Testing thermal gradient driving force for grain boundary migration using molecular dynamics simulations

Strong thermal gradients in low-thermal-conductivity ceramics may drive extended defects, such as grain boundaries and voids, to migrate in preferential directions. In this work, molecular dynamics simulations are conducted to study thermal-gradient-driven grain boundary migration and to verify a previously proposed thermal gradient driving force equation, using uranium dioxide as a model system. It is found that a thermal gradient drives grain boundaries to migrate up the gradient, and the migration velocity increases under a constant gradient owing to the increase in mobility with temperature. Different grain boundaries migrate at very different rates owing to their different intrinsic mobilities. The extracted mobilities from the thermal-gradient-driven simulations are compared with those calculated from two other well-established methods, and good agreement between the three different methods is found, demonstrating that the theoretical equation of the thermal gradient driving force is valid, although a correction of one input parameter should be made. The discrepancy in the grain boundary mobilities between modeling and experiments is also discussed. (C) 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.