Atomic packing in multicomponent aluminum-based metallic glasses

Three-dimensional atomic configurations have been established for Al-based multicomponent metallic glasses (MGs). This was achieved via computer simulations employing effective pair-potentials, which were derived from ab initio molecular dynamics simulation data using the inverse Monte Carlo (IMC) method. The ab initio and IMC structural models were validated using structure factors and extended X-ray absorption fine structures obtained from synchrotron X-ray experiments. The Al-based MGs are characterized by solute-centered quasi-equivalent clusters. These coordination polyhedra of different types and sizes intermix in the multicomponent alloy, resulting in improved glass-forming ability for the Al-La-Ni alloys when compared with binary Al-La and Al-Ni systems. Our survey of a large number of Al-solute systems using ab initio calculations demonstrates that the topological short-range order (cluster type, size and coordination number of the solute) correlates directly with the Al-solute bond length (or the effective atomic size ratio). The differences between our findings and previously proposed structural models are also discussed.