Dislocation Patterns: Experiment, Theory and Simulation

Abstract

Dislocations are the elementary carriers of plastic flow. It follows that understanding the mechanical properties of crystalline solids involves the knowledge of the basic properties of dislocations, of their dynamics and of their interactions with various types of obstacles. Among the latter, the most troublesome are dislocation themselves, as the mutual interactions of dislocations are both short and long ranged. When dislocation-dislocation interactions are predominant, the flow properties of a material depend on individual as well as collective dislocation properties in a complex manner which is still not well understood. The most striking feature is, then, the spontaneous formation of organized patterns consisting of alternating dislocation-rich and dislocation poor regions (e.g., cells, subgrains, veins or walls, channels…). These microstructures exhibit more or less well-defined periodicities, usually in the micrometer range. Such collective phenomena are relatively unimportant at small strains, since the total dislocation density is small. They may, however, play a prominent role on flow properties as soon as the total dislocation density stored in the deforming crystal reaches a critical value. It follows that investigations on dislocation patterning are important in two respects, -i) as an example of self-organization in a dynamical system and -ii) as a necessary intermediate step in the view of developing more physical approaches of plasticity, based on dislocation theory. For an extensive review of these questions, see Kubin (1993).