Structural evolution during heat treatment of mechanically alloyed Al-Cu-Fe-(Si) alloys

Structural evolution during mechanical alloying and subsequent heat treatment of Al₆₅Cu₂₀Fe₁₅ and Al₆₅Cu₂₀Fe₁₀Si₅ was studied by X-ray diffractometry (XRD), transmission electron microscopy (TEM) and differential scanning calorimetry (DSC). The Al₆₅Cu₂₀Fe₁₅ and Al₆₅Cu₂₀Fe₁₀Si₅ powders milled for 10 h showed a layered structure consisting of Al-, Cu- and Fe-rich layers. DSC traces obtained from the powder during heating, up to 600°C, showed two exothermic peaks with peak temperatures of 330 and 440°C in Al₆₅Cu₂₀Fe₁₅ and 330 and 500°C in Al₆₅Cu₂₀Fe₁₀Si₅ powders. The lower exothermic peaks correspond to the formation of Al₂Cu and Al₇Cu₂Fe phases from the layered structure. The second high temperature exotherms correspond to the formation of Al(Fe,Cu) and 1/1 cubic approximant in the Al₆₅Cu₂₀Fe₁₅ powder and to the formation of Al₁₃Fe₄ adn 1/1 cubic approximant in the Al₆₅Cu₂₀Fe₁₀Si₅ powder. The Al₆₅Cu₂₀Fe₁₅ and Al₆₅Cu₂₀Fe₁₀Si₅ powders annealed for 5 h at 750°C showed microstructure consisting of Al(Cu,Fe) and Al₁₃Fe₄ phases, and Al₁₃Fe₄, icosahedral and new approximant phases, respectively. The partial substitution of Fe by Si increased the stability of the 1/1 cubic approximant and icosahedral phases.