Mechanical properties of bulk metallic glasses

The mechanical properties of bulk metallic glasses, including their superior strength and hardness, and excellent corrosion and wear resistance, combined with their general inability to undergo homogeneous plastic deformation have been a subject of fascination for scientists and engineers. The scientific interest stems from the unconventional deformation and failure initiation mechanisms in this class of materials in which the typical carriers of plastic flow (dislocations) are absent. Metallic glasses undergo highly localized, heterogeneous deformation by formation of shear bands, a particular mode of deformation of interest for certain applications, but which also causes them to fail catastrophically due to uninhibited shear band propagation. Varying degrees of brittle and plastic failure creating intricate fracture patterns are observed in metallic glasses, quite different from those observed in crystalline solids. The tension–compression anisotropy, strain-rate sensitivity, thermal stability, stress-induced crystallization and polyamorphism transformations, are some of the attributes that have sparked engineering studies on bulk metallic glasses. Understanding of the glass-forming ability and the deformation and failure mechanisms of bulk metallic glasses, has given insight into alloy compositions and intrinsically-forming or extrinsically-added reinforcement phases for creating composite structures, to attain the combination of high strength, tensile ductility, and fracture toughness needed for use in advanced structural applications. The relative ease of fabricating metallic glasses into bulk forms, combined with their unique mechanical properties, has made these materials attractive options for possible applications in aerospace, naval, sports equipment, luxury goods, armor and anti-armor systems, electronic packaging, and biomedical devices.