Abstract
The distinctive characteristic of the metallic glass-forming system is that the variation in viscosity with temperature obeys Vogel-Fulcher-Tammann (VFT) relationship in the undercooled state and Arrhenius relationship in the high temperature region. A dimensionless index has thus been proposed based on the Arrhenius-VFT crossover and the classical nucleation rate and growth rate theory to evaluate the glass-forming ability (GFA). The indicator G(a) is expressed with the combination of Tg, the glass transition temperature, Tx, the onset crystallization temperature, Tl, the liquidus temperature, T0, the VFT temperature, and a a constant that could be determined according to the best correlation between G(a) and the critical cooling rate (Rc). Compared with other GFA indexes, G(a) shows the best fit with Rc, with the square of the correlation coefficient (R2) being 0.9238 when a = 0.15 for the 23 various alloy systems concerned about. Our results indicate the crossover in the viscosity variation has key effect on GFA and one can use the index G(a) to predict Rc and GFA for different alloys effectively.
Highlights
Viscosity characterizes the relaxation time of the atoms or molecules in a liquid, and its magnitude plays a key role in the formation of glass phase
The correlation is performed firstly by considering the relationship between Rc and the nucleation rate and growth rate[12,13,14], the parameter is proposed by connecting the slope change in the viscosity curve with Rc
The data of 23 glass-forming alloys including bulk metallic glass (BMG), like vitreloy, etc. and marginal glass-forming systems (Rc is more than 103 K/s) is collected, as given in Table 1, for their parameters used in equation (15) can be found in literatures
Summary
Viscosity characterizes the relaxation time of the atoms or molecules in a liquid, and its magnitude plays a key role in the formation of glass phase. This raises the question that how to consider the crossover from Arrhenius-VFT in viscosity in judging GFA in metallic systems.
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