Quasicrystals from glass devitrification

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 Zr2Ni and fcc Hf2Ni phases in the Zr65Al7.5Ni10Cu17.5 and Hf65Al7.5Ni10Cu17.5 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 Zr2Ni and fcc Hf2Ni 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 Zr65Al7.5Ni10Cu7.5Pd10, Zr70Al7.5Ni10Cu12.5 and Hf65Al7.5Ni10Cu12.5Pd5 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.