Dislocation pattern formation - Simulations of annealing in two dimensions

A two-dimensional discrete dislocation dynamics code was developed and used to simulate dislocation patterning. For the present study of annealing, both glide and some climb were allowed in the simulations. In these circumstances patterning takes place even in the absence of external stresses and of dislocation sources. A triangular underlying lattice was assumed, with the three slip systems equally populated initially. Well-defined dislocation walls and cells are observed to form from random initial conditions. The structure coarsens with time, i.e. the typical size of the cells increases as annealing takes place (the smaller cells shrink and disappear from the structure). In the spirit of a bottom-up multiscale approach, a new simulation methodology is suggested, in which the discrete moving objects are dislocation wall segments rather than individual dislocations. The most important rule governing the dynamics of the dislocation walls is local conservation of the net Burgers vector. The new coarse-grained simulation method is designed to give much closer correspondence with the "microscopic" discrete dislocation dynamics results than previously available approaches.