Cu-Zr-Ag bulk metallic glasses based on Cu8Zr5 icosahedron

Based on the cluster line criterion, the Ag addition into the Cu8Zr5 cluster composition is investigated for the search of ternary Cu-Zr-Ag bulk metallic glasses with high glass forming abilities. Two initial binary compositions Cu0.618Zr0.382 and Cu0.64Zr0.36 are selected. The former one corresponds to a deep eutectic point; it is also the composition of the Cu8Zr5 icosahedron, which is derived from the Cu8Zr3 structure. The latter one, which can be regarded as the Cu8Zr5 cluster plus a glue atom Cu, is the best glass-forming composition in the Cu-Zr binary system. Two composition lines (Cu0.618Zr0.382)(1-x)Ag-x and (Cu0.64Zr0.36)(1-x)Ag-x are thus constructed in the Cu-Zr-Ag system by linking these two compositions with the third constitute Ag. A series of Cu-Zr-Ag bulk metallic glasses are found with 2-8 at.% Ag contents in both composition lines. The optimum composition (Cu0.618Zr0.382)(0.92)Ag-0.08 within the searched region with the highest T-g/T-l = 0.633, is located along the cluster line (Cu0.618Zr0.382)(1-x)Ag-x where the deep eutectic Cu0.61Zr0.382 exactly corresponds to the dense packing cluster Cu8Zr5. The alloying mechanism is discussed in the light of atomic size and electron concentration factors. (c) 2006 Elsevier B.V. All rights reserved.