Identification of the onset crystallization time in metallic glasses at isothermal conditions

An approach for determination of the onset crystallization time (tons) at isothermal annealing of metallic glasses similar to that used in the DSC analysis for the onset crystallization temperature is proposed. The analysis performed in the framework of the Kolmogorov-Johnson-Mehl-Avrami model has shown that the volume fraction transformed at tons (Xons) increases from 0 to 0.05 with the Avrami exponent increasing from 1.5 to 12. It has been found that the values of Xons determined from the experimental kinetic crystallization curves for the Fe85B15 glass at 628 K, for the Fe40Ni40P14B6 glass at 662, 649 and 617 K and for the Fe40Co40P14B6 glass at 695 K are in good agreement with the calculated ones. New possibilities for analysis of nucleation behavior in glasses using the relation established between the kinetic and structural data are discussed.