Quasicrystalline and related crystalline phases in rapidly solidified Al‒Fe alloys

The microstructural characteristics of quasicrystalline and related crystalline phases in rapidly solidified Al‒5 to 20 at% Fe alloys have been investigated by detailed transmission electron microscopy. Rapid solidification of Al‒5 to 20 at% Fe alloys produces a variety of metastable phases, depending upon alloy composition and cooling rate: microquasicrystalline, decagonal, Al_mFe, Al₆Fe and Al₁₃ Fe₄, in order of increasing thermodynamic stability. The Al-Fe microquasicrystalline phase consists of clusters of nm scale randomly oriented icosahedral particles, distributed in the form of either primary solidification particles or a fine scale two phase cellular structure. The microquasicrystalline phase has a solute content (≈Al₆Fe) which is lower than the Al-Mn icosahedral phase (≈ Al₄Mn). The Al‒Fe decagonal phase has a periodicity of 1·65 nm along the tenfold symmetry axis, forms as a primary solidification product, and has a solute content (≈Al₉Fe₂) which is similar to the Al‒Mn decagonal phase (≈Al₄Mn). Detailed selected area electron diffraction analysis shows a close similarity between the decagonal, Al_mFe and Al₁₃Fe₄ phases, suggesting that the Al_mFe and Al₁₃Fe₄ phases may be approximants of the Al‒Fe decagonal phase.