Discrete dislocation simulation of the ultrasonic relaxation of non-equilibrium grain boundaries in a deformed polycrystal

For the first time, the relaxation of disordered dislocation arrays in a model 3 x 3 columnar polycrystal under ultrasonic action is studied using the discrete dislocation approach. A l l grains contain three non-parallel slip systems located at an angle of 60 degrees to each other. The non-equilibriu m state of the grain boundaries is modeled using two finite edge dislocation walls with Burgers vector of opposite signs, which are equivalent to a wedge junction disclination quadrupole. It is shown that ultrasonic treatment causes a significant rearrangement of the lattice dislocations and their gliding towards the grain boundaries. It results in a decrease in the internal stress fields associated with the presence of non-equilibriu m grain boundaries and relaxation of dislocation structure. The model predicts an existence of optimal amplitude, at which the maximu m relaxing effect can be achieved. Dependence of the relaxation of dislocation structure on the grain size is also investigated .