Effect of Mo Addition on the Formation of Metastable fcc Zr₂Ni and Icosahedral Phases in Zr–Al–Ni–Cu Glassy Alloy

We investigated the transformation behavior at the initial crystallization stage in the Zr–Al–Ni–Cu–Mo glassy alloy. In the Zr₆₅Al_7.5Ni₁₀Cu_12.5Mo₅ alloy, the crystallization reaction changes to two reactions and the first reaction corresponds to the nanoscale fcc Zr₂Ni phase formation. The two-stage crystallization reaction is also observed in the Zr₆₅Al_7.5Ni₅Cu_17.5Mo₅ alloy, where the primary phase is the nanoscale icosahedral quasicrystalline phase. The difference in the primary phase between the two alloys is attributed to the difference in the chemical affinities of Mo with Cu and Ni. The formation of nanoscale icosahedral and fcc Zr₂Ni phases leads to the hypothesis that the icosahedral short-range order exists in the glassy state of the Zr–Al–Ni–Cu alloy as a unit structure in both phases.