MSE Colloquium: Yuri Mishin, Stress-driven grain boundary motion and grain rotation

Professor, Department of Physics and Astronomy, George Mason University

All dates for this event occur in the past.

264 MacQuigg Labs
105 W. Woodruff Ave.
Columbus, OH 43210
United States

Abstract

 

mishin_fig1.jpg

Recent research has led to the recognition that many grain boundaries (GBs) in crystalline materials can couple to applied shear stresses and are moved by them in a manner similar to dislocation glide. For curved GBs, this “coupled” GB motion creates a driving force for grain rotation. These coupled processes can lead to interesting phenomena in polycrystalline, and especially nanocrystalline materials, such as stress-induced grain growth and stress-induced grain rotation.

This talk will provide a brief overview of the current knowledge of the coupling effect, focusing on recent molecular dynamic (MD) simulations of grain shrinkage, growth and rotation. The coupling effect can lead to an unusual process in which the rotation increases the misorientation angle and thus the GB free energy. At very high temperatures, the grain rotation can cause GB premelting and eventually melting of the material. Applied shear stresses can accelerate, retard or even reverse the grain shrinkage, leading to stress-induced grain growth. The dynamics of grain rotation observed by MD are compared with existing theoretical models.

 

mishin_fig9.jpg

The simulations demonstrate that the grain shrinkage is always accompanied by both coupled GB motion and GB sliding. Sliding of a curved GB always requires a change of its dislocation content, i.e. either annihilation or creation of dislocations. The MD simulations indicate that propagation of dislocation content along the GB by a chain of dislocation reactions can be responsible for the dislocation annihilation and GB migration. The impact of coupled GB motion and grain rotation on materials phenomena is discussed.

Bio

Yuri Mishin is Professor of Physics at George Mason University, Virginia. He obtained a MS degree in Metal Physics and PhD degree in Solid State Physics from the Moscow Institute of Steel and Alloys, Russia. After working for a few years at the National Institute of Aviation Materials in Moscow, he received an Alexander von Humboldt Research Fellowship to continue research on diffusion in metals and alloys at the University of Muenster, Germany. He worked for a few years at Virginia Tech (MSE Department) before joining George Mason University. Mishin’s research interests include theory of phase transformations in alloys; thermodynamics, kinetics and statistical mechanics of materials interfaces; atomic interaction models for large-scale simulations; modeling and simulations of mechanical behavior of materials, and a number of other topics. He developed several widely used models of interface diffusion, constructed several widely used atomistic potentials, and proposed a number of generalizations of interface thermodynamics to solid-fluid and solid-solid interfaces in materials.