Critical density of dislocations during their rearrangement into polygonization walls


I. M. Frantsevich Institute for Problems of Materials Science of the NAS of Ukraine, Krzhizhanovsky str., 3, Kyiv, 03142, Ukraine
Electron Microscopy and Strength of Materials - Kiev: Frantsevich Institute for Problems of Materials Science NASU, 2019, #25


It is shown in the work that the arrangement of randomly distributed dislocations into polygonization walls occurs due to the absence of symmetry of the intrinsic stresses of dislocations. There is an unstable maximum of intrinsic stresses along the distance to the dislocation. When it is overcome, the tangential stress from the dislocation begins to fall when the probe dislocation becames close, therefore, at a high dislocation density, forming of polygonization walls begins. In the crystal at the very early stages of deformation, regions appear where stresses are reduced or increased compared to the average value; therefore, some regions with an initially increased dislocation density can be “seeds” for the appearance of dislocation walls due to their higher stresses. It has also been shown by the method of dislocation dynamics for dislocations only with an edge orientation that the onset of the process of cell formation depends both on the friction stress of the lattice and on the initial dislocation density. The evolution of the dislocation ensemble continues until the stresses acting on the dislocations are equal to the friction stress. The restructuring of the structure begins only when the critical density of dislocations is reached. Unfortunately, due to the initial heterogeneity of the distribution of dislocations, it is difficult to calculate the critical dislocation density with sufficient high accuracy.

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