STABILITY AND TRANSFORMATION TO CRYSTALLINE PHASES OF AMORPHOUS ZR-AL-CU ALLOYS WITH SIGNIFICANT SUPERCOOLED LIQUID REGION

Crystallization from the supercooled liquid region was examined for an amorphous Zr65Al7.5Cu27.5 alloy with a significant supercooled liquid region before crystallization, with the aim of investigating the reason for the appearance of the wide supercooled liquid region. The crystallization takes place through the precipitation of a b.c.t. Zr2(Cu, Al) single phase which grows with a dendritic mode. The Avrami exponent (n value) and the activation energies for the nucleation and crystallization are 3.7, 260 and 230 kJ mol-1 respectively. Based on existing structural data as well as the present results, it is presumed that the appearance of the supercooled liquid region is due to the difficulty of growth resulting from the necessity of long-range redistribution of Al at the solid-liquid interface and to the difficulty of precipitation of Zr2(Cu, Al) caused by the large solid-liquid interfacial energy resulting from the highly dense random packed structure consisting of elements with significantly different atomic sizes and attractive bonding nature.