Combined atomistic and mesoscale simulation of grain growth in nanocrystalline thin films A.J. Haslam a , D. Moldovan a , S.R. Phillpot a , D. Wolf a, * , H. Gleiter b a Materials Science Division, Argonne National Laboratory, Argonne, IL 60439, USA b Institute for Nanotechnolgy, Forschungszentrum Karlsruhe, Germany Accepted 1 June 2001 Abstract We have combined molecular-dynamics (MD) simulations with mesoscale simulations to elucidate the mechanism and kinetics of grain growth in nanocrystalline palladium with a columnar grain structure. The conventional picture of grain growth assumes that the process is governed by curvature-driven grain-boundary (GB) migration. Our MD simulations demonstrate that, at least in a nanocrystalline material, grain growth can also be triggered by the coor- dinated rotations of neighboring grains so as to eliminate the common GB between them. Such rotation–coalescence events result in the formation of highly elongated, unstable grains which then grow via the GB migration mechanism. These insights can be incorporated into mesoscale simulations in which, instead of the atoms, the objects that evolve in space and time are discretized GBs, grain junctions and the grain orientations, with a time scale controlled by that associated with grain rotation and GB migration and with a length scale given by the grain size. These mesoscale simulations, with physical insight and input materials parameters obtained by MD simulation, enable the investigation of the topology and long-time grain-growth behavior in a physically more realistic manner than via mesoscale simu- lations alone. Ó 2002 Elsevier Science B.V. All rights reserved. Keywords: Grain growth; Grain rotation; Grain-boundary migration; Atomistic simulation; Mesoscale simulation; Multiscale simulation; Nanocrystalline materials 1. Introduction The conventional picture of grain growth, derived from extensive studies of coarse-grained polycrystals, is that the process is driven by the reduction of the total area of the grain boundaries (GBs) in the material (for recent reviews, see [1,2]). The underlying mechanism involves curvature- driven GB migration, i.e., the motion of the GBs towards the center of their curvature. This curva- ture arises from the fact that the Herring relation [3] for the dihedral angles between the GBs joined at the triple junctions cannot be satisfied unless the GBs are curved. For a given grain diameter, d, this curvature is of the order of 1=d ; nanocrystal- line materials are therefore particularly unstable against grain growth, i.e., grain coarsening can Computational Materials Science 23 (2002) 15–32 www.elsevier.com/locate/commatsci * Corresponding author. E-mail address: wolf@anl.gov (D. Wolf). URL: www.msd.anl.gov/groups/im. 0927-0256/02/$ - see front matter Ó 2002 Elsevier Science B.V. All rights reserved. PII:S0927-0256(01)00218-X