Dynamic fragility and reduced glass transition temperature as a pair of parameters for estimating glass forming ability

The paper considers the development of the glass forming ability (GFA) parameter proposed by Senkov F1 = (Tg − To) / (0.5(Tl + Tg) − To) (where Tg is glass transition temperature, Tl is liquidus temperature and To is the temperature at which the configurational entropy becomes zero). As a result of more accurate development we introduced the parameter F2 = 16F1 − log 0.5(Tl − Tg) − 14 that has similar correlation with the critical cooling rate Rc as F1. The advantage of F2 in relation to F1 is that this parameter is more sensitive. Starting from the idea that fragility and glass forming ability should be related, we develop a relation from which the GFA parameter FK = (Tg − To) / (Tl − To), that was presented only as idea by Takeuchi et al., follows. The nature of FK is different from the reduced glass transition temperature Trg and there is no correlation between these two parameters. The influence that Trg has on GFA has been taken into account by defining a new parameter FKA = 16FK / 17 + Trg / 17. The parameter FKA has the best correlation with Rc for a large group of metallic and nonmetallic glasses (R2 = 0.951). The parameters F1 and FK exactly indicate that in the case when different glass forming alloys have the same Rc, the relationship between fragility and reduced glass transition temperature 1/Trg = const/m + 1 is fulfilled. When Trg is a constant, the parameters F1, FK and FKA are single functions of fragility and behave as 1/m.