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 and 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.