FORMATION OF AMORPHOUS METALS BY SOLID-STATE REACTIONS

Until recently, amorphous metals were closely associated with rapid quenching, since they were usually prepared by a quenching technique and were therefore regarded as quenched-in liquids. In 1983, it was found that amorphous metals can also be prepared by a reaction within the solid state during an isothermal annealing below the crystallization temperature. The glass formation can be due to a destabilization of the crystalline phase by an interdiffusion reaction, as in the case of a hydrogen absorption or the interdiffusion in layered transition-metal-transition-metal composites. Since quenching processes are not involved, bulk amorphous samples can be formed. Related processes take place during glass formation by mechanical alloying, where ball milling first forms an ultra-fine-layered composite powder from the initially elemental crystalline powders with a subsequent solid-state amorphization transformation. The structural similarity of the samples shows that the amorphous state should be considered as a metastable phase which can be equally approached by quenching from the liquid state and by a crystal-to-glass transition via a solid-state reaction. Besides the basic phenomena associated with the crystal-to-glass transition, the experimental processes are described, the amorphous state is characterized using physical properties and the glass-forming ranges are compared with those of melt-spun samples. © 1990 Taylor & Francis Ltd.