Prediction of Glass-Forming Compositions in Metallic Systems: Copper-Based Bulk Metallic Glasses in the Cu-Mg-Ca System

Abstract

A novel methodology for predicting specific compositions for glass-forming alloys based on efficiently packed atomic cluster selection, liquidus lines, and ab initio calculations is presented. This model has shown applicable adaptation to many known metallic and ceramic oxide glassforming systems and has led to the discovery of soon to be reported Ag-and Zn-based bulk metallic glasses (BMGs). As a model system, glass formation in the Cu-Mg-Ca ternary system has been assessed using this alloy design methodology, which has led to the discovery of a number of Cu-based BMGs with compositions ranging from Cu-33 to 55 at. pct, Mg-18 to 45 at. pct, and Ca-18 to 36 at. pct. Included in this work are the calculated values of associated cluster binding energies and correlations between physical and thermal properties of these glassy compositions, which show significant physical evidence to support the likely existence of such clusters.

Synthesis of Ag-based bulk metallic glass in the Ag–Mg–Ca–[Cu] alloy system

“…Z C < 0.2 mm) when injection cast. This could also be an effect of a reduction in the average atomic radius of the alloy, or, perhaps the substitution of a larger atom (either Ag, Mg, or Ca) with the smaller Cu atom to the coordination shell of a cluster which will effectively reduce its packing efficiency, resulting in a reduction in GFA [3,4]. Further, the addition of a fourth element of different atomic size to the system effectively creates additional short-range structures/clusters of different atomic centres and may contribute to hindering atomic rearrangement during crystallization, often referred to as the 'confusion principle' [12].…”

“…The Ag-Mg-Ca ternary and Ag-Mg-Ca-Cu quaternary systems were selected for detailed analysis, since: (i) all elements have simple electronic structures and are thermodynamically compatible, forming multiple deep binary eutectics and relatively low temperature intermetallics with relatively similar negative (with the exception of Ag-Cu) heats of mixing (dependent on composition); (ii) each of the constituent elements display a large difference in atomic radius and the required specific radius ratios favoured for glass formation (Cu -128 pm, Ag -144 pm, Mg -160 pm, and Ca -196 pm), which geometrically allows for a larger compositional range of efficiently packed clusters [3,4], and (iii) glass formation in the binary Ag-Ca system has been reported over a broad composition range [5] and high GFA in the Ca-rich region of both the Ag-Mg-Ca ternary and Ag-Mg-Ca-Cu quaternary system has been confirmed by Amiya and Inoue [6], with the Ca 60 Mg 20 Ag 20 and Ca 60 Mg 20 Ag 10 Cu 10 alloys exhibiting a critical casting diameter (D C ) of 4 and 7 mm, respectively. Copper was specifically selected for this work as it too has exceptionally high electrical and thermal conductivity and has a similar, simple electronic configuration to Ag with a full d-electron shell and single s-electron in its outer shell.…”

A Physical Model for Metallic Glass Structures: An Introduction and Update

“…27 The structure-forming clusters are defined by assigning the first shell occupancy so that the cluster composition closely matches the glass composition. If the cluster composition does not match the glass composition, then a ''stoichiometric remainder'' of atoms needed to match the glass composition is determined, and these atoms are placed in interstices between clusters.…”

Fabrication of bulk metallic glasses at the region of multiple quasi-peritectic reactions

“…1, which clearly validates that our BMGs are deviated from the eutectic composition. According to the composition site of Cu-based BMG [23,24] on the ternary Ca-Cu-Mg phase diagram shown in Fig. 1 [22], it is reasonably to infer that the dual quasi-peritectic reactions U 2 and U 3 play an important role for the formation of Cu-based peritectic BMGs.…”