A new criterion for glass forming ability of bulk metallic glasses

Abstract

The relationship between R_c and the ratio d/e of Δd to Δe 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_cs of other Zr–Al–Ni–Cu alloys are predicted by using the fitted formula. The R_cs 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 ΔT_x parameters are not suitable for the criteria for GFA of BMGs.