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 Zr₆₅Al_7.5Ni₁₀Cu_17.5 and Hf₆₅Al_7.5Ni₁₀Cu_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 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 Zr₆₅Al_7.5Ni₁₀Cu_7.5Pd₁₀, Zr₇₀Al_7.5Ni₁₀Cu_12.5 and Hf₆₅Al_7.5Ni₁₀Cu_12.5Pd₅ 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.