Phason-strain field and grain growth: a scanning focused ion beam and transmission electron microscopy study in Al-Li-Cu icosahedral phase

We succeeded to favour grain growth in single-phased Al-Li-Cu quasicrystal samples by annealing treatment under confined atmosphere. Using scanning fo cused ion beam (FIB) microscopy we can image the monograins with a good spa tial and angular resolution. FIB observations carried out on Al-Li-Cu quasi crystal samples show that grain size, which is below 0.1 mm in the starring samples, reaches 0.5 mm after 10 days annealing. It reveals regular grain boundaries both before and after annealing. According to electron diffracti on performed on these samples, the grain growth is accompanied by a reducti on of the deviations to icosahedral symmetry, i.e., a phason-strain field r eduction. Since, for symmetry reasons, the phason-strain field in Al-Li-Cu quasicrystal is not coupled to the phonon strain field, its reduction canno t be a consequence of phonon strain elimination. Our observations suggest t hat phason-strain field elimination occurs during grain growth. We propose an interpretation for such effect based on the grain boundary displacement. In this frame it is shown that grain boundary displacement is associated w ith phason-strain relaxation. (C) 2000 Elsevier Science B.V. All rights res erved.