Seminar Speaker: Kinga Unocic, Oak Ridge National Laboratory

Insight into Materials Degradation in Extreme Environments with in situ/operando Electron Microscopy

Abstract

Materials utilized in advanced technologies such as aerospace, nuclear reactors, and power plants are constantly exposed to severe and extreme conditions of temperature, stress, and environmental exposure, the combination of which is known to have a deleterious effect on materials performance, durability, and lifetime. Advanced electron microscopy-based characterization techniques play a vital role in correlating materials’ microstructure to materials degradation phenomena because of multi-length scale imaging and microanalysis capabilities. However, new insight into materials behavior under extreme environments can be further elucidated using in situ microscopy techniques. The recent development of specialized holders for in situ experimentation, coupled with state-of-the-art scanning transmission electron microscopes, are enabling a new level of mechanistic understanding of interfacial chemical reactions for a broad range of materials systems and as a function of temperature, flowing gas, pressure, and/or mechanical stimuli. In this presentation, the nanoscale oxidation mechanisms and kinetics for a model ß-NiAl system were characterized using an in situ STEM-based closed-cell gas reaction (CCGR) system, which permits the direct visualization of dynamic structural and chemical changes during high-temperature oxidation at high spatial resolution. This system is composed of a MEMS-based gas cell with microfabricated heater devices and a controlled gas delivery system. Using this approach, site-specific oxidation initiation sites were identified, Al2O3 oxidation kinetics were measured, and chemical changes were spatially resolved using analytical electron microscopy techniques. In addition to dry gas environments, there is an interest in understanding the role of water vapor on high-temperature corrosion mechanisms. Thermal barrier coatings (TBC) for example are used to protect turbine blades from high-temperature degradation; however, TBC lifetimes can be substantially decreased in the presence of water vapor and combustion gas. The methods and protocols, as well as the many challenges associated with introducing and quantifying water vapor in MEMS-based closed-cell reactor systems, will be discussed in comparison to conventional high-temperature laboratory scale testing. Correlation of in situ testing with laboratory testing is crucial for developing and improving existing computational models.

Biography

Kinga Unocic is a Senior R&D Staff Scientist in the Center for Nanophase Materials Sciences at Oak Ridge National Laboratory. She received her M.S. degree in Metallurgical Engineering from AGH University of Science and Technology in Krakow Poland and her Ph.D. in Materials Science and Engineering from the Ohio State University in 2008. Her current research focuses on developing and applying analytical and in situ/operando electron microscopy techniques to investigate environmental effects on material properties and behavior with an emphasis on innovative materials processing, alloy development, mechanical behavior, radiation effects, high-temperature oxidation, corrosion, and catalysis. She is active in professional societies with leadership roles in the TMS Young Leaders Program (secretary, vice-chair, and chair), the TMS Diversity Committee (vice-chair and chair), TMS Corrosion and Environmental Effects Committee (vice-chair and chair), the TMS High-Temperature Alloys Committee, Additive Manufacturing Bridge Committee and in conference symposia organization for TMS, M&M, MS&T, ICMCTF and NACE. She has received several notable recognitions: the 2010 TMS Young Leader Professional Development Award, the 2017 TMS-JIM Young Leaders International Scholar Award, the 2019 ORNL finalist in the YWCA Tribute to Women, and the 2023 TMS Brimacombe Medalist Award