Notes on the glass-forming ability of bulk metallic glasses

Schroers replies: In the section of my article that Jianbo Liu cites , I did not attempt to report correlations with glass-forming ability but simply to state how GFA is defined—namely, by the critical cooling rate, which also establishes a critical casting thickness.

In their work, the Tsinghua University researchers report a correlation with GFA and try to understand and predict why glasses form. Their work is based on an idea by Takeshi Egami and Yoshio Waseda. ¹ The Tsinghua group essentially confirms the well-established Hume-Rothery rules—in particular, that for a specific size difference between two metallic atoms, only a limited range of compositions will form solid solutions.

I agree with Liu that destabilizing solid solutions is a requirement for glass formation, but it is at most a minimum one. However, predicting and quantifying GFA through identifying compositional limits of solid solutions is insufficient. Beyond those solution limits, mixtures often form intermetallic phases, homogeneous crystalline phases that compete with the glass in terms of stability. Moreover, intermetallics can be difficult to consider in molecular dynamics simulations that have been used by the Tsinghua group, depending on the simulations’ assumptions. In summary, the Tsinghua group’s finding is a requirement for glass formation; however, it is insufficient to predict glass-forming ability in a quantitative manner and is certainly not suited to act as a predictor for glass formation.