Thermodynamic basis for cluster kinetics: Prediction of the fragility of marginal metallic glass-forming liquids

Due to the inaccessibility of the supercooled region of marginal metallic glasses (MMGs) within the experimental time window, we study the cluster kinetics above the liquidus temperature, T-1, to acquire information on the fragility of the MMG systems. The thermodynamic basis for the stability of locally ordered structure in the MMG liquids is discussed in terms of the two-order-parameter model. It is found that the Arrhenius activation energy of clusters, Delta h, is proportional to the chemical mixing enthalpy of alloys, Delta H-chem. Fragility of the MMG forming liquids can be described by the ratio of the absolute Delta Hchem value to the glass transition temperature, Tg. The manner of vitrification during rapid solidification is an important factor for the discrepancy between the data presented in this paper and the prediction of the two-order-parameter model concerning the relation between Delta h and the liquid fragility.