Comparison of bulk metallic glass formation between Cu-Hf binary and Cu-Hf-Al ternary alloys

Optimized compositions for bulk metallic glass (BMG) formation have been determined for the Cu-Hf binary and Cu-Hf-Al ternary systems. The Cu-Hf-Al BMG-forming composition region is identified to correlate with the (L -> Cu10Hf7 + CuHf2 + CuHfAl) eutectic reaction. The eutectic temperature is reduced by nearly 50 K relative to that of the binary eutectic, demonstrating the significant role of the third element Al in stabilizing the liquid. The fragility parameter D* of the Cu55Hf45 binary and Cu49Hf42Al9 ternary supercooled liquid was determined from relaxation time measurements, indicating that Al incorporation also leads to a stronger liquid. The combination of these thermodynamic and kinetic effects is responsible for the dramatic enhancement of glass-forming ability from the Cu-Hf binary to the Cu-Hf-Al ternary.