Composition origin of Cu-Zr bulk metallic glasses understood via a “dual-cluster” model of binary eutectics

1Dual-cluster model was introduced to understand the short-range order of three eutectics of Cu61.8Zr38.2, Cu56.0Zr44.0 and Cu45.7Zr54.3 in binary Cu-Zr system.2The dual-cluster formulas of each eutectic were obtained, which composed of two chemical units derived from two corresponding eutectic phases.3Structural origin of three metallic glasses with best glass forming abilities Cu64Zr36, Cu56Zr44, and Cu50Zr50 were explained by the interpreted chemical units with e/u approximate to 24. Cu-Zr is an essential binary bulk glass-forming system with the three best bulk metallic glasses at Cu64Zr36, Cu56Zr44, and Cu50Zr50, which are eutectic or near-eutectic compositions. The current study reveals their composition origin by interpreting these eutectics via a “dual-cluster” model, where a eutectic is composed of two single-cluster-based chemical units derived from the corresponding eutectic phases in simple integer proportions. Each chemical unit represents a stable liquid formulated by the cluster-plus-glue-atom model. For example, eutectic Cu61.8Zr38.2 is deciphered as [Cu-Cu7Zr5]Cu1+4{[Zr-Cu10Zr6]Cu1} = Cu61.6Zr38.4, where the former is from eutectic phase Cu8Zr3 and the latter from another eutectic phase Cu10Zr7. The excellent glass forming composition Cu64Zr36 within this eutectic zone originates from the chemical unit of the Cu8Zr3 phase, [Cu-Cu7Zr5]Cu1 = Cu64.3Zr35.7. Two other eutectics, Cu56.0Zr44.0 and Cu45.7Zr54.3, are also interpreted using this dual-cluster model, leading to suitable glass formers Cu56Zr44 and Cu50Zr50.