THE MECHANISMS OF PLASTIC RELAXATION IN SINGLE-CRYSTAL DEFORMATION

Plastic flow in crystals is never quite uniform. Plastic strain gradients develop and internal stresses build up as deformation progresses. In the last few years it has been suggested that specific dislocation mechanisms of plastic relaxation relieve these stresses and create the microstructure. These mechanisms are described. The first mechanism to operate is cross-slip, which lays down the framework of dislocation cells. The second mechanism is secondary slip, which completes the formation of relatively stress-free dislocation cells and subdivides the crystal into mutually misoriented regions. The third mechanism, which operates when the microstructure contains cells, is local slip within dislocation-rich load-bearing cell walls. Depending on the orientation of the cell walls, this third mechanism produces either work hardening or dynamic recovery.