Molecular simulations using the quasi-continuum method were performed to understand the mechanical response at the nanoscale of grain boundaries under simple shear. The energetics and mechanical strength of 18 Σ <110> symmetric tilt grain boundaries and two Σ <110> asymmetric tilt grain boundaries were investigated in Cu and Al. Special emphasis was placed on the evolution of far-field shear stresses under applied strain and related deformation mechanisms at zero temperature. The deformation of the boundaries was found to operate by 3 modes depending upon the grain boundary equilibrium configuration: grain boundary sliding by uncorrelated atomic shuffling, nucleation of partial dislocations from the interface to the grains, and grain boundary migration. This investigation showed that (1) the grain boundary energy alone cannot be used as a relevant parameter to predict the sliding of nanoscale high-angle boundaries when no thermally activated mechanisms were involved; (2) the E structural unit present in the period of Σ tilt grain boundaries was found to be responsible for the onset of sliding by atomic shuffling; (3) grain boundary sliding strength in the athermal limit showed slight variations between the different interface configurations, but has no apparent correlation with the grain boundary structure; (4) the metal potential plays a determinant role in the relaxation of stress after sliding, but did not influence the grain boundary sliding strength; here it was suggested that the metal potential has a stronger impact on crystal slip than on the intrinsic interface behavior. These findings provide additional insights on the role of grain boundary structure in the deformation processes of nanocrystalline metals.

Mechanical Behavior of Σ Tilt Grain Boundaries in Nanoscale Cu and Al - a Quasicontinuum Study. F.Sansoz, J.F.Molinari: Acta Materialia, 2005, 53[7], 1931-44