Melting enthalpy ΔHm for describing glass forming ability of bulk metallic glasses

A new melting enthalpy ΔHm criterion for the prediction of glass forming ability (GFA) of alloys is proposed and five Zr–Al–Ni–Cu bulk metallic glasses (BMG) with critical dimension Zmax up to ∅ 7.5 mm are also developed by us in the light of the optimum ΔHm of Zr–Al–Ni–Cu alloy system. And then, we researched the relationships between ΔHm and two GFA parameters (critical cooling rate Rc and Zmax) of five bulk metallic glass (BMG) systems, such as Mg–Ni–Nd, Pd–Cu–Si, La–Al–Ni–Cu, Zr–Al–Ni–Cu and Zr–Ti–Ni–Cu–Be, respectively. The results show that the relationships between ΔHm and Rc are all concave upward parabolas, and the optimum ΔHms for Mg–Ni–Nd, Pd–Cu–Si, Zr–Al–Ni–Cu, Zr–Ti–Ni–Cu–Be and La–Al–Ni–Cu are 10.3960 kJ mol−1, 21.2202 kJ mol−1, 19.7146 kJ mol−1, 18.1455 kJ mol−1 and 13.1558 kJ mol−1, respectively. On the contrary, the relationships between ΔHm and Zmax are all concave downward parabolas, and the optimum ΔHms for Mg–Ni–Nd, Pd–Cu–Si, Zr–Al–Ni–Cu, Zr–Ti–Ni–Cu–Be and La–Al–Ni–Cu are 10.5530 kJ mol−1, 21.0830 kJ mol−1, 19.6603 kJ mol−1, 19.7231 kJ mol−1 and 13.1173 kJ mol−1, respectively. Furthermore, other BMGs’ Rcs or Zmaxs predicted by above-mentioned relationships satisfactorily agree with the tested results, which indicates that these relationships are reliable. However, the predicted results are reliable only if the main components are similar with the fitted BMGs or the additive is sparkle enough that the alloy’s character does not change. On the whole, the ΔHm can act as a criterion for quickly predicting the alloy’s GFA and be helpful for the development of new BMGs.