Transition from a strong-yet-brittle to a stronger-and-ductile state by size reduction of metallic glasses

Amorphous metallic alloys, or metallic glasses, are lucrative engineering materials owing to their superior mechanical properties such as high strength and large elastic strain. However, their main drawback is their propensity for highly catastrophic failure through rapid shear banding, significantly undercutting their structural applications. Here, we show that when reduced to 100 nm, Zr-based metallic glass nanopillars attain ceramiclike strengths (2.25 GPa) and metal-like ductility (25%) simultaneously. We report separate and distinct critical sizes for maximum strength and for the brittle-to-ductile transition, thereby demonstrating that strength and ability to carry plasticity are decoupled at the nanoscale. A phenomenological model for size dependence and brittle-to-homogeneous deformation is provided. A long-standing goal in engineering is to create better structural materials with enhanced useful properties for particular applications, commonly attained by constructing specific microstructures. Typical examples include martensites for strengthening, reinforced concrete for toughening and cellular structures for energy absorption. It was recently reported that extrinsic size also strongly affects crystalline properties at the submicrometre scale 1,2 , providing the opportunity to use feature size as a design parameter in attaining superior mechanical properties.