Al-Co-Cu-Si and Al-Co-Cu microcrystalline and quasicrystalline phases of decagonal symmetry

On the basis of HREM and electron diffraction studies and of previous X-ray single crystal diffraction results, we confirm the existence on a non-quasicrystalline microcrystalline state for the decagonal Al63Cu17.5Co17.5Si2 alloy at room temperature. The HREM results are compared to those obtained for the Al65Cu17.5Co17.5 alloy. Moreover for the first time, a high temperature phase transition towards a quasicrystalline state is revealed in the two compounds.