Abstract

Size effects in plasticity have received much attention in recent years, due to increased resolution in experimental capabilities, and the development of materials at small geometric and microstructural length scales. In particular, the hardness of many materials have been shown to decrease with increasing depth of indentation, the so-called indentation size effect (ISE). In order to circumvent the coupled effects of extrinsic strain gradients, as are encountered in nanoindentation, microcompression testing is perhaps the most straight forward method to understand the effect of geometric length scale on deformation behavior. In these experiments, a columnar structure is fabricated, typically using Focused Ion Beam (FIB) machining from a thin film or bulk specimen, with diameters on the order of tens of microns down to 100 nanometers. The columns are then compressed using a nanoindenter outfitted with a flat punch indenter. As in the indentation experiments, results for many materials show a general trend of increasing strength with decreasing deformation volume. However, the result is not ubiquitous. In this talk, results from both indentation and microcompression experiments in microstructurally varied materials (e.g., single crystalline, fine-grained, nano-porous metals) will be presented. The extent to which a material exhibits a size effect in strength will be discussed in terms of microstructure (in relation to the mean free path for dislocation motion) and the effect of finite size on self organized critical behavior.