Prediction of Bulk Metallic Glass Formation in Cu-Zr-Ag-Hf System by Thermodynamic and Topological Modeling

Cu based bulk metallic glasses (BMGs) are widely studied because of their high glass forming ability (GFA) and interesting combination of properties such as high strength coupled with good ductility and low cost. With these attributes, Cu based BMGs are being projected as promising materials for practical applications. The process of glass formation in metallic systems is a challenging task and alloys should be cooled from the liquid state at rates faster than a critical cooling rate (R-c) to resist crystallization. Interestingly, composition plays an important role in achieving easy glass formation, which is usually measured in terms of R-c. In the present work, attempt has been made to identify the composition for easy glass formation in Cu based quaternary system by theoretical approach. A GFA parameter P-HS, which is a product of enthalpy of chemical mixing (a dagger H-chem) and mismatch entropy normalized with Boltzmann's constant (a dagger S-sigma/k(B)) is used to identify the best glass forming composition in Cu-Zr-Ag-Hf system. Further, a new parameter P-HSS, which is a product of P-HS and configurational entropy (Delta S-config/R) is found to illustrate strong correlation with GFA. An attempt has also been made to correlate P-HSS parameter with critical diameters and R-c using reported data in Cu-Zr-Ag-Hf system.