Formation of icosahedral phase from amorphous Zr65Al7.5Cu12.5Ni10Ag5 alloys

The kinetic behavior of quasicrystalline phase formation in amorphous Zr65Al7.5Cu12.5Ni10Ag5 alloys has been studied by using differential scanning calorimetry (DSC), x-ray diffractometry, and transmission electron microscopy. DSC trace obtained during continuous heating from 473 to 873 K shows two distinct exotherms with peak temperatures of 727 and 776 K. The first and second exothermic reactions, respectively, correspond to the formation of quasicrystalline phase from the amorphous matrix and the formation of tetragonal CuZr2 and hexagonal Zr6NiAl2 phases from the previously formed quasicrystalline phase. Partial replacement of Cu by Ag enhanced the formation of quasicrystalline phase from the amorphous structure. Johnson-Mehl-Avrami analysis of isothermal transformation data suggests that the formation of quasicrystalline phase is not entirely polymorphic in nature and may involve partitioning of solute at a later stage. (C) 2000 American Institute of Physics. [S0003-6951(00)04833-6].