Nanoquasicrystallization in Metallic Glasses

Nanoquasicrystallization in Zr-based glassy alloys was investigated. It is found that the nano scale icosahedral quasicrystalline phase (I-phase) is formed by addition of the elements, which obstruct the glass-forming ability (GFA) in the glassy alloy. The primary phase of fee Zr₂Ni phase in the Zr₆₅Al_7.5Ni₁₀Cu_17.5 glassy alloy with high GFA changes to the fcc Zr₂Ni plus I-phases by substitution of noble metals or Zr for only 1 at% Cu. Since each phase is precipitated independently and the icosahedral local atomic configuration exits in the fee Zr₂Ni and I-phases, they are originated from the same local structure in the Zr-based glassy alloy with high GFA. We found that the icosahedral local structure is strongly correlated with the stability of the supercooled liquid state. The origin of the icosahedral local structure is combination of Zr + Cu and Zr + Al + Ni elements. In these alloy systems, the I-phase is easy to precipitate as a primary phase by addition of a very small amount of appropriate element. From the present results, it is concluded that the icosahedral local structure stabilizes the supercooled liquid state. We suggest that the high GFA for the preparation of bulk glassy alloy is attributed to the stability of icosahedral local structure.