People have been using metals and alloys for thousands of years and have constantly improved their strength and performance through developing new ways to make them. This process of improving the metals has relied largely on guess and check. Although people have become better at guessing and faster at checking, the foundational knowledge to intelligently design stronger, safer, more resilient metals is still missing. Part of the challenge in improving metals and alloys is that their performance is dependent on the type, density, and distribution of trillions of defects that are not much bigger than a few atoms. Two important types of these defects are dislocations, which allow metals to deform, and grain boundaries, which act as barriers to dislocations as they move through the metal. The character of a grain boundary influences how easily dislocations can move through the material, and in turn, affects the strength of the metal. However, a direct link between the character of a grain boundary and how strong of a barrier it is to dislocation motion has not been established. By looking at grain boundaries at ultra-small length scales of one millionth of a meter and smaller, this project will establish that direct link. To do so, electron microscopes, capable of imaging materials down to the level of individual atoms, will be used to see how dislocations accumulate in the material near grain boundaries while the material is being bent. Artificial intelligence (AI) will be built into the electron microscopes in order to rapidly and automatically explore tens of thousands of grain boundaries to obtain a statistical understanding of how grain boundary character is connected to its strength. This understanding will be instrumental in guiding the development of new metals and alloys that are stronger, safer, and longer lasting in application. The broader outreach of this work includes integrating high school students from underrepresented communities in a summer internship research program. These interns will work closely with graduate students supported by the program to investigate the strength of metals and will also develop lesson plans incorporating virtual reality elements to take back to their classes in the following school year. The summer internship will also include visits to the Novelis research center, a global Al company with research headquarters near Atlanta.
The central role of grain boundaries has long been recognized in dictating the mechanical behavior and failure susceptibility of metals and alloys. However, efforts to understand how variations in grain boundary characteristics affect material properties have been hampered by an incomplete understanding of what determines the strength of individual grain boundaries. The purpose of this project is to determine the characteristics that dictate grain boundary strength, here defined as the barrier strength that grain boundaries pose to dislocation propagation. A new adaptive remeshing electron backscatter diffraction (AR-EBSD)-based approach will be developed, combining in-line processing and automated adaptive grid remeshing to rapidly sample the tens of thousands of grain boundaries needed to build a library to which machine learning approaches can be applied. This approach will be coupled with transmission electron microscopy (TEM) characterization and atomistic simulations to correlate grain boundary strength with dislocation transfer mechanisms. This coupled approach will facilitate an unprecedented exploration of grain boundary space in terms of the number of grain boundaries investigated, allowing rigorous grain boundary strength functions to be established. In addition, the multiscale electron microscopy techniques developed over the course of the proposed work will be a widely applicable addition to the materials characterization toolbox in investigating material deformation under ambient and extreme conditions. Furthermore, a pipeline for underrepresented minorities to engage in STEM research will be created by a “visualizing science†summer internship program for high school students from underrepresented communities. These interns will work with graduate students supported by this program to investigate the ductile fracture behavior of metals, learn mechanical testing and characterization techniques, and visit the Novelis research center, a global Al company with research headquarters near Atlanta. To enhance the broader impact of this program, the interns will also develop lesson plans incorporating virtual reality elements to take back to their high school classes.
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.
