Equilibrium Statistical Mechanics of Grain Boundaries (12/06/25)
Speaker and Affliation:
Prof. Nikhil Chandra Admal,
Department of Mechanical Science and Engineering, University of Illinois Urbana-Champaign
When?
12th June, 2025 (Thursday), 3.30 PM (India Standard Time)
Where
KPA Auditorium, Dept. of Materials Engineering, IISc, Bangalore
Abstract:
Grain boundaries (GBs) play a fundamental role in the mechanical behavior of polycrystalline materials. The structure of GBs determines some of their fundamental properties such as their intrinsic energies and mobilities, and interaction with bulk defects like dislocations and vacancies. Traditionally, the macroscopic degrees of freedom (DOFs) — specifically, misorientation and inclination — have served as descriptors for GBs. However, experiments and simulations suggest that macroscopic DOFs alone are inadequate for fully describing GB properties. There is a growing consensus that the atomic-scale configuration of a GB, known as a microstate, has a significant impact on GB-mediated phenomena. Moreover, GBs undergo microstate transformations, which reinforces the importance of exploring these configurations. The primary aim of this work is to establish a statistical mechanics model for GBs, interpreting their effective properties as statistical averages derived from microstates that align with prescribed macroscopic DOFs.
In this talk, we will present a statistical mechanics framework specifically designed for GBs. We will focus on how to enumerate all microstates in a GB ensemble, which is defined by imposing constraints on the macroscopic degrees of DOFs. Since a microstate represents an atomic-scale description of a GB, the microstate space is vast, making it a computationally intensive task to navigate. Given the universal impact of bicrystallography on GB characteristics, we will show that, in stark contrast to the multitude of microstate DOFs, there is a much smaller set of bicrystallography-informed mesoscale DOFs, termed mesostates, that dictate the intrinsic properties of GBs. We will detail the enumeration of GB mesostates and explore the calculation of internal energy, free energy, and entropy of GBs as statistical averages over these mesostates, along with predictions of GB phase transitions observed in experiments and molecular dynamics simulations.
About the Speaker :
Nikhil Chandra Admal is an Assistant Professor in the Department of Mechanical Science and Engineering at the University of Illinois Urbana-Champaign (UIUC). He previously served as a Postdoctoral Research Scholar at UCLA and earned his Ph.D. in Aerospace Engineering and Mechanics from the University of Minnesota. His research focuses on multiscale modeling of interface mechanics in polycrystalline materials and 2D heterostructures, with current work on grain boundary-mediated plasticity, recrystallization, and nanoscale friction phenomena. Prof. Admal received the NSF CAREER Award in 2023.