Abstract

Dr. Kevin Hemker
Johns Hopkins University

"Characterizing the Mechanical Behavior of Materials for MEMS and Nanocrystalline Metals"

Monday March 3, 2008
4:00 - 5:00 pm
WIL Room 101
Please join us beforehand for refreshments

ABSTRACT:

Abstract: Micro-tensile testing and TEM have been employed to characterize the small-scale and scale-specific mechanical behavior of materials for MEMS and nanocrystalline thin films. MEMS structures are often deposited far from microstructural equilibrium and the mechanical properties of these materials will be shown to be strongly processing, microstructure and temperature dependent. The extremely high hardness and strength of nanocrystalline materials have been well-documented, but operative deformation mechanisms in these materials have proven to be much harder to quantify. In the second study, recent experimental observations of twinning and grain growth in nc-Al will be used to underscore the novel deformation mechanisms operative in nanocrystalline metals.

Of particular interest is the extended plasticity that occurs as a result of stress-induced discontinuous grain growth. Efforts to model this growth with traditional driving forces have proven less than satisfactory, and the importance of grain boundary pinning and the role of stress assisted grain boundary migration appear to be more important. The significance of this finding with respect to the reliability of thin film nanocrystalline devices cannot be ignored, as the mechanical behavior of these structures appears to not only be different than that of microcrystalline metals but dynamic as well.

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