Are Metallic Glasses Brittle or Ductile?

Crystalline metals generally exhibit ductility which is enabled by dislocation sliding. We show here that metallic glasses, which carry ductility through shear banding as opposed to dislocation sliding, exhibit ductility only in certain stress fields and such ability is an intrinsic property. Such ability, only depending on chemistry and fictive temperature of the metallic glass, manifests in the ability to form stable shear bands that carry plasticity. We measured this quantity, ▽σ_DB for a range of metallic glasses to represent the material class of metallic glasses.<br/>If a metallic glass behaves ductile or brittle in a given application is determined by the comparison between ▽σ_DB and the applied stress field, ▽σ_app; if ▽σ_DB &gt; ▽σ_app the metallic glass will behaves brittle, if ▽σ_DB &lt; ▽σ_app the metallic glass will behaves ductile, and |▽σ_app |-▽_DB indicates how ductile.<br/>Measured ▽σ_DB, and the concept of comparing it with ▽σ_app can explain the mechanical properties of metallic glasses and their apparent contradicting brittle and ductile characteristics. Proposed concept allows to determine the behavior of a metallic glass in an application and lays the foundation of using metallic glasses as structural materials.