Speaker:Yuri Mishin, Physics, George Mason University

Title: Atomic structure and dynamics of grain boundaries

Abstract: Grain boundaries are critical elements of materials microstructure. I will start by reviewing their geometric description and atomic structure as revealed by computer modeling and experimental observations. While low-temperature grain boundary structure is well ordered and can be readily described by the structural unit model, most boundaries become increasingly disordered with temperature and turn into a liquid-like layer near the bulk melting point. After discussing possible driving forces of grain boundary motion, I will focus on the recently discovered "military" mechanism of this process, which is observed at relatively low temperatures. In this mechanism, grain boundaries can be moved by applied shear stresses; in turn, grain boundary motion produces shear deformation of the material traversed by the boundary. This motion coupled to shear deformation occurs by highly coordinated atomic displacements and does not require atomic diffusion. It displays a variety of dynamic regimes ranging from stick-slip behavior to strongly driven Brownian motion, to random walk. There is an interesting parallel between the coupled boundary motion and sliding friction of surfaces. I will conclude by discussing some of the recently proposed models and atomistic computer simulations of the nonlinear dynamics of this process.

Time: Friday, October 5, 2007, 1:00-2:00 p.m.

Place: Science and Technology Building I, Room 242

Presentation files: [pdf]

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