SIMULATION OF DISLOCATION MICROSTRUCTURES IN 2 DIMENSIONS .2. DYNAMIC AND RELAXED STRUCTURES

Dynamic dislocation structures produced by externally applied stresses and mutual interaction forces, and relaxed structures formed after the removal of the applied stresses, have been simulated by a computer technique based on molecular dynamics. The model employs a two-dimensional array of straight, mixed dislocations on orthogonal slip planes. Equations of motion which account for viscous drag in glide and climb motion, inertial forces, externally applied stresses and interaction forces due to other dislocations are integrated under boundary conditions which simulate various deformation conditions. Specifically, low-temperature deformation under constant stress and cyclic stress, where dislocation motion is restricted to glide, and high-temperature deformation under constant stress, where both glide and climb are permitted, are investigated. Low-temperature deformation is characterized by the formation of cell-like structures at relatively low applied stresses, where the interaction between dislocations dominates dislocation motion, and by random structures at high stresses, where the applied stress is more important. Cyclic stresses lead to cell formation at all levels and frequencies investigated. Relaxed structures generally possess a regularity having characteristics dependent on the severity and type of prior deformation. High-temperature deformation followed by relaxation is characterized by random structures of lower total dislocation density than the initial structures, due to annihilation of dislocations and the greater degree of freedom for motion provided by climb.