A comparison of the transient behavior of nucleation in Fe40Co40P14B6 and Fe40Ni40P14B6 metallic glasses

Abstract

The isothermal crystallization kinetics of Fe40Co40P14B6 glass has been experimentally studied in the temperature range between 671 and 708 K. The kinetic curves were analyzed within both the widely used Avrami model and the analytical combination (called as the KK model) of the integral form of Kolmogorov’s equation of mass crystallization kinetics and the Kashchiev’s transient nucleation approach. The parameters of the Avrami model (the Avrami exponent, n, and time τA) were determined. It has been established that (i) the values of n increase from 5.8 to 9.4 as the annealing temperature is increased such indicating the enhancement of transient behavior of nucleation and (ii) the Arrhenian temperature dependence of τA is very close to that for the time corresponding to the maximum rate of crystallization. It has been established that the KK model correctly approximates the experimental kinetic crystallization curves of Fe40Co40P14B6 glass and the values of crystallization (τc) and transient nucleation (τns) times which are parameters of the model have been determined. The analysis has shown that the nucleation rates in Fe40Co40P14B6 glass are well below the steady-state values and this deviation which is proportional to a τns/τc ratio increases with the annealing temperature, while Fe40Ni40P14B6 glass demonstrate the opposite behavior of transient nucleation with temperature. The reason of the differences in the transient nucleation behavior in these glasses is considered in terms of a ratio of the activation energies for the τns and τc times, while the enhanced values of the onset crystallization times in Fe40Co40P14B6 glass compared with those in Fe40Ni40P14B6 glass at the same reduced temperatures are discussed in terms of their crystallization times and the degree of non-stationarity of nucleation rate.