Achieving superior glass forming ability of Zr–Cu–Al–Ni–Ti/Ag bulk metallic glasses by element substitution

• New Zr-based BMGs with critical diameter of at least 20 mm were obtain by element substitution.
• With the increase of Ag content, the GFA of Zr57Cu20Al10Ni8Ti5 − xAgx BMGs improved continuously.
• The super-high GFA in this work is believed to be related with the improved atomic packing fraction.
• The mechanical property was improved by fully substituting Ti with Ag of the alloy Zr57Cu20Al10Ni8Ti5.

In the present paper, glass forming ability (GFA) of Zr57Cu20Al10Ni8Ti5 − xAgx (x = 0, 1, 2, 3, 4, 5) bulk metallic glasses (BMGs) are studied using conventional copper mold suction casting method. The critical diameter of amorphous rod is improved from 8 mm of Zr57Cu20Al10Ni8Ti5 to 20 mm of Zr57Cu20Al10Ni8Ag5 by fully substituting Ti with Ag. The great improvement of GFA is attributed to the enlarged negative mixing enthalpy, large atomic packing fraction, and low critical cooling rate, which are − 32.026 kJ/mol, 0.761, and 2.5 K/s, respectively. The mechanical property is also improved by substituting Ti with Ag. The yield strength, ultimate strength and plastic strain are enhanced from (1469 MPa, 1490 MPa and 0.1%) for Zr57Cu20Al10Ni8Ti5 BMG to (1612 MPa, 1746 MPa and 2.1%) for Zr57Cu20Al10Ni8Ag5 BMG, respectively.