Glossary

Bulk metallic glass, often abbreviated BMG, is a metal alloy with an amorphous, non-crystalline atomic structure rather than the ordered grain structure found in conventional metals. The word “bulk” is important: it means the alloy can be produced in sections at least about 1 millimeter thick, rather than only as extremely thin ribbons or foils like early metallic glasses.

What makes a bulk metallic glass unusual is that it solidifies without normal crystallization, so the atoms remain in a disordered, glass-like arrangement. Because of that structure, BMGs are often associated with very high strength, high hardness, large elastic strain limits, good wear resistance, and good corrosion resistance compared with many conventional crystalline alloys. At the same time, they are still metals, not window glass, and in some loading conditions they can show limited ductility or brittle fracture behavior, which is one reason their use has to be matched carefully to the application.

From a manufacturing standpoint, bulk metallic glasses are especially interesting because many of them can be cast or molded into near-net-shape parts with fine detail and tight tolerances, using processes that in some ways resemble a hybrid of metal casting and plastic injection molding. That makes them attractive for small precision components such as gears, cases, medical parts, sporting goods, and certain aerospace or high-performance components where a combination of precision, strength, and reduced machining is valuable.