A modified synthetic driving force method for molecular dynamics simulation of grain boundary migration

The synthetic driving force (SDF) molecular dynamics method, which imposes crystalline orientation-dependent driving forces for grain boundary (GB) migration, has been considered deficient in many cases. In this work, we revealed the cause of the deficiency and proposed a modified method by introducing a new technique to distinguish atoms in grains and GB such that the driving forces can be imposed properly. This technique utilizes cross-reference order parameter (CROP) to characterize local lattice orientations in a bicrystal and introduces a CROP-based definition of interface region to minimize interference from thermal fluctuations in distinguishing atoms. A validation of the modified method was conducted by applying it to simulate the migration behavior of Ni < 1 0 0 > and Al < 1 1 2 > symmetrical tilt GBs, in comparison with the original method. The discrepancies between the migration velocities predicted by the two methods are found to be proportional to their differences in distinguishing atoms. For the Al < 112 > GBs, the modified method predicts a negative misorientation dependency for both the driving pressure threshold for initiating GB movement and the mobility, which agree with experimental findings and other molecular dynamics computations but contradict those predicted using the original method. Last, the modified method was applied to evaluate the mobility of Ni Sigma 5 < 1 0 0 > symmetrical tilt GB under different driving pressure and temperature conditions. The results reveal a strong driving pressure dependency of the mobility at relatively low temperatures and suggest that the driving pressure should be as low as possible but large enough to trigger continuous migration. (C) 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.