ChEMS Department Seminar

Event Date/Time: 
January 18, 2018 - 9:10am
Event Location: 
3540 EB
Speaker: 
Shirin Kaboli
ECCI, EBSD and EPSC Characterization of Dislocations and Twins in Polycrystalline Materials Deformed at High P--T Conditions

Abstract

Slip and twinning systems are important mechanisms for plastic deformation of polycrystalline materials under high pressure-temperature conditions. Quantitative characterization of dislocations and twins is performed via electron channeling contrast imaging (ECCI) coupled with electron backscatter diffraction (EBSD) in a field emission scanning electron microscope (FE-SEM). In comparison to trans- mission electron microscopy (TEM) on thin foils, characterization of crystal defects in bulk samples in SEM is advantageous due to a straightforward and non-destructive surface preparation and a wide field of view for statistically reliable results. However, characterization of dislocations is particularly challenging due to the difficulty associated with positioning the bulk sample under known and accurate two-beam diffraction conditions. To overcome this difficulty, I introduce a novel methodology based on analysis of bend contour contrast in ECCI, also known as real space crystallography in TEM. For twin identification, I explain an EBSD-based methodology by comparing the theoretical and experimental pole figures for a specific twin law. Furthermore, I describe in-situ Synchrotron X-ray diffraction deformation experiments and elastic plastic self-consistent (EPSC) modeling to estimate the internal stress state of a material, utilizing the slip and twinning systems identified with ECCI and EBSD. I demonstrate the practice of these techniques in characterization of a number of polycrystalline materials in particular, magnesium alloys, α-alumina and diopside minerals deformed at high pressure-temperature conditions.

Bio

I have a multidisciplinary background beginning in Materials Science and Engineering and extending to Geoscience and High Pressure Physics. I completed a Ph.D. in Materials Engineering at McGill University in 2015. I then took a postdoctoral research position at the High Pressure Science and Engineering Center (HiPSEC) at the University of Nevada, Las Vegas (UNLV). My research is focused on under- standing the mechanical behavior of polycrystalline materials at high pressure-temperature conditions and interaction between deformation processes and phase transformations. For high pressure experimentation, I conduct in-situ Synchrotron X-ray diffraction deformation experiments at the Advanced Photon Source (APS) at the Argonne National Laboratory (ANL). Materials under study span a wide range including metals and alloys, ceramics and Earth materials. I perform quantitative characterization of crystal defects at the nanoscale using channeling and diffraction-based techniques in a field emission scanning electron microscope (FE-SEM). Combinations of these experimental and analytical techniques help with a better understanding of the grain-scale processes that control the large-scale mechanical behavior of polycrystalline materials.