Ion beam-irradiation induced structure transformation in alpha-AlMnSi

Structure changes of an alpha-AlMnSi phase, irradiated with 1.5 MeV Xe+ ions at room temperature, have been studied by transmission electron microscopy (TEM). At an irradiation dose of 3.4 x 10(13) ions/cm(2), the primitive cubic alpha-AlMnSi phase transformed to a bcc phase. But the unit cell parameter (a=1.268 nm) remained the same. With an increase of irradiation dose, the bcc phase became amorphous at 3.4 x 10(14) ions/cm(2). The bcc phase structure consists of two MacKay icosahedral atomic clusters in each unit cell. A pseudo ten-fold rotational axis has also been obtained via electron diffraction in the specimens irradiated to 5.1 x 10(13) ions/cm(2). This quasicrystal-like structure was found for the first time during the radiation-induced crystalline-to-amorphous phase transformation, Annealing of the fully amorphized specimens was performed with in situ TEM. The alpha-AlMnSi phase started to form at 350 degrees C and was fully crystallized at 500 degrees C. The bcc phase and quasicrystal-like structures were not observed during the crystallization processes.