Decagonal quasicrystals in Al-Co and ternary alloys containing Cu and Ni

Investigation of a series of Al-Co-(Cu,Ni) alloys of composition adjacent to Al3Co is reported. The metastable nature of the Al-Co decagonal phase produced by rapid solidification was confirmed. This phase was found to form preferentially at compositions of about 72-74 at.% Al. At lower cooling rates, achievable by conventional solidification, decagonal-like metastable structures can be formed in the same compositional range, corresponding to the binary Al5Co2-Z range of the equilibrium phase diagram (Grushko et al., J. Alloys Comp., 233 (1996) 279). The relation between these binary phases and the stable decagonal phases in Al-Co-Cu and Al-Co-Ni is discussed.