Abstract
The formation of quasicrystalline approximants in rapidly solidified Al-Co-Fe-Cr alloys was investigated. Alloys of atomic composition Al71Co13Fe8Cr8, Al77Co11Fe6Cr6 and Al76Co19Fe4Cr1 were produced using melt spinning and arc melting methods and their microstructural characterization was carried out by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. Up to the present there is no consensus in the literature regarding the formation of quasicrystalline phase or quasicrystalline approximants in the Al71Co13Fe8Cr8 alloy. This work presents, for the first time, a detailed structural characterization of selected alloys in the Al-Co-Fe-Cr system close to the atomic composition Al71Co13Fe8Cr8. The results indicated the samples to be composed, mostly, by two intermetallic phases, which are quaternary extensions of Al5Co2 and Al13Co4 and are quasicrystalline approximants. Although the Al5Co2 phase has already been reported in the Al71Co13Fe8Cr8 alloy, the presence of the monoclinic Al13Co4 is now identified for the first time in the as cast state. In the binary Al-Co system a quasicrystalline phase is known to form in a rapidly solidified alloy with composition close to the monoclinic and orthorhombic Al13Co4 phases. This binary quasicrystalline phase presents an average valence electron per atom (e/a) between 1.7 and 1.9; thus, in addition to the Al71Co13Fe8Cr8 alloy, the compositions Al77Co11Fe6Cr6 and Al76Co19Fe4Cr1 were chosen to be within the region of formation of the quaternary extension of the Al13Co4 phase and also within the (e/a) of 1.7 to 1.9. However, no quasicrystalline phase is present in any of the studied alloys. The Al-Co-Fe-Cr system, around the compositions studied, is composed of quaternary extensions of Al-Co intermetallic phases, which present solubility of Fe and Cr at Co atomic sites.
Published Version
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