Precipitation of icosahedral phase from amorphous Zr_65Cu_17.5-xAl_7.5Ni_10Ag_x (x=0,5) alloys

摘要

Crystallization behavior of amorphous Zr_65Cu_17.5Al_7.5Ni_10Ag_x(x=0.5) alloys prepared by melt spinning and injection casting techniques has been studied using differential scanning calorimetry, x-ray difractometry, and transmission electron microscopy. Ag addition changes crystallization sequence of the amorphous phase. The amorphous Zr_65Cu_17.5Al_7.5Ni_10 alloy crystallizes via simultaneous precipitation Of icosahedral phase and NiZr_2 phase in the first crystallization step whereas that in Zr_65Cu_12.5Ni_10Ag_5 alloy crystallizes via precipitation of only icosahedral the Phase. Partial replacement of Cu by Ag in Zr_65Cu_17.5Al_7.5Ni_10 alloy stabilized the Icosahedral phase relative to competing intermetallic phases resulting in suppression of The precipitation of the NiZr_2 phase, enhancement of the precipitation of icosahedral Phase, and reduction of undercooled liquid range. Crystallization behavior of the Amorphous Zr_65Cu_12.5Al_7.5Ni_10Ag_5 alloy is not affected by cooling rate during Solidification. Johnson-Mehl-Avrami analysis of isothermal transformation data Suggests that the formation of the quasicrystalline phase is not entirely polymorphic in Nature and may involve partitioning of the solute at later state.