Calculations of amorphous-forming composition range for ternary alloy systems and analyses of stabilization of amorphous phase and amorphous-forming ability

Abstract

The amorphous-forming composition range (AFCR) was calculated for 338 ternary amorphous alloy systems on the basis of the database given by Miedema's model in order to examine the applicability of the model, to analyze the stability of the amorphous phase, and to determine the dominant factors influencing the ability to form an amorphous phase. The mixing enthalpies of amorphous and solid solution phases were expressed as a function of alloy compositions on the basis of chemical enthalpy. Based on the Eshelby and Friedel model, an elastic enthalpy term was added to the model for the solid solution. Furthermore, an average melting temperature of the constituent elements was added to the model as the topological enthalpy in an amorphous phase. An amorphous phase was assumed to have been formed at the composition where the enthalpy of an amorphous phase was smaller than that of a solid solution. The AFCR was calculated for 335 systems except for the Al-Cu-Fe, Al-Mo-Si and Au-Ge-Si systems. The calculated results are in agreement with the experimental data for Cu-Ni and Al-Ti-based systems. For typical amorphous alloy systems exemplified by the Zr-, La-, Fe- and Mg-based systems, it was recognized that the calculated AFCR had been overestimated as a result of the model being simplified. We have also shown that the elastic enthalpy term arising in a solid solution phase stabilizes the amorphous phase, and the stabilization mechanism is particularly notable in Mg-based amorphous alloy systems. Short-range order plays an important role in the formation of Al-, Fe- and Pd-metalloid based systems. The following factors have a great influence on amorphous-forming ability: (1) three empirical rules for the achievement of high AFA, (2) melting temperature and viscosity at the melting temperature, (3) elastic enthalpy arising in a solid solution, and (4) short-range order observed in an amorphous phase. The importance of the latter two factors was only identified as a result of the present study.