The plastic deformation of a quasicrystal was simulated by using a numerical relaxation scheme. A shear stress was applied to a quasi-periodic icosahedral atomic configuration of Lennard-Jones particles, and the nucleation of dislocation dipoles which moved in a slip plane was observed. Climb motion, and the dissociation of a perfect dislocation into a pair of partials, was also found. In one simulation, which assumed a nearly defect-free periodic approximant, plastic deformation via the creation of dislocation dipoles which moved by glide within the slip plane was observed. Their normal vector pointed along a 2-fold axis that was perpendicular to the shear direction. The Burgers vector was parallel to the shear direction which was directed along a 2-fold symmetry axis. The moving dislocations left behind a plane of misfits in the form of a stacking fault; as had been found earlier by means of numerical analysis of a 2-dimensional quasi-crystalline model. Further dislocation dipoles nucleated and then moved along the stacking fault; thus resulting in a factor of 3.6 decrease in the yield strength. The stacking fault thus weakened the quasicrystal and had to be considered when investigating experimentally observed softening. The presence of the stacking fault increased the energy of the system. Another simulation used a sample which had the same quasi-crystalline structure, but also contained a single perfect dislocation with its Burgers vector along a 4-fold symmetry axis. Under the influence of a shear stress, this dislocation split in such a way that the Burgers vectors of the resultant partial dislocations were parallel and had equal moduli. During motion within the bulk of the specimen, the mutual separation of the partials remained constant. The elastic energy which was produced by dissociation of the perfect dislocation was thus used to create the stacking fault between the partials. Before the dislocations left the quasicrystal at its lower border, the surface tension was reflected by a decrease in the dislocation distance. Although the shear direction and orientation of both the Burgers vector and dislocation core supported glide motion, climb motion was observed because the slip plane did not correspond to any plane of quasi-crystalline symmetry. The dislocations then moved within a plane of 3-fold symmetry that was closest to the slip plane. The reversibility of dislocation motion was also demonstrated. In particular, the stacking fault was removed when the dislocations propagated in the opposite direction.

C.Dilger, R.Mikulla, J.Roth, H.R.Trebin: Philosophical Magazine A, 1997, 75[2], 425-41