Dislocation structures and their relationship to strength in deformed nickel microcrystals

The present work uses focused ion beam methods to prepare samples for transmission electron microscopy in order to quantitatively characterize changes in the dislocation substructures obtained from undeformed and deformed pure Ni microcrystals having sample diameters that range from I to 20 mu m. Following deformation, the dislocation density measured in the microcrystals is on average in excess of their expected initial density, with an apparent trend that the average density increases with decreasing microcrystal size. These dislocation density data are used to assess the contributions of forest hardening to the flow strength of the microcrystals. The combined effects of lattice friction, source-truncation hardening and forest hardening are found to be insufficient to fully account for the large flow strengths in smaller microcrystals. (C) 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.