ON THE TRANSITIONS OF THE ICOSAHEDRAL AND DECAGONAL PHASES TOWARDS EQUILIBRIUM PHASES IN AL-CU-MN ALLOYS

In rapidly solidified Al-Cu-Mn alloys, the quasicrystalline phases (icosahedral and decagonal) are metastable. In this Letter, the transitions of the icosahedral (i) and decagonal (d) phases towards the equilibrium periodic phases have been studied by means of differential thermal analysis, X-ray diffraction and transmission electron microscopy. The nature of the crystalline phases formed on heating was in agreement with the equilibrium phase diagram (Koster et al. 1966). Evidence is shown of a hierarchy of stability between the i and d phases: on heating, the i phase is transformed into the d phase.