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 T_g/T_x - 2T_g/(T_g + T_l) (T_g the glass transition temperature, T_x the onset crystallization temperature and T_l 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 R_c for glass formation among all currently available GFA indicators, including T_rg(=T_g/T_l), ΔT_x(=T_x - T_g), ΔT_rg(=(T_x - T_g)/(T_l - T_g)), δ(=T_x/(T_l - T_g)), γ(=T_x/(T_g + T_l)), γ_m(=(2T_x - T_g)/T_l), φ(=T_rg(ΔT_x/T_g)^0.143), α(=T_x/T_l), β(=T_x/T_g + T_g/T_l), β(=T_x × T_g/(T_l - T_x)²) and ζ(=T_g/T_l + ΔT_x/T_x). An empirical equation is induced to elucidate the R_c 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.