Quasicrystalline and crystalline phases and their twins in rapidly solidified Al---Mn---Fe alloys

Abstract

Three alloys of composition Al---5at%Mn---5at%Fe, Al---7at%Mn---7at%Mn---7at%Fe and Al---10at%Mn---10at%Fe were studied in the melt-spun condition. The Al---5Mn---5Fe alloy showed the formation of stellar-shaped icosahedral particles surrounded by aluminium. A large number of these particles were found to be twinned with one of the fivefold symmetry axes as the twin axis. By a careful tilting experiment in the transmission electron microscope, it has been shown that at 45° from the twin axis along a twofold direction, the <1T³0> type zone axes of the twinned and untwinned parts of the icosahedral grain coincide, and at 90° from the twin axis their <1T0> zone axes coincide. In the two other alloys the icosahedral, Al₃Fe and aluminium phases formed at wheel surface velocities above 12 m/s. At slower wheel velocities only the Al₃Fe and aluminium formed. Through the similarities in the electron diffraction patterns, the twinned icosahedral and Al₃Fe phases are shown to be related to a decagonal phase.