APPLICATION OF FRAGILITY CONCEPT TO METALLIC-GLASS FORMERS

The fragility concept proposed for glass formers with covalent or ionic bonding properties is applied to metallic glass formers for the first time. The fragility, m, which was estimated from the activation energy for viscous flow at the glass transition temperature for the data reported by Davies, is about 110, e.g., m = 99 for Fe(41.5)Ni4(1.5)B(17) and m = 109 for Pd40Ni40P20, implying that metallic glass formers are extremely fragile. The parameters in the Vogel-Fulcher equation for the temperature dependence of viscosity also support fragile characteristics of metallic glass formers. The data reported by Chen et al., however, give intermediate values of about m = 50, e.g., m = 52 for Pd77Cu6Si17. To draw any definitive conclusion, viscosity data determined experimentally at around glass transition for thermally stable glass former systems might be necessary.