Place: Euromat 2009, Glasgow, UK
For ultra-fine grained and nanocrystalline metals grain boundary sliding is considered to contribute significantly to the plastic deformation and hence to the exceptional properties of these materials, i.e. high strength combined with large ductility. Grain boundary sliding is determined by details of the atomistic structures and the strength of the inter-atomic bonds across the grain boundary. Density functional theory (DFT) calculations are performed to quantify generalized-stacking fault energy (γ) surfaces of bulk aluminum ((111) plane) and of different grain boundaries (Σ3 symmetric tilt, Σ3 and Σ11 symmetric twist grain boundary). This allows us to describe the atomistic structures as well as possible paths of grain boundary sliding. The climb-nudged elastic band method is used to calculate the transition paths for grain boundary sliding and to quantify the threshold stresses to initiate this process. Knowing the threshold stress for grain boundary sliding and the work of separation for grin boundary fracture enables us to model dislocation-grain boundary interaction as well as the competition between grain boundary sliding and fracture.