INTERFACE-DRIVEN ALLOYING AND METALLIC GLASS FORMATION IN NANO-MULTILAYERS IN AN IMMISCIBLE Y-Nb SYSTEM

摘要

Several new amorphous alloys were obtained in an immiscible Y-Nb system by room tempera- ture l90 keV xenon ion mixing of Y-Nb multilayered films, which were designed to include a sufficient fraction of interfacial atoms and thus possessed a high free energy comparable to that of the amorphous state. In addition, two metastable f.c.c. phases were formed in Y-rich and Nb-rich multilayered films, re- spectively. The growth kinetics of the f.c.c. phases and their effect on the composition range of amorphiza- tion are also discussed. To understand the observed unusual alloying behaviors, a Gibbs free-energy diagram was constructed based on Miedema's model. The diagram included the free-energy curves of all the involved phases as well as that of the Y-Nb multilayered films including the extra interfacial free energy and thus gave a qualitative and reasonable interpretation to the formation of metastable alloys upon ion mixing. Furthermore, some multilayered films with a sufficient fraction of interfacial atoms were subjected to steady-state thermal annealing, which also resulted in the formation of the Y-Nb amorphous phases, suggesting that alloying in this immiscible system was actually driven by the interfacial free energy.