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

A high quality single grain of Al63Cu17.5Co17.5Si2 was studied by high resolution 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 2πn/10 (n=0, …, 4) around the tenfold axis, allow us to accurately explain the peak splitting of the quasicrystal diffraction peaks, if we consider the domains periodic along the twofold ‘P’ direction (direction of the phason-strain) and quasiperiodic along their corresponding orthogonal twofold ‘D’ axis. This 1D quasicrystal is transformed into the 2D decagonal quasicrystal at 830°C. ity anomalies were observed at about 770°C and interpreted as resulting of a phason ordering transformation.