Effective diffusion coefficients and thermal stability of the structure of metallic glass Fe$_{48}$Co$_{32}$P$_{14}$B$_{6}$

Using the results of electron microscopic studies of partially crystallized samples of metal glass Fe$_{48}$Co$_{32}$P$_{14}$B$_{6}$, the linear growth rate of eutectic colonies in the temperature range 679–717 K has been determined. According to these data, within the framework of the classical theory of crystallization, the effective coefficients of diffusion, which control the growth, have been calculated. The temperature dependence of the effective diffusion coefficients in Fe$_{48}$Co$_{32}$P$_{14}$B$_{6}$ glass has been found to be well approximated by an Arrhenius-type equation, and its values in the range of crystallization temperatures of glasses turned out to be approximately 2–3 orders of magnitude lower than in industrial Fe$_{40}$Ni$_{40}$P$_{14}$B$_{6}$ glass. We have determined the values of the effective diffusion coefficient and the volume density of crystallites at the onset crystallization temperature, and a correlation between preexponential factors and activation energies has been established. The parameters characterizing effective diffusion in the glass under study are shown to be in good agreement with the published data for eutectic crystallizing metallic glasses. It has been found that the physical reason for the increased thermal stability of the iron-cobalt glass structure in comparison with Fe$_{40}$Ni$_{40}$P$_{14}$B$_{6}$ is the lower mobility of atoms at the glass/crystal interface.