On the new criterion to assess the glass-forming ability of metallic alloys

Based on the analysis of time–temperature-transformation (TTT) diagrams of glass-forming liquids using the fragility concept, a dimensionless criterion ω, expressed by Tg/Tx − 2Tg/(Tg + Tl) (Tg the glass transition temperature, Tx the onset crystallization temperature and Tl the liquidus temperature), is proposed for quickly evaluating the glass-forming ability (GFA) of metallic glasses. From the available experimental data reported in the literature, the criterion ω exhibits the strongest correlation with the critical cooling rate Rc for glass formation among all currently available GFA indicators, including Trg(=Tg/Tl), ΔTx(=Tx − Tg), ΔTrg(=(Tx − Tg)/(Tl − Tg)), δ(=Tx/(Tl − Tg)), γ(=Tx/(Tg + Tl)), γm(=(2Tx − Tg)/Tl), φ(=Trg(ΔTx/Tg)0.143), α(=Tx/Tl), β(=Tx/Tg + Tg/Tl), β(=Tx × Tg/(Tl − Tx)2) and ζ(=Tg/Tl + ΔTx/Tx). An empirical equation is induced to elucidate the Rc in different metallic alloys based on the measured ω value of the corresponding alloy. It is also demonstrated that this ω criterion has a strong ability to measure or/and predict the GFA of cryoprotectants and oxide glasses, especially in the case of cryoprotectants.