PURDUE
U N I V E R S I T Y
MSE SEMINAR
Dr. Josh Kacher
Department of Materials Science and Engineering
University of California, Berkeley
“In situ and tomographic characterization of dislocation-defect interactions”
Abstract
Transmission electron microscopes have played a critical role in building our knowledge base of the
atomic structure and composition as well as the electronic and magnetic state of materials. This
information is given as a two-dimensional snapshot of the material state and requires a posteriori analysis
to reveal the reaction or processing pathway, or to correlate with a macroscopic property. However, using
electron tomography it is feasible to reconstruct from a series of images a three-dimensional
representation of the internal structure in an electron transparent foil. In this talk, I will demonstrate how
electron tomography can be applied to dislocation/defect interactions using diffraction contrast imaging.
Additionally, I will present a number of techniques that facilitate the combination of three-dimensional
analysis with in situ deformation in the electron microscope, providing quasi-four dimensional analysis of
dislocation interactions. This approach will be applied to understanding fundamental material deformation
mechanisms including dislocation interactions with grain boundaries and strain instabilities during the
deformation of Al-Mg alloys.
Bio
Josh Kacher received his B.S. in applied physics from Brigham Young University in 2008 and a Masters
in mechanical engineering in 2009. He received a Ph.D. in materials science and engineering under the
advisory of Professor Ian Robertson from the University of Illinois at Urbana-Champaign in 2012. His
work there focused on understanding dislocation interactions with defects such as grain boundaries using
innovative in situ TEM deformation and electron tomography techniques. Currently, he is a post doctoral
research associate working with Professor Andrew Minor at the University of California, Berkeley. His
research interests include understanding the dislocation mechanisms responsible for the Portevin-Le
Chatelier effect in Al-Mg alloys as well as working with computational groups to develop and characterize
novel dilute rhenium alloys.
Date: Monday, December 8, 2014
Time: 9:30-10:30 am
Location: PHYS 238