---

Dan S. Gianola

Ph.D. Candidate, Department of Mechanical Engineering, The Johns Hopkins University

Microsample Tensile Testing of Nanocrystalline Aluminum Thin Films

Nanocrystalline materials have received considerable interest due to deviations in mechanical properties in comparison to their coarse-grained counterparts.   Molecular dynamics and direct transmission electron microscopy studies have evidenced an apparent change in the underlying mechanism that controls plastic deformation in materials with grain sizes that are less than ~50 nm, in which a transition occurs from normal dislocation slip to grain boundary sliding and partial dislocation activity.  Attempts to characterize the mechanisms that govern the mechanical response are inhibited by the challenges associated with direct mechanical testing of submicron thin films.  To link these nanoscale mechanisms with macroscale responses, a unique microsample testing apparatus is utilized to test submicron thin films using various testing modalities.  In addition, the introduction of a novel in-situ peak profile analysis using high intensity synchrotron beams has allowed for the linking of plastic deformation mechanisms to macroscale mechancial behavior.  This technique is based on well known diffraction profile analysis methods, in which the peak broadening is a result of the limitation of coherent scattering volumes (e.g. grain size) and the existence of inhomogeneous lattice strains. The latter has been shown to be caused by dislocation density, dipole polarization, and dislocation character.  This study serves to use these techniques to characterize the unfamiliar mechanisms in nanocrystalline materials.