Shear response of the Σ9 ⟨110⟩ {221} symmetric tilt grain boundary in fcc metals studied by atomistic simulation methods

The shear response of the $\ensuremath{\Sigma}9⟨110⟩{221}$ symmetric tilt grain boundary (GB) in three fcc metals Cu, Al, and Ni has been studied by atomistic simulation methods with the embedded atom method for interatomic potentials and with a bicrystal model. By applying an energy minimization procedure, it was found that there are two optimized structures of this particular GB at zero temperature for all the three metals studied. Shear of bicrystals at room temperature has been studied by the molecular-dynamics simulation method. Various kinds of structure evolution behavior have been found for this GB depending on the shear direction: (1) pure GB sliding; (2) GB atomic shuffling accompanied by lattice dislocation emission from the GB; and (3) GB migration coupled with GB sliding, namely, GB coupling motion. The GB coupling motions can differ in the direction and distance of the GB migration depending on the shear direction. An analysis with the aid of the coincidence site lattice theory indicates that the structure evolution behavior can be attributed to several elementary structure transformations inherent to this particular GB. A pair parameter $(\ensuremath{\lambda},\ensuremath{\kappa})$ is proposed to describe the GB coupling motions.