Fully 3-dimensional atomistic molecular dynamics studies were made of strain-induced grain boundary mobility in nanocrystalline Ni at room temperature. The position of a statistically significant number of grain boundaries was monitored as a function of the strain level for a strain rate of 3.3 x 108/s for 2 different interatomic potentials. The results showed the grain boundaries migrating with velocities of 2 to 3m/s, depending upon the interatomic potential used. Detailed analysis of the process showed that grain boundary migration was accompanied by grain rotation and in many cases dislocation emission. The results suggested that grain rotation, grain boundary sliding, and grain boundary migration occurred simultaneously in nanocrystalline metals as part of the intergranular plasticity mechanism. The effects of free surfaces present in the sample on these related mechanisms of plasticity were investigated in detail and it was found that the presence of free surfaces lowers the flow stress observed for the samples and increased the amount of grain boundary sliding, while actually decreasing the average velocity of grain boundary migration parallel to itself. Finally, observations were made of grain coalescence in samples with a free surface. The results were considered in terms of the coupling of grain boundary sliding and migration.

Strain-Driven Grain Boundary Motion in Nanocrystalline Materials. D.Farkas, S.Mohanty, J.Monk: Materials Science and Engineering A, 2008, 493[1-2], 33-40