Structure and decomposition behaviour of rapidly solidified Al-Fe alloys

The structure and decomposition behaviour of rapidly solidified Al-5, 10 and 15 at% Fe alloys have been investigated by detailed transmission electron microscopy and differential scanning calorimetry. Rapid solidification produces a variety of metastable phases: microquasicrystalline, decagonal, Al_mFe, Al₆Fe and Al₁₃Fe₄, in order of increasing thermodynamic stability. The rapidly solidified microstructure depends upon the alloy composition and cooling rate. Primary and cellular particles of the microquasicrystalline phase are preferred at higher cooling rates, and primary or eutectic particles of the Al_mFe phase are preferred at lower cooling rates. With increasing iron content, the microquasicrystalline phase is replaced with primary particles of the decagonal phase. After annealing at moderate temperatures, the microquasicrystalline phase in Al-5 and 10 at% Fe decomposes into Al_mFe and Al₆Fe, and the microquasicrystalline phase in Al-15 at% Fe decomposes into Al_mFe. After annealing at higher temperatures, the Al_mFe, Al₆Fe and decagonal phases then decompose into stable Al₁₃Fe₄.