METASTABLE PHASES FORMATION INDUCED BY MECHANICAL ALLOYING

Elemental aluminium, titanium and iron powders with compositions of Al90Ti10, Al55Ti45, Al65Ti25Fe10, respectively, were mechanically alloyed in a planetary ball mill. The sequence of phase formation was characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), and differential scanning calorimetry (DSC). Various metastable phases were experimentally observed: supersaturated solid solution Al(Ti) for Al90Ti10, amorphous phase and L1(2)-Al3Ti compound for Al55Ti45, amorphous phase and supersaturated solid solution Al(Ti,Fe) for Al65Ti25Fe10, and an fcc crystalline phase was inevitably found in those alloys. The formation of the fee crystalline phase has been critically assessed. The results suggest that the fee crystalline phase seems to be metastable and it cannot be solely attributed to the contamination from the milling atmosphere under the present experimental conditions.