Quasicrystal formation in a Zr-based bulk metallic glass

Zr65Ni10Cu7.5Al7.5Ag10bulk metallic glass with a diameter of 2 mm and a length of 50 mm was prepared by copper-mould casting. The metallic glass obtained follows two-step crystallization reactions with the initial formation of metastable quasicrystals from amorphous phase, followed by the formation of a stable intermetallic Zr2Cu from the post-formed quasicrystals. In this paper, the microprocess of the amorphous-to-quasicrystalline transformation of Zr65Ni10Cu7.5Al7.5Ag10bulk metallic glass was studied in detail by TEM and high resolution TEM coupled with nanobeam EDX. It was found that the amorphous-to-quasicrystalline transformation in the present system does not follow the traditional nucleation/growth mechanism. Instead, it undergoes a series of inter-processes and follows the sequence of phase transformation of amorphous→FCC Zr2Ni → Tetragonal Zr2Ni → Quasicrystals. Nanobeam EDX revealed that atomic diffusion was involved in all inter-processes of the phase transformations, suggesting that the amorphous-to-quasicrystalline transformation in the present bulk metallic glass is a non-polymorphous reaction.