MSE Virtual Seminar Series: Ashwin Shahani, University of Michigan

Description

Revealing new modes of grain growth at elevated temperatures via three-dimensional X-ray microscopy

Ashwin Shahani, University of Michigan

A wide range of physical systems are composed of domains of different crystallographic orientation, from dusty plasmas to colloidal crystals to polycrystalline metals. The stability of granular materials depends on the motion of the grain and interphase boundaries. Such boundaries are non-equilibrium defects and are thus expected to evolve over time during annealing. Our traditional understanding is that the capillary pressure across a grain boundary drives its migration. However, this view alone cannot explain the richness in grain growth dynamics. This is because it does not take into account many other confounding factors that perturb boundary trajectories, such as a local density of second phase precipitates and stored strain energy in dislocations. The microstructural consequences of these effects remain an enigma, due to the lack of suitable models and also the difficulty in reconstructing the interfacial dynamics through a post mortem characterization. Our goal is to shine new light on the underlying microstructural evolution through nondestructive laboratory- and synchrotron-based imaging. Our work integrates multiple techniques, including X-ray absorption and diffraction tomography, to watch grain growth in three dimensions and as a function of time. Following the in situ experiments, advances in data science methods and high performance computing open the doors to a wealth of information on the interfacial orientations, curvatures, and velocities. These metrics provide direct evidence of new and unexpected mechanisms of grain growth, including grain rotation and translation. They also serve as benchmark data that can be used to inform and validate simulations, e.g., molecular dynamics and phase field.

Dr. Ashwin J. Shahani is an Assistant Professor in the Department of Materials Science and Engineering at the University of Michigan. He earned his BS degree from Cornell University and his PhD degree from Northwestern University, both in the field of Materials Science and Engineering. His research group specializes in the development and application of in situ characterization methods for the study of phase and structural transformations in metals, from solidification to grain growth. His awards include the Air Force Young Investigator Research Program in 2017, the Army Young Investigator Research Program in 2018, and the National Science Foundation CAREER Award in 2019.

For Webinar information please contact Kyle Page (kmp265@cornell.edu)