FORMATION OF METASTABLE PHASES FROM AMORPHOUS STATE

Since Duwez et al. prepared the first metallic glasses by rapid quench ing, a large number of contributions have been published dealing with the estimation of glass-forming ability in terms of the critical cooli ng rate. Recently, metallic glasses have been prepared successfully al so by using quenching rates of the order of 1 K s(-1). It is obvious t hat the principal parameter determining glass-forming ability are stru ctural and energetic relations in the material. Present theories of ea sy glass formation focus on the role of clusters (associations) in the molten alloy. Accepting the existence of clusters in the melt, it see ms evident that their role for the formation of the amorphous structur e lies in the preservation of the short-range ordering of these cluste rs upon quenching; such ordering then inevitably has to have important influence on the formation of the nuclei of the crystalline phase for ming in the amorphous structure. We report on the study of crystalliza tion of amorphous Fe-B, Pd-Si: Pd42.5Ni42.5P15 and Pd40Ni40P20 alloys. The formation of crystalline phases has been investigated by differen tial thermal analysis (DTA), differential scanning calorimetry (DSC), electrical resistivity, transmission electron microscopy (TEM) and ED methods. The structures have been analyzed with respect to the concept of formation of short-range ordered clusters in the melt and of metas table phases upon crystallization. (C) 1997 Elsevier Science S.A.