Structural mechanism for ultrahigh-strength Co-based metallic glasses

The atomic packing and electronic structure for Co43Fe20Ta5.5B31.5 metallic glass (MG) were explored by extended X-ray absorption fine structure measurement and first-principles calculation. It is shown that the short-range order in this MG is of a (Co, Fe)B2-like, but not (Co, Fe)23B6-like, crystallographic structure. A network-like medium-range order can be formed via the build-up of B-centered Z9 〈0, 3, 6, 0〉 Voronoi polyhedra. The intrinsic strengthening mechanism is attributed to the formation of strong covalent bonding between B and Co (Fe).