Topological criteria for amorphization based on a thermodynamic approach

The effects of composition, atomic radii, atomic size ratios, and elastic constants of the constitutive elements on the glass-forming ability of metallic glasses have been identified using a thermodynamic model. This model is based on the comparison of the Gibbs free energy and entropy between a nonequilibrium crystalline solid solution and the undercooled liquid. According to this model, the glass-forming ability (reduced glass transition temperature, T g ∕ T m ) of an alloy should increase with (a) an increase in the atom size and/or shear modulus of the solvent; (b) an increase in the bulk modulus of a solute; and (c) a decrease in the melting temperature of the alloy. At constant values for other parameters, the glass-forming ability is maximum at a certain concentration and relative atomic size of a solute. Recently, these topological criteria have been successfully used to produce a number of Ca-based bulk metallic glasses.