CAREER: Role of Grain Boundary Complexion Transformations on Long-Range Interfacial Diffusion Effects

About This Grant

NON-TECHNICAL SUMMARY Movements of atoms in solids govern many material properties and behaviors. For example, Li ions must move through solid-state batteries to release electricity, and then move back again to recharge. The known ‘highways’ of atomic motion are atomic-scale interfaces that exist between atomic building blocks called grains. Such interfaces are therefore called grain boundaries. While atoms are known to quickly move through grain boundaries, it is unclear how the rate of atomic motion changes if the atomic structures or chemistry of the grain boundaries change as well. It is possible that the rate of atomic motion may change by several orders of magnitude. This project studies how changes in grain boundaries directly affect long-range movement of atoms. Experiments examine atomic motion by studying uniquely fabricated ceramics that are made of bonded samples with different compositions, which causes certain atoms to move from one side to the other, and a variety of advanced electron microscopes are used to characterize materials on the atomic-scale. Computational models are also employed to complement experiments and understand how materials behave on the molecular level. The overall mission of this research has a wide-ranging impact on several industries related to the energy transition planned by the United States. For example, new knowledge gained from this research is likely to provide new insights about hydrogen degradation effects on steels while transporting or storing hydrogen gas, or metal dusting degradation effects on Ni alloys that are used in petrochemical plants. This research also focuses on boosting education outcomes of students at the University level as well as in grades K-12. Hands-on ceramic processing demonstrations are teaching K-12 students how ceramic materials are made, and virtual/mixed reality modules are used to accelerate training on electron microscopes and expose younger generations to how we characterize materials using state-of-the-art research facilities. TECHNICAL SUMMARY This CAREER project investigates effects of grain boundary complexion transitions on long-range mass transport in bulk ceramics and develops virtual and mixed reality applications to (i) reinvigorate materials-related curriculum at Louisiana State University and (ii) educate K-12 students, their parents, and their teachers. The research is based on prior knowledge that grain boundary complexion transformations discontinuously change bulk material behavior, yet atomic-scale mechanisms associated with diffusivity through various complexions remain unknown. This proposal evaluates grain boundary thermodynamics in ceramic diffusion couples, involves atomic-resolution microanalysis of interfaces, and uses Monte Carlo grain growth simulations of complexion-driven abnormal grain growth, while also employing in-situ electron microscopy experiments and Density Functional Theory calculations. The project is divided into 2 Research Objectives: (I) Identify Mechanisms of Discontinuities in Grain Boundary Diffusivity Related to Grain Boundary Complexion Transitions, and (II) Elucidate Effects of Interfacial Diffusion on Complexion Propagation and Microstructure Evolution. The Education Objective is to develop virtual and mixed reality training modules for electron microscopes, namely a scanning electron microscope training module for an undergraduate technical elective course, and a transmission electron microscope training module for advanced users. The Outreach Objective is to inspire K-12 students by using hands-on experiments related to ceramic processing and interactive virtual reality activities. Overall, this work provides a universal understanding of interfacial solid-state diffusion, thereby providing new insights useful to solving issues related to the energy transition, such as (i) hydrogen permeation and embrittlement in iron and nickel alloys, (ii) metal dusting degradation in steels and superalloys, and (iii) interfacial transport efficiency in next-generation solid-state ion batteries. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.