FORMATION, STRUCTURE, AND CRYSTALLIZATION OF AL-RICH METALLIC GLASSES

The formation, structure, and the crystallization of Al85YxNi15-x are studied using x-ray diffraction and differential scanning calorimetry. The results show two distinct glasses depending on composition. Y-ric h glasses (x greater-than-or-equal-to 8) are homogeneous with a well-d efined glass transition. The x-ray diffraction patterns have a single main peak. These glasses crystallize through a nucleation and growth p rocess. Y-poor glasses (x<8) do not show a glass transition and have a shoulder on the high-angle side of the main peak in their x-ray diffr action patterns. We show that the shoulder peak is due to quenched-in Al nuclei. These glasses are shown to crystallize through the growth o f these nuclei. Y-rich glasses (x greater-than-or-equal-to 8) are more stable as demonstrated by the presence of the glass transition and th eir higher crystallization temperature, enthalpy, and activation energ y. The occurrence of a prepeak for all compositions is attributed to Y -Y pairs.