Dislocation-Source Shutdown and the Plastic Behavior of Single-Crystal Micropillars

Dislocation dynamics simulations have been used to study the stress-strain response of single-crystal micropillars containing initial dislocation networks generated via a relaxation procedure intended to approximate real thermal annealing processes. We find that, when such networks are loaded, they exhibit periods of plastic deformation, caused by the operation of single junction-stabilized spiral sources, followed by intervals of purely elastic straining when the sources shut down. The results provide insight into the mechanisms responsible for the experimentally observed staircase stress-strain behavior.

Figure 1

Dislocation configurations in a single-crystal micropillar oriented in the $[0\overline{1}1]$ direction. (a) Dislocation configuration before relaxation. (b) Dislocation network arising from full relaxation of the dislocation structure displayed in (a).

Figure 2

Stress-strain curves corresponding to three different initial dislocation configurations in 400-nm-diameter micropillars. The initial dislocation densities are about the same for all three configurations. The sensitivity of the stress-strain responses to the initial dislocation configurations is clearly observed.

Figure 3

Schematic diagram of a typical dislocation-source configuration. Under uniaxial compression, the dislocation line lying on the slip plane experiences the external loading and glides on the slip plane. Note that the joint node O must moves along the intersection line CD. When the joint node meets the surface, the dislocation source ceases to operate.