The collective grain movement of nanocrystalline metals and its temperature dependence were studied by using molecular dynamics simulations. First, a unit structure that consisted of eight Al grains in the regular hexagonal shape with 5nm grain size was prepared, and then an analysis model was made by arranging the same 144 unit structures in the 2-dimensional periodicity. Thus the total number of grains was 1152. Various collective grain deformations occurred at different temperatures under tensile loading. In the case of 100K, shear bands formed by the collective grain deformation could be observed remarkably. On the other hand, in the case of 300 or 500K, no remarkable inhomogeneous deformation such as shear bands occurred. This might be due to the different accommodation mechanism for geometrical misfits by local shear deformation at each different temperature. In order to investigate the effect of the collective grain deformation on the macro-scale mechanical properties, the stress–strain curve for the model with 144 unit structures and an averaged strain–stress curve for the 60 cases of a model with one unit structure were compared. Consequently, it was found that the inhomogeneous plastic deformation mode such as a shear band could influence the strength of nanocrystalline metals.

Collective Grain Deformation of Nanocrystalline Metals by Molecular Dynamics Simulations. T.Shimokawa, T.Kinari, S.Shintaku, A.Nakatani: Modelling and Simulation in Materials Science and Engineering, 2006, 14[5], S63-72