IMX Talks - Grain Boundaries are Natural Brownian Ratchets: directional GB anisotropy

The motion of grain boundaries (GBs, i.e., natural defects in polycrystals separating single-crystal grains of different orientations) gives rise to microstructure evolution of polycrystalline materials. 
Classical models for GB motion posit that GB velocity, v=MF, where M is a constant (temperature-dependent) mobility and F is the driving force. 
Reversing the sign of F implies that the magnitude of the GB velocity is unchanged but with motion in the opposite direction. We show that this proposition is true only under a very restrictive set of conditions and a large population of GBs possess directionally-anisotropic migration behavior. We develop a Markov-chain Monte Carlo method that explains this phenomena and demonstrates that the inequivalence of back and forth motion leads to akin to ``Brownian ratchets''. We demonstrate how non-equilibrium thermal/mechanical perturbations can give rise to directional GB migration and show how oscillating stress or temperature accelerates grain growth. Finally, we demonstrate this effect through a novel set of experiments in-situ in a transmission electron microscope.
 
 Bio : David Srolovitz is the author of over 500 research papers on materials theory/simulations of defects, microstructure, deformation, and film growth and has an h-index of 100 and garnered ~36,000 citations.  He is a Member of the US National Academy of Engineering, Fellow of MRS, TMS, ASM, Institute of Physics and is the winner of the MRS Materials Theory Award.  He was a staff member at Exxon Corporate Research and Los Alamos National Laboratory and the Executive Director of the Institute for High Performance Computing in Singapore.  Previously, a professor at Princeton University (department head, institute director, the University of Pennsylvania (institute director), the University of Michigan, Yeshiva University (dean), and the City University of Hong Kong (department head, institute director). He has held faculty positions in Materials Science, Mechanical Engineering, Aerospace Engineering, Computer Science, Physics, Applied Physics and Applied Mathematics.