Design of Cu-Zr-Al and Cu-Zr-Al-Sn bulk amorphous alloys with high glass-forming ability

The thermodynamic driving force is used to obtain the initial mixing ratio of binary eutectics to design Cu-based bulk metallic glasses. By adjusting approximately 5% proportionality coefficients from the primary mixing ratios of eutectic units, we directly locate amorphous compositions with critical casting diameter of 5 mm (Cu47.5Zr45.1Al7.4) and 7 mm (Cu47.3Zr45.8Al6.4Sn0.5) in Cu-Zr-Al and Cu-Zr-Al-Sn systems, respectively. Using the Cu-Zr-Al alloys as an example, the improvement of glass-forming ability (GFA) is systematically analyzed based on thermodynamics and atomic-scale structure. A relatively lower driving force for crystallization and larger populations of Cu-centered full icosahedra with the large tendency to form MROs jointly contribute to the stability of liquid. With regard to topology, the closer local atomic size ratio compared with the ideal value for icosahedral packing around the Cu atom may be the dominant factor for the higher number of Cu-centered full icosahedra and enhanced GFA.