Grain boundary influence on material properties became increasingly significant as grain size was reduced to the nanoscale. Nanostructured materials produced by severe plastic deformation techniques often contained a higher percentage of high-angle grain boundaries in a non-equilibrium or energetically metastable state. Differences in the mechanical behaviour and observed deformation mechanisms were common due to deviations in grain boundary structure. Fundamental interfacial attributes such as atomic mobility and energy were affected due to a higher non-equilibrium state, which in turn affects deformation response. In this research, atomistic simulations employing a biased Monte Carlo method were used to approximate representative non-equilibrium bicrystalline grain boundaries based upon an embedded atom method potential, leveraging the concept of excess free volume. An advantage of this approach was that non-equilibrium boundaries could be instantiated without the need of simulating numerous defect/grain boundary interactions. Differences in grain boundary structure and deformation response were investigated as a function of non-equilibrium state using Molecular Dynamics. A detailed comparison between copper and aluminium bicrystals was provided with regard to boundary strength, observed deformation mechanisms, and stress-assisted free volume evolution during both tensile and shear simulations.

Non-Equilibrium Grain Boundary Structure and Inelastic Deformation Using Atomistic Simulations. G.J.Tucker, D.L.McDowell: International Journal of Plasticity, 2011, 27[6], 841-57