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Vol.35, No.7, 865 ~ 872, 1997

Title

Structural Relaxation in Al-Base Amorphous Alloys and Property of Their Bulks

김영환 , 주영한 , 배동수 Yeong Hwan Kim , Yeong Han Joo , Dong Soo Bae

Abstract

The anneal-induced enthalpy relaxation behavior was examined calorimetrically for the amorphous (Al_(1-x)Y_x)_(80)Ni_(20)(0.25≤X≤0.75) alloys with a ribbon shape. When the samples annealed at temperatures below T_g or T_x are heated, an excess endothermic reaction (enthalpy relaxation) occurred above the annealing temperature (T_a) followed by a broad exothermic reaction. The onset peak temperature (T_m) of the endothermic reaction increased in a continuous manner with the annealing time (t_a). The exothermic reaction is thought to be due to the annihilation of various kinds of frozen-in defects and the endothermic one to the development of topological and compositional short-range ordering among the constituent atoms. The enthalpy relaxation was easily occurred with Y content. The easiness of the structural relaxation with Y content can be well explained by the interaction between Al and Y atoms as predicted from the difference in the melting temperature of compounds corresponding their compositions in the equilibrium phase diagrams. A bulky amorphous alloy with a diameter of 2㎜ was obtained by water quenching for Al_(20)La_(50)Ni_(20) composition. The amorphous nature of bulky alloy had a relaxed structure more than that of a ribbon shape, while a n amorphous nature was nearly the same.

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