On the high glass-forming ability of Pt-Cu-Ni/Co-P-based liquids

Abstract The continuous and isothermal crystallization diagrams of the Pt 42.5 Cu 27 Ni 9.5 P 21 and the Pt 60 Cu 16 Co 2 P 22 bulk glass forming compositions are determined using calorimetric experiments. In the case of the Pt 42.5 Cu 27 Ni 9.5 P 21 bulk metallic glass, the formation of the primary crystalline phase can be prevented by rapid cooling in a conventional DSC. In contrast, for similar cooling conditions, the formation of the primary precipitating compound in Pt 60 Cu 16 Co 2 P 22 cannot be prevented in a conventional DSC as also observed in in-situ synchrotron X-ray scattering experiments. This is attributed to a critical overheating, above which remaining structures dissolve, resulting in a drastic increase of the degree of undercooling, similar to what is observed in Zr-based BMGs. Using the classical nucleation theory, the combined thermodynamic and kinetic data are used to model the isothermal crystallization data for Pt 42.5 Cu 27 Ni 9.5 P 21 , yielding an interfacial energy value of 0.11 J/m 2 between the primary nucleating crystal and the liquid. This value is three times higher than the value for good Zr-based glass-formers, suggesting that the interfacial energy plays a pivotal role in the exceptionally high glass-forming ability of Pt-P-based systems and compensates for the fragile liquid behavior and the large driving force for crystallization.