Role of Electronic Structure on Ductility of Iron-Based Bulk Metallic Glasses*

Composition effects on the mechanical properties of iron-based amorphous steel alloys have been investigated, with attention to the metalloid content and the relative impact of boron, carbon and phosphorous. Phosphorous-containing amorphous steels exhibited enhanced plastic strains and fracture strengths. Moreover, the plastic strain increased with the decrease in shear modulus. The shear moduli are appreciably lower than those reported for previous amorphous steel compositions that did not contain phosphorus, and the Poisson's ratios obtained are correspondingly high. The ductility of amorphous steels can be improved by chemically tuning the elastic properties which are determined by the amorphous structure and chemical bonding. First-principles electronic structure calculations show that ductility can be improved by partially replacing elements such as boron and carbon that create ionic and covalent bonds with other elements such as phosphorous that favor metallic cohesion.