STABLE ICOSAHEDRAL AL-PD-MN AND AL-PD-RE ALLOYS

A thermodynamically stable quasicrystalline phase with an icosahedral structure was found to be formed at atomic compositions of Al70Pd20Mn10 and Al70Pd20Re10 in conventionally solidified and fully annealed states as well as in a rapidly solidified state. The substitution of Mn by Re leads to an increase in the intensity of the X-ray reflection peaks resulting from the fundamental lattice, while the intensity of the superlattice reflection remains unchanged. This result suggests that Re and Mn atoms occupy predominantly the fundamental lattice site and the superlattice site is occupied by Pd. These icosahedral alloys with an ordered structure remain stable up to the onset temperature of fusion and the icosahedral Al-Pd-Mn alloy has solidification morphology of an icosidodecahedron with a size of 0.3 mm. The formation and stability of these icosahedral alloys were examined in terms of electronic parameter and atomic size and the criterion of the high stability was clarified to be analogous to that for the Hume-Rothery type compounds. © 1990, The Japan Institute of Metals. All rights reserved.