Calculations of dominant factors of glass-forming ability for metallic glasses from viscosity

The calculation models in which the viscosity is used as a main parameter are proposed for the estimation of the three glass-forming ability (GFA) factors: critical cooling rate (Rc) for formation of glassy phase, reduced glass transition temperature (Tg/Tm) and supercooled liquid range (ΔTx≡Tx−Tg), where Tg, Tm and Tx are the glass transition, melting and crystallization temperature, respectively. The Rc and Tg/Tm were analyzed on the basis of the homogeneous nucleation and growth theory by the construction of a time-transformation diagram for the crystallization of metallic glass. On the other hand, ΔTx was calculated on the basis of a free volume theory proposed by Beukel and Sietsma, and then was related with Rc calculated from the time–transformation curve. The calculations were carried out for Fe-, Pd-, Pt-, Zr-, Mg-based metallic glasses for which the viscosity is expressed by Vogel–Fulcher–Tammann equation or the Doolittle equation. The calculated results summarized in Rc−Tg/Tm and Rc−ΔTx diagrams agree with the experimental data qualitatively. It was shown that all the GFA factors of metallic glasses can be calculated from viscosity. These results indicate that the viscosity is the key parameter for the determinations of Rc, Tg/Tm and ΔTx.