Thermodynamics and fragility of Fe-based glass forming melts

• Data on the thermodynamics of Fe-based glass-formers are provided.
• Thermodynamic and kinetic fragility of Fe-based glass-formers are determined.
• A method to derive viscosity from thermal data is elaborated.

Methods to determine the fragility index, m, both in thermodynamic and kinetic terms are reviewed and applied to two Fe-based glass formers, Fe40Ni40P14B6 and Fe41Co7Cr15Mo14C15B6Y2. The thermodynamic fragility is obtained from entropy curves based on experimental data of the liquid specific heat and of the enthalpy of transformation from glass or liquid to crystal phases.The thermodynamic fragility appears systematically higher than the kinetic one because of the large scatter of data and their extrapolation to obtain the Kauzmann temperature of vanishing entropy.A practical method to estimate the viscosity of glass formers in the undercooling regime was derived from the fragility index and its correlation with parameters of the VFT equation. It provides reasonable agreement with experimental data.