The mismatch entropy for bulk metallic glasses: A thermodynamic approach

Abstract Based on the thermodynamic fragility model, a new parameter ( S σ /k B )/ M is proposed to evaluate the glass-forming ability (GFA) of metallic glasses, where M and S σ / k B are the fragility of the superheated melts and the mismatch entropy normalized by the Boltzmann constant, respectively. A positive relationship between ( S σ /k B )/ M and glass forming ability is observed for both bulk metallic glasses and marginal metallic glasses, and an eutectic alloy with ( S σ /k B )/ M larger than 0.17 can be selected as a bulk glassy forming candidate. As most alloys can obtain the temperature dependence of viscosity above liquidus temperature, ( S σ /k B )/ M can be used as a prediction parameter for high GFA. Although both high and low M values can work in determining GFA, the high GFA of bulk metallic glasses is primarily due to the large mismatch entropy ( S σ / k B >0.17).