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

Cu-Zr is an essential binary bulk glass-forming system with the three best bulk metallic glasses at Cu ₆₄Zr ₃₆, Cu ₅₆Zr ₄₄, and Cu ₅₀Zr ₅₀ , 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 Cu _61.8Zr _38.2 is deciphered as [Cu-Cu ₇Zr ₅]Cu ₁+4{[Zr-Cu ₁₀Zr ₆]Cu ₁} = Cu _61.6Zr _38.4, where the former is from eutectic phase Cu ₈Zr ₃ and the latter from another eutectic phase Cu ₁₀Zr ₇. The excellent glass forming composition Cu ₆₄Zr ₃₆ within this eutectic zone originates from the chemical unit of the Cu ₈Zr ₃ phase, [Cu-Cu ₇Zr ₅]Cu ₁ = Cu _64.3Zr _35.7. Two other eutectics, Cu _56.0Zr _44.0 and Cu _45.7Zr _54.3, are also interpreted using this dual-cluster model, leading to suitable glass formers Cu ₅₆Zr ₄₄ and Cu ₅₀Zr ₅₀.