Bulk metallic glasses, referred to commonly as metallic glasses, are technically defined as alloys with critical cooling rates low enough to allow the formation of layers of over 1mm in thickness. Colloquially, they are a metallic alloy that exploits the favorable properties of both metals and glasses, including flexibility, strength, and durability.
Ordinary metals are crystalline solids, with high density, conductivity, and strength. Their molecules are ordered in a lattice structure, and disruptions in that lattice structure are known as dislocations. Common metals have approximately one dislocation in one billion molecules, or 10^14 dislocations in a cubic centimeter. It is these dislocations, rather than the natural ordering of metals, that ultimately define the properties of metals.
Glasses, on the other hand, are amorphous, or non-crystalline, solids. As anyone who has broken a window knows, glasses are brittle when solid; however, they become molten and exhibit fluid properties at high temperatures. This characteristic, known as the “glass transition,” allows glasses to be molded into creative and complex shapes.
These physical characteristics of glass and metals significantly affect their processing potential. During processing, metals display plasticity – the permanent deformation of the metal material. Glasses, however, with no lattice structure or dislocations, instead displays elasticity – a reversible deformation of the material under a force. Both plastic deformation and elastic deformation are necessary when shaping complex objects, yet neither glass nor metal can fully encompass both properties.
This is where bult metallic glasses come into play. “We combine two previously mutually exclusive properties,” remarked Jan Schroers, Associate Professor of Mechanical Engineering & Materials Science at Yale University, resulting in the metallic alloys known as bulk metallic glasses. Joining advanced structural properties – strength, durability, and deformation – with the flexibility sufficient for molding complex shapes, these bulk metallic glasses are a ‘super-metal’ of sorts, an enhanced alloy with a range of capabilities.