Deformation Behavior

Although metallic glasses synthesized by rapid quenching from the melt were first discovered in 1960 by Duwez and coworkers at Caltech, the study of the mechanical behavior of metallic glasses only started in the early 1970s. Metallic glasses were found to deform elastically and exhibit negligible plasticity in uniaxial tension. Despite a limited macroscopic tensile plastic strain (<0.5%), exceptionally high strain (~100) was observed to take place within localized shear bands. One of the scientific questions naturally arises: how does a shear band nucleate and propagate in a medium presumably consisting of randomly packed atoms? Several theories, including the freevolume model and the dislocation model, were subsequently proposed to address the shear band formation and propagation. It was impossible to carry out irrevocable experiments to prove these theories at that time due to the limited size of the samples, and thus a poorly defined stress state during mechanical testing, and the lack of advanced analytical tools. However, the situation changed after the successful development of bulk metallic glasses (BMGs) in many alloy systems, e.g., Zr-, Mg-, Pd-, La-, Cu-, Ti-, and Febased. As a result of this development, research of BMGs has been very active, especially in the area of mechanical deformation.