Dual-cluster formulas for eutectic-type bulk metallic glasses and experimental verification in Zr-Al-Fe-Cu system

Abstract

Composition rule of binary and some ternary bulk metallic glasses (BMGs) has been empirically solved by using the composition formulas of the cluster-plus-glue-atom model. However, multi-component BMGs such as Zr-Al-Ni-Cu with exceptionally high glass-forming abilities cannot be well understood with the model. In the present work, these special compositions were addressed following the dual-cluster formulism for eutectic point interpretation. A eutectic-type metallic glass is regarded as being composed of two clusters plus two, four, or six glue atoms, where the clusters are nearest-neighbor coordination polyhedra derived from the two eutectic phases. In particular, the eutectic Zr54.3Cu45.7 is formulated as [Cu-Zr8Cu6 + Zr-Cu4Zr9]Cu5Zr = Zr19Cu16 ≈ Zr54.3Cu45.7, where the two clusters are derived from eutectic-related phases CuZr and CuZr2. The BMG compositions of Zr55Al10Ni5Cu30 ≈ (Zr19)(Al3.5Ni2Cu10.5) and Vit-1 Zr41.2Ti13.8Ni10Cu12.5Be22.5 ≈ (Zr14Ti5)(Ni3.5Cu4.5Be8) are well reproduced with this basic composition formula. The composition of Pt42.5Cu27Ni9.5P21 BMG is considered as (Pt13Cu8Ni3)(P6), which is derived from the eutectic point of Pd80P20 = [Pt-P2Pt8 + Pt-Pt12]Pt2P4 = Pt24P6. As an experimental verification of the empirical composition design method, the BMG compositions in the biomedical alloy system of Zr-Al-Fe-Cu are explored with Zr72.4Cu27.6 ≈ [Cu-Zr14 + Zr-Cu4Zr9]Cu4 = Zr24Cu9. A quaternary composition of Zr63.5Al9Fe4.5Cu23 = (Zr21Al3)(Fe1.5Cu7.5) alloy is finally obtained, at which a critical glass formation size of 10 mm is reached by copper mold suction casting. The BMG alloy shows a room temperature compressive plastic strain of 6.5%. Keywords: Bulk metallic glasses, Eutectics, Zr-Al-Fe-Cu, Dual-cluster formula, Composition design