Microstructure matters: why smaller is often (but not always) stronger
Event details
| Date | 30.09.2013 |
| Hour | 13:15 |
| Speaker |
Dr. Erica Lilleodden, Helmholtz-Zentrum Geesthacht, Germany Bio: Erica Lilleodden is a Materials Scientist at Helmholtz-Zentrum Geesthacht in Germany. Her research efforts are focused on mechanisms of deformation and fracture in structural materials, with particular interest in the effects of microstructural and geometric length-scales. She received her Ph.D in 2002 from Stanford University, working with W.D. Nix on size effects in plasticity of metallic thin films. She then spent nearly 3 years at Lawrence Berkeley Laboratory and University of California Berkeley as a Post Doctoral Fellow and Lecturer, where she used micro-Laue diffraction and in situ TEM techniques to study heterogeneities in plastic deformation. She moved to Germany in 2004 as a Humboldt Fellow at the Forschungszentrum Karslruhe investigating the deformation of nanoporous gold and developing small-scale mechanical testing methods. In 2006 she moved to the Institute of Materials Research at GKSS (now called Helmholtz-Zentrum Geesthacht), where she is Head of the Department of Experimental Materials Mechanics (since February 2010). |
| Location | |
| Category | Conferences - Seminars |
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 has become a widely used 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. It is demonstrated here that the critical parameter which dictates the presence of a size effect is not the sample size or deformation volume alone, but rather the relative deformation length-scale relative to the representative microstructural length-scale. This observation holds for both microcompression and conventional nanoindentation experiments, and can be used to model size effects in terms of classical laws. The talk will focus on single crystalline, high purity Mg and the Mg alloy AZ31 of two orientations associated with dislocation plasticity (i.e., no twinning), where the active slip systems for the two orientations have significantly different Peierls barriers. In this way, the influence of intrinsic lattice strength and alloying content can be differentiated. Additional results from other “microstructurally rich” materials will also be drawn upon to support a picture of size effects in plasticity as dependent on the interplay between microstructural and geometric length-scales.
Practical information
- General public
- Free
Organizer
- Frauenrath Holger [[email protected]]
Contact
- Frauenrath Holger [[email protected]]