Dislocation glasses: aging during relaxation and coarsening.

The dynamics of dislocations is reported to exhibit a range of glassy properties. We study numerically various versions of 2D edge dislocation systems, in the absence of externally applied stress. Two types of glassy behavior are identified (i) dislocations gliding along randomly placed, but fixed, axes exhibit relaxation to their spatially disordered stable state; (ii) if both climb and annihilation are allowed, irregular cellular structures can form on a growing length scale before all dislocations annihilate. In all cases both the correlation function and the diffusion coefficient are found to exhibit aging. Relaxation in case (i) is a slow power law, furthermore, in the transient process (ii) the dynamical exponent z approximately 6, i.e., the cellular structure coarsens relatively slowly.

Debye screening of dislocations.

Debye-like screening by edge dislocations of some externally given stress is studied by means of a variational approach to coarse grained field theory. Explicitly given are the force field and the induced geometrically necessary dislocation (GND) distribution, in the special case of a single glide axis in 2D, for (i) a single edge dislocation and (ii) a dislocation wall. Numerical simulation demonstrates that the correlation in relaxed dislocation configurations is in good agreement with the induced GND in case (i). Furthermore, the result (ii) well predicts the experimentally observed decay length for the GND developing close to grain boundaries.

Dislocation patterning: from micro- to mesoscale description

During the plastic deformation of crystalline material the dislocations, being the carriers of the plastic flow, tend to form different patterns. Because of the long range nature of dislocation-dislocation interaction, the origin of this self-ordering phenomenon is still an open question. The paper presents a stochastic two-dimensional model derived directly from the properties of individual dislocations making it possible to investigate the problem on a mesoscale. Numerical results obtained in double slip configuration indicate the development of cell structure with fractal character.