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 omega, 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 (CFA) of metallic glasses. From the available experimental data reported in the literature, the criterion omega exhibits the strongest correlation with the critical cooling rate R, for glass formation among all currently available GFA indicators, including T(rg)(=T(g)/T(l)), Delta T(x)(=T(x) - T(g)), Delta T(rg)(=(T(x) - T(g))/(T(l) - T(g))), delta(=T(x)/(T(l) - T(g))), gamma(=T(x)/(T(g) + T(l))), gamma(m) (=(2T(x) - T(g))/T(l)), phi(=T(rg)(Delta T(x)/T(g))(0.143)), alpha(=T(x)/T(l)), beta(=T(x)/T(g) + T(g)/T(l)), beta(=T(x) x T(g)/(T(l) - T(x))(2)) and zeta(=T(g)/T(l) + Delta T(x)/T(x)). An empirical equation is induced to elucidate the R(c) in different metallic alloys based on the measured omega value of the corresponding alloy. It is also demonstrated that this omega criterion has a strong ability to measure or/and predict the GFA of cryoprotectants and oxide glasses, especially in the case of cryoprotectants. (C) 2009 Elsevier B.V. All rights reserved.