Nucleation rate and nanocrystallization of Co60-(Fe, Mn)18-Nb6-B16 amorphous alloys in the frame of instantaneous growth approximation

Instantaneous growth approximation is based on the fact that the time required by a new nucleus to reach its saturation size is negligible in comparison with the time required for the whole crystallization process. This approximation has been applied to analyze the kinetics of the nanocrystallization process of Co60Fe18−xMnxNb6B16 (x = 0 and 4) alloys. Direct application of JMAK theory leads to divergences at very high transformed fractions. Although this divergence could be due to some artifacts, it can also be solved after a reinterpretation of the geometrical impingement effect on nanocrystalline systems. A modified Arrhenius relationship can be used for a general description of the double dependency of nucleation rate on the transformed fraction (only through the local activation energy) and the temperature.