Thermodynamic Basis for Glass Formation in Cu-Zr Rich Ternary Systems and Their Synthesis by Mechanical Alloying

Abstract

Topological factors such as mismatch entropy and configurational entropy, along with thermodynamic entity such as enthalpy of chemical mixing, are found to control glass formation in metallic systems. Taking both these factors into consideration, a parameter called P HS was proposed to correlate glass forming ability successfully in the Cu-Zr-Ti system. The parameter P HS (=∆H chem × ∆S σ /k B ) is a product of enthalpy of chemical mixing and mismatch entropy. Our study indicates that the more negative is the PHS value within the configurational entropy (∆S config/R) range of 0.9 to 1.0, the higher is the stability of glassy phase resulting in a larger diameter of bulk metallic glass rods. Observed theoretical predictions are supported by experimental results in which the compositions with high negative P HS resulted in easy amorphous phase formation in comparison with less negative P HS compositions by mechanical alloying. This criterion was extended to Cu-Zr-Al and Cu-Zr-Ag systems as well, thus establishing a strong correlation between P HS and the glass forming ability of alloys. The role of size effect, probability of atomic arrangements, and heat of formation among constituent elements in obtaining a larger dimension bulk metallic glasses was addressed in this study.