Molecular dynamics simulations of glass formation and crystallization in binary liquid metals

The glass formation of binary liquid metals is studied using molecular dynamics simulations, where the atomic interactions are modeled with a Sutton-Chen many-body potential. We use model binary alloy systems (Cu*₅₀Cu**₅₀), which differ in their atomic radii and/or cohesive energies between Cu* and Cu**. First, when we change the atomic size ratio λ (λ≤1.0) only, we find that there are three regimes defined by the magnitude of λ upon cooling. When λ is close to 1.0, crystallization occurs. Glass formation occurs at moderate λ values. When the λ is small, the alloy phase separates into pure phases. Second, when we vary λ and the cohesive energy ratio ε (ε?≤1.0) along the line in constant energy density space (ε/λ³=constant), glass formation occurs at moderate λ values, but phase separation is not observed at any λ. Therefore, we find that the energy density is the dominant parameter in controlling the phase separation behavior of metallic alloys. From the studies of structural properties, we find that the fivefold symmetry becomes prominent in glasses and shows a maximum at λ=0.85 in both cases. Finally, when we only vary ε, while keeping λ constant, the system shows a very limited glass forming regime (ε<0.3), indicating that the atomic size ratio λ is more crucial to frustrate the crystallization.