ACTIVE SLIP IN ALUMINUM MULTICRYSTALS

Plate-type tensile specimens composed of 1-6 large pure-aluminum grains were characterized carefully for grain shape and orientation. They were then deformed to strains between 1-8%, the stress-strain curves were recorded, and the slip traces or etch pits were analyzed using optical microscopy. In parallel, the internal stress fields in the specimens were calculated using anisotropic elastic finite element modeling. These techniques allowed a resolved shear stress (RSS) to be associated with each observed slip system. Observed were 84 {111} and 4 {110} slip planes. Dislocation nucleation was inferred to have taken place at grain boundaries, specimen edges, existing slip bands, and at grain interiors. Three general kinds of nucleation events were inferred: (1) a wholly RSS-driven event at specimen edges or grain boundaries and extending for long distances in the crystals, (2) an RSS-assisted/local dislocation mechanism at grain boundaries that also extends for large distances but which nucleates at moderate RSS's, and (3) local mechanisms which can occur at very low RSS and which usually remain local, near grain boundaries, existing slip bands, and other microstructural features. Other generalizations are drawn from the large body of data generated from these experiments and calculations.