Since the quasicrystals became ones of the constructional materials, science concentrated on their mechanical properties. Single-quasicrystals are materials which useful properties are most needed in automobile, aircraft and space fields. They are good thermal conductors (in one direction), possess a high hardness and structure stability at high temperature. The microstructure and electron diffraction pattern of two-subgrain single quasicrystals of Al-Cu-Co alloys was studied. Two-subgrain single quasi-crystals of Al-Cu-Co alloy were obtained using a modification of the IFC method. All the single quasi crystals obtained through solidification on substrate were examined by Laue diffraction. The subgrain of the mosaic of the single quasi-crystals was examined by X-ray topography oscillation method (modification of the Auleytner method). It has been determined that low angle boundaries generate phasonic defects, which may propagate along a tenfold symmetry axis. To confirm this, tenfold electron diffraction patterns (EPD) obtained for single quasi-crystals in the as-grown state were compared with those after annealing at 100°C. The presence of subgrain boundaries in single quasicrystals increases the concentration of phasonic defects in them. The assumption that the subgrains boundary generates phasons is also confirmed by the fact that FWHM of X-ray reflexes measured for as-grown single quasi crystals containing a low-angle boundary (two subgrain) were always larger than for single quasi crystals without such boundary (one subgrain).

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