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 L1₂-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 fcc crystalline phase has been critically assessed. The results suggest that the fcc crystalline phase seems to be metastable and it cannot be solely attributed to the contamination from the milling atmosphere underthe present experimental conditions.