title: Quasicrystals and related approximant phases in Mg-Zn-Y.
abstract: As-cast microstructure of Mg-rich Mg(68)Zn(28)Y(4) has been investigated by a detailed transmission electron microscopy study. The as-cast Mg(68)Zn(28)Y(4) alloy consisted of three different types of phases: 10-20 m size primary solidification phase, dendritic phase grown from the primary phase and a eutectic structure formed at the later stage of solidification. The primary solidification phase has an icosahedral structure with a large degree of phason strain. 1/1 rhombohedral approximant phase with lattice parameters a=27.2 A and =63.43 degrees is first observed in Mg-Zn-Y system. The rhombohedral structure can be obtained by introducing phason strain in the six-dimensional face centered hyper-cubic lattice. The decagonal phase nucleates with orientation relationship with the icosahedral phase, and Mg(4)Zn(7) nucleates with orientation relationship with the decagonal phase, indicating a close structural similarity between the three phases. Gradual depletion of Y during solidification plays an important role in heterogeneous nucleation of decagonal and Mg(4)Zn(7) phases from icosahedral and decagonal phases, respectively.
authors.affiliation: Department of Metallurgical Engineering, Center for Noncrystalline Materials, Yonsei University, 134 Shinchon-dong, Seodaemun-ku, Seoul 120-749, South Korea.
authors.forename: S
authors.initials: S
authors.lastname: Yi
authors.forename: E S
authors.initials: ES
authors.lastname: Park
authors.forename: J B
authors.initials: JB
authors.lastname: Ok
authors.forename: W T
authors.initials: WT
authors.lastname: Kim
authors.forename: D H
authors.initials: DH
authors.lastname: Kim