Quasicrystals from glass devitrification

Abstract

It was found that the nano-icosahedral phase was formed in the devitrification stage of Zr- and Hf-based glassy alloys. The primary phases are metastable fcc Zr 2Ni and fcc Hf 2Ni phases in the Zr 65Al 7.5Ni 10Cu 17.5 and Hf 65Al 7.5Ni 10Cu 17.5 glassy alloys, respectively. By substitution of 5 at.% Pd for Cu, the primary phase changes to an icosahedral quasicrystalline phase in both alloys. The addition of elements, that have a positive or weak chemical affinity with one of the constitutional elements in the Zr–Al–Ni–Cu and Hf–Al–Ni–Cu glassy alloys is effective for the precipitation of the icosahedral phase. The icosahedral phase also precipitated with a slight deviation from the composition with a high glass-forming ability. Since an icosahedron is contained as a structure unit in the icosahedral, fcc Zr 2Ni and fcc Hf 2Ni phases, it is concluded that these phases are correlated with the local icosahedral order of the glass. The high-resolution transmission electron microscopy images of the as-spun Zr 65Al 7.5Ni 10Cu 7.5Pd 10, Zr 70Al 7.5Ni 10Cu 12.5 and Hf 65Al 7.5Ni 10Cu 12.5Pd 5 alloys reveal a possibility of the existence of the icosahedral ordered regions. It is, therefore, concluded that the existence of icosahedral short- or medium-range order stabilizes the glassy state in the Zr- and Hf-based multicomponent alloys.