Composition effects on glass-forming ability and its indicator γ

Glass formation and glass-forming ability (GFA) in the La_(100-x)[Al_0.412(Cu,Ni)_0.588]_x (x = 30-44.6 at.%) system were studied in detail, and effectiveness of the phenomenological GFA indicator γ, defined as T_x/(T_g + T_l) (T_x onset crystallization temperature, T_g glass transition temperature and T_l liquidus temperature), is also discussed. Our experimental data indicate that γ is generally reliable in estimating the GFA of the current alloy system. Based on the framework of phase competition and crystallization kinetics, composition effects on GFA and its indicator γ in both simple regular and irregular eutectic systems were further analyzed. It was confirmed that γ is capable of representing the GFA of most alloys in both eutectic systems but might be less accurate in assessing the GFA of the compositions whose decisive competing crystalline phase during cooling is different from that upon devitrification. In the latter cases, the measured T_x value upon devitrification is not sufficient to indicate the crystallization resistance of the real competing phase during cooling.