ChEMS Seminar: Insight into Defect-Grain Boundary Interactions using Quantitative In Situ Microscopy Techniques

Friday, April 6, 2018 - 3:00 p.m. to Saturday, April 7, 2018 - 3:55 p.m.
McDonnell Douglas Engineering Auditorium (MDEA)
Mitra Taheri

Department of Materials Science and Engineering
University of Drexel, Philadelphia, PA

Abstract: While significant advances have been made in elucidating atomic-scale mechanisms that control properties of polycrystalline materials for a wide range of applications, the need for predictive understanding of material response based on microstructural features still exists. The properties of these materials are dictated by the distribution and organization of defects (from zero to three dimensional) and their interaction with one another. Interfaces, such as grain boundaries, domain walls, and even heterostructure interfaces play a particularly important role in property development. It is the structure, mobility, angle, and strength of these interfaces, and perhaps more importantly, the way in which these interfaces are affected by point defects, dislocations, among other microstructural features, that dictate strength, radiation tolerance, conductivity, and polarization behavior. With the ability to characterize materials behavior with high temporal and spatial resolution, we can potentially fill in gaps in the current understanding of interfacial and defect-driven phenomena that define material properties. In this talk, I will discuss current research of radiation damage at the nanoscale, and how damage mechanisms evolve as a function of grain boundary character. The development of radiation tolerant materials has long been a goal in the nuclear energy community, and various approaches have been taken to tailor microstructure toward in order to defect accumulation. The use of high sink density materials, such as nanocrystalline, multilayered, and even porous materials, has been explored extensively. Additionally, progress has been made with advanced chemistries, such as the use of high entropy alloys, and processing methods, such as grain boundary engineering. What remains unclear is what exactly contributes to defect absorption efficiency in these various interfaces. This talk presents results from systematic studies of absorption processes at characteristic interfaces, or sinks, using in situ and ex situ TEM imaging coupled with quantitative techniques, such as precession electron diffraction and strain mapping. A clear emerging dependence is the role of grain boundary plane. Even with fixed macroscopic degrees of freedom, it is clear that the microscopic degrees of freedom are instrumental in controlling the efficiency of grain boundaries with respect to interstitial absorption. The results provide a platform from which a new model of sink efficiency can be obtained, and have implications in developing thermally stable, radiation tolerant materials.

Bio: Mitra Taheri is the Hoeganaes Associate Professor in the Department of Materials Science & Engineering at Drexel University. At Drexel, she runs the “Dynamic Characterization Group,” which focuses primarily on the use of cutting edge in situ microscopy to develop and characterize various materials. While at Drexel, she has received both the NSF and DOE Early Career awards, an ONR Summer Faculty Fellowship, and has been a visiting scholar at the Politecnico di Milano, in Milan, Italy. Taheri received her Ph.D. in Materials Science & Engineering (MSE) from Carnegie Mellon University. As a Ph.D. student, she received a US Steel Graduate Scholarship, a Materials Research Society Graduate Student Award, a full member to Sigma Xi, and was a visiting scholar at RWTH Aachen University in Germany, the National Center for Electron Microscopy (LBL), and the Northwestern University’s Center for Atom Probe Tomography. Following her doctoral studies, Taheri was an NRC Postdoctoral Fellow at the Naval Research Laboratory (NRL) and a Director’s Postdoctoral Fellow at Lawrence Livermore National Laboratory (LLNL), where she and her group at LLNL won an R&D 100 award, a Nano-50, and the Microscopy Society of America’s Microscopy Innovation Award.

Host:  Martha Mecartney