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

We have examined the effect of Ti and cooling rate on the crystallization of Zr62-xTixCu20Ni8Al10(0 less than or equal to x less than or equal to 10) amorphous alloys. Ti stabilizes an icosahedral phase in Zr62-xTixCu20Ni8Al10(0 less than or equal to x less than or equal to 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 less than or equal to x less than or equal to 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. (C) 2000 American Institute of Physics. [S0003-6951(00)04739-2].