Amodeo, N.M. Ghoniem, 1990, Dislocation dynamics. I. A proposed methodology for deformation micromechanics Dislocation dynamics. 11. Applications to the formation of persistent slip hands, planar arrays, and dislocation cells , Phys. Rev. 

P. Rudolph, Ch. Frank-Rotsch, U. )uda, F.-M. Kiessling, 2005, "Scaling of dislocation cells in GaAs crystals by global numeric simulation and their restraints by in situ control of stoichiometry , Mater. Sci. Eng. A 400-401, 170-174. 

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