The Topology and Electronic Stability of Solvent-Rich Metallic Glasses

Abstract

Solvent rich BMGs (>77% solvent element) are unique among bulk glass-formers (of which most are rich in solute element content), in that they are often quite ductile and exhibit physical, chemical and functional traits more akin to the solvent element. A major fundamental aim of this project was to be explore the effects of topology and composition on the glass-forming ability of solvent rich glasses based on geometric packing efficiency/ cluster models that focus on structural aspects of glass-formation and electro-chemical aspects of the constituents based on electronic contributions and magic number theory. The specific rules that dictate glass-formation were analysed with respect to small atom solvent, medium atom solvent and large atom solvent subgroups of ternary alloys with respect to the atomic size of all constituents. (This was also extended to pseudo-binary type topologies). A comprehensive analysis of existing solvent-rich glasses along with a complimenting experimental program were undertaken to decipher more specific criteria for solvent-rich glass-formation. The approach intends to focus on solvent-rich compositions which shall ideally introduce predominantly metallic bonding among the atomic constituents by maximising the like-like atomic bonds in the amorphous structure. Potentially leading to extended ductility and increases the likeliness that the resultant material may exhibit many of the characteristic properties of the solvent metal. A number of new metallic glasses and in some cases bulk metallic glasses were discovered though the course of this study. It was found that topology was playing a significant role in glass-formation for all the three atomic size categories, and that different glass-forming criteria not only existed for compositions in the three solvent size categories but also for the different atomic size and coordination families within each category, encompassing solute and solvent centred clusters, shared solute atom topological arrangements and varying degrees of medium range order all contributed in various ways for different topologies, which dictate and limit maximum solvent/solute contents for each case. Relationships between atomic bonding bridges and magic number theory were also observed in relation to glass forming ability and thermal stability.