Relation between short-range order and crystallization behavior in Zr-based amorphous alloys

Abstract

We have examined the effect of Ti and cooling rate on the crystallization of Zr62−xTixCu20Ni8Al10(0⩽x⩽10) amorphous alloys. Ti stabilizes an icosahedral phase in Zr62−xTixCu20Ni8Al10(0⩽x⩽10) alloys. Without Ti (x=0), crystallization produces cubic and tetragonal intermetallic phases, and the crystallization temperature shows no dependence on the cooling rate at which the amorphous alloy was produced. The alloys containing Ti (3⩽x⩽10) precipitate an icosahedral quasicrystalline phase upon annealing, and show a significant reduction of crystallization temperatures with decreasing cooling rates of casting. We propose that the undercooled melts and amorphous alloys have icosahedral short-range order. The degree of short-range order or medium-range order in the amorphous alloys increases with decreasing cooling rate. Crystallization is easier when the precipitating phase resembles the short-range order of the amorphous solid. Therefore, the crystallization temperature is reduced when the precipitates are icosahedral. The dissimilarity between the structures of the precipitates and the short-range order in amorphous Zr62Cu20Ni8Al10 may be one of the reasons for its very wide supercooled liquid region.