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The indentation size effect has been linked to the generation of geometrically necessary dislocations that may be impacted by intrinsic materials properties, such as stacking fault energy, and extrinsic defects, such as statistically stored dislocations. Nanoindentation was carried out at room temperature and elevated temperatures on four different metals in a variety of microstructural conditions. A size effect parameter was determined for each material set combining the effects of temperature and existing dislocation structure. Extrinsic defects, particularly dislocation density, dominate the size effect parameter over those due to intrinsic properties such as stacking fault energy. A multi-mechanism description using a series of mechanisms, rather than a single mechanism, is presented as a phenomenological explanation for the observed size effect in these materials. In this description, the size effect begins with a volume scale dominated by sparse sources, next is controlled by the ability of dislocations to cross-slip and multiply, and then finally at larger length scales work hardening and recovery dominate the effect. [ABSTRACT FROM AUTHOR]

Abstract: Measurements of submicron spheres and pillars of silicon single crystals have exhibited a strain-hardening capacity equal to or greater than their metallic counterparts. Stress–strain characteristics are reported for diameters ranging from 40 to 400nm. Evaluations were performed with nanoindentation-based atomic force, scanning and transmission electron microscopies. Values of strain-hardening exponents up to unity in nanospheres are attributed to a size effect variation on the rate of increase of contact area with deformation. A surface-mediated dislocation nucleation concept is shown to be consistent with length scale effects partially modified by geometry as well as size. It is proposed, but not proven, that the modification relates to greater constraint in compact spheres as opposed to tall pillars. [Copyright &y& Elsevier]