The key step in exploiting a new type of bulk metallic glass (BMG) is to judge quickly the glass forming ability (GFA) of the alloys. The mole melting enthalpies of BMGs are calculated using the weighted averages principle. The reliability and limitation of the T rg criterion for GFA are discussed, and the reason why the T rg of BMGs presently is more than 0?5 is also discussed. In addition, two new criteria, DH mg and DG g , for GFA are presented. The GFA sequence of BMGs is calculated using the DH mg criterion, the result agrees with that of Inoue and Shibata and R c criterion. Furthermore, as an example, the R c of the alloys developed by Dong Chuang et al. are calculated using DH mg and DG g . The ascending sequence of these alloys calculated by the DH mg criterion agrees with that of Dong Chuang et al. In contrast, the result using the DG g criterion is contrary to that of Dong Chuang et al., indicating that the DH mg criterion is better and more convenient than the DG g criterion. The optimum DH mg was found to be -15?16 kJ mol -1 .

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The relationship between Rc and the ratio d/e of Δ d to Δ e is discussed based on five bulk metallic glass (BMG) systems, which show all concave upward parabola relations. The second derivative value of the fitted curve reflects glass forming ability (GFA) and the sensitivity to composition of GFA. The greater the second derivative value, the higher is the GFA and the stronger is the sensitivity to composition. Furthermore, the parabola relations are demonstrated comparing the predicted Rc with the practical Rc in a Mg–Ni–Nd system, and indirectly reasoned by using a Pd–Cu–Si system and a Zr–Ti–Ni–Cu–Be system. Based on the above-mentioned results, the Rcs of other Zr–Al–Ni–Cu alloys are predicted by using the fitted formula. The Rcs are among 4–20 K s−1, which is coherent to the practical preparation condition and indirectly shows reliability of the related parabola relations. The fitted formula can be applied to the cases of the invariability of the primary components of the alloy system. In addition, Trg and Δ Tx parameters are not suitable for the criteria for GFA of BMGs.

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