Phase transformations in decagonal Al-Cu-Co-Si alloy

A high quality single grain of Al63Cu17.5Co17.5Si2 was studied by high reso lution X-ray diffraction (synchrotron radiation) as a function of annealing temperature, until its transformation into the decagonal quasicrystal. An assembly of phason-strain quasicrystalline domains with orientations which differ by 2 pin/10 (n=0,...,4) around the tenfold axis, allow us to accurat ely explain the peak splitting of the quasicrystal diffraction peaks, if we consider the domains periodic along the twofold 'P' direction (direction o f the phason-strain) and quasiperiodic along their corresponding orthogonal twofold 'D' axis. This 1D quasicrystal is transformed into the 2D decagona l quasicrystal at 830 degreesC. Intensity anomalies were observed at about 770 degreesC and interpreted as resulting of a phason ordering transformation. (C) 2000 Elsevier Science B. V. All rights reserved.