Structure and Stability of Quasicrystalline Al–Mn Alloys

Publisher Website
Google Scholar
Abstract
The quasicrystalline (qc.) phase with the icosahedral symmetry in melt-spun Al 100- x Mn x ( x =14, 17, 20) has been investigated by X-ray diffraction, TEM and DSC. Nearly single phase quasicrystal is obtainable for Al 80 Mn 20 when the quenching rate is sufficiently fast, while slower quenching rate produces an alternative metastable phase called T phase. On heating, the qc. phase in Al 80 Mn 20 changes to T phase at around 300°C and then at around 600°C to the stable hexagonal Al 4 Mn, whereas the qc. phase in Al 86 Mn 14 crystallizes directly to the stable orthorhombic Al 6 Mn. Heat evolution of the latter reaction is 0.40 kcal/mol, while those of the qc. phase to T phase and T phase to the hex.-Al 4 Mn in Al 80 Mn 20 are 0.12 and 0.17 kcal/mol, respectively. Atomic model of the qc. phase with a stoichiometric composition of Al 78.35 Mn 21.65 is proposed.