Atomic structures of symmetrical and asymmetrical facets in a near Σ = 9{2 2 1} tilt grain boundary in copper

Atomic structures in a Σ = 9{2 2 1} tilt grain boundary (GB) grown by Bridgman solidification of a tricrystal are determined through high-resolution transmission electron microscopy and numerical simulation. Atomic models are simulated via molecular dynamics annealing using an n-body potential fitted on copper properties including its stacking fault energy. Symmetrical and asymmetrical facets are thus identified. Mainly asymmetrical facets are observed, namely Σ = 9{11, 11, 1}||{1 1 1} and also small parts of incommensurate {1 1 0}||{1 1 1}. The symmetrical facets are described by a quasi-mirror plane atomic structure. A specific GB structural unit is recognized as a Lomer unit. Its GB Burgers vector depends on the GB structure itself. Further analyses of these models and of accommodating dislocations are successfully carried out at the atomic level within the framework of the continuous structural unit approach.