Molecular dynamic simulations of grain boundary sliding were performed on Cu/Cu one-phase bicrystal and Co/Cu two-phase bicrystal models. The grain boundary sliding and migration behaviors of the Co/Cu bicrystals were different from those of the Cu/Cu bicrystals, and the Co/Cu sliding behavior was less related to the free volume, than that of Cu/Cu. In the Co/Cu(2 2 1) grain boundary model, the pore structure units were formed on the Cu side very near the Co/Cu interface, not just at the interface. The onset of grain boundary sliding in the Co/Cu bicrystals was due to the uncorrelated atomic shuffling induced by the pore structure units. (C) 2009 Elsevier B.V. All rights reserved.