Ion irradiation-induced phase transformation in Al-Cu-Co-Ge decagonal quasicrystal

The ion irradiation-induced phase transformation in a Al-Cu-Co-Ge decagonal quasicrystal has been studied by means of in situ transmission electron microscopy. Prior to ion irradiation, typical single decagonal quasicrystalline HRTEM images and electron diffraction patterns along the tenfold axis were observed. The HRTEM image clearly showed the decagonal quasicrystal structure and revealed no apparent defects in the unirradiated material. After a 1.5 MeV Xe+ ion irradiation to a dose of 4.3 x 10(14) ions/cm(2), electron diffraction and HRTEM images indicated that the original, single quasicrystal had transformed into amorphous and bcc crystalline components. Moreover, the amorphous component had the same composition as the original quasicrystal, and the bcc crystalline component lacked aluminum as compared with the quasicrystal. The crystalline component was much more resistant to amorphization than the quasicrystalline structure. The phase transformation and separation observed in the Xe+ ion irradiated Al-Cu-Co-Ge quasicrystal were due to irradiation-induced defect accumulation and compositional segregation. During the annealing of the Xe+ ion-irradiated specimen, the electron diffraction pattern of the crystalline phase component did not change with the increasing temperature. However, a transition from amorphous-to-quasicrystal was observed during annealing at different temperatures.