The formation of an Al-Cu-Co type decagonal quasicrystal in an [AlCuFe]-[AlCoNi] pseudo-binary alloy system

Pseudo-binary IQC100−x DQC x alloys made from mixing Al62Cu25.5Fe12.5 icosahedral quasicrystal (IQC) and Al70Co15Ni15 decagonal quasicrystal (DQC) together in progressively increased proportions were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDAX). In this way the transition from IQC to DQC was manifested by the evolution of their constituent phases. The formation of these phases was found to follow the evolution of their valence electron concentration per atom (e/a) lines in the Al–(Cu,Ni)–(Fe,Co) pseudo-ternary phase diagram. An Al–Cu–Co type decagonal phase was found in the annealed IQC80DQC20 alloy. This phase is characterized by transmission electron microscopy (TEM) and by high-resolution electron microscopy (HREM). The study proved that it is a superstructure of the DQC phase. The possible origin of its formation was discussed according to the variation of its DQC formation e/a-constant line in the Al–(Cu,Ni)–(Fe,Co) alloy system.