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

Three alloys of composition AI-5at%Mn-5at%Fe, AI-7at%Mn-7at%Fe and Al-10at%Mn-10at%Fe were studied in the melt-spun condition. The AI-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 $(1\tau^30)$ type zone axes of the twinned and untwinned parts of the icosahedral grain coincide,and at 90 ° from the twin axis their $(1\tau0)$ zone axes coincide. In the two other alloys the icosahedral, $AI_3Fe$ and aluminium phases formed at wheel surface velocities above 12 m/s. At slower wheel velocities only the $AI_3Fe$ and aluminium formed. Through the similarities in the electron diffraction patterns, the twinned icosahedral and $Al_3Fe$ phases are shown to be related to a decagonal phase