A new criterion for glass forming ability of bulk metallic glasses

The relationship between R-c and the ratio d/e of Delta d to Delta 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 R-c with the practical R-c 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 R(c)s of other Zr-Al-Ni-Cu alloys are predicted by using the fitted formula. The R(c)s 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, T-rg and Delta T-x parameters are not suitable for the criteria for GFA of BMGs.