Simulation of the Effect of Ultrasound on the Dislocation Structure of Deformed Polycrystals

Abstract

Computer simulation was used to study the relaxation of disordered systems of dislocations in the stress field of nonequilibrium grain boundaries upon ultrasonic treatment (UST). The effect of ultrasound is simulated by an oscillatory shear stress applied to the crystal. Edge dislocations in a model grain with three nonparallel slip systems located at an angle of 60° to each other were examined. The nonequilibrium state of grain boundaries is simulated with the aid of a quadrupole of wedge disclinations located at its junctions. This study showed that the UST caused a rearrangement of the dislocation structure and led to a reduction of internal stresses. The amplitude of ultrasound and the degree of the nonequilibrium state of grain boundaries (strength of the disclination quadrupole) significantly affect the relaxation of the dislocation structure. There are optimum values of the UST amplitude, at which a maximum reduction of the internal stresses is achieved. This study also investigated the dependence of the degree of relaxation of internal stresses on the amount of dislocations in the grain.